UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

The Puncture Vine
in California

ETHELBERT JOHNSON

BULLETIN 528

MAY, 1932

UNIVERSITY OF CALIFORNIA PRINTING OFFICE
BERKELEY, CALIFORNIA

FOREWORD

Among the various weeds that are contributing' to agricultural
losses, in California, the puncture vine has rapidly become one of the
most harmful. In certain counties it is causing enormous losses, and
rendering almost worthless large acreages of valuable land. More-
over, it is spreading, the agencies responsible for its dissemination
being many and difficult to control. But, the important point is that
it can be prevented from spreading itself generally over the state if
proper measures are followed.

This bulletin is a genuine contribution to the knowledge of the life
history and habits of puncture vine and of practical methods for its
control. It will be welcomed by those growers who now have infesta-
tions of the weed, and also by those who wish the information which
will enable them to recognize the plant and to stamp out incipient
infestations effectively.

Mr. Ethelbert Johnson, the author of this bulletin, is affiliated with
the State Department of Agriculture. This organization plays a very
active part in combating the weed problems of the state, particularly
in enforcing the various regulatory measures which have for their
purpose the prevention of the introduction and spread of noxious
weeds. Its weed work is thoroughly organized. A number of agen-
cies are cooperating with it in an attempt to solve the weed problems
of the state. Although progress has been made, much is yet to be done
along the lines of investigation, education, and regulation. Through
the combined and organized efforts of all agencies concerned Cali-
fornia may hope for a, practical solution of her most acute weed
problems. ^ , TT -^

1 W. W. ROBBINS,

Botanist, Experiment Station.

THE PUNCTURE VINE IN CALIFORNIA

ETHELBERT J0HNS0N2

ORIGIN, DISTRIBUTION, AND DISSEMINATION

The earliest reported collection of puncture vine (Tnhulus terres-
tris L.) in California was made at Port Los Angeles in 1903 by
Davidson/ 8 ' who then commented on the species as "a probable per-
manent introduction from Arizona." Parish (33 > 34) reports that it was
"abundant" at Colton in 1908 and that "a few plants" were collected
at San Bernardino the same year; he credits C. P. Fox with having
found specimens at Bakersfield in 1905. Creditable observers state
that puncture vine was in fact introduced into California some years
before these collections. Thus Charles F. Collins, formerly Tulare
County Horticultural Commissioner, recalls having first seen the plant
at Dinuba in 1901 ; and some of the older ranchers in Kern and Tulare
counties claim to have known it for about forty years.

Whatever the date of its original introduction, it did not appar-
ently become abundant enough to attract much attention until about
1912, when Kent S. Knowlton, then Horticultural Commissioner of
Kern County, recognized in it a potentially serious economic weed
pest and sent specimens to the State Commission of Horticulture
for determination. Essig (9) records that specimens from Placer
County were received by the Commission, and that puncture vine was
reported from Glenn County and from the coast side of the mountains
west of the San Joaquin Valley before 1914.

From 1912 on, Knowlton (27) repeatedly called attention to the
menace of puncture vine in the San Joaquin Valley, and urged that
stringent measures be taken to stamp it out at any cost in areas
where it occurred only as a light infestation.

Shortly after the creation of the State Department of Agriculture
in 1919, the county horticultural commissioners assisted in a prelim-
inary survey of the puncture vine situation in California. The distri-
bution of the plant in 1920 was noted by Johnson (16) as follows :
It has now spread over a large area in the Upper San Joaquin Valley, and is
found in a nearly unbroken line along- the railroads northward to San Joaquin
County. In the Sacramento Valley it has been found at Woodland, Durham, and
Marysville, and is reported as widespread along the railroads in Tehama County.

1 Received for publication, April 2, 1932.

2 Deputy Agricultural Commissioner, Orange County, California State Depart-
ment of Agriculture.

4 University of California — Experiment Station

South of Techachapi the puncture vine is found from the Mexican border
through the Imperial and Coachella valleys to the coastward valleys of Riverside,
San Bernardino, Los Angeles, and Orange counties.

From the rapidity of its spread in the upper San Joaquin Valley in the last
ten years it is to be expected that the pest will continue to extend its limits from
these newer centers of infestation until something is done to check it.

At the time of this preliminary survey it was not known in the
north coast counties, nor east of the Sierras; but by 1925 it had
reached Glen Ellen in Sonoma County and Lone Pine in Inyo County,
and in every subsequent year still further encroachments were
recorded.

The year 1924 saw an especially heavy infestation of puncture
vine. A series of conferences to determine whether the pest could
not be better controlled by persistent statewide efforts led the State
Department of Agriculture, in the fall of 1925, to offer a basic plan (17)
which, with some modifications, was adopted in most sections of the
state. (18) In some counties where puncture vine is not common, all
infestations have been treated at county expense. In others the
county has treated roadsides and county property only, private prop-
erty owners being' required to control their own infestations. In
still other counties the roadsides have been systematically treated,
but the only control measures practiced on private property have been
voluntary. In only two or three counties where the infestations are
exceedingly heavy have county roads not been treated. The State
Highway Commission has practiced puncture-vine control throughout
its extensive system, and the various railroads have cooperated in
accordance with local practices.

The extent of the operations against puncture vine in California
may be noted from the following figures, 3 representing the total
expenditures by the counties for that purpose, exclusive of the cost
of equipment, and not including amounts expended by individuals,
by the railroads, and by the State Highway Commission: 1927,
$113,155.31; 1928, $163,402.02; 1929, $159,855.55; 1930, $110,402.36.

Puncture vine is presumably a native of the Sahara Desert, whence
it had spread throughout the Mediterranean region before the dawn
of history. The early records of it in literature have been reported
by Pickering : (35)

Tribuliis terrestris of the Desert and its borders from the Atlantic to Hindu-
stan and Lake Baikal. Called in Italy "tribolo" or " Tribolo terrestre" (Lenz),
in Greece "trivoli," or by the Turks "demio dikieni" (Sibth.), in Egypt "Khar-
choum el-nageh," or by the Nubians "kenyssa kou" (Del.), in tropical Arabia
"kotaba" (Forsk.), in Egyptian "seroji" — (transl. Matth.) : the "trivolos"

8 From Annual Keports, California State Department of Agriculture.

Bul. 528]

The Puncture Vine in California

is mentioned in the Septuagint translation of Hosea X.8, and in Matthew VII.16,
as growing in Palestine: T. terrestris was observed by Delile in both Lower and
Upper Egypt by Forskal p. 88 in Tropical Arabia, by Denham in Nigritia, and
was received by A. Eichard from Senegal and Abyssinia. Northward and west-
ward from Egypt, the "trivolos" is mentioned by Aristophanes lys. 576; by
Theophrastus VI. 5 as having ' ' erevinthos ' '-like leaves ; the ' ' trivolos hersaios ' '
by Dioscorides as growing about houses and along rivers; the "tribulus ,, by
Virgil Geor. i.153, and as a weed in gardens by Pliny xvii 44 to xxii 12: T. ter-
restris is described by Lobal pi. 84, and Morison ii. pi. 8 ; is termed ' ' t. terrestris
ciceris folio seminum integumento aculeate' ' by Tournefort inst. 266; was ob-
served by Desfontaines in Barbary; by Lenz in Italy; by Sibthorp, Chaubard,

Fig. 1. — Puncture vine in ballast.

and Fraas, frequent in waste and cultivated ground from the Peloponnesus to
the Dardanelles ; is known to grow in southern Eussia and from Caucasus along
the border of Siberia as far as Lake Baikal (Ledeb.) ; was received by Fischer
from Thibet ; and was observed by myself, indigenous on the Deccan. In Austral
Africa, may have arrived without European intervention; but clearly by European
colonists was carried to the Mauritius Islands (Drege, Boj., and A. Dec).

According to Georgia/ 11 ' it was early introduced into the range
lands of the middle western United States by the importation of live-
stock, especially sheep, from the Mediterranean countries, and is also
found along the Atlantic seaboard. It is now abundant throughout
the Southwest. The relation of the railroads to its introduction and
distribution in California is apparent (fig. 1). Its rapid spread from
those centers of infestation was concurrent with, and without doubt
largely resulted from, the development of automobile travel in this
state.

6 University of California — Experiment Station

The automobile (fig. 2) has given the puncture vine a very much
easier and more rapid means of dissemination than that afforded by
nature ; but although the automobile has been the chief means of
spreading puncture vine locally, the railroads apparently have been
responsible for most of the primary infestations ; witness the fact that
the first infestation in any locality has almost invariably followed the
railroad right-of-way, usually in the vicinity of a stock-loading corral.

Fig. 2. — Keady dissemination of puncture vine by rubber-tired vehicles.

The burs are frequently carried in the wool or hair of animals, and
are found in hay, straw, and other feed, in sand and other material
used for bedding in stock cars, and in ballast hauled from infested
gravel pits.

From a primary infestation, it ma}^ be picked up by automobiles
(fig. 2) or by other means, and carried to roadsides, camps, parks,
playgrounds, city streets (fig. 3), vacant lots, and agricultural land.

Once introduced into cultivated soil, it is readily picked up by
implements and dragged through the field, and may be spread over a
considerable area before its presence is realized.

The airplane is a new and potentially important means of bring-
ing puncture vine into new localities by carrying the burs in its tires
from one landing place to another/ 29 ' 37) Agricultural products from

Bul, 528] The Puncture Vine in California 7

infested districts frequently carry the weed. Not only hay, straw,
and manure, but melons, cotton, potatoes, and other products, and
picking- boxes, ladders, tents, and, in fact, almost anything else that
comes in contact with the pest, are potential carriers.

DAMAGE FROM PUNCTURE VINE

The losses caused by puncture vine in California are unquestion-
ably very high; but there is probably no basis on which the actual
damage could be estimated.

Fig. 3. — Puncture vine growing in parkway, Bakersfield.

Damage to Crops. — Puncture vine can readily be carried by
various crops that come in contact with it. In many of the districts in
which it is under control, shipments of potential carriers are inspected
before delivery is permitted. Rejections of alfalfa and other hay,
melons, grain, cotton-seed, milo maize, nursery stock, and cantaloupe
seed have been recorded.

In cultivated crops puncture vine is especially troublesome,
because its rapid growth, its long season, and its uneven germination
make cultivation costs considerably higher. In crops such as melons,
grapes, and cotton, which require hand work for harvesting, an
infestation will increase the cost very materially ; and in seasons when
labor is scarce, pickers have sometimes refused to work in badly
infested fields and vineyards. Jumper (25) quotes Wallace Sullivan,
Kings County Farm Advisor, as follows :

It costs probably $15.00 more per acre for cultivation where puncture vine
has seriously infested fruit lands, and grape pickers fight shy of vineyards overrun
with the barbed pest. Added cost of cultivation has been placed at $10.00 per
acre with cotton and truck crops. Some cotton growers were forced to pay from
one-quarter to one-half cent above the regular wage scales to get their crop picked

8 University of California — Experiment Station

last year (1924), because of puncture vine infestations. Such cost amounts to
from $3.75 to $7.50 per bale or from $6.00 to $12.00 per acre where a bale and
a half of cotton was grown to the acre.

Losses to citrus fruits from decay in transit have also been traced
to puncture vine in the orchard, where the picking sacks had been
allowed to touch the ground and the burs had penetrated the skin of
the fruit so as to permit decay fungi to enter.

In at least one case, puncture-vine burs have been found in bulk
raisins purchased on the retail market.

Damage to Land Values. — The losses in valuation of land badly
infested with puncture vine are difficult or impossible to estimate, but
they are certainly very great. Some infested land is unquestionably
not worth the cost of controlling the weeds. Banks are said to inquire
into the practices of their clients as to puncture-vine control. Rental
values in the San Joaquin Valley, according to C. H. Stiles of McFar-
land, as quoted by Jumper, (25) "dropped from the customary $25.00
per acre for good land to $18.00 or $20.00 per acre if puncture vine is
allowed to overrun the place, and badly infested pieces depreciated
in sale value as much as 25 per cent because of the infestation. ' '

Injury to Persons. — The barefoot boy is almost unknown in sec-
tions where puncture vine is prevalent. Injuries to cotton and grape
pickers are not uncommon. The handling of melons carrying
puncture-vine burs has frequently resulted in injuries. Infections
following puncture-vine wounds have occasionally been reported.

Injury to Animals. — The grade of wool is lowered by the pres-
ence of puncture-vine burs in large quantities. Mechanical injuries
to animals as well as to persons are frequent. Cattle, horses, sheep,
swine, and dogs have all been known to receive wounds from puncture-
vine burs. Mouth injuries are occasionally noted, but not so fre-
quently as might be presumed from the prevalence of the weed in
certain sections. Harold L. Pomeroy, who, when Horticultural Com-
missioner of Kern County, worked closely with the county veterina-
rian and personally observed numerous cases of injury to livestock,
stated in an unpublished report (1923) :

We found many instances where sheep had slowly starved to death, the cause
of death being- a mystery to the owner. They would not eat and would not seek
food, but would lie down and slowly dwindle away. Examinations proved that
the sheep had picked up mature burs in their feet, the prongs causing such a
soreness that they could no longer walk. We found cases where both sheep and
cattle had eaten these burs and had their stomach linings punctured. Horses
have had their mouths so full of burs that they could no longer chew their food.

A disease of sheep in South Africa caused by grazing on green
puncture vine is described by Stent. (40 '

Bui/. 528] The Puncture Vine in California 9

Authentic cases of serious injury to livestock in California from
feeding" infested hay are rare. In an investigation undertaken by
Neville, (30) alfalfa hay containing large quantities of puncture-vine
burs was fed for a period of eight weeks to six of each of the follow-
ing animals : cows, calves, sheep, and hogs. No injury to any of the
animals was noted, either during the time of observation or on post-
mortem examination; nor was any loss of weight or condition noted
that could be traced to the puncture vine.

Milk cows have been reported by dairymen to fall off materially
in milk flow when first fed infested hay.

i§£ *

■£*"*"

'^NkJ^'^' «*

* y^ ,v

...» ™ 4^ s **»«f>

HHNKj**,

f^r^

Fig. 4. — Prostrate, trailing habit of puncture vine.

Damage to Tires. — The spines on puncture-vine burs are stout
enough to penetrate the tread of a pneumatic tire, and, if the tread
is worn thin enough, can readily cause a puncture. Bicycle tires
and well-worn fabric tires have frequently been punctured, but
instances of punctures in cord or heavy balloon tires are rare. The
spines probably do not penetrate into the tread much beyond their
own length, as the working of the tire tends to pulverize them before
they can damage the tube. Airplane tires, of lighter construction
than automobile tires, have been reported punctured by burs on
the landing field. (29)

DESCRIPTION AND CHARACTER OF THE PLANT

The name " puncture vine" or "puncture weed," generally
adopted in California, is credited to Kent Knowlton, former Kern
County Horticultural Commissioner. This name of itself has done
much to keep the weed before the public mind. The earlier names
by which it was known are "ground bur nut" and "caltrop." Other
local names by which it is sometimes called include ' ' Texas sandbur, ' '
"Texas longhorn," "bullhead," "Arizona thistle," and "heel-bur."

10 University of California — Experiment Station

Puncture vine is thus described by Smiley : (39)

Habit : Mat-forming' annual with many prostrate branching stems 10 inches
to 2.5 feet long, conspicuously jointed, slender and weak, bearing short, silky,
spreading hairs, or some of the stems ascending. Leaves numerous, compound,
1.5 to 2.0 inches long, formed of 5 to 7 pairs of leaflets, each leaflet about %
inch long, oval in shape and ending bluntly, grayish-green in color due to the
covering of silky hairs on both surfaces; leaf -stalks short with a pair of small
stipules at base. Flowers solitary in the leaf-axils, about y<% inch broad, short
stalked; calyx of 5 persistent, jointed, hairy sepals; corolla of 5 yellow petals,
longer than the sepals and broadening from the base, early falling away;
stamens 10, alternately longer and shorter; ovary 5-celled, covered with erect
hairs and surmounted by a short style ending in a 5-ridged stigma; the ovary
ripening into a spiny fruit about % inch broad which at maturity splits into 5
parts (carpels), each containing 3 to 5 seeds and armed with 2 to 4 spreading,
unequal and rigid, often curving spines, the longest ^4 inch in length.

The root system consists of a simple taproot branching" into a
network of very fine rootlets, which surround the soil particles so as
to take the utmost advantage of the soil moisture. This root habit
enables the puncture vine to live under conditions of drought
survived by few other plants.

The stems radiate from the crown, branching freely. In open
ground the habit is prostrate, exposing- the maximum number of burs
to the feet of passing animals or the tires of vehicles (fig. 4). Where
the growth is very dense, the ends of the stems turn upward; and
in the shade of alfalfa, the plant may grow almost erect; when
growing along fences and other obstacles it may trail like a vine.

The leaves grow in pairs on opposite sides of the stem. They are
composed of several pairs of small oval leaflets which give the plant
such an attractive appearance that it has sometimes been carefully
tended as an ornamental or lawn plant. The stems frequently have
a reddish color; like the foliage, they are densely covered with silky
hairs, which no doubt serve as a protective covering from heat and
drought, and which give to the entire plant a silvery appearance.

The flowers, which are borne in the axils of the leaves, are bright
yellow and add to the attractiveness of the plant, The petals are
usually open only in the morning, closing shortly after noon, except
in cloudy weather. The plant is therefore less easily found in the
afternoon than in the morning.

The fruit (fig. 6) consists of a cluster of five of the spiny nutlets
or burs by which the weed is best known. The nutlets, which fall
apart at maturity, are adapted to dissemination by animals or rubber-
tired vehicles because one of the two spines usually points upward
whichever way the bur lies on the ground (fig. 5A).

Bul. 528]

The Puncture Vine in California

Lt-^1„.^._ _ - : ^:„

Fig. 5. — A, The usual position of puncture-vine burs with one point upward ;
B, puncture-vine seedlings; C, burs cut open to show position of seed cavities; J),
work of field mice on burs; E, fruit after treatment with oil; note the separation
of the carpels (burs).

Fig. 6. — Green puncture-vine fruit.

12 University of California — Experiment Station

The number of burs produced of course varies greatly with the
size of the plant. Under exceptionally favorable conditions of soil,
moisture, and light, plants have been known to reach a spread of 20
feet in diameter. A plant covering an area of approximately 400
square feet, observed by W. B. Camp at Shafter in October, 1923, was
computed to have produced an average of 10 fruits per square inch,
or a total of 2,880,000 burs. On the other hand, fully matured plants
not more than 2 or 3 inches across may be found in hard, dry ground.
A plant 3 months old observed by Paul L. Higley at Bakersfield in
July, 1926, was found to have 820 mature bur clusters, 445 immature
bur clusters, and 419 blossoms and buds.

The seeds, enclosed within the horny tissue of the bur, are pro-
tected by the spines and by the warty protuberances on the outer
side of the nutlet or bur. Within the bur the seeds lie one above the
other, separated by the same hard, horny tissue that composes the
outer walls of the bur. The seed nearest the stylar end is the largest
and usually sprouts first, the other seeds following in the order of
their position in the bur. If there is sufficient moisture to germinate
but one of the seeds in the bur, the others may remain dormant until
conditions are favorable for germination.

The number of seed cavities in each bur varies from 1 to 4
(fig 5(7). Of 25 burs taken at random from a sample, 10 were found
to have produced 3 seed cavities each, all of which contained fully
formed seeds; 10 were found to have 2 seed cavities each, 6 of these
10 burs containing 2 seeds each, 2 containing but 1 seed each, and 2
containing no fully formed seeds; 5 burs were found to have but 1
seed cavity each, 2 of these burs each containing a fully formed seed,
and 3 containing none. The average number of seed cavities in the
sample was 2.20 per bur; the average number of fully formed seeds,
1.84. Five burs, or 20 per cent, contained no fully formed seeds. In a
duplicate sample incubated in the laboratory 72 per cent of the burs
tested germinated one or more sprouts each.

LIFE HISTORY

Season of Growth. — The normal period of growth of puncture
vine is from late spring until fall, the beginning of the period of
active growth varying from year to year. Growing plants have, how-
ever, been found in all months, although they are very susceptible to
frost. Thus specimens were collected at Terminal Island, Los Angeles
County, on January 12, 1927, and at McPherson, Orange County, on
February 24, 1930.

Bul, 528]

The Puncture Vine in California

For four seasons, 1923-1927, F. R. Brann kept a record of the
number of plants that sprouted under natural conditions on a vacant
lot at Visalia (table 1). No plants were allowed to form seed during
this period. The lot, 200 by 150 feet, was in a generally moderate
degree of infestation for several years before 1922. In April, 1922,
the lot was cleared of weeds, and thereafter the puncture vine was
hoed and burned four times during the season, no check being made
as to the number of plants destroyed. Beginning in May, 1923, the
young plants were pulled by hand at frequent intervals, and a record
was kept of the number found and destroyed upon each inspection.
Since 1927, parts of this lot have been used for testing various treat-
ments, hence further data on the number of plants recurring over the
entire plot under natural conditions are not available.

TABLE 1

Seasonal Growth of Puncture Vine in a Plot 200 By 150 Feet Under

Natural Conditions, at Visalia, California, 1923-1926*

Year

Date

Number
of plants
destroyed

Year

Date

Number
of plants
destroyed

1923

May 16

482

276

258

391

126
585
816
184
217
123

87
112

52
9

1925
1926

May 15

715

June 1

May 28

305

June 18

229

July 7

June 27

137

July 20

July 8

July 29

1924

May 6 ..

April 13

May 30

April 28

518

June 12

May 13

348

June 23

May 29

213

July 7

192

July 20

316

July 6

213

July 12

July 23

October 2

July 27

July 29 ...

* From data compiled by F. R. Brann, Tulare County Horticultural Commissioner.

The accumulated germination as shown in table 1 was compared
with the mean temperatures at Visalia for the corresponding periods,
the temperature data being calculated as accumulated temperatures
above 55° F, beginning with April 1 of each season.

The trend of the germination curves followed the accumulated
temperature curves with remarkable regularity through the month

University of California — Experiment Station

dcci//r?t//(?fec/ Germ/nof/on

dcci/mu/ofed 7e/7?perafc/re

/soo

u //oo

^ 900

SOO

Tofa/ 5eoso/7o/ /?o/'/?fo//

/9£S

/924

/9£S

/S>£<5

Fig. 7. — Effect of May and June temperatures upon the seasonal germination
of puncture vine under natural conditions at Visalia, 1923-1926, inclusive. The
upper curve indicates accumulated germination of puncture vine to July 15 of
each season on a plot 150 by 200 feet. (Compare table 1.) The center curve
indicates accumulated temperatures above 55° F for the months of May and June
of the corresponding season. The lower curve indicates rainfall.

Bul. 528] The Puncture Vine in California 15

of June, when they diverged widely. The correlation between the
accumulated germination for May and June of each season, and the
accumulated temperatures for the same period, as shown in figure 7,
is very high (+ 0.907 ± 0.027). During that period of each year the
soil moisture was presumably sufficient for germination, provided the
temperatures were favorable. When the mean temperatures in these
two months were relatively high, in 1924 and 1926, the rate of germi-
nation was rapid; and when the May and June temperatures were
relatively low, in 1923 and 1925, the rate of germination was slower.
In each case the rate of germination fell off sharply about the middle
of July, approximately 90 per cent of the total number of plants for
the season having sprouted by that time, a fact indicating depletion
of soil moisture.

There is no apparent correlation between total seasonal rainfall,
practically all of which occurs in the winter months in that locality,
and the germination of the puncture vine. The two years of high
total germination, 1924 and 1926, were both seasons of low rainfall.
However, repeated observation show that puncture-vine seed can be
made to sprout in abundance if sufficient moisture is provided during
the warmer months. Thus rains in southern California in August,
1927, and again in September, 1929, followed by warm temperatures,
caused the sprouting of multitudes of puncture-vine seeds which nor-
mally would have remained dormant until the following season. The
concurrence of late spring rains and abnormally high temperatures
in 1931 made the puncture vine that year more abundant than ever
before.

Longevity of Puncture-Vine Seed. — Little is known as to the prob-
able life of puncture-vine seed. Darlington (7) records that the seeds
of many common weeds are capable of remaining alive and germinat-
ing after lying buried in the soil for over forty years. One may
reasonably assume that the seeds of puncture vine, with their resist-
ance to heat and drought, are at least as long-lived as the seeds of
most other weeds. The Visalia plot (table 1) showed no diminution
in the number of plants appearing each year for a period of four
years, other than might be explained by seasonal variation. Subse-
quent observations of a part of the same plot that has remained undis-
turbed for five years longer indicate that to date (1931) an abundance
of viable seed still remains in the soil.

Maturity and Seed Production. — During the normal growing
season, the plants mature very rapidly. A plant under observation
by W. B. Camp, at the United States Cotton Field Station at Shafter
in 1926, averaged one blossom a day on each branch during the most

University of California — Experiment Station

active period of growth. The blossoms were tagged and dated, and
samples were collected of burs of various ages from the time of
blossoming. These samples were held until the following season and
germinated in the laboratory (table 2). The least mature sample to
germinate was 10 days old, while the sample 11 days old germinated
nearly as well as fully matured seed. The variations in the germina-
tion tests for the various samples no doubt result chiefly from the
small number of burs in the sample. The 8, 9, and 10-day samples
decayed after 7 days in the incubator, while the others continued
to germinate for a longer period.

The rigidity of the spines roughly indicates the stage of maturity.
The spines of young burs are soft and flexible, not sharp to the touch ;
they gradually become sharper and more rigid as the seed approaches
maturity. A sample of burs collected from plants at Colton in July,
1922, at the stage when the spines were still fairly flexible and the
points just beginning to feel sharp, when tested in 1925 germinated
2 out of 25 burs, or 8 per cent.

TABLE 2

Germination' Test of Puncture- Vine Burs of Various Ages from the Time
of Blossoming, Collected at Shafter, in 1926*

Age, days

Number

of burs in

sample

Number
germi-
nated

Per cent
germina-
tion

Length

of test,

days

Ripe

* Collected by W. B. Camp.

Germination. — Puncture-vine seeds sprout most rapidly during the
warmest weather, moisture and other conditions being equal. A num-
ber of samples in different stages of maturity were tested in duplicate
to determine the effect of temperature on germination. One lot from
each sample was incubated at a day temperature of 30° C (86° F)
and a night temperature of 20° C (68° F). The other lot was incu-
bated at a day temperature of 35° C (98° F) and a night temperature

Bul. 528]

The Puncture Vine in California

of 20° C. In every case the lot incubated at the higher temperature
showed a more rapid rate of germination and a higher total number
of sprouts. The results are represented graphically in figure 8.

An appreciable difference in the rate of germination may be noted
between burs picked before shattering, newly matured burs, and
mature burs from the previous season. A further check made on a
number of burs in different states of maturity indicates that germina-
tion is very rapid in seed one year old or more. Approximately 90

/O 20 JO

90 /£0

T//r?e /n Doys

Fig. 8. — Rate of germination of typical samples of puncture-vine burs in
different states of maturity, as influenced by temperature. Heavy lines indicate
lots incubated at day temperatures of 35° C and night temperatures of 20° C.
Light lines indicate lots incubated at day temperatures of 30° C and night
temperatures of 20° C. a, Burs picked before shattering; b, same, dried before
incubating; c, burs shattered, current season; d, burs one year old.

per cent of the number of viable burs of such seed germinated within
the first 3 days of incubation, and practically all germinated within
10 days. Fleshly matured seed, however, germinated very slowly,
few if any sprouts appearing for the first 10 days. Very little germi-
nation could be induced in the first 60 or 90 days, and germination
was not completed in most cases for 200 days or more. The tendency

18 University of California — Experiment Station

of seeds to mold or rot when kept in a moist incubator for a long
period undoubtedly explains the relatively low total germination of
some of the samples. The burs picked before shattering apparently
show a, more rapid rate of germination than the freshly matured burs,
though not necessarily a higher total.

These tests indicate that puncture vine enters a period of rest or
dormancy upon reaching maturity, even under conditions of tempera-
ture and moisture most favorable for germination. They further
indicate the unreliability of short-time germination tests on seed of
the current year's crop, and the need for caution in interpreting
results of treatments of newly matured burs.

That greenhouse tests are even less reliable than incubator tests
may be seen from table 3. Samples of both treated and untreated
burs were tested in duplicate, one lot in soil in the greenhouse, the
other in blotters in the incubator. The greenhouse-tested lots were
generally lower in germination than the incubator-tested lots. In
several of the incubator tests a number of th,e burs which remained
ungerminated were still undecayed at the termination of the test, and
possibly contained viable seed. Goss (12; has recently described an
improved method of germination in which sterile soil is used in the
incubator instead of cloth or blotters. Although comparative tests
are not reported, the new method is expected to prove more reliable
than the blotter method.

To obtain a reasonably accurate germination test of the current
season's burs, one must hold the sample for a period of at least 6
months before testing. Approximately the same result may be ob-
tained by incubating for a like period, but this method is less reliable
because of the probability of losing some of the seeds by mold or
decay. A quicker way of approximating viability is to soak the sample
in water until the burs soften, when they can be cut into without
difficulty, and one can readily see from a cross section which seeds
are normal in size and which are shriveled. The appearance of the
seed is a fairly reliable indication of viability. For example, a
laboratory germination test of a certain lot of burs showed sprouts
in 35 out of 49 burs, or 72 per cent. Out of 25 burs from the same
lot which were cut open and examined, 20, or 80 per cent, contained
apparently viable seeds; the difference is well within the probable
error for such small samples. Another sample showed apparently
viable seed in 97 out of 100 burs dissected, while 86 per cent of a
duplicate sample germinated when incubated in the laboratory.

Viability of seeds in burs treated with Diesel oil may readily be
detected in this manner, as the penetration of the oil into the bur

Bul, 528]

The Puncture Vine in California

can easily be followed. When burs are treated with colorless chemi-
cals, however, inspection does not immediately show whether or not
the germinability of a seed has been affected.

The dormant or resting state of newly matured seed undoubtedly
protects the plant against the late rains which might cause seeds to
sprout too late for the plants to mature before frost. The nature of
the protection thus afforded to the seed is not known, but is probably
associated with moisture absorption. The change, whatever it may
be, is apparently not completed until the burs shatter from the plant.

TABLE 3

Comparison of Greenhouse Tests with Incubator Tests for Germination

of Puncture- Vine Burs

(Greenhouse tests continued 55 days, incubator tests 61 days.)

Greenhouse test,
per cent germinated

Incubator test

Sample No.

Per cent
germinated

Ungerminated*

seeds, per cent

undecayed

4
4

14
6

7
8

18
8

22
3
11
2
7
6
6

J4
5

23
17

* In some of the incubator tests in this series a number of burs which remained
ungerminated at the end of the 61-day period were still undecayed and possibly
contained viable seed.

Burs which are picked from the plant when still green, even if fully
developed, will germinate more quickly than ripened burs of the
current season's growth, although the total germination may be less.
When the resting period is interrupted by picking the burs or killing
the plant before the dormant stage is reached, the rate of germination
is apparently accelerated. The length of this resting period has not
been determined. The newly matured burs tested in the laboratory
did not reach 50 per cent of their total germination until they had
been in the incubator about 90 days; old, mature burs, on the other
hand, completed about 90 per cent of their total germination in the
first 3 days. Burs picked when still green reached 50 per cent of
their total germination in 10 to 20 days.

2'0 University of California — Experiment Station

CONTROL OF PUNCTURE VINE

The fact that early attempts to control puncture vine were largely
a failure is easily understood. The only method offered before 1922
was that suggested for annual weeds in general : cultivating or cutting
to prevent the formation of seed, and burning plants that may already
have formed seed. (23) As puncture vine sprouts irregularly through-
out the season and produces seed at an early stage of growth, one
must go over an area repeatedly at frequent intervals in order to
make progress in control by cultivation. Although this method is
satisfactory on cultivated land in the hands of a careful operator,
puncture vine on roadsides and other uncultivated land affords a
continual source of reinfestation if not controlled.

Natural Enemies. — Small rodents are fond of puncture-vine seeds
and will gnaw into the burs to get at them (fig. 5D). Rabbits readily
devour the young shoots and sometimes eat off the runners down to
the crown. Turkeys are said to be especially fond of the crowns of
puncture-vine plants. Several species of aphis occasionally attack
puncture vine, sometimes severely injuring it, and dodder is some-
times found growing upon it; otherwise, this weed in California
seems unusually free from attack by insects, diseases, and parasites.

Treatment of Infested Products. — The removal of puncture vine
from grain and seed crops, wool, and other products which normally
go through a cleaning process, presents no unusual difficulty ; but the
disposal of bulky products such as hay, straw, manure, and screenings,
when infested with puncture vine or other noxious weed seeds, pre-
sents a problem of some magnitude unless the material can be utilized
on the premises where it was produced. Infested material is not
welcome in territory where an effort is being made to keep these
weeds under control. Since such products are for the most part of
small value, any process that will add materially to their cost
without correspondingly increasing their value must be considered
impracticable.

With the ordinary milling process used in the manufacture of
alfalfa meal, the smaller puncture-vine burs work their way through
the screens into the finished product. When passed through mesh
not larger than % 2 inch, however, the meal is pulverized finely enough
to destroy the seed of puncture vine. A process whereby the meal
is ground to nearly the consistency of flour and bolted through fine-
mesh screens has afforded an outlet for a considerable quantity of
infested hay which otherwise could be disposed of only locally. It

Bul. 528] The Puncture Vine in California 21

is impossible to find any puncture-vine burs in this product, or to
germinate any seed from it.

Although the greater part of the straw, chaff, and other organic
refuse containing weed seeds is now waste, and can be destroyed
without loss if necessary to prevent the spread of weed seeds, a
considerable amount is used as manure in the orchards of southern
California. The general practice in recent years is towards less
cultivation in the orchards; and the introduction of weed-infested
manure and straw, without the intensive cultivation necessary for
weed control, is liable to result in the establishment in the orchard of
puncture vine and other weeds difficult of eradication.

The composting or fermentation of manure has long been known
to destroy weed seeds. Pammel (32) in Iowa found that seeds of most
weeds were destroyed after one month of composting ; in 5 weeks only
a very small percentage of any seed germinated; and in 60 days, of
52 kinds of seed tested, all were destroyed. Fruwirth (10) in Germany
found that a small number of seeds germinated after ' ' cold ' ' fermen-
tation of the ordinary yard manure, but none survived after "hot"
fermentation (60° to 80° C).

The destruction of the viability of weed seeds by the composting
of manure suggests the use of a similar process for straw and other
bulky organic material. Waksman, Tenney, and Diehm (43) in New
Jersey found that decomposition of such material in the composting
process results largely from breaking down of the cellulose and
similar components of plant tissues by microorganisms. These micro-
organisms require large quantities of available nitrogen and phos-
phorus, both of which are present in sufficient quantities in manure ;
but in straw and similar material, nitrogen is low and must be added.

To determine the effect of decomposition, accelerated by the
liberation of ammonia, on the germination of puncture vine contained
in organic refuse, two sample of cleanings were taken after the
conclusion of Neville 's (30) puncture-vine feeding experiments at the
Los Angeles Union Stockyard previously noted, and removed to
Pomona on May 23, 1928. Stack No. 1, composed of 3,500 lbs. of
cleanings from the feed boxes, consisting largely of straw and burs,
was treated with 200 lbs. of ammonium sulfate and 200 lbs. of ground
limestone. Stack No. 2, composed of 7,200 lbs. of cleanings from the
corrals, consisting largely of manure and burs, was treated with 300
lbs. of a : monium sulfate and 300 lbs. of ground limestone. The stacks
1 down in alternate layers of cleanings, sulfate of ammonia,
ore. cleanings, and ground limestone, with flat tops to facilitate

2*2 University of California — Experiment Station

watering. Each stack was covered with approximately 1,000 lbs. of
barley straw and watered at frequent intervals throughout the experi-
ment. In 3 months stack No. 1 had settled to approximately one-fourth
its original volume, and stack No. 2 to approximately one-third. In 6
months the interiors of the stacks were examined and found to have
become thoroughly decomposed. No puncture-vine burs were recog-
nizable, nor could any sprouts be germinated from the samples. No
analysis was made of the product. It resembled good barnyard
manure, was odorless, and crumbled readily. The sample from stack
No. 1 was grayish in color; that from stack No. 2, yellowish. When
the stacks were torn down 14 months after the treatment the outer
layers, no doubt because they could not be kept wet during the
process, had not yet decomposed, and contained an abundance of
puncture-vine burs which germinated readily.

Mechanical Control. — Any means of destroying the entire plant
is sufficient to control puncture vine, provided only that it be applied
before the seed is formed, and repeated whenever new plants appear.

Cultivation by any of the ordinary tillage implements when the
plants are in the seedling stage is the easiest and quickest way to
control the pest. The more rapidly the seeds can be made to germi-
nate, the sooner will the supply be exhausted from the soil. Frequent
irrigation during the warmest part of the season will hasten germina-
tion; plowing or deep cultivation will retard it.

Hand pulling or hoeing may be used to control small patches or
to supplement cultivation in spots not reached by the tillage imple-
ment. If no burs have formed, the plants may safely be left on the
ground. If only immature burs incapable of shattering are present,
the plants should be carefully gathered and burned, as some of these
burs will probably contain viable seeds. If, as is most often the case,
any of the burs have shattered or are sufficiently mature to. shatter
when lifted, the plants must be treated in place with chemicals or
the burs carefully picked up by hand, if the infestation is to be
eliminated.

Scraping with a road grader is an inexpensive means of destroying
numbers of young plants on th,e roadside, but only serves to spread
the burs if done after seed is formed (fig. 9). To be of value in the
control of puncture vine, scraping must always be supplemented by
other work.

The management of various crops so as to keep puncture vine
under control is sometimes a serious problem. Such crops as late
potatoes, melons, and beans, as well as some varieties of grapes,
cannot be worked during the latter part of the summer; and unless

Bul. 528] The Puncture Vine in California 23

hand work is resorted to, puncture vine will continue to sprout and
grow to maturity from seeds remaining' in the soil, as long as sufficient
heat and moisture are present, Alfalfa also presents a difficult prob-
lem. In a good stand of young alfalfa in vigorous condition, cut at
the proper stage, puncture vine does not mature seed ; but if hay free
from puncture-vine burs is to be produced on infested soil, special
attention must be given to control on the borders and in spots where
the stand is thin.

Fig. 9. — Puncture vine on roadside, Kern County.

Heat. — Burning is, of course, adequate as a control measure if
both plants and burs are destroyed. However, it requires a great
amount of heat to consume green plants, and this method is impracti-
cable on a large scale. To determine the effect of heat on germination
of puncture vine, heavily matted vines were treated with 50 per cent
oil emulsion. The dead plants were fired when dry, but they were
not completely consumed. A sample taken after treatment with oil
but before firing gave a germination test 4 of 7 per cent, as against 52
per cent in an untreated check sample. A sample taken after firing
tested 12 per cent. The apparent increase, though within the probable
error for such tests, may have been caused by an interruption of the
resting period, which increased the rate of germination (see page 18).
In another series of tests, the flames were fed with fuel oil until the
plants were entirely consumed, and although many burs remained,
no germination could be induced. It apparently made no difference
whether the plants were first killed with oil and resprayed before
burning or whether the burning was done immediately after treat-

4 Becords of all germination tests reported herein are on file in the State-
Federal Seed Laboratory at Sacramento.

2'4 University of California — Experiment Station

ment. When the previous treatment completely destroys the viability
of the seeds, as is usually the case where Diesel oil is used, no
additional benefit is, of course, derived from the burning other than
the removal of dead vegetation.

No germination was reported in tests of burs treated with heat
from a weed torch nor in burs treated by live steam from a railroad
engine.

Qualities of Chemicals Required for Control. — A herbicide, to be
satisfactory for the control of puncture vine under all conditions,
must be cheap, readily available, easy to apply, and harmless to the
soil and to animals, and must be capable of killing not only the plant,
but also the seed. Certain petroleum products, particularly Diesel
oil, more nearly meet all of these requirements than any other chem-
icals tested. Sulfuric acid, arsenicals, and chlorates, however, have
all been successfully used for puncture vine under special circum-
stances. A great many other compounds are also useful as weed
killers, among which may be mentioned copper sulfate, copper nitrate,
iron sulfate, ammonium sulfate, sodium bisulfate, sodium chloride,
sodium carbonate, sodium hydroxide, sodium bichromate, hydrochloric
acid, nitric acid, carbolic acid, and formaldehyde. Any of these
chemicals will readily kill young puncture-vine plants; but only
certain petroleum derivatives are known to kill the seeds as well.

Quantities of Chemicals Required. — The quantity of a chemical
solution required to treat a given area varies so greatly with the
density of foliage, the chemical used, the style of equipment, the
manner of application, and the efficiency of the operators, that it is
difficult to estimate except by experience. Thorough coverage is more
important with oil, which is applied to kill the seeds in all states of
maturity, than with chemicals which are applied to kill the plants
only. On the other hand, because of its spreading qualities, less oil
is required to obtain thorough coverage than is possible with water
solutions. Pipal (36) in Indiana applied oil to wild garlic at the rate
of 75 gallons per acre. For various water solutions on morning-glory
and other weeds, 100 to 400 gallons per acre is recommended by work-
ers at several different experiment stations. Brown and Streets (6)
in Arizona recommend 200 gallons of sulfuric acid solution per acre
for puncture vine. Gray (13) noted that about 300 gallons of an
arsenical spray solution per acre is required for the treatment of
wild morning-glory. In field practice 1,000 gallons of spray solution
per acre is sometimes required to cover dense vegetation.

Equipment for Application of Chemicals. — Since chemical control
measures have been extensively employed, a great variety of equip-

Buu 528]

The Puncture Vine in California

ment has been utilized for the spraying of puncture vine and other
weeds. The designing of special equipment for weed spraying is
somewhat complicated by the requirement that it be adapted for
handling various chemicals, including oil, strong acids and corrosives,
and powerful oxidizing agents, for which the usual type of orchard
spraying equipment is not fitted.

One of the first rigs designed exclusively for weed spraying em-
ployed a rotary gear pump. Pumps of this type will deliver a large
volume of material with a small amount of power ; they are inexpen-
sive, and reasonably durable, provided the spray material is well
screened against grit and sand. A 1-inch rotary gear pump may be

Fig. 10. — Weed sprayer with compressed air atomization and multiple nozzle.

(From Ext. Cir. 54.)

operated at a pressure of 75 to 100 pounds. High pressure appears
to be of less importance than volume of material in the spraying of
weeds, especially puncture vine. A number of such rigs have been
used in various parts of the state.

Another rig designed especially for weed spraying utilized the
principle of atomization with compressed air instead of a pressure
pump (fig. 10). This type of rig, though also incapable of high
pressures, is adaptable to various problems encountered in weed
spraying. By regulating the proportions of fluid and air, one can
obtain a spray of almost any degree of fineness. This type of sprayer
also makes an excellent weed burner, utilizing atomized oil for fuel.

The most common type of orchard sprayer employs a plunger
pump, developing relatively high pressures of 200 to 400 pounds,

26 University of California — Experiment Station

the capacity depending' upon size and style. Such a sprayer may
be readily adapted for weed spraying.

In hand equipment the types used for garden spraying have been
used also for weed spraying. The compressed-air knapsack sprayer
is generally favored over the displacement type. A hand pump with
a trombone-like action, equipped with a knapsack tank, has been used
for spot spraying' of puncture vine.

If acids or corrosive chemicals are used, . a wood-stave tank is
preferable to a metal one. So-called "porcelain-lined" cylinders
should be replaced with brass, bronze, or solid porcelain. If oil is
used, a metal tank is better, but wood stave may be used if care is
taken to fill it with water occasionally to prevent shrinking. Rubber
parts should be replaced with fiber where possible. A specially
treated gasoline hose now obtainable withstands Diesel oil much
better than the ordinary spray hose.

Application should be made with a spray rod. A spray gun is
excellent for tall dense growth, but not for prostrate weeds like
puncture vine.

The type of nozzle varies with the kind of weeds to be sprayed.
A nozzle delivering a cone-shaped spray is satisfactory if so con-
structed as to give a uniform mist throughout the cone; but with a
nozzle which delivers most of the material at the periphery, uniform
coverage cannot easily be obtained. A fan-shaped spray is usually
preferred for spraying strips of weeds, and a cone-shaped spray for
spot spraying-. Several nozzles are sometimes used on a single rod
(fig. 10) or on a boom attached to the rig.

Sulfuric Acid. — A 2 per cent solution of sulfuric acid is recom-
mended by Brown and Streets (6) in Arizona for the control of punc-
ture vine. In this dilution it is probably the cheapest material avail-
able for the purpose. The same investigators found that dilutions
of 2 to 10 per cent can be used effectively on a large variety of weeds.
Aslander (2) observed that sulfuric acid is more effective in a dry
atmosphere and at higher temperatures. Because it does not affect
the germination of the seeds, it is effective only for use on young
plants. Although not injurious to the soil and nonpoisonous to
animal life, it is very disagreeable to use as a spray, for it will eat
the clothing and burn the flesh; but with reasonable precautions it
can be handled safely. In dilute solutions it is highly corrosive to
metal. The standard types of spray rigs are quickly damaged by
its use. No satisfactory equipment for large-scale spraying* of sulfuric
acid has yet been developed.

Buu 528] The Puncture Vine in California 27

Gray (13) found that acid sludge (a by-product from oil refineries,
containing about 50 per cent sulfuric acid) gave encouraging results
on morning-glory, and believed the action to be due partly to the
highly toxic constituents of petroleum distillates removed by the
sulfuric acid in the refining process. That these constituents, if
present, are combined with the sulfuric acid rather than with the
tarry residue obtained upon hydrolyzing the acid sludge is indicated
by tests made in the San Fernando Valley in 1927 with acid sludge
in which the acid was removed or neutralized. Neither a 10 nor a 20
per cent solution of the neutralized acid sludge had any apparent
effect on puncture-vine plants.

Crude acid sludge in concentrations of 2%, 5, 10, and 20 per cent
was applied to puncture vine in the Imperial Valley in 1925. At the
2y 2 per cent concentration the plants were wilted ; at 5 per cent they
were killed within 24 hours. The treatment did not affect the viability
of the seeds. The treated burs in every case showed a higher germina-
tion than the untreated check sample, possibly because of an
interruption of the resting period.

Arsenic. — A number of compounds of arsenic are effective weed
killers. Aside from numerous proprietary preparations, the com-
pounds most commonly used are sodium arsenite and arsenic acid,
both obtainable in either liquid or solid form. Arsenic acid has been
used in Queensland in the destruction of prickly pear, White-
Haney {45) reporting it to be the most effective specific for the purpose.
Johnson (21) found it more effective than other arsenic compounds on
Russian knapweed and other deep-rooted perennials. Sodium arsenite
is somewhat cheaper than arsenic acid and equally effective for annuals
like puncture vine. All arsenic compounds, being poisonous to
animals, cannot safely be used to spray vegetation to which grazing
animals have access, Sodium arsenite is said to be particularly attrac-
tive to livestock. Soluble compounds of arsenic may be absorbed
through the skin. A solution or paste of lead acetate, ferric hydroxide,
or other antidote should be kept on hand when arsenic is being used.
Vegetation burns somewhat less readily when sprayed with arsenic.
A poisonous gas, arsine, having the odor of garlic, is given off when
weeds sprayed with arsenic are burned.

Soluble arsenic compounds readily kill the plants, but not the
seeds, of puncture vine. A large number of samples of burs treated
with arsenic, mostly in the form of proprietary preparations, have
been sent to the Seed Laboratory for germination tests. (19) While
some of the tests showed a very low germination, the results were by
no means uniform, ranging from to 73 per cent. In general, the

28 University of California — Experiment Station

tests on green burs ran lower than those on mature burs; but since
many of these tests were continued for less than 4 months, the results
cannot be said to be conclusive (see page 18). Perhaps arsenic,
when applied to the plant, may be carried into the green seed pods
to a sufficient extent to affect germination. That translocation of
arsenic takes place in plants has been demonstrated in the wild
morning-glory (Convolvulus arvensis) by Kennedy and Crafts, (26)
and in the prickly pear (Opuntia inermis) by White-Haney. (44) The
variable results with arsenic might be explained by variations in the
condition of the plants at the time of spraying, the degree of maturity
of the burs possibly affecting the movement of the poison into
the seeds.

The effect of arsenic on the soil has received the attention of a
number of investigators. McGeorge (28) in Hawaii, with an average
rainfall of 200 inches, found no arsenic below the surface 4 inches
of soil to which sodium arsenite had been applied as a spray annually
for 5 years at the rate of 3 applications per year, 5 pounds of arsenic
(As 2 3 ) per acre being used for each application. He concluded
that "soils possess strong fixing power for arsenic, and that when a
sodium arsenite spray is used for destroying weeds, the arsenic will
ultimately be deposited in the surface soil, there to remain in spite
of the leaching effect of rains or irrigation." Aslander (3) also found
that arsenic penetrates the soil but slowly. He permitted a N/10
solution of sodium arsenite to leach through a 15-cm core of soil. In
one type of soil having a reaction of pH 5.77, arsenic was found in
a concentration of only N/1,000 after 34 days, increasing to about
N/500 10 days later. In another soil having a reaction of pH 7.87,
a trace of arsenic was found after 18 days, increasing to N/400 in 30
days. On the other hand, Schulz and Thompson, (38) working in the
north central states, found that the leaching of arsenic from surface
soil was very rapid and extensive, although they did not show to
what depth the arsenic penetrated the soil. Variations in soil com-
position were shown by each of these workers to influence the amount
of arsenic retained. Greaves and Carter (15) found that sodium arse-
nite was "less toxic to ammonifiers and nitrifiers in a loam soil than
in a sand, and still less toxic in an organic loam than in a silt loam,"
probably in part because of a combination of the arsenic with the
organic colloids in the soil.

Where weeds have been sprayed with arsenic acid, subsequent
vegetative growth is more vigorous than on unsprayed areas. It is
well known that plants are stimulated by small quantities of arsenic,
whereas larger amounts are toxic. Schulz and Thompson, (38) inves-

Buu 528] The Puncture Vine in California 29

tigating the relative toxicity of arsenious acid, sodium acid arsenite,
orthosodium arsenite, and sodium arsenate, found a decrease in tox-
icity in the order named. Greaves and Carter (15) found that the total
number of microorganisms in soil was greatly increased by the appli-
cation of arsenic; but that "although comparatively large quantities
of arsenates (salts of arsenic acid) may accumulate in a soil without
injuring its beneficial microflora, only small quantities of sodium
arsenite may accumulate without producing ill effects. ' '

Gray, (13) working at Centerville, California, found that all of the
plots "to which an ounce or more of arsenic trioxide (as sodium
arsenite) had been applied per square yard were barren of all vegeta-
tion, except morning-glory, for 14 months, notwithstanding the leach-
ing by the rains of two winters," and suggested the use of this
material to sterilize fence rows and roadways. (14)

Schulz and Thompson (38) found that the presence of arsenic in
the soil did not prevent the germination of seeds of various kinds
but interfered with root development, so that the seedlings, other
than rye, died after attaining a height of 2 or 3 inches.

Chlorates. — Puncture-vine plants are readily killed by chlorate
solutions in concentrations of 2 per cent or more, but Ball (4) has shown
that chlorates do not kill the seeds (fig. 11). In several series of
tests, the treated burs actually showed an increased percentage of
germination, possibly because of interruption of the resting period.

Chlorates have a detrimental effect on the soil (46) and are therefore
not suitable for use in agricultural land, although the injury prob-
ably does not last more than a year or two unless excessive amounts
are used, since chlorates are relatively unstable compounds and tend
to break down into the less toxic chlorides. In a number of instances,
injury to fruit trees followed the application of chlorates to weeds
in the orchard. Aslander (3) found that chlorates penetrate the soil
freely and decompose but slowly. It required 10 weeks for sodium
chlorate to decompose in soil kept at 30° C (86° F), and decomposition
proceeded much more slowly at lower temperatures. This fact un-
doubtedly explains the temporary sterilization of soil treated with
chlorates. The number of puncture-vine plants recurring the same
season is less after treatment with chlorate than where other methods
of treatment are used. For the purpose of soil sterilization, however,
chlorates are more costly and less permanent than sodium arsenite.

Chlorates are relatively harmless to animals, except in excessive
quantities.

When intimately mixed with dry organic matter, chlorates are
highly combustible ; and when they are used as weed killers, the

University of California — Experiment Station

sprayed herbage presents an unusual fire hazard. This fact is of no
great importance in the control of puncture vine because of its
prostrate habit, unless the growth of the weed is exceptionally heavy
or unless it is in proximity to dense, dry vegetation. Certain pre-
cautions should, however, be taken in the handling of chlorates. The
clothing and shoes of workers should be fireproofed and waterproofed,
and the wood parts of the spray rig kept wet and washed frequently ;
for, under conditions of low humidity, chlorate-saturated clothing or
wood may become ignited even by friction.

Fig. 11. — Comparative effect of oil and chlorates on the germination of
puncture vine. A, treated with oil — no germination; B, treated with chlorate, %
lb. per gallon — 40 per cent germination in 8 days; C, treated with chlorate, 1 lb.
per gallon — 33 per cent germination in 8 days ; J), untreated — 73 per cent germina-
tion in 8 days.

Sodium chlorate is the only chlorate compound extensively used
as a weed killer. Chlorates of ammonium, barium, calcium, mag-
nesium, potassium, and zinc, though effective, are more costly. One
proprietary preparation contains a mixture of sodium chlorate with
calcium chloride, the latter, which is deliquescent, being added for
the purpose of reducing the fire hazard. Willard (46) in Ohio found
the mixture "at least as effective as sodium chlorate in proportion

Bul. 528] The Puncture Vine in California 31

to its chlorate content, but not equal to sodium chlorate pound for
pound." Offord and d'Urbal (31) have shown that the addition of
calcium chloride definitely decreases the toxicity of sodium chlorate.
The extent to which the fire hazard is actually reduced by the presence
of calcium chloride has not been satisfactorily demonstrated. Theoreti-
cally, the calcium chloride would draw enough moisture at normal
humidity to prevent sprayed herbage from becoming readily ignited ;
but in the dry atmosphere which may occur in most sections of Cali-
fornia at any season, experience has proved that the fire hazard
cannot be minimized, and that organic materials saturated with
chlorate ignite very readily in spite of the presence of calcium
chloride.

Diesel Oil and Other Petroleum Products. — Various petroleum
products have been tested as weed killers from time to time. Jones
and Orton (24) in Vermont, in 1899, reported unfavorably on the use
of kerosene as compared with other chemicals as a herbicide. Thomp-
son and Robbins (42) in Wisconsin, however, found kerosene as effective
as gas oil and more effective than either fuel oil or gasoline for killing
barberries, although the action was very slow, and complete killing
was not noted in some instances for nearly a year after treatment.
Arthur (1) in 1913 commented on the effectiveness of orchard heating
oil as a weed exterminator; Pipal (36) in the following year recom-
mended it for the control of wild garlic in Indiana; and Talbot (41)
reports that waste crankcase oil thinned with kerosene is effective
for the same purpose. Gray (13) in California reported, after testing
a number of petroleum distillates on miscellaneous weeds: "The
cheaper distillates were more effective than refined distillates such
as kerosene and similar products. Petroleum products containing a
large percentage of aromatic and cracked oils were more effective
than those containing a lesser percentage."

Horticultural Commissioners Call, Stroup, and Rutherford in
1922 made tests of petroleum oils on puncture vine, each reporting
a marked reduction the following year in the infestations treated.
Bourcart (5) attributes the temporary sterilization of the soil by
petroleum to the generation of petroleum vapors, and comments on
the production of a more intense vegetation after the evaporation
of the petroleum, a result repeatedly observed in California. Pipal (36)
found that orchard heating oil, even when thoroughly mixed with the
soil, had no appreciable effect on the germination of wheat and corn
planted immediately after treatment, although it reduced the germina-
tion of garlic bulblets ; whereas crude petroleum applied in the same
manner had a marked injurious effect on germination of the grain.

32 University of California — Experiment Station

A large number of different types of petroleum oil, including
both commercial grades and special distillates, have been tested as
to their effects on puncture vine and other weeds. Practically all
those tested killed the tops of the plants. Some types failed to pene-
trate the crowns, however, so that new growth appeared after treat-
ment. A considerable variation was noted in the effects on seed
germination. Diesel oil in general was found most satisfactory. Of
29 laboratory germination tests of puncture-vine burs treated with
Diesel oil in various parts of the state, 15 showed no germination;
3 showed 1 per cent; 6, 2 per cent; 3, 3 per cent; 1, 4 per cent; and 1,
6 per cent. Two lots of crude oil showed and 1 per cent respectively,
and waste cylinder oil, 1 per cent. Various types of fuel oil showed
0, 9, 33, 49, and 83 per cent germination, respectively ; and distillates
showed almost as much variation, individual samples ranging from
to 49 per cent germination. 5

By reason of its superiority in destroying the viability of seeds,
Diesel oil and similar grades known as orchard heating oil, smudge
oil, gas oil, tops, and slop distillate, have been extensively used in
California for the control of puncture vine. Diesel oil is a commercial
grade of petroleum of great variability. It is readily available in
quantity at a low cost. It is stored in bulk at various distributing
centers, chiefly in the larger cities and at maritime points, its principal
use being for fuel in marine and industrial engines. In the fruit-
growing sections, a large amount is stored for orchard-heating pur-
poses. The principal item in the cost of oil is freight; hence the
price is necessarily determined by the distance from the refinery.
Where the cost of Diesel oil is too great, waste crank case oil or
crude oil may be used, if thinned with distillate to a consistency which
will permit its being sprayed. The more highly refined oils and
distillates are not recommended, for they cannot be depended upon
to destroy the viability of the seeds.

Used as a spray, Diesel oil is a cheap and effective herbicide, not
only for puncture vine, but for all types of annuals; for grasses,
which, because of their concealed growing points, are not affected
by many chemicals; for noncreeping perennials such as artichoke
and other thistles; and for destroying the viability of seeds. It is
especially valuable for destroying vegetation in ditches, fencerows,
firebreaks, roadsides, or similar locations. It also aids in burning
dead vegetation.

5 Records of all germination tests reported herein are on file in the State-
Federal Seed Laboratory, Sacramento, California,

Bul. 528] The Puncture Vine in California 33

In spraying' puncture vine with oil, unless the application is
thorough, some of the burs may not receive enough oil to destroy
the seeds, The green burs before shattering apparently do not absorb
oil so readily as the dry burs, probably because of the moisture con-
tent. Furthermore, the seeds are borne towards the center of the
bur cluster, where they are protected by the woody portion of the
bur (fig. 6), and unless a sufficient quantity of oil is applied to pene-
trate to the seed cavities, some of the seeds may not be killed. For this
reason a second application is sometimes recommended ; for the oil
penetrates the seed cavities more readily after the green burs have
dried and shriveled, exposing the thinner side walls of the burs
(fig. 5E). In this connection, the importance of thorough application
in the first treatment is apparent, Where a satisfactory grade of oil
is used, and the application is thorough, the kill is satisfactory, and
little, apparently, is to be gained from a second application ; but in
the case of heavily matted vines, or vines growing in dense vegetation,
thorough coverage is difficult, and in this case a second treatment is
advisable as an additional safeguard. The effect of burning after
treatment with oil has already been discussed (page 23).

Oil Emulsions. — In order further to reduce the cost of oil as a
spray for weeds, attempts were made to emulsify it with water,
according to the formula for crude oil emulsion as sometimes applied
to dormant deciduous fruit trees. The first Diesel oil emulsions for
weed spraying were prepared in 1925 by Whit C. Barber, Kern
County Horticultural Commissioner. One emulsion was prepared
with 50 per cent each of oil and water, and one with a mixture of
25 per cent oil and 75 per cent water. In each case 2 pounds of
caustic soda per 150 gallons was added, and the mixture agitated in
a power sprayer. The 50 per cent emulsion was fairly stable; the
25 per cent separated somewhat after standing for some time. Both
mixtures were effective in killing the plants. The 50 per cent emul-
sions gave a fairly satisfactory kill on the seeds, the treated sample
testing 7 per cent germination as against 87 per cent for the untreated
check sample. The 25 per cent mixture reduced the germination to
47 per cent,

When emulsions of many different grades of oil were attempted,
the results were not always so satisfactory. The desirable type of
emulsion for weed killing is the water-in-oil type, (20) in which the oil
is in the external phase and comes first into contact with the plant
tissues.

The invert, or water-in-oil, type of emulsion, with Diesel oil, is
chocolate brown or black in color, and tends to spread on an oiled

34 University of California — Experiment Station

surface and to collect in drops on a water surface. The obvert, or
oil-in -water, type is whitish in color, spreading on a water surface
and collecting on an oiled surface.

A considerable variation in emulsifiability of different lots of
Diesel oil was experienced, regardless of the emulsifier used. The
consistency of the 50 per cent emulsion was nearly always satisfactory,
but the 25 per cent sometimes refused to emulsify with the oil in
the external phase; at other times the emulsion became too heavy
to spray and had to be thinned by the addition of more oil. These
difficulties with the 25 per cent emulsions, it was found, could be
mitigated in a number of ways, such as by reducing the quantity of
emulsifier used, adding other substances, reducing the speed of the
agitator, or stopping agitation entirely after the emulsion was
made ; but the 25 per cent mixture was generally unsatisfactory for
inexperienced operators.

It was soon discovered that certain lots of Diesel oil would emulsify
with the oil in the external phase without the addition of any sub-
stance as emulsifier, and that the same difficulty with thickening or
failure to emulsify was experienced with certain lots of oil whether
or not an emulsifier was used. Analysis of samples of known behavior
showed that the only variable factor which might account for the
differences in emulsifiability was the asphalt content. The limits
of satisfactory asphalt content, expressed as asphalt by evaporation,
appear to be from 2 to 5 per cent. (22) Diesel oil is readily obtainable
within this range.

If the asphalt content of an otherwise satisfactory product is too
low, as evidenced by failure to emulsify with the oil in the external
phase, it can be raised by the addition of crude oil or hot road oil.
If it is too high, so that the emulsion tends to become too thick to
spray, the remedy is to use the oil in greater proportion, or to dilute
it with an asphalt-free distillate, or to use it unemulsified.

Various petroleum products and distillates in emulsion with water
were tried, and germination tests were made of a number of samples
taken from plots treated in the field with oil emulsions of both types.
In some cases a complete kill was obtained, but not so universally as
where oil was used full strength. Thoroughness of application un-
doubtedly has an important bearing on the results of the germination
tests; for the amount of oil actually applied to the surface of the
plant tissues is reduced when emulsions are used. In some cases
the treated sample showed as much as two-thirds as many viable burs
as the untreated sample ; but in most cases the viability of the treated
samples was less than 5 per cent. Where Diesel oil emulsion was

Bul, 528] The Puncture Vine in California 35

used with the oil in the external phase, the results were practically
the same as where Diesel oil alone was used: approximately one-ha'f
of the samples showed no germination, and none showed more than
10 per cent.

Little study has been given to the chemistry of Diesel oil. Being
a residual product, it is extremely variable. In an attempt to deter-
mine what constituents of petroleum are of the greatest value for
weed control, a number of petroleum products were applied in water
emulsions to puncture vine in 1927. These products included fractions
high in phenolic bodies and in organic acids, heavy and light fuel
oils, residues or extracts from the Dubbs and Edeleanu processes,
and tar or sludge with the acid removed or neutralized.

Of these various materials, only three, the residuum from the
Dubbs process and two extracts from the Edeleanu process, were
effective in killing the plants completely. Each of these products,
as well as other of the more effective petroleum products, such as
Diesel oil and waste crank-case oil, contains relatively large pro-
portions of either aromatics (C n H 2n _ ) or olefins (C n H 2n ), thus tend-
ing to confirm Gray's observations (13) previously noted (page 31).
The products containing phenolic bodies and organic acids in high
proportions killed the stems, but not the crowns of the plants; for
new shoots started out after the treatment. None of the products in
this test completely destroyed the viability of the seed. The fact that
all were applied in emulsion, with a relatively large proportion of
water and with the water in the external phase, may account for the
failure to obtain a more complete kill. Diesel oil in 50 per cent emulsion
with the oil in the external phase, applied as a check, gave a complete
kill of the seeds as well as the plants. Probably some of the products
tested, or other similar products, or a combination of them, when
used undiluted, or combined with an oil having a sufficient asphalt
content to form an emulsion with oil in the external phase, would
give as good results as Diesel oil, or better ; but unless such a product
could be made available in sufficient quantity and at a low enough
cost, it is not likely to replace Diesel oil as a weed killer.

Soil Sterilization. — The possibility of soil sterilization to prevent
the recurrence of puncture vine in areas where much seed is present
in the soil has received some consideration. The most pressing prob-
lem in puncture-vine control is its elimination from roadsides and
similar areas from which it is chiefly spread, and in such situations
there is no objection to permanent sterilization of the soil.

A plot at Visalia infested with puncture vine was treated in 1927
by Frank R. Brann, Tulare County Horticultural Commissioner,

36 University of California — Experiment Station

with a proprietary preparation consisting- principally of sodinm arsen-
ite. This plot to date (1931) is reported as still barren of puncture
vine, even when irrigated, whereas a check plot continues to sprout
the weed each season, although none has been permitted to form seed
for more than eight years.

An attempt to apply the sterilizing solution on a larger scale in
Tulare County in November, 1928, was less successful, however, and
had very poor results. The effects of arsenic and of chlorate com-
pounds on the soil have already been discussed (pages 28 to 29).
Sodium chloride, sodium hydroxide, calcium chloride, and many other
salts, as well as crude oil (3G) also inhibit the growth of weeds, but
the excessive amount required to sterilize the soil makes their use
for this purpose prohibitively expensive.

A series of puncture-vine plots was treated in Orange County in
May, 1930, with sodium arsenite, sodium chlorate, and Diesel oil.
These plots were repeatedly disturbed by the road grader during
the 1930 season, so that no check could be kept of the number of
puncture-vine plants which appeared; but none were found in any
of the plots except the untreated check plot. In 1931, up to July 15,
but 6 puncture-vine plants appeared in the sodium arsenite plot, 55
in the sodium chlorate plot, 52 in the oil plot, and 41 in the untreated
check plot.

A further series of 16 soil-sterilization plots, each of 1 square yard,
was laid out, and twelve different chemical solutions were applied.
Milo seed was sown before the chemicals were applied, and its germina-
tion was used as an index of the degree of soil sterilization. There
was no germination in the plots treated respectively with arsenious
acid, sodium arsenite, sodium chlorate, and a proprietary preparation
containing copper salts. Check plots were thickly covered with milo
seedlings. The more promising treatments were therefore repeated,
first in square-yard plots and later in 100-square-yard plots containing
miscellaneous weeds.

In the arsenic plots in which the arsenic was in excess of 1 ounce
of As 2 3 per square yard, a few seedlings appeared, but soon died.
In the chlorate plots, the weeds sprouted freely, but had a yellowish
unhealthy color, and eventually died in all plots containing in excess
of 4 ounces of sodium chlorate per square yard.

In May, 1931, arsenic as sodium arsenite was applied to several
miles of roadside in Orange County. To date (April, 1932), no annual
weeds have appeared where the soil has remained undisturbed, with the
exception of a small amount of water grass (Echinochloa crus-galli) .
The following soil types were included in the area treated : Chino clay

Bui* 528] The Puncture Vine in California 37

loam, Chino silty clay loam, Chino silty clay (heavy phase), Hanford
sand, Hanford fine sandy loam, Ramona loam, and peat.

The permanence of the treatment is yet to be determined; but
the results to date justify the belief that much greater progress can
be made in the control of puncture vine by a more extensive use of
soil sterilization.

SUMMARY

Puncture vine has been known in California since 1903, and prob-
ably was introduced some years earlier. It appeared first along the
railroads, but spread rapidly in the state along with the increase of
automobile travel. Although tires have been the principal means of
dissemination, it is also carried by animals, by various crops and
products, and by almost any object with which it comes in contact.

The longevity of puncture-vine seed is not known. A plot on
which no seed has matured for the past eight years has continued to
sprout seed each season in undiminished quantities.

The seasonal growth appears to be correlated with soil moisture
and temperature. Under nonirrigated conditions, 90 per cent of the
total number of plants for each season sprouted by July 15 on one
plot observed. The total number of plants sprouted was highest in
those seasons when the May and June temperatures were highest,
those being the only months of sufficiently high temperatures during
which favorable soil-moisture conditions were present. Summer rains
increase the rate of germination, while fall rains, after the mean
temperature has dropped, have no apparent effect, nor is the rate
affected by the amount of winter rainfall.

Burs incubated at relatively high temperatures invariably showed a
higher rate of germination than burs incubated at lower temperatures.

The period from blossoming to maturity of seed is very brief
during the season of rapid growth. Burs picked less than 10 days
from the time of blossoming failed to germinate, but a large per-
centage germinated when the burs were permitted to remain on the
plant 10 days or more.

Puncture-vine seed apparently requires a resting period after
maturity before germination will take place at a normal rate ; but
after the resting period germination is rapid. Burs of the current
season should be held for at least 6 months before being tested for
germination.

If the plant is killed or the burs are picked before the natural
ripening process is complete, germination is accelerated, apparently

38 University op California — Experiment Station

because of interruption of the physiological processes that are
responsible for the resting period.

The approximate viability of puncture-vine seed may be estimated
by inspection. If the burs are soaked overnight in water and cut
open, the number containing apparently sound seed checks fairly
closely with a laboratory germination test of the same sample.

Composting of infested manure is suggested for the destruction of
puncture-vine seed. A test was made of the effect on puncture-vine
seeds of the decomposition of straw and other organic refuse in the
making of artificial manure. Seeds in the interior of the compost
stack were destroyed, but the exterior was not sufficiently decomposed
to kill the seeds.

For the control of growing puncture vine, cultivation and cutting
are satisfactory methods, if done often enough to prevent the forma-
tion of seed. Heat from a weed torch or from live steam may be used
to destroy puncture vine, but burning of green plants without previous
treatment is too slow and too expensive to be practical.

A number of chemicals may be used to kill puncture-vine plants,
but none except certain petroleum products are known to kill the
seeds in all stages.

Diesel oil is more satisfactory for the purpose than other grades
because of its availability, its low cost, its high proportion of aromatic
and cracked oils, and its ability to emulsify satisfactorily with water
when the asphalt content lies within the range of 2 to 5 per cent. It
possesses the property of penetrating the burs of puncture vine and
killing the seed as well as the plant, even when in emulsion with water,
provided the oil is in the external phase of the emulsion. The effec-
tiveness of oil in destroying seeds depends on the completeness of
coverage in application.

Soil may be sterilized by means of chemicals to prevent the growth
of puncture vine.

The following methods are recommended for the control of
puncture vine :

First treat with oil to kill the seeds, if present, without dis-
turbing the vines. Whenever young plants appear, and before the
burs form, cut off just below the crown; or spray with oil or any
cheap chemical weed killer. Encourage sprouting of seeds remaining
in the soil by frequent irrigation during the summer. Do not plow
mature burs under.

Bul, 528] The Puncture Vine in California 39

ACKNOWLEDGMENTS

The writer gratefully acknowledges the valuable assistance of
Miss Grace M. Cole, formerly Botanist in charge of the State-Federal
Seed Laboratory at Sacramento, in making the numerous germination
tests cited herein; of E. R. deOng, formerly Research Assistant in
the Division of Entomology and Parasitology, College of Agriculture,
University of California, for valuable information concerning petro-
leum oils; of W. B. Camp, formerly in charge of the United States
Cotton Field Station at Shafter, for detailed observations on the
phenology of puncture vine ; of Lome S. Neville of Los Angeles,
Whit C. Barber of Bakersfield, the late Frank R. Brann of Visalia,
and many other coworkers among the county agricultural commis-
sioners, deputies, and inspectors for material assistance in various
phases of the work ; and of Dr. W. W. Robbins, Professor of Botany,
University of California, for valuable suggestions in the preparation
of the manuscript.

40 University of California — Experiment Station

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Bul, 528] The Puncture Vine in California 41

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45 White-Haney, J.

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146:158-168.

STATION PUBLICATIONS AVAILABLE FOE FREE DISTRIBUTION

BULLETINS

No. No.

253. Irrigation and Soil Conditions in the 433.

Sierra Nevada Foothills, California.
263. Size Grades for Ripe Olives.

279. Irrigation of Rice in California. 435.

283. The Olive Insects of California.
310. Plum Pollination.

331. Phylloxera-Resistant Stocks. 439.

343. Cheese Pests and Their Control.

348. Pruning Young Olive Trees.

349. A Study of Sidedraft and Tractor

Hitches.

357. A Self-Mixing Dusting Machine for 440.

Applying Dry Insecticides and Fun-
gicides.

361. Preliminary Yield Tables for Second- 445.

Growth Redwood.

364. Fungicidal Dusts for the Control of 446.

Bunt. 447.

369. Comparison of Woods for Butter Boxes.

370. Factors Influencing the Development 448.

of Internal Browning of the Yellow

Newtown Apple. 449.

371. The Relative Cost of Yarding Small

and Large Timber. 450.

373. Pear Pollination.

374. A Survey of Orchard Practices in the

Citrus Industry of Southern Cali- 452.

fornia. 454.

379. Walnut Culture, in California.
386. Pruning Bearing Deciduous Fruit 455.

Trees.
389. Berseem or Egyptian Clover. 456.

392. Fruit Juice Concentrates.
893. Cron Sequences at Davis. 458.

394. I. Cereal Hay Production in California.

II. Feeding Trials with Cereal Hays. 459.

395. Bark Diseases of Citrus Trees in Cali-

fornia. 462.

396. The Mat Bean, Phaseolus Aconitifolius. 464.
404. The Dehydration of Prunes.

406. Stationary Soray Plants in California. 465.

407. Yield, Stand, and Volume Tables for 466.

White Fir in the California Pine

Region. 467.

408. Alternaria Rot of Lemons. 468.

409. The Digestibility of Certain Fruit By-

products as Determined for Rumi- 469.

nants. Part I. Dried Orange Pulp 470.

and Raisin Pulp.

410. Factors Influencing the Quality of Fresh 471.

Asparagus After It is Harvested.

416. Culture of the Oriental Persimmon in 472.

California. 473.

417. Poultry Feeding: Principles and Prac-

tice^ 474.

418. A Study of Various Rations for Fin-

ishing Range Calves as Baby Beeves.

419. Economic Aspects of the Cantaloupe 475.

Industry. 476.

420. Rice and Rice By-Products as Feeds 477.

for Fattening Swine.

421. Beef Cattle Feeding Trials, 1921-24. 479.
423. Apricots (Series on California Crops

and Prices).

425. Apple Growing in California. 480.

426. Apple Pollination Studies in California.

427. The Value of Orange Pulp for Milk 481.

Production.

428. The Relation of Maturity of California 482.

Plums to Shipping and Dessert 483.

Quality. 484.

431. Raisin By-Products and Bean Screen-

ings as Feeds for Fattening Lambs. 485.

432. Some Economic Problems Involved in 487.

the Pooling of Fruit.

Power Requirements of Electrically
Driven Dairy Manufacturing Equip-
ment.

The Problem of Securing Closer Rela-
tionship between Agricultural Devel-
opment and Irrigation Construction.

The Digestibility of Certain Fruit By-
Products as Determined for Rumi-
nants. Part II. Dried Pineapple
Pulp, Dried Lemon Pulp, and Dried
Olive Pulp.

The Feeding Value of Raisins and
Dairy By-Products for Growing and
Fattening Swine.

Economic Aspects of the Apple In-
dustry.

The Asparagus Industry in California.

A Method of Determining the Clean
Weights of Individual Fleeces of Wool.

Farmers' Purchase Agreement for Deep
Well Pumps.

Economic Aspects of the Watermelon
Industry.

Irrigation Investigations with Field
Crops at Davis, and at Delhi, Cali-
fornia, 1909-1925.

Economic Aspects of the Pear Industry.

Rice Experiments in Sacramento Val-
ley, 1922-1927.

Reclamation of the Fresno Type of
Black-Alkali Soil.

Yield, Stand and Volume Tables for
Red Fir in California.

Factors Influencing Percentage Calf
Crop in Range Herds.

Economic Aspects of the Fresh Plum
Industry.

Prune Supply and Price Situation.

Drainage in the Sacramento Valley
Rice Fields.

Curly Top Symptoms of the Sugar Beet.

The Continuous Can Washer for Dairy
Plants.

Oat Varieties in California.

Sterilization of Dairy Utensils with
Humidified Hot Air.

The Solar Heater.

Maturity Standards for Harvesting
Bartlett Pears for Eastern Shipment.

The Use of Sulfur Dioxide in Shipping
Grapes.

Adobe Construction.

Economic Aspects of the Sheep In-
dustry.

Factors Affecting the Cost of Tractor
Logging in the California Pine
Region.

Walnut Supply and Price Situation.

Poultry Houses and Equipment.

Improved Methods of Harvesting Grain
Sorghum.

I. Irrigation Experiments with Peaches
in California. II. Canning Quality
of Irrigated Peaches.

The Use, Value, and Cost of Credit in
Agriculture.

Utilization of Wild Oat Hay for Fat-
tening Yearling Steers.

Substitutes for Wooden Breakpins.

Utilization of Surplus Prunes.

The Effects of Desiccating Winds on
Citrus Trees.

Drying Cut Fruits.

Asparagus (Series on California Crops
and Prices).

BULLETINS — {Continued)

No.

488. Cherries (Series on California Crops

and Prices).

489. Irrigation Water Requirement Studies

of Citrus and Avocado Trees in San
Diego County, California, 1926 and
1927.

490. Olive Thinning and Other Means of

Increasing Size of Olives.

491. Yield, Stand, and Volume Tables for

Douglas Fir in California.

492. Berry Thinning of Grapes.

493. Fruit Markets in Eastern Asia.

494. Infectious Bronchitis in Fowls.

495. Milk Cooling on California Dairy

Farms.

496. Precooling of Fresh Fruits and Tem-

peratures of Refrigerator Cars and
Warehouse Rooms.

497. A Study of the Shipment of Fresh

Fruits and Vegetables to the Far East.

498. Pickling Green Olives.

499. Air Cleaners for Motor Vehicles.

500. Dehydration of Grapes.

501. Marketing California Apples.

502. Wheat (Series on California Crops

and Prices).

503. St. Johnswort on Range Lands of

California.

504. Economic Problems of California Agri-

culture. (A Report to the Governor
of California.)

No.

505. The Snowy Tree Cricket and Other

Insects Injurious to Raspberries.

506. Fruit Spoilage Disease of Figs.

507. Cantaloupe Powdery Mildew in the

Imperial Valley.

508. The Swelling of Canned Prunes.

509. The Biological Control of Mealybugs

Attacking Citrus.

510. Olives (Series on California Crops

and Prices).

511. Diseases of Grain and Their Control.

512. Barley (Series on California Crops

and Prices).

513. An Economic Survey of the Los

Angeles Milk Market.

514. Dairy Products (Series on California

Crops and Prices).
515.! The European Brown Snail in Cali-
fornia.

516. Operations of tho Poultry Producers

of Southern California, Inc.

517. Nectar and Pollen Plants of California.

518. The Garden Centipede.

519. Pruning and Thinning Experiments

with Grapes.

520. A Survey of Infectious Laryngotrache-

itis of Fowls.

521. Alfalfa (Series on California Crops

and Prices).

CIRCULARS

No.

115. Grafting Vinifera Vineyards.

178. The Packing of Apples in California.

212. Salvaging Rain-Damaged Prunes.

230. Testing Milk, Cream, and Skim Milk

for Butterfat.
232. Harvesting and Handling California

Cherries for Eastern Shipment.

239. Harvesting and Handling Apricots and

Plums for Eastern Shipment.

240. Harvesting and Handling California

Pears for Eastern Shipment.

241. Harvesting and Handling California

Peaches for Eastern Shipment.

244. Central Wire Bracing for Fruit Trees.

245. Vine Pruning Systems.

248. Some Common Errors in Vine Pruning

and Their Remedies.

249. Replacing Missing Vines.
253. Vineyard Plans.

257. The Small-Seeded Horse Bean (Vicia

faba var. minor).

258. Thinning Deciduous Fruits.

259. Pear By-Products.

261. Sewing Grain Sacks.

262. Cabbage Production in California.
265. Plant Disease and Pest Control.

269. An Orchard Brush Burner.

270. A Farm Septic Tank.

No.

279. The Preparation and Refining of Olive

Oil in Southern Europe.
282. Prevention of Insect Attack on Stored

Grain.
288. Phylloxera Resistant Vineyards.
290. The Tangier Pea.
292. Alkali Soils.

294. Propagation of Deciduous Fruits.
296. Control of the California Ground

Squirrel.
301. Buckeye Poisoning of the Honey Bee.

304. Drainage on the Farm.

305. Liming the Soil.

307. American Foulbrood and Its Control.

308. Cantaloupe Production in California.
310. The Operation ef the Bacteriological

Laboratory for Dairy Plants.

316. Electrical Statistics for California

Farms.

317. Fertilizer Problems and Analysis of

Soils in California.

318. Termites and Termite Damage.

319. Pasteurizing Milk for Calf Feeding.

320. Preservation of Eruits and Vegetables

by Freezing Storage.

321. Treatment of Lime-induced Chlorosis

with Iron Salts.

322. An Infectious Brain Disease of Horses

and Mules (Encephalomyelitis).

13m-5,'32