UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 CIRCULAR No. 289 
 
 May, 1925 
 
 OAK FUNGUS IN ORCHARD TREES 
 
 BY 
 
 A. H. HENDEICKSON' 
 
 ^^ 
 
 Oak fungus (Armillaria mellea) is a root disease of widespread 
 economic importance in California. It attacks most of the common 
 deciduous fruit trees and is also found on many other plants including 
 annuals and perennials. As its common name indicates, the native 
 oak trees are generally considered the source of infection. The disease 
 spreads underground and often kills orchard trees over a considerable 
 area. Trees replanted in infected orchards from which diseased trees 
 have been removed usually die within a few years unless resistant 
 species are used. 
 
 APPEARANCE AND BEHAVIOE 
 
 The characteristic behavior of trees infected with this disease makes 
 it comparatively easy to identify the fungus. Diseased trees may die 
 at any time during the year. Their roots show flat white fan-shaped 
 mycelium (a thin felted sheet of fungous threads) between the bark 
 and the wood. This mycelium is usually confined to the roots, and only 
 in exceptional cases does it extend into the trunk above ground. The 
 odor of a freshly dug root from a diseased tree is distinctive and is 
 described by W. T. Home as having a ''sharp, rather agreeable mush- 
 room smell." The presence of the flat white mycelium and peculiar 
 mushroom odor serves as an excellent means of identifying this disease. 
 Roots of fruit trees attacked by it decay rather quickly. The advanc- 
 ing edge of the fungus is usually shown by a darkening of the wood. 
 
 Slender brown or purple thread-like cords are sometimes found 
 on the surface of the roots. These root-like organs are the rhizomorphs 
 by which the fungus spreads underground from tree to tree. It is 
 believed that the rhizomorphs are the principal means of spreading the 
 disease. They are not always present in abundance on fruit tree roots 
 and are often passed unnoticed. Whenever one of these rhizomorphs 
 
 * Assistant Professor of Pomology, University of California. 
 
Z UNIVERSITY OF CALIFORNIA^ EXPERIMENT STATION 
 
 comes in contact with a tree root, it quickly enters and in time infects 
 the entire root system. 
 
 During the rainy season clumps of toadstool sporophores often 
 appear near the crown of the diseased trees. These toadstools are of 
 a light tan color on the top, usually showing light brown scales. The 
 loAver surface is white and is made up of fine delicate structures known 
 as gills, which bear the spores or reproductive bodies. The size of 
 these clumps varies considerably. They may consist of comparatively 
 few toadstools, or they may be as much as two feet in diameter. The 
 spores, which are produced in great numbers, apparently do not attack 
 living plants, and hence there is nothing to be gained by destroying the 
 toadstools. Ordinarily, the whole clump turns dark within a few 
 days, becomes infested with the larvae of certain fungous gnats, and 
 melts down to a slimy mass. While the spores are not thought to be 
 important in disseminating the disease, the presence of one of these 
 clumps indicates that the fungus is established in the tree and that 
 the tree is doomed to die within a comparatively short time. Usually, 
 the whole tree dies suddenly (fig. 1) but occasionally one side may 
 die and leave the remainder apparently healthy. This condition seems 
 due to the fact that the roots on one side are killed before the disease 
 has become established throughout the root system. The remainder of 
 the tree generally dies within a year or two. When a fruit tree has 
 once become infected, it is inevitably killed. After the disease reaches 
 the crown, treatments with disinfectants or by surgery have not proved 
 effective. There are but few, if any, authentic cases where an infected 
 tree has survived more than one or two seasons after treatment. 
 
 One of the chief characteristics of the disease is its manner of 
 spreading. From the original source of infection, the disease spreads 
 outward from tree to tree in all directions. The infected area is 
 irregularly circular in outline, and the border usually contains one or 
 more trees showing various stages of injury. 
 
 SOUECES OF INFECTION 
 
 In the treatment of any plant disease, a knowledge of the source 
 of infection is important in order that the disease may be stopped, if 
 possible, before it attacks plants under cultivation. Armillaria mellea is 
 found on many native species, including the oak, willow and madrono. 
 The indigenous oak trees probably form the chief source of infection, 
 but it is not known whether all oaks carry the disease. 
 
 It is not difficult to find, in orchards which have been long owned 
 by one family, authentic cases where the disease has developed in areas 
 from which oak trees had been removed many years before. Oak roots 
 
CiRC. 289] 
 
 OAK FUNGUS IN ORCHARD TREES 
 
 decay very slowly and may remain in the soil twenty or thirty years 
 after the tree has been cut down. It seems as if the disease attacks the 
 roots of the fruit trees only when they come into contact with the 
 oak root fragments. Thus, the fruit trees may not be killed for many 
 years after the orchard is planted. Apparently the pieces of oak roots 
 are a potential source of infection until after they are completely 
 decayed. It has also been observed that many Armillaria spots develop 
 in orchards planted along streams or old water courses. The source of 
 
 Fig, 1. — Mature apricot tree killed by oak fungus during the growing season. 
 
 infection in these cases may be the native vegetation along the banks 
 or the fragments of roots carried down by the flood waters and 
 deposited on the adjoining land and covered with sediment. 
 
 Nursery trees may also form a source of infection, as the disease 
 has been found, in a few cases, on nursery trees. It is probable that 
 only a very small proportion of trees are diseased as they come from 
 the nursery. 
 
 In Tasmania,* Armillaria has been reported to have spread from 
 underground drains made of wood. When tile was substituted for 
 the wood, the rate of spread of the disease was appreciably diminished. 
 
 * Bulletin 57. Root-Eot of Fruit Trees, by H. M. Xieholls 
 Stock Department, Tasmania. 
 
 Agricultural and 
 
4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Relative Susceptihility of Species. — Nearly all of the deciduous 
 fruit trees grown in California are susceptible to the disease. Only 
 three exceptions have thus far been discovered. The three species 
 w^hose resistance seems to be vv^ell established, are the French pear, 
 Pyrus communis; Northern California Black Walnut, Juglans cali- 
 fornica hindsii; and the Fig, Ficus carica. Oak fungus also attacks 
 raspberries, blackberries, and many ornamental shrubs, and has been 
 found on rhubarb and potato plants. English or Persian walnuts 
 (fig. 2) and many hybrids between the English and other species are 
 not resistant. Prunus davidiana, recently introduced as a stock for 
 peaches, and pear trees on Japanese stock, which may include a mixture 
 of several species, show more or less susceptibility. Some of the pear 
 root stocks used recently for their resistance to pear blight, have not 
 been grown long enough in districts infected with Armillaria to 
 determine their degree of resistance. 
 
 Of the three principal rootstocks used for stone fruits, observation 
 seems to indicate that myrobalan is the most resistant, surpassing either 
 the peach or the almond root. Some growers are replanting their 
 infected areas with myrobalan seedlings, to be topworked later with the 
 desired varieties. None of these plantings are as yet old enough to 
 show decisively whether or not this method is better than the usual 
 practice of planting budded nursery trees. In some districts the 
 apricot root on heavy soil seems to show a comparatively high degree 
 of resistance, but on sandy soil, this root is killed very quickly. 
 Peaches and cherries are known to be susceptible. 
 
 Factors in the Bate of Spread of the Fungus. — The kind of soil iti 
 which the fruit trees are growing usually seems to exert little influence 
 on the rate of spread of the fungus. The disease has been found in 
 soils of many types, ranging from light sand to heavy clay and adobe, 
 but, dry, gravelly soils and the sandy sediment soils often found along 
 creek beds seems to show a somewhat more rapid spread of the disease 
 than do the heavy clay types. 
 
 In some parts of the state, there is an impression among growers 
 that irrigation tends to increase the rate of spread of the disease, but 
 this belief has not, as yet, been substantiated. Irrigation may be a 
 means of causing the disease to die out by hastening the decay of 
 infected roots. This, if true, would be a means of quickly making an 
 infected piece of soil safe for planting. The rate of spread of the 
 disease shows great variation in different regions. The loss may range 
 from one or two to forty or fifty trees a year. Where the annual losses 
 are large it appears that several diseased spots have coalesced to form 
 
CiRC. 
 
 OAK FUNGUS IN ORCHARD TREES 
 
 a single large area, covering sometimes several acres. Limited observa- 
 tions seem to show that with prunes and apricots in adobe soil, the rate 
 of spread is considerably slower than where these fruits are on gravelly 
 or loamy soil. 
 
 The vigor of the individual tree does not seem to have any effect 
 on its resistance to the disease. Young and vigorous trees are as liable 
 to attack as old ones. With old trees, the presence of the disease may 
 
 Fig. 2. — Walnut tree on English walnut root killed by oak fungus. 
 
 be suspected for a year or more before death occurs, but young trees 
 die very quickly after the first indications are given by the drying and 
 falling off of the leaves. 
 
 The belief has long been held among growers that so long as its 
 native host is alive, the fungus does not leave it to attack fruit trees. 
 While this contention may be difficult to prove, it is an interesting fact 
 that many examples have been found of prune and apricot trees grow- 
 ing for years in close proximity to oak trees without contracting the 
 
b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 disease. There is some evidence to show that Armillaria exists in an 
 oak tree but does not kill it. While the oak tree is living, the fungus 
 is apparently unable to penetrate to the cambium layer. After the 
 death of the host the disease spreads throughout the dead or dying 
 roots. In the case of fruit trees, the fungus is apparently able to 
 penetrate to the cambium immediately. 
 
 History of a Typical Orcliard Infected with Armillaria. — A strik- 
 ing example of how oak fungus spreads is shown in the accompanying 
 map of an orchard in Santa Clara County (fig. 3). The part of the 
 orchard shown on the map originally contained 1297 prune and apricot 
 trees planted in 1894 on the square system, 22 feet apart. French 
 prunes, part of which were grafted on myrobalan and part on almond 
 root, made up the majority of the planting. The apricots were top- 
 worked to Sugar prunes when seven years old. It is interesting to note 
 that these trees, as shown in the northeast corner of the map, have 
 withstood the advance of the disease fully as well as, if not better than, 
 the French variety on Myrobalan and on almond root. 
 
 Losses first occurred when the trees were five or six years old, and 
 have been continuous since that time. Where trees died the vacancies 
 were refilled with prune trees, but these second plantings did not long 
 survive. Next, apples were tried, and although somewhat more resist- 
 ant to the fungus, they were removed because this fruit did not pay. 
 Then, for a time the vacant spaces were devoted to garden vegetables 
 and alfalfa. Finally, walnuts were planted. Part of the first planting 
 of walnuts was on English root. These trees were killed after a few 
 years. The remaining walnut trees which were grafted on the Cali- 
 fornia black w^alnut stock survived and at the present time are about 
 12 or 14 years old and are bearing satisfactory crops. 
 
 Judging from the apparent age of the replanted walnut trees the 
 area now infected with oak fungus started from four or five points 
 or sources. These original spots gr?vv in size and finally coalesced to 
 form the irregular shaped area shown within the dotted lines on the 
 map (p. 7). It seems that one area began near the lower southeast 
 corner, where the orchard approaches the banks of a creek. It is 
 probable that infection started from the native trees along the bank. 
 Other infected areas developed in various places and gradually spread 
 until they came together to form one large diseased patch. The owner 
 of the orchard still remembers the approximate location of the oak 
 trees which were cut down more than 30 years ago. In some cases the 
 location of these oaks apparently coincides with what seem to have 
 been the beginning points of the disease in the orchard. 
 
Giro. 289" 
 
 OAK FUNGUS IN ORCHARD TREES 
 
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 Fig. 3. — A typical example of an Armillaria-infected orchard, and how the 
 disease slowly but surely spreads over the whole area if not checked during its 
 early stages. This part of the orchard originally contained 1297 prune and 
 apricot trees planted in 1894. Missing places are now principally planted to 
 walnut trees on resistant stocks. 
 
8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 At the present time approximately 860 trees of the original plant- 
 ing have been killed. This amounts to a loss of nearly 66 per cent in 
 23 years. In other words, the average loss was about 37 trees a year 
 on an area of about 14 acres. The economic loss resulting from the 
 death of 37 mature prune trees each year, together with the non- 
 productive period which must elapse before the replanted walnuts 
 come into bearing amounts to a considerable sum. 
 
 A study of this orchard, which is no different from many others in 
 various parts of the state, is of peculiar interest, because of the very 
 evident lessons it imparts. It shows first, the inexorable progress of 
 the fungus when once established in a prune or apricot orchard ; 
 second, the economic loss resulting from the death of bearing trees; 
 and third, the best solution as yet found for this problem : viz., replant- 
 ing with disease-resistant trees such as walnuts on California black 
 Avalnut root. 
 
 METHODS OF CONTEOL 
 
 Up to the present time no method of treatment intended to control 
 this disease, after it is discovered, has been effective. The solution of 
 the problem seems to lie in lessening the losses by checking the spread 
 of the fungus. Isolating the diseased trees by digging trenches around 
 the diseased area or by replanting with resistant stocks after the orig- 
 inal trees have died will accomplish this. Trenching around the 
 infected area at a safe distance beyond the visible limits of the fungus 
 may be expected to give a reasonable amount of protection for the 
 remainder of the orchard. This method, however, is practicable only 
 when the diseased area is relatively small. It is also beset with danger 
 because diseased roots may be left outside the barrier. 
 
 In the case of many plant diseases, one of the principal methods of 
 control is by pruning off diseased parts and by burning or plowing 
 under infected material. This method is not applicable to controlling 
 a root disease of a large tree. When a diseased tree is dug out of the 
 soil, it is not practicable to remove all of the roots. The idea of 
 disinfecting the soil presents itself in this connection. 
 
 Various chemicals have been tested for this purpose. Up to the 
 present time, the tests have not been particularly successful. Disin- 
 fecting the holes from which diseased trees have been removed with 
 such materials as copper sulfate, formalin, sodium cyanide and carbon 
 bisulfide has not proved to be a reliable method of permanently pre- 
 venting infection of the replanted trees. Neither has the application 
 of hydrated lime to the soil around trees adjoining diseased areas 
 proved to be effective in preventing the spread of the fungus (fig. 4). 
 
CiRC. 289] 
 
 OAK FUNGUS IN ORCHARD TREES 
 
 In Tasmania, excellent results are reported from the application 
 of permanganate of potash or iron sulfate on the main roots of trees 
 infected with Armillaria. Similar treatments (fig. 4) applied to trees 
 in California using Weed Killer (proprietary arsenic compound).* 
 
 Fig. 4. — Partly diseased prune tree with main roots uncovered for treatment 
 with disinfecting materials. No useful results obtained. 
 
 permanganate of potash/* iron sulfate,* formaldehyde and Bordeaux, 
 all failed to control the disease. Likewise, treatments w^ith various 
 
 * Tliese materials have been used by Col. G. E. Stockle of Mountain View 
 on a c-onimercial scale for several vcars without success. 
 
10 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 chemicals by so-called tree doctors have not checked the spread of 
 the fungus. 
 
 Barriers. — Armillaria spreads underground from tree to tree by 
 means of root-like fungous strands known as rhizomorphs. Healthy 
 
 »^.r 
 
 Fig. 5. — Portion of a narrow concrete barrier built around an oak fungus 
 area to prevent spread of the disease. 
 
 trees are thus infected from adjacent diseased ones. Theoretically, 
 the disease can be checked by preventing the underground spread of 
 these rhizomorphs. Various methods to accomplish this purpose have 
 been suggested and carried out to a limited extent. The chief idea 
 
CiRC. 289] 
 
 OAK FUNGUS IN ORCHARD TREES 
 
 11 
 
 in this method of control is to dig around the diseased area a trench 
 of sufficient depth to extend below the area occupied by roots. This 
 trench may simply be refilled after cutting off all crossing roots and 
 later reopened for the same purpose ; or it may be lined with material 
 
 J 
 
 Fig. 6.^J'.c(-;iusr tills uiii' hUiali infected iv-; - .,.,-.., ...- wall, the 
 
 barrier, faintly shown on the right of the photograph, failed to prevent the 
 spread of the fungus. The barrier should have been placed one tree row farther 
 away from the diseased area. 
 
 like tar-paper; or it may have constructed in it a narrow concrete 
 (fig. 5) wall extending from slightly below plowing depth to the 
 bottom of the trench. 
 
12 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 The chief objection to the use of the concrete barrier is its cost. 
 The enclosed area is, therefore, usually made as small as possible. 
 The danger in this practice lies in the fact that although the trees 
 bordering the diseased area are apparently healthy, they may have one 
 
 Fig. 7. — Stump of English walnut tree killed by oak fungus. The graft 
 union was covered with soil and the disease entered the scion above the graft 
 union. The black walnut root was not injured and sent up several sprouts 
 after the top had died. 
 
 or more infected roots. In this case, the disease soon makes its appear- 
 ance outside of the barrier. This has actually happened in two 
 instances known to the writer. In one case when a tree outside of the 
 
CiRC. 289] OAK FUNGUS IN ORCHARD TREES 13 
 
 barrier died, the source of infection was traced to a root which 
 extended to the wall, but which was not observed to be infected when 
 the barrier was built (fig. 6). For safety the barrier should be put 
 not closer than between the second and third rows of healthy trees 
 surrounding the diseased area. 
 
 CONCLUSIONS 
 
 Oak fungus is a root disease attacking many common deciduous 
 fruit trees and ornamentals. All root stocks used at the present time 
 for stone fruits are more or less susceptible to attack. Apples are 
 usually considered highly resistant, especially if grown on Delicious 
 stock, and the French pear root is practically immune. The fig and 
 California black walnut are also highly resistant to this fungus. If 
 the infected area is limited in extent, as in the case of young orchards 
 when the disease is first noticed, it may be possible to check further 
 progress of the fungus by enclosing the diseased spot with a concrete 
 barrier as described in this paper. When the diseased area is extensive 
 it should be replanted with one or more of the resistant species. In 
 replanting with either pears on French root or with walnuts on black 
 walnut root, care must be taken to see that the graft union (fig. 7) is 
 not covered with soil, because cases have been observed w^here the 
 susceptible scion was attacked by the disease, while the root Avas not 
 affected. 
 
STATION PUBLICATIONS AVAILABI^E FOR FEEE DISTRIBUTION 
 
 BULLETINS 
 No. No. 
 
 253. Irrigation and Soil Conditions in the 352. 
 
 Sierra Nevada Foothills, California. 
 
 261. Melaxiima of the Walnut, "Juglans 353. 
 
 regia." 354. 
 
 262. Citrus Diseases of Florida and Cuba 357. 
 
 Compared with Those of California. 
 
 263. Size Grades for Ripe Olives. 
 
 268. Growing and Grafting Olive Seedlings. 358. 
 
 273. Preliminary Report on Kearney Vine- 
 yard Experimental Drain. 359. 
 
 275. The Cultivation of Belladonna in Cali- 361. 
 
 fornia. 
 
 276. The Pomegranate. 362. 
 
 277. Sudan Grass 363. 
 
 278. Grain Sorghums. 
 
 279. Irrigation of Rice in California. 364. 
 
 280. Irrigation of Alfalfa in the Sacramento 
 
 Vallev. 366. 
 
 283. The Olive Insects of California. 
 
 285. The Milk Goat in California. 367. 
 
 286. Commercial Fertilizers. 
 
 294. Bean Culture in California. 368. 
 
 304. A Study of the Effects of Freezes on 
 
 Citrus in California. 369. 
 
 310. Plum Pollination. 370. 
 
 312. Mariout Barley. 371. 
 
 313. Pruning Young Deciduous Fruit Trees. 
 
 319. Caprifigs and Caprification. 372. 
 
 324. Storage of Perishable Fruit at Freezing 
 
 Temperatures. 374. 
 
 325. Rice Irrigation Measurements and Ex- 
 
 periments in Sacramento Valley, 
 1914-1919. 375. 
 
 328. Prune Growing in California. 
 
 331. Phylloxera-Resistant Stocks. 376. 
 
 334. Preliminary Volume Tables for Second- 
 
 Growth Redwood. 377. 
 
 335. Cocoanut Meal as a Feed for Dairy 379. 
 
 Cows and Other Livestock. 380. 
 
 339. The Relative Cost of Making Logs from 
 
 Small and Large Timber. 381. 
 
 340. Control of the Pocket Gopher in Cali- 
 
 fornia. 382. 
 
 343. Cheese Pests and Their Control. 
 
 344. Cold Storage as an Aid to the Market- 383. 
 
 ing of Plums. 
 
 346. Almond Pollination. 384. 
 
 347. The Control of Red Spiders in Decidu- 
 
 ous Orchards. 
 
 348. Pruning Young Olive Trees. 385. 
 
 349. A Study of Sidedraft and Tractor 386. 
 
 Hitches. 
 
 350. Agriculture in Cut-over Redwood Lands. 287. 
 
 Further Experiments in Plum Pollina- 
 tion. 
 
 Bovine Infectious Abortion. 
 
 Results of Rice Experiments in 1922. 
 
 A Self-mixing Dusting Mackine for 
 Applying Dry Insecticides and 
 Fungicides. 
 
 Black Measles, Water Berries, and 
 Related Vine Troubles. 
 
 Fruit Beverage Investigations. 
 
 Preliminary Yield Tables for Second 
 Growth Redwood. 
 
 Dust and the Tractor Engine. 
 
 The Pruning of Citrus Trees in Cali- 
 fornia. 
 
 Fungicidal Dusts for the Control of 
 Bunt. 
 
 Turkish Tobacco Culture, Curing and 
 Marketing. 
 
 Methods of Harvesting and Irrigation 
 in Relation to Mouldy Walnuts. 
 
 Bacterial Decomposition of Olives dur- 
 ing Pickling. 
 
 Comparison of Woods for Butter Boxes. 
 
 Browning of Yellow Newtown Apples. 
 
 The Relative Cost of Yarding Small 
 and Large Timber. 
 
 The Cost of Producing Market Milk and 
 Butterfat on 246 California Dairies. 
 
 A Survey of Orchard Practices in the 
 Citrus Industry of Southern Cali- 
 fornia. 
 
 Results of Rice Experiments at Cor- 
 tena, 1923. 
 
 Sun-Drying and Dehydration of Wal- 
 nuts. 
 
 The Cold Storage of Pears. 
 
 Walnut Culture in California. 
 
 Growth of Eucalyptus in California 
 Plantations. 
 
 Growing and Handling Asparagus 
 Crowns. 
 
 Pumping for Drainage in the San 
 Joaquin Valley, California. 
 
 Monilia Blossom Blight (Brown Rot) 
 of Apricot. 
 
 A Study of the Relative Values of Cer- 
 tain Succulent Feeds and Alfalfa Meal 
 as Sourses of Vitamin A for Poultry. 
 
 Pollination of the Sweet Cherry. 
 
 Pruning Bearing Deciduous Fruit 
 Trees. 
 
 Fig Smut. 
 
 No. 
 
 87 
 
 113 
 
 117 
 
 Alfalfa. 
 
 Correspondence Courses in Agriculture. 
 
 The Selection and Cost of a Small 
 Pumping Plant. 
 
 House Fumigation. 
 129. The Control of Citrus Insects. 
 136. Melilotus indica as a Green-Manure 
 Crop for California. 
 
 Oidium or Powdery Mildew of the Vine. 
 
 Feeding and Management of Hogs. 
 
 Some Observations on the Bulk Hand- 
 ling of Grain in California. 
 
 Irrigation Practice in Growing Small 
 Fruit in California. 
 
 127. 
 
 144. 
 151. 
 152. 
 
 154. 
 
 CIRCULARS 
 No. 
 155. 
 157. 
 160. 
 161. 
 164. 
 165. 
 
 Bovine Tuberculosis. 
 Control of the Pear Scab. 
 Lettuce Growing in California. 
 Potatoes in California. 
 Small Fruit Culture in California. 
 Fundamentals of Sugar Beet Culture 
 under California Conditions. 
 
 166. The County Farm Bureau. 
 
 167. Feeding Stuffs of Minor Importance. 
 170. Fertilizing California Soils for the 1918 
 
 Ci'op. 
 173. The Construction of the Wood-Hoop 
 
 Silo. 
 178. The Packing of Apples in California. 
 
CmCVhARS— (Continued) 
 
 No. 
 179. 
 
 184. 
 190. 
 199. 
 202. 
 
 203. 
 208. 
 
 209. 
 210. 
 212. 
 214. 
 
 215. 
 217. 
 
 220. 
 228. 
 231. 
 232. 
 
 233. 
 234. 
 
 235. 
 
 236. 
 
 237. 
 
 238. 
 239. 
 
 240. 
 
 241. 
 
 243. 
 
 244. 
 245. 
 247. 
 248. 
 
 249. 
 250. 
 
 Factors of Importance in Producing 
 
 Milk of Low Bacterial Count. 
 A Flock of Sheep on the Farm. 
 Agriculture Clubs in California. 
 Onion Growing in California. 
 County Organizations for Rural Fire 
 
 Control. 
 Peat as a Manure Substitute. 
 Summary of the Annual Reports of the 
 
 Farm Advisors of California. 
 The Function of the Farm Bureau. 
 Suggestions to the Settler in California. 
 Salvaging Rain-Damaged Prunes. 
 Seed Treatment for the Prevention of 
 
 Cereal Smuts. 
 Feeding Dairy Cows in California. 
 Methods for Marketing Vegetables in 
 
 California. 
 Unfermented Fruit Juices. 
 Vineyard Irrigation in Arid Climates. 
 The Home Vineyard. 
 Harvesting and Handling California 
 
 Cherries for Eastern Shipment. 
 Artificial Incubation. 
 Winter Injury to Young Walnut Trees 
 
 during 1921-22. 
 Soil Analysis and Soil and Plant Inter- 
 relations. 
 
 The Common Hawks and Owls of Cali- 
 fornia from the Standpoint of the 
 
 Rancher. 
 Directions for the Tanning and Dress- 
 
 of Furs. 
 The Apricot in California. 
 Harvesting and Handling Apricots and 
 
 Plums for Eastern Shipment. 
 Harvesting and Handling Pears for 
 
 Eastern Shipment. 
 Harvesting and Handling Peaches for 
 
 Eastern Shipment. 
 Marmalade Juice and Jelly Juice from 
 
 Citrus Fruits. 
 Central Wire Bracing for Fruit Trees. 
 Vine Pruning Systems. 
 Colonization and Rural Development. 
 Some Common Errors in Vine Pruning 
 
 and Their Remedies. 
 Replacing Missing Vines. 
 Measurement of Irrigation Water on 
 
 the Farm. 
 
 No. 
 
 251. Recommendations Concerning the Com- 
 
 mon Diseases and Parasites of 
 Poultry in California. 
 
 252. Supports for Vines. 
 
 253. Vineyard Plans. 
 
 254. The Use of Artificial Light to Increase 
 
 Winter Egg Production. 
 
 255. Leguminous Plants as Organic Fertil- 
 
 izer in California Agriculture. 
 
 256. The Control of Wild Morning Glory. 
 
 257. The Small-Seeded Horse Bean. 
 
 258. Thinning Deciduous Fruits. 
 
 259. Pear By-products. 
 
 260. A Selected List of References Relating 
 
 to Irrigation in California. 
 
 261. Sewing Grain Sacks. 
 
 262. Cabbage Growing in California. 
 
 263. Tomato Production in California. 
 
 264. Preliminary Essentials to Bovine Tuber- 
 
 culosis Control. 
 
 265. Plant Disease and Pest Control. 
 
 266. Analyzing the Citrus Orchard by Means 
 
 of Simple Tree Records. 
 
 267. The Tendency of Tractors to Rise in 
 
 Front; Causes and Remedies. 
 
 268. Inexpensive Lavor-saving Poultry Ap- 
 
 pliances. 
 
 269. An Orchard Brush Burner. 
 
 270. A Farm Septic Tank. 
 
 271. Brooding Chicks Artificially. 
 
 272. California Farm Tenancy and Methods 
 
 of Leasing. 
 
 273. Saving the Gophered Citrus Tree. 
 
 275. Marketable California Decorative 
 
 Greens. 
 
 276. Home Canning. 
 
 277. Head, Cane, and Cordon Pruning of 
 
 Vines. 
 
 278. Olive Pickling in Mediterranean Coun- 
 
 tries. 
 
 279. The Preparation and Refining of Olive 
 
 Oil in Southern Europe. 
 
 281. The Results of a Survey to Determine 
 
 the Cost of Producing Beef in Cali- 
 fornia. 
 
 282. Prevention of Insect Attack on Stored 
 
 Grain. 
 
 283. Fertilizing Citrus Trees in California. 
 
 284. The Almond in California. 
 
 The publications listed above may be had by addressing 
 
 College of Agriculture, 
 
 University of California, 
 
 Berkeley, California. 
 
 12m-5,'25