l*« "K Division of Agricultural Sciences UNIVERSITY O F CALIFORNIA '*th&? CITRUS PROPAGATION J. C. JOHNSTON KARL W.OPITZ EDWARD F. FROLICH CALIFORNIA AGRICULTURAL Experiment Station Extension Service CIRCULAR 475 Citrus Propagation . . . is usually accomplished by commercial nurserymen, and many grow- ers do not want to devote either the time or space to the project. This circular explains propagating operations, leaving it to the individual reader whether or not he wishes to do the work himself or purchase his stock from commercial sources. The information given here re- places part of the material formerly included in Extension Circular 96. Four aspects . . . of citrus propagation are discussed here Growing seedlings from seed page 3 Growing nursery trees page 8 Growing citrus trees from cuttings page 16 Topworking citrus trees page 20 THE AUTHORS: J. C. Johnston is Agriculturist, Emeritus, Agricultural Extension Service, Riverside; Karl W. Opitz is Agriculturist, Agricultural Extension Service, Tulare County; Edward F. Frolich is Principal Laboratory Technician, Department of Horticultural Science, Los Angeles. JUNE, 1959 Growing Seedlings From Seed Many different methods are used in the production of citrus nursery trees. No set of rules will apply to all citrus- growing areas. For the beginner grow- ing citrus nursery stock is complicated and hazardous. Successful growers have largely worked out for themselves the many problems peculiar to their local conditions. Instructions and suggestions are offered here as a basis on which to proceed. Selection of Soil In growing citrus seedlings from seed the most important single factor is the texture and fertility of the soil ; the qual- ity of the trees depends on this more than on anything else. The best citrus seedbed soil is a well- drained sandy loam, free from gravel and stones, and at least 12 inches deep. This type of soil produces good root sys- tems and permits digging with a mini- mum of root injury. To avoid soil-borne disease and citrus nematode, select virgin soil whenever possible. If you use cultivated land, choose a location that has not been planted to citrus and that has not re- cently been fertilized with organic ma- terials. If you must use old citrus soil, fumigate thoroughly before planting. Good fumigants are DD, at the rate of 700 to 1,200 pounds per acre; Vapam, at the rate of 1 quart in 400 gallons of water for 100 square feet of soil; or Mylone, at 2 pounds of 50 per cent in bran per 100 square feet. Work the My- lone into the soil and apply water 6 inches deep by basin or sprinkler. Locate your seedbed in a convenient place so you can inspect it frequently. For small seedbeds you can fill a frame of 12-inch boards with suitable soil. This gives excellent drainage and permits locating the bed in any con- venient sunny place. You can improve the soil by adding peat moss to form one fourth of the volume. Select well-drained, disease-free soil for the seedbed. i I j A ........ XX i.J. JL> PI u f I -Sill fij r 1 Construction of frame or lathhouse To grow large numbers of seedlings, a lathhouse is desirable. A common method of construction is to erect a frame of 4 x 4-inch posts, 8 feet high, with suitable braces. The sides and top are then covered with lath, with spaces between equal to the width of the lath, so as to give half shade. For convenience the lath is usually made up in movable sections. On top of the house the lath should lie north and south. Instead of lath, fabric shading such as saran cloth may be used; it may be more economical and just as satisfactory. For small seedbeds a movable lath or fabric frame, supported a short dis- tance above the seedlings, is ample. In coastal areas this frame may be covered with cheesecloth, but in windy or hot locations lath is better. A 1 x 6-inch board, forming the base of the lathhouse or frame, will help exclude rodents and other small animals. One-inch mesh chicken wire may be necessary in addi- tion to the base board and the lath or cloth. Where moles are a problem, ex- tend the chicken wire 8 inches below the soil level. Selection of seed The rootstocks most commonly used in California are sweet orange, Cleo- patra mandarin, Rough lemon, grape- fruit, trifoliate orange, Sampson tangelo, and Troyer citrange. The best sources of seed are vigorous old trees that have remained free from disease. Whenever possible, take seed from trees known to produce vigorous uniform seedlings that make good trees when budded to the varieties that are to be grown. Many nurserymen own or have access to such trees. Extraction of seed As citrus seeds are injured by drying, it is best to leave them in the fruit until planting time. Extract seeds by making a cut around the center of the fruit, but be careful not to injure the seed. Then twist the fruit apart, and squeeze the seeds onto a sieve where they are washed free from the pulp. (Various kinds of extractors have been used, but in some cases they have caused too much dam- age to the seed). The numbers of seed per fruit and size of individual seed vary widely. Fruit from cool, coastal areas usually contain fewer seed than fruit from warmer areas. Number and size of seed from individ- ual trees vary from season to season. Fruits tend to contain more seed in heavy crop years. The average number of seeds per fruit is likely to be about 10 to 15 < with Sampson tangelo and Troyer citrange, 15 to 20 with sweet orange, sour orange, and Rough lemon, 25 to 40 with trifoliate orange, and 40 to 50 with grapefruit. The approximate number of seeds per pound is as follows: Sweet and sour orange 3,000 to 3,500 Troyer citrange 2,500 to 2,600 Trifoliate orange 2,200 to 2,400 Grapefruit 2,200 to 2,500 Cleopatra mandarin 5,000 to 6,000 Storage of seed If you must keep the seeds for a time after extraction, spread them on a cloth or screen in a shady place till their sur- face is dry. An electric fan will hasten the process. As soon as the surface is dry, protect the seed from further dry- ing, and store them in a cool place till planting time. If you store them in a refrigerator, keep the temperature be- tween 35° and 40° F. Trifoliate orange seed stored at these temperatures for three to four weeks will germinate more uniformly. Examine the seed occasion- ally to make sure it does not mold. You also can store seed without dry- ing if you treat it with a good fungicide. The fungicide treatment will protect the seed from mold, and also control albi- [4] nism (failure of seedlings to develop green color). That's why treatment is recommended even when you plant the seed at once. The following fungicides have given good results: (8 hydroxyquinoline), Fermate, Arasan, mercury bichloride. Use them according to the manufactur- er's instructions. Dusts are more con- venient and therefore preferable. After treatment some nurserymen place the seed in damp sphagnum moss or in a sealed plastic bag to protect it from drying during storage. Treatment against brown rot Citrus seeds often carry one or more of the brown rot fungi ( Phytophthora spp.). Infected seeds do not germinate, but they infect the nursery soil, some- times causing serious loss of seedlings. The disease does not alwavs cause trou- ble in the nursery, but the infection is carried with the trees when they are planted. Infected nursery trees develop slowly and often turn yellow and fail to grow. Infection of the nursery by diseased seed can be prevented by treating the seed with hot water just before planting. The treatment controls the brown rot fungi, and also improves germination so that more seedlings will be obtained from a given amount of seed. The recommended treatment is as fol- lows: immerse the seed for four minutes in well agitated water held between 120° and 125° F. Temperatures up to 130° F are safe and the time can be extended to 10 minutes. Hot-water treatment on stored seed treated with Arasan has been found safe. Treatment on seed treated with the other fungicides mentioned is presumed to be safe but this has not been proved experi- mentally. If the seed is to be planted at once and not stored, apply the recommended fungicides after the hot-water treatment. Preparation of seedbed Make the seedbed firm and as level as possible, to prevent erosion and quick runoff of irrigation water. Harrow or rake the surface into a fine state of tilth. Have the seedbed ready so the seeds can be planted promptly after being taken from the fruit. This is the time to control the damp- ing-off fungus, Rhizoctonia spp. one of the most serious causes of loss in citrus seedbeds. The fungus kills young seed- lings by girdling the stem soon after they appear above the ground. To help control the disease, sprinkle the soil with a solution of special semesan. Three ounces in 17 gallons are enough for 1,000 square feet. After drying to a depth of 2 to 3 inches, acidify the surface inch of soil by applying l 1 /^ ounces of alumi- num of sulfate per square foot and rake the chemical into the upper inch. This produces an acid reaction in the soil which retards the growth of the damp- ing-off fungus without injury to the seed- ling. Planting the seeds Begin planting as soon as the soil warms up in the spring and complete the job at least by the latter part of May. In planting the seeds, make shallow furrows 1% to 3 inches apart by press- ing a board into the soil to a depth of y 2 inch. Place the seeds 1 inch apart in the furrows. Seeds may be planted broadcast, but better seedlings usually develop from spaced plantings. In either type cover the seeds to a depth of % inch with clean river sand or sphagnum moss; this aids in the control of disease and prevents the soil from baking. It is a wise precaution to fumigate the sand before using as it is occasionally infested by nematodes injurious to the seedlings. Good fumigants are chloro- picrin, methyl bromide, or chlorobrome propane. Use them according to direc- tions. [5] Citrus seeds usually germinate slowly; under most conditions they will require about 30 days to appear. Bottom heat will hasten germination. A soil tempera- ture of 80° to 85° F is best. Irrigation of the seedbed Proper irrigation is important for the successful growth of the seedlings. Irri- gation may be needed every 1 to 3 days until the seedlings are up; and every 7 to 10 days after they are well established. After the seedlings have emerged in large beds, overhead sprinklers provide the most effective method of irrigation. Small beds may be watered by portable lawn sprinklers. Keep the soil moist at all times during the growing season but never allow it to become soggy, or dry and baked. Fertilization Do not fertilize the seedbed unless necessary; citrus seedlings are less sub- ject to disease when they are grown with- out fertilization. If fertilization is necessary, use a chemical nitrogen carrier. Ammonium sulfate is preferred by some nurserymen because it is not readily leached from the soil and leaves an acid residue which helps control damping-off. Apply fertilizer by dissolving it in water at the rate of 1 teaspoonful per gallon and distributing it over the beds with a sprinkling can at a rate not ex- ceeding 1 gallon per square yard. This will give about 1 pound to 150 square feet. The solution may burn some leaves if allowed to dry, but a light sprinkling will remove the chemical before it causes injury. Do not use organic fertilizers because they encourage the growth of disease- producing fungi. Disease control Damping-off, one of the most diffi- cult problems in the nursery, can be pre- [6 vented with aluminum sulfate as stated on page 5. If brown rot fungus becomes estab- lished in the nursery in spite of the sug- gested precautions, destroy the seedlings and start over with clean seed and soil. The fungus attacks leaves, stems, and roots of the seedlings and cannot be eliminated from the soil without destroy- ing the seedlings. Pest control The most common pests on citrus seedlings are the citrus red mite or red spider, the citrus bud mite, citrus thrips, and aphids. The citrus red mite feeds on leaves causing them to look gray and dry. The mite is red but, because of its small size, difficult to see. Control: spray with light medium oil, Ovex, Aramite, demeton, Kelthane, Tedion, or Neotran. Apply whenever you can see the mites. The bud mite may infest seedlings in coastal areas. These mites are so small you will probably not notice them; they distort the foliage and retard growth. Control: spray with oil, chlorobenzilate, or a mixture of the two. Apply when- ever you see the mites. Citrus thrips is most common in the intermediate and interior areas. They are small (about 1/30 inch long), light yellow, cigar-shaped. Thrips rasp the leaves as they are developing, causing scarred, distorted leaves and retarded growth. Control: spray with tartar emetic and sugar, DDT, dieldrin, para- thion, malathion, or Sabadilla. In many localities thrips have developed immu- nity to one or more of these materials. Aphids of several species attack citrus seedlings. Control: spray with nicotine sulfate, rotenone, malathion, or para- thion, or Demeton; or dust with a 10 per cent nicotine dust. Other insects occasionally attack citrus seedlings. Directions for control are listed in the University of California Agricultural Extension Service Mimeo, Three nucellar seedlings from one Troyer citrange seed. "Spray Program for California Citrus Fruits." You can get it from your local Farm Advisor. Use suggested materials as directed on the package. Most of these materials are poisonous; observe care- fully the precautions printed on the label. Culling the seedbed Cull the seedbed to eliminate all weak, off-type or diseased seedlings. A single seed will often produce several seedlings. One of them may grow from a sexually produced embryo that develops as a re- sult of pollination. These seedlings differ from their parents and occasionally are too weak to become satisfactory root- stocks. These variants should be culled. The other seedlings arise like buds, from the cells that surround the sack con- taining the sexual embryo. This part of the seed is known as the nucellus, and the seedlings which grow from it are called nucellar seedlings. Since this tis- sue is derived directly from the seed par- ent, the seedlings which grow from it are like the seed parent: they are uni- form and, if the parent has been properly selected, they will make good rootstocks. In certain varieties the sexual embryo fails to develop, and all or nearly all the seedlings grow from nucellar embryos and are like the seed parent. Seedlings of Rough lemon, Sampson tangelo, and Troyer citrange are usually all like their seed parents and thus require a mini- mum of culling. Seedlings of sour orange, sweet orange, trifoliate orange and grapefruit are more variable and require culling. Discard seedlings with crooked or deformed roots (left). Plant normal, good-sized seedlings (right). [7] Getting seedlings ready for transplanting Citrus seedlings are ready to trans- plant when they are 8 to 12 inches high. Well-grown seedlings will reach this size 6 to 12 months after the seed was planted. Before digging, thoroughly wet the soil to a depth of 18 inches, so that the seedlings may be loosened with a long- tined spading fork and removed from the soil with a minimum of root injury. Discard all seedling with diseased, crooked, or deformed roots. For convenience in handling and planting, sort the seedlings into several uniform sizes and tie them in bundles of 50 to 100. Plant the seedlings immedi- ately after digging. Keep the roots covered at all times; never expose them to the sun, nor allow them to become dry. Do not keep seed- lings in water after they are dug; this practice frequently causes them to die after they have been planted. If the seedlings are to be shipped or kept in storage, have their roots packed in damp sphagnum or peat moss. They can be placed in boxes or wrapped in wet burlap. Growing Nursery Trees Growing citrus trees in your own nurs- ery may save you some of the expense involved in setting out a new orchard or in replanting extensively. However, well- grown citrus nursery stock requires knowledge, much labor, and some capi- tal. You should go into such a venture only if you can budget your time so the young trees receive regular attention. Advantages of nursery-grown trees Growing trees in a nursery as com- pared with planting seedlings directly in the orchard offers the following advan- tages : You can care for the seedlings more easily. You can eliminate weaker trees. Loss of a tree in the nursery is less serious than in the orchard. Except for digging cost, growing trees in the nursery is less expensive. Selection of soil Select medium-textured soils free from injurious salts. Heavy chiy soil makes balling difficult and is hard to work. Light (sandy) soil requires frequent ir- rigation and fertilization. Your first choice should be virgin soil or soil used for crops other than citrus. If you have to plant on old citrus soil (even after an interval of 10 years) fumi- gate with heavy dosages of DD or with Vapam, or Mylone before planting. On recently leveled soil apply one or two irrigations before planting. This will settle the soil and permit releveling when necessary. Spots are usually present that require extra care and fertilization. Two or three years of cropping to legumes or hay, followed by releveling helps to get the soil in proper shape. Have a supply of good-quality irriga- tion water available at all times. [8] Selection of site If soil and water conditions are satis- factory, select the warmest available spot as the nursery site. Frost-free locations are frequently steep, and you may have to take steps to prevent soil losses by erosion. You may try terracing or contour planting. Where this is not practical, a well-man- aged sprinkler system will help prevent run-off. Have suitable access roads to facilitate cultural operations and to remove the trees when dug. A windbreak is desirable if your site is exposed to strong breezes. Selection of rootstock Select rootstock according to your needs; they differ in vigor and growth habit. Rough lemon and Troyer citrange seedlings grow rapidly and produce uni- form, upright seedlings which are easy to handle in the nursery. Sour orange, Cleopatra mandarin, and trifoliate seedlings are somewhat less vigorous but also produce good, upright, easy-to-handle seedlings. Sweet orange and grapefruit seedlings tend to produce a bushy type of growth which is not easy to handle. Sampson tangelo seedlings are similar to sweet orange. They grow best in areas intermediate between coast and desert. But under some conditions they are dif- ficult to transplant and do not reach bud- ding size as quickly as other stocks. For the best advice regarding citrus rootstock for your locality consult your Farm Advisor. Planting the nursery Planting time. The best time for planting citrus seedlings in the nursery is in the spring as soon as danger from frost is past. You may plant trifoliate orange seedlings and Troyer citrange in late fall or winter but the frost hazard to Troyer may delay planting until early spring. Spacing. Plant in rows far enough apart to permit the use of a small tractor or horse-drawn cultivator. In most cases, 4 feet is sufficient. The seedlings are usu- ally set 10 to 12 inches apart in the row. Some nurserymen prefer to plant double rows in which the seedlings are spaced 12 inches apart each way, staggered, with the rows placed about 5 feet apart. This system requires more hand cultivation and is somewhat more troublesome to work but permits planting more trees per acre. Row length and direction. Row length is generally determined by soil type and kind of irrigation. For medium- textured soils, rows 200 feet long are about right. In most of California it does not mat- ter which direction the rows run in rela- tion to sunlight. But if you get strong winds from one direction it will be easier to train the bud shoots when your rows run with the direction of the wind. If you plan to use orchard heaters for frost protection, heating is made easier if you leave lanes at intervals of about 20 feet. You may do this by leaving every fifth or sixth row unplanted. Planting operation. Work soil to good tilth and firm it. Then, to obtain Correct use of a dibble for making holes into which youna trees may be set. "'. **** straight rows, stretch a wire tightly over the ground and press it in. The soil must be wet enough so you can make a good planting hole with a dibble. Thrust the dibble into the ground along the mark made by the wire. If salt tends to accumulate on the soil surface, the trees do better when planted in* the irrigation furrow. Irrigate imme- diately following planting. Set the seed- lings the same depth they grew in the seedbed. To avoid air pockets made by the dib- ble, use this tool to firm the soil about the roots. Thrust the dibble into the ground at an angle with the point about 3 to 4 inches away from the tree and parallel to the planting hole. When the dibble bar is straightened perpendicu- larly it firms the soil about the roots and prevents them from drying out. Make the planting hole large enough so that the roots will not be bent or curled. The tap roots must be positioned so they grow downward. If the roots are too long and limber, chop them off with a sharp ax or pruning shears. Always balance cutting of roots by removing a portion of the top. Cultivation Cultivation primarily serves for weed control. Do not allow weeds to grow near the nursery trees because they compete with the seedlings and are costly to con- trol after they become large. In the win- ter a weed cover will increase the frost hazard. Some nurserymen use weed-killing sprays instead of tilling the soil. They use sledlike devices that can be moved along the nursery rows to provide pro- tection to the trees while spraying the weeds. This use of herbicidal sprays re- places frequent cultivation and elimi- nates the need for special cultivating tools. Irrigation Irrigation of nursery trees is the most important cultural operation. Over- irrigated trees grow poorly and turn yel- low. Lack of water stunts growth and causes many buds to die before they unite with the stock. Trees that are too wet or too dry are more subject to frost damage than properly watered trees. Furrow irrigation is usually satisfac- tory. Sprinklers not only provide irriga- tion but may also give some degree of pest control and be used to overcome erosion problems in the nursery. Fertilization Fertile, well-drained soils grow good nursery trees. However, fertilization is usually needed to maintain satisfactory growth and color. A light application of a good chemical source of nitrogen (ammonium nitrate or calcium nitrate) is suggested. Make the application along the tree row at the rate of 1 pound of fertilizer to every 100 feet of row. You may apply this as often as necessary. Wet the soil thor- oughly after applying concentrated fer- tilizers. At the first indication of mottle leaf, treat the trees with zinc oxide at the rate of 1% pounds per 100 gallons of spray. This material may be combined with any of the insecticides mentioned under pest control (page 6) except with oil. Time for budding Usually small seedlings lined out in the spring will not be ready for budding until a year later. The minimum Pest Control You must control harmful insects and plant diseases. Consult your lo- cal Farm Advisor or Agricultural Commissioner for the best materials and methods of application. L 10] size for budding is determined by the size of the buds. Most nurserymen prefer at least pencil size stock because seed- lings that are more slender than that are too limber to handle easily. Slender stocks do not force the bud to grow con- tinuously and must be tied more fre- quently. If the stock is large enough be- cause of favorable growing conditions, spring-planted seedlings may be budded in the fall. In most instances when seedlings are ready by fall, they should be budded. The time to start fall budding usually is late September. Place buds early enough in the season so they will unite with the stock, but late enough so that the buds will not start growth. This gives you a better chance to get a bud take before the seedling gets too large. It also tends to yield larger nursery trees with smoother bud unions. Remove suckers (undesirable shoots), growing below the budding point at least three weeks before budding, or else do not cut them off until budding time. Late pruning of suckers tends to tighten the bark, make budding difficult, and lessen the chances of a good take. Bud as soon as possible after an irriga- tion to be sure there is enough moisture. The seedlings should have a clear straight trunk at least six inches above the soil. There is no excuse for budding lower than 6 inches. Trouble from brown rot gummosis can often be traced to low budding. Selection of budwood Use only buds from the best dis- ease-free, high-producing trees for propagation. When possible, bud each block of nursery trees from a single par- ent source. This helps to avoid introduc- tion of undesirable types and insures more uniform tree behavior in the or- chard. Since sporting branches occasionally develop, avoid off-type growth when you select budwood. Homemade rig used to protect trees when spraying the soil around them with weed-killing chemicals. Be especially careful when choosing buds for propagation on trifoliate and trifoliate hybrid rootstocks. Use only nucellar buds or buds from trees grown on trifoliate rootstock, disease-free, and with excellent production records. Make sure that the buds are free from exocortis (scaly butt) and other transmissible dis- eases such as Psorosis and stubborn dis- ease. Take nuclear buds for propagation di- rectly from the parent nucellar tree or from mature seedling trees budded to nucellar citrus varieties. Once you place a nucellar bud on a stock that has been previously budded, there is no further certainty that progeny from this line will be disease-free. In choosing budwood you will usually find the best type on the next to the last flush of growth, or the last flush after growth hardens. But you also may get perfectly good buds several cycles below the last, up to the point where the bark is no longer green. A round budstick will yield more usable buds, but you can use angular wood that has hardened when you cannot find better material. Buds in [in the axils of large leaves are best. Small leaves on the budstick signify poor nu- trition and these buds will undoubtedly start to grow later than well-nourished buds. Cutting and storing budwood You may cut budsticks at the time of budding, or you may cut and store them for several weeks. Most budders store budwood that is not used within a day or two after it is cut. Do not use moldy or water-soaked buds. At the time of cutting, clip off all leaves and cut the sticks into convenient lengths to handle. At no time allow the budsticks to dry out. Bundle them as soon as possible, label them as to date, name, and source, put them in a good storage medium, and store them in boxes or folded damp burlap sacks in a cool, dark place. A good storage medium is damp peat moss or coarse sawdust. Wet the mate- rial thoroughly and squeeze out the free water before placing the budsticks in it. Damp vermiculite is also a good mate- rial in which to store buds. Another method of storing budwood is to place the sticks in sealed polye- thylene bags and hold them under re- frigeration at about 40° F. Do not add moisture to budsticks stored in plastic bags. There will be enough moisture in good budwood to hold it until they are ready for use. Budding Use the shield or "T" bud method. It gives excellent results, with a minimum of trouble. Take a good sharp knife with a rounded point. Slice a bud from a bud stick with a shield-shaped piece of bark about one inch long. Cut deep enough to include a sliver of wood with the bud. Holding the bud between thumb and knife blade, make a perpendicular cut on the stem of the seedling. Then, with the blade held at an angle, make a hori- zontal cut at the upper end of the per- pendicular cut. This is done to open the bark at the upper end of the perpendicu- lar cut. Finally, insert the bud in the opening at the junction of the cuts. Be careful to place the bud with the right end up — leaf base down. Wrap the buds with rubber strips, waxed cloth, or plastic tape. In tying the buds, start above the bud and work down so the bud is not moved out of place. Tie the buds firmly but not so tightly as to impede growth. Cover fall buds completely with the wrap. Spring buds should have the eye exposed because often the buds may start to grow before the wrap is removed. Newly budded trees must not be al- lowed to wilt. To get uniform appearing trees and to facilitate handling, bud all trees in a row at the same time and at the same height (6 to 8 inches above the soil). THE STEPS USED BUDDING Slice bud as shown Bud will look like this >• Make "T" cut in bark of seedling stem Insert bud in S "T" slot Wrap with jf rubber, wax cloth, or plastic tape [12] Unwrapping and forcing the buds Unwrap fall buds after they are well heeled in — about one month to six weeks after budding. Some kinds of rubber wraps need not be removed; they de- teriorate and fall off. Spring buds take more quickly than fall buds. Usually you may remove the wrap after three weeks of good growing conditions. Force fall buds by lopping or by re- moving the top 3 to 6 inches above the bud just before spring growth starts. Lopping is accomplished by breaking or partly cutting the stem so that the top lies over on the ground. Small budlings must be lopped so the top will continue to nourish the root. You force spring buds by lopping as described above when the bud wraps are removed. Buds may fail to start if you delay lopping too long. If the buds fail to shoot within six weeks after lopping, bend or shake the lops to make sure they are not too strongly attached. Some of the buds may have to be forced by cutting off the top. Lops. To get the most benefit out of lops, leave them on the tree throughout spring and summer if possible. If growth from the bud is weak and the lop must be removed in order to facilitate culti- vation, leave the stub until the following spring. If you remove the stub on weak growing budlings too early, you may lose the bud and occasionally the seed- ling. Because of frost hazard, do not remove the stub in late autumn. If the bud shoots are well above the top of the stake by fall, remove the lops then. No harm results if the lops remain until digging time. When you make the final cut on the stub, you may hasten healing of the pruning wound if you cover it with a good asphalt emul- sion preparation. Staking To develop straight trunks, citrus bud shoots usually require some support. Most nurserymen use lxl inch redwood stakes, four feet long, or sharpened four- foot laths. Drive laths about 6 to 8 inches into the ground, about an inch away from the bud shoot and with the narrow side op- posite the shoot. This allows the leaves to give some support to the stem and per- mits the "head" to develop evenly. Use soft twine, raffia, or "twistems," to tie the shoots so they will grow into straight trees. The ties must be tight enough to prevent the budlings from Left: Lopped trees on which the graft is making good growth. Right: Training budded trees. !■** . , whipping in strong winds, but the ties must not pinch the shoot. Use no more ties than necessary. If you keep raffia moist while working, tying is quicker and more satisfactory. Remove all suckers by rubbing off be- fore they get so big they have to be cut with shears. Training For the retail nursery trade and some growers, heading the trees in nursery is necessary. To get the best spacing of branches, allow shoots to grow a foot or two above the stake and cut them back to the desired height — usually 30 inches. Allow three to five well-placed limbs to develop on the trunks, and remove all other shoots. Many commercial nurserymen, instead of "heading" trees in the nursery, en- courage the bud shoots to grow straight up the stake, as high as they will in one season. Trees grown this way are usually called whips or canes. This procedure eliminates a certain amount of suckering and usually produces trees of larger cali- per (diameter). When the trees (whips) are cut back to 28 or 30 inches above the ground at the time of digging, this has the effect of balancing top and root. The head is easily developed in the field after transplanting. Whips are much easier to dig and handle than headed trees — espe- cially when extra handling of fumigation and dipping is required. Another advan- tage is that whips are easier to ball. Digging the budlings Balled trees. Most citrus trees are dug with a ball of earth adhering to the roots. This gives you more time between digging and planting. Balled trees start growth sooner after being set out in the orchard than trees handled bare root. Trees to be balled should be trimmed to the desired height a week or two be- fore balling. The shape of citrus nursery balls is determined by the distribution of the root system of the trees to be moved. Save enough roots to insure safe trans- planting but keep the soil attached at a minimum for easy handling. Balls 7 to 8 inches in diameter and 16 to 18 inches deep are used in most California soil types. Balling. Use a special balling spade. Have the soil moist but not wet. Thrust the spade all the way straight down 3 to 4 inches from the trunk on all four sides. This will cut all lateral roots and make a ball about 8 inches in diameter. After the last thrust leave the spade in position and dig the soil away from the back of the spade so as to leave a hole for lifting out the ball. Thrust the spade down again on the opposite side of the ball and then with a shovel cut under the ball so as to sever the tap root at the desired depth. Lift the ball out on the balling spade and place it on a piece of burlap or other suitable wrapping material. If the bur- lap is placed on a light bench the hand- ling will be easier. Wrapping the ball. To tie the wrap, slip the spade from under the ball and fold the wrap around the ball. Gather the wrap around the trunk of the tree and tie it in place as close to the soil surface as possible. Next make three evenly spaced half hitches around the ball and pass the twine under the ball and up the opposite side to the trunk, where it is tied securely. Have the lowest half hitch near the bottom of the ball to protect the ball from spreading when wet. If the tree must be held for several weeks, use twine that has been treated with a fungicide to resist decay. Bare rooting. Bare-root trees must be handled quickly and carefully. Never permit the roots to dry. Defoliate and whitewash the trees just before digging. Advantages of bare rooting: it permits inspection of the root system. It allows you to retain more of the root system than on balled trees. Two-year old trees handle better bare-rooted than balled. On very heavy soils, bare rooting is pre- [14] THE STEPS USED IN BALLING Lifting ball out of hole on balling spade. Balling spade 16 inches long. Circle shows diameter of ball. Cutting tap root with shovel. Finished ball. [15] ferred to balling, especially when the trees are to be moved to lighter soils. You can best dig bare-root trees in early spring. You may dig balled trees from the time the ground can be worked after the danger of frost is past until the weather turns hot. Do not dig during dry windy weather. Some fall digging of citrus trees is done every year. However, the frost haz- ard keeps many growers from planting at that time which limits the demand for fall-dug citrus trees. In the citrus-growing sections along the coast (and during the very early spring also, inland) when the weather is cool and overcast, you may transplant bare-root trees successfully with some of the leaves remaining. If you have reason- able doubt that you can keep the trees from wilting, you had better defoliate at digging time. Handling dug nursery trees Bare-root nursery trees must be dug quickly and the roots placed in damp peat moss, mud, or vermiculite until planted. If you do not plant the trees at once, keep them in a cool, shady place. You may store balled trees in a shady place for a few days or in a lathhouse for several weeks if necessary. Balled trees may even be held a day or two in the open, provided the soil around their roots is not allowed to dry. If you hold them until new growth develops, balled trees are liable to sunburn and should be sprayed with whitewash. Do not allow the balls of earth to become hard and dry at any time. If this happens, immerse the balls in water until soaked through. The best way to forestall such accidents is to pack the balls in damp sawdust in bins and sprinkle frequently. Since citrus trees can be stored from a few days up to several weeks, it is best to hold them after digging until there is favorable weather for planting; or to dig and plant the same day under the most advantageous conditions. Growing Citrus Trees from Cuttings Citrus trees may also be propagated by rooting stem cuttings. This method is used principally for producting plants which are grown and sold in containers. Also, in years when seeds of a desired rootstock are not available in sufficient quantities, cuttings may be rooted from nursery seedlings of the previous year; these cuttings can then be budded as described for seedlings. Citrus trees grown from cuttings reach the same size as trees of the same variety budded on one of its own seedlings, with the single exception of Eureka lemon. Grown from cuttings Eurekas have not proved to be long-lived on their own roots. In their first two or three years, cut- ting-grown trees are not as well anchored [16 in the soil as trees budded on seedlings. In extremely windy locations you should stake young cuttings to protect them from being blown over. Another possible trouble with cutting- grown rootstocks in some areas may de- velop at the time of balling the nursery tree. The root systems in many cases spread more laterally than do those of ] seedlings and only a few roots can be included in the standard nursery ball. In these cases the trees are better dug and moved bare-root. . The speed and ease with which cut- tings form roots varies with the differ- ent species of citrus. Lemons, limes, and citrons root most readily; mandarins are the slowest and most difficult. Grapefruit, sweet orange, trifoliate orange, the cit- ranges, and sour orange are in-between. Selection of cutting material Cuttings from young seedlings (young clones) of any species root much more readily than cuttings from old clones of the same species. Roots from old clones tend to be more lateral; those from young clones send roots straighter down; cuttings from extremely young seedlings are almost as tap-rooted as seedlings. The best cutting material is growth that has just matured. The largest number of recently ma- tured cuttings is available in June or July, having resulted from the spring flush of growth. In areas where there are several flushes a year, you may find good cutting material in any month. Some propagators prefer winter cuttings taken from the north side of the tree; these root very well if the trees have been main- tained in good condition throughout fall and winter. Shoots from trees which re- cently have been oil sprayed do not fur- nish satisfactory cuttings. The oil in- creases leaf drop when the cuttings are placed in the propagating frames. Cutting procedure The best cut is one squarely across the base; it will result in the formation of more roots and give a better root dis- tribution than a slanting cut. The posi- tion of the basal cut as related to the buds on the stem is immaterial. Most satisfactory are terminal cuttings 3 to 6 inches long, with mature leaves and consisting of a single growth flush. Strip leaves from the area near the base so you can place the cutting easily in the rooting medium. Leave 3 to 6 leaves on each cutting. And keep the cuttings moist during all handling operations after removal from the tree. Treatment with hormones Some citrus species benefit by a treat- ment with rooting hormones. Lemons, limes, citrons, citranges, and trifoliates respond to a treatment of indole butyric acid (IBA) in talc at from 3,000 to 8,000 ppm. This material can be obtained as a commercial preparation labeled Hor- modin powder. Number two powder con- tains 3,000 ppm IBA, and number three powder 8,000 ppm. To apply the ma- terial, moisten the base of the cutting and then dip it into the powder to a depth of about % inch. Be careful that there is no bead of free water at the base of the cutting, because this would pre- vent the powder from adhering to the tissue. Some of the more difficult materials, such as Satsuma mandarin, benefit from a quick dip into IBA at 10,000 ppm. To make this solution, dissolve IBA crystals at the rate of 20 mg in 1 cc of alcohol, and add an equal volume of water. Dip the base of the cutting into the solution about % inch deep for one or two sec- onds. Rooting the cuttings Cuttings may be rooted in any struc- ture that will maintain a high humidity and give a good light intensity. The two main choices are closed propagation beds or frames, and a mist system by which the cuttings are placed under water mist sprays which can be turned on or off. Closed frames are satisfac- tory, but require more attention than the mist system. Citrus cuttings under mist will leach badly if they are slow to root, and have to be fertilized peri- odically. Such leaching does not occur in the closed frames. Place the cuttings about 1 inch deep [17] Twig grafting lemon on trifoliate orange. Left: Cuts at top of rootstock and base of scion. Center: Rootstock and scion tied with rubber strip. Right: The same combination after two months in propagating case. in any well-aerated medium such as ver- miculite, sand, or sand and peat. Space them far enough apart so at least a por- tion of every leaf is exposed to light. Bottom heat is essential except during the very warmest seasons. A minimum temperature of 75° F has worked well for rooting, but the optimum tempera- ture has not yet been determined. In closed frames you can control the air temperature by adding or removing shade. Never allow the leaves of the cut- tings to wilt. Syringe the foliage and the inside of the frame daily in normal weather, and more often during periods of extreme high temperature. Give the cuttings as much light as possible but hold air temperatures inside the frames below 100° F to prevent burning of the foliage. Lemon cuttings will produce good roots within four to six weeks; oranges [18] in six to eight weeks; mandarins will take up to four months or more. These periods will vary with the weather and the conditions of the cuttings. Removal of cuttings After the cuttings are rooted they are hardened off by gradually reducing the humidity in the frames. If the mist sys- tem is used, harden the cuttings by grad- ually decreasing the "on" period and in- creasing the "off" period. Remove the cuttings and plant them either in containers or in a nursery row. In extremely warm or dry weather pro- tect them from direct noonday sun. A shingle placed on the south side of the cutting works well in the nursery row. Twig grafting Twig grafting, a method sometimes used in cutting work, employs two or three cuttings grafted together. Two cut- tings will give a desired rootstock-scion combination; three cuttings a combina- tion of rootstock, scion, and interstem. For twig grafting use the same type of material as described above for cuttings. Select material that will have as nearly as possible the same diameter at the graft. Keep at least three leaves on the top or scion piece; at least one leaf on the lower or stock piece; and also one leaf on the interstem if used. Make a sloping cut V2 to % inch long at the base of the scion piece and at the upper end of the rootstock piece. Hold the two pieces together with thumb and fore- finger of one hand so that the sloping cuts cover each other. Then wrap the union with raffia or a rubber strip by making several turns as illustrated on page 18. A number 16 or 18 stationer's rubber band which has been cut makes a good wrapping material. To start the wrapping, hold one end of the strip be- tween middle finger and forefinger of the hand holding the cuttings. Some experience is necessary to judge the tension of the tie: if too loose, the pieces may spread apart or shift; if too tight, the bark will be damaged. You need not seal the cut surfaces, as the high humidity will protect them from drying. Unions at the graft should heal in three to four weeks, at which time the tie can be loosened or removed. How long it takes to root these combinations depends on the piece on the base. Ma- terials that root readily as cuttings also root readily as the basal portion of the grafted plant; those that are slow as cuttings are also slow as the rootstock of the graft. [19 J Topworking Citrus Trees Citrus growers sometimes wish to change established groves to other va- rieties. It is often cheaper to graft exist- ing trees to another variety than to pull out the stumps and plant new trees. Top- worked trees will also come back into production sooner than nursery trees. Trees to be topworked must be thrifty and free of fungus or virus diseases that would affect the new top. If you are in doubt whether your trees are suitable for topworking, call in your Farm Ad- visor or another competent person. Topworking of citrus trees can be done by budding or grafting. Either method may be used on any size of tree, 'but in most areas younger trees are budded while large trees are grafted. In some areas, particularly central Cali- fornia, budding is preferred for trees of all ages. Topworking by budding Budding can be done in two ways: either directly into the trunk or scaffold limbs, or into new shoots of heavily cut- back trees. The last method gives a good percentage of buds to take, but some time is lost in growing the shoots; also, more follow-up work is required. Most bud- ding is done directly in the scaffold limbs. Select the branches in which you will place buds and remove all growth which would be in the way. Sometimes branches besides those to be budded are left; these are called nurse limbs. You may do the budding in the fall, at the same time as the pruning, or, a practice followed more generally, the fol- lowing spring when the bark is slipping well. Start spring buds three to four weeks after budding by either cutting back the branches or by girdling (re- moving a strip of bark ^ inch or more wide completely around the branch) 2 to 3 inches above the bud. Buds placed in the fall are held dormant by not cut- ting back or girdling the branches until the next spring. Be careful to avoid split- ting when cutting off large branches: remove most of the weight of the branch with a first cut farther out on the limb and then make a second cut closer to the bud. •..• •«* :*.•■• «•*'.? * * . • ' v> ' .* Topworking by budding. Left. Bud partially inserted. Right: Bud is inserted and ready for wrapping. [20] Budwood for topworking should be larger than that described in the section on budding nursery trees. On large limbs two buds are often placed at the same height so that they can be tied with one wrapping operation. Make a T-cut in the limb where the bud is to be placed, and lift the bark to insert the bud. If the bark is too thick to manipulate well, thin it with a knife to about % inch. Select budsticks about ^ inch in di- ameter. Cut the bud from the budstick and insert it in the bark incision as de- scribed on page 12. Be careful not to place buds in an inverted position. For topworking make the shield (bark and a thin layer of wood attached to the bud) about IV2 to 2 inches long. With a shorter shield there is the danger of bark growing over it and smothering the buds. After the buds are inserted, tie them in by wrapping over them with waxed bud- ding cloth or plastic tape. After three to four weeks remove the wraps and examine the buds to see if they have remained alive. If callus tissue has grown over the bud, cut the tissue away carefully, otherwise the bud may become buried and will fail to start. If the buds look all right, shorten or girdle the branches; this should start the buds growing. After the new shoots have made good growth, cut the branches off flush with the bud, and seal the cut surface with a pruning compound. Make this last cut at an angle; this will give better healing Topworking by grafting. Left: Scion showing two cuts. Right: Stock with two scions inserted. [21] and, on vertical branches, will prevent water standing on the wound surface. Topworking by grafting Grafting of old citrus trees is done with the bark graft. Dehorn trees and set the scions in the main scaffold limbs ; or cut off these trees below the branches and set the scions in the main trunk. When grafting into the scaffold branches, leave some branches on for nurse limbs, both for shade and to maintain the root system until the new scions develop foliage. Graft at a time when the rootstock bark separates readily from the wood. About a day after cutting a tree back, the bark will tighten; thus, if the graft- ing is not done immediately after cut- ting, wait about a month until the bark loosens again, at which time the stumps are re-cut and grafted. Here are directions for a bark graft- ing method that has proved satisfactory : cut off the branches and make vertical slits (2 1 /2 to 3% inches long) in the bark of the stub where the scions are to be placed. These cuts extend through the bark to the wood and are from 4 to 6 inches apart around the stub. Select scionwood from firm, current season's growth, or from wood as old as two or three years. The diameter may vary from % 6 to % inches. Cut a scion as illustrated, with a long sloping basal cut 2% to 3 inches long. Sometimes a second sloping cut % inch long is made on the opposite side. Leave at least two good buds above the longer cut. Lift the bark on one side of the cut on the stump high enough to insert the scion, and push down the scion with the long cut facing in toward the wood. One side of the scion should fit snugly against the unlifted portion of the bark on the stump. A little cut surface on the face of the scion should still be visible above trie rim of the stump after the scions are inserted. Don't make scions longer than neces- sary; long scions are in danger of dry- ing before the union can form. The scions may be nailed in place with thin flat-headed nails, or tied with several loops of cord, friction tape, or vinyl tape around the stump. On some very large stumps baling wire has been used suc- cessfully. Take care to have a good fit and enough pressure to hold the scions securely at the point where the top edge of the stump and the cut surface of the scions join; most of the strength of the new union will be in this area. After the scions are fastened, seal all cut surfaces with a pruning or grafting compound to prevent drying. Protection after grafting After grafting, protect the scions and trunk from burn resulting from direct sunshine on exposed surfaces. White- wash trunks and branches on the south side and shade the scions with ventilated paper bags or other material to keep di- rect sunlight from striking them. As the scions start to grow, tear the bags to let the shoots come through into the sun- light. Keep an eye on the material you used at grafting time to tie the scions; loosen or remove the ties before they cut into the bark. In areas where strong winds may break the scions out as they grow, nail 1 x 2-inch boards to the stump for sup- port. These boards should extend 3 to 4 feet above the graft. Tie the shoots loosely to them. Many propagators pre- fer to protect against breakage by merely cutting back or pinching the longer shoots to keep them short and bushy. Rub off all shoot growth on the stump immediately around the new buds and grafts so they won't compete with the new top. If nurse limbs have been left on the stump, cut them back or remove them before they interfere with the new growth from the scions. [22] Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture co-operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Service. 15m-6,'59(9602)JF [23] INFORMATION on questions concerning citrus crops see your farm advisor. Here are the addresses of County Directors and Farm Advisors in the leading California citrus counties: 'r Butte County — P.O. Box 991 (Post Office Building), Oroville Fresno County — 1720 South Maple Avenue, Fresno 1 Glenn County — County Building, 607 5th Street, Orland Imperial County — Court House, El Centro Kern County — P.O. Box 791 (2610 M Street), Bakersfield Los Angeles County — 808 North Spring Street, Room 800, Los Angeles 12 Orange County — 1104 West 8th Street, Santa Ana Riverside County — Post Office Building, Room 7, Riverside Sacramento County — 310 Post Office Building, 7th and K Street, Sacramento 2 San Bernardino County — 566 Lugo Avenue (County Agricultural Building), San Bernardino San Diego County — 4005 Rosecrans Street, Building 1, San Diego 10 Santa Barbara County — P.O. Box 126 (Federal Building), Santa Barbara Tulare County — P.O. Box 990 (Post Office Building), Visalia Ventura County — 52 North California Street, Ventura