vision of Agricultural Sc UNIVERSITY OF C A L I F O R N m ■ ■ ■ ■MB MBB| wi r ^ "■ wij'-^' -M §8 to seeds. If the temperature goes to 130° F, reduce the holding time to 5 minutes at this figure. Test for viability To avoid planting seed that may not be viable, you may apply a chemical test to a representative sample of the seed. The chemical 2, 3, 5-triphenyltetrazolium chloride (T.T.C.) causes living seed tis- sue to turn red. It has no color reaction with dead seed. Preparation of seedbed soil Make the seedbed firm and level to pre- vent erosion and irrigation run-off. Har- row or rake the surface into a fine tilth. Ready the seedbed so the planting opera- tion can proceed quickly to avoid loss through drying. To help prevent damping-off caused by the Rhizoctonia spp. fungi 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 or 3 inches, acidify the surface soil by applying l 1 /^ ounces of aluminum sulfate per square foot and evenly rake the chemical into the upper inch. The acidification retards growth of the damp- ing-off fungi without injury to the seed- lings — provided the chemical is applied as directed. Planting seed Soil temperature of unheated seedbeds should be at least 55°F before planting. Heated beds are usually held at about 80°F. In California, earliest unheated seedbeds are usually planted in March. (Trifoliate and Troyer seed may be planted in February without danger of rotting.) Electrically heated beds may be planted whenever seed is available. To evenly space seeds, make shallow furrows 1% to 3 inches apart by lightly pressing the edge of a lath into the soil to make a furrow about % inch deep. Place the seeds about 1 inch apart, and lightly cover them with % to % incn of coarse builders sand. (If you suspect the sand carries nematodes or fungi, you can de- stroy these organisms by fumigating the sand at the same time you treat the seed- bed soil.) Sphagnum moss can be used in place of sand. Covering the seed with sand or sphagnum moss aids in the con- trol of damping-off and prevents soil from baking. Citrus seeds germinate slowly; under most conditions they require about 30 days to emerge, although bottom heat may cut down the time by a third. Soil temperatures of 80° to 85° F are optimum for root growth. Irrigating the seedbed Satisfactory seedling growth depends on proper irrigation. Until the seedlings emerge you may have to sprinkle the bed every 1 to 3 days. After they become well established every 7 to 10 days in warm weather may be frequent enough. A tensi- ometer inserted in the root zone will help you decide when to apply moisture. After most of the seedlings are ger- minated and the bed takes on a good green color, you may utilize an overhead sprinkling system. Where flooding is practicable this system may also be suc- cessfully employed. The important thing is to irrigate evenly and often enough to obtain maximum growth. Never allow the bed to become soggy or dry and baked. Fertilizing seedlings It is easier to grow citrus seedlings in naturally fertile soil than in soil deficient in plant food. Fertilization with organic materials may predispose small seedlings to root rot and to damping-off. If fertilizer is needed use a chemical nitrogen carrier such as ammonium sulfate, calcium ni- trate or ammonium nitrate. Dissolve fer- tilizer in water at the rate of 1 teaspoon per gallon and distribute it over the beds with a sprinkling can at a rate not exceed- ing 1 gallon per square yard. This pro- vides about 1 pound to 150 square feet. [7] The solution may burn some of the leaves if it is allowed to dry; a light sprinkling with tap water removes the chemical be- fore it causes injury. Do not repeat more often than necessary to insure normal growth. Diseases of citrus seedlings Disease prevention is more satisfactory than attempting to control organisms after they infect the plants. If you use properly treated seed planted in suitable soil and irrigated as indicated, you are not likely to experience serious seedbed losses due to fungus disorders. In addition to the aluminum sulfate treatment you may wish to prevent spread of damping- off by sprinkling the seedbed with Fer- mate® every other irrigation at the rate of 2 tablespoonfuls per gallon of water. Rhizoctonia and certain Phytophthora fungi grow best under warm moist condi- tions. Thickly planted seed and poorly ventilated hotbeds predispose seedlings to infection from these pathogens. Pest control The most common pests of citrus seedlings are citrus red mite (red spider), citrus bud mite, citrus thrips, aphis and various leaf eating worms. Occasionally grasshop- pers or false chinch bugs invade the seed- bed. (See "Annual Treatment Guide for California Citrus Crops" for control of these and other insect pests.) Frequent seedbed inspection is necessary in order to detect and treat insect and mite in- festation before they grow to damaging proportions. Culling the seedbed Cull the seedbed to eliminate weak, off- type and diseased seedlings. A single seed often produces more than one seedling. 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 are frequently too weak to become satisfactory rootstocks. They should be discarded. Some seedlings may be much more vigorous than the average. These, too, should be discarded as they are likely to be sexually produced and, therefore, different from the seed parent. Severe culling now will reduce problems and expense later on. Other seedlings arise like buds from cells surrounding the sack containing the sexual embryo. This part of the seed is known as the nucellus, and the seedlings which grow from it are called nucellar seedlings. Because this tissue is derived directly from the seed parent, seedlings growing from it are like the seed parent : they are uniform and, if the parent has been properly selected, make good root- stocks. In some kinds of citrus seedlings the sexual embryo fails to develop, and all or nearly all grow from nucellar embryo and are like the seed parent. Seedlings of Alemow (C. macrophylla) rough lemon, Sampson tangelo, and Troyer citrange are usually like their seed parents. Seedlings of sour orange, sweet orange, trifoliate orange and grapfruit produce less nucel- lars (more zygotics) and require more culling. Citrus seedlings also differ in vigor and habit of growth. Alemow, rough lemon and Troyer citrange seedlings grow rap- idly and produce uniform, upright plants which handle easily in the nursery. Most trifoliate orange seedlings are more thorny and less vigorous. Sour orange and Cleopatra mandarin seedlings grow slower and tend to bush somewhat, but are easily directed toward upright growth. Sweet orange and grapefruit seedlings bush more than the previously mentioned root- stocks. Sampson tangelo starts slowly and tends to be bushy. Digging, selecting and handling seedlings Citrus seedlings are ready to transplant when they are 8 to 12 inches high. Well- grown seedlings reach this size 6 to 12 months after the seed is planted. Before digging, thoroughly wet the soil to a depth of 18 inches; dig when dry enough to handle. A long-tined spading fork or straight spading shovel is less likely to injure the trees during digging. Gently shake off excess soil and remove at once to a cool, shady, damp place. Discard all seedlings with diseased, crooked or deformed roots. You will save yourself a lot of time, expense and grief if you use special care to plant or sell only the best stock available. For convenience in handling and plant- ing, sort seedlings into three or four uni- form sizes. Tie or wrap them in bundles of 50 to 100, and plant as soon as possible after digging. Keep roots covered at all times; never expose them to the sun, nor allow them to become dry. Do not keep seedlings in water after they are dug, as this frequently causes them to die after planting. If seedlings are to be shipped or stored, pack their roots in moist sphagnum or peat moss. They may be held in ventilated boxes or wrapped in wet burlap. Citrus seedlings. The two on left are excellent; middle two are acceptable; two on right are not suitable for planting. [9] 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 an extensive replanting program. Well-grown citrus nursery stock re- quires knowledge, much labor, and some capital. Go into such a venture only if you can budget your time so that young trees receive regular attention. Why grow trees in a nursery? Growing trees in a nursery as compared with planting seedlings directly in the or- chard provides the following advantages: • You can care for the seedlings and budded trees more easily and more satisfactorily. • 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 Medium-textured, well-drained soils free from injurious salts and rocks are most desirable. Clay soils are difficult to ball and hard to work. Sandy soils require frequent irrigation and fertilization. Soil with no crop history, dry-farmed grain land, or land farmed to crops other than citrus is not likely to be contami- nated with organisms harmful to citrus and should be used if available. If you must use old citrus soil or soils containing citrus nematodes, fumigate the nursery site well ahead of planting. (See "Annual Treatment Guide for California Citrus Crops" for fumigation recommendations. ) On recently leveled soil apply one or two irrigations before planting. This will settle the soil and permit releveling when necessary. Problem spots may require special care and fertilization. Two or three years of cropping to legumes or hay helps put the soil in excellent tilth. Water Satisfactory tree growth depends on an abundant supply of good-quality irriga- r tion water. If you must use soil or water containing excess salts, construct perma- nent broad-based furrows and plant in the furrow bottom. Sprinkler irrigated nursery stock re- quires high-quality water. Somewhat lower-quality water may be used if sprin- kling is done at night when the evapora- tion rate is low. With nurseries having permanent fur- rows and provisions for tail water, removal of running water during cold periods may provide satisfactory frost protection. < Choosing the site If soil and water conditions are satisfac- tory, select the warmest available spot as the nursery site. Low frost-hazard loca- tions are frequently steep, and you may have to take steps to prevent soil erosion. Planting on the contour, terracing, sod < strips or mulching may be necessary. Suitable access roads facilitate cultural operations and digging and hauling the trees. Exposed areas may require windbreak protection. Planting the nursery When to plant. The best time to plant citrus seedlings is in early spring as soon as danger of frost is past. You may plant trifoliate orange and Troyer citrange seedlings in late fall or winter, but frost hazard to Troyer may delay planting un- til early spring. Spacing. Plant in rows far enough apart to permit the use of cultivator tools. In most cases the distance between rows should not exceed 4 feet. Set the seedlings " [10] 10 to 12 inches apart in the row. Straight rows and evenly spaced nursery trees are easy to care for. Some nurserymen prefer to plant double rows 12 inches apart with the trees staggered (alternately spaced). The distance between each double row set is 4 to 5 feet. The double row system permits more seedlings to be planted but usually requires more hand weed control. Nursery rows. Row length is generally determined by soil type and the method of irrigaton. For furrow-irrigated, medium- textured soils, 200 feet is about right. In California it does not matter which direction the rows run in relation to sun- light. However, if strong prevailing winds blow from one direction you will find it easier to train bud shoots if rows run in the direction of the wind. Nursery heating and spraying is easier if drive lanes about 20 feet apart are pro- vided. By leaving out one or two rows at this interval, you may provide good access for frost protection and for pest-control operations. Planting operation. Work the soil to a good tilth and firm it. To obtain straight rows, stretch a wire tightly over the ground and walk on it to press it in. The soil must be moist enough to make a good planting hole with a dibble. Thrust the dibble into the soil along the mark made by the wire. Set the seedlings the same depth they grew in the nursery. 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 perpendicularly, it firms the soil about the roots and prevents them from drying out. Make the dibble hole large enough to accommodate all the roots. If the roots are bent or curled you will probably pro- duce a poor tree. Tap roots must be posi- tioned to grow downward. If roots are too long and limber chop them off with Two types of dibbles used to make holes for seedlings, and to flm soil around roots after planting. a sharp ax or pruning shears. Always balance root pruning by removing the proportionate amount of the top. A thorough irrigation helps settle the soil about the roots and provides the seed- lings with needed moisture for growth. If the transplants are planted in the fur- row bottom, settling by irrigation helps provide good contact with soil and water. Cultivation If cultivation is necessary for weed con- trol, work the soil as shallowly as possible. Do not allow weeds to grow in the nursery row ; they compete with the seedlings and are hard to control without damage to the trees after they become large. A weed cover in the winter increases frost hazard. Some nurserymen use weed-killing sprays instead of tilling the soil. To pro- tect trees against herbicide drift, shield them against the spray. [ii Home-made sled. Shields prote ct nursery Trees Trom w eed-oil spray. If soil sterilants are applied, use with extreme caution. Most soil steri- lants, used at the rates which orchard trees will tolerate, damage newly planted seedlings. Use of herbicidal sprays replaces fre- quent cultivation and eliminates the need for special cultivating tools. Irrigation Nursery tree irrigation is the most impor- tant cultural operation. Overirrigated trees grow poorly and turn yellow. Lack [12] of water stunts growth and causes buds to die before they unite with the stock. k Trees that are too wet or too dry are more subject to frost damage than are properly watered trees. Furrow irrigation is usually satisfac- tory and is a must if the water contains injurious salts. Sprinkler irrigation may be used where erosion is a problem. Mite infestations may be reduced when the nursery is sprinkled. On the other hand, loss of de- sirable insecticide residues may reduce pest-control effectiveness. Fertilization Fertile well- drained soils help grow good nursery trees. To maintain adequate soil fertility, chemical nitrogen is usually necessary. A light application of ammo- nium nitrate, calcium nitrate, ammonium sulfate or urea spread down the tree row at the rate of 1 pound of fertilizer to every 100 feet is sufficient. Apply as often as necessary to maintain satisfactory growth. Wet the soil thoroughly after fertilizing. At the first indication of mottle leaf, treat trees with zinc oxide at the rate of iy 2 pounds per 100 gallons of spray. This material may be combined with insecti- cides needed for pest control. Time for budding Small seedlings lined out in the spring normally require a year's growth in the nursery row before budding. The mini- | mum size for budding is determined by the size of the buds and the rootstock. Most nurserymen prefer at least pencil- sized stock because slender seedlings are too limber to handle easily ; furthermore, small seedlings do not force the buds to grow vigorously and the bud shoots must be tied frequently. If the stock is large enough because of favorable growing conditions, spring-planted seedlings may be fall budded. Fall budding is often preferred to spring budding. The time to start fall budding is after the middle of September. Place buds early enough so they will unite with the stalk, but late enough to avoid shoot growth. Spring budding begins as soon as the bark slips easily and may continue until mid-summer. In areas where frost is a problem spring budding should not be later than early May. Trees budded after that time are more subject to cold injury in fall and winter. Whether you bud in the fall or in the spring, you should strive to insert the buds before stock is larger than % inch diameter at the point of insertion. If the seedling is larger than this you will find it harder to get a good "take" ; the bud union will be more pronounced, and the bud shoot will be more subject to breakage at the union. Remove suckers beneath the point where you intend to bud as soon as possi- ble after they appear. To prevent sucker- ing and sunburning some nurserymen enclose the seedling trunk with paper, foil, or plastic tubes to an inch or two above the point where the bud will be in- serted. Pruning should not be done less than 3 weeks before budding; it causes the bark to tighten and lessens the chances for a good bud take. Bud as soon as possible after an irriga- tion. Ample moisture helps insure cambial activity, and the barks slips easier. The seedling should have a clean, straight trunk at least 6 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. Selecting budwood Use buds from the best producing, true- to-type, disease-free trees for propagation. Where possible, bud each block of nurs- ery trees from a single parent source. This helps to insure more uniform tree behavior in the orchard. Since bud sports develop rather fre- quently with all citrus, avoid off-type growth when you select budwood. Cut off sport limbs whenever they appear in bud- wood "mother" trees. Be particularly careful when choosing buds for propagation on trifoliate and ri3] trifoliate hybrid rootstocks. Use only nu- cellar buds, or buds from high-producing trees grown on trifoliate rootstock and preferably indexed for the exocortis vi- rus. Make sure the parent trees meet State requirements for freedom from virus dis- eases such as exocortis, Psorosis, stub- born, and tristeza. In tristeza-infected areas it is difficult to choose budwood not contaminated with this virus. It is highly desirable to use tristeza-free budwood in all propagation, and it is imperative that it be used when budding tristeza suscep- tible rootstocks such as Alemow. Take nucellar buds for propagation directly from the parent nucellar tree or from seedling trees budded to nucellar varieties. Once you place a nucellar bud on a previously budded stock there is no certainty that progeny from this line will be disease free. In choosing budwood you will usually find the best material on the next to the last flush of growth, or the last flush after it matures and hardens. You may also get perfectly good buds several cycles be- low the last, up to the point where the bark is no longer green. A round bud- stick will yield more usable buds, but you can use angular wood that has hardened when you cannot find better material. Buds in the axils of large, healthy leaves are best. Small leaves on the budstick signify poor nutrition and these buds usually start growth later than well- nourished buds. Cutting and storing budwood You may cut budsticks just prior to bud- ding, or you may cut and store them for several weeks. Most budders store bud- wood that is not used more than a day or two after it is cut. Do not use dried, moldy, or water-soaked buds. At the time of cutting, clip off all leaves and cut the sticks into convenient lengths to handle. Never allow buds to dry out. Bundle them as soon as possible and label them as to date, name, source and regis- tration number. Put them in a good stor- age medium or polyethylene bag, and store them in boxes or folded clean, damp, burlap sacks in a cool, dark place. Budwood storage media are damp peat moss, newspaper, coarse sawdust and vermiculite. Wet the material thoroughly before using and allow the free moisture to drain away prior to covering the bud- sticks. Budwood stored in sealed polyethylene bags does not need additional moisture nor does it need to be packed in a holding medium. It is held under refrigeration from 40° to 50°F. Budding Use the shield or "T" bud method. Prop- erly done, it gives excellent results, with a minimum of effort. A good sharp knife with a rounded point is used to slice buds from the bud- sticks. Large buds for insertion into pen- cil sized and larger stocks should be cut up to an inch long and deep enough to include a sliver of wood. Smaller buds may not include wood. Here is the procedure: Slice the bud from the stick and hold it between the thumb and knife blade. Make a perpen- dicular cut on the stem of the seedling. With the blade held at an angle make a second incision horizontally at the upper end of the first cut. This is done to open the bark where you want to insert the bud. Finally, shove the bud into the opening at the junction of the cuts. Be careful to place the bud with the right end up — leaf base down. Wrap bud with plastic tape, rubber strips, or waxed cloth immediately. In wrapping buds, start above bud and work down to avoid moving the bud out of place. Tie 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 bud shoots may start before the wrap is removed. Newly budded trees must not be al- lowed to wilt. [14] THE Slice bud as shown ,1 Bud will look like this STEPS USED IN BUDDING s Make "T" cut in bark of seedling stem To get uniform trees and facilitate handling, bud all trees in the row at the same time and at the same height (6 to 8 inches above the soil) . Unwrapping and forcing buds Unwrap fall buds after they are well cal- loused in— 1 to 2 months after budding. (Some kinds of rubber wraps need not be removed; they deteriorate and drop off.) Spring buds take more quickly than do fall buds. Usually you may remove the wrap after 2 to 3 weeks of good growing conditions. Force fall buds by lopping or by re- moving the top 3 to 4 inches above the bud just before spring growth starts. Lop by breaking or partly cutting the stem so that the seedling top lies on the ground. * i .^K y- ■- --■ P .... -. - i ■- > * j /I Budling, showing seedling top bent over to force bud to grow. Insert bud in f "T" slot Wrap with ' rubber, wax cloth, or plastic tape Small budlings should be lopped so the top may continue to nourish the root. Force spring buds by lopping or bend- ing immediately, or a day or two after bud wraps are removed. Buds may fail to start if you delay lopping too long. If some buds fail to shoot within 6 weeks after lopping, bend or shake lops to make sure they are not too strongly attached. Some buds may have to be forced by cut- ting off the top. To get the most benefit out of lops leave them on the trees throughout spring and summer. (Usually, however, they are removed after the bud shoots make 28 to 30 inches of growth.) If growth from the bud is weak and the lop is in the way, leave the stub until the following spring. If you remove the stub on weakly grow- ing budlings too early, you may lose the bud and — occasionally — the seedling. Because unhealed cuts predispose trees to frost damage, do not remove stub after the first of September. If bud shoots are above 30 inches by fall remove the lops then — although no harm results from let- ting lops or stubs remain until digging time. When you cut the stub off, you may hasten healing of the pruning wound by covering the cut with a good asphalt emulsion preparation. Staking To develop straight trunks, citrus bud shoots usually require some support. Many nurserymen use lxl inch redwood [15] 1 £5 ^ Tying budlings (grown as canes) to stakes. stakes, 4 feet long, or sharpened 4-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 opposite the shoot. This allows the leaves to give some support to the stem and permits the "head" to develop evenly. Use soft twine, raffia, plastic tape or "twistems" to tie shoots so they will grow into straight trees. The ties must be tight enough to prevent the budlings from 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 [16] 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. Instead of "heading" trees in the nursery, many commercial nurserymen encourage 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 proce- dure eliminates a certain amount of suck- ering and usually produces trees of larger diameter. When trees (whips) are cut back to 28 or 30 inches above the ground at the time of digging, it 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, especially when extra handling of fumigation and dipping is required. Another advantage 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 allows more time between digging and planting. Balled trees start growth sooner after being set out in the orchard than do trees handled bare root. Trees to be balled should be trimmed to the desired height a week or two before 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 transplanting 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 cuts all lateral roots and makes a ball about 8 inches in diameter. After the last thrust, leave spade in position and dig soil away from the back of the spade so as to leave a hole for lifting out the ball. Thrust spade down again on the opposite side of the ball, and then with a shovel cut under the ball so as to sever tap root at desired depth. Lift the ball out on the balling spade and place it on a piece of burlap or other suitable wrapping mate- rial. If burlap is placed on a light bench, handling 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 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 bot- tom 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. In interior and desert areas, defoliate and whitewash trees just before digging. In cool and humid coastal regions this may not be necessary. Atlvantages of bare rooting: It per- mits inspection of the root system. It also 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 preferred to balling, especially when 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, frost hazard keeps many growers from planting at that time — which limits the demand for fall- dug citrus trees. [17] STEPS USED IN BALLING Balling spade 16 inches long. Circle shows diameter of ball. Cutting tap root with shovel. Finished ball. Lirting ball out of hole on balling spade. Wrapping ball with burlap. In citrus-growing sections along the coast (and during early spring inland also) when the weather is cool and over- cast, you may successfully transplant bare-root trees having some leaves re- maining. If you doubt that you can keep the trees from wilting, it is best to defo- liate 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 18 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 soil around their roots is not allowed to dry. If they are without shade protection until new growth devel- ops, the 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, wet the balls until soaked through. The best way to forestall such accidents is to pack the balls in damp sawdust in bins and sprinkle as frequently as necessary. 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 Stem Cuttings Citrus trees may also be propagated by rooting stem cuttings. This method is used principally for producing plants which are grown and sold in contain- ers. 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 bud- ded as described for seedlings. Generally, citrus trees grown from cut- tings reach the same size as trees of the same variety budded on one of its own seedlings. Eureka lemons grown from cuttings are weak and have not proved to be long-lived on their own roots. In their first two or three years, cutting- grown trees are not as well anchored in the soil as are trees budded on seedlings. In extremely windy locations, 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 should be dug and moved bare-root. The speed and ease with which cuttings form roots varies with the different spe- cies 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; cut- tings 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 [19 north side of the tree; these root well if the trees have been maintained in good condition throughout fall and winter. Shoots from trees which recently have been oil sprayed do not furnish satisfac- tory cuttings. The oil increases leaf drop when cuttings are placed in the propa- gating 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 distribu- tion than a slanting cut. The position 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 three to six leaves on each cutting. Keep cuttings moist during all handling operations after removal from the tree. Treatment with hormones Some citrus species benefit by a treatment with rooting hormones. Lemons, limes, citrons, citranges, and trifoliates respond to a treatment of indolebutyric acid (IBA) in talc at from 3,000 to 8,000 ppm. This materal can be obtained as a com- mercial preparation labeled Hormodin® powder. Number 2 powder contains 3,000 ppm IBA, and number 3 powder 8,000 ppm. To apply material, moisten base of the cutting and 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, as this would prevent pow- der from adhering to the tissue. Some of the more difficult materials, such as Satsuma mandarin, may benefit from a quick dip into IBA at 10,000 ppm. To make this solution, dissolve IBA crys- Wta Propagating frame for stem cuttings. [20] tals 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 i/4 inch deep for one or two seconds. Rooting and removal of cuttings Cuttings may be rooted in any structure that maintains high humidity and gives good light intensity. The two main choices are closed propagation beds, or a mist system by which the cuttings are placed under water mist sprays which can be turned on or off. Closed frames are satis- factory, but require more attention than the mist system. Citrus cuttings under mist leach badly if they root slowly. To improve their condition fertilize periodi- cally. Leaching does not occur in the closed frames. Place the cuttings about 1-inch deep in any well-aerated medium such as vermic- ulite, sand, or sand and peat. Space them far enough apart so at least a portion of every leaf is exposed to light. Bottom heat is essential except during the warmest seasons, A minimum tem- perature of 75°F works well for rooting, and optimum temperature appears to be between 80° and 90°F. In closed frames you can control the air temperature by adding or removing shade. Never allow the leaves of the cuttings to wilt. Syringe the foliage and the inside of the frame daily in normal weather, and more often during periods of extreme high tempera- ture. Give the cuttings as much light as possible, but hold air temperatures inside the frames below 100°F to prevent burn- ing of foliage. Lemon cuttings produce good roots within 4 to 6 weeks; oranges, citranges and trifoliate orange in 6 to 8 weeks; mandarins will take up to 4 months or more. These periods will vary with the weather and condition of the cuttings. After the cuttings are rooted they are hardened off by gradually reducing hu- Rooted cutting ready for transplanting. midity in the frames. If the mist system is used, harden cuttings by gradually decreasing the "on" period and increas- ing the "off" period. Remove cuttings and plant them in containers or in a nursery row. In hot or dry weather protect 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 cuttings gives a desired rootstock-scion combina- tion; three cuttings a combination of root- stock, scion, and interstem. For twig grafting use the same type of material as described above for cuttings. Select material that will have as nearly 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 2 months in propagating frame. 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 one leaf on the inter- stem if used. Make a sloping cut % 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 forefinger 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 shown just above (a number 16 or 18 station- er's rubber band which has been cut makes a good wrapping material). To start the wrapping, hold one end of the strip between middle finger and fore- finger 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 hu- midity will protect them from drying. Unions at the graft should heal in 3 to 4 weeks, at which time the tie can be loos- ened or removed. How long it takes to root these combinations depends on the piece at the base. Materials rooting read- ily 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. Remove cut- tings when root length totals 6 to 8 inches. [22] Topworking Citrus Trees Citrus growers sometimes wish to change established groves to other varieties. It is often cheaper to graft existing trees to another variety than to pull out the stumps and plant new trees. Topworked trees will also come back into production sooner than nurs- ery 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 Advisor or another com- petent person. Topworking of citrus trees can be done by budding or grafting. Either method may be used on any size of trees, but in most areas younger trees are budded while large trees are grafted. In some areas, particularly Central California, 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 per- centage of bud take, but some time is lost in growing the shoots; also, more follow-up work is required. Most budding is done directly in the scaffold limbs. Select the branches in which you will place buds and remove all growth which is in the way. Usually some unbudded branches are left as "nurse" limbs. You may bud in the fall, or, more gen- erally, the following spring when the bark slips well. Start spring buds 3 to 4 weeks after budding by cutting back the branches or by girdling (removing 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 cutting back or girdling the branches until the next spring. Be careful to avoid splitting when cutting off large branches: remove most of the weight of the branch with a first cut far- ther out on the limb, and then make a second cut closer to the bud. 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, scrape it with a knife to thin it 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 (pages 14-15) . 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 1% to 2 inches long. With a shorter shield there is the danger of bark grow- ing over it and smothering the buds. After buds are inserted, tie them in by wrapping over them with waxed budding cloth or plastic tape. After 3 or 4 weeks remove wraps and examine buds to see if they have re- mained alive. If callus tissue has grown over the bud cut the tissue away care- fully — 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 gives better healing on vertical branches, and prevents water standing on the wound surface. All nurse branches should be removed so that all the growth goes into the new top. [23] '• •' • i»«."!T v *.' •'.*•'* 43§6: • *•"!•. ■.••.':*. iv":'^-'' .< •• ".•* :•••*••'• :;..'\%«"<£.r.« '• •-*.' -^ .'* ;*•**»■ *. • •• ' v* -$jv$%\ : •'•' * *••■ r:*- • ".,*;• • £\H§ Topworking by budding. Left: bud partially inserted. Right: bud inserted and ready for wrapping. 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 graft- ing into the scaffold branches leave some branches on as nurse limbs, both for shade and to maintain the root system until new scions develop foliage. Graft when the rootstock bark sepa- rates readily from the wood. About a day after cutting a tree back the bark tight- ens; thus, if the grafting is not done im- mediately after cutting wait about a month until the bark loosens again, at which time re-cut and graft the limb stubs or stump. Here are the directions for a bark graft- ing method which has proved satisfac- tory: cut off the branches and make verti- cal 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 3 to 5 inches apart around the stub. Select scion- wood from firm, current season's growth, or from wood as old as two or three years, the diameter may vary from %g to % inches. Cut a scion (see page 25) with a long sloping basal cut 2 1 /o 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 bark on one side of the cut on the stump high enough to insert the scion, and push down 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 the rim of the stump after the scions are inserted. Don't make scions longer than neces- sary, as long scions can dry out before unions can form. The scions may be nailed in place with thin flat-headed nails, or tied with several loops of cord, fric- tion tape, or vinyl tape around the stump. On some very large stumps baling wire has been used successfully. 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 sur- face 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 graft- ing compound to prevent drying. Protection after grafting After grafting, protect the scions and trunk from burn resulting from direct sunshine on exposed surfaces. Whitewash trunks and branches on the south side and shade the scions with ventilated paper bags or other material to keep direct sun- light from striking them. Scions may also be protected from the sun by covering 24 Topworking by bark grafting. Left: scion, showing two cuts. Right: stock, showing vertical slits in bark and two scions inserted. with white latex paint. As the scions start to grow, tear the bags to let the shoots come through into the sunlight. 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 support. These boards should extend 3 to 4 feet above the graft. Tie the shoots loosely to them. Many propagators prefer 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. Eventually, all shoots below the scions will require removal. [25] To simplify the information, it is sometimes necessary to use trade names of products or equip- ment. No endorsement of named products is intended nor is criticism implied of similar products not mentioned. 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. 15w-6,'68(J7)VL