UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION CIRCULAR No. 248 June, 1922 SOME COMMON ERRORS IN VINE PRUNING AND THEIR REMEDIES By FEEDEEIC T. BIOLETTI Pruning cannot be reduced to a few mechanical rules. There is no simple answer, that is not misleading, to such questions as: How should you prune a two year old vine ? or, How many spurs should be left on a six year old Muscat ? It would be almost impossible to find two vines that should be pruned absolutely alike. Each vine is a special case. To watch an expert prune one vine will not aid a beginner to prune another unless the reasons for the cuts are explained and understood. These reasons, however, are based on a few relatively simple prin- ciples. If these principles are known, a good method can be devised and most serious errors avoided. Some of these principles are : 1. Each year the vine bears a crop and develops the buds which produce the crop and growth of the following year. 2. The condition of a vine at the end of a year determines how much crop it can bear and how much growth it can make the next year. 3. The more crop a vine bears in one year the less growth it can make in the same year, and vice versa. The last statement indicates that growth and bearing vary inversely, but this is true only roughly, and within somewhat narrow limits. If the crop is reduced to zero we get maximum growth, but if we reduce the growth to zero, the crop disappears also. Neither of these extremes can be reached by winter pruning, but they can be approached closely. If we prune off most of the fruit buds the vine will yield little crop and will make a vigorous growth. This can be carried on indefinitely if the patience and the bank account of the grower hold out. If we leave most of the fruit buds, the vine will try to produce a very large crop and may even succeed for one year. During this year the growth will be small and if Prin- ciple 2 above is true, it will have little crop or growth the next year. Repetition of this attempt the second and the third year may result in the actual death of the vine or at least in excessive weakness from which it recovers with difficulty. 2 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION One year of the kind of pruning shown in figure 1 might, with a vigorous vine, give 25 per cent or even 50 per cent more than a normal crop, but the grapes would be of inferior quality and the next year's crop so much below normal that there would be a net loss. If con- tinued, the vines would be permanently weakened or killed. The vine shown in figure 2 had been pruned the previous year to one cane of moderate length and two renewal spurs. It made an extremely healthy and vigorous growth. Fig. 1. — A Zinf andel ' ' pruned for crop. ' ' A short life and a merry one. When the photograph was taken the vine was well prepared to give a very large crop of good grapes the following year. Leaving three or four fruit canes of three to five feet and four or five renewal spurs of one to two buds would have enabled it to do this and also to produce a growth of good canes for the next crop. Instead of this, the method of pruning adopted was to leave all the canes, thirteen, and to leave them of full length, together with their laterals. This 'left approximately eighty feet of cane instead of the fifteen feet which would have been sufficient. The results in growth are shown in figure 3. During the third year the vine shown in figure 3 made about eighty feet of excellent fruiting canes. This year, the fourth year, it has made hardly a single foot. What growth it has made consists prin- cipally of slender twigs from five inches to fifteen inches long, half- ripened, and with poorly developed buds. It has made one poor cane about two feet long at the extreme end and one sucker about three feel long from near the ground. CIRCULAR 248] SOME COMMON ERRORS IN VINE PRUNING Fig. 2. — A three year old Sultanina pruned "for all the traffic will bear." (1) End of fruit cane of previous year. (2, 3) Eenewal spurs of previous year. Fig. 3. — A vine in tlie same vineyard a year later. "More than the traffic would bear." (1, 2) Ends of fruit canes of two years before. 4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION It probably produced a large crop of inferior grapes. With such weak growth the fruit could not have been good. The prospects for the coming crop are meager. All that can be done with such a vine is to cut it back to the old wood and grow a crop of canes for the crop of two years hence. A consideration of the three principles mentioned indicates how we are to avoid both disastrous extremes. We must leave enough fruit buds on a normal vine at the winter pruning to enable it to bear a good crop the following year and still have surplus strength to produce enough vigorous, mature buds for the next crop. Whether we have succeeded will be determined at the pruning of the following winter. If the vine has gained in size and vigor, we have not utilized its bearing capacity fully and the number of fruit buds left should be increased. If it appears weak it has been over- taxed and the number should be decreased. In this way the vigor of the strong vines is utilized to obtain larger crops and the weak vines fortified so that they will give larger crops the following year. This course of procedure applies not only to vines but to parts of vines, to arms and spurs. A thick, vigorous spur on a Muscat should have three or more buds ; a weak spur, if it is necessary to leave it at all. only one. A vigorous fruit cane on a Sultanina should be left four or five feet long, with twelve to twenty buds, a weaker cane, only two to three feet, with half the number of buds. This principle carefully carried out will maintain the vigor of the vines and the regularity of the crop. Figure 4a is representative of a young Muscat vine or other short pruned variety, or the arm of an old vine. In either case it consists of a vigorous side with two large canes and a weak side with two small canes. In figure 4c one cane has been left on each side and both cut to about the same number of buds. The result will probably be that the weak side will produce several small bunches of poor grapes and make little or no growth, while the strong side will drop its blossoms, produce little or no fruit, and be still more vigorous next year. In figure 4b the length of the spur or the number of buds is in proportion to the vigor of the cane. The vigorous cane has been allowed four fruit buds and will probably produce several large bunches of good grapes and make a moderate growth for next year. The weak cane has been cut back to one bud and will produce little or no fruit. Its energies will therefore be expended on producing stronger and more vigorous canes. The result at the next pruning will be that the two Circular 248] SOME COMMON ERRORS IN VINE PRUNING 5 sides of the vine or arm will be more nearly equal in vigor and size and equally capable of bearing an average crop. hS^r Fig. 4. — Differential pruning. Another principle which requires attention if the vines are to be permanently profitable is : 4. The amount and quality of all growth depends on the amount of sunshine it receives. Failure to bear in mind this principle introduces serious difficulties in certain forms of cane and cordon pruning. In a common method of pruning the Sultanina and the Sultana, several fruit canes are taken from near the ground and tied vertically b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION to the top of a high stake. In consequence of their position, the shoots from the top buds grow more vigorously and shade the shoots from below. The next year when it becomes necessary to supply new fruit canes, only weak and inferior canes are to be found below. If these are tied up the crop is small. If the canes at the top are taken there Fig. 5. — A young Emperor vertical cordon. is nothing to tie them to. This condition becomes worse each year if the method is continued. Finally, it is usual to leave the last canes permanently to develop into three, four or five trunks and to leave spurs at their tops where the only good canes are to be found. This is a definite abandonment of the cane system and all that remains is a vine with multiple trunks which are difficult and expensive to handle, and which requires head pruning with spurs, a method not fruitful with these varieties. Circular 248] SOME COMMON ERRORS IN VINE PRUNING 7 The trellis system, in which the canes are tied horizontally to wires, avoids these troubles by exposing the head of the vine to the sun, thus insuring a perennial supply of vigorous fruit canes at a place where they can be used. A vine started with the upright system is with difficulty changed to the trellis system. This system is described in Circular 191 of this Station. Fig. 6. — An old Emperor vertical cordon. In the vertical cordon system, commonly adopted for the Emperor, similar difficulties ensue. The vine is given the form of a long upright trunk about four and a half feet high. On this trunk, when the vine is young, are developed spurs or arms equally distributed every six to ten inches from the top to near the ground (see fig. 5). Within a year or two the lower spurs, shaded by the growth at the top of the trunk, weaken and produce small and inferior canes. Finally nothing grows except at the top and the 8 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION cordon character of the vine is lost. The growth, concentrated at the top, becomes very vigorous, and loses the ability to bear on short spurs which is one of the advantages of the cordon (see fig. 6). The horizontal cordon system, in which the trunk of the vine is carried horizontally at about thirty-six inches from the ground to the next vine, intensifies the cordon effects by making the trunks twice as long as in the vertical form and makes it permanent by insuring a continuous growth on all parts of the trunk, which is equally exposed to the sun along its whole length. This system is described in Circular 229 of this Station. The errors discussed are : 1. Failure to modify the pruning according to the strength of the vine or of the cane. This results in irregular crops and irregular vines and a serious decrease in quality and average crop. 2. Serious injury to the vine or its destruction by attempting to obtain excessive crops without regard to the annual growth. 3. Adopting systems which" in their nature cannot be permanent, i.e., vertical canes and vertical cordons. These errors are discussed more fully and methods of avoiding them explained in other publications which can be obtained by appli- cation to the College of Agriculture, Berkeley, California. The following supplementary references may be found useful : 1. Vine Pruning in California, Bulletin 241-246. (Amount of pruning, pp. 29-31 ; vertical canes, pp. 93-95 ; vertical cordons, pp. 95-97.) 2. Pruning the Seedless Grapes, Circular 191. (Methods of cane pruning. ) 3. Cordon Pruning, Circular 229. (Horizontal unilateral vine cordons.) 4. Vine Pruning Systems, Circular 245. (Types of pruning recom- mended for California.)