FRUIT THINNING WITH CHEMICAL SPRAYS 33 



so that all trees cannot be sprayed with the same results on one par- 

 ticular day. 



The more southern peach areas often experience winters with in- 

 sufficient chilling to break completely the rest period of the trees. 

 This results in a relatively long period of bloom development. Under 

 such conditions dinitro bloom sprays would obviously be less adapted 

 for thinning than in areas where delayed dormancy is no problem. 



According to the data presented in table 9 the various forms of 

 dinitro material when used at the same concentration of the active 

 ingredient have resulted in about the same amount of thinning. An 

 exception to this is DN 289 (23 percent triethanolamine salt of 

 dinitro-ortho-sec-butylphenol). In a New York test (table 9) this 

 material proved about as effective as other dinitro chemicals when 

 used at about one-half the concentration of toxicant. 



Under some conditions dinitro sprays may overthin young peach 

 trees. The fruit-set records for the 4- and 8-year-old Elberta trees 

 (23 and table 9) chemically thinned in 1944 in New York illustrates 

 this point. The wood growth of the 4-year-old trees was very vigor- 

 ous and had fewer fruit buds per foot of growth than the 8-year-old 

 trees. As a result, the normal set of 21 percent on the young trees 

 constituted a satisfactory crop and all treatments overthinned. With 

 the much heavier bloom on the older trees a reduction in set from 

 22 to 6 percent was required for adequate size. 



As is true with apples, success with chemical thinning sprays on 

 peaches is based on the assumption that fruit set will be in excess 

 of that required for a commercial crop of satisfactory size and 

 quality. Aside from possible frost hazards, peach trees in normal 

 vigor generally set heavily, provided favorable weather occurs during 

 the blossoming period. While the danger of overthinning most peach 

 varieties with dinitro sprays is not great, nevertheless, for greatest 

 safety dinitro sprays should be used on a trial basis until properly 

 evaluated for a particular set of environmental conditions. 



Peaches form their fruit buds laterally on the current season's 

 shoots and are not so subject to biennial blossoming as is the case 

 with the apple, which forms its fruit buds terminally on both spurs 

 and shoots. However, the yield of peach trees may vary considerably 

 from year to year, depending on the amount and type of shoot 

 growth produced the previous season. In addition to the improve- 

 ment in size and quality of the current crop, one of the most striking 

 benefits from bloom thinning of peaches is the increased shoot growth 

 and bud formation for the next crop (23). This is especially notice- 

 able in nonirrigated regions when a heavy fruit set is accompanied 

 by a dry growing season such as was experienced in an Elberta ex- 

 periment in New York during the 1944 growing season. 



In this experiment the dinitro -thinned trees yielded essentially the 

 same quantity of fruit as the hand-thinned check trees. At harvest- 

 time the fruits from hand-thinned trees averaged 1% to 2 inches in 

 diameter while those from the chemically thinned trees attained a 

 size of 214 to 2% inches. The average length of terminal growths was 

 10.6 inches for hand-thinned trees and 15.6 inches for chemically 

 thinned trees. Counts of fruit buds on 50 terminals from each treat- 

 ment showed that the hand-thinned trees had formed an average of 



