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overcome this difficulty and reduce its cost by the use of suitable thinning sprays. 

 In California excessive sets of apricots, prunes, plums, peaches, apples and olives 

 are common. Hand thinning is an almost industry vd.de practice and a major product- 

 ion cost. Consequently, experimenters and growers here are quite interested in the 

 possibilities of chemical thinners on all the aforementioned fruits. Almonds, 

 cherries and walnuts are about the only deciduous tree fruit crops which appear 

 to be grown without much concern about oversetting. 



Experiments by Drs, Lilleland and Uriu indicate that dinitro materials have 

 considerable promise as fruit thinners on freestone peaches, plums, prunes, and 

 apricots. These fruits blossom over a rather long period but the r/eather is 

 rarely too poor for good sets and the risk of overthinning, although it may occur 

 occasionally, is not great. There is, also, interest in gro\rth substances such 

 as chloro IPC and Peach Thin 322 (sodium salt of naphthalamic acid for thinning 

 freestone peaches applied at or shortly after bloom. On apples, interest in Amid- 

 Thin is prevalent. Therefore, much experimental yrork is being done v/ith chemical 

 thinners. 



Cling peaches, which are grown in greater volume than freestone, are entire- 

 ly hand thinned, however. The size reqxiirement for cling peaches is 2-3/8 inches 

 in diameter. There is no premium paid for fruit that are larger than that. The 

 growers objective is to thin just enough so that this size represents about 90 

 percent of his total tonnage. An average size of 6? ram (2,6 inches) is needed to 

 give 90 percent of the fruit above 2-3/8 inches (61 mm). To thin beyond this 

 requirement results in a loss in total volume with no compensating increase in 

 price for additional size, Dr, L, D. Davis, over a period of years, has developed 

 a method wherety a person, by making a number of fruit size measurements about 10 

 days after the start of pit hardening (reference date) of cling peaches, can 

 determine about how much thinning must be done so that 90 percent of the crop vn.ll 

 be about 2-3/8 inches at harvest time and still get maximum yield. For example, 

 if the fruit averages 32 mm in diameter at reference date heavy thinning Yd.ll be 

 necessary, if 35 mm moderate thinning and if 38 mm little or no thinning may be 

 needed to result in the desired size at harvest time. Data as to reference date 

 and prevailing sizes at that time are collected in the various cling peach districts 

 through the efforts of State and County workers and passed on to the growers. 

 This, it seems to me, is an unusually precise means of handling the thinning 

 problem. Such precision \Tith chemical thinning procedures is probably unattain- 

 able, so for this crop hand thinning is the preferred procedure even though a 

 costly one. 



Hormones appear to have real promise in other ways in fruit production, also. 

 For example, Dr, Crane has found that concentrations ranging from 2$ - 75 PPni 

 of 2,U,5-T sprayed on apricots at the start of pit hardening have pronounced 

 influence on apricot fruit size and time of maturity. (This is the same material 

 T;hich failed to control our Mcintosh drop last fall,) On apricots this material 

 greatly improves fruit size and hastens maturity sufficiently so that treated 

 trees may be harvested a fe\T days to more than a week ahead of unsprayed fruit, 

 depending on the fruit district. This response is highly desirable on apricots 

 since size and earliness are important in the price received for eastern fresh 

 fruit shipments. This m.aterial, even though applied many weeks ahead of harvest, 

 controls preharvest drop, also. It's a three-in-one spray for apricots. Since 

 the apricot is a stone fruit you might expect to get the same responses on other 

 stone fruits such as peaches. Unfortunately, the overall response on peaches is 



