- 9 - 



have been good. In applying hormone sprays, the important factor 

 is to apply a given number of grams of actual material per acre 

 whether applied as dilute or as a concentrate spray. Thus, success 

 with these materials is dependent on the accuracy of your applica- 

 tions. 



Limited studies have been made on chemical thinning with con- 

 centrate sprays. In 1966, C.G. Forshey and M.B. Hoffman in New 

 York, stated that practical experience has shown that thinning re- 

 sults are more consistent if the concentration does not exceed 2X 

 ( New York State Aqr. Exp. Sta. Res. Circ. No. 4 ). More recently, 

 BTF! Rogers and A.H. Thompson, in Maryland, i nves tigated the effec- 

 tiveness of concentrated thinning sprays--rangi ng from 3X to 33X-- 

 and reported their findings in Volume 94 (No. 1) of the Journal of 

 the American Society for Horticultural Science . Their results are 

 summarized below. 



A four year study with Rome Beauty apple trees (1964-1967) 

 showed that carbaryl (Sevin*) at concentrations of IX to 33X sig- 

 nificantly thinned this variety 3 out of 4 years. In 1966, the 

 year of failure, the fruit set on the check trees was low and no 

 significant thinning occurred when dilute spray was compared with 

 carbaryl sprays delivered at 33X volume. The use of carbaryl at 

 concentrations up to 33X generally produced fairly consistent re- 

 sults. In 1967, however, carbaryl at 33X thinned less than the IX 

 spray. 



In 1-year experiments, carbaryl at, IX, 3X and 6X significantly 

 thinned Jonathan apple trees in 1964, and NAA at IX, 3X and 6X sig- 

 nificantly thinned Golden Delicious in 1967. The dilute spray of 

 NAA was more effective than the concentrated ones, however. 



The studies in Maryland, therefore, indicate that apple trees 

 can be thinned at concentrations as high as 33X. However, much 

 more work is needed before broad recommendations can be made. Since 

 thinning results are somewhat unpredictable, it is questionable 

 whether growers should thin more than a small fraction of the more 

 valuable mid- and late-season varieties with highly concentrated 

 thinning sprays until experience has shown satisfactory results. 



*Trade name 



*************** 



All pesticides listed in this publication are registered and cleared 

 for suggested uses according to Federal registrations and State laws 

 and regulations in effect on the date of this publication. 



When trade names are used for identification, no product endorsement 

 is implied, nor is discrimination intended against similar materials 



