- 8 



9^JL 12^^S^}!^3^J:^§^SS}-3JLSi}-J£}^J^9Jf. A^^j_ Cjl^j? ical^ We£^ci_^ qnt r ol In The Orch ar d 

 is n ow available through your County Extension Service or by writing to the Mail- 

 ing Room, University of Massachusetts, Amherst, Massachusetts. This circular con- 

 tains our suggestions for the use of herbicides labeled for orchards. 



I I I I I I I I I I I I I I 



CHEMICAL THINNING OF APPLES 



Franklin W. Southwick 



Department of Horticultural 



Science 



The crop in most orchards in 1963 was not excessive on our leading varieties 

 so I would anticipate a rather heavy bloom in many Mcintosh blocks. Some chemical 

 thinning may be desirable if good pollinating weather prevails at blossomtime and 

 a late spring frost is not a serious threat. Some moderate thinning of heavy 

 setting Mcintosh trees is usually necessary to assure annual flowering. This is 

 a much more important reason for thinning Mcintosh in this area than the necessity 

 for improving fruit size. On the other hand, many other early to late apple vari- 

 ties need chemical thinning not only to improve the chances of annual flowering 

 but also to significantly improve fruit size. 



The problem of chemical thinning Mcintosh has been given sufficient attention 

 so that we know that Lt can be satisfactorily done with either NAD (Amid-Thin) or 

 Sevin when these are applied from 1 to 3 weeks after petal-fall. Sevin is an 

 extremely safe and reliable thinner over a very wide range of concentration. Data 

 shown in Table 1 illustrate this point very clearly. Sevin thinned to the same 

 degree at all concentrations from 1/4 to 2 lbs. per 100 gallons of water. Since 

 Sevin has no temporary size depressing action on persisting apples and causes no 

 visible foliar effects, it has these advantages over NAD. The primary advantage 

 NAD has over Sevin as a chemical thinner of Mcintosh is that NAD thinned trees 

 may occasionally exhibit a heavier "return or repeat" bloom than similar trees 

 thinned to the same degree with Sevin. 



Table 1. The Influence of Chemical Thinners on Fruit Set and Size of Mcintosh 

 Apples. 1963. 



Amounts of Sevin (50% wettable) used in 100 gals, of water. 

 ^Fruit size measurements made Sept. 4, 1963 (35 fruits at random per tree). 



