CHEMICAL WEED CONTROL CIRCULARS ARE NOW AVAILABLE 



The 196S Revision of Special Circular ^15 entitled "Controllinfj; 

 Weeds in Small Fruit Plantings With Chemicals" and Special Circular 283 

 entitled "Cliemical Weed Control Recommendations for Tree Fruits" are 

 now available. Copies may be obtained through your County Extension 

 Service or by writing to the Mailing Room, University of Massachusetts, 

 Amherst, Massachusetts. 



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CHEMICAL THINNING OF APPLES 



F. W. Southwick 

 Department of Plant and Soil Sciences 



Chemical thinning has been discussed for a good many years in this 

 publication and elsewhere, so I presume most fruit growers are aware 

 that we have such satisfactory thinning materials as NAD (Amid-Thin) , 

 NAA (naphthaleneacetic acid) or its sodium salt, sold under a variety 

 of labels and Carbaryl (Sevin) . The details related to the use of these 

 compounds for thinning most of our varieties are contained in Special 

 Circular 189 which is available from the University of Massachusetts or 

 from your Regional Fruit Specialist. 



It is the intention here to show some recent data comparing sever- 

 al types of chemical thinning treatments, plus scoring, on "return" 

 bloom of some very biennial varieties. Experimenters and growers have 

 been generally successful in obtaining annual flowering of such varie- 

 ties as Mcintosh, Golden Delicious and Wealthy following the use of 

 chemical thinners. However, it is much more difficult to obtain con- 

 sistent annual flowering, even following heavy chemical thinning, on 

 such varieties as Baldwin, Early Mcintosh and Puritan. Consequently, 

 we have emphasized in our recent work the relative effectiveness of dif- 

 ferent chemical thinners for stimulation of flowering. We have been in- 

 terested, also, in what thinning treatments, if any, should be used once 

 a moderate-to-heavy "return" bloom is obtained. 



In Table 1 are some data obtained over a 2 -year period on some 

 Early Mcintosh where scoring, in addition to the chemical thinning, was 

 tried in 1953. 



The data in Table 1 show quite clearly that "return" bloom in 1964- 

 is primarily related to the degree of thinning in 1963. Sevin, which 

 thinned slightly but significantly, improved fruit size somewhat, but 

 the reduction in fruit set was so slight that those trees receiving two 

 applications of Sevin (at petal fall and again 10 days later) in 1963 

 were barren, like the checks in 1964. Our attempts to improve the 

 "return" bloom on these rather lightly thinned Sevin-treated trees by 

 scoring (severingthe bark completely in 3 places - each ring of severed 

 bark about 1/2 inch apart) about 4 weeks after full bloom also failed. 

 Scoring increased "return" bloom in only one instance (Treatment 3) . 



