18 



chemical-thinning treatment would be one using a moderate level of carbaryl in 

 combinations with NAA. Acceptable thinning should be achieved without causing 

 overthinning or severely depressing the predator mite population. 



Table 1. Effects of naphthaleneacetic acid (NAA), benzyladenine (BA), and 

 carbaryl (50 % WP) on fruit set and fruit weight of Mclntosh/M.7 apple trees. 



Fruit/cm limb circumference Fruit weight (g) 



Carbaryl (1 Ib./lOOgal.) Carbaryl (1 Ib./lOOgal.) 



Treatment^ (-) (+) (-) (+) 



Control 

 BA, 50 ppm 

 NAA, 5 ppm 

 NAA, 7.5 ppm 



Average 8.9 **^ 5.6 144 ** 160 



^Treatments were applied as a dilute spray on May 26, 17 days after full bloom. 

 NAA was applied as Fruitone N" and carbaryl as Sevin" (50 % WP) . 



YTreatment effects on fruit set or weight were significantly different (5 % 

 level, Duncan's New Multiple Range Test) if not followed by a common letter. 



^The effects of carbaryl on fruit set and fruit weight were significant at the 

 1 % level (Duncan's New Multiple Range Test). 



BA is in the developmental stages as a chemical thinner. It is the only 

 chemical used alone that adequately thinned Mcintosh. It has performed equally 

 well as a thinner over the past 5 years on Mcintosh as well as on other 

 cultivars. BA presently is being sold as a branching agent on Christmas trees 

 and is also 50% of the active ingredients of Promalin'". We will continue to 

 evaluate this compound. 



Experiment Two 



A block of 16-year-old Mcintosh on MM. 106 was selected, and just prior to 

 bloom 70 limbs were tagged and the blossom clusters were counted. Limbs were 

 selected that had a wide range of blossom densities, some having as few as 15 

 and others having as many as 350. A dilute thinning spray containing 2.5 ppm 

 NAA and 1 lb. carbaryl per 100 gal. was applied with an airblast sprayer on May 

 27, 16 days after full bloom. Fruit set was determined at the end of June 

 drop . 



