Do Bloom Applications of Apple 

 Fungicides Affect Fruit Set? 



Daniel R. Cooley 



Department of Plant Pathology^ University of Massachusetts 



Duane W. Greene 



Department of Plant & Soil Sciences, University of Massachusetts 



We reported previously [Fruit Notes 56(4): 18- 

 1991] that researchers in Great Britain found that 

 fungicide captan may be toxic to apple pollen, 

 and thereby reduce fruit set. Since then, a test 

 in Virginia has shown similar reductions in fruit 

 set, apparently caused by captan applied at 

 bloom. Furthermore, growers have on occasion 

 speculated that sterol-inhibiting fungicides re- 

 duce fruit set. In the work reported here, we 

 asked two questions. First, does captan or the 

 sterol-inhibiting fungicide, fenarimol, applied 

 at bloom reduce fruit set? Second, does captan 

 or fenarimol interact with oil or copper to 

 reduce fruit set? 



In 1992, mature Mclntosh/M.7 apple trees 

 were selected at the University of Massachu- 

 setts Horticultural Research Center in 

 Belcherlown. In the first experiment, six limbs 

 of similar blossom density were selected per 

 tree. Three of the limbs were treated with 

 copper hydroxide (Kocide 50 WP, 2 lbs/100 

 gal.) at tight cluster. Each of the three limbs 

 treated with copper hydroxide and each of the 

 three not treated with it were sprayed with 

 captan (Captan 50 WP, 2 lbs/100 gal.) or 

 fenarimol (Rubigan 1.6 EC, 12oz./100gal.)or 

 left untreated. A second experiment was iden- 

 tical except that oil (1 gal./lOO gal.) appUed at 

 tight cluster replaced the copper hydroxide 

 treatment. For both experiments, fungicide 

 applications began when the primary blossoms 

 were expanded completely, and captan and 

 fenarimol applications continued at seven- or 

 ten-day intervals, respectively, until mid-June. 

 Treatments were applied to the drip point using 

 a handgun. After June drop was complete, final 



19, fruit set was counted on each limb, 

 the In the first year of study, captan and fenarimol, with 



or without oil or copper hydroxide application, did not 



Fruit Notes, Fall, 1994 



15 



