13. 



EXCESSIVE APPLE BUD ABSCISSION IN 1980: WAS IT CAUSED 

 BY TARNISHED PLANT BUG FEEDING OR COLD TEMPERATURES? 



1 2 



Ronald J. Prokopy^, Geoffrey L. Kubbell« 



William M. Coli , and William J. Lord 



At the Horticultural Research Center in Belchertown, as well 

 as in a number of commercial orchards, we observed an unusual 

 amount of apple bud abscission this year. The majority of abscissed 

 buds which we observed never exceeded 1/4 inch in length and turned 

 dark brown shortly after tight cluster. Some reached 1/2 - 3/4 

 inch long before abscission occurred, with the calyx cup then turn- 

 ing yellow. In some cases, all 5-7 buds in a cluster abscissed. 

 Usually, however, there were at least one or two healthy buds per 

 cluster. 



Our examination of approximately 300 flower bud clusters in 

 each of 8 commercial orchards revealed an average of 1.6 and 9.2% 

 abscissed buds in 1978 and 1979, respectively. This year, an aver- 

 age of 18.11 of the buds in these same 8 orhcards was abscissed, 

 with one orchard reaching 36.71 abscission. Our sample consisted 

 almost exclusively of 'Mcintosh' and 'Red Delicious' trees, with 

 the level of abscission about the same on each. Abscission levels 

 appeared to be greater on 'Cortlands', although we sampled few trees 

 of this cultivar. This observation is in agreement with bloom data 

 obtained from other experiments involving these cultivars. 



In an earlier study (FRUIT NOTES 42(2): 10-14, 1977), we showed 

 that feeding by tarnished plant bug (TPB) adults on apple flower buds 

 from the silver tip up to the tight cluster stage could result in 

 substantial bud abscission. The large number of TPB adults captured 

 on our white monitoring traps from silver tip to tight cluster in 

 commercial orchards this year suggested to us that TPB adults may 

 have been principally responsible for the high level of bud abscission. 



At our research block at the Horticultural Research Center, we 

 had placed cages over several hundred dormant buds in early April 

 to prevent entry of TPB and other insects. Abscission of uncaged 

 buds on these trees was high (68%) , but it was nearly as great (54%) 

 for the caged buds. The large number of TPB adults (7.2/trap by 

 tight cluster) in this block may have accounted for most or all of 

 the 14% difference here, but these adults obviously were not the 

 principal cause of bud abscission. 



1 



Extension Entomologist 

 2 



Research Technician 

 3 



Pest Manager Specialist, Entomology 

 4 



Extension Pomologist 



