Effects of Gibberellin Synthesis 

 Inhibition on Feeding Injury by 

 Potato Leafhopper on Apple 



Kathleen Leahy, Duane Greene, and Wesley Autio 



Department of Plant & Soil Sciences, University of Massachusetts 



Overview 



Although the gibberellin synthesis inhibitor 

 Apogee (prohexadione-calcium) was introduced in 

 apple primarily as a horticultural tool to reduce shoot 

 length and thereby decrease the amount of necessary 

 pruning and associated costs, the inhibition of 

 gibberellin synthesis has also shown beneficial effects 

 in controlling some important pests of apple. The most 

 dramatic effect has been seen on the shoot-blight phase 

 of the bacterial disease fire blight, but some effects 

 have also been seen on flush-growth-feeding insects 

 such as green apple aphid and obliquebanded leafroller. 

 To date, however, no studies have been published on 

 the effects of Apogee on potato leafhoppers Empoasca 

 fabae (Harris) (Byers et al., 1997; Paulson and Hull, 

 1999;Yoderetal., 1999). 



Potato leafhoppers are occasional orchard pests in 

 the mid-Atlantic and Northeast. These insects are not 

 able to winter in the north. They overwinter in the 

 southern United States and migrate northward on storm 

 systems over the course of the spring and early summer. 

 In apple, they feed in vascular tissue in rapidly- 

 developing shoot tissue. In mature trees, this injury is 

 not generally considered serious, although in young 

 trees it may be necessary to apply control measures 

 for a moderate to severe infestation. There is, however, 

 some evidence that potato leafhoppers may play a role 

 in facilitating the shoot-blight phase of fire blight, by 

 introducing feeding wounds in susceptible tissue on 

 which Erwiuia amylovora, the bacterium which causes 

 fire blight, is growing epiphytically (on leaf surfaces), 

 allowing the bacteria to invade the leaf and cause 

 infection (Koehler, 2000; Pfeiffer et al., 1999). 



Since potato leafhoppers feed directly on tissue 



likely to be affected by gibberellin synthesis inhibition, 

 we thought that the possibility of suppressing or even 

 completely controlling these leafhoppers with Apogee 

 or a similar gibberellin synthesis inhibitor was strong 

 enough to warrant further study. This work was done 

 as part of a larger study looking at the interactions of 

 gibberellin synthesis and potato leafhoppers with fire 

 blight. 



Materials & Methods 



A 200-tree section of a block of 15-year-old 

 Mclntosh/M.7 at Scott Farm in Dummerston, Vermont 

 was used for the study. A randomized-complete -block 

 design was used, with ten replications and two trees 

 per treatment within each replication. Buffer trees were 

 employed within the row, and a buffer row was 

 employed between treated rows. Apogee was applied 

 at the rate and timings recommended for commercial 

 growers in this area, 12 oz per 100 gallons dilute at 

 early petal fall (May 12) and a second application at 

 the same rate when growth would have been expected 

 to resume, June 1 . 



There were two levels of two treatments used in 

 this experiment: Apogee treated and non-treated, and 

 potato leafhoppers excluded or permitted. The 

 insecticide Provado (imidacloprid) was used for 

 exclusion, at the highly reduced rate of 0.5 oz per 100 

 gallons dilute recommended by researchers at the 

 Cornell Hudson Valley Laboratory (Scaffolds 

 newsletter, June 2001). Provado was applied when 

 potato leafhoppers began to appear in the orchard, June 

 22, and was re-applied when numbers appeared to be 

 resurging, July 20. 



Shoot length was measured using a measuring tape 



Fruit Notes, Volume 67, Winter, 2002 



