6 



POTATO LEAFHOPPER IN HASSACHUSETTS APPLE ORCHARDS 



Kathleen Leahy, Ronald J. Prokopy, and William M. Coli 



Department of Entomology 



University of Massachusetts 



In 1986, many growers, private consultants, and Extension workers noted a 

 "new" type of injury on terminal leaves of apple, consisting of general off- 

 coloration as well as a strong marginal yellowing or burning of the leaves. 

 Since the injury was not particularly severe and no causative agent was found, 

 in most cases it went unremarked during the growing season. It was not until 

 the fall, when Extension workers and private consultants from the Northeast 

 gathered to share information, that the problem was recognized as a widespread 

 phenomenon, and the injury was definitively identified as caused by the potato 

 leafhopper, (PLH) Empoasca fabae . Over the decades, this insect is known to 

 have been an occasional pest of apples, but this has been the most notable 

 outbreak in recent years. 



Nymphs and adults of PLH are pale green in color, and tend to move rapidly 

 (often in a sideways fashion) when disturbed. In contrast, nymphs and adults 

 of the white apple leafhopper (the only other leafhopper likely to be seen in 

 Massachusetts apple orchards) are pale yellow to whitish in color and move more 

 slowly when disturbed, usually straight ahead. An additional distinguishing 

 character visible with a hand lens is a rather distinctive whitish "H" pattern 

 on the top of the thorax of a PLH adult. And, of course, the location (new, 

 succulent terminal growth) and type of damage (yellowing and "burn" as opposed 

 to stippling) are also diagnostic. 



PLH overwinter as adults in the South, and move northward in warm masses 

 of air, usually beginning in June. They fall out when the warm air collides 

 with cooler northern air. Eggs are laid in the veins and petioles of newly- 

 developing foliage of a variety of plants. Nymphs feed on tender terminal 

 leaves. There are two and possibly three generations of PLH here in the 

 Northeast. Luckily, apple is not the most favored host of this insect. It was 

 discovered in 1841, feeding on beans. By the late 1800's it had become a pest 

 of potatoes, its preferred host. Other favored hosts include clover, alfalfa, 

 and beets. Fortunately, most (but not all) PLH apparently leave apple trees 

 after completing the first generation. By that time, the growth of terminal 

 foliage in most orchards has hardened off to an extent where PLH prefer other 

 plants having more succulent foliage. However, in plantings of young trees or 

 on older trees producing vigorous mid- to late season growth, PLH can continue 

 to be a problem until August. 



The first evidence observed in 1987 of PLH on apple in Massachusetts was 

 on July 8 in a Wilbraham orchard. Over the next few weeks, PLH continued to 

 disperse into most locations in Massachusetts. In general, infestations have 

 been heavier this year than they were last. To illustrate, in surveys during 

 July in 18 orchards participating in the second-stage IPM program, we found 

 about 10? of terminals of bearing trees in sprayed (control) blocks manifesting 

 signs of PLH injury. 



In most cases observed in 1987, PLH injury first appeared as a general 

 off-coloration (partial yellowing) of new terminal growth. It was only after 



