Scaffolds 99 index

HUDSON VALLEY LEAFROLLERS

(Harvey Reissig whr1@nysaes.cornell.edu, Entomology, Geneva)

Two species of leafrollers, Variegated Leafroller (Platynota flavedana) and Sparganothis Fruitworm (Sparganothis sulfureana), have occasionally damaged fruit in the Hudson Valley, and have apparently become serious problems in some orchards during the last several years because they have developed resistance to organophosphate insecticides. The variegated leafroller is found from Kingston (in Ulster County) south to the Rockland County line, in a narrow band bordered by the Hudson River on the east and the Marlboro mountain range on the west. The Sparganothis fruitworm is found predominantly in Columbia County on the east side of the Hudson River and north to Albany. It is also prevalent in western New York, but is currently not a pest in commercial apple orchards there.

Both species overwinter as third-instar larvae in the orchard ground cover and begin feeding in early spring on weeds and plants under trees. Larvae pupate in the ground cover, and adult moths emerge shortly after petal fall. Adults lay eggs on apple leaves during June; eggs hatch and larvae are found from late June to July. A second flight begins in late July. These larvae may feed on fruit in late summer until they reach the third instar, at which time they spin down into the ground cover to overwinter.

Larvae of the summer generation may use dead leaves to build a feeding shelter beneath the apple. Most of the larvae from the overwintering generation probably feed primarily on leaves in the late summer, but they may occasionally damage fruit. This late-season damage is less extensive than that from the summer generation of larvae but usually consists of tiny pinholes on the fruit surface.

Males of both species can be monitored in pheromone traps, but numbers caught in the traps cannot be related to potential fruit damage in the orchard. Because these species are a serious problem only in certain orchards, the most reliable way to determine if a specific block requires treatment would be to monitor larval populations during June and July. No formal techniques have been developed to sample these larvae. Likewise, no formal studies have been done to estimate an economic threshold level for initiating summer treatments. It would not usually be considered economically feasible to apply special treatments to control these leafrollers unless at least 3-5% fruit damage was anticipated. This threshold represents a larger value than the cost of the spray, but leafroller sprays are often not able to completely eliminate damage. Depending on the material used, special leafroller sprays may also harm mites and beneficials and could increase the cost of mite management.

Several parasites attack leafroller larvae, keeping them to relatively low levels in unsprayed orchards. Because these parasites are susceptible to insecticides, they are not effective in controlling leafrollers in sprayed commercial orchards. Leafrollers in the Hudson Valley are resistant to the commonly used organophosphate insecticides. Other chemicals available for use are the same as those commonly used to control OBLR (Lorsban, Lannate, B.t., Asana, Penncap-M). Larger larvae are more difficult to kill with these materials, so sprays should be targeted against small larvae whenever possible.

BY DEGREES

Obliquebanded leafroller in the earliest western N.Y. sites should be reaching the 90% hatch point by now, as predicted by the developmental model (810 DD, base 43°F, after the first moth catch). By 950 DD, these populations should be essentially 100% hatched. The current (7/6) DD accumulations in Geneva, according to our most scientifically precise measurements, is 893.

HOW TO AVOID BEING SPOTTED

(Art Agnello ama4@nysaes.cornell.edu, Entomology, Geneva)

A number of orchards in western N.Y. have turned up with surprisingly high levels of 1st generation spotted tentiform leafminer mines this season, which is actually not so surprising considering the ideal weather conditions they had this spring for mating and laying eggs. With the high temperatures of the last (and those forecast for the next) several days, the second generation moths should be nearing peak levels this week. The injury caused by the second and third generations is identical to that caused by the first, but second-generation injury is most damaging to the tree. Third-generation STLM is usually not a problem if the second brood was controlled properly. Proper timing is essential for both the assessment of STLM densities and control, if required. Sampling for sap-feeding mines should be done at approximately 690 degree-days (base 43°F) after the start of the flight of the second generation.

Sap feeding mine caused by early spotted tentiform leafminer instars on leaf underside

This flight began on June 28 in Geneva (which puts the DD tally at 687). Sampling guidelines can be found on pp. 85, 93—94, and 102 in the Recommends.

A decision regarding the third generation is generally not required unless the density of the second brood exceeded two mines per leaf. In recent years, an average of 8% of sampled orchards have required a treatment for second-generation STLM.

Several insecticides are effective against this pest, including Provado, Vydate, Lannate, and Asana. All of these products except for Provado are detrimental to predatory mites. Depending on the product chosen, application can be made anytime from initial egg deposition until larvae enter the tissue-feeding stages. Sampling is, of course, recommended before any spray is applied. If Provado is chosen, the manufacturer recommends aiming for the period 10—14 days after the flight starts. Unfortunately, if mines haven't yet begun to show up, this approach requires that you predict the need for a treatment based on either moth numbers or past field history, neither of which has been shown to be a very reliable indicator of actual pressure. According to our experience with this material, waiting until the appearance of early sap-feeding mines will give a better picture of problem blocks, and is still timely enough to effectively manage economic populations.

End of this issue: Scaffolds 1999 Index