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 Insects and Mites

    European red mite egg hatch is underway.  The silver lining in the cool wet weather is that mites and leafminers don't like it any more than we do.  It will still be important to check foliage about a week after Petal fall, but this is not looking like a year for big mite and leafminer problems.  The same goes for tarnished plant bug, which seems to act up as an apple pest in years with warm dry spring weather.  That said, I'll be checking traps at Highmoor on Monday and may have to eat my words.  But I doubt it.

    One pest that might not mind this kind of weather, given that it has done well in Nova Scotia for a long time, is winter moth.  Massachusetts has had a marked increase in this pest in recent years, and it's showing up in New York as well.  Thresholds for this and other bud and blossom feeding caterpillars are not well defined, but finding more than 5 or 6 per 100 fruit clusters is cause for concern.

    The following article is by Peter Jentsch of the Cornell University Hudson Valley Lab.

"The period leading up to bloom of apple in the Hudson Valley has its share of the 'usual suspects', and pink applications to manage early season insect pests have been considered a standard practice.  The insects driving these early season applications may be yearly culprits such as green fruitworm or rosy apple aphid, or those that have slipped through the previous years' schedules, as we've seen with increasingly common San Jose scale infestations.  Prebloom applications have also included management of insects resistant to seasonal cover sprays of organophosphates and requiring newer chemistries for effective control, such as those used for obliquebanded leafroller.  Pink applications are often used in mixed variety blocks to reduce plum curculio populations from damaging earlier fruit-setting cultivars, allowing bees to continue working on the later varieties in years of extended bloom periods.

   It's uncommon that we find an insect that doesn't fit the bill.  This spring in the Hudson Valley, however, we've been finding unusually high numbers of an uncommon pest known as winter moth, Operophtera brumata (L.).  The larva, which may possibly be mistaken for the speckled green fruitworm, feeds on the flowering buds and terminal cluster leaves of apple, with feeding damage and webbing signs that field scouts typically come to expect from the overwintering OBLR larva.  It also resembles the green pug, Chloroclystis rectangulata, particularly in the first 2 instars, but may be distinguished by the several white stripes in later instars of the winter moth, as opposed to the single reddish dorsal stripe in the green pug.

   The winter moth is in the family Geometridae, a group of Lepidoptera noted for their 'looper' or inchworm-like movements.  A non-native species, the moth was introduced to North America from Europe, where it continues to be a commercial fruit pest.  It is common to eastern Canada, British Columbia and Vancouver, Oregon, Washington, and coastal Massachusetts and Rhode Island, with pockets of infestations in various parts of New England.  Its occurrence in the Hudson Valley is not a first-time event, yet given its dramatic presence and the damage it appears to be causing this year, it is certainly noteworthy.  These insects are most likely to be found in commercial orchard apple blocks that did not receive a prebloom pyrethroid or OP application this season.

   As is often the case with newcomers, the occurrence may be in part due to a shift away from traditional commercial management practices of prebloom applications, as well as the insect's diverse feeding habits and unique ability to relocate under windy conditions.  The larva will feed on a variety of plants of both deciduous and coniferous species, appearing to prefer fruiting species such as apple, blueberry, cherry, and crabapple.  They have also been found to feed on the oaks, maples, basswood, ash, and certain spruces such as Sitka spruce (in Scotland).

   Winter moth eggs hatch early in the spring when temperatures average 55F, occurring when approximately 20-50 DD (base 50°F) have accumulated.  The larvae tunnel into buds where they begin their feeding.  Once a bud has been consumed from within, the caterpillar will migrate to other buds and repeat the process.  In years such as this, when cool weather conditions delay tree phenology, delayed bud opening can lead to bud death as the caterpillars have a longer time to feed.  The older larvae will feed in the expanding leaf clusters and may cause severe defoliation in high populations.  In these later stages they may eat flower buds and feed on developing fruitlets.  Damaged sites heal, and appear at harvest as a flat or concave area with a corky surface, or if severe feeding occurs, damage results as a deep corky cleft.

   Newly hatched larvae often crawl up tree trunks and produce a long strand of silk, which makes them buoyant in the air.  This type of dispersal method is known as "ballooning", and allows larvae to be transported to areas where they are not expected to be a problem, such as the center of orchard blocks.

   Spring larvae are pale green caterpillars with a white longitudinal stripe running down each side of the body.  Winter moth larvae have just 2 pairs of prolegs and move in a typical inchworm-looping pattern.  The green head and prolegs are useful scouting keys.  The larvae reach approximately one inch in length at full maturity.  They will continue to feed until mid-June, at which time they migrate into the soil for pupation.  They will stay in the pupal stage until they emerge in late fall as moths.

   Adults of the winter moth emerge from the soil typically in late November and can be active into January.  The adults are attracted to lights and can often be found flying around streetlamps at night.  The male moths are small, light brown to tan in color and have four wings that are fringed with small elongate scales, giving the hind margins a fringed appearance.  The female is gray, with small vestigial wings and is unable to fly.  She is usually found at the base of trees, where she emits a sex pheromone that attracts numerous male moths.  After mating, the female deposits an egg cluster on tree trunks and branches, in bark crevices, under bark scales, or elsewhere.  After oviposition, the adults die, leaving the egg to overwinter.

   A dormant oil spray to the trunks and branches of trees may be helpful in killing the overwintering eggs before they hatch.  Egg clusters are often laid beneath bark flaps and loose lichen and may be well protected from oil sprays.  Caterpillars may also invade host plants by ballooning onto them after treatment has been applied.  Dipel is one of the few materials registered for managing winter moth.  Bacillus thuringiensis (B.t. kurstaki), specific to caterpillars of butterflies and moths, works very well on the younger larvae of winter moth while they are free feeders (not in the buds).  Spinosad, another biorational compound, works well against larvae and would be effective against the complex of lepidopteran larvae on apple during the prebloom period.  Insecticides such as Lorsban (also registered on winter moth) and the pyrethroids used to manage the prebloom insect complex will also be effective in controlling the winter moth."