Worm Wise : Pre-bloom Lep. Management Strategies of Apple.

After a high of 85 degrees on a very fine Easter Sunday in the Hudson Valley, we find ourselves at tight cluster with our first flight of oriental fruit worm, lesser apple worm and the emergence of first instar pear psylla nymph in our research orchards this morning. We now need to consider management of the early ‘worm’ complex during this period from pink through bloom.

Upcoming fungicide applications for apple scab provide an insect pest management window. San Jose scale, tarnish plant bug and dogwood borer aside for a moment, the early worm complex can be found in most commercial apple during the pre-bloom period beginning with the emergence of the green fruit worm (GFW). In Highland, we traditionally have our first flight of GFW in early March yet our first capture of this insect was on the 10th of April this season. A warm start was followed by a mild spring bringing us to tight cluster in McIntosh (HVRL Scouting Report).

This GFW group is comprised of at least three different lepidopteran species whose larvae feed on the foliage, flowering parts and developing fruit of pear and apple. An in-depth look at this insect complex can be found in the NYSAES station bulletin by Chapman, P.J., Link, S.E. 1974.

In the Hudson Valley it’s a fairly predictable event to catch the GFW adult flying during the warmest days of early March, yet the damage to fruit can be sporadic from year to year. This group, comprised of many species includes the speckled green Fruitworm, Othosia hibisci (Guenee), the widestriped green Fruitworm (Lithophane antennata), and the humped green fruitworm (Amphipyra pyramidoides) among others that are aptly named after predominate physical features the larvae exhibit. Many other lepidopteran follow the GFW complex during the pre-bloom period and include the redbanded leafroller, spotted tentiform leafminer, oriental fruitworm, lesser apple worm, codling moth and emerging larval populations of overwintering obliquebanded leafroller (OBLR).

The GFW and OBLR are of greatest concern to commercial fruit growers prior to and shortly after bloom with many control measures used against these two insects effective in managing the secondary lepidopteran pests.

Scouting & Insect Biology: The adult GFW complex are members of the noctuid family of lepidopteran insects and as their group name suggests, they fly at night. Flight begins during apple bud development and peaks at tight cluster with flight completed by the pink stage. Pheromone traps should be used to determine adult male presence of all major fruit feeding Leps. followed by scouting for presence of larva in developing fruit clusters and shoot tip terminals.

GFW adults have a wingspread of about 1.5 inches. The forewings are grayish pink; each is marked near the middle with 2 purplish gray spots, outlined by a thin pale border with the hind wings lighter in color than the forewings.

Females begin oviposition on twigs and developing leaves when apples are in the half-inch green stage. GFW eggs are about 3/8” in diameter and 3/16” in height. GFW eggs are white with a grayish tinge and ridges radiating from the center . The egg takes on a mottled appearance shortly before hatch. A female will deposit only 1 or 2 at any given site, laying several hundred eggs from late March to mid-May in the Hudson Valley.
In the northern regions of the Champlain Valley and throughout the mid-Hudson Valley, the GFW can be a severe pest on early developing apple. The GFW larva pass through 6 instars, the early stages possessing a grayish green body, brown head and thoracic shield. Mature larvae, about 1.5” in length, have a light green body and head. A number of narrow white stripes run along the top of the body with wider, more pronounced white line runs along each side. The areas between the stripes are speckled white.

Early stages of larvae feed on foliage and flower buds, found inside rolled leaves or clusters Mature larvae will damage flower clusters during bloom, feeding on developing fruit and foliage 2 weeks after petal fall with peak populations during bloom . The fruit remaining on the tree will have both shallow and deeply indented corky scars at harvest, indistinguishable from obliquebanded leafroller injury.

Larva then drop to the ground, burrow into the soil to pupate, and overwinter 2-4 inches into the soil to emerge the following spring as adults.

Management: In years of heavy infestation pressure from GFW, as much as 10% fruit injury can occur. Employing adult pheromone trap captures will provide growers with information on GFW presence and the onset of adult flight. Scouting for larva to determine levels of pest pressure should begin shortly after tight cluster. Although NY has not developed thresholds for this pest, a provisional threshold of 1 larva or feeding scar per tree has been used to begin applications in Massachusetts. A more conservative threshold should be applied in high valued apple varieties on dwarfing rootstock of high-density planting systems. If GFW populations historically cause economic injury to fruit, management should begin from tight cluster to pink to target the pre-bloom Lepidoptera complex.

The GFW complex and OBLR are less susceptible or resistant to most organophosphates, with the possible exception of chlorpyrifos (Lorsban, IRAC Class 1B). If Lorsban were used as a pre-bloom foliar application, it would also control San Jose scale. The caveat being reduced control of SJS observed by Hudson Valley growers. Asana, Ambush / Pounce, Baythroid, Danitol, Warrior, pyrethroids in IRAC Class 3, tend to have highest efficacy against larva under cooler temperatures (< 72oF). Generally, as temperature increases, larva metabolize / detoxify pyrethroid chemistries more effectively, while OP’s, Carbamates and newer chemistries tend to be more stable and less susceptible to this phenomenon. The Bt products such as Biobit, Dipel, Javelin, and MVP (IRAC 11 B2) also have a low impact on beneficial mite and are very effective against OBLR and the GFW complex, but relatively ineffective against the Codling Moth (CM). The Bt products can be used through bloom as needed and their use should be optimized by employing multiple applications at 5-7 day intervals at the low-labeled rate (1 lb./A of Dipel 10.3 DF for example). Intrepid (methoxyfenozide) (IRAC 18A) another reduced risk insecticide very effective against the larva, imitates the natural insect molting hormone and works by initiating the molting process. Intrepid is quite safe to birds, fish, and most beneficial insects. Proclaim (emamectin benzoate) (IRAC 6), a second-generation avermectin insecticide related to Agri-Mek, is also an excellent insecticide against the GFW complex while having a low impact on beneficial mites. If European red mite (ERM) has emerged, Proclaim, used with a penetrating adjuvant, would reduce early ERM populations. As a reminder, penetrating surfactants in some years can increase uptake of the fungicide Captan to cause phytotoxicity to foliage and fruit. Altacor (chlorantraniliprole) (IRAC Class 28), Delegate (spinetoram) and Entrust (spinosad) (IRAC Class 5), have been used successfully against the surface feeding and internal Lep. complex. However, the placement for these materials has been predominately at the onset of hatch of the summer generation larva of OBLR, providing excellent results in NY State. Resistance Management:
As we would be managing the overwintering OBLR larva at the same time as we would the control of GFW, we should consider these applications in light of OBLR management through out the remainder of the season. Development of insecticide resistance is dependent on the volume and frequency of applications of insecticides and the inherent characteristics of the insect species, we should limit one insecticide class (often requiring multiple applications of the same class) to a single generation of pest for resistance management purposes. The present model for insecticide resistance management (IRM) practices then is to use a single insecticide class for a single generation of insect pest. For example, an IRM program against the lepidopteran complex, specifically OBLR and CM, would use effective insecticides of three different IRAC classes for each generation, throughout the season.

For Timing examples:
I. Insecticide (Class A) 1 application @ TC-P for GFW and overwintering OBLR, or PF for OBLR, RBLR, LAW, OFM larva

II. Insecticide (Class B) 2-3 applications @ 14d; first emergence of 1st generation CM and 1st brood OBLR larva based on degree-day models.

III. Insecticide (Class C) 1 application @ first emergence of 2nd brood OBLR larva and CM as needed based on degree-day models.

In studies from Michigan in 2008, research on codling moth neonate larvae has shown a seven to eightfold resistance to Imidan (phosmet), six-tenfold resistance to Warrior (lambda-cyhalothrin), 14-16-fold resistance to Intrepid (methoxyfenozide) and sixfold resistance to Avaunt (indoxacarb), but no resistance to Assail (Acetamiprid) and Spintor (spinosad).

Given the historic failures the apple industry has experienced managing the leafroller and internal worm complex, we should consider designing programs to maintain the effectiveness of these excellent IPM tools beginning early in the season well before the heat of the battle begins.