Strategies of Pre-bloom Insect Pest Management in Apple

Overview: Temperatures dipped below freezing in most Hudson Valley sites with 29.7F recorded at the HVRL research orchard this morning. Snow is predicted for April 18th, Saturday into Sunday. Horticultural oil should not be sprayed for at least two days to allow foliage to harden off. The 39 year mean date for pink is 4/22 (+/-14D) while McIntosh bloom in Highland, NY the mean is May 1st (+/- 15d).

Live DWB feeding in cankers of tree

Dogwood borer (DWB) management should be well underway or completed in apple blocks on dwarfing rootstock. In the field we are seeing the pupal stage of DWB and, as such, they are provided more protection from directed trunk applications of insecticides within this pupal case. In 2019 DWB adult flights began in late May. We will loose the use of Lorsban (chlorpyrifos) in NYS tree fruit production over the next year. Mating Disruption (MD) for DWB is highly effective in blocks over 5 acres and is a viable and economic alternative to chlorpyrifos. Begin DWB MD prior to the first flight of the adult clearwing moth seasonally.

Postponing pre-bloom ‘pink’ sprays until flowers are very near opening is risky. However, this season we have seen delayed insect emergence given cool temperature. Little to no feeding activity has been observed in flower clusters during scouting observations. That said, waiting to make the pink application would be prudent. Intermittent rains are forecast with relatively high winds to reduce coverage through early next week. There appears to be application windows for a pink application that include Sunday and Thursday mornings.

Mullein plant bug, Campylomma verbasci (Meyer), on Red Delicious Fruitlets

As cool weather lingers for the next 7-days, slow development of flower clusters will be seen, and an insecticide application as close to late pink as possible should be made. Applying an insecticide during pink will in most years, provide greater protection from the endemic and migratory insect pests directly feeding on developing foliage, flowers and fruitlets from early bloom to petal fall, lasting on average 9.4 days. This is especially important in high density, high valued wholesale & direct retail production systems. Apple grown in small to moderate size orchards have most of the acreage surrounded by wooded hedgerow and forest edge, most susceptible to the migrating plum curculio.

A broad-spectrum insecticide applied at pink buys you time and reduced risk. Greater pollination time in mixed setting varieties during long but cool spring when honeybee flight is suppressed. Pest management ‘insurance’ with time needed to move through the extended cool bloom periods for bees to linger a day or two longer before bee removal. This is especially so in mixed blocks with late varieties. And most importantly, protects the king fruitlet against the pest complex in years of delayed pollination due to a cooling trend, later in the bloom cycle.

Selection of pest management tools for pink should be based on historical apple injury levels by the pest complex. Selection for lepidopteran larva ‘worms’, plum curculio and as needed the plant bug complex should be based on insecticide efficacy. Management using a pyrethroid alone (works best in cooler temperatures) is a viable option, while a tank mix containing a pyrethroid with a diamide or spinosad, or pre-mix containing pyrethroid and diamide, would provide excellent control (see pest management tool options below).

Tree Phenology: In the mid-Hudson Valley we find ourselves at tight cluster in most of our varieties, with early pink seen in Zestar and Ginger Gold. A cool, now cold spring brings temperatures hovering at the freeze mark as we approach late tight cluster in McIntosh, in-line with our 39 year mean phenology of McIntosh of April 17th Scouting Report.

Dogwood Borer larva

Dogwood borer larva

Insect complex: If San Jose scale was observed on fruit in 2019, may have already been addressed with early horticultural oil at 2-3% during delayed dormant, and is still manageable with 1% oil and excellent coverage at tight cluster through pink. However, if Captan residue is present, avoid the use of oil, employing Esteem WP during the pre-bloom period without the use of oil or and other penetrants.

Tarnish plant bug appears as temperatures rise above 70F and has not yet been observed causing injury to flower clusters this season. As temperatures rise, TPB management is best accomplished using Beleaf 50SG or pyrethroid tools.

Rosy Apple Aphid (RAA) can be managed using contact, translaminar or systemic insecticides during the prebloom timing. It is often managed successfully at petal fall using the neonicotinoid class of insecticides. Movento used at Petal Fall for San Jose scale management requires a penetrant, will also control RAA and early wooly apple aphid colonies.

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, with our first adult capture of this insect on the 23rd this season. Populations of this insect appear to be very low this season.

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.

We are also expecting orchard overwintering obliquebanded leafroller larva to emerge and begin feeding on developing flowers, 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.

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.

Degree-Day Modeling for Codling Moth in 2019.

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.

Scouting for TPB should be conducted along the orchard edges and where broad leaf weed hosts provide higher TBP populations. Feeding sites will exhibit bleeding droplets of sap from fruitlets while TPB adults can be observed on warm days (>70F) in developing clusters from TC through 1st cover.

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.

OBLR young larva early May

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 where it is not providing sufficient control of this pest.

The pyrethroids Asana, Ambush or Pounce, Baythroid, Danitol, Warrior, pyrethroids in IRAC Class 3, tend to have highest efficacy against Lep. larva and TPB under cooler temperatures (less then 72F). Generally, as temperature increases, larva metabolize or detoxify pyrethroid chemistries more effectively, while OP’s, Carbamates and newer chemistries tend to be more stable and less susceptible to this phenomenon.

TPB injury to Gala.
Hudson, NY 2008

Pre-mixes that include a pyrethroid such as Besiege in IRAC Classes 3A & 28 (H), Gladiator EC in Classes 3A & 6 (M), Endigo ZC in Classes 4A & 3A (M) and Leverage 360 (H) in Classes 4A & 3A are rated moderate to high for management of internal lepidopteran while the pre-mixes such as Minecto Pro (H) in IRAC Classes 6 & 28 and Voliam Flexi WDG (H) in Classes 4 & 28, do not contain the pyrethroid component, both excellent against the lep complex yet likely providing lower levels of TPB management.

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), Exirel (Cyantraniliprole), Verdepryn 100SL (Cyclaniliprole) (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.

Lastly, Verdepryn 100SL(Cyclaniliprole) is a new diamide distributed by Summit Agro USA. Label rates range between 5.5-11.0 fl.oz./A with research trials indicating strong efficacy against PC and the lep. complex. It has a total of 27.0 fl. oz./A per season (in NYS) and 3 applications per season restriction, 14 day re-application interval and 7 day PHI.

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. With this in mind, 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 targeting 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 (Ex. Pyrethroid IRAC 3) ) 1 application @ TC-P for GFW and overwintering OBLR, or PF for OBLR, RBLR, LAW, OFM larva

II. Insecticide (Class B (Ex. Diamide IRAC 28)) 2-3 applications @ 14d; first emergence of 1st generation CM and 1st brood OBLR larva based on degree-day models.

III. Insecticide (Class C (Ex. Spinetoram IRAC 5) 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.