Bloom … Waits For No Man: Insect Pest Management up to and through Bloom

Overview: Over the past 7 days we’ve seen temperatures hang on to means in the 50’s with only a hand full of April days skimming into the low 60’s through the mid-Hudson Valley. The lingering tight cluster and pink are nearing an end, and we find ourselves in early bloom in our early flowering varieties over the past few days. Our 2020 tree phenology is close to the 2019 date for first bloom in McIntosh. In flight we’ve been seeing the moth complex of oriental fruit worm (OFM), redbanded leafroller, Spotted Tentiform Leafminer (STLM) and the emergence of early instar pear psylla nymphs for the past week (HVRL Scouting Report of 27 April).

Weather Forecasts: Heavy rain fell at the HVRL with 0.41′ and strong Northwesterly wind night. Rains (0.32″) continuing through today are expected. Temperatures in the upper 60’s will move trees from pink into bloom beginning this weekend through the remainder of the week. Good pollination conditions begin Saturday into the week for king set in the lower and mid-Hudson Valley, with temperatures remaining cool. Extended bloom of 9 days or more may occur if forecasts hold.

As our trees exit pink, later varieties may remain in pink through the next few days. If pre-bloom applications have not yet been made, then a pink application should be considered (See Strategies of Pre-bloom Insect Pest Management in Apple). NEWA forecast of a combined infection event for apple scab is occurring and as such, growers without protectant fungicides will be coving up to include kick-back materials, providing a late pink insecticide window in blocks still at the pink stage.

Insects of primary concern during the pink stage include the San Jose Scale, Rosy apple aphid, obliquebanded and red banded Leafrollers, mullen plant bug and the tarnish plant bug. Plum curculio (PC) may be a problem if high temperatures (warmer nights and 70’s for a number of days) drive them out of hibernation sites and into the orchard. However, cool night temperatures are in the forecast to keep PC in the woodlands for this coming week. Keep an eye on the temperature.

Orchard Honeybee Management: In years when king fruitlets set well before lingering lateral flowers (>5mm in diameter) they become most attractive and susceptible to PC injury during periods of extended bloom IF PC are active. Honey bee removal timing can be critical if temperatures rise during the latter part of bloom, and fruit are set with PC becoming active.

If this event occurs, contact your bee keeper. If he is unable to pull bees out in a timely fashion and in a worse case scenario such as “onset of PC activity and scars on fruit”, let him know you are placing rolled screening at the hive entrance at first light, prior to morning bee activity, so as to make a timely petal fall application. You can lose a high percentage of your crop, especially along the edge, if you postpone the petal fall application at the onset of PC activity.

As we enter bloom, we are limited to the exclusive use of ‘bee friendly’ materials. Mating disruption for dogwood borer, peach tree borers and codling moth / oriental fruit worm should be applied now if it hasn’t yet been done. Use of Bt products for oblique banded leafroller and foliar feeding ‘worms’ such as Green Fruitworm and Red Banded Leafroller that appear as temperatures increase.

The use of Assail is labeled for bloom applications and will reduce Mullein Plant Bug. IF historical damage has occurred or is observed on developing fruitlets during scouting is can be applied. Note: Assail (acetamiprid) has very little activity on PC, and as such, should be reserved for use against codling moth and apple maggot later in the season as needed.

In-Depth:
Historical Tree Fruit Phenology: A cool start was followed by a very cool spring bringing us to early green tissue on March 15th, green tip on March 23rd, 1/2″ green on the 6th April, tight cluster on the 13th of April and full pink in McIntosh (M26 on the east hillside) on the 27th of April and as of the 1st of May we are looking at 1st bloom in McIntosh in the Hudson Valley Research Lab orchard.

If pink applications were made across the orchard using materials active against the lepidopteran complex, you are not likely to need to be concerned with the endemic population of worms. Scouting along the edges is always recommended as woodland moths and other pests can blow in during heavy wind and establish in otherwise clean orchards. One such pest is a beetle known as the locust leafminer (Odontota dorsalis) a serious pest of black locust (Robinia pseudoacacia) and will occasionally attack apple. The foliage of heavily infested trees will appear scorched or burned or under low pressure will skeletonize clusters of leaves along the orchard edge.

We haven’t seen codling moth (CM) at the lab yet, however if you plan on using mating disruption you need to have have your dispensers or ties on hand and out at first flight of CM. If you looking to disrupt mating for both CM / OFM, NOW IS THE TIME TO PUT MATING DISRUPTION OUT IN ACREAGES OF 5 ACRES OR MORE. More on specific moth mating disruption (OFM, LAW & CM).

Upcoming fungicide for apple scab and fire blight applications also provide an insect pest management window. 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. 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). High impact of the Bt’s has been observed on cloudy warm days with high levels of feeding and low impact on the product from UV light.

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 28th of April 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.

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. 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. This event often begins at 1st-2nd cover.

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.