Getting Wild and Wooly: Woolly Apple Aphid Management: July 20th, 2019

Aerial Colony of WAA.

Synopsis: Emerging populations of Woolly Apple Aphid (WAA) have been reported this season, most problematic in mid-late season varieties of apple. The cyclical use of pyrethroids for BMSB management in August-September is likely reducing late season biological controls that play an important role in maintaining low levels of this insect pest. Increasing foliage reduces the efficacy of all contact materials. The use of a penetrant at rates that will help dissolve the insect and leaf cuticle should be strongly considered with applications well outside of Captain residuals.

Now is the time to scout for WAA as populations will be increasing and management options become limited as we near harvest.

Diazinon has been shown to provided excellent activity against WAA… BUT… it must reach the insect beneath layers of foliage and ‘wooly’ covering. As is the case for use of Movento SC Insecticide Spirotetramat, the use of a penetrant, for example horticultural oil, requires the 0.25% rate or 32.0 oz./ 100 gal. rate. This simply can not be over stated. It is essential for systemic activity of this product.

If need be and time avails, summer prune in blocks with WAA prior to management, especially in larger trees with heavy canopy such as M26, M7’s and larger.

If this insect appears just prior to and through harvest, management will require the use of short PHI materials (7 day or lower), effective at eliminating the insect colony, reducing honeydew created by the pest along with the white cottony fibers to assure the fruit is commercially acceptable.

Insecticide options for WAA. Note: Rate for Admire Pro used for soil application.

Further discission:

Biology: Woolly Apple Aphid (WAA) is native to North America, occurring in most apple-growing areas of the world, tending to be a sporadic pest in orchards in the northeastern United States. It typically occurs in noticeably high numbers only every few years. However, the increase of WAA in successive years may be due to the reduction of predatory insects caused by late season management using the pyrethroid class of insecticides to manage the stink bug complex.

Adults: Several wingless generations of WAA are produced on apple trees throughout the season. Some winged females are produced that could migrate to other apple trees or to elm, if it is present. Rarely, sexual forms of the WAA and eggs are produced on apple trees, overwinter in crevices
of the bark.

Nymphs: The majority of nymphs are borne alive on apple trees by an unmated female. The WAA nymph passes through four instars, changing in size from 0.6 mm (.02 in.) long in the first to 1.3 mm (.05 in.) long in the fourth instar. The nymphs are dark reddish-brown with a bluish-white waxy covering that becomes more extensive in the later instars. The first instar nymphs (crawlers), which are considerably more active than later instars, are a dispersal stage. They initiate aerial colonies in the spring from overwintering root infestations. The crawlers are carried by wind from tree to tree within an orchard or nursery, or move downward from the branches to initiate colonies on roots.

Damage: Cottony-white aerial colonies are found most frequently on succulent tissue, such as current season’s growth, water sprouts, unhealed pruning wounds, or cankers.

Heavy infestations can cause honey dew and sooty mold on the fruit, and galls on the plant parts. Underground colonies may be found throughout the year on the root systems of orchard trees or nursery stock. Severe root infestations can stunt or kill young trees, but usually cause little damage to mature trees. WAA can also transmit perennial apple canker, Pezicula malicorticis Jacks.

Biological Control of WAA by Aphelinus mali

Biological Control: The WAA is frequently parasitized by Aphelinus mali, a tiny wasp that is also native to North America. Parasitized aphids appear as black mummies in the colony. A. mali has been successfully introduced to many apple-growing areas of the world, and is providing adequate control of the WAA in several areas. It does not provide sufficient control in commercial orchards in the northeastern United States because of its sensitivity to many commonly used insecticides; however, the wasp is thought to reduce WAA populations in abandoned orchards. Because the woolly apple aphids are somewhat protected by their waxy covering, regular spray programs may not provide adequate control. High volume applications of recommended insecticides may be necessary to penetrate the wax. Failure to control aerial infestations can result in underground infestations on susceptible rootstocks. Chemical control of root infestations is not possible; resistant rootstocks provide the only defense against underground infestations.

Rootstock Susceptability: Failure to control aerial infestations can result in underground infestations on susceptible rootstocks. Chemical control of root infestations is not possible; resistant rootstocks provide the only defense against underground infestations. The Mailing-Merton (MM) rootstock series was developed to provide resistance to WAA infestation. The M-9 series, M-26, M-27 are all susceptible to WAA. Its reproduction on these hosts is primarily parthenogenetic, that is reproduction without mating.

Management: Because the woolly apple aphids are somewhat protected by their waxy covering, regular spray programs may not provide adequate control. Management of the WAA should then include higher volume applications (>100 GPA) then what would be used for apple maggot and codling moth this time of the season as foliage is very dense. The waxy covering protecting the insect from desiccation necessitates the use of a penetrant, providing more effective access to directed contact of the active ingredient to the developing WAA colony. Few insecticides are labeled and effective for use in NYS. Failure to control aerial infestations can result in underground infestations on susceptible rootstocks. Chemical control of root infestations is not possible; resistant rootstocks provide the only defense against underground infestations.

PHI will dictate the use of material choice nearing harvest. Diazinon (High degree of control) and Beleaf 50SG (Moderate Control) having a 21 day PHI. Movento 240 SC (High degree of control), also very effective earlier in the season. Movento takes time for systemic activity to occur (roughly two to three weeks).

Admire Pro 4.6SC (Label) and Assail 30SG are two neonicotinoid options that should also be considered based on a 7 day PHI. Other products such as horticultural oils (Pure Spray, Bio-Cover) and soap (M-Pede; Gowan) may be options for conventional and organic growers requiring zero days to harvest (0 PHI), yet may prove challenging if high temperature or slow drying conditions prevail. This may cause fruit russett or phytotoxicity on susceptible varieties.

Soil application of Admire Pro 4.6SC using chemigation into root-zone through low-pressure drip, trickle, micro-sprinkler or equivalent equipment has a range of 7.0 – 10.5 fl.oz./A. and may be more effective against WAA then foliar applications. Pome Fruit – Soil Application Restrictions Pre-Harvest Interval (PHI): 21 days Maximum ADMIRE PRO SYSTEMIC PROTECTANT allowed per year: 10.5 fluid ounces/Acre (0.38
lb AI/Acre)

Foliar applications of Admire Pro 4.6SC, which has shown only moderate degrees of efficacy, should be applied at rates of 2.8 fl.oz./A and incorporate a wetting agent or spreader.

foliar application differs from soil application rates. Foliar rate of

Note: Mixing formulations of diazinon or Danitol with Captan or Captec have caused crop injury in the past. Therefore, diazinon and Captan formulations should not be tank-mixed. This type of phytotoxicity results from either a direct interaction of the active ingredients or an interaction of the “inert” ingredients in one formulation that enhances the toxicity of the other one. (reference from Russ Holze and Dave Rosenberger)

Diazinon is an excellent material against the WAA. It is principally used prebloom for control of San Jose scale or postbloom for broad-spectrum control of major pests. It is generally less persistent than other standard phosphates. Diazinon should not be used in combination with copper. Diazinon alone has been shown to cause russeting / finish problems on R.I. Greening, Golden Delicious, and Baldwin. No injury has been reported on McIntosh or varieties closely related to Mc with few observations on other varieties. Note that the material should not be used in tank mix with Captan under slow drying conditions, strong acids & alkalis and copper-containing compounds.

Spirotetramat (Movento) is a tetramic acid registered for the control of a number of indirect pests in pome fruits and stone fruits, primarily aphids (including woolly apple aphid), mealybugs, pear psylla, and San Jose scale. It has systemic activity, exhibiting 2-way movement in the plant, both upwards in the xylem to new shoots and leaves, and downwards in the pholem to the root tissues. Its mode of action is as a Lipid Biosynthesis Inhibitor (LBI), and it is active by ingestion against immature insects feeding on treated plants. Additionally, adult females have exhibited reduced fecundity and offspring survival. That said, Movento requires a penetrant such as 0.25% horticultural oil or NIS. The use of Captain for late season disease management should be avoided when using a penetrant. Intervals of 14d on either side of a Captan application residue dependent on environmental conditions, foilar susceptibility, temperature, have been recommended. Secondarily, Movento will take 14 days or longer to express efficacy as a systemic insecticide.

Acetamiprid (Assail) belongs to the neonicotinoid group of insecticides (along with *AdmirePro and *†Actara). It was registered by the US EPA under the reduced risk pesticide policy and is considered a replacement for older OP insecticides. Assail has a spectrum of effectiveness across several insect groups, and is active against pests such as plum curculio, apple maggot, internal leps, aphids, leafhoppers, leafminers, San Jose scale, European apple sawfly and mullein plant bug, plus pear pests such as pear psylla and Comstock mealybug.

Imidacloprid (*Admire Pro, *Leverage) is a broad spectrum contact and locally systemic chloronicotinyl insecticide with low mammalian toxicity. It is primarily effective against aphids, whiteflies, thrips, scales (crawlers), pyslla, leafhoppers, mealybugs, some beetle and weevil species, and leafminers. The original *Provado formulation has been replaced by *AdmirePro, which is labeled on pome and stone fruits for aphids (except woolly apple aphid), leafminers, leafhoppers, San Jose scale, pear psylla, mealybug, Japanese beetle, cherry fruit flies and San Jose scale. It has also shown activity against pear midge when applied at petal fall. It is additionally labeled for use as a soil-applied product against woolly apple aphid. This material has no direct effect on mite, beneficial or phytophagous, but is hard on the predator beetle Stethorus punctum. Mite flare-up is often a secondary effect associated with use of Imidacloprid during the season in Hudson Valley orchatds..

Horticultural Soap, if timed before strong rains, may reduce honeydew on fruit and foilage prior to harvest. However, be aware that soaps can cause russetting when applied prior to very warm or hot temperatures (>75F).