Woolly Apple Aphid Management As We Near Harvest: July 28th, 2018

Aerial Colony of WAA.

Synopsis: Woolly Apple Aphid (WAA): Increasing populations of Woolly Apple Aphid have been reported this season, most problematic in mid-late season varieties of apple. The use of the pyrethroid class for BMSB management in August-September is likely reducing biological control that plays an important role in maintaining low levels of this insect pest.

If this insect appears during harvest, management may 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.

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

Management: of the WAA should include higher volume applications (>100 GPA) then what would be used for apple maggot and codling moth. 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.

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 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.

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)

Insecticides for Use in Managing the Woolly Apple Aphid

Overview: The WAA tends to be a sporadic pest in orchards in the northeastern United States, occurring in high numbers only every few years. However, through the use of pyrethroids for the control of the brown marmorated stink bug we are seeing frequent and high infestations of this insect pest on apple over the past few years. Since the WAA is frequently parasitized by Aphelinus mali, a tiny wasp that is also native to North America, the use of pyrethroids late in the season have likely reduced the biological control provided by this important parasitoid.

Biology: The woolly apple aphid is considered to be native to North America, and can be found in most apple-growing areas of the world. The WAA feeds mainly on apple, but can also be found on pear, quince, mountain ash, hawthorn, and cotoneaster.

WAA Infestation of Pruning Cuts.

Life Cycle: The majority of nymphs are borne alive on apple trees by the un-mated 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.

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. This insecticides has caused russeting or related finish problems on Golden Delicious, R.I. Greening, and Baldwin. No injury has been reported on McIntosh or closely related varieties yet only limited observations have been made 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.

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 effect on any mites, beneficial or phytophagous, but is hard on Stethorus. Mite flare-up is often associated with use of Imidacloprid during the season.

About Peter J Jentsch

Peter J. Jentsch serves the mid-Hudson Valley pome fruit, grape and vegetable growers as the Senior Extension Associate in the Department of Entomology for Cornell University’s Hudson Valley Laboratory located in Highland, NY. He provides regional farmers with information on insect related research conducted on the laboratory’s 20-acre research farm for use in commercial and organic fruit and vegetable production. Peter is a graduate of the University of Nebraska with a Masters degree in Entomology. He is presently focusing on invasive insect species, monitoring in the urban environment and commercial agricultural production systems throughout the state
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