Make the most of biocontrol

David Biddinger

“Mite flare-ups come from either the loss of predators such as T. pyri or a growth hormone-like stimulatory effect, called hormolygosis, caused by pyrethroids and some neonicotinoid insecticides,” Biddinger said.

The insecticides are like steroids for the mites. “Hormolygosis can cause pest mites to have more generations in a year and, more importantly with late season BMSB sprays, cause the fall mite females to lay many more overwintering mite eggs than normal. When these mite eggs hatch around bloom time the next spring, even if predatory mites have survived the sprays, they can’t increase fast enough to keep up with all the spider mites at petal fall to first cover.”

Hormolygosis is now thought to be the major cause of mite flareups.

Biddinger recommends growers battling European red mite and two-spotted spider mite stop using pyrethroids if possible. Substitute a neonicotinoid such as Venom/Scorpion and Actara (thiamethoxam) if preharvest intervals allow.

If a summer miticide is needed, use a selective one such as Envidor (spirodiclofen), Nealta (Cyflumetofen), and Zeal (etoxazole) as complete sprays rather than alternate-row-middle sprays. Other miticides are toxic to T. pyri.

“Recent trials have shown that Agri-Mek (abamectin) plus oil at petal fall plus seven-day timing generally gives seasonal control of mites without hurting the predator mites,” Biddinger said. “The disadvantage is that you have to treat generally before you know you have a problem, which is against the principle of biological control. On the other hand it is cheap and effective. It can help you to bring pest mite populations back into equilibrium with predatory mites for the next season if you have been using harsh pesticides in the past for BMSB or mitigate the effects of mites, at least if you are still using them.”

Woolly apple aphid

Parasitic wasps and flies help control San Jose scale and woolly apple aphid. Woolly apple aphid is not an invasive insect. “It is one of America’s unique contributions to the worldwide apple pest community,” Biddinger said.

This “made in the USA” label gives something of an advantage when it comes to biological control, he said.

Aphelinus mali, a tiny parasitoid wasp, appears resistant to most organophosphate insecticides, including diazinon, and seems to tolerate single applications of some neonicotinoids midseason without flareups, he said. Almost as important in controlling WAA in the mid-Atlantic are several species of syrphid fly larvae.

“Other generalist predators such as green and brown lacewings, minute pirate bugs, and some lady beetles may prey on WAA colonies when the nymphs and colonies are still small and unprotected by the waxy white coating and white filaments that protect larger nymphs and adults,” he said.

Here are Biddinger’s guidelines and control strategies for minimizing the impact on biological control while still giving acceptable management of woolly apple aphid:

—Use resistant rootstocks if possible. WAA feeding on roots is especially harmful to smaller dwarf trees. Keep a close eye on what appear to be varieties favored by the pest, such as Fuji, Rome, Greening, York, and Ginger Gold.

—Conserve biological control if possible.  The Pennsylvania Tree Fruit Production guide contains ratings of various pesticides’ impact on A. mali and syrphids.

—Avoid pyrethroids, including combination products like Endigo (lambda-cyhalothrin and thiamethoxam), Lannate, and the insect growth regulator Rimon (novaluron), which consistently flare WAA.

—Use Delegate (spinetoram) for first generation codling moth, but use Altacor (rynaxypyr) or Belt (flubendiamide), which won’t affect WAA biological control, for second generation.

—Avoid multiple applications of neonicotinoid insecticides after June and try to restrict use to products that are “softer” on beneficials, which include Calypso (thiacloprid), Assail (acetamiprid) and Provado (imidacloprid), at lower-than-maximum rates. Multiple applications of all products other than Calypso can also affect mite biological control, he said.

“For late season control of BMSB, neonicotinoids are the least disruptive control options, but we have seen evidence that at least Belay (clothianidin) may flare mites the following season,” Biddinger said. “Depending on the timing, these sprays may also affect WAA biocontrol, but in general, sprays after mid-September probably don’t have much effect, as WAA populations have crashed at this point and the biocontrol agents are moving to overwintering sites.”

—Diazinon is the most effective and cheapest product for control of WAA, he said. It is the only labeled use for this product and only a single application is allowed or necessary. “If you also have San Jose scale (SJS) in your orchards, Movento (spirotetramat) will control both pests even if you timed the spray early in the season (around first cover) for SJS crawlers,” he said.

“When used with a penetrant adjuvant or oil, Movento has proven very effective in controlling both pests, albeit at a much higher cost than diazinon. None of the neonicotinoids have proven effective on WAA.”

—Another relatively cheap option, if you have had both SJS and WAA problems in the previous season, is to use Lorsban Advanced (chlorpyrifos) at tight cluster in a higher rate of water to get complete coverage, he said.

The label for all chlorpyrifos products allows for only pre-bloom applications (only as late as 1/2-inch green). Later applications will kill bees. Most growers have Lorsban-resistant rosy apple aphid, but this spray may in some cases help with control of this pest and also tarnished plant bug.

San Jose scale

San Jose scale is a relatively easy pest to control with many different control options added in the last ten years, Biddinger said. “It is a pest that is better prevented than cured.” It is also a dangerous pest to leave uncontrolled.  After a few years of heavy infestation, limbs and even small trees can be killed, and the percentage of infested fruit can reach more than 80 percent in only a season or two.

He believes the resurgence of this pest is due to three things: disruption of biological control agents by BMSB sprays; a move away from the use of dormant oils; and a lack of thorough spray coverage from growers using low spray volumes or only a single side application.

SJS is normally considered a secondary pest because it has been easily controlled with a dormant oil spray to supplement biological control agents, which consist mostly of various species of tiny chalcid wasps (Aphytis and Encarsia species) that attack the scale under their waxy covering and some predators that attack the mobile stage called crawlers, he said. These predators are generalists that eat many small insects and include minute pirate bugs (Anthocoridae), the predatory mite T. pyri, and predaceous mirid plant bugs.

“This biological control, however, can easily be disrupted by some broad-spectrum insecticides such as pyrethroids, Lannate, and some neonicotinoid insecticides that are used for BMSB,” he said. “I would guess from the recent flares of SJS due to late summer/fall BMSB sprays that it is the wasps attacking the overwintering generation of SJS that are the most affected by the sprays.”

Biddinger recommends that growers use oil spray applications alone or with an insecticide at the dormant to green-tip stage and use spray volumes of 100 gallons per acre or more on larger trees to control overwintering scale.

Growers need to be very careful about the insecticides they use at this pre-bloom stage because those with residual or systemic activity can kills bees when bloom occurs.

Insect growth regulators like Esteem (pyriproxyfen), Centaur (buprofezin), and Movento seem to be effective against scale and have fewer impacts on bees and other beneficial insects. •