European red mites hurt apple trees by destroying the photosynthetic part of the leaves, turning them bronze. This damage reduces the trees' vigor and makes the fruit smaller and poorly colored. In addition, apple yield drops for the following year. In the past, these mites were controlled solely by chemicals. However, very few pesticides are effective on the mites.
Fortunately, European red mites have a natural predator mite called Amblyseius fallacis . Unfortunately, previous research incorrectly concluded that the predator mite did not arrive in the trees until June. So growers were applying insecticides early in the season to kill other pests, not realizing that the insecticides also were killing the predator mites, according to Rick Foster, associate professor of entomology at Purdue.
Foster, Mike Stanyard, a former graduate student in entomology, and Travis Hill, a graduate student in entomology, found that the predator mite remained in the apple tree over winter, contrary to the earlier research. They also discovered that if the predator mites were killed before the trees bloom, they would not return the entire growing season and the European red mite population would go unchecked. If the predator mites weren't killed off, European red mite levels would normally remain low.
These findings showed that growers could use biological control to reduce the European red mite population. Foster advocates spraying selected insecticides, which kill other apple pests, early in the growing season so the predator mite is not harmed. The predator mite then survives to eat the European red mites, reducing the need for chemicals to control the mites.
Foster's findings have been taught to growers around Indiana through several Purdue University Cooperative Extension Service programs. "Many apple growers have changed their spraying habits based on our research," Foster says. He says combining biological control with pesticides at carefully selected times saves growers money and spares the environment.
Foster says most growers following the program have gone from two or three miticide sprays per season to zero or one application. One spray application costs $60 per acre. With more than 4,000 acres of apple trees in Indiana, Foster's findings could save growers at least $240,000 per season.
CONTACT: Foster, (765) 494-9572, e-mail, Rick_Foster@entm.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, firstname.lastname@example.org
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