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Using several methods provides best control of gypsy moths

Weekly News Article Published: June 10, 2008 by the Central Office

MADISON – Aerial spraying to control gypsy moth in Wisconsin has been completed for this year, but state forestry officials say the end of aerial spraying doesn’t mean the end of options for controlling this tree-defoliating pest.

Gypsy moth caterpillar

“Gypsy moth outbreaks are best controlled using a combination of management tools,” says Andrea Diss-Torrance, Suppression Program Coordinator with the Department of Natural Resources.

Diss-Torrance says aerial spraying of insecticide typically kills 85 to 95 percent of the population, and that alone is usually enough to prevent defoliation and even nuisance problems. However, if the population is very high it may be necessary for people who want to protect their tree to supplement the spray with other management tools to get good control.

“The weather last summer was very favorable for gypsy moth and we started this year with a bumper crop of eggs in some areas,” Diss-Torrance says. “Even if you kill 95 percent of a very high population with a spray, you may still be left with too many caterpillars and need to consider using additional management tools to get the control you want.”

People should check trees now for egg masses from this spring. Pictures of egg masses can be found on the state’s gypsy moth control program Web site [exit DNR].

Egg masses will be torn up and pale beige by early June, and any caterpillars that could have hatched this spring will have done so. Undersides of large branches of oaks are a favorite spot for gypsy moths to lay their eggs. If there are more than 100 egg masses on a tree, it indicates there was a very high starting population of caterpillars this spring.

Even in areas that were sprayed, landowners may want to consider having a certified arborist check trees to see if a second spray of individual trees may be necessary to get the necessary control. People can search for a certified arborist for hire through the Wisconsin Arborists Association Web site [exit DNR].

For homeowners with gypsy moths, putting sticky barrier bands up on trees and collecting caterpillars under burlap bands can help reduce the population of the pest on yard trees. Directions for how to use these controls are on the gypsy moth Web site under the Management Options for Yard Trees link.

In July, if homeowners see the brown pupae or white female moths on trees or siding, they can be knocked down with a broom or hose and then crushed.

“Avoid crushing the female moths with your hands or feet or her scent will get on you and male gypsy moths will be attracted to you in high numbers, “ warns Diss-Torrance. “While the males are harmless, this can be a nuisance.”

Later this month, watch for caterpillars hanging on the trunk of trees that have been killed by the fungal disease Entomophaga maimaiga or the viral disease NPV.

“The wet weather we have had this spring is favorable for Entomophaga,” Diss-Torrance says. “We are hoping that this introduced, specific fungus will cause an epidemic among the gypsy moth and cause the outbreak to collapse like it did in 2004 in the Milwaukee area.”

People who would like their property or neighborhood included in the 2009 Suppression Program spraying should contact county and local officials in July to report gypsy moth infestation and request that the county participate in the Suppression Program.

Contact information is also available on the Gypsy Moth [exit DNR] Web site by clicking on a blue or red county on the map. Choose “contacts” from the left side menu on the next page that appears. Call the community contact for residential areas or the county contact for rural woodlots. If there is no community contact listed, call the county and your local public works department, community forester, or town clerk.

For properties with too many trees to make a ground-based spray affordable or physical control feasible, private aerial sprays can be arranged for 10 or more acres. A guide for doing this is also available online.

Gypsy moths seldom kill trees on their own. Mature, healthy trees can generally withstand two to three consecutive years of heavy defoliation. Instead, trees can be killed by the combination of stresses caused by defoliation, drought, soil compaction, other insects, and much more. If drought conditions occur this summer, you can help your trees stay healthy by watering them for one to two hours each week, during weeks with no rain. Do not fertilize this year or next if trees are defoliated. This can cause them to overextend themselves by producing too much foliage, too fast, with limited energy reserves.

For publication requests or questions, or to report gypsy moth infestations to the DNR call 1-800-642-6684 and choose menu option # 2 anytime 7 a.m. to 10 p.m., seven days per week.

CONTACTS: Andrea Diss-Torrance, Suppression Program Coordinator, Wisconsin Department of Natural Resources, 608-264-9247

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