All treatments have concluded for 2018.


Gypsy moth is a Federal and State quarantined leaf-eating insect that is a serious threat to forest and urban trees as well as ornamental plants. This pest is not native to North America and has the potential to defoliate trees year after year causing significant environmental, economic, and quality-of-life issues.

You may be wondering why do we treat for gypsy moth, and why is it such a concern for Iowa? Gypsy moth is not part of the natural ecosystem, and doing nothing is not the same as letting nature take its course.

Gypsy moth has no significant enemies to keep the pest population in check. A single gypsy moth caterpillar can consume as much as one square foot of leaves per day, and large pest outbreaks can devastate entire forest and urban areas, leaving a bleak winter-like appearance in mid-summer. Infestations of this pest are taken very seriously for the following reasons.

Eastern Iowa is considered to be in the transition zone of gypsy moth advancement. Small pockets of infestation are becoming more common in northeastern Iowa, as would be noticed from the natural advancement of this pest. The established 'western' front for gypsy moth is now considered to be 35 miles east of the Mississippi River.

As the gypsy moth continues to advance, and as more small pockets of gypsy moth infestation become common ahead of the front, the management strategy has been to "slow the spread" of the pest. The best way to control low populations of gypsy moth over a large area is to use mating disruption. This strategy uses the pheromone attractant of the female gypsy moth to confuse the male moth in finding a mate, which in turn limits or controls natural reproduction of the pest. This strategy is especially effective when the pest density per area is low to moderate in size.

Determining Treatment Locations

Iowa is currently included in the Gypsy Moth Slow the Spread Foundation (STS). STS provides the framework for states to determine the areas that need to be managed for gypsy moth. This program focuses on early detection of low level gypsy moth populations, and then disrupts the normal build-up and spread of gypsy moth in those locations.

What to Expect on Treatment Day

Foray® Btk Applied to Control Gypsy Moth
Black Moshannan State Park; Philipsburg, PA

Untreated test areas were
completely defoliated

A helicopter will begin early in the day and treatment is estimated to take 2-3 hours to complete. Flying low to target tree canopy, the application process may be noticeably loud.

Foray® 48B is a biological insecticide that contains Bacillus thuringienses kurstaki (Btk). Btk is a naturally occuring soil bacteria found all over the world that interferes with the gypsy moth caterpillars' digestive system eventually killing the caterpillars. Foray® 48B is the most widely used formulation of Btk since 1988.

Treatment occurs when trees have enough foliation and the caterpillars have reached a certain size. Sites are sprayed twice, 3 to 14 days apart, because not all gypsy moth caterpillars hatch and begin feeding at the same time.

Btk works because the caterpillar's stomach and digestive system is alkaline, and triggers an endotoxin that Btk naturally produces. The endotoxin kills cells and dissolves holes in the lining of the caterpillar's gut. People, other mamals, reptiles, fish, and birds have acidic digestive systems and cannot trigger Btk to produce the toxin. Various strains of Btk have been used commercially in the United States since 1958 on insect pests of food, forage crops, and in forrest. Btk is commonly used by organinc vegetable farmers up to the day of harvest.