• The Minnesota Department of Agriculture (MDA), in collaboration with federal, state, and local partners, slow the spread of gypsy moth populations in Carleton, Hennepin, Lake, and St. Louis counties in 2018. Surveys revealed six distinct areas where monitoring traps caught a high numbers of moths. These results, combined with the trap records of previous years and follow-up site surveys, prompted the MDA and the Minnesota Gypsy Moth Program Advisory Committee to develop a treatment project for 2018.

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  • Treatments for gypsy moth in Minnesota can have two different goals. An eradication treatment, in the pre-infested area, is designed to completely eliminate a population of gypsy moths. A Slow-the-Spread (STS) treatment, is designed to reduce the gypsy moth population by two-thirds.
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  • To reach these goals, several products are available to target gypsy moths. Btk and mating disruption are useful for most projects.
  • Btk, short for Bacillus thuringiensis var. kurstaki, is a common soil bacterium that has been isolated and mass produced for maximum effectiveness against gypsy moth. It is organic certified and has a proven safety record. Visit the Minnesota Department of Health's webpage for human health risk information about Bacillus thuringiensis.
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  • Mating disruptants take advantage of the natural pheromone attractant of the female gypsy moth. Flooding the treatment area with the pheromone confuses the male gypsy moth's search for a mate and, if mating success is limited, fewer eggs are laid and fewer caterpillars are expected to hatch the following year.
  • The MDA's annual trapping program is the first step in determining where a treatment may take place. Our small cardboard traps are baited with a scent that lures in the male gypsy moths, where they become trapped in the sticky coating on the trap's interior. If multiple catches in a single trap are found, more traps in and near that location are set the following year. This helps to outline a possible infestation.
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  • Once trapping survey data are analyzed, an alternate life stage survey is conducted in areas with high numbers of male moths. If a gypsy moth egg mass is found, this confirms that a reproducing population exists. Finding even one egg mass often leads to proposing the site for treatment, since there are undoubtedly more egg masses – gypsy moths hide their egg masses very well. Moreover, each egg mass contains 500-1,000 eggs, which allows for moth numbers to increase rapidly.
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  • The next step is to examine egg mass survey results, past history, and survey data from the current year. Habitat suitability for gypsy moth is also taken into consideration. Urban environments with an abundance of oak and other trees, relatively few predators, and lots of sheltered spots for laying egg masses provide ideal gypsy moth habitat. Based on this information, recommended treatment sites are proposed.
  • At this point the local involvement process begins. Before treatments begin, local officials and the public are notified of our proposal, and public meeting are conducted in the treatment areas as part of an environmental assessment process. These public meetings not only allow us to explain what is proposed and why, but allows citizens to have their comments included in the assessment. We emphasize that this is a proposal. The final treatment decision comes at the end of this process, when the environmental assessment is signed by representatives from the U.S. Forest Service, the U.S. Animal & Plant Health Inspection Service, and other cooperating agencies.
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  • U.S. Postal carrier routes are used to identify residents within the proposed treatment area, and the MDA attempts to notify everyone in the area by mail. Because treatments are weather dependent, exact spray dates are estimated. Exact dates and times will be announced as soon as possible through local media, the MDA's toll-free telephone line and on this website. Local law enforcement, health departments, schools, and hospitals will also be notified.
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  • Because of its ability to defoliate trees year after year, the gypsy moth is a significant environmental, economic, and quality-of-life issue. Therefore, infestations and the treatments are taken very seriously. This insect pest is not native to North America and has no natural enemies to keep its population in check. Urban neighborhoods in the northeastern United States, much of the Atlantic Seaboard and Lower Michigan have been devastated by repeated defoliation by the gypsy moth.
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  • If sites are left untreated in Minnesota, here is what residents can expect within 5 to 10 years: In May/June, caterpillar numbers in any single backyard will reach into the thousands or even millions. Oak trees and other host trees and shrubs will be bare by the beginning of summer. Trees may grow a second set of leaves if they are healthy, but they will be weakened. If the tree is already stressed, as many urban trees are, they may die. If trees are defoliated for a second year in a row, they could die, falling victim to other pests because of their weakened state.
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  • As thousands of caterpillars feed, there is an audible sound of caterpillar droppings falling to the ground. Like any other excess nutrient, droppings get into runoff water and into the local watershed. Each caterpillar sheds its bristly skin four or five times as it grows, and the skins pile up. The bristles may become airborne and irritate human eyes, skin and respiratory systems. In fact, many people develop a rash if they come into contact with the bristles. It becomes extremely unpleasant to work or play outdoors; the caterpillars will also crawl on houses and may get inside.
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  • Caterpillars pupate in July, offering some respite to humans. The adult moths emerge shortly afterwards, and thousands of male moths begin fluttering around during the day, searching for females to mate with (female gypsy moths don't fly). Females lay eggs, resulting in thousands of unsightly egg masses, visible and hidden, reachable and out of reach, waiting through the winter to start the cycle over. Eventually the moth population will crash, but will re-establish over several years and repeat the devastation.
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  • Treatment at high infestation levels is more costly than the current low level of infestation and is typically funded in part or completely at the local level – often by individual property owners. Homeowners may have the option of not having their property treated once gypsy moth becomes established, but they will be unable to prevent neighbors from participating in local spray programs or using far more toxic pesticides than a public program might use. There is also considerable cost in removing dead trees and a decline in property value because of the loss of mature trees.
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  • These are the effects of individuals living in a gypsy moth-infested area, but what about the broader implications? When gypsy moth becomes generally established, counties go into quarantine status, meaning that no outdoor household articles may be moved to non-quarantines areas without proof they have been inspected and found free of gypsy moths. Individuals moving to new places, loggers transporting pulp wood, and nursery growers shipping their stock are all covered by the quarantine. Quarantines increase regulations, increasing costs to consumers. Minnesota has a responsibility to neighboring states to slow the spread of this pest. Not treating does not mean that we are letting nature take its course; the gypsy moth is not a part of Minnesota's natural ecosystem, and is a serious threat to our environment.
  • Spray aircraft normally arrive at urban sites at sunrise or shortly after. On average, a 640-acre block (one square mile) takes about a half-hour to spray with a plane or two hours by helicopter. The aircraft flies over the treatment block, making sequential passes. It will be very low (about 50 feet above the treetops), and loud.
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The MDA offers the following tips to residents in and around the treatment area:
  • The residue will not damage a vehicle's finish, but residents may wish to park vehicles indoors to avoid having to wash them after the application. Soapy water will remove any residue on outdoor items.
  • The treatment product has no known health effects for humans, but to avoid it residents may wish to stay indoors during the treatment and keep windows closed for a half hour after application; and
  • The airplane noise may spook pets, so residents may wish to keep them indoors during the treatment;
  • For the moth treatment to work, it must begin early in the morning. Residents may be awakened on that day by the noise of the low-flying airplane. MDA apologizes for any inconvenience;

Treatment products are determined based on the results of annual survey trapping, alternate life survey results, and size of the treatment area. Depending on the product, treatments are conducted to target either very young caterpillars or adult moths. In areas that have many male moths captured and where egg masses are found during the alternate life stage survey, Btk is used due to the evidence of a reproducing population. In areas with lower male moth captures over a more extensive area and where no egg masses are found during the alternate life stage survey, mating disruption is used.

Btk is used against small caterpillars and is applied in May-June. Since insect development is temperature dependent, an unusually cool or warm spring affects this timing. Treatments occur twice, about a week apart, to catch late-hatching caterpillars. Spraying normally takes place early in the day when low winds and high humidity allow the spray droplets to land on tree tops where they will be the most effective, and also because fewer people are active outside. A site will typically be finished before children are walking to school or people are heading to work. Learn more health risk information about Bacillus thuringiensis from the Minnesota Department of Health and see our frequently asked questions on human and environmental health.

Treatments targeting adult moths will take place in July, just before the male moths emerge from their pupal cases. Aircraft will fly very low (about 50 feet above the treetops) and be loud. There will only be one application over each treatment area. Spray planes will start very early in the morning but are able to fly for most of the day if weather is favorable. People on the ground may or may not detect any product coming out of the airplane, but be assured that it is being distributed in a swath beneath the aircraft.