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Home > Plants, Pests & Pest Control > Pest Management > Gypsy Moth Program > Treatments

Gypsy Moth Treatments


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    • The Minnesota Department of Agriculture (MDA), in collaboration with federal, state, and local partners, is proposing to slow the spread of gypsy moth populations in Hennepin, Pine, and Winona counties. Surveys in 2016 revealed three 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 proposed treatment project for 2017.

      In order to reduce current populations of gypsy moths and slow the growth of future generations of this forest pest, the MDA proposes to treat a total of about 1,120 acres of land with a biological insecticide called Bacillus thuringiensis var. kurstaki, or Btk, and about 1,751 acres with mating disruption. Three treatment blocks have been identified and named for their geographic locations: Richfield in Hennepin County, Hinckley in Pine County, and Pine Creek in Winona County (see maps at bottom of page). Habitat within the proposed treatment areas include many of the trees species considered susceptible to gypsy moth defoliation.

      For the most up-to date information on treatments call 888-545-MOTH (6684).

        A copy of the Decision Notice and Environmental Assessment may be obtained by emailing a request to Gypsy.Moth@state.mn.us.

      • Healthy treeTreatments 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. An STS treatment, in the slow the spread area, is designed to reduce the gypsy moth population by two-thirds.

        To reach these goals, several products are available to program managers to target gypsy moths. Most commonly, 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. Visit the Minnesota Department of Health's webpage for human health risk information about Bacillus thuringiensis.

        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 has successfully treated over 827,000 acres since 1980.

      • 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.

        Once trapping survey data are analyzed, an alternate life stage survey is conducted in area with high numbers of male moths. If a gypsy moth egg mass is found, this confirms that a producing 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.

        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 data, recommended treatment sites are proposed.

      • At this point the local involvement process begins. Before treatments begin, local officials and the media 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.

        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. Once treatments are approved based on caterpillar development, spray locations are determined on a daily basis, based on local weather conditions. Local media will be notified the day before a treatment takes place. People may call the toll-free line to find out the spray schedule. Local law enforcement, health departments, schools, and hospitals will also be notified.

      • Aerial view of damage caused by gypsy moth

        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. Its native range is Europe, Asia, Siberia and northern Africa. 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.

        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 through June. 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.

        Gypsy moth frass and leaf litter covering a picnic tableAs 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.

        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.

        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.

        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 insidious 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 as such it 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.

        Spray plane Spray helicopter

      • 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 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 frequently asked questions.

        • 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.

          Disrupt II pod 

      • Proposed Btk Blocks (two blocks, a total of 1,135 acres)

        Ely Block (565 acres)

        The northern edge of the boundary starts just north of the intersection of East Camp Street and 2nd Ave East and runs roughly parallel to East Madison Street. The western edge of the block follows 2nd Ave East south to Lookout Ridge Road. The eastern edge starts at the intersection of North 14th Ave East and East Madison Street running 1.1 mile south.

        The block is completely within the city boundary of Ely. There are no federal or state lands within the block.

        2016 Ely Proposed Btk Treatment Block. Map created by the MDA.

        Two Harbors Block (570 acres)

        The block is just west of the city of Two Harbors. The far eastern edge of the block runs parallel to 20th Street stretches west for just over 1 mile (5,550 feet). From the intersection of 7th Ave, the eastern edge runs 1/3 mile north and ½ a mile south past the intersection of Hwy 61 and Scenic Old Hwy 61. The northern edge of the block is 880 feet north of and roughly parallel to Valley Road. The southern edge is parallel to and about ½ mile north of Stanley Road. The block is roughly centered on the junction of County Road 10 and County Road 11.

        The northeast tip of the block is within the city boundary of Two Harbors. There are no state or federal lands within the block.

        2016 Two Harbors Proposed Btk Treatment Block. Map created by the MDA.

        Proposed Mating Disruption Blocks (three blocks, a total of 6,236 acres)

        Houston block (960 acres)

        Houston block stretches from the southern boundary of the city of Houston south into the bluffs. The northern boundary of the block runs along East Mons Street and the southern runs along County Road 4. The western block boundary is parallel to and about 1/10 of a mile west of Westgate Drive (if it continued south of Co Rd 13). The block is bounded on the east by State Highway 76.

        The northern portion of the block is within the city boundary of Houston. There are no federal or state lands within the block.

        2016 Houston proposed MD treatment block. Map created by the MDA.

        Mound Prairie block (2,987 acres)

        The Mound Prairie block is an irregularly shaped block is just under 2 miles west of the town of Hokah. The south east corner is near the intersection of State Highway 44 and County Road 20. Drawing a line west 1.6 miles to Von Arx Drive forms the southern boundary. From here, the western edge continues north and slightly west 2.8 miles, past State Hwy 16, to a point just north of Carlson Road. The northern boundary goes east 1 mile to County Road 21, then follows the road ¾ mile southeast. At this point the boundary dips south ¾ mile to just north of County Road 16 and continues east .6 mile. Turning south 1.6 miles to the intersection of State Highway 44 and County Road 20, forms the eastern edge.

        The western edge of this block intersects parts of the Mound Prairie Scientific and Natural Area. There are no other state lands nor any federal lands within the rest of the block.

        2016 Mound Prairie proposed MD treatment block. Map created by the MDA. 


        Reno block (2,289 acres)

        The Reno block is an irregularly shaped block located between Freeburg and Reno. The southwest corner starts at a point .4 mile west from the intersection of County Road 249 and Nelson Valley Road. The southern edge goes 2 ¼ miles west, just past Bramble Road. The western boundary continues 1.4 miles north to County Road 249. The northern boundary roughly follows County Road 249 east 2.6 miles. Turning south ½ mile to the southeast corner forms the eastern edge of the block.

        There are no federal or state lands within the block.

         2016 Reno proposed MD treatment block. Map created by the MDA.


        The MDA offers the following tips to residents in and around the treatment area:

        • 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;
        • The airplane noise may spook pets, so residents may wish to keep them indoors during the treatment;
        • 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 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.

        Over the years, the MDA has eradicated gypsy moth infestations on thousands of acres across the state using this method. In the Twin Cities metro area, the MDA has successfully eliminated multiple infestations over the past 30 years. These efforts protect forest health, property values, and the state's tourism industry


        MDA Contact

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    MDA Contact

    Arrest the Pest