Spraying tree pests

Winter: Preplanning

1. Organize a neighborhood or town meeting to discuss the spray operation. Ask your local forester, county extension agent, or other knowledgeable person to attend and discuss forest pests including gypsy moth and forest tent caterpillar (FTC) biology and control, the use of pesticides, and address landowners' concerns.

2. Obtain permission to spray from each landowner involved. Ideally, permission should be granted in writing. Spraying the property of a landowner who has not granted permission is a violation of state law. Many people have concerns about spraying pesticides regardless of the reason or type of pesticide involved. Be aware of your neighbors wishes or their reactions regarding plans to spray and actual spraying activities.

3. To be effective, the spray block should be at least 10 acres, and 80 percent of the forested area in the spray block needs to be treated. Large forested tracts contiguous to the area being protected may require treatment of a border strip along the edge to prevent reinfestation by FTC of the sprayed area. The width of the strip should be at least 100 yards.

4. Secure funding. Possible funding could include assessments of the landowners based on acres or feet of lakeshore to be treated. Similar spraying in the past has cost $50 or more/acre depending on treatment size, location, etc.

5. Determine acreage to be treated. Prepare maps or make a mosaic of aerial photos. Sources of photos for determining acreage and making maps include the soil and water conservation Office or online aerial photos. Some spray services have the capability of taking aerial photos which will provide a current picture of the treatment area.

6. Contact aerial applicators. Provide maps and acreage estimates. Obtain bids for supplying Bt (and sticker, if recommended) or the pesticide of choice and application costs on a per acre basis. Ask for bids for both one and two applications with the understanding that the second application is optional at your determination. One application is usually sufficient to protect tree foliage, particularly if the forest is made up of only a few different tree species. Two sprays may be necessary to reduce caterpillar nuisance and to protect foliage when forest composition is diverse. A list of licensed aerial applicators can be obtained through the MN Department of Agriculture. This link leads to an external site.

7. Negotiate and develop a contract with the aerial applicator of your choice. Your local DNR forester can furnish you with a sample contract.

8. Provide the name, address, and phone number for the contact person who will act as project supervisor and liaison between the applicator and the landowner group.

Spring: Prespray

1. Set up a network of caterpillar and foliage watchers throughout the spray area to monitor development. Members of the network should be well distributed to represent all parts of the treatment area. Observers should identify observation trees with numerous egg masses within 8–10 feet of the ground for good visibility.

2. In April, begin to monitor the egg masses. Egg masses should be inspected every day after April 20. Record date of hatching and then watch the development of the caterpillars. Treatment timing will be based on caterpillar length and foliage development (see below).

3. Foliage should also be observed by network members. Oaks will be slower in leaf development than other hardwoods. Be sure that leaf development is based on the slowest tree species present that constitutes a significant component of the forested area to be protected.

4. Set up a system for efficiently and quickly contacting landowners in the treatment area. Remind landowners that the area will be sprayed, and spraying will usually occur during the month of May.

Spring: Spraying

1. Determine the proper time for spraying. Caterpillar lengths and foliage development will vary, but generally should be ½-inch for caterpillars and ½ their normal length for leaves.

Caution: During very high populations, the young caterpillars may eat the foliage off as it appears. If this occurs, time the operation on the size of the caterpillars alone. Unfortunately, heavy leaf consumption may lower the success of the spray.

2. Notify the applicator that he or she has six days to spray.

3. Notify the landowners to alert them to the six-day spray window. Be prepared to notify landowners when the applicator arrives so that all stay informed. This will allow concerned people to leave or stay indoors during the actual spraying.

4. The project supervisor should be on hand to assess weather conditions and to monitor application. The supervisor should have the authority to stop the spray operation if weather conditions change, the contract specifications are not being followed, or if the operator is acting in an unsafe manner.

5. If a second spray is needed, it should be scheduled to occur 3–5 days after the first.