Update on gypsy moth spray window dates

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included. 

Last week we introduced the new gypsy moth spray window zone map. Growers should note that spray windows dates have been identified for zone 2 – all compounds and zone 3 – Dimilin.


Each year Michigan Department of Agriculture and MSU Extension evaluate the progress of gypsy moth egg hatch in order to set the opening and closing dates for the gypsy moth spray window. This year we have refined the process using historical degree day accumulation data available online through MSU IPM Resources at: http://www.ipm.msu.edu/landscapeipm/gddlandchart.htm . The state has been divided into five gypsy moth spray window zones that roughly correspond to historical degree day trends. These zones are comprised of the counties shown below.

2007 Gypsy moth spray window zones

Zone 1 - Includes the counties of Berrien, Cass and Monroe
Zone 2 - Includes the counties of Allegan, Barry, Branch, Calhoun, Clinton, Eaton, Genesee, Gratiot, Hillsdale, Ingham, Jackson, Kalamazoo, Kent, Lapeer, Lenawee, Livingston, Macomb, Montcalm Oakland, Ottawa, Saginaw, Saint Clair, Saint Joseph, Sanilac Shiawassee, Tuscola, Van Buren, Washtenaw and Wayne.
Zone 3 - Includes the counties of Arenac, Bay, Benzie, Clare, Gladwin, Grand Traverse, Huron, Isabella, Lake, Leelanau, Manistee, Mason, Mecosta, Midland, Manistee, Muskegon, Newaygo, Oceana, Osceola and Wexford.
Zone 4 - Includes the counties of Alcona, Alpena, Antrim, Baraga, Crawford, Delta, Dickinson, Gogebic, Houghton, Iron, Iosco, Kalkaska, Marquette, Menominee, Missaukee, Montmorency, Ogemaw, Ontonagon, Oscoda, Otsego and Roscommon.
Zone 5 - Includes the counties of Alger, Charlevoix, Cheboygan, Chippewa, Emmet, Keweenaw, Luce, Mackinac, Presque Isle and Schoolcraft.

Gypsy moth spray window dates

The accompanying chart shows actual and projected open/close dates for application of the two groups of pesticides used for regulatory treatment of gypsy moth in nursery stock and Christmas trees.

Open – Dimilin (150 DD*)
Open – all other compounds (200 DD)
Close – Dimilin
(700 DD)
Close – all other compounds (800 DD)
April 23
May 4
June 9 (projected) **
June 15 (projected)
April 30
May 7
June 15 (projected)
June 20 (projected)
May 3
May 15 (projected)
June 21 (projected)
June 27 (projected)
May 14 (projected)
May 21 (projected)
June 28 (projected)
July 4 (projected)
May 20 (projected)
May 27 (projected)
July 3 (projected)
July 11 (projected)

* DD = Degree Days at base 50 degrees F.
** Projections are based on 30 year historical degree day data.

Since gypsy moth development will vary by location, you will need to monitor development around your farm. Weather conditions will affect caterpillar development and may effect end date of the spray windows. Growers should watch the Landscape CAT Alerts for additional announcements.

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