Extensive Gypsy Moth Infestation in South Monroe Co, Mi

Asked June 11, 2013, 11:54 AM EDT

I live next to a mixed oak/maple woods on 22 acres on Secor Road in sourth Monroe Co, MI, just north of Toledo and Lambertville, MI. We are currently in about the 3-4th week of a huge Gypsy Moth caterpillar infestation which has/is de-leafing all the mature oaks on our property and in the woods. We annually have some infestation but this is the largest and most destructive I have seen....mature caterillars today literally covering house, entering garage, doorways, with thick leaf detritus and droppings each day covering everything, and munching their way through the woods. I understand that they will soon go in a pupa stage, and probably too late now to treat with sprays or Bt. Is there something we can do now for next Spring to ward off yet another outbreak ? Will there be any spraying in our county this year or next ? Any advice would be appreciated. I have pictures available to forward if needed. thanks, Tom Heferle

Monroe County Michigan insect issues gypsy moth horticulture

1 Response

Hi Tom,
Sorry to hear about all your gypsy moth caterpillars. I know it's not pleasant when there is an outbreak. You are correct - It is too late for a Bt spray this year. There are probably only 2 more weeks or so before the caterpillars pupate. I expect they will be pretty much gone by July 4.

Although most insecticides applied as a cover spray will control gypsy moth larvae, the problem is getting the insecticide up into the trees where the larvae feed, without the insecticide raining down on yourself, your neighbors, and various other organisms. There are some systemic insecticides that are injected into the base of the tree. Most have imidacloprid as the active ingredient (the toxic stuff) and that usually isn't very effective on caterpillars The products may take anywhere from a few days to weeks to move into the canopy. By then, I would expect the caterpillars will be spinning cocoons to pupate, so you'd likely be wasting money and insecticide this year.

I don't believe there is any cooperative Bt spray program in MI like there was in past years. A few counties in northern lower MI still have some kind of gypsy moth program. For example, Gina Conrad still runs a gypsy moth program in Gladwin County. You might contact Gina - she is probably handling egg mass surveys and spray contracts herself (gconrad@gladwinco.com). Unfortunately, Monroe Co. is not real close to Gladwin Co., so that may not help much. I will send Gina a note to see if she knows of other counties in SE Michigan that may be hiring someone to spray Bt. If so, you might be able to get a better price.

Also, gypsy moth populations typically collapse 1-2 years after a big outbreak like the one you are describing. In some years, a fungus builds up and kills high numbers of the large caterpillars. The fungus has to have the right temperature and rain conditions, however, so in some years, it just doesn't do much. However, the virus disease will build up in the population, regardless of weather. You can pretty much count on outbreaks collapsing after 2-4 years, even without any fungus. You can tell when an outbreak is likely to collapse by looking at the egg masses. If the egg masses that are laid this summer are on the small side (similar to a quarter or smaller), it's a good sign. That indicates many female moths had a sub-lethal level of virus and the population is on the way down. If the egg masses are mostly large (2-3 inches long and thick) this summer, then you will really want to see about finding someone who can apply Bt next May. The Bt spray would need to be applied after most egg masses have hatched, and after the oak leaves have started to grow, but while the caterpillars are still small.

If I can find more information for you, how can I reach you?