GYPSY MOTHS ARE BACK!! (BUT THEY WANT US TO CALL THEM SPONGY MOTHS NOW)
After several years without much gypsy moth activity, we have seen the pesky bugs make a comeback in some parts of Michigan.
The best control measure is aerial spraying with Btk, a bacteria. That is what gypsy moth suppression programs use. But if you are not in a spray area, there are other solutions to the problem.
In addition to being messy, with fuzzy worms and worm poop, they can cause a significant stress to our trees. Defoliation of oaks in repeated years can make the trees susceptible to invasion by the 2LCB (two-lined chestnut borer), an insect that can kill the oak just as surely as the emerald ash borer kills ash trees. THAT IS THE BAD NEWS!
HERE IS THE GOOD NEWS!
The same product that we use to treat and prevent ash borers can be used to treat and prevent both of these pests. An injection in the late fall with emamectin benzoate can give up to two years of control of gypsy moths and two to three years of preventing the borers from killing the trees.
Or if it is spring time and the gypsy caterpillars are actively feeding, we can control them with soil injected insecticides, sometimes trunk injected insecticides. An average tree can be treated for $100 to $150. Large trees somewhat more. This does not provide enough residual to be relied upon for borer control, however.
COST OF TREATMENT FOR BOTH GYPSY MOTH CONTROL AND BORER CONTROL
If you measure around the tree at about 4 feet above ground level and call us with that measurement, we can give you an exact estimate of the cost to treat. The average large oak tree may cost $200 to $300 for two years of control of borers and at least one year of gypsy moth control. And even though there may not be enough chemical in the tree for a second year of gypsy moth control, the killing of 99% of the gypsy moths one year means very few egg masses will be on that tree, so not many if any gypsy moths the next year.
If there are multiple trees at one address or multiple trees in a neighborhood getting treated, the cost can be less. On large trees we usually use the high dose of emamectin benzoate (10 ml per diameter inch). This large dose requires that the injection is made into the active xylem (the upmoving sap stream), not into the cambium layer and not just under the bark.
The fall treatment is done late in the season, when the leaves are starting to fall, so that none of the product goes into this year's leaves. Smaller doses of emamectin or injections too early may result in little if any control of the pesky caterpillars and too little of the insecticide present for borer control.
COST OF IN SEASON TREATMENT WITH SOIL APPLIED INSECTICIDE
For this treatment we use acephate (brand name Lepitect) by soil injection. If this is done in late April or early May, the young caterpillars will die as soon as they start feeding. As mentioned above, the per tree cost is usually 100-150 dollars. The usual dosage of this product is one ounce per 5 diameter inches injected into the soil around the base of the tree.