Spongy moth on oaks and shade trees
Btk works on spongy moth only while the caterpillars are small. UMass Extension's test is the head: caterpillars with all-black heads, under about ¾ inch, are susceptible, and those with yellow markings on the head are much less so. In Massachusetts hatch comes in the first week of May. The Thuricide label says to spray at the second or third instar and repeat in two weeks; the Monterey label says to spray as buds swell, before the leaves are fully open.
At a glance
- Damage
- Leaves chewed to the main veins; whole oaks stripped by late June
- Type
- Chewing
- Settings
- Garden
- Threshold
- See profile
- Ally
- Bacillus thuringiensis kurstaki
- Rate
- Label rate — 4 tsp per gallon of water on the Thuricide and Monterey B.t. shade-tree and ornamental directions
How to confirm it
Hairy caterpillars up to 2–3 inches (5–8 cm) long with five pairs of blue dots and then six pairs of red dots down the back. In winter, look for tan, fuzzy egg masses about 1½ inches long on trunks, stones and outdoor furniture.
Identification, lifecycle, degree days and every control option are on the full Spongy moth profile. Not sure it is this pest? Answer four questions about the damage.