Seeing holes in leaves on deciduous trees? This sugar maple was showing interveinal holes and closer inspection revealed fall cankerworm (Alsophila pometaria) larvae on the leaf undersides. Larvae are pale green (although you’ll often see darker races too) and blend in with newly emerged foliage. They are about 8-12 mm long right now but can they eat! Oye.
Where populations were high last year, monitor for larvae on several hosts such as Acer, Celtis, Fagus, Tilia, Quercus, Ulmus etc. A foliar application of the bio-insecticide Dipel (Bacillus thuringiensis, B.t.). can help to significantly reduce populations and subsequent injury. Click here for a video.
You can often find fall cankerworm larvae suspended by threads that dangle from leaves… or crawling on your shirt during a nice spring walk (Photo: Chris Hsia). Everyone was complaining about them in the greater Hamilton/Ancaster area last spring.
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Seeing holes in newly emerged leaves but all you can find are dark, fuzzy little caterpillars? Gypsy moth larvae have also begun to feed. Look for holes in leaves and turn over inspect leaf undersides for tiny larvae. We often see both Gypsy moth larvae and cankerworm larvae feeding on the same leaves. Gypsy moth larvae may also hide in bark crevices during the day (Photo: Gypsy moth larva on Fagus sylvatica, J. Llewellyn).
Management of Gypsy moth larvae can be achieved using Bacillus thuringienesis (B.t., Dipel, Foray) and spinosad (Success) insecticide, with good coverage, especially in the first 2 weeks after larvae start to feed. Some keen homeowners can install a burlap skirt at the base of the tree to create a shady, protected area for larvae to hide during the day (this behaviour usually peaks near the end of May). Homeowners will need to inspect burlap skirts and underlying bark crevices daily (1-3 pm is best) and remove/destroy larvae. Sticky bands around trunks during the June/July flight period will help trap flightless females and keep them from laying eggs on the bark. The sticky band trapped females will also attract males to the sticky surface J
Forest tent caterpillars (Malacosoma disstria) are coming into their heavy feeding period. They hatched a few weeks ago and are quietly feeding on new leaves, especially sugar maples and red oaks. They have been a problem on sugar maples in Eastern Ontario for the last couple of years. (Photo: late instar larvae of forest tent caterpillar, J. Llewellyn)
There are pockets of heavy forest tent caterpillar populations, especially in eastern Ontario. This insect is a periodic pest of maple syrup sugar bushes and of deciduous forest stands, as well as urban trees. Manage larvae with foliar applications of the bioinsecticide Bacillus thuringienesis (B.t., Dipel, Foray).