BANNER Year For Gypsy Moth Larvae!

Posted on May 28, 2020 by Jen Llewellyn  

Jen is Nursery Crops Specialist, OMAFRA and works with commercial tree nurseries and landscape industries.

Seeing holes in newly emerged leaves but all you can find are dark, fuzzy little caterpillars?  Gypsy moth larvae have dispersed and begun to feed on trees and shrubs.  Look for holes in leaves and turn over to inspect leaf undersides for tiny larvae.  We often see both Gypsy moth larvae and cankerworm larvae feeding on the same leaves.  Their favorite hosts seem to be species of Quercus (Oaks), Acer (Maple), Fagus (Beech), Tilia (Linden), Betula (Birch) and they can even be found on Picea pungens (Colorado blue spruce).

First instar Gypsy moth (Lymantria dispar) larvae have hatched and are dispersing!  Gypsy moth larvae may also hide in bark crevices during the day (Photo: Gypsy moth larva on Fagus sylvatica leaf, J. Llewellyn).

Larvae produce silken threads and take a ride in the wind in hopes of landing on other delicious botanical hosts.

Gypsy moth larvae may also hide in bark crevices during the day (Photo: Gypsy moth larva on Fagus sylvatica leaf, J. Llewellyn). 

Management of Gypsy moth larvae can be achieved using Bacillus thuringienesis (B.t., Dipel, Foray, Xentari) biological insecticides and spinosad (Success) naturalyte insecticide, with good coverage, especially in the first 2 weeks after larvae start to feed.  

Winter and early spring scouting for Gypsy moth egg masses has indicated EPIC levels of the moth larvae can be expected in much of southern Ontario this year!

Gypsy moth Cultural Management: Some keen horticulturalists 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.  Although this monitoring method wouldn’t be practical for commercial sugar bushes and woodlots, it will work well for host trees around the house yard and farm buildings.

For great images and management information check out our FREE insect scouting App Bugfinder, on Apple and Google Play!

Fall Cankerworm.  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 only about 5-8 mm long right now but oye, can they eat!

Where populations were high a couple of years ago (Hamilton, Ancaster, Niagara), monitor for larvae on several hosts such as Acer, Tilia, Quercus, Ulmus etc.  A foliar application of the bio-insecticide Dipel/Foray or Xentari (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 area last spring.

Forest tent caterpillars (Malacosoma disstria) are just starting to come into their heavy feeding period. They hatched a couple of weeks ago and are quietly feeding on new leaves, especially sugar maples and red oaks (Photo: late instar larvae of forest tent caterpillar, J. Llewellyn).

There were pockets of heavy forest tent caterpillar populations in 2018, especially in eastern Ontario.  There may only be mild-moderate populations this year so inspect your sugar maples for this pest.  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, Xentari).

Author: Jen Llewellyn, Nursery Crops Specialist, OMAFRA