An Ill Wind That Blows No Good….#GypsyMoth 2021

The warmer weather has supported the continued hatch and excitement for first instar Gypsy moth (Lymantria dispar) larvae this week!  The cool temperatures of last week had larvae huddled up in wait.  But the sudden heat and warm breezes have convinced 1st instar larvae to climb up to the top of their egg mass hosts, cast out a tiny thread and balloon out in the air in hopes of landing on a desirable plant host.  But there are so many larvae in some areas….they are also landing on you and me.  

First instar Gypsy moth (Lymantria dispar) larvae have hatched and are dispersing, especially in the Southwestern part of the province! 

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

Larvae lucky enough to hatch on a desirable host will begin feeding on emerging foliage…the rest will climb to the top of the tree to disperse on tiny silken threads (see video above) in hopes of landing on other delicious botanical hosts.  Some of the few hosts they won’t feed on include red maple (Acer rubrum) and they don’t usually feed on conifers such as hemlock and cedar…but this year the competition is so fierce that they might be desperate enough to take a BITE.  

For more info on the Biology and Management of Gypsy moth see my YouTube video, Gypsy Moth in the Landscape (below): 

In 2020, the Ontario Ministry of Natural Resources and Forestry (see above) observed record-breaking areas of defoliation in southern Ontario since the moth’s introduction over 50 years ago. Nearly 600,000 hectares of trees were defoliated by this pest last year, beating the original record of 350,000 hectares in 1991. OMNRF is predicting moderate to severe defoliation in Gypsy moth hot spots in 2021.

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          Over the next few weeks, look for holes in leaves and turn over inspect  leaf undersides for tiny, dark, fuzzy 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, Acer, Fagus, Tilia, Betula and they can even be found on Picea pungens! Gypsy moth larvae may also hide in bark crevices during the day (Photo: Gypsy moth larva on Fagus sylvatica leaf, J. Llewellyn). 

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Larvae do not all hatch at once.  This makes spraying tricky.  It will likely require at least 2 to 3 applications of insecticide this year because of the early season heat and the record-breaking population levels. 

Management of Gypsy moth larvae can be achieved using Bacillus thuringienesis (Bioprotec, Dipel, Foray, ReVokBTK, Thuricide HPV, Thuricide 48LV, B.t.K) biological insecticides and spinosad (Success) naturalyte insecticide, with good coverage, especially in the first few weeks after larvae start to feed on foliage.  Dragnet & others (permethrin) is registered and also the injectable Treeazin (azadirachtin) and can be effective for older instar larvae when biologicals are less effective. 

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 and early June). 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

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Arboriculture, Insects, landscape, Nursery Production, Weekly Nursery Landscape Report and tagged , , , , , , . Bookmark the permalink.

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