Spongy Moth (Gypsy Moth) on Maple and Oak
Typical defoliation on a Norway Maple
Gypsy Moth - now called the Spongy Moth (Lymantria dispar) is an introduced species of moth that is a defoliator (it eats leaves). The moth Larvae are present every spring/summer - usually in low numbers but has large outbreaks every 5 to 10 years in Ontario. This moth Larvae can eat most leaves, preferring oak but will eat pretty much all hardwoods. They will even eat spruce if there is lots of competition . Like most defoliators the eggs are timed to hatch just as the leaves are finishing emerging (mid to late May) so there is an easy to consume food source.The adult does not eat. The flightless females lay their eggs on bark (or on a underhang of a house or furniture) Larvae hatch on the bark and spread out through the tree. They have a nasty trick common to most silk spinners - the very young larvae can crawl out to the tip of a limb - lay out a long string of silk and using the wind literally parachute to another tree on the silk strand . Dont panic if they almost completely defoliate the tree - more often than not - most trees will regrow their leaves that year - see pictures below.
Female laying eggs on bark
Spongy Moth Pupae (cocoon) nearly always found in a crevice
Spongy Moth Caterpillar. (5 pairs of blue dots running down the back behind head)
How to Control it.
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1. Destroy the egg Masses (late summer thru to spring) right on the bark. removing the egg masses is very effective. Scrap them off the bark with stiff bristle brush . You can drop the egg masses onto the grass as the scrubbing ruined the protective web holding the eggs and they will freeze over winter if on the ground . Scrap all that you can see ( tape the brush to a pole to reach up higher). look for other egg masses around your property ( gypsy moth love undersides of decks, window sills and wood patio furniture
2. Bt insecticides (BTK ) . Can be purchased at most hardware stores and garden centres. The Insecticide is actually a bacteria that makes crystals in the Caterpillar's stomach that prevents them from eating and they die. You can do it your self. Apply the BTK as soon as you see the Caterpillars. It has a residual of about 1 week and then needs to be reapplied. You will need to buy a spray applicator and you may not be able to reach higher limbs. BTK is non toxic to everything that isn't a moth larvae.
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3. Burlap the trunk. The Caterpillars move up and down the trunk. Burlap wrapped around the trunk forms an effective barrier. The City of Toronto has an excellent website on how to do it. https://www.youtube.com/watch?v=oYf1F4-isRk
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4. Hire an Arborist. Arborists know how to identify Spongy moth and can help you control it if its damaging your trees.
Did You Know: There are natural pathogens that kill Spongy Moth Caterpillars. A Virus called NPV and a Fungus (called Entomophaga maimaiga) are responsible for leaving Caterpillars dead on the trunk. Unfortunately, The Caterpillars often have done some significant damage before these two pathogens knock them back
July 04, 2021. Norway Maple completely defoliated Union, Ontario
July 18, 2021. new leaves well on their way
August 02, 2021. a complete set of new leaves