The Friyay Report – July 8th, 2021

Flightless, adult female Gypsy moths are crawling up trunks and laying their eggs in bark crevices. Ontario is seeing moderate-severe infestation levels of Gypsy moth (Lymantria dispar) across southern Ontario again this year. But we have some good news to report!
Adult male Gypsy moths are a dull brown colour with minor wing markings. Note their plumose antennae which they use to pick up the scent of the female sex pheromones. Males are noticeable by their crazy, zig-zag flight pattern, always on the move to find a mating partner. Adults typically only live for a few days, so motivated to mate they don’t even feed.
Larval pathogens like this virus (Nuclear Polyhedrosis Virus, NPV) that infected the larva on the right, leaving it dead and in an inverted “V” position. Larval pathogens have caught up with they Gypsy moth this year, causing widespread larval mortality, at least 30% in many of the outbreak areas that I have observed. The virus is common once the insect reaches peak populations due to overcrowding and easier transmission.
Gypsy moth larva which I suspect may be infected with the larval fungus, Entomophaga maimaimaga. This fungus can infect larvae but requires moisture to be able to infect and spread from dead larval carcasses. Thankfully the weekly rains that many areas of experienced have led to significant levels of larval infections.
Late instar Gypsy moth on Colorado spruce (Picea pungens)

Ontario has seen moderate-high levels of Gypsy moth (Lymantria dispar) infestations on several deciduous trees (Betula, Quercus, Acer platanoides, Malus, Tilia and Picea etc.) with hungry larvae causing severe defoliation in some cases. Where spruce and pine trees have been significantly defoliated, recovery is not likely and even if the evergreen does continue to live, it will never be able to replace its canopy.

Late instar Gypsy moth on what used to be a full canopy of crabapple (Malus)

Irrigation during the continued summer heat will be more important than ever this month to help defoliated deciduous trees put on a new set of leaves. Even complete defoliation can be tolerated by most healthy deciduous trees, once.

Sticky bands around trunks during the July flight period will help trap flightless adult female Gypsy moths and keep them from laying eggs on bark, trapping females will attract males to the sticky surface. Pheromone-baited sticky traps are also available to help reduce populations of adult males.  GET YOUR TRAPS OUT NOW!

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Look for large, white powdery insect scales on the twigs of Magnolia this month!

Magnolia scale adults are white and will be turning pink-orange in the next few weeks.  They will producing dark-coloured crawlers under these protective shells, usually at the beginning of August.  (Magnolia scale do not produce eggs but give birth to live young). As we get later into July, pick the scale shell off and look for juicy flesh as a sign that reproduction has not yet begun.  Insecticides are not very effective at this time and won’t be effective until crawlers emerge from under mother scales in August.  However, you can scrub the fleshy scales off the twigs at this time to give immediate management of this pest. In late September-mid-October, treat infested trees with horticultural oil for excellent management of this pest.

European elm scale on Ulmus glabra

European elm scale (Gossyparia spuria) crawlers will be hatching soon, look for tiny bright yellow nymphs on new twigs of elm (e.g. Camperdown elm ).  Adult females are 2 mm long (tiny), oval, brown with a whitish fringe around their body.  This can be an injurious pest on elm, we often see copious amounts of sooty mold and twig dieback.  You can also scrub this scale insect off of the twigs.  This pest is also very vulnerable to dormant horticultural oil applications in late fall/early spring when no leaves are present. The overwintering nymphs migrate to the bark crevices at the end of the growing season.

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Have white grubs been an issue in your nursery?  Preventative applications of Acelepryn (chlorantraniliprole) and Intercept (imidacloprid) are registered for white grubs (nursery production) and July is a good time to use these products (during the adult flight period).     [Beneficial nematode applications for white grubs (e.g. European chafer) will be effective in early-mid August where there is regular irrigation available to keep soil moist and support nematodes].  GrubGONE (Bacillus thuringiensis var Gallerae is also registered for the larval stage of white grubs).

Japanese beetle adults are flying and feeding on leaves of woody plants (Syringa, Tilia, Ulmus, Prunus, Rosa).  Look for metallic, coppery-green beetles with white tufts of hairs along the edge of their abdomens. Biological insecticide options include BeetleGONE (B.t.G).

 Potato leafhoppers NYMPHS (photo above) and ADULTS are still feeding on deciduous trees on the newest growth.  Now that the second flush of leaves have hardened off, potato leafhoppers can’t do much more than cause minor leaf flecking and so management techniques are no longer required. 

LHopInjuryMonitor for potato leafhopper on nursery crops such as maple, elm, and hackberry (Acer, Ulmus, Celtis). Leafhoppers (and aphids) suck plant sap from soft, expanding foliage and cause foliage to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed.  We can sometimes see this in the landscape, and this year is no exception.  

Potato leafhopper Nymphs are about 2 mm long and scuttle SIDEWAYS, rather quickly, across the leaf and to the other side (they don’t have wings to fly away). Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source).  Older, hardened off foliage is not usually as susceptible.  Leafhopper adults (right) are winged, very mobile, tiny, pale yellow-green jumping insects that are easily disturbed when you approach infested foliage. It almost looks as though they are being flicked off of the foliage.

EAB adults casting shadows on leaves (Markham) EAB_EurAsh  Seeing ash tree with dieback, vertical bark cracks and d-shaped exit holes? Emerald ash borer is the cause. Injectable insecticides may be used to protect ash trees from new infestations of Emerald Ash Borer (Agrilus planipennis).  Trees must be actively transpiring in order to maximize insecticide uptake into the cambium (clear, warm, sunny days).   Registered injectable insecticide products include: AceCap 97, Ima-Jet and Tree-Azin.  Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer at:  http://www.omafra.gov.on.ca/english/crops/insects/eab-bbb-manage.htm.  Emerald ash borer adults start to emerge when the black locust (Robinia pseudoacacia) are blooming.

Where Fletcher scale (Taxus scale, Parthenolecanium fletcheri) has been a problem in the past, monitor for crawlers and early instar nymphs (photo above) on twigs and needles of Eastern white cedar (Thuja occidentalis) or yews (Taxus spp.). Some of those Fletcher scale crawlers (click here for video) and will be settling down on tender new growth and growing larger and browner and flatter for the rest of the summer.

Several insecticides are registered for management of Fletcher scale crawlers in the nursery (cyantraniliprole, acephate, dimethoate, hort oil, insecticidal soap). Try insecticidal soap in the landscape.   Careful, the summer rate of horticultural oil may be phytotoxic on some hosts, especially when temperatures are hot and humid > 26C.

Two-spotted spider mites (TSSM) are loving the heat and actively feeding on several deciduous and herbaceous plants, especially in container production, causing chlorosis and leaf flecking (photo above) on several deciduous and woody ornamentals.

Two spotted spider mites are small but the damage is significant so catch them early on crops of historical mite significance.  They typically infest the lower leaf surface, making it look dirty with the naked eye.

Teranychus urticae | Guide to Nursery and Landscape Arthropod Pests of  Ontario

Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs. You may also see cast skins and clear eggs. (photo: Dave Cheung)

TSSM miticides include: DynoMite/Sanmite, Vendex, Kanemite, Floramite, Avid and Nealta.  Apollo is registered in outdoor nursery crops to knock down the egg stage and newly hatched nymphs.  In the greenhouse, biocontrol agents should be brought in to coincide with the first sign of TSSM.  Phytoseiulus persimilis is a predatory mite that feeds on TSSM when temperatures are below 26oC and it is a good choice when TSSM populations are low-moderate.  Amblyseius californicus is a predatory mite that can be brought in ahead of TSSM appearance (because it can find other sources of food).

Monitor for nymphs and adults of maple spider mite on red and silver maples with a history of mite damage.  

Oligonychus aceris | Guide to Nursery and Landscape Arthropod Pests of  Ontario

Maple spider mite nymphs and adults are brown with black backs and found on the undersides of foliage this time of year.  Populations are usually only minimally damaging on foliage. Miticides may be required where pest pressure is heavy (container grown trees with overhead irrigation).  Miticides include Vendex, Floramite and Kanemite.

Did you know we have a songbird that is a striking Indigo BLUE?

Indigo Bunting (Birds of Fort Bowie NHS) · iNaturalist
The male Indigo Bunting, yep, here in Ontario! (Photo: the very talented Dawn Scranton from Cornwall, Ontario)

If you frequent open grassy fields with scrub, especially on the edges of other habitats like forests, you have probably heard the song of the Indigo Bunting. The song of the male bird is a high-pitched buzzed “sweet-sweet, chew-chew, sweet-sweet”, lasting two to four seconds, sung to mark his territory to other males and to attract females. This small seed-eater is really getting to be more common and is a very successful breeder here in Ontario. They are more often heard, than seen. I was lucky enough to get two long looks at these beauties so far this year.

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
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