These Cloudy, Hazy, Humid Days are Numbered

U.S. forest fires make the Big Smoke even smokier, but there's no risk to  human health, expert says | CBC News
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Looking up at the sky today, it was so hazy you couldn’t see much but a fuzzy-looking grey. This is a different kind of overcast than what we normally get to experience. Hundreds of wildfires are burning in the west and prevailing winds are carrying the smoke eastward to Ontario and beyond. “The layer of smoke is in the upper atmosphere and it is not affecting air quality”, Peter Kimbell, a warning preparedness meteorologist for Environment Canada based in Ottawa, told CBC Toronto. Get ready for some cooler weather on its way for Wednesday 🙂

Adult male Gypsy moth
Adult Male Gypsy moths (Lymantria dispar) can be found flying in crazy, zig-zag patterns near the ground still in much of southern Ontario. Many areas are seeing lower populations than last year, thanks to larval diseases that either killed larvae or reduced their ability to reproduce.

Gypsy moth adults have been flying for a couple of weeks now and will likely be flying for a week or so more since we are still seeing viable pupa, many areas saw populations of younger (smaller) caterpillars just as the majority of the population started pupating in late June. Starting around mid-late August, once Gypsy moth egg laying is complete, horticulturalists can scrape off egg-masses, collect them and destroy them to reduce populations next spring. Or you can wait until late October, to give egg parasitoid wasps a chance to do their egg parasitism thing. Encourage your neighbours to remove and dispose of egg masses to have even greater efficacy on the local population. Remember, females cannot fly, which limits their spread. The main dispersal is the first instar larvae that blow in the wind to find new hosts soon after hatching in May.

Photo of brown, fuzzy egg masses of Gypsy moth
Fuzzy, brown egg masses of Gypsy moth on Colorado spruce! This is a peak year so a best practice is to scout all trees on any property you are responsible for. Scrape egg masses into a container and destroy them to help reduce GM populations next spring and summer.


Growing Degree Days: 600-900 GDD Base 10oC

1. Daucus carota (Queen Anne’s Lace, full bloom)

2. Cirsium arvense (Canada thistle, full bloom to seed development)

3. Hydrangea arborescens ‘Grandiflora’ (white flowers turning green)

4. Sorbus aucuparia (fruit starting to turn yellow)

bugfinderlogo the ultimate scouting app for woody plants in the nursery and landscape. Free download on Apple and Google Play!



Are you noticing webbed masses of yellow-brown, fuzzy larvae with dark heads feeding on leaves of deciduous trees and shrubs this summer? Fall webworm (Hyphantria cunea) nests are starting to become more noticeable now. 

salix-fall webworm 1

Look for larval nests on deciduous trees such as Juglans, Betula, Fraxinus and Prunus.  This year we are starting to see them on several hosts.  Just like other insects, Fall Webworm larvae have boom and bust periods in their life cycles.  Larvae can be found feeding on foliage inside the strong webbing over the twigs and leaves.  Larvae are light yellow with dark spots, covered in light hairs and will flick their abdomens conspicuously when a predator approaches.  Where possible, manually remove webbed larval masses and destroy them.  Larval tents expand to encompass more and more foliage every few days so it is possible to SPOT spray infested trees with Dipel/Foray (in the evening) to suppress populations where pruning is not possible.

Euonymus scale is starting to produce a SECOND generation of crawlers at this time.  Look for tiny, orange crawlers or brown nymphs in among the adult scale populations on leaves and stems.  Crawlers are the most susceptible life stage and are sensitive to applications of contact insecticides, even insecticidal soap and the summer rate of horticultural oil.  Mind the high temperatures as some pesticides can burn foliage when its hot and humid out.  Kontos is one of our newest insecticides registered for scale insects in the nursery.  It can also be used as a drench. 

whiteGrubClose            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].  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.

Japanese Beetle Mating Pair
Japanese Beetle Feeding on Leaf

In the landscape and nursery, Japanese Beetle adults can be effectively managed with BeetleGONE (Bacillus thuringiensis var. Gallerae), this biological insecticide available in Ontario.  Adulticide insecticides for JB in the nursery also include Imidan.  Pheromone traps for JB are extremely good at attracting the adults.  Always place traps far AWAY (I mean away) from susceptible host trees and shrubs (e.g. Rosa, Prunus, Tilia, Syringa, Ulmus etc.). Empty traps regularly to keep them effective at containing JB adults.

PM Physocarpus
Powdery mildew on Physocarpus
Powdery mildew on Rosa

We have seen lots of powdery mildew on deciduous flowering shrubs (Amelanchier, Rosa, Physocarpus) and herbaceous perennials.  Monitor for white, powdery residue on the tops and bottoms of leaves.  Protect new foliage with fungicide applications [e.g. Banner, Heritage Maxx, Compass, Switch, Milstop, Regalia (biofungicide), Tivano] in the nursery. Where the disease pressure is moderate to high, fungicides are not going to be very effective as they have limited curative action.

IMG_2748_01 Magnolia scale adults are white and will be turning pink-orange in the next couple of 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). 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.

European elm scale ADULT FEMALES from

European elm scale (Gossyparia spuria) crawlers have hatched and can the tiny bright yellow nymphs can be found on new twigs of elm (e.g. ).  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 (I’ve done it and it worked well).  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.

Dead EAB adult found on ground under recently injected ash tree

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 conductive tissue.   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:


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 (acephate, carbaryl, 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.

black vine weevil
Black vine weevil adult, note brown flecking on the fused elytra (photo: Dave Cheung)
The smaller, Strawberry root weevil adult (photo: Dave Cheung)

Continue to monitor for Black Vine Weevil (Otiorhynchus sulcatus) ADULTS in the FIELD and in CONTAINER PRODUCTION on Rhododendron, Taxus, Thuja, Picea and Euonymus and several other ornamental hosts. Applications of nematodes in container production will be effective if you wait to early September to apply them. Strawberry root weevil (Otiorhynchus ovatus) can also be a problem in field production of evergreens, larvae can cause significant root feeding damage and weaken plants. 

IMG_0321 Signs of strawberry root weevil adults include brown, flagging shoot tips (and small girdling marks at the base of the flagged shoot) . The most common host for this type of damage is Thuja occidentalis (eastern white cedar).  SRW flagging is common on Thuja and does not usually negatively impact tree health. 

2020 Nursery Scout Mitchell Staffen demonstrating how to detect weevils hiding out in foliage

To scout for adult weevils, place a tarp or large piece of cardboard under the tree, shake branches vigorously over the board and look for brown-black weevils “playing dead”.  Insecticides for adult weevils in the nursery include Silencer, Pounce and Flagship.  Remember, adult weevils feed at night.  Spray insecticides in late evening to target adults and reduce UV degradation (e.g. Pounce, Silencer).  

  clmexithole  Cedar leaf miner next generation larvae are starting to feed on tender new foliage.  A light sheering of tips in early August should give good knockdown of CLM larvae.  Cygon is registered as a foliar application for CLM larvae in early August in the nursery.


Remember all that boxwood leafminer you were trying to manage this spring in the landscape?  Well the next generation of larvae are feeding on this year’s growth NOW, although you can’t see any signs of them yet.  A sheering of 2021 growth will eliminate many of the lovely, leafy homes they’ve found.  They will die of desiccation in those clippings over the next several weeks, but its still a good idea to collect them and dispose of them for good sanitary practices.

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Invasive Species, IPM, landscape, Weekly Nursery Landscape Report and tagged , , , , , , , , , , , , . Bookmark the permalink.

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