Fast times in the Ontario Landscape


This past week was way above average for temperatures for the beginning of May.  This has increased the GDD accumulations and hastened plant and insect development.  Many plants that normally bloom sequentially are blooming (and pollinating) at the same time, Aye Caramba!! Allergy sufferers everywhere are paying the price 😦

On top of that, there is a chance of frost in many areas on Thursday morning, and Friday isn’t completely out of the question either.  Take cover.

For Plant Phenology Indicators,  the Acer platanoides (Norway maples) are in full-late bloom, the Amelanchier laevis is in full-late bloom, the Cercis canadensis (redbud) are in early bloom, the Magnolia x soulangiana (saucer magnolia) is in full bloom, the purple-leaf sandcherry (Prunus x cistena) are in full bloom. This puts is at about 55-100 GDD Base 10C.  Plant phenology models for IPM can be found starting on pg. 39 of OMAFRA Guide 841, Guide to Nursery and Landscape Plant Production & IPM.   Many of these models are based on Donald Orton’s COINCIDE.

PLEASE NOTE: The Following Pesticide Recommendations are meant for Exception Uses (e.g. agriculture) under the Cosmetic Pesticide Ban unless the active ingredient is listed under Class 11 pesticides in Ontario Regulation 63/09, effective April 22, 2009.

The Crop Protection Guide for Nursery and Landscape Plants (OMAFRA publication 840) contains the crop pest recommendations for nursery and landscape plants that was previously found in publication 383. Publication 840 is a .pdf file, accessible online and on cd.  The pest recommendations can also be found on our online, searchable database:  Check out NurseryTracker on your phone or tablet!!!

Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests.

Gymnosporangium rusts (e.g. Cedar-apple rust, Cedar-hawthorn rust, Cedar-Quince rust) are sporulating and spores are landing on apple, crabapple, serviceberry pear, quince and hawthorn to infect leaves.  Continue to protect foliage, especially before rain events in the next week or so.

PearTrellisRustJuniperPear Trellis Rust will be sporulating soon on Savin type Junipers, likely in the next batch of warm, humid/wet weather so fungicide application to pear trees should be in place before the next warm rain.

We’ve got quite a few pests hatching, emerging, mating, laying eggs (or getting ready to) on their host plants this week……

<a href="/clm/species/lymantria_dispar"><em>Lymantria dispar</em></a> (Gypsy Moth) larva.

GYPSY MOTH egg masses are hatching and first generation larvae are blowing around on threads as a method of dispersal. When larvae start to feed on foliage, some control can be achieved using Bacillus thuringienesis (Dipel, Foray) and spinosad (Success) insecticide in the first 2 weeks after egg hatch. Dipel doesn’t work as well on older larvae but Success should be effective then.  Don’t forget to monitor Colorado spruce for Gypsy moth larvae!  Some keen homeowners 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 prevent females from laying eggs above sticky bands and will attract males to the sticky surface.

Elm Leafminer Adults laying eggs on leaves (

Elm leafminer adult sawflies (



Several species of leafminers, such as birch leafminer and elm leafminer, are active at this time and laying their eggs in new foliage.  Where systemic insecticides are not an option, the summer rate of horticultural oil applied to new leaves may interfere and suppress resulting populations of leaf mining larvae.

Once ash trees have leafed out, injectable insecticides may be used to protect the trees from new infestations of Emerald Ash Borer (Agrilus planipennis). Trees must be actively transpiring in order to maximize insecticide uptake into the cambium. Registered injectable insecticide products include: AceCap 97, Confidor 200 SL and Tree-Azin. Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer at:

Birches with a history of BRONZE BIRCH BORER infestation should be pruned by now. Symptoms appear as branch tip death, branch death and death of the leader and progresses quite quickly. Destroy pruned material to prevent emergence of beetles. Natural resistance to this pest can be enhanced through activities that improve plant health, such as light fertilizing (May, October), irrigating and removing any weeds and grasses that provide competition for the tree. Betula pendula is most susceptible to this pest and should be avoided in areas of known BBB infestation. Betula nigra (River birch) and its selections have been shown to be quite tolerant to BBB attack. Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer at:

WoolyBeech2 WoolyBeech1WOOLLY BEECH APHID will be starting to feed on beech as new leaves emerge over the next week or two. These aphids are small and green but they cover themselves with bright white wooly strands and produce honeydew. Population are usually not threatening to tree health but applications of Insecticidal Soap can be very effective at reducing populations of young nymphs, especially when adequate spray coverage on LEAF UNDERSIDES.

Honeylocust Plant Bug Single Close

Ominous shaddow of the mighty (little) honeylocust plant bug on a gold cultivar of Honeylocust

Where HONEYLOCUST PODGALL MIDGE and HONEYLOCUST PLANT BUG was a problem in the past, monitor trees for overwintered adult midges and hatching nymphs of plant bugs. Adult midges will be laying eggs on buds in early spring (reddish eggs on buds and new leaves). Recent research in Oregon suggests that delayed dormant oil applications targeting the first couple of egg clutches can help reduce the incidence of pod gall midge. This involves applications of product early in the season, starting just before foliar emergence.  Plant bug nymphs will start to feed on newly emerging leaves, shake new leaves over a clipboard to quantify populations of plant bug nymphs.  Most contact insecticides work very well against this pest.

VLB larvae

 VIBURNUM LEAF BEETLE larvae are hatching and feeding on the emerging foliage of soft-leaved Viburnum at this time (V. trilobum, V. opulus, V. dentatum etc.). The larvae are vulnerable to chemical control only during the first 7-10 days after hatch. Larvae feed on the interveinal tissue from the undersides of the leaves. Keep that in mind if you are doing insecticidal applications (Success, Actara, horticultural oil).


Monitor for STEM MOTHERS of Balsam twig aphid eggs on terminal buds on fir, white spruce, Colorado spruce and juniper, they are susceptible to insecticide applications. These tiny, bluish grey aphid stem mothers can be found on and around terminal buds as they break. Apply Diazinon, Malathion and Tristar on warm days (55 to 78 GDD Base 10oC OR before bud caps loosen off) to target these stem mothers and prevent the damaging generation that follows.    This is your only opportunity to manage this pest.  Click here for  photos


A fungus gnat (left) and shorefly (right) caught on a yellow sticky card.  Both of these pests can transmit Black Root Rot and other pathogens.

Fungus gnat and Shorefly adults (OMAFRA) from the ONFLORICULTURE blog 


For those of you growing in protected structures like greenhouses and year-round polyframes, you may be interested to know that Ontario has a new Floriculture Blog!  Just enter your email in the Follow box and reply to the confirmation email and you will receive notifications of new articles.  Regular articles and photos are provided by our very own Greenhouse IPM Expert, Sarah Jandricic in Vineland 🙂



About Jen Llewellyn

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

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