Hot, Humid Days are Here

Cedar-Apple Rust (Gymnosporangium juniperi-virginianae) on Eastern red cedar (Juniperus virginiana) is FINALLY sporulating after the rains we just had!

Gymnosporangium rusts, like this Cedar-Apple Rust gall, are finally sporulating! These rusts overwinter on perennial gall on the evergreen Juniperus hosts. In the spring, they are stimulated to sporulate during warm, wet periods. We’ve had the heat, but its been so dry….these galls have been sitting dormant. Until this week. Good news: the alternate Rosaceous hosts (Malus, Crataegus, Amelanchier etc.) have leafed out and those leaves have hardened off, making them very tolerant of rust infections this late in the spring. Soooo, the poor Gymnosporangium rust spores will have a difficult time infecting the Rosaceous hosts, meaning we can expect much LESS rust diseases on our apples, crabapples, serviceberry and hawthorns.

Plant Phenology Indicators: GDD Base 10C: 180 to 200 +
1. Aesculus hippocastanum (horsechestnut, late bloom)                                                               2. Cornus alternifolia (pagoda dogwood, full to late bloom)                                                          3. Spiraea nipponica (snowmound spirea,  full bloom)
4. Robinia pseudoacacia (very early bloom)
5. Prunus serotina (black cherry, mid bloom)

bugfinderlogoFor great images and management information check out our free scouting App Bugfinder, on Apple and Google Play.  

The Crop Protection Guide for Nursery and Landscape Plants (OMAFRA publication 840) contains the crop pest recommendations for nursery and landscape.  Download it onto your phone or computer for easy reference.

CornusSeptoriaLeafSpot                 Leaf  spots on deciduous flowering shrubs are showing up because of the cool, wet conditions we had during leaf emergence.  Leaf spots appear as purplish to brown, with yellow to brown necrotic margins.  Several fungi (Colletotrichum, Elsinoe, Septoria etc. ) cause leaf spots on ornamentals. When the second flush of leaves start to emerge in overhead irrigated containers, you may want to protect new growth with a foliar application of fungicide (Banner, Heritage Maxx, Palladium, Nova, Daconil, Dithane). Once container grown stock is planted in the field, the disease symptoms diminish.


image0008                                    Fireblight is a systemic bacterial disease that causes twig and branch dieback and bark cankers on large limbs and the main stem. It infects apple and pear trees through flower or through recent wounding (e.g. pruning, hail damage).  It can also be found on mountain ash (Sorbus aucuparia).  It is a serious disease in juvenile trees but can impact small to medium sized trees in the landscape.  It is important to watch for late blossoms, called ‘rat tail’ blossoms, which are very susceptible to infection by this bacteria.  DO NOT PRUNE MALUS, PYRUS or SORBUS DURING THE GROWING SEASON to avoid introducing this bacterial disease into healthy trees. Protectant bacteriacidal products include Streptomycin, Copper and biological suppressants such as Kasumin, BlightBan, Bloomtime, Serenade.

EAB adults casting shadows on leaves (Markham)

Seeing ash tree with dieback, vertical bark cracks and d-shaped exit holes? Look up to see tiny, bullet-shaped shadows of the Emerald ash borer in the next few weeks (EAB adults start to emerge when the black locust (Robinia pseudoacacia) are blooming. Injectable insecticides may be used to protect ash trees from new infestations of Emerald Ash Borer (Agrilus planipennis).  Trees must be actively transpiring, post-bloom, 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:


Peach tree borer (Synanthedon exitosa) adults will be flying any day now. Look for cankered regions and chewed bark/wood in the lower stems of Prunus (e.g. Prunus x cistena) as a sign of larval damage.  These clear-wing moths resemble wasps and adult males are attracted to pheromone baited sticky traps.   Bark applications of insecticides (Delegate, Rimon) should begin when adults are found in peak numbers on sticky traps. Pheromone traps can also be placed outside of the Prunus crop, to attract frisky males away from your cherry plants.

WoolyBeech2 WoolyBeech1 WOOLLY BEECH APHID are feeding on beech. These aphids are small and green but they cover themselves with bright white, woolly strands and produce honeydew droplets that cling to the woolly masses. Populations are usually not threatening to tree health. Applications of Insecticidal Soap can be very effective at reducing populations of young nymphs, especially when adequate spray coverage on LEAF UNDERSIDES.

Where HONEYLOCUST PLANT BUG was a problem in the past, monitor trees for tiny, green, wingless, nymphs (see above image).  Plant bug nymphs and adults were a problem in many areas last year as these sucking insects caused stunting, malformation, chlorosis and senescence of leaves (see lower image).   Shake new leaves over a white surface to assess populations of plant bug nymphs.  Most contact insecticides work very well against this pest.


Reducing populations of honeylocust plant bug now is important since multiple generations will be cycling over the next few weeks.


                    Are you seeing discoloured, blemish-like spots on the foliage of pear trees?  This is the Pear Leaf Blister mite (Eriophyes pyri) and populations seems to be building in many parts of southern Ontario.  The mites overwinter under the outer bud scales where they feed on the developing buds. By petal fall, the mites will lay eggs and remain protected from predators within the leaf blisters. The mite is difficult to manage once it moves into the blister-like leaf domiciles it creates by feeding on the leaf tissue in the early spring.  This mite pest does not usually threaten plant health. Management of pear leaf blister mite is often timed for the fall to treat the mites while they are in the outer bud scales.


JuniperTipBlightClose Brown shoots on juniper may be a symptom of juniper tip blight (Kabatina blight). A small grey band or pinched grey canker with black fruiting structures can be found at the base of the infected shoot, this is where the spores come from. Pruning is not suggested once new growth appears, as it will help spread this disease. Where cankers are found, copper and Dithane are registered to protect emerging new growth this spring and summer.

TaxusScaleMay_15AM          Fletcher scale (Taxus scale) nymphs are actively feeding on Thuja and Taxus and are getting larger.  They have a distinctive white stripe down their backs.  You will probably notice the honeydew first.  This scale is difficult to manage at this size but an application of systemic insecticides (Cygon, Orthene in the nursery) may help reduce populations in hot spots.  It is entering its most rapid growth/feeding phase.

Pine Needle Scale settled nymphs.

Pine needle scale crawlers are emerging in CONTAINER production and some Southwest facing landscapes. Crawlers and nymphs are susceptible to applications of acephate, carbaryl, dimethoate, horticultural oil, insecticidal soap, malathion.  Good coverage is required to effectively reduce populations of this armored scale insect pest.

EuonyScaleCrawlersEuonymus scale (Unaspis euonymi) is a tiny little armored scale that covets evergreen Euonymus fortunei in the garden or landscape.  Newly hatched crawlers (above) are orange, they crawl slowly over the plants looking for some juicy tissue to settle and feed on. Crawlers and newly settled nymphs are susceptible to insecticides, including insecticidal soap, the summer rate of horticultural oil, Lagon and Orthene.  Kontos is also effective against Euonymus scale in the nursery and can also be used as a container soil drench (a great alternative to foliar spraying).

Box tree moth (Cydalima perspectalis) larvae are PUPATING in Toronto, which means that many of them are no longer susceptible to insecticides at this time.   Scout the boxwood for activey feeding larvae before you spray B.t.  Otherwise, wait for Second generation larvae in late June/early July.

Pine bark adelgid appear as tiny yellow nymphs (photo above, Dave Cheung).  Look for small, woolly-white masses with eggs and nymphs underneath.

PineBarkAdelgidJune1Charlotte            These pine bark adelgid nymphs will be moving to feed on emerging foliage and will cover themselves in a woolly coating soon, making them much less susceptible to contact insecticides.  Avoid using horticultural oil on white pine as it will dull the glaucus sheen to the needles.  Other options include insecticidal soap, acetamiprid, dimethoate, malathion.

neodiprion sertifer damage on scots pine
neodiprion sertifer larva on scots pine

Where needles on Mugo/Scots pine are disappearing, look closely for dark headed European pine sawfly larvae (Sawflies have >6 pairs of prolegs) with long stripes down their body.  They can sometimes be found on Eastern white pine.   Young sawfly larvae are susceptible to applications of insecticides such as Success, Pounce/Dragnet, Tristar.


YelHeadSpruceSflyLarvaDamageWatch for needle tips to turn straw-coloured as the first sign of 1st instar larval feeding of yellow headed spruce sawfly in the next week. (Remember…Sawflies have >6 pairs of prolegs). The biggerthey are, the harder they fall.

Effective insecticides include Success and Pounce but they become less effective as spruce sawfly larvae mature.  Insecticidal soap can give good suppression if coverage is excellent.

Appearance - Eastern Kingbird - Tyrannus tyrannus - Birds of the World

The Eastern Kingbird (Tyrannus tyrannus) is a favorite songbird for many of us, and one of the last species to migrate north. I’ll never forget the time I was a kid, standing in my canoe, holding onto branches of an overhanging basswood to catch a glimpse of an Eastern Kingbird fuzzy, white chicks in the nest. Eastern Kingbirds are one of our flycatchers, often perching at the top trees, posts or along utility lines. They fly with very shallow, dipping around dramatically, usually accompanied by metallic, sputtering calls. This incredible photo was taken by Frank Lehman and can be viewed on

About Jen Llewellyn

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

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