May 10 Nursery-Landscape Report: “Those Darling Buds of May”

Well it’s the Friday of the Victoria Day long weekend and although it’s going down to 2-3C in many areas tonight and tomorrow night, I don’t see any risk of frost for areas south of Barrie. Keep in mind that tender new growth of Euonymus and Boxwood can be extra sensitive to cool temperatures so protecting them from low temperature injury may be warranted in more northern parts of southern Ontario.  It’s just no fun when they get injured….
Start applying FERTILIZER in the field and landscape where soils are dry and warm to facilitate root growth and maximize the uptake of fertilizer nutrients (usually when leaves have emerged and expanded). A soil test will show deficiencies that can be corrected through supplemental fertilizing. It has been shown that applications of nitrogen to cold, wet soils results in loss of nitrogen to the environment.

PLANT PHENOLOGY indicators this week, A) north of 401, include: Acer platanoides (Norway maple, full bloom); Cornus mas (Cornelian cherry dogwood, late to finishing bloom); Cercis canadensis (just a few blooms); Magnolia soulangiana (Saucer magnolia, full bloom); Acer saccharinum (just starting leaf out)
B) Niagara: Acer platanoides (Norway maple, many full bloom); Magnolia soulangiana (Saucer magnolia, full bloom); Cercis canadensis (early bloom)); Acer saccharinum (leafing out)
If you are referring to the Monitoring tables in the 2009 edition of publication 383, Nursery and Landscape Plant Production and IPM, look at Table 4-6 on pg. 66. We are at 55-100 GDD Base 10C.

<em><a href="/clm/species/malacosoma_americanum">Malacosoma americanum</em></a> (Eastern Tent Caterpillar) web nest.

Eastern tent caterpillar (tent with early instar larvae)

EASTERN TENT CATERPILLARS have hatched and the tiny, black fuzzy larvae hide inside webby tents found in branch crotches. Young larvae hide in webby tents during the day, remove and destroy tents during daylight hours in the first week or two after their appearance and destroy. Young larvae come out of their tents to feed at night, try an application of the biological insecticide B.t (Dipel, Foray) on the foliage during the evening hours. Larvae will turn black and die approximately 3-5 days after eating the B.t. residue on the foliage.

GYPSY MOTH egg masses are hatching in container production (e.g. Picea pungens) and will be hatching in the next week or so in field production and in the landscape (when trilliums are in full bloom). Some control can be achieved using Bacillus thuringienesis (Dipel, Foray) and spinosad (Success) insecticide in the first 2 weeks after egg hatch. 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.

<a href="/clm/species/plagiodera_versicolora"><em>Plagiodera versicolora</em></a> (Imported Willow Leaf Beetle) adult on willow.

Imported Willow Leaf Beetle

Adults of the imported WILLOW LEAF BEETLE (Plagioderaversicolora) are found on Salix (Willow) this time of year. The beetles were feeding on the leaves, chewing conspicuous holes and notches into them. They are easily recognizable by their shiny, metallic black to bluish-green color. Adults overwinter in cracks within the bark on the host tree and start feeding in the spring. They will soon be laying yellow eggs on the underside of leaves, which will hatch 2 weeks after that. The larvae will feed on the interveinal tissue on the underside of the leaves and damage can be significant. The adults can be found feeding in field production and in the landscape in the coming weeks. Low toxicity insecticides registered for this pest include Success 480 SC. Other insecticides include Malathion, Orthene and Sevin. Avoid Sevin application when Salix is in bloom.

VLB larvae

Tiny, early instar Viburnum leaf beetle larvae feeding on leaf undersides as foliage is emerging (J. Llewellyn)

 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).

BIRCH LEAFMINER adults (small, black sawflies) are emerging, mating and will be starting to lay eggs on expanding birch leaves. Systemic insecticides are registered to manage this pest in nursery production. Injectable insecticides (AceCap 97, TreeAzin) are registered for this pest in the landscape.

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.

Where HONEYLOCUST PODGALL MIDGE was a problem in the past, monitor trees for overwintered adult midges. These adults will be emerging as the buds start to swell. Adults 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 before foliar emergence.

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 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:

<a href="/clm/species/otiorhynchus_sulcatus"><em>Otiorhynchus sulcatus</em></a> (Black Vine Weevil) adult, pupa and larva.

Black vine weevil. From left to right: newly emerging adult, pupa, larva (D. Cheung)

In PRODUCTION NURSERIES where BLACK VINE WEEVIL larvae are a problem in container crops (e.g. perennials, evergreens), soils have reached the 10-12oC threshold and treatment with beneficial nematodes, Heterohabditis bacteriophora (H.b.) should be completed. Since Heterohabditis nematodes require moist, warm soil, we find that they do not work well in the landscape/field unless ample, supplemental irrigation can be provided for the 10 days following application. In container production, Met 52 Granular can also be used prevenatively, at the time of potting, to help control all stages of black vine weevil. In the LANDSCAPE and GARDEN, check for overwintered LARVAE of black vine weevil on Rhododendron, Taxus, Thuja, Euonymus etc. in the garden and treat with nematodes as soil temperatures warm up.


PINE BARK ADELGID eggs and nymphs are present on white pines (Pinus strobus), and Pinus contorta. Once eggs hatch, an application of insecticide (Malathion, Orthene, Tristar) may be warranted where populations are high. Check out the factsheet from Michigan State University for some excellent photos: (

<a href="/clm/species/mindarus_abietinus"><em>Mindarus abietinus</em></a> (Balsam Twig Aphid) fir.

Newly hatched “stem mother” of Balsam twig aphid on fir

BALSAM TWIG APHID stem mothers are/have hatched and the tiny, bluish grey aphids can be found on terminal buds as they break. Growers can 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.

<a href="/clm/species/pissodes_spp"><em>Pissodes sp.</em></a> (White Pine Weevil) adult.

white pine weevil adults (2)

Overwintering PINE WEEVIL adults are active and are mating on young twigs of evergreens when the Forsythia starts to bloom. Monitor for small black/brown snout beetles around the foliage. Where populations are high, an application of contact insecticide (e.g. carbaryl) on foliage may help reduce numbers. Common weevil pests include white pine weevil (1/4 inch long, two white spots on the back), northern pine weevil and pales weevil (1/2 inch long, brownish black). Pine root collar weevils also overwinter as adults (developmental stages are overlapping), but they feed and lay their eggs at the root collar. Cygon applications to terminals for white pine weevil egg laying should be finishing up at this time in the nursery.

Overwintering EUROPEAN PINE SAWFLY eggs will be starting to hatch soon. Larvae feed in clusters on last year’s (and older) needles. Colonies can be removed and destroyed when larvae are still young. Larvae are greenish-yellow with dark head. They rear their abdomens up in unison when alarmed. They can often be found on the top half of the tree, on the NE side.

<a href="/clm/species/cacopsylla_buxi"><em>Cacopsylla buxi</em></a> (Boxwood Pysllid) nymph on boxwood.

Young boxwood psyllid nymph (D. Cheung)

Where leaf cupping and distortion was a problem last year, look for tiny, nymphs of the BOXWOOD PSYLLID hiding and feeding from inside the emerging buds and leaves. The nymphs are yellowish-green at first but later secrete a white, waxy substance that can be seen on new foliage and on the nymphs themselves. Treat with systemic insecticides (e.g. dimethoate) to reduce populations of newly hatched nymphs when new growth appears. Carbaryl is toxic to honeybees so avoid carbaryl applications on plants that are blooming.

Boxwood Leafminer injury, leaf undersides

Boxwood Leafminer injury, leaf undersides

Where BOXWOOD LEAFMINER was a problem last year, treat new growth with a systemic insecticide (dimethoate) once adults midges start to mate and and lay eggs (in about 2 weeks) to limit damage from new generation larvae.


Tarspot on Norway maple (August) (

TAR SPOT appears as large, circular spots on the leaves of Norway maple (as well as other Acer sp) in late summer and fall. The fungus overwinters on fallen, infected leaves and sporulates in the spring when the new foliage is emerging and susceptible to disease, usually after a rain event. This is usually around late bloom on Norway maple. Where tar spot is a problem, protect emerging leaves before rain events with fungicides (Banner, Compass) where warranted.

FIREBLIGHT of apple and pear. The window of infection starts once FLOWERS ARE BLOOMING. Most fireblight infections enter the delicate flower tissue. Protect flowers and emerging leaves with bactericidal products such as Kasumin (Grp 24) and Streptomycin (Grp 25) during bloom. For suppression of fireblgiht in the landscape with Class 11 biological fungicides, Blightban C9-1 and Bloomtime can be used during bloom of apple and pear. CHECK IT OUT! Prediction models for Fireblight Activity in southern Ontario May 16-22 can be found here:  (English)   (French)

APPLE SCAB causes diffuse-looking spots along leaf veins and often leads to premature leaf drop in JuneNote: copper should be avoided beyond 1/2″ green tip stage (as leaves are emerging) to avoid potential phytoxicity issues. Where ornamental crabapples are further along in leaf emergence, try fungicides such as Nova (Grp 3, rotate with other fungicides to avoid resistance), Pristine (Grp 7, 11), Compass (Grp 11), Captan (Grp M) and Manzate (Grp M) . For supression of apple scab in the landscape with Class 11 fungicides, Serenade Max (Bacilus subtilis) and sulphur can be used to help protect emerging foliage from this disease.

There are several species of GYNOSPORANGIUM rusts that sporulate on the Juniper host in warm, wet conditions in May. Examples include CEDAR-APPLE RUST, cedar-hawthorn rust, cedar-quince rust and pear trellis rust. Gymnosporangium rusts produce bright orange, gelatinous sporulation masses from perennial galls or directly on twigs and stems of Juniper. These sporulating masses send spores that will infect the alternate host, the Rosaceous plants such as apple, pear, serviceberry etc. to cause bright orange lesions on leaves in summer. Monitor for bright orange sporulation on Juniper during warm, wet weather and protect Rosaceous plants with fungicides such as Nova (Grp 3), Pristine (Grp 7, 11), Daconil (Grp M) and Manzate (Grp M).
PLEASE NOTE: The previous 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.

pub840coverjl  The 2013 Crop Protection Guide for Nursery and Landscape Plants (previously 383, now publication 840) can now be found at:
This 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 supporting guide publication 841, GUIDE TO NURSERY AND LANDSCAPE PLANT PRODUCTION AND IPM will be online soon.

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

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Arboriculture, Insects, IPM, landscape and tagged , , , , . Bookmark the permalink.

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