May 24 Nursery-Landscape Report

You have reached Jen Llewellyn for the sixth edition of the 2013 OMAF and MRA Nursery and Landscape Report, updated on Friday, May 24th.

Environment Canada is calling for cool, sunny weather this weekend, with temperature ranging from 15-19oC in many areas. They aren’t calling for showers until next Tuesday. There is a risk of frost in some areas of southern Ontario tonight, check your local forecast for overnight lows if you have nursery stock that is still tender or flowering. There’s a full moon Saturday night 🙂

Frost Protection. The surest way to protect tender new foliage and flowers is to cover them. Some growers use light weight thermal blankets and some use leftover poly. The coldest temperatures are usually experienced between the hours of 2:00 and 5:00 am. If you are irrigating to reduce frost injury, start irrigating before temperatures dip down below 0oC. The act of freezing releases heat from the irrigation water molecules and warms the surface of the plant so tissue does not freeze. Unfortunately, ice formation may actually physically damage tender new shoots because it is so heavy. You’ll have to use your discretion about night time irrigation. Another option is to increase air flow around the plants. By blowing away the cold air that settles around the plants, you can reduce some of the low temperature injury. Some growers have tried using fans from their airblast sprayers with some success.

Apply fertilizer in the field and landscape where soils are moist 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, there isn’t a huge difference in plant development between zones yet this spring.
A) North of 401: Aesculus hippocastanum (early bloom-mid bloom, Prunus cistena (full-late bloom), Cercis canadensis (late bloom to petal fall, Lonicera korolkowii (mid bloom), Spiraea vanhouttei (mid-full bloom) Syringa vulgaris (full bloom)
B) Niagara: Cercis canadensis (late bloom to petal fall) Aesculus hippocastanum (mid bloom), Prunus cistena (full to late bloom), Lonicera korolkowii (full bloom), Spiraea vanhouttei (mid-full bloom) Syringa vulgaris (full bloom), Viburnum carlesii (full bloom)
C) London area: if you would like to report plant phenology events, please contact me.
D) Leamington-Windsor: if you would like to report plant phenology events, please contact me.

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 4-4 on pg. 64.

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 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.

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

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: Emerald ash borer adults start to emerge when the black locust (Robinia pseudoacacia) are blooming.

The regulated areas for Emerald Ash Borer can be found at:
The regulated areas for EAB outlines restrictions on the movement of all ash species (Fraxinus sp.) materials and all species of firewood from these regulated areas of Ontario and Quebec.

As of April 5, 2013, the Asian Long Horned Beetle is considered to be eradicated from Canada (Ontario). It was detected in the southern part of the City of Vaughan and the north east part of the City of Toronto. The Asian Long-horned Beetle was last detected inside the regulated area in Toronto in December, 2007. The Asian Long-horned Beetle Infested Place Order is no longer being enforced. This means that tree materials, including nursery stock, trees, logs, lumber, wood, and wood and bark chips from tree species that are susceptible to the Asian Long-horned Beetle, may once again be freely moved out of, or through, this area.


Some Fungal and bacterial blights (e.g. Pseudomonas blight on Syringa) of woody stock can often be attributed to stressful conditions experienced under poly and also the extreme shifts in temperature once the poly is removed. Pseudomonas bacterial blight on deciduous shrubs looks very similar to low temperature injury, and often the two conditions go hand-in-hand. In container nurseries, where Pseudomonas blight on lilac (and other deciduous flowering shrubs) was a problem last season, you may want to consider an application of copper as buds start to swell. (Research also indicates that the copper becomes more effective if combined with Dithane.) The bacteria overwinter next to the buds and can infect leaf tissue once bud caps split open. Again, infection and spread of this bacterial disease can be reduced where temperatures and humidity levels are moderated (i.e. ventilation under poly) and new foliage is more gradually hardened off to outdoor conditions.

In PRODUCTION NURSERIES where black vine weevil larvae are a problem in container crops (e.g. perennials, evergreens), wait until soils reach at least a consistent 10-12oC and treat with beneficial nematodes, Heterohabditis bacteriophora (H.b.). This should result in a significant reduction in populations within two weeks. 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 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 when soil temperatures warm up.

Take a look at the roots of poor looking turf and field grown ornamentals and look for populations of European chafer, May/June Beetle larvae and other white grub species in the soil. Preventative applications of Intercept (imidacloprid) are registered for white grubs (nursery production) and the application period is in June and July (during the adult flight period). Beneficial nematode applications are not recommended this time of year and are much more effective when applied to early instar larvae, mid-August to early-September.


Dutch Trig is registered for Dutch Elm Disease on Ulmus americana species in Canada. This is a new registration (fall, 2009) that contains a biological organism that induces an immune response to help the tree fight off DED infections. Arbotect-20-S (thiabendazole) is the registered injectable fungicide treatment. Injections of these fungicides should be made on sunny days during leaf emergence to maximize uptake.

Where new growth is emerging on Malus sp., the overwintering fruiting structures of apple scab on last year’s fallen foliage may still be infecting spring growth, especially during warm, leaf wetness periods. Apple scab appears as a blotching along veins and also on fruit, it is often associated with early leaf drop. Where appropriate, protect new growth before rain events with fungicides throughout leaf emergence (until leaves harden off). The apple scab fungus grows best at temperatures between 16-24oC, a leaf wetness period is required for the spores to germinate and infect emerging leaves. Intervals between fungicide applications can be longer during dry weather. Some newer fungicides registered for apple scab include: Banner Maxx and Serenade Max (a biological).

Where Malus and Pyrus are blooming and beginning to leaf out and it is WARM and WET, applications of bactericidal products (Copper, Kasumin (new), BlossomProtect (bio)) can help reduce the incidence of Fire blight infections during WARM, WET weather this spring. The weather this weekend is perfect for the spread and infection of Fireblight. Fireblight infection causes dead shoots on Malus and Pyrus, sometimes killing young nursery stock.

Monitor overwintering, galls of cedar-apple rust, cedar-quince rust and cedar-hawthorn rust and branch swellings of pear-trellis rust on Juniper. After a rain event, these juniper galls will begin producing slimy, orange projections during warm, wet/humid weather. These projections contain the spores that will infect the alternate Rosaceous hosts: Malus, Crataegus, Amelanchier, Pyrus etc. They have already sporulated in container production and are NOW sporulate in the FIELD after the recent rain. Keep Rosaceous and Juniper hosts separated from eachother where possible. Apply protectant fungicides (such as Nova) to Rosaceous hosts when the Juniper galls start to sporulate this spring. For photos of galls:

Black knot is easy to see on Prunus sp. at this time. Monitor gardens and adjacent wild areas for Prunus shrubs and trees for large black growths on previous years twigs. If you have the time to prune, prune the cankers out, back quite close to the main stem BEFORE LEAVES EMERGE. Destroy all pruned twigs. Pruning too shallow retains the undetectable, developing canker on the tree and does nothing to limit the disease. Fungicides may give some suppressions when sprayed at green tip, pre-bloom and blossom time. Fungicides include Daconil and Maestro. Fungicides need to be applied ahead of precipitation events during bloom and shoot emergence In the nursery/orchard, Daconil has been shown to be the most effective fungicide. (Fruit-bearing mature Prunus: Daconil cannot be applied after shuck split or fruit will be injured). For more information:

We saw the very beginning of powdery mildew starting on Physocarpus in the landscape this week. Monitor for white, powdery residule on the tops and bottoms of leaves. This is a very wooley type of powdery mildew and is very aggressive on this host (causes leaf and stem dieback). Protect new foliage with fungicide applications (e.g. Switch, Milstop, Regalia (bio)) where disease pressure is moderate to high. Prune out and destroy light infestations.

Aphids are quite numerous on herbaceous and woody ornamentals this spring! Green peach aphid is one of the most common species and melon aphid and foxglove aphid are also quite common. This year we are seeing large colonies of black bean aphid (Aphis fabae) on deciduous flowering shrubs and Euonymus. Aphids are sucking insects that cause stunting, malformation and coat plants in honeydew. They also attract ants. Various insecticides are registered to manage aphids in greenhouses including Endeavor, Intercept and Enstar EW. Where populations aren’t economically damaging, biological control (e.g. Aphidius, Aphidoletes) may provide excellent management when introduced on a regular basis. Biocontrol suppliers include Koppert, Plant Products and Canadian Hydrogardens. In outdoor grown container nurseries, we saw aphids on Euonymus alatus and Spiraea this week.

Woolly beech aphid will be found feeding on European beech (Fagus sylvatica), on the undersides of leaves. The aphids overwinter as eggs, hatch at bud bread and give birth to live young as leaves have expanded. They secrete a white, waxy substance that covers their body and makes it appear “woolly”. Insecticidal soap or a strong stream of water can help reduce numbers of woolly aphids before they coat the undersides of the leaves. Infestation does not usually reduce host vigour, but honeydew production attracts other insects (ants, bees, wasps) and sooty mould.

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.

Mites and Wasps that cause spindle and bladder gall on maple trees are active and starting to lay their eggs where maple foliage is starting to emerge. A delayed dormant/summer spray of horticultural oil (e.g. Landscape Oil, PureGreen Spray Oil) that has “summer” rates and uses on the label may be able to help reduce the number of successful leaf galls this year. AVOID horticultural OIL applications on SUGAR MAPLE, as it is phytotoxic to their foliage. These gall pests do not harm the health of the tree, but can look unsightly.

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.

Eastern tent caterpillars are feeding and making webby tents in branch crotches. The larvae can cause severe defoliation in May, where populations are high. 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. Where larvae are a little larger and start to feed during daylight hours, 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 larvae (2nd and 3rd instar) can be found on various hosts. Some early control can be achieved using spinosad (Success) insecticide in the first 2 weeks after egg hatch. B.t. will work better later once they are settled in their feeding site (most areas now). 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.

Viburnum leaf beetle larvae are feeding on the underside of Viburnum leaves. Look for tiny yellow larvae with black markings. 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).

Gymnosporangium rusts may still be sporulating on Junipers. See above for more info.

Where new foliage is emerging on conifers, monitor for needlecast and blight diseases in the area. Diplodia tip blight on 2 and 3 needled pines and Rhizosphaera needlecast and Stigmina on blue Colorado spruce are our most common needlecast diseases in Ontario. Diplodia tip blight appears as brown, stunted needles at the tips of branches. Rhizosphaera appears as brown-purplish needles from the previous year’s growth, symptomatic needles begin to drop in late spring. Stigmina appears on green and chlorotic needles, but doesn’t always lead to needle drop. To confirm it is Rhizosphaera, look at the undersides of the needles. Those little white dots (stomata) will turn black and the black spots will protrude during sporulation. New, soft growth is especially susceptible to foliar diseases, but infection may also take place later in the season (we don’t know). Where there is a history of damage, treat with registered fungicides (copper oxychloride, Banner Maxx, Daconil) as buds start to open and protect new foliage. Apply fungicides prior to precipitation events (spore dispersal). Unfortunately, most of these blights and needlecasts can be found sporulating for much of the year.

The first generation of Euonymus scale crawlers will be hatching in the field and landscape in the next few weeks. Euonymus scale look like tiny white flecks (males) and tiny brown sea shells (females) along twigs and the undersides of leaves. Look for bright, orange crawlers around populations of adults and on the undersides of leaves and twigs. Where insecticide applications are warranted, multiple applications may be required to get good knockdown since crawler emergence is staggered over a few weeks. Try insecticidal soap and the summer rate of horticultural oil.

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 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 insecticides 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. Where boxwood leafminer was a problem last year, treat new growth with a systemic insecticide (dimethoate) to limit damage from new generation larvae. Treat with insecticides such as insecticidal soap, carbaryl (Sevin) or dimethoate

Balsam twig aphid 2nd generation nymphs are bluish-grey aphids that can be found on new foliage of fir (Abies sp.) at this time. This generation of adelgid has a wooly covering and so pesticide application is a lot less effective. Apply Diazinon, Malathion and Tristar where populations are high and efforts to target stem mothers were unsuccessful.

Overwintering pine weevil adults are active and are mating on young twigs of evergreens at this time. 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.

Overwintering European pine sawfly larvae have hatched. Larvae feed in clusters on last year’s (and older) needles and our nursery scout is finding them in container production. 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. There are several insecticides registered for this pest. A low toxic pesticide choice is Success or Dragnet. Closely examine twigs of Pinus sylvestris, Pinus mugo, Pinus nigra.

Taxus or Fletcher Scale nymphs are feeding on foliage of Thuja and Taxus and starting to produce shiny, clear, sticky honeydew. Applications of insecticides may give some suppression of this pest but nymphs are quite large now and were more susceptible in mid-to-late summer of last year. These nymphs will be feeding and producing copious amounts of honeydew in the next few weeks.

Cedar leaf miner larvae have resumed feeding from the inside of leaf scales. Tear along the margin of green and brown tissue and check for the presence of tiny, yellow/green larvae with dark heads (to confirm CLM is the cause of the browning foliage). We have seen quite a bit of CLM in field grown Thuja on sandy soils this spring. They will be pupating and emerging as adults in the next few weeks. Adulticides (malathion) are registered for the moth life stage in nursery production.

Pine false webworm larvae will be found on white pine When eggs hatch, larvae snip off foliage and make webby nests near the trunk. The larvae clip off more needles and pull them into the webby nest where they feed on them. The larvae feed mainly on older growth and will only eat the current year’s growth when all else has been consumed. The new nests can be dislodged with a strong stream of water.

Cooley spruce gall adelgid and eastern spruce gall adelgid will be forming galls on new twigs of spruce at this time. Galls do not usually have much effect on plant growth but appear unsightly in summer when they turn brown. Where populations are high, the adelgids are susceptible to chemical control (or horticultural oil applications when dormant) when buds start to swell. Target pesticide applications to the undersides of shoot tips. Use wettable powder formulations on blue spruce to prevent foliar discolouration. Heavy populations of spruce gall adelgid are often a sign of some other underlying cause of stress or root problem in the tree.

Monitor for spruce spider mites on conifers with a history of mite damage. Spruce spider mite nymphs and adults are brown with black backs and found on new foliage this time of year. Miticides registered for SSM include Floramite and Kanemite. Miticides may be required where pest pressure is moderate to heavy.

Pine shoot beetld adults have emerged. The tiny beetles take flight after 2-3 days where temperatures reach 10-12oC (I know, it’s hard to believe we’ve had that). Adults lay eggs underneath the bark of stressed or dead pine trees and stumps. Those larvae will develop later in April and May. Remove brood material (i.e. trap (sentinel) logs, snags, dead/dying trees) before new progeny adults emerge (210 GDD, Base 10oC) to comply with the CFIA. All brood material must be burned, chipped (less than 2cm diameter) or buried (30 cm deep) to comply with CFIA standards.


About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
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