A slow, wet start to spring


Cornus mas in Early bloom

Due to the cool, overcast weather, we haven’t been receiving much heat in most parts of southern Ontario. In Guelph, the Cornus mas (Cornelian cherry dogwood) is just starting to bloom, many still in flower bud, the Acer saccharinum (silver maples) are in full bloom and the Acer rubrum (red maples) and Acer saccharum (sugar maples) are just starting to bloom. This puts is at about 1-25 GDD Base 10C.

Winter desiccation is even more visible than usual on evergreens due to the long, cold winter. Drying winds and warm, sunny days in late winter caused foliage to lose water. Because the ground is (usually) frozen, roots can not replenish lost water from the foliage and the foliage dries out and becomes brown. Newly-transplanted evergreens are even more susceptible because of their reduced root systems and ability to store water. Quite often, the damage is on the afternoon-sun side of the plant. Take heart, as long as buds are not damaged, the emergence of new growth should hide most of the winter burn.
Now is a great time to use dormant horticultural sprays for overwintering nymphs and eggs of insects that are exposed on twigs and branches. Overwintering scale insects that are sensitive to dormant oil applications include magnolia scale, San Jose scale, golden oak scale, juniper scale, Fletcher scale and overwinter spruce gall nymphs if they aren’t covered in white, woolly mass yet. (Note that dormant oil applications are not effective on oystershell scale and euonymus scale). Mite eggs that overwinter exposed on twigs are also sensitive to dormany oil and include: spruce spider mite, European red mite and maple spider mite on silver/red hybrids).


Boxwood Psyllid nymph on Boxwood

Boxwood Psyllid nymph on Boxwood (mid-May)

Monitor boxwood for bud swell and hatching of overwintering boxwood psyllid eggs. Boxwood psyllid eggs hatch just as buds are starting to break and expose tender new shoots. Psyllid nymphs are green and blend in very well with new growth of boxwood. Their feeding causes cupping and distortion of new growth. Spray with insecticidal soap or contact insecticides at first sign of bud break and repeat 2-3 times to suppress populations of hatching psyllids. Systemic insecticides, such as dimethoate, are registered for use in commercial nurseries.
Look for overwintering White Pine Weevil adults in around the leaf litter below the trunks of white pine and spruce. They will become quite active in the next couple of weeks and will be laying their eggs under the bark of the terminal shoot from last year. Place freshly cut logs on the ground and check them during the day for small grey/brown/white weevils clinging to the under surface. Spray terminals with insecticides (e.g. Cygon is registered for nursery crops) as adults become active and start laying eggs on terminals.
Monitor for overwintering Balsam twig aphid eggs on terminal buds on fir, white spruce, Colorado spruce and juniper, they are susceptible to dormant oil applications. Eggs will be hatching in the coming weeks and developing into stem mothers (nymphs). The tiny, bluish grey aphid stem mothers can be found on 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.    Click here for  photos


In PRODUCTION NURSERIES where black vine weevil larvae are a problem in container crops (e.g. perennials, evergreens), where soils reach at least a consistent 10-12C 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.
Now is a great time to prune out overwintering egg masses on various ornamentals.
Sliver-barnds of overwintering egg masses of Eastern tent caterpillar can be found clinging to small twigs of Prunus, Malus and Crataegus and area easily seen glistening in sunny days.


Photo of brown, fuzzy egg masses of Gypsy moth

Fuzzy, brown egg masses of Gypsy moth on Colorado spruce

Brown, fuzzy egg masses of Gypsy moth can be found on undersides of branches and trunks of several species of trees and shrubs including Quercus (oak), Fagus (beech), Ulmus (elm), and also Picea pungens (Colorado spruce).
Viburnum leaf beetle egg masses can still be pruned out and destroyed at this time (where leaves haven’t begun to emerge yet), to avoid destructive populations this spring. Look for raised bumps on the undersides of 1 and 2-year-old twigs. The bumpy caps can be picked off to reveal the yellow eggs underneath. Monitor these eggs as they will hatching into larvae as foliage emerges. 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).


Filbert blight Cankers on Cornus avellena from: torontogardens.blogspot.com

Monitor ornamental Corylus sp. for signs of Filbert Blight. This is a fungal disease that causes rows of small, black, crescent-shaped cankers along dead stems. Remove cankered shoots, 20-30 cm behind visible cankers, when plants are dormant. Disinfect pruning shears between each cut. Do not prune once new growth starts emerging. Corylus avellena ‘Contorta’ is particularly susceptible. Spray fungicides to protect new growth, starting at bud swell to bud break. Registered fungicides for this disease include: Copper oxychloride 50, Copper Spray and Flint (Compass).


The 2013 Crop Protection Guide for Nursery and Landscape Plants (publication 840) can now be found at: http://www.omafra.gov.on.ca/english/crops/pub840/p840order.htm
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 http://www.dkbdigitaldesigns.com/clm

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
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