May 24 long weekend is here! Although it may not be our provincial bird, the common loon has a signature call that is well known and often tied to fond memories of camping and cottaging (Photo: Radio Canada). This bird is no stranger to cold water and cold temperatures that often characterize Ontario springs. The cool temperatures have extended leaf emergence of many woody ornamentals, which is not good. When coupled with wet conditions, a prolonged leaf emergence period can lead to increased leaf diseases (e.g. apple scab). Leaf diseases are really starting to make themselves known in the landscape and nursery.
Plant Phenology indicators this week, Hamilton/Niagara/GTA/London: Plant Phenology Indicators: GDD Base 10C: 90-110
- Acer platanoides (Norway maple, late to finishing bloom)
- Acer saccharum (sugar maple, fruit development, leafing out)
- Amelanchier spp. (serviceberry, full to late bloom)
- Spiraea vanhoutei (bridal wreath spirea, mid-bloom)
- Syringa vulgaris (common lilac, mid bloom)
- Prunus x cistena (purple leaf sandcherry, full bloom)
If you are referring to the Phenology and Monitoring tables in OMAFRA publication 841, Guide to Nursery and Landscape Plant Production & IPM, look at the Tables starting with 2-3 on pg. 39. This puts us at about 90-110 GDD Base 10C in areas south of Hwy 9. Areas in the southwest corner of the province will be more advanced.
PLEASE NOTE: The Following Pesticide Recommendations are meant for Exception Uses (e.g. agriculture-nursery production or trees in the landscape) 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. Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests.
CONTAINER PRODUCTION NURSERIES-
In production nurseries where black vine weevil larvae are a problem in container crops (e.g. perennials, evergreens), monitor containers for larvae and pupae. Treat soils with Heterohabditis bacteriophora (H.b.) or Met52. This should result in a significant reduction in populations in under two weeks. Order your nematodes in advance. Since Heterohabditis nematodes require moist, warm soil, we find that they work best in container production. Met52 can also be applied preventatively at potting.
Monitor boxwood foliage for boxwood psyllid nymphs as the Cercis canadensis begins to bloom, Acer platanoides are in late bloom and Magnolia x soulangeana are dropping petals. Boxwood psyllid eggs hatch just as buds are starting to break and expose tender new shoots. Psyllid nymphs are yellow-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.
Where dogwood (Cornus spp.) has had issues with fungal leafspots (e.g. Septoria) in the past, protect emerging foliage with fungicides before precipitation or irrigation events as the Amelanchier sp. and Cercis canadensis are blooming. Leafspots are often circular or angular with a bright purple border, making shrubs look unsightly by early summer.
In container nurseries, where Pseudomonas blight on lilac (and other deciduous shrubs) was a problem last season, you may want to consider an application of copper as they bud out. 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. Or uncover crops earlier, when they are still dormant. Plants will outgrow this damage with the next flush of growth.
DECIDUOUS WOODY AND HERBACEOUS PERENNIALS- Field & Landscape
Birches with a history of bronze birch borer infestation should have been pruned by now to prevent spread of this pest. Its a good idea to avoid pruning susceptible birch (especially Betula pendula) when the black locust trees are blooming (emergence of adults) to prevent extra attraction of these borers. 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.
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, IMA-jet and Tree-Azin. 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. It is a good idea to avoid pruning susceptible ash trees when the black locust trees are blooming (emergence of adults) to prevent extra attraction of these borers.
The Asian Long Horned Beetle was detected in the vicinity of Pearson International Airport in Toronto/Mississauga and efforts are continuing to eradicate this beetle from the area. The Asian Long-horned Beetle Infested Place Order is being enforced in the area encompassing: all parts of the City of Toronto and City of Mississauga, in the Province of Ontario, located within the area commencing at the point of intersection between Dixie Road (formerly Hwy. 4) and Derry Road (formerly Hwy. 5) and proceeding northeastward along the south side of Derry Road to Bramalea Road. 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 not move out of, or through, this area.
Take a look at the roots of poor looking evergreens (Thuja, Picea, Pinus) and field grown ornamentals and look for populations of European chafer, May/June Beetle larvae and other white grub species in the soil. Sandy soils are especially hospitable to white grub species. 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.
Boxwoods in the landscape not looking so good coming out of the winter? Are you seeing a lot of yellow leaves? Can you see any yellow-green spots?
Carefully break open the leaf with your knife or finger nail, look for tiny yellow larvae inside. These are boxwood leafminer larvae and they will be pupating soon. The tiny orange midge adults will be emerging out of these leaves when the new growth emerges. Adult midges will be laying their eggs on newly emerged leaves and those eggs will hatch into the next generation of leaf miners. Treating new foliage with insecticides just prior to or at the beginning of leaf emergence can help reduce successful egg hatch and leafminer establishment. You can also prune out new foliage in August and the clippings will desiccate, making it impossible for the leafminer to complete its lifecycle.
Where Ironwood trees (Ostrya virginiana) were infested with anthracnose spots last year, you may consider an application of broad spectrum fungicide (e.g. copper) as buds start to swell. The usual symptoms caused by this fungus, Apiosporopsis carpinea, are irregular necrotic spots ranging in size from pinpoints to 5-6 mm in diameter. They will increase in number and coalesce during the season and will cause marginal and apical browning, curling and leaf cast.
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: http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2003/03hrt03a4.htm
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).
Fireblight and Apple Scab….see post from May 3, 2017.
Where honeylocust podgall midge was a problem in the past, monitor trees for overwintered adult midges soon. 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). 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.
Where foliage is starting to emerge on honeylocust, monitor for newly hatched nymphs of the honeylocust plant bug. You can find them by shaking branches over a light coloured surface and examining it for fallen nymphs. By controlling the first generation of nymphs, you can really reduce the damage from this pest.
Eastern tent caterpillars have hatched and these black fuzzy larvae are feeding and making webby tents in branch crotches. The larvae can cause severe defoliation in May, where populations are high. 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 eggs are starting to hatch! The egg masses appear as raised, buff coloured fuzz on tree trunks, fence posts, buildings and other sheltered locations.
Gypsy moth larvae have begun to emerge (when trilliums are in bloom), some control can be achieved using Bacillus thuringienesis (B.t., 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.
Viburnum leaf beetle eggs are hatching and larvae can be found feeding on lower leaf surfaces. 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 egg casings underneath. 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).
Overwintered adults of Pine bark adelgid have laid their eggs. Look for the woolly masses on the bark of white pine, usually near buds. Pick open the woolly-ness with a pin and use a hand lens to find tiny, yellow-brown eggs. These eggs will hatch in the next week or two. Hatched nymphs can be managed with insecticides such as dimethoate and acetamiprid.
Look for yellow-brown nymphs of Fletcher scale (Lecanium fletcheri). The newly hatched crawlers in late June-July are more susceptible to pesticides but these overwintering scale nymphs may still be susceptible to registered contact and systemic pesticides. Where heavy populations are detected, spraying asap may help reduce damage and honeydew. These scale insects produce a lot of honeydew in June. Monitor Taxus (yew) and Thuja (eastern white cedar)
Monitor for Balsam twig aphid stem mothers near buds on fir, white spruce, Colorado spruce and juniper. The tiny, bluish grey aphid stem mothers can be found on terminal buds as they break.
Tap branches over a dark surface to see tiny whitish Balsam twig aphid stem mothers (use a hand lens to confirm id). 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.
Overwintering white pine weevil adults have finished mating and laying eggs on last year’s terminal leader (white pine, Serbian spruce, Colorado spruce). Monitor for small black/brown snout beetles around the foliage and in the duff layer below the canopy. Its getting late but an application of insecticide on last year’s leader may help reduce successful egg-laying and damage to this year’s leader.
Monitor for eggs (left), nymphs (right) and adults of spruce spider mite on conifers with a history of mite damage (Abies, Picea, Thuja). Spruce spider mite eggs appear as very tiny, round, reddish-brown spheres that adhere to the UNDERSIDES of twigs and foliage. YOU WILL REQUIRE A HAND LANDS TO SEE THEM CLEARLY. Monitor lower branches, on the North and Eastern side of the tree, this is where most of the feeding damage is done. Miticides will be effective when nymphs and adults are present.
Pine shoot beetle adults are laying their eggs. The tiny beetles take flight after 2-3 days where temperatures reach 10-12oC. 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 10C) 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.
Brown shoots on juniper may be a symptom of juniper tip blight (Kabatina blight). A small grey band or pinched grey canker can be found at the base of the infected shoot, this is where the spores come from. Where plants are still dormant, PRUNE OUT DEAD SHOOTS during DRY conditions (and remove shoots) to reduce disease spread. Disinfect pruning shears between each cut (e.g. rubbing alcohol, other sterilants) to reduce disease spread. 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 again in late summer. [Juniper tip blight caused by Phomopsis sporulates in early spring whereas that cause by Kabatina sporulates in late summer. ]
Dothistroma needle blight is a fungal disease affecting pines (Austrian, mugo). The fungus overwinters on infected needles and will sporulate during wet weather. Persistant cool, wet weather favours disease development. Where infestations are affecting plant health, protect emerging needles with fungicides (copper, daconil) until they are fully grown.