VARIOUS ORNAMENTALS:
Winter desiccation is evident on many evergreens this spring. Drying winds and warm, sunny days in late winter caused foliage to lose water. Because the ground was still frozen, roots could not replenish lost water from the foliage and the foliage dried out and became 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.
Where nursery stock continues to be maintained in a polyhouse, caution should be taken when applying pest control sprays. Temperatures in the polyhouse can spike on clear sunny days, causing the chemical to injure foliage. Ventilation holes should be cut to keep high temperatures and high humidity at bay. High humidity has been linked to distortion and stunting of new growth on vines and shrubs and should be addressed where these symptoms have been observed. 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 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 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.
Low temperature injury is quite common on new growth of Euonymus in the spring, even if air temperatures dont fall all the way down below 0oC. The new growth on broadleaf evergreens is especially sensitive to low temperature injury. Where broadleaf evergreens are putting out new growth in the field or in uncovered container beds, consider protecting new growth from low temperature injury (air temp 2-3oC and below). Methods of preventing low temperature injury include night time watering, copper applications and removing cold air masses through air circulation (fans). Low temperature injury damage foliage appears water soaked in the 24 hour period following the low temperature event. Tissue then turns brown or brown-black and falsely resembles disease. The damaged tissue may come under attack by weak fungal and bacterial pathogens (Pseudomonas bacteria, Colletotrichum anthracnose), giving a misdiagnosis of the original cause of the problem.
If you are bringing in SOD (Sudden Oak Death, Phytophthora ramorum) host nursery stock from high risk areas, you may want to monitor for SOD symptoms. Camellia, Rhododendron, Viburnum, Pieris, Kalmia and Syringa are considered to be high risk host genera, as they are most common genera found positive for SOD in retail and wholesale nurseries. Fungicides registered for SOD in nurseries include: Acrobat 50 WP, Chipco Aliette WG and Subdue Maxx.
For a complete list of SOD regulated hosts, read more here.
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 Heterohabditis bacteriophora (H.b.). This should result in a significant reduction in populations in under 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 2 weeks following application. In the LANDSCAPE and GARDEN, check for overwintered LARVAE of black vine weevil on Rhododendron, Taxus, Thuja, Euonymus etc. in the garden. Where soils are cold and moist you can try an application of nematodes (Steinernema kraussei, NemasysL) to help reduce the population of larvae in the next few weeks.
Take a look at the roots of stressed out sod and field grown ornamentals and look for populations of European chafer, May/June Beetle larvae and other white grub species in the soil. Only preventative applications of pesticides 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.
DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:
Monitor ornamental Corylus sp. for signs of Filbert Blight, NOW IS THE TIME TO PRUNE THEM OUT. This is a fungal disease that causes rows of small, black, crescent-shaped cankers along dead stems. Corylus avellena Contorta is particularly susceptible. Remove cankered shoots, 20-30 cm behind visible cankers, when plants are dormant. 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).
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 summer.
Black knot is easy to see on Prunus sp. (cherry) at this time. Monitor gardens and adjacent wild areas for Prunus shrubs and trees for large black knots on previous years twigs. If you have the time to prune, prune the cankers out quite close to the main stem BEFORE LEAVES EMERGE. 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 Maestro. More information.
Applications of horticultural oil should be carried out in the coming weeks (daily temperatures between 4oC and 12oC are ideal). Timing of dormant oil applications are critical since freezing temperatures, mixing with sulphur and applying at the dormant-rate on actively growing tissue may result in injury. Apply dormant oil on clear mornings to facilitate rapid drying. The oil provides a barrier that restricts both respiration and movement of overwintering insects. It is quite effective for the management of overwintering spruce gall adelgids, scales and mite eggs (including spruce spider mite, European red mite, maple spider mite on silver/red hybrids). Keep in mind that most of these insects overwinter on the undersides of leaves and twigs. Since the oil droplets come out of solution so easily, frequent agitation is VERY important during application. Some plants listed as sensitive to dormant oil applications include: Japanese maple, red maple, sugar maple, hickory, walnut, blue junipers, blue Colorado spruce, white pine, red oak, and to a lesser extent: yew and cedar.
The nymphs of many scale insects have overwintered on twigs and are visible at this time. Heavy infestations can be pruned out and destroyed where possible (or use horticultural oil). Some species of scale to monitor for include: Magnolia scale, Fletcher scale, Euonymus scale, golden oak scale, fruit Lecanium scale and juniper scale.
Remember the maple spider mite (Oligonychus aceris) injury you saw on the silver-red maple hybrids last year? The tiny, red, overwintering eggs of those maple spider mites can be found on the leaf scar, just below the bud for this years growth, on last years twigs. The mite eggs are tiny flat, red spheres and are just barely visible, you will need a hand lens to see them. Where populations caused damage last year, applications of horticultural oil prior to leaf emergence should help smother eggs and reduce the population.
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, a little later on. Adults will be laying eggs on buds in early spring (reddish eggs on buds and new leaves). Recent research in Oregon suggests that 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.
Manually remove and destroy the egg masses of Eastern tent caterpillar where they are still dormant. The egg masses appear as swollen, shiny grey bands around small twigs of cherry, crabapples and hawthorns. They actually glisten in the sunlight. The larvae form tents in branch crotches and can cause severe defoliation where populations are high. Larvae will be hatching very soon in SW Ontario (just as the Norway maples are starting to bloom and forsythia is blooming) and the small tents are easily removed by hand.
Gypsy moth egg masses can be scraped off and destroyed at this time. The egg masses appear as raised, buff coloured fuzz on tree trunks, fence posts, buildings and other sheltered locations. When populations are high, you can find them on almost any overwintering object, even on leaf litter! When larvae begin to emerge, 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 will help prevent females from laying eggs above sticky bands and will attract males to the sticky surface. Extremely high populations of egg masses were noted in the Great Lakes region, including Toronto and Mississauga last year. Rainy weather last June helped spread diseases that kill GM larvae before they pupate, but there is still a residual population in many areas.
Viburnum leaf beetle egg masses can still be pruned out and destroyed at this time, 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.
EVERGREENS:
Where the Cornelian cherry dogwood (Cornus mas) is not blooming yet, the overwintering nymphs of pine bark adelgid are susceptible to chemical control. Avoid horticultural oil applications on (white pine) foliage as it can cause discolouration, direct sprays to the bark. Nymphs will be laying eggs in the coming weeks and those young nymphs are susceptible to pesticide applications (Malathion, Orthene, Tristar) until their white, waxy covering has developed (2nd nymphs at 32-340 GDD Base 10oC).
Overwintering pine weevil adults will be starting to emerge from leaf litter and mate on young twigs of pine in the next few weeks. 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. In SW Ontario, white pine weevil adults will be active when the Forsythia are in full bloom.
Cooley spruce gall adelgid and eastern spruce gall adelgid overwintering females appear as tiny (youll need a hand lens to see them), grey/blue fuzzy spots at the base of buds, on the undersides of twigs. They are just barely visible with the naked eye. 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 buds start to swell. Target pesticide applications to the undersides of shoot tips. Use wettable powder formulations on blue spruce to prevent foliar discolouration.
Monitor for eggs of spruce spider mite on conifers with a history of mite damage. Spruce spider mite eggs appear as very tiny, round, reddish-brown spheres that adhere to the UNDERSIDES of twigs and foliage this time of year. You will require a hand lens to see them clearly. Monitor lower branches, this is where most of the feeding damage is done. These eggs are susceptible to dormant oil applications in the next few weeks, where temperatures permit and plant species are not sensitive.
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 stem mothers (nymphs) will be developing later this month. The tiny, bluish grey aphid stem mothers can be found on terminal buds. Apply Diazinon, Malathion and Tristar on warm days (55 to 78 GDD Base 10oC) to target these stem mothers (before the bud caps loosen off).
Photos:
Pine shoot beetle adults have emerged. 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 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.
