Rain is in the forecast for much of southern Ontario for the next 24 hours. There is a chance of thunderstorms in some areas. This is FANTASTIC weather for shopping at the local garden centre and watering in newly planted landscapes.
DECIDUOUS WOODY AND HERBACEOUS
Dutch Trig is available for Dutch Elm Disease on Ulmus americana species in Canada. This injectable treatment contains a biological organism that induces a plant immune response to help stimulate the tree’s defense mechanisms for fighting off DED infections. Arbotect-20-S (thiabendazole) is the registered injectable fungicide treatment. Injections should be made on sunny days during leaf emergence to maximize uptake.
Aphids are starting to show up on the newest growth of 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.
In early spring we often see the black bean aphid (Aphis fabae) on deciduous flowering shrubs and Euonymus.
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 often see aphids first on Euonymus alatus and Spiraea this week.
Now is the time to order your pheromone lures and sticky wing traps for Peach tree borer and Viburnum Borer. Are you seeing sparse foliage and dieback on your ornamental Prunus? Peach tree borer (Synanthedon exitosa) larvae can be found just inside the bark of stems at/below the soil line of ornamental Prunus at this time. Look for cankered regions and chewed bark/wood in the lower stems of Prunus (Prunus x cistena) as a sign of larval damage.
The clearwing moths that emerge in a few weeks time resemble wasps. Adults are very much attracted to sticky wing traps that are baited with peach tree borer pheromones. Place pheromone traps out in early-mid June (approximately 390 GDD Base 10oC, ‘Red Prince’ Weigela in full bloom) and monitor for peak flight of adults. You can expect peak egg hatch around 10-14 days later, if you are thinking of treating newly-hatched larvae. The same ‘clearwing moth’ pheromones and traps can be used to monitor for Viburnum borer. Viburnum borer chews the stem (at and below the soil line) and causes significant injury to container grown Viburnum. Viburnum borer will be starting to emerge in container production in a few weeks. To purchase traps, try ordering from IPM suppliers such as http://www.naturalinsectcontrol.com and Plant Products. Some growers are trying soil drench applications of beneficial nematodes (Steinernema carpocapsae) after peak adult flight, as a biological way to control hatching larvae. We have seen some pretty good suppression of clearwing moth borers using nematodes as a drench!
Monitor for needlecast and blight diseases on older foliage where new foliage is emerging on pine and spruce. Diplodia tip blight on 2 and 3 needled pines and Rhizosphaera needlecast (see photos above) 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 can also be found on spruce and 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. 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 so management can be difficult.
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. Nymphs will be feeding and producing copious amounts of honeydew in the next few weeks.
Spruce budworm (Choristoneura fumiferana) is feeding on the new needles of trees in the SW. In spring, the overwintering larvae feed on male flowers and may mine buds and needles. Older larvae feed on expanding shoots, destroying them before they can fully elongate. The small, green larvae are detected by the small patches of browned foliage that have tiny nests made of shoots wrapped together by silk. Larvae can cause defoliation and also browning of the needles. B.t. (Dipel) is an excellent biological insecticide for suppressing spruce budworm populations in mid-late spring (spray foliage in the evening).
Monitor for eggs and the first generation of Euonymus scale crawlers in container production, they should be hatching in the next couple of weeks. Euonymus scale look like tiny white (males) and brown, sea-shell (females) flecks 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. Lower toxicity options inlclude insecticidal soap and the summer rate of horticultural oil.
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.
Monitor for Spruce spider mites as buds are breaking, nymphs and adults will be feeding on new growth. Miticides registered for SSM include Floramite and Kanemite. Miticides may be required where pest pressure is moderate to heavy.