Lots of hairy caterpillars can be found feeding openly on foliage of nursery and landscape ornamentals this time of year. Above you will see Hickory tussock Moth (Lophocampa caryae, Family: Erebidae left photo) and the very common Virginian tiger moth (Spilosoma virginica, Family: Erebidae, Subfamily Arctiinae, right photo). Try to avoid the Hickory Tussock moth larvae if you can, the hairs can cause itchy skin rashes on some people.
Magnolia scale females have given birth to live young, and these tiny, dark crawlers have started to venture out to feed on twigs. In the landscape, insecticide applications (e.g. insecticidal soap, horticultural oil, or traditional insecticides) can be used if you are trying to manage the crawler stage of this pest.
Pick off scales to reveal dark grey crawlers (eggs with legs) underneath. Many crawlers will hide underneath the female scales for days before they venture out, meaning they are protected from insecticide applications in the first couple of weeks.
The crawlers will gradually emerge out from under the dead female mothers. Contact insecticides (traditional insecticides, insecticidal soap, horticultural oil) can be used to manage crawlers once they emerge and start feeding on twigs (mid-late August).
If you miss the Magnolia scale crawlers, don’t worry. They overwinter as tiny, dark grey nymphs on the undersides of twigs. It is advisable to go in with a fall horticultural oil sprays (with emphasis on contacting undersides of twigs) to significantly reduce the population in late October. Many horticulturalists say that fall dormant oil applications are the BEST way to manage this pest issue.
Plant Phenology indicators this week.
Solidago canadensis in early bloom; Sorbus aucuparia with fruits turning from yellow to orange; Hydrangea paniculata ‘Grandiflora’ and Hibiscus syriacus (full bloom). This puts us at 1000-1150 GDD Base 10oC depending on location.
2019 OMAFRA publication 840, Crop Protection Guide for Nursery and Landscape Plants. It contains important information on managing nursery and landscape pests and weeds. Save it on your mobile device! Print it and have it in your vehicle! To view the pdf, click HERE.
Are you seeing webbing around the ends of branches on deciduous trees such as ash, birch, walnut and cherry? Look inside the webbing and look for yellow, fuzzy caterpillars. These are fall webworm caterpillars and they usually start to become more noticeable on the ends of branches this time of year. Prune out nests and destroy them to prevent future generations from infesting your trees. Pole loppers are an awesome tool for managing fall webworm caterpillar nests! Spot spraying with B.t. (e.g. Dipel) may be effective.
Have white grubs been an issue in your nursery or landscape? Preventative applications of Acelepryn are registered to help protect nursery crops from this pest and they are effective any time the larval stage is present in the root zone. Intercept applications should be finishing up by now. ALSO: Beneficial nematode applications for white grubs in the landscape (e.g. European chafer) are very effective at this time where treated soils can be kept moist.
Japanese beetle adults are still flying and feeding on leaves of woody plants (Betula, Syringa, Tilia, Ulmus, Prunus, Rosa). Look for metallic, coppery-green beetles with white tufts of hairs along the edge of their abdomens. Populations are low-moderate in a lot of areas across southern Ontario this year.
Adulticide insecticides for JB in the nursery include BeetleGONE and Imidan. Pheromone traps for JB are actually a little too good at attracting the adults. Always place traps far away from susceptible host trees and shrubs (e.g. Betula, Rosa, Prunus, Tilia, Syringa, Ulmus etc.).
DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:
We have seen a lot of powdery mildew on deciduous flowering shrubs (Amelanchier, Rosa, Physocarpus, Quercus) and herbaceous perennials. Monitor for white, powdery residue on the tops and bottoms of leaves. Protect new foliage with fungicide applications [e.g. Switch, Milstop, Regalia (biofungicide), Tivano]. Where the disease pressure is moderate to high, fungicides are not going to be very effective. It is getting a bit late in the season for managing this disease. Powdery mildew ovewinters on fallen foliage, remove infected foliage out of gardens, collect and dispose to minimize disease next year.
What a banner year for mites! Two-spotted spider mites (TSSM) are feeding on several types of deciduous woody (Viburnum and Spiraea and many deciduous flowering shrubs and perennials in container production). Look for chlorotic leaves with stippling, use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs. These mites are small but the damage is significant so catch them early. Miticides registered for this mite in the greenhouse include: Sanmite, Vendex, Kanemite, Floramite, Avid. In the greenhouse, biocontrol agents should be brought in to coincide with the first sign of TSSM. Phytoseiulus persimilis is a predatory mite that feeds on TSSM when temperatures are below 26oC and it is a good choice when TSSM populations are low-moderate. Amblyseius californicus is a predatory mite that can be brought in ahead of TSSM appearance (because it can find other sources of food). Stethorus punctillium is a new beetle that is a good predator of TSSM.
There are lots of mites feeding on deciduous trees, Acer, Ulmus, Fagus, Quercus, Malus and shrubs (Amelanchier, Rosa, Spirea etc.). Usually damage this time of year is inconsequential for tree health. However some mite species (e.g. Oligonychus sp. on Acer, Quercus) overwinter as eggs on the host plant, making fall horticultural oil applications a must where populations are high.
Taxus or Fletcher Scale NYMPHS have settled on needles and twigs and are feeding. As they become older, they are more difficult to kill with insecticides. Several contact and systemic insecticides are registered for this pest in the nursery.
Monitor for Black vine weevil ADULTS in the FIELD and LANDSCAPE for Rhododendron, Taxus, Thuja and Euonymus. Mark your calendar for September 7 to make applications of nematodes against the larval stage of this pest. Strawberry root weevil can also be a problem in field production of evergreens, adults are still active. Signs of strawberry root weevil adults include brown, flagging shoot tips (and small girdling marks at the base of the flagged shoot) on Thuja (eastern white cedar). To scout for adult weevils, place a tarp or large piece of card board under the tree, shake branches vigorously and look for brown-black weevils “playing dead”. Insecticides for adult weevils in the nursery include Flagship, Silencer, Met 52. Remember, adult weevils feed at night (nocturnal). Spray insecticides at night to target adult feeding and reduce UV degradation (e.g. Pounce, Scimitar).
Is your evergreen Euonymus fortunei infested with Euonymus scale? Look under the brown, female Euonymus scale shells to see what development life stage they are at. Orange, fleshy bags under the scale shell are immature females (which will persist into 2019) (Photo: Melissa Huntley). Tiny, orange crawlers (eggs with legs) can also be seen at this time. The crawlers are susceptible to several insecticides, including insecticidal soap, the summer rate of horticultural oil as well as traditional insecticides (in the nursery only, including Kontos). Apply insecticides 2-3 times, about a week apart to smother successive crawlers of this pest.
Cedar leaf miner (CLM) next generation larvae are starting to feed on tender new foliage. A light sheering of tips in mid-late August should give good knockdown of this next generation of CLM larvae. Cygon is also registered as a foliar application for CLM larvae in early August in the nursery.
Monitor for nymphs and adults of spruce spider mite 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. Click HERE for a short video. Miticides registered for SSM include Floramite and Kanemite. Miticides may be required where pest pressure is moderate to heavy (container grown conifers with overhead irrigation). Populations in field production and in the landscape usually become even more active when the cooler weather returns in September. A lot of damage can occur in Sep-Oct-November so keep monitoring spruce spider mite populations in the nursery and treat where you find >10 mites per branch shake.
American Goldfinches are one of the latest breeding songbird species we have in Ontario, likely due to their fondness for thistle seeds and seed wings. You may be interested to know that they feed almost exclusively on seeds (where as other species will feed on insects when they are breeding). Keep your bird feeders well-stocked to help support one of our sweetest songbirds this month!