We recently cracked a case of stunted, distorted leaves and premature leaf drop on honeylocust this week….
Multiple cultivars were affected including many of the popular varieties growing in Canadian landscapes.
Several samples were taken and viewed under the dissecting microscope and voila, we finally caught them in action….eriophyid mites could be found feeding on the youngest foliage. Eriophyid mites are quite difficult to detect as they are less than 1 mm in length, are whitish-clear, carrot-shaped and have their legs all clustered around the head. Eriophyid mites are a relatively common mite in outdoor ornamentals and ONCE CONFIRMED, can be managed through cultural pruning and the application of targeted pest control products. We see them doing some minor damage on crabapple sometimes in the nursery.
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, especially when applied late evening.
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 white Hickory Tussock moth larvae if you can, the hairs can cause itchy skin rashes on some people.
Plant Phenology Indicators this week:
Solidago canadensis in early bloom; Sorbus aucuparia with fruits are orange; Hydrangea paniculata ‘Grandiflora’ flowers turning pink and Hibiscus syriacus (full to late bloom). This puts us at 1000-1200 GDD Base 10oC depending on location. (Keep in mind, there are several species of Solidago in Ontario)
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.
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 to enable nematodes to swim to their prey.
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. Although they came out pretty quickly in early July, 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.).
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. Landscape: Rhapsody, Milstop, Regalia (biofungicide), Tivano]. In the nursery, serveral fungicides are registered for this disease, check the Compendium of Pests starting on pg. 16 of the Crop Protection Guide for Nursery and Landscape Plants. Where the disease pressure is high, fungicides are not going to be very effective. Powdery mildew ovewinters on fallen foliage, remove infected foliage out of gardens, collect and dispose to minimize disease next year.
Teranychus urticae (Two-spotted Spider Mite).” width=”638″ height=”424″>
What a banner year for mites! Two-spotted spider mites (TSSM) are feeding on several types of deciduous woody (Viburnum, Hydrangea, Sumbucus and Spiraea and many deciduous flowering shrubs and perennials, especially 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 and Nealta. 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.
For more information on MITES of NURSERY AND LANDSCAPE PLANTS check out my post: 2020 – The Year of the Mites
Taxus or Fletcher Scale NYMPHS have settled on needles and twigs and are feeding. As they become older, they produce protective layers of waxes over their bodies and become more difficult to manage 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 if more of a problem in field production of evergreens, adults are still active.
Signs of strawberry root weevil adults include brown, flagging shoot tips (and small chewed or girdled stems at the base of killed (flagging) shoots) 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. 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 in. Orange, fleshy bags under the scale shell are immature females in container production (which will persist into 2021, above photo: Melissa Huntley). A few tiny, orange crawlers (eggs with legs) may be seen at this time, but most of the population exists as settled nymphs (orange-brown) in the landscape. The crawlers are susceptible to several insecticides, including insecticidal soap, the summer rate of horticultural oil as well as traditional insecticides (in the nursery there are several products, including Kontos).
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.
Have you noticed American Goldfinches are a little less shy these days? I have had them just 1 metre away, snacking on our the seed heads of our Cosmos, as we sit quietly in our garden. Goldfinches are raising their young right now and need all the seeds they can find! They are strict vegetarians. Keep your feeders stocked of black sunflower seed and nyger seed! (Photo by the Amazing Elizabeth Klisiewicz!)