Ontario has seen moderate-high levels of Gypsy moth (Lymantria dispar) infestations on several deciduous trees (Betula, Quercus, Acer, Celtis, Tilia etc.) with hungry larvae (photo above: Dave Cheung) causing severe defoliation in some cases. Irrigation during the continued heat wave will be more important than ever this month to help defoliated trees put on a new set of leaves. Even complete defoliation can be tolerated by most healthy trees. Usually we see some rainy periods during larval feeding, supporting natural pathogens of the caterpillars…but this year was so dry….naturally occuring larval disease incidence was low to non-existent, increasing the likelihood of 2021 being another banner year for Gypsy moth. Parasitoid wasps of GM eggs are our best hope for seeing some relief from this pest next year.
Sticky bands around trunks during the July flight period will help trap flightless adult female Gypsy moths (above) and keep them from laying eggs on bark, trapping females will attract males to the sticky surface. Pheromone-baited sticky traps are also available to help reduce populations of adult males. GET YOUR TRAPS OUT NOW!
Magnolia scale adults are white and will be turning pink-orange in the next few weeks. They will producing dark-coloured crawlers under these protective shells, usually at the beginning of August. (Magnolia scale do not produce eggs but give birth to live young). As we get later into July, pick the scale shell off and look for juicy flesh as a sign that reproduction has not yet begun. Insecticides are not very effective at this time and won’t be effective until crawlers emerge from under mother scales in August. However, you can scrub the fleshy scales off the twigs at this time to give immediate management of this pest. In late September-mid-October, treat infested trees with horticultural oil for excellent management of this pest.
European elm scale (Gossyparia spuria) crawlers will be hatching soon, look for tiny bright yellow nymphs on new twigs of elm (e.g. Camperdown elm ). Adult females are 2 mm long (tiny), oval, brown with a whitish fringe around their body. This can be an injurious pest on elm, we often see copious amounts of sooty mold and twig dieback. You can also scrub this scale insect off of the twigs. This pest is also very vulnerable to dormant horticultural oil applications in late fall/early spring when no leaves are present. The overwintering nymphs migrate to the bark crevices at the end of the growing season.
Have white grubs been an issue in your nursery? Preventative applications of Acelepryn (chlorantraniliprole) and Intercept (imidacloprid) are registered for white grubs (nursery production) and July is a good time to use these products (during the adult flight period). [Beneficial nematode applications for white grubs (e.g. European chafer) will be effective in early-mid August where there is regular irrigation available to keep soil moist and support nematodes]. GrubGONE (Bacillus thuringiensis var Gallerae is also registered for the larval stage of white grubs).
Potato leafhoppers NYMPHS (photo above) and ADULTS are still feeding on deciduous trees on the newest growth. Now that the second flush of leaves have hardened off, potato leafhoppers can’t do much more than cause minor leaf flecking and so management techniques are no longer required.
Monitor for potato leafhopper on nursery crops such as maple, elm, and hackberry (Acer, Ulmus, Celtis). Leafhoppers (and aphids) suck plant sap from soft, expanding foliage and cause foliage to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed. We can sometimes see this in the landscape, and this year is no exception.
<img class="" src="http://dkbdigitaldesigns.com/clm/sites/default/files/imagecache/Image_node/images/CLM-_5.jpg" alt="Empoasca fabae (Potato Leafhopper) nymph.” width=”319″ height=”220″><img class="" src="http://dkbdigitaldesigns.com/clm/sites/default/files/imagecache/Image_node/images/CLM-3065.jpg" alt="Empoasca fabae (Potato Leafhopper) adult.” width=”329″ height=”219″> Potato leafhopper Nymphs (left) are about 2 mm long and scuttle SIDEWAYS, rather quickly, across the leaf and to the other side (they don’t have wings to fly away). Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source). Older, hardened off foliage is not usually as susceptible. Leafhopper adults (right) are winged, very mobile, tiny, pale yellow-green jumping insects that are easily disturbed when you approach infested foliage. It almost looks as though they are being flicked off of the foliage.
Seeing ash tree with dieback, vertical bark cracks and d-shaped exit holes? Emerald ash borer is the cause. Injectable insecticides may be used to protect ash trees from new infestations of Emerald Ash Borer (Agrilus planipennis). Trees must be actively transpiring in order to maximize insecticide uptake into the cambium (clear, warm, sunny days). Registered injectable insecticide products include: AceCap 97, Ima-Jet and Tree-Azin. Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer at: http://www.omafra.gov.on.ca/english/crops/insects/eab-bbb-manage.htm. Emerald ash borer adults start to emerge when the black locust (Robinia pseudoacacia) are blooming.
Where Fletcher scale (taxus scale, Parthenolecanium fletcheri) has been a problem in the past, monitor for crawlers and early instar nymphs (photo above) on twigs and needles of Eastern white cedar (Thuja occidentalis) or yews (Taxus spp.). Some of those Fletcher scale crawlers (click here for video) and will be settling down on tender new growth and growing larger and browner and flatter for the rest of the summer.
Several insecticides are registered for management of Fletcher scale crawlers in the nursery (acephate, carbaryl, dimethoate, hort oil, insecticidal soap). Try insecticidal soap in the landscape. Careful, the summer rate of horticultural oil may be phytotoxic on some hosts, especially when temperatures are hot and humid > 26C.
Two-spotted spider mites (TSSM) are loving this weather and actively feeding on several deciduous and herbaceous plants, especially in container production, causing chlorosis and leaf flecking (photo above) on several deciduous and woody ornamentals.
<img width="455" height="302" class="" src="https://i2.wp.com/dkbdigitaldesigns.com/clm/sites/default/files/imagecache/Image_node/images/CLM-000120.jpg" alt="<a href="/clm/species/teranychus_urticae"><em>Teranychus urticae</em> Two spotted spider mites are small but the damage is significant so catch them early on crops of historical mite significance. Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs.
TSSM miticides include: DynoMite, Vendex, Kanemite, Floramite, Avid and Nealta. Apollo is registered in outdoor nursery crops to knock down the egg stage and newly hatched nymphs. 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).
<img class="" src="https://i0.wp.com/dkbdigitaldesigns.com/clm/sites/default/files/imagecache/Image_node/images/CLM-000157.jpg" alt="Oligonychus aceris (Maple Spider Mite) adult on maple.” width=”342″ height=”227″> Monitor for nymphs and adults of maple spider mite on red and silver maples with a history of mite damage. Maple spider mite nymphs and adults are brown with black backs and found on the undersides of foliage this time of year. Populations are usually only minimally damaging on foliage. Miticides may be required where pest pressure is heavy (container grown trees with overhead irrigation). Miticides inclue Vendex, Floramite and Kanemite.
Birding Tip for late July:
Unlike other song bird species, American goldfinches (Spinus tristis) have been waiting all these months to breed. They actually don’t nest until July when milkweed, thistle, and other plants have produced their fibrous seeds, which goldfinches incorporate into their nests and also feed their young (above photo: female goldfinch on Canada thistle from thebackyardnaturalist.com). Goldfinches are strict vegetarians and will not feed on plant pests, unless one flies into their mouth. You may find them to be a little outgoing these days, allowing you to watch them more closely as they tug away on seed heads. They were tugging on the seed heads of the Cosmos in my garden this week while I sat just 8 feet away!