Gypsy moth larvae have donned their yellow heads and are much longer than 2.5 cm…..which means they are no longer susceptible to the biocontrol Bacillus thuringiensis (B.t./Dipel/Foray). Success naturalyte insecticide can be used to reduce populations of larvae, as well as other traditional insecticides such as those containing permethrin. Many parts of southern Ontario have some heavy pockets of larval feeding this year. Larvae will feed for another 7-14 days and then pupate on trunks and under large branches. Homeowners can manually destroy larvae (or flick larvae into a bucket of soapy water) during the day when many of the larvae can be found resting in groups on trunks. Tree bands can help reduce larvae from travelling up and down the stem each day.
Some ingenious horticulturalists install burlap skirts around tree trunks to attract resting Gypsy moth larvae, where they can be easily collected and destroyed. (photo courtesy: Meadowood Tree Service).
Have you seen fuzzy caterpillars with tufts of white hairs on their backs feeding on ornamentals in the nursery or landscape? They might look cute but they do A LOT of damage if there are groups of them. They are white-marked tussock moths (Orygia leucostigma). They can be found feeding on some of your favorite deciduous shrubs and trees. Where large groups can be found, try foliar applications of Bacillus thuringiensis (B.t., Dipel). B.t. is a biological insecticide that kills caterpillars after they ingest it by feeding on treated foliage. It does not harm other types of insects. Caterpillars usually die 2 or 3 days after ingestion.
Look for larvae (10-15 mm long) of Yellow-headed spruce sawfly feeding on tender new needles of spruce (e.g. Colorado spruce). When they run out of new growth, they will move to older needles in the landscape. Larvae are green with lighter longitudinal stripes, yellow-brown heads. There are several insecticides registered including Dragnet, Dylox, Pounce and Success to target young larvae. This is a damaging pest of spruce in the GTA and has caused significant damage to spruce trees in the landscape. Remember, Sawflies have Six or more pairs of prolegs! And they aren’t susceptible to B.t/Dipel/Foray.
Honeylocust plant bug NYMPHS and ADULTS are plaguing Honeylocust trees in urban areas. The tiny, green plant bugs will fall off the foliage if you give the branch a little shake over a light surface. In the landscape, treat nymphs with Insecticidal Soap to reduce populations. Adults are very mobile and much more difficult to contact with insecticides. Overlapping life stages exist at this point, management with insecticides is more difficult than it was during leaf emergence (put a note in your calendar for May 7, 2021!).
Potato leafhoppers NYMPHS and ADULTS are still feeding on woody nursery stock on the newest growth. 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. Older, hardened off foliage will become flecked from leafhopper feeding, but it is minor.
Monitor populations and treat NYMPHS with insecticides when new foliage is emerging. Potato leafhoppers are also attracted to yellow sticky cards, for monitoring. Registered insecticides include Tristar and Altus, Actara/Flagship.
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. Migrating potato 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? Look up to see tiny, bullet-shaped shadows of the Emerald ash borer. 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.
One of the most persistent scale insect pests known to horticulturalists, the Euonymus scale (Unaspis euonymi). It is a tiny little armored scale that covets evergreen Euonymus fortunei in the garden or landscape. Adult females have a brown cover that resembles a brown oyster shell. The smaller males have a white, narrow cover and they resemble white flecks with the naked eye.
The good news is, the most susceptible life stage, the Euonymus scale crawlers, have hatched and are starting to colonize feeding sites on new shoots. The tiny little orange crawlers can be found on shoots and leaf undersides. Crawlers look like “eggs with legs”. In the landscape, crawlers can be managed with the summer rate of horticultural oil and insecticidal soap.
Once they settle (above), Euonymus scale crawlers lose their legs and become “nymphs”. They also become a duller orange-brown. They become more ridged looking and enlarge as they grow while sucking plant juice from the mouthparts on the under side of their heads.
In the nursery, Euonymus scale crawlers and newly settled nymphs are susceptible to insecticides, including insecticidal soap, the summer rate of horticultural oil, Lagon and Orthene. Kontos is a new insecticide for Euonymus scale that can also be used as a container soil drench (a great alternative to foliar spraying).
The dead adult (above) scales will often persist on stems and leaves, long after they have died…giving the plant an appearance of severe infestation. Usually the dead scales are washed off by rain over time. Applications of water or the summer rate of horticultural oil may help speed up that process. A second generation of crawlers usually appears about 6-7 weeks after the first, depending on how warm their location is. So mark your calendars appropriately for a second generation around the second week of August.
Where Fletcher scale (taxus scale, Parthenolecanium fletcheri) has been a problem in the past, monitor for dark brown “bumps” on twigs and needles of Eastern white cedar (Thuja occidentalis) or yews (Taxus spp.).
Pick off the brown Fletcher scales and look for white grain-like eggs. You will see eggs in container grown hosts at this time, and perhaps a few crawlers starting to hatch. In the field and landscape, eggs laying is still on-going.
Some of those Fletcher scale eggs will have “legs” (crawlers) (click here for video) and will be looking for tender new growth to feed on.
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 starting to show up on several deciduous and herbaceous plants, especially in container production. Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs.
Two spotted spider mites are small but the damage is significant so catch them early on crops of historical mite significance. Miticides registered for this mite in the greenhouse 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).
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 June:
Here’s a really cool songbird that you’ve probably heard before, but likely never seen. The coy little Warbling Vireo is getting to be a common singer on the edges of forests, most notably near water. They are very good at hiding behind foliage, high in the tree tops, making it difficult to identify them. Make it easy on yourself, most birds can be identified by their song and various call notes. I learned by listening to Walton & Lawson’s “Birding By Ear”. CLICK HERE to listen to the warbling vireo’s song. (Photo credit: Missouri Dept Conservation).