Plant and Insect Development is 2 Weeks + Ahead of Last Year!

Dead Gypsy moth Larva hanging from leaf mid vein, killed by virus

Is this a Gypsy moth larva doing yoga? NO! Its the symptoms of infection by a naturally occuring Nucelar Polyhedrosis Virus (NPV). We are starting to see larvae succumbing to NPV in infested forested areas, likely due to understory canopy buffering against wind and rain dispersal of NPV particles. They say one infected larva can be a source of as many as 1 Million virus particles! Thanksfully, NPV is specific to Gypsy moth.

NPV-infected Gypsy moth larva, note the inverted “V” shape to the cadaver.

               Larval disintegration by NPV, late stage.  We are expecting to see more and more infectections of NPV showing up, but will it be enough to cause significant knockdown of the population?  We are also expecting to see infection and larval mortality from Entomophaga maimaiga, a fungal larval pathogen.  The fungus is more common after rainy periods.  Get your rain dance on!

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 subsp. Kurstaki (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 record-breaking pockets of larval feeding populations this year.  However, we are seeing different larval instars out there, some larvae are as small as just 1.5 cm long while others are 3.5 cm!  These stragglers may require an extra application of insecticide where populations are threatening plant health.

Larvae will feed for another 7-14 days and then pupate on trunks and under large branches and other immobile objects in the landscape.  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 intercept larvae from travelling up and down the stem each day.  KEEP YOUR MASK ON WHEN HANDLING LARVAE AND COVER UP, BODY HAIRS CAN CAUSE AN ALLERGIC REACTION IN SOME PEOPLE. 

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).

*Note: many of the pests found in ONnurserycrops blog can be found in BugFinder, the ultimate scouting app for woody plants in the nursery and landscape. Now available on Apple and Google Play. 

Image result for tussock moth  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.

<a href="/clm/species/pikonema_alaskensis"><em>Pikonema alaskensis</em></a> (Yellowheaded Spruce Sawfly) larva.<a href="/clm/species/pikonema_alaskensis"><em>Pikonema alaskensis</em></a> (Yellowheaded Spruce Sawfly) larva.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.

HLPBMonitoringJune_17_01HonLocPlantBugNymphWingBudsLateMayJLAHoneylocust 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 1, 2022!).

LHopInjury                    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.

<a href="/clm/species/empoasca_fabae"><em>Empoasca fabae</em></a> (Potato Leafhopper) nymph.<a href="/clm/species/empoasca_fabae"><em>Empoasca fabae</em></a> (Potato Leafhopper) adult.  Potato leafhopper wingless 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.

EAB adults casting shadows on leaves (Markham) EAB_EurAsh  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:  Emerald ash borer adults start to emerge when the black locust (Robinia pseudoacacia) are blooming.

<a href="/clm/species/unaspis_euonymi"><em>Unaspis euonymi</em></a> (Euonymus Scale) on euonymus.                          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.

<a href="/clm/species/unaspis_euonymi"><em>Unaspis euonymi</em></a> (Euonymus Scale) on euonymus.

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).

<a href="/clm/species/unaspis_euonymi"><em>Unaspis euonymi</em></a> (Euonymus Scale) on euonymus.  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.

<a href="/clm/species/parthenolecanium_fletcheri"><em>Parthenolecanium fletcheri</em></a> (Fletcher's Scale) adult and eggs.

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.

IMG_0196 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.

<a href="/clm/species/teranychus_urticae"><em>Teranychus urticae</em></a> (Two-spotted Spider Mite).  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).

<a href="/clm/species/oligonychus_aceris"><em>Oligonychus aceris</em></a> (Maple Spider Mite) adult on maple. 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.

Seeing Frogs in the Landscape & Forest?

Spring Peepers are commonly encountered, one of our smallest frogs it sure has a HUGE VOICE to make up for it.  Their spring peeping is one of our first signs on spring in southern Ontario.

About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Insects, IPM, landscape, Nursery Production and tagged , , , . Bookmark the permalink.

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