Here Comes The Humidity


John Wilmot, the most infamous of the Restoration rakes. He knew my pain.

The air was so dry up until just recently, it was SO nice.  You know? If you’re like me, humidity is an important thing. Sure it means more plant diseases are in our future.  But it also rakes havoc with my hair.  The higher the relative humidity, the bigger my hair gets.  Perhaps this is an evolutionary advancement, trying to trap more air to insulate my head? Ugh.

Climatologists are expecting daytime temperatures in the high 20’s for the next several days (except near the great lakes).  And this heat is bringing waves of thunderstorms and high relative humidity.  Precipitation and high humidity create the PERFECT conditions for fungi and bacteria to germinate, invade and reproduce on ornamental plants.  Which makes now an even more important time to protect new growth on ornamental plants, especially those receiving overhead irrigation.  But hay, you don’t need to check the weather…… just the mirror 🙂

Plant Phenology indicators this week, Hamilton/Niagara/GTA/London (120-150 GDD Base 10C)

  1. Aesculus hippocastanum (full bloom)
  2. Amelanchier laevis (serviceberry, late to finishing bloom)
  3. Cercis canadensis (full to late bloom)
  4. Gleditsia triacanthos (full bloom)
  5. Lonicera korolkowii (full bloom)
  6. Prunus x cistena (late to finishing bloom)
  7. Prunus serotina (early bloom)
  8. Sorbus aucuparia (early to mid bloom)
  9. Spirea x vanhouttei (bridal wreath spirea, full bloom)
  10. Syringa vulgaris (full to late bloom).

If you are referring to the Phenology and Monitoring tables in OMAFRA publication 841, Guide to Nursery and Landscape Plant Production & IPM, look at the Tables starting with 2-3 on pg. 39.  This puts us at about 30-55 GDD Base 10C in areas south of Hwy 9.  Areas in the southwest corner of the province will be more advanced.

PLEASE NOTE: The Following Pesticide Recommendations are meant for Exception Uses (e.g. agriculture-nursery production or trees in the landscape) under the Cosmetic Pesticide Ban unless the active ingredient is listed under Class 11 pesticides in Ontario Regulation 63/09, effective April 22, 2009.

The Crop Protection Guide for Nursery and Landscape Plants (OMAFRA publication 840) contains the crop pest recommendations for nursery and landscape.  The new 2016 version of Publication 840 will be available online in the next few weeks.  The pest recommendations can also be found on our online, searchable database:  Check out NurseryTracker on your phone or tablet!!!

Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests.

CONTAINER PRODUCTION +/- FIELD, LANDSCAPE ISSUES-              Evergreen + Deciduous


Do you grow ornamental Prunus?  Do you have problems with dieback after the crop flushes out in the spring (Purple leaf sandcherry, above photo) ?

<a href="/clm/species/synanthedon_exitiosa"><em>Synanthedon exitiosa</em></a> (Peachtree Borer) damage.

Ever see frass, sawdust at the base of the stem (photo above) ?

<a href="/clm/species/synanthedon_exitiosa"><em>Synanthedon exitiosa</em></a> (Peachtree Borer) larva.

And white borers just under the bark (photo above) ?

Several species of Prunus (e.g. Prunus x cistena, P. serotina) are susceptible to the Greater Peachtree Borer (Synanthedon exitosa).  Now is the time to start putting out peachtree borer pheromone-baited sticky wing traps in the nursery.  Hang traps on NON-PRUNUS crops and hedgerows to attract Male Peachtree borer moths away from susceptible Prunus (cherry) crops.  The males will get stuck in the sticky trap and will be unable to fulfill their *destiny*.  Meaning less PTB borers next year.   Pheromones and sticky wing traps are available from several suppliers, including Natural Insect Control.


Taxus or Fletcher scale nymphs (Photo: L. Stitt)

Fletcher scale NYMPHS (Lecanium fletcheri) are a lot more noticeable this week on Taxus.  These scale nymphs are becoming a lot more difficult to manage with insecticides.  These scale insects produce a lot of honeydew in June.  Monitor Taxus (yew) and Thuja (eastern white cedar) for crawlers in late June/early July.

<a href="/clm/species/otiorhynchus_sulcatus"><em>Otiorhynchus sulcatus</em></a> (Black Vine Weevil) adult damage on yew.<a href="/clm/species/otiorhynchus_sulcatus"><em>Otiorhynchus sulcatus</em></a> (Black Vine Weevil) adult.

In production nurseries where black vine weevil are a problem in container crops (e.g. perennials, evergreens), monitor crops for adults.  Adults will chew semi-circle notches out of leaf margins.  Adults hide in dark, damp places during the day (e.g. under pots, under pot rims, other crevices). Adulticides for black vine weevil include: Actara, Scimitar, Sevin and Thionex.  In September, treat container media of damaged crops with Heterohabditis bacteriophora (H.b.) or Met52.   Met52 can also be applied preventatively at potting.

<a href="/clm/species/plagiodera_versicolora"><em>Plagiodera versicolora</em></a> (Imported Willow Leaf Beetle) adult on willow.<a href="/clm/species/plagiodera_versicolora"><em>Plagiodera versicolora</em></a> (Imported Willow Leaf Beetle) eggs on willow.<a href="/clm/species/plagiodera_versicolora"><em>Plagiodera versicolora</em></a> (Imported Willow Leaf Beetle) larvae.

Imported Willow leaf beetle (Plagiodera versicolora) is pretty common on Salix in containers and in the field. Adults overwinter inside cracks within the bark of the host tree. Adults emerge in spring to feed and lay eggs on the underside of leaves. The yellow eggs are laid in an irregular pattern and hatch within a few days. The larvae feed on the undersides of leaves for about 3-4 weeks before pupating on the underside of leaves. The pupae are yellowish brown with black markings. There are multiple generations a year.


Bacterial leaf spot diseases can be a real issue on ornamentals after periods of high temperatures couple with high humidity.  The coming week’s weather is the PERFECT CONDITIONS that support bacterial leaf spots!  Bacterial leaf spots often are very vein-limited.  Leaf veins will outline the margin of the spots, making them appear the way farm fields do from a low altitude airplane.  Protect emerging growth with bactericidal sprays, such as Copper, Kasumin and suppression using the biologicals Serenade/Rhapsody and Regalia Maxx.  There are several susceptible crops but we often see bacterial leaf spot on Hydrangea, Hibiscus, Populus, Salix, Magnolia, Syringa.

Leaf spot on Cornus (T. Lohrer)

Where dogwood (Cornus spp.) has had issues with fungal leafspots (e.g. Septoria) in the past, protect emerging foliage with fungicides before precipitation or irrigation events as the Amelanchier sp. and Cercis canadensis are blooming.  Leafspots are often circular or angular with a bright purple border, making shrubs look unsightly by early summer.


<a href="/clm/species/thrips_calcaratus"><em>Thrips calcaraus</em></a> (Introduced Basswood Thrips) adult.<a href="/clm/species/thrips_calcaratus"><em>Thrips calcaraus</em></a> (Introduced Basswood Thrips) damage.

Introduced Basswood thrips (Thrips calcaratus) has been found inside buds and among emerging leaves on Tilia americana. Introduced Basswood thrips can cause severe damage that often leads to some defoliation.  We have seen it in some other nurseries (field production) this spring.  Introduced basswood thrips is most damaging on Tilia Americana. It overwinters in the soil, adults emerge as basswood buds are breaking.  Adults feed on buds, sometimes killing them and causing them to drop.  Females lay eggs along leaf midrib on leaf underside.  Larvae appear in early June.  Feeding of larvae and adults can cause damage and premature leaf drop.  Researchers believe there is only one generation per year. If damage starts to become evident on Tilia, treat with Success (spinosad) a naturalyte insecticide that is very effective against western flower thrips (and several other Lep and sawfly, beetle pests). Another biological option is Beauvaria bassiana (Botaniguard, Bio Ceres) and it is often used in rotation with Success due to resistance to spinosad of Western Flower Thrips in gh crops.

Once ash trees have leafed out, injectable insecticides may be used to protect the trees from new infestations of Emerald Ash Borer (Agrilus planipennis). Trees must be actively transpiring in order to maximize insecticide uptake into the cambium. Registered injectable insecticide products include: AceCap 97, Confidor 200 SL, IMA-jet and Tree-Azin.  The regulated areas for EAB outlines restrictions on the movement of all ash species (Fraxinus sp.) materials and all species of firewood from these regulated areas of Ontario and Quebec.

The Asian Long Horned Beetle was detected in the vicinity of Pearson International Airport in Toronto/Mississauga and efforts are continuing to eradicate this beetle from the area. The Asian Long-horned Beetle Infested Place Order is being enforced in the area encompassing: all parts of the City of Toronto and City of Mississauga, in the Province of Ontario, located within the area commencing at the point of intersection between Dixie Road (formerly Hwy. 4) and Derry Road (formerly Hwy. 5) and proceeding northeastward along the south side of  Derry Road to Bramalea Road. This means that tree materials, including nursery stock, trees, logs, lumber, wood, and wood and bark chips from tree species that are susceptible to the Asian Long-horned Beetle, may not move out of, or through, this area.

EuropeanChaferLarvaSoilECLarvaPinus          Take a look at the roots of poor looking evergreens (Thuja, Picea, Pinus) and field grown ornamentals and look for populations of European chafer, May/June Beetle larvae and other white grub species in the soil. Sandy soils are especially hospitable to white grub species.  Preventative applications of Intercept (imidacloprid) are registered for white grubs (nursery production) and the application period is in June and July (during the adult flight period). Beneficial nematode applications are not recommended this time of year and are much more effective when applied to early instar larvae, mid-August.


Boxwoods in the landscape not looking so good coming out of the winter?  Are you seeing a lot of yellow leaves? Can you see any yellow-green-brown spots?


Boxwood Leafminer pupae (Photo: L. Stitt)

Carefully break open the leaf with your knife or finger nail, look for tiny orange pupae inside.  These are boxwood leafminer ADULTS SHOULD BE EMERGING SOON.

<a href="/clm/species/monarthropalpus_buxi"><em>Monarthropalpus buxi</em></a> (Boxwood Leafminer) adult.

Boxwood Leafminer Adult (Photo: D. Cheung)

The tiny orange midge adults will be emerging out of these leaves when the new growth emerges.  Adult midges will be laying their eggs on newly emerged leaves and those eggs will hatch into the next generation of leaf miners.  Treating new foliage with insecticides just prior to or at the beginning of adult emergence can help reduce successful egg hatch and leafminer establishment.  You can also prune out new foliage in August and the clippings will desiccate, making it impossible for the leafminer to complete its lifecycle.

<a href="/clm/species/dasyneura_gleditschiae"><em>Dasyneura gleditschiae</em></a> (Honey Locust Pod Gall Midge) galls.<a href="/clm/species/dasyneura_gleditschiae"><em>Dasyneura gleditschiae</em></a> (Honey Locust Pod Gall Midge) adult.


Galls on Honeylocust leaves before leaves have expanded! (Photo: L. Stitt)

Where honeylocust podgall midge was a problem in the past, monitor trees for overwintered adult midges soon. These adults will be emerging as the buds start to swell. Adults will be laying eggs on buds in early spring (reddish eggs on buds and new leaves). Research in Oregon suggests that delayed dormant oil applications targeting the first couple of egg clutches can help reduce the incidence of pod gall midge. This involves applications of product early in the season, starting before foliar emergence.

<a href="/clm/species/diaphnocoris_clorionis"><em>Diaphnocoris clorionis</em></a> (Honey Locust Plant Bug) nymph.

Honeylocust Plant bug NYMPHS (D. Cheung)

Where foliage is starting to emerge on honeylocust, monitor for newly hatched nymphs of the honeylocust plant bug.  You can find them by shaking branches over a light coloured surface and examining it for fallen nymphs.  By controlling the first generation of nymphs, you can really reduce the damage from this pest.

<a href="/clm/species/lymantria_dispar"><em>Lymantria dispar</em></a> (Gypsy Moth) larva.

Gypsy moth larvae have hatched and 1st instar larvae spin threads in order to blow and disperse to other hosts.  So you’ll find them just about everywhere at first, until they find the right host and settle down to start feeding on leaves.   Some control can be achieved using Bacillus thuringienesis (Dipel, Foray) and spinosad (Success) insecticide once they settle in their new feeding site.

<a href="/clm/species/pyrrhalta_viburnicola"><em>Pyrrhalta viburnicola</em></a> (Viburnum Leaf Beetle) damage on viburnum.

Viburnum leaf beetle egg masses can still be pruned out and destroyed at this time (where leaves haven’t begun to emerge yet), to avoid destructive populations this spring. Look for raised bumps on the undersides of 1 and 2-year-old twigs. The bumpy caps can be picked off to reveal the yellow eggs underneath. Monitor these eggs as they will hatching into larvae as foliage emerges. The larvae are vulnerable to chemical control only during the first 7-10 days after hatch. Larvae feed on the interveinal tissue from the undersides of the leaves, keep that in mind if you are doing insecticidal applications (Success, Actara, horticultural oil).


Fireblight of Malus

Now is the time that Fireblight (apple, pear) Foliar (floral) applications of products for Fireblight (such as copper, Kasumin, streptomycin) should continue to reduce numbers of fireblight bacteria on floral structures (stigmas) throughout the bloom period.  The floral stigmas are the main entry point for fireblight into the tree.  Fireblight is a big concern right now because the crop is in full bloom, we’ve had warm temperatures and rain and there is so much disease inoculum from previous years.  The most recent Ontario Fireblight Prediction Models can be found below:


Black knot is easy to see on Prunus sp. at this time. Monitor gardens and adjacent wild areas for Prunus shrubs and trees for large black growths on previous years twigs. If you have the time to prune, prune the cankers out, back quite close to the main stem BEFORE LEAVES EMERGE. Destroy all pruned twigs. Pruning too shallow retains the undetectable, developing canker on the tree and does nothing to limit the disease. Fungicides may give some suppressions when sprayed at green tip, pre-bloom and blossom time. Fungicides include Daconil and Maestro. Fungicides need to be applied ahead of precipitation events during bloom and shoot emergence In the nursery/orchard, Daconil has been shown to be the most effective fungicide. (Fruit-bearing mature Prunus: Daconil cannot be applied after shuck split or fruit will be injured). For more information:


white pine- white pine weevil damagewhite pine-white pine weevil

Wite pine weevil larvae are starting to hatch and feed just under the bark on last year’s central leader.  They damage all the conductive tissue under the bark reducing sap flow up to the developing 2016 central leader, causing it to wilt and turn brown.  Look for wilting leaders and white, legless larvae under the bark of last year’s leader.

<a href="/clm/species/oligonychus_ununguis"><em>Oligonychus ununguis</em></a> (Spruce Spider Mite) adults on cedar.

Monitor for  nymphs of spruce spider mite on conifers with a history of mite damage (Abies, Picea, Thuja). Spruce spider mite eggs appear as very tiny, round, reddish-brown spheres that adhere to the UNDERSIDES of twigs and foliage this time of year. YOU WILL REQUIRE A HAND LANDS TO SEE THEM CLEARLY. Monitor lower branches, on the North and Easter side of the tree, this is where most of the feeding damage is done. These eggs are susceptible to dormant hort oil applications in the next few weeks, where temperatures permit and plant species are not sensitive.  Miticides will be effective once eggs hatch to nymphs, usually around bud break and early foliar emergence.

Pine shoot beetle adults have emerged. The tiny beetles take flight after 2-3 days where temperatures reach 10-12oC. Adults lay eggs underneath the bark of stressed or dead pine trees and stumps. Those larvae will develop later in April and May. Remove brood material (i.e. trap (sentinel) logs, snags, dead/dying trees) before new progeny adults emerge (210 GDD, Base 10C) to comply with the CFIA. All brood material must be burned, chipped (less than 2cm diameter) or buried (30 cm deep) to comply with CFIA standards.

JuniperTipBlightClose Brown shoots on juniper may be a symptom of juniper tip blight (Kabatina blight). A small grey band or pinched grey canker can be found at the base of the infected shoot, this is where the spores come from. Where plants are still dormant, PRUNE OUT DEAD SHOOTS during DRY conditions (and remove shoots) to reduce disease spread. Disinfect pruning shears between each cut (e.g. rubbing alcohol, other sterilants) to reduce disease spread. Pruning is not suggested once new growth appears, as it will help spread this disease. Where cankers are found, copper and Dithane are registered to protect emerging new growth this spring and again in late summer.  [Juniper tip blight caused by Phomopsis sporulates in early spring whereas that cause by Kabatina sporulates in late summer. ]


Dothistroma needle blight (

Dothistroma needle blight is a fungal disease affecting pines (Austrian, mugo).  The fungus overwinters on infected needles and will sporulate during wet weather.  Persistant cool, wet weather favours disease development.  Where infestations are affecting plant health, protect emerging needles with fungicides (copper, daconil) until they are fully hardened off.

Protect Spruce and Pines for needlecast diseases.  See my blog post from May 20, 2016.

Protect Evergreens Now, New Growth is Emerging!






About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Arboriculture, Diseases, IPM, Nursery Production, Weekly Nursery Landscape Report and tagged , , , , . Bookmark the permalink.

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