June 13: OMAF Nursery & Landscape Report

Environment Canada is calling for much cooler, sunny weekend with  temperatures ranging from 19-21oC in many areas.  What perfect weather for weeding and rehabilitating old garden beds and planting more trees, shrubs and perennials!

The cool, weather we experienced this spring slowed down leaf emergence and allowed for the successful infection of several plant pathogens on woody ornamentals.  The proof is in the high level of anthracnoses, leaf spots and and other leaf diseases, such as…..TaphrinaRedOak  Oak leaf blister (Taphrina caerulescens) on red oak.  Oak leaf blister is not usually an issue but this year it is rampant in the landscape.  Although it looks unsightly, it does not significantly impact tree health as you might have guessed, its too late to do anything about it now.

There is still A LOT of dieback in the landscape and many horticulturalists are predicting that its not over yet.  Winter injury (e.g. freeze\thaw or low temperature injury) causes damage to the conductive tissue under the bark. During cool, wet springs like this one, damaged trees and shrubs may still be able to send enough water up to expanding foliage and twigs to keep them going for a while.  But once it becomes hot and dry, those compromised branches and twigs will not have enough live conductive tissue to support the canopy and branches will “suddenly fail”.  I’ve seen this happen as late as mid-July.  If you see branches crashing over the next few weeks, chances are it’s not Verticillium wilt….it could very well be winter injury.  When in doubt, slice through the inner wood of the branch and look for greenish-black discolouration of inner vascular tissue as a sign of Verticillium.  Diagnostic labs, such as the University of Guelph Pest Diagnostic Clinic and A&L Biologicals can test for wilt diseases to confirm diagnosis.

Plant Phenology indicators this week.

A) North of 401 (250-300 GDD Base 10oC): Kolkwitzia amabilis (full bloom), Cornus alternifolia (full bloom), Robinia pseudoacacia (late bloom), Acer saccharinum (dropping seed), Viburnum opulus (full bloom), Viburnum dentatum (early-full bloom), Weigela florida (early-full bloom)

B) Niagara(300-400 GDD Base 10oC):: Catalpa speciosa (early bloom), Syringa reticulata (early bloom), Kolkwitzia amabilis (late bloom), Lonicera korolkowii (late bloom), Cornus alternifolia (full bloom), Robinia pseudoacacia (late to finishing bloom), Viburnum opulus (full-late bloom), Viburnum dentatum (full bloom), Weigela florida (full bloom)

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


1) Arboriculture and Landscape Professionals:  ISA Workshop: “IPM in the Woody Landscape”.  Tuesday, July 15 at the University of Guelph Arboretum Centre.  Come spend the day learning about current pests and physiological problems on trees and shrubs.  This workshop will be led by Jen Llewellyn with Dr. Shannon Shan and Sean Fox. CEU’s are available!  To register, contact Kathleen at ISA Ontario at 1-888-463-2316 or info@isaontario.com

2) GrowersNursery Growers Research Auction.  Wednesday, July 16 at Winkelmolen NurseriesLandscape Ontario’s Growers Group invites you to its annual fundraising auction
No admission fee or RSVP required. Bid on top quality plant material and tour the production farm while helping raise funds for industry research and scholarships.  All winning bidders will be entered into a draw for a special prize. Enjoy lunch, network with peers and bid on fantastic items – something for everyone!

  • Farm Tours:  10:00 a.m. – 11:30 a.m.
  • Lunch and Refreshments:  11:45 a.m. – 12:45 p.m.
  • Live Auction: 1:00 p.m. – 4:00 p.m.


Have white grubs been an issue in your nursery?  Preventative applications of Intercept (imidacloprid) are registered for white grubs (nursery production) and the application period is in late June and July (during the adult flight period for the adult stage).  Adult Japanese Beetles will be flying soon.  To help qualify for the Japanese beetle certification program, an application of Intercept on container stock should made between mid-June to July (adults flight period).  The cut-off period for Intercept applications to comply with the JB Certification program this year may be as early as July 31st.  Beneficial nematode applications for white grubs (e.g. European chafer) are not effective at this time.


 Dutch Trig is registered for Dutch Elm Disease on Ulmus americana species in Canada.  This is a new registration (fall, 2009) that contains a biological organism that induces an immune response to help the tree fight off DED infections.  Arbotect-20-S (thiabendazole) is the registered injectable fungicide treatment.  Injections of these fungicides should be made on sunny days during leaf emergence to maximize uptake.

dsc_0096We have seen more powdery mildew on deciduous flowering shrubs and herbaceous perennials.  Monitor for white, powdery residue on the tops and bottoms of leaves.  Protect new foliage with fungicide applications (e.g. Switch, Milstop, Regalia (biological) and Tivano) where the history of disease pressure is moderate to high.  In its early stages, powdery mildew can be confused with hard water spots and pesticide residues on foliage. If you are still unsure, get out your hand lens and look for powdery, wooly, raised fungal growth for powdery mildew. Dried residue from hard water looks like tiny, white crystals on the surface.

FIREBLIGHT of apple and pear. The window of infection starts once FLOWERS ARE BLOOMING. Most fireblight infections enter the delicate flower tissue. Protect flowers and emerging leaves with bactericidal products such as Kasumin (Grp 24) and Streptomycin (Grp 25) during bloom. For suppression of fireblgiht in the landscape with Class 11 biological fungicides, Blightban C9-1 and Bloomtime can be used during bloom of apple and pear. CHECK IT OUT! Prediction models for Fireblight Activity in southern Ontario May 23-29 can be found by clicking here.

<a href="/clm/species/synanthedon_exitiosa"><em>Synanthedon exitiosa</em></a> (Peachtree Borer) adult male. Peach tree borer (Synanthedon exitosa) adults are flying for the next few weeks. Look for cankered regions and chewed bark/wood in the lower stems of Prunus (Prunus x cistena) as a sign of larval damage.  The clearwing moths that emerge resemble wasps.  Adults are very much attracted to sticky wing traps that are baited with peach tree borer pheromones. Place pheromone traps out in early-mid June (‘Red Prince’ Weigela in full bloom) and monitor for peak flight of adults.  You can expect peak egg hatch around 10-14 days later, if you are thinking of treating newly-hatched larvae (stem treatment Thionex).  The same ‘clearwing moth’ pheromones and traps can be used to monitor for Viburnum borer.  Viburnum borer chews the stem (at and below the soil line) and causes significant injury to container grown Viburnum.  Viburnum borer will be starting to emerge in container production at this time.  To purchase traps, try ordering from IPM suppliers such as www.greatlakesipm.com and www.naturalinsectcontrol.com.   Some growers are trying soil drench applications of beneficial nematodes (Steinernema carpocapsae) after peak adult flight, as a biological way to suppress hatching larvae.

EAB adults casting shadows on leaves (Markham)

EAB adults casting shadows on leaves (Markham)

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.   Registered injectable insecticide products include: AceCap 97, Confidor 200 SL and Tree-Azin.  Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer.   Emerald ash borer adults start to emerge when the black locust (Robinia pseudoacacia) are blooming.

The regulated areas for Emerald Ash Borer have changed and can be found here.

Adult bronze birch borer beetles are actively laying eggs on the bark of susceptible birch (e.g. Betula pendula).  Symptoms of larval boring damage appear as branch tip death, branch death and death of the leader and progresses quite quickly.  Destroy pruned material to prevent emergence of beetles. Natural resistance to this pest can be enhanced through activities that improve plant health, such as light fertilizing (May, October), irrigating and removing any weeds and grasses that provide competition for the tree.  Betula pendula is most susceptible to this pest and should be avoided in areas of known BBB infestation.  Betula nigra is an excellent alternative in high pH soils and it has has been shown to be quite tolerant to BBB attack.  Confidor injectable insecticide is labelled for bronze birch borer.

 ADULT Potato leafhoppers are feeding and laying eggs on the newest leaves of maple (Acer platanoides, A. saccharum).  Our nursery scout found them on Acer platanoides, Acer rubrum last week and we have already seen damage.  Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source).  Older, hardened off foliage is not usually susceptible.  Leafhoppers adults are winged, are 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. Adult potato leafhoppers blow in from the south and will feed and lay their eggs on newly expanding leaf tissue.  The soft, succulent growth we have this year is especially susceptible. Leafhopper nymphs will be hatching soon and appear as tiny, flightless, yellow-green insects that move sideways, very rapidly across the leaf. Leafhoppers (and aphids) suck plant sap from expanding foliage and cause foliage to wilt, become off-coloured, flecked and stunted.  Potato leafhoppers are especially damaging because they cause foliage to become stunted and deformed, with brown-black margins (“hopper burn”). PotLHDamageAcer

Leafhopper injury also appears as bronzing or stippling on more mature leaves.  Monitor populations and treat the 1st generation NYMPHS with insecticides before damage becomes economically threatening.  Leafhoppers are also attracted to yellow sticky cards, for monitoring.  Registered insecticides include Tristar and Sevin XLR.  http://dkbdigitaldesigns.com/clm/species/empoasca_fabae

Aphids are quite numerous on herbaceous and woody ornamentals this spring.  They do well in cool weather because leaves stay soft and easy to feed on.  Green peach aphid is one of the most common species and melon aphid and foxglove aphid are also quite common.  Aphids are sucking insects that cause stunting, malformation and coat plants in honeydew.  They also attract ants. Various insecticides are registered to manage aphids in outdoor production nurseries including Endeavor, Tristar and Trounce.  In greenhouses insecticides include Endeavor, Intercept and Enstar EW.  Where populations aren’t immediately economically damaging, biological control (e.g. Aphidius, Aphidoletes) may provide excellent management when introduced on a regular basis.  Biocontrol suppliers include Biobest, Koppert, Plant Products and Canadian Hydrogardens.

image0006Gypsy moth larvae (3rd and later instars) are moving into their heaviest feeding period in the next couple of weeks.  We have been finding GM larvae feeding on Colorado spruce!  Larvae can be found on various deciduous trees and evergreens (Colorado spruce!).  Some larval management can be achieved using spinosad (Success) insecticide, Dipel, Foray etc. (B.t.,Bacillus thuringiensis). Some keen homeowners can install a burlap skirt at the base of the tree to create a shady, protected area for larvae to hide during the day (this behaviour usually peaks near the end of May).  Homeowners will need to inspect burlap skirts and underlying bark crevices daily (1-3 pm is best) and remove/destroy napping larvae.  Sticky bands around trunks during the June/July flight period will help prevent females from laying eggs above sticky bands and will attract males to the sticky surface.

<a href="/clm/species/lepidosaphes_ulmi"><em>Lepidosaphes ulmi</em></a> (Oystershell Scale) willow.

Oystershell scale crawlers have hatched.  Look for very tiny (2-3 mm), whitish-grey, oyster-shell shaped hard scale insects stuck on twigs and branches of deciduous trees and shrubs such as ash, birch, bittersweet, hackberry, lilac, redbud, beech and dogwood.  Crawlers (light tan) are sensitive to insecticidal soap, horticultural oil, malathion and other insecticides (Viburnum opulus blooming, Aesculus hippocastanum late bloom). Two-three applications of insecticides may be necessary since crawlers hatch over 1-3 week period.

Maple spider mite (Olygonychus aceri) can be found feeding on the undersides of leaves of red and red x silver maple hybrids.  They look just like their cousins, spruce spider mites.  We saw some mild damage in nursery grown trees this week.  When populations are high, damage can cause significant leaf chlorosis and stippling and sometimes, premature leaf drop.  Try miticides (Floramite, Kanemite, Vendex, insecticidal soap) where populations are high.


Where new foliage is emerging on conifers, monitor for needlecast and blight diseases in the area.  Diplodia tip blight on 2 and 3 needled pines and Rhizosphaera needlecast and Stigmina on blue Colorado spruce are our most common needlecast diseases in Ontario.  Diplodia tip blight appears as brown, stunted needles at the tips of branches.  Rhizosphaera appears as brown-purplish needles from the previous year’s growth, symptomatic needles begin to drop in late spring.  Stigmina appears on green and chlorotic needles, but doesn’t always lead to needle drop.  To confirm it is Rhizosphaera, look at the undersides of the needles.  Those little white dots (stomata) will turn black and the black spots will protrude during sporulation.  New, soft growth is especially susceptible to foliar diseases, but infection may also take place later in the season (we don’t know).  Where there is a history of damage, treat with registered fungicides (copper oxychloride, Banner Maxx, Daconil) as buds start to open and protect new foliage.  Apply fungicides prior to precipitation events (spore dispersal).  Unfortunately, most of these blights and needlecasts can be found sporulating for much of the year.

image0009image0010    The first generation of Euonymus scale crawlers have hatched in container production and will be in the field and landscape very soon.  Euonymus scale look like tiny white flecks (males) and tiny brown sea shells (females) along twigs and the undersides of leaves.  Look for bright, orange crawlers around populations of adults and on the undersides of leaves and twigs. Where insecticide applications are warranted, multiple applications may be required to get good knockdown since crawler emergence is staggered over a few weeks.  Try insecticidal soap and the summer rate of horticultural oil.

WhPineWeevilCrossSectLarvaeDiebackTerminalColSpruce                     Look for crooked, wilting and browning terminal shoots on pine and spruce, it could be boring larvae from white pine weevil.  Where appropriate, slice into bark and look for tiny, fat, white, legless grubs feeding in the cambium.  Insecticide control is too late at this point, prune out and destroy all symptomatic terminals and train a new leader.

Look for tiny larvae of  Yellow-headed spruce sawfly feeding on tender new needles of spruce (e.g. Colorado spruce) 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 York region and has caused significant damage to spruce trees.

Larvae of European pine sawfly are feeding in clusters on last year’s (and older) needles and our nursery scout is finding them in many places.  Larvae are greenish-yellow with dark head.  They rear their bodies up in unison when alarmed.  They can often be found on the top half of the tree, on the NE side. There are several insecticides registered for this pest.  A low toxic pesticide choice is Success or Dragnet.  Closely examine twigs of Pinus sylvestris, Pinus mugo, Pinus nigra. 

Pine false webworm larvae will be found on white pine   When eggs hatch, larvae snip off foliage and make webby nests near the trunk.  The larvae clip off more needles and pull them into the webby nest where they feed on them.  The larvae feed mainly on older growth and will only eat the current year’s growth when all else has been consumed.  The new nests can be dislodged with a strong stream of water.

Taxus or Fletcher Scale NYMPHS are still developing h on foliage and twigs of Taxus and Thuja.

Taxus mealybug nymphs will be showing up.  Adult mealybugs are bright white (3-5 mm), waxy looking flat insects that barely move.  They can be found on twigs of older Taxus in field production in hedges.  They produce honeydew therefore, black sooty mould is apparent on infested plants.  Where populations are high, nymphs are sensitive to applications of insecticidal soap, horticultural oil, Trounce, Sevin and many others.

Cedar leaf miner larvae are pupating and tiny, grey-white adult moths are emerging.  Tear along the margin of green and brown tissue and check for the presence of hollowed out tissue to confirm it is leafminer.  We have seen quite a bit of CLM in field grown Thuja on sandy soils this spring.  Adulticides (malathion) are registered for the moth life stage in

Monitor for nymphs and adults of spruce spider mite on conifers with a history of mite damage.  Spruce spider mite nymphs and adults are brown with black backs and found on new foliage this time of year.  Miticides registered for SSM include Floramite and Kanemite.  Miticides may be required where pest pressure is moderate to heavy.

The 2013 Crop Protection Guide for Nursery and Landscape Plants   (previously 383, now publication 840) can be found at:  http://www.omafra.gov.on.ca/english/crops/pub840/p840order.htm   It contains the crop pest recommendations for nursery and landscape plants that was previously found in publication 383.  Publication 840 is a .pdf file, accessible online and on cd.

Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests. Check out www.dkbdigitaldesigns.com/clm

About Jen Llewellyn

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

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