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Frequent precipitation events continue to shower outdoor ornamentals with too much love. Leaf diseases are rampant, making plants look scraggly in some areas with prolonged leaf wetness periods. The second flush of growth on woody plants is looking better than the first, but still. Prunus species (cherry) are showing obvious shot hole leafspot caused by the fungus Blumeriella jaapii (above photo, Melissa Huntley).
Maple anthracnose, caused by several fungi continue to plague all species of maple trees and can even be found infesting native maple trees up in cottage country.
Septoria leaf spot continues to infect several different species of deciduous trees and shrubs, it’s favorite seems to be Cornus species (dogwood) most years.
Several bacterial leaf spot pathogens (Pseudomonas, Xanthomonas species) are loving this warm, wet weather. They often cause “angular” leafspots that are main limited, a tell-tile sign that it is a bacterial disease. (Photo: Pseudomonas leaf spot on Magnolia, Melissa Huntley).
Plant Phenology indicators this week: 500-600 GDD Base 10oC) : Catalpa speciosa (late bloom), Syringa reticulata (finishing bloom), Sambucus canadensis (full bloom), Hydrangea arborescens ‘Grandiflora’ (early bloom), Daucus carota (very very early bloom), Yucca filamentosa (early bloom).
Japanese beetle adults have been sited in several regions of southern Ontario. Adults can cause significant feeding injury on foliage and flowers of linden, elm, Japanese tree lilac, cherry, birch and several others. Adulticide insecticides are registered, including Sevin and Imidan. Pheromone lures are available to trap adult males but beware that they may be too effective and attract more beetles than you really wanted. Floral lures are reasonably effective and will help keep your Japanese beetles away from your trees and more in the bottom of your trap. Have soapy water in the bottom of your traps so that once the beetles fall in, they perish.
Now is the best time for preventative applications of insecticides for white grubs (Japanese Beetles, European chafer, June beetles) on nursery stock. Acelepryn and Intercept insecticides are registered to manage white grubs and to keep nursery stock grub free in order to fulfill certification standards of the Canadian Food Inspection Agency. European chafer adults are still out mating and feeding on broadleaf trees (especially Tilia species).
Adult Black Vine Weevils and Strawberry root weevils are feeding on various evergreen and deciduous hosts in field and container grown ornamentals. Look for Strawberry root weevil adults in spruce, eastern white cedar and sometimes in juniper. SRW’s will chew notches in small twigs, girdling them and causing the shoots to turn brown. Adults can be suppressed in nursery production with insecticides such as Actara, Scimitar SC, Sevin and Thionex. Monitor for adults by placing out wet boards or burlap on the ground underneath the crop. Monitor for weevils under the board/burlap during the day. Alternatively you can shake the canopy onto a light coloured sheet and count adults that fall on the sheet. Beneficial nematodes (Heterohabditis bacteriophora) are still very effective for larval and pupal stages in Container Production.
Gypsy moth larvae are finishing feeding as they are late instar larvae at this time and will soon be pupating. They hide during the day (in bark crevices and underside of twigs, leaves) and can often be found on oak, elm, beech etc. and also Colorado spruce. Success is a good lower toxicity choice but many broad spectrum insecticides will give good knockdown if it can reach the elusive larvae. Sticky bands around trunks during the July flight period will help trap female Gypsy moths and will attract males to the sticky surface as well.
We are seeing powdery mildew on deciduous flowering shrubs (Amelanchier, Rosa, Quercus) 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 (bio)) where the history of disease pressure is moderate to high.
Fall webworm adults laying their eggs recently on the foliage of deciduous trees (cherry, ash, apple, birch etc.). Fall webworm larvae form very strong webby tents on the ends of branches from where the feed inside on foliage. Prune out fall webworm nests and destroy to reduce the next generation of adults. There are several generations of fall webworm that cycle through the summer and become more numerous by August and September.
A few Emerald ash borer adults may still flying and feeding on ash leaves at this time. Look for adults casting shadows on leave in upper canopy on sunny days.
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, 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.
Emerald ash borer was recently found in Thunday Bay, ON. The regulated areas for Emerald Ash Borer in Ontario and Quebec can be found at:
Potato leafhoppers NYMPHS and ADULTS are feeding on woody nursery stock. Monitor for potato leafhopper on nursery crops such as Acer (platanoides, saccharum), Quercus and Ostrya. Adults will fly away quickly but nymphs are about 2 mm long and scuttle SIDEWAYS, rather quickly, across the leaf and to the other side (they don’t have wings). Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source). Older, hardened off foliage is not usually as susceptible.
Potato Leafhoppers suck plant sap from soft, expanding foliage and cause foliage and stems/petioles to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed. Other species of leafhoppers only cause stippling of leaves. Older, hardened off foliage will become flecked from potato leafhopper feeding. Potato leafhoppers are believed to secrete a toxic substance through their feeding.
Leafhoppers are also attracted to yellow sticky cards, for monitoring. Registered insecticides include Tristar and Sevin XLR.
Aphids are BRUTAL outdoor ornamentals this year. 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.
Two-spotted spider mites (TSSM) is showing 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. Miticides registered for this mite in the greenhouse include: DynoMite, Vendex, Kanemite, Floramite, Avid. 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).
European fruit lecanium scale on deciduous trees such as oak, ash and maple have laid their eggs and CRAWLERS are starting to hatch. Crawlers are still hiding under the protective cover of the adult female shells in the field/landscape. Development will be faster on infested container grown ornamentals. Check out our new video to see crawlers. In the landscape, well place applications of insecticidal soap and or the summer rate of horticultural oil can be effective but 2-3 applications, about a week apart are necessary to target staggered, slow crawler emergence.
Fletcher scale crawlers and nymphs are active on eastern white cedar (Thuja) and yew (Taxus) at this time and are very susceptible to insecticides. Several insecticides are registered to manage this pest in the nursery. Try insecticidal soap and where possible the summer rate of horticultural oil in the landscape.
Look for crooked, wilting and browning terminal shoots on pine and spruce with sap weeping and cankered-looking bark, 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 for white pine weevil is too late at this point, prune out and destroy all symptomatic terminals and train a new leader.
Look for newly hatched larvae of Redheaded pine sawfly (small yellow larvae with black spots and a reddish head feeding on OLD needles) on red and Scots pine. Success (spinosad) is a good, low toxicity choice to manage sawfly larvae. Several other insecticides are effective in nursery production including Pounce.
White pine has a sawfly feeding on them at this time, but usually the damage is minimal. These are introduced pine sawflies, Diprion similis. They are gregarious and consume only the outer, tender parts of the needles, so the damage appears as straw-like remains of these needles. Older larvae consume the entire needle. They will also feed on older needles. Success and Pounce are effective against sawfly larvae in the nursery.
Look for larvae (15 mm long) of Yellow-headed spruce sawfly feeding on tender new needles of spruce (e.g. Colorado spruce) and 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. Just remember, the bigger they get, the harder they fall.
Cedar leaf miner (CLM) ADULT moths may still be active, there are several moth species that are leafminers of Thuja.
Tear along the margin of green and brown tissue and check for the presence of hollowed out tissue to confirm it is cedar leafminer damage. 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 nursery production. *****Wait until mid August to do a light sheering of cedar tips to remove the next generation of larvae*****
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 conifers with overhead irrigation). Miticides inclue Vendex, Floramite and Kanemite.
Spruce spider mites are quite active on Thuja, Picea and Abies this summer. Monitor lower branches, on the North and East side of the tree, this is where most of the feeding damage is done. Shake branches over a flat white surface and look for tiny moving “specks”. You will need a hand lens to make out their light brown heads and legs and their black backs. You can also just harvest short twigs from this years growth from inside the canopy and examine them closely with your hand lens. Miticides (e.g. Floramite, Vendex) will be effective against both nymphs and adults where populations are very active.
While you are monitoring for spruce spider mite, look for faster moving, pale tan coloured mites that could be feeding on the spruce spider mites. Predatory mites can sometimes help suppress populations of phytophagous (pest) mites, so keep an eye out for them when making pest management decisions.
PLEASE NOTE: The previous 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.
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