Nursery and Landscape Report for August 26, 2010

Now is the time to start putting out rodent bait for vole control in the nursery and landscape (especially where container plants are pot tight).  With all the seeds and fruit available this time of year, rodents are beginning to breed heavily and build up their numbers for the winter months ahead.  By putting out bait in September, you can prevent populations from getting out of control.  Place bait stations in areas known to be infested such as grassy fence rows, weedy patches and walkways between containers and polyhouse frames.  Try to have about 10 bait stations per acre of production area.  Remember to rotate zinc phosphide baits with other baits (e.g. bromidialone, brodifacaum, defethalone) since the voles will become bait shy with repeated use of zinc phosphide.  Where large areas of field production exist, broadcast application of baits may give some control where tunnels and past damage are evident.


Monitor for common leaf diseases such as leaf spot and anthracnose on herbaceous perennials and deciduous shrubs (Rosa, Prunus, Cornus) and deciduous trees.  These leaf diseases are more prevalent under late-day irrigation since foliage does not dry off before the evening, prolonging the leaf wetness period and encouraging disease sporulation and infection.  Keep disease-prone ornamentals on a strict, earlymid morning watering schedule to reduce leaf wetness periods and you will notice that the next flush of growth is much nicer.  There are several different fungicides labelled for foliar diseases, including Rhapsody (a biological).

Keep on the lookout for late-season aphid infestations in outdoor grown herbaceous and woody ornamentals.  Late-season injury is usually not as devastating to plant health as injury that occurs in the spring.  Where populations are causing economic injury, several insecticides are registered to control aphids in the nursery.  Try repeated applications of insecticidal soap to reduce aphid populations in the landscape.

Check for adults of black vine weevil and strawberry root weevil hiding in plants such as Picea, Rhododendron, Taxus, Thuja and Euonymus in field and container (woody and herbaceous) production nurseries and the landscape.  Adult weevils feed at night but can be found hiding deep in foliage or just under leaf litter during the day and adults ¡°PLAY DEAD¡± in the daylight.  Adult feeding is insignificant but their presence and level of feeding will give you an indication of feeding pressure from the subsequent population of larvae.  In nursery production, Pounce and Thiodan are registered to manage the adult stages of weevils.  Applications of beneficial nematodes (e.g. Heterohabditis bacteriophora) should be planned for early-mid September.  Nematodes are much more effective in containers where soil moisture can be maintained.

Tiger moth caterpillars can often be found feeding on nursery crops this time of year.  These are very fuzzy yellow-to-white coloured caterpillars, often with coloured tufts of hairs on their backs.  In the nursery, these late season leaf-feeding moth larvae can be knocked down with broad spectrum insecticides.  Dipel (Bacillus thuringiensis) is an effective biological approach (although it will take 2-3 days to see mortality).

Japanese beetle adults may still be active.  Look for large, coppery-green metallic beetles (13mm long) with distinctive white tufts of hairs around the sides of their abdomen feeding in groups on foliage and flowers.  They are attracted to floral lures and Japanese beetle sex pheromones and can be easily trapped (always use traps as far away from your production blocks as possible) for manual disposal.  The adults will feed on the flowers (Rosa) and foliage (Tilia) of many woody and herbaceous plants.  They lay their eggs in grassy areas and the larval stage feeds on the roots of grass.  If adult populations become economically threatening, applications of Sevin, Malathion or Imidan may be warranted.

Bagworm has been reported widely in the neighbouring United States.  This is a moth whose caterpillar stage feeds on foliage from inside a protective ¡°case¡± that looks like it was made out of tiny bits of wood.  Look for them on cedar, spruce, and several different deciduous hosts including honeylocust and crabapple.  Foliage will turn brown and become quite sparse.  Closer examination may reveal brown cases attached to leaves and twigs and if you wait you will see the larvae move around and stick their heads out of the cases to feed.  At the end of the season, ¡°bags¡± can be found on branch tips and resemble small conifer cones.  The bags can be picked off and destroyed in the fall to prevent the next generation from hatching next spring.  Please give me a call if you are seeing this pest.


Early leaf drop and fall colour is visible on trees and shrubs in the landscape.  This is especially true of woody plants on roadsides, high sandy knolls or compacted sites.  Some areas of the province have received very little precipitation during the many heat waves this summer.  Some plants are going into senescence early as a stress response.  It happens every year.

Powdery mildew is an issue on highly susceptible ornamentals (Amelanchier, Rosa, Syringa) with the hot, dry weather we had.  Monitor for powdery, white residue on the tops of leaves as a symptom of this disease.  Powdery mildew can lead to chlorotic, stunted foliage that may drop prematurely.  Sulphur and copper are exempt for use as fungicides in the landscape.  In the nursery, effective preventative fungicides include Banner MAXX, Compass, Nova, MilStop, Rhapsody (B. subtilis) etc.

Monitor for downy mildew on herbaceous perennials and deciduous shrubs (Rosa, Prunus, Cornus).  Downy mildew is rearing it¡¯s ugly head on field crops around southern Ontario and the Great Lake States so be on the lookout for purplish-red to brown lesions with a downy mass of spores on lesion undersides just after irrigation.  These leaf diseases are more prevalent under late-day irrigating since the foliage does not get a chance to dry before night-time.  The leaf wetness period is more prolonged, encouraging disease sporulation and infection.  Keep disease-prone ornamentals on a strict, early-mid morning watering schedule to reduce leaf wetness periods.  Acrobat fungicide was recently registered to help combat downy mildew on ornamentals.  Bacterial leaf spot may be evident on deciduous shrubs and herbaceous perennials.  Bacterial leaf spot looks purplish red spots that are often delineated by leaf veins.  It looks a lot like downy mildew but there is no fuzzy growth (sporulation) on lower leaf surface when you hold it is a moist baggie (or just after irrigation).  Bacterial diseases may be suppressed with copper fungicides and reduced leaf wetness periods.

Pear trellis rust (Gymnosporangium fuscum) is evident on pear trees this year in the landscape.  Look for bright orange-red lesions on the tops of pear leaves.  It is too late to do anything about this disease, leaves were infected during warm, wet conditions in May (from infected Juniperus sabinae, the overwintering host).

Birch Catkin bug has been quite prolific on several birch trees in southern Ontario landscapes in the last few years.  This plant bug is tiny (about 4 mm long) with an ¡°X¡± on their membraneous wings (you¡¯ll need a hand lens to see the x).  They can be found in large groups, feeding on the catkins (and the seeds inside) of birch trees.  They are just a nuisance and do not cause any harm to the tree.

Take a close look at the foliage of Norway, silver and red maples for halos that are filled in with tiny, black spots.  This is tar spot on maple.  The tiny, black, tar-like spots that make up the larger circular black lesion are the fruiting structures that will produce spores next spring).  Fungicides are ineffective at this time of year.  The lesions show up so late in the season that they have little effect on tree health, but may be a symptom that the tree is under stress.

Magnolia scale is rampant this year and there have been several calls of very high populations in the landscape.  Right now, magnolia scale appears as large, pinkish-orange scales.  They have laid their eggs and those crawlers have hatched.  Pick off the scale insect and look at the underside for tiny, white grains, those are the eggs.  You may also find the crawlers under the parent scale.   Look with a hand lens to see if egg cases are empty (hatched).  Crawler hatch usually starts late July to early August (~1200 GDD 10oC).  If you want to try insecticides against the crawler stage, make sure you are making at least 3 repeated applications, 7 days apart.  This will have much better knockdown since crawler emergence is staggered.  Insecticidal soap and the summer rate of horticultural oils should give good knock down.  Malathion, Orthene and Sevin are registered for this pest in the nursery.

Beech Scale crawlers will be hatching soon (from early August to mid-September). Adult females are covered in a white, wooly mass when mature and so they are easy to monitor this time of year.  Beech scale can be found on the bark of large beech trees (¡Ý 40cm DBH), mostly on the trunk and on the major limbs.  Although the scale insect does not kill the tree, beech scale seems to predispose the tree to other problems and create wound sites that facilitate the entry of beech bark disease (Nectria coccinea var. faginata).  Beech bark disease is a devastating fungal disease that has caused the death of several native and introduced beech trees in Ontario.  So far, the scale and the disease have been found in beech forests throughout much of southern Ontario (including cottage country).  Monitor scale populations for crawlers and treat crawlers about 3 times, every 7-10 days to target staggered emergence.  Use insecticidal soap and Landscape Oil or other registered chemical insecticides when peak hatch occurs, in the next couple of weeks or so.  Fall and spring (dormant) applications of horticultural oil may also reduce beech scale populations.

Fall webworm nests are quite noticeable on tree branches.  They can be seen on Betula (birch), Fraxinus (ash) and Juglans (esp. black walnut), Prunus (cherry) and Malus (apple, crabapple) etc.  Look for webbed tents on the ends of branches with fuzzy, cr¨¨me-coloured caterpillars inside.  The tents can be easily pruned out and destroyed (e.g. squished).  Pruning out infested branches can be quite effective right now since there are multiple generations of this pest through late summer.  Chemical pesticides are virtually ineffective because of the tough web.  Keep in mind that many predators, parasites and pathogens attack fall webworm.  Damage from the fall webworm is usually insignificant to tree health, late in the season.  Telescoping pruners can be an excellent tool for IPM in the landscape.

Emerald ash borer adults may still be flying in south western Ontario.  TreeAzin (azadirachtin, neem) has an emergency use registration (until August 31) for emerald ash borer on ash.  The regulated areas for Emerald Ash Borer can be found at:

Look for honeylocust spider mite on cultivated honeylocust (Gleditsia).  These orange mites can be found feeding on leaf undersides in late summer.  Where damage is causing leaf drop and dieback in the nursery, a miticide application may be warranted.

Two-spotted spider mites (TSSM) are active on greenhouse and field grown ornamentals (woody and herbaceous).  They love this hot weather and populations can increase dramatically within a week or so.  Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs, on the UNDERsides of leaves.  The upper surface of leaves appears as stippled and slightly chlorotic.  These mites are small but the damage is significant so catch them early.  Miticides registered for this mite in the greenhouse include: DynoMite, Vendex, Shuttle, Floramite, Avid and Kelthane.  Miticides registered for this pest on nursery crops include: Apollo (eggs and newly hatched nymphs), Floramite, Vendex, Dyno-Mite, Kanemite, Forbid, Kelthane.


We saw White Pine Blister Rust sporulating on the lower leaf surfaces of Ribes (currant) this week in Guelph.  This host is responsible for new infections on white pine in late summer each year.  White pine blister rust is known to cause lethal branch and stem cankers on white pine in the nursery, landscape and forest.  There are no fungicides registered for this disease in Canada. Keep currants far away from your white pine crops.  When white pine is dormant, prune out and destroy cankered branches to help reduce disease incidence and progress.  Unfortunately, once cankers reach the main stem tree mortality is unavoidable, remove and destroy all above-ground tissue when plants with trunk cankers are dormant.

For those of you growing Scots and Austrian pine, Lophodermium needlecast could be starting to sporulate in your production area.  Look for brown, fallen needles with tiny, black football-shaped fruiting bodies running the length of the needle.  Where more than 10% of the trees are infested, Michigan State University recommends fungicide applications during warm, humid weather in August and September.  Registered fungicides to help protect healthy tissue include Copper spray, Daconil, Dithane and Manzate.

Adults of Pales weevil are active.  These reddish-brown weevils will feed briefly on twigs of pine (especially Scots pine) and other conifers and are susceptible to contact insecticides (Sevin 50W) at this time.  Cornell University suggests monitoring for adult weevil activity by placing freshly cut pine discs around the base of trees that attract adult weevils for monitoring during daylight hours.  High populations of adults will cause some twig girdling and flagging.  The bulk of the injury is carried out by the larvae, which feed on underground stems and roots.

Taxus or Fletcher Scale (Parthenolecanium fletcheri) crawlers may be migrating around foliage of Thuja and Taxus.  Look for honeydew, black sooty mould and small, brown bumps (dead adult females) on foliage. The nymphs are pale tan, flattened, and about 1-2 mm long.  Applications of insecticides are not nearly as effective against settled these older nymphs as they were for the crawlers.  In the nursery, systemic insecticides may be warranted where populations are significant.

Cedar leaf miner larval populations were very damaging this spring.  The next generation of larvae are feeding inside the tips of foliage.  Applications of systemic insecticides and pruning infested tips should be targeted for early-mid August to catch the next generation of young larvae.

Monitor for nymphs and adults of spruce spider mite on conifers with a history of mite damage.  Some of the eggs might have hatched in the cool, wet weather we¡¯ve been having.  Spruce spider mites are very active in the fall and do a lot of damage at this time.  SSM nymphs are tan coloured with dark backs, and move at a moderate pace. Adults have darker black backs. Miticides registered for this pest include Kanemite, Floramite and Vendex.

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