Nursery and Landscape Report for August 7, 2009

Environment Canada is calling for hot, humid weather for the next few days.  Showers are expected on Saturday afternoon and evening with gusting winds from the southwest.  Sunny should be mainly sunny with a high of 30oC.

Growing Degree Day summaries are from Environment Canada and are base temperature 10oC (August 5).

The Pesticides Act has been amended by the Cosmetic Pesticides Ban Act, 2008 and Ontario Regulation 63/09 that have taken effect on April 22, 2009.  For more information on the legislation call the Ministry of Environment information line at: 1-800-565-4923 or see the Ministry of the Environment¡¯s website at  http://www.ene.gov.on.ca/en/land/pesticides/index.php

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.

VARIOUS ORNAMENTALS:

Reminder: Alkaline water (>pH 7.0) that has a high concentration of bicarbonates can actually reduce the action of many pesticide products including: *Cygon*, Dipel, Dylox, Furadan, Imidan, Kelthane, Malathion, Orthene, Pounce, Pyrate, Sevin.  It helps to mix the pesticides as close to the application period as possible and to mix only the amount needed for that application (ie. Avoid using tank mixes that have been sitting around for several hours).  Ground water sources in southern Ontario can contain high levels of bicarbonates.   Try using acidified water or rain water (cistern water) for you sprayer tank.

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 or ¡°bag¡±.  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 bags attached to leaves and twigs and if you wait you will see the larvae move around and stick their heads out of the bags to feed.  Dipel (Bacillus thuringiensis) may still be effective at this stage of larval development.  At the end of the season, bags can be found on branch tips and resemble small conifer cones.  Please give me a call if you are seeing this pest.

Check for adults of black vine weevil and strawberry root weevil on crops such as Picea, Rhododendron, Taxus, Thuja and Euonymus in field production nurseries and the landscape.  BVW are about 1.5 cm long, black, with mottled brown flecks on their backs.  SRW are about 0.8 cm long, reddish brown.    Adult weevils can be found hiding deep in foliage or just under leaf litter during the day.  In nursery production, Pounce and Thiodan are registered to manage the adult stages of weevils.  Applications of beneficial nematodes are no longer effective at this time.  The next window for nematodes to target the next generation of larvae in soil will be September.

Summer rate applications of horticultural oil (e.g. Landscape Oil) may be used (where permitted) so that treated foliage dries before the heat of the day.  To avoid phytotoxicity, try to apply oils once leaves have hardened off (where possible) and avoid applications on hot days.  Some uses of summer oil include:  scale insect crawlers, European red mites and mealybugs.

DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:  

Monitor for common leaf diseases such as leaf spot, anthracnose and downy mildew on herbaceous perennials and deciduous shrubs (Rosa, Prunus, Cornus).  These leaf diseases are more prevalent under late-day irrigation since the leaf wetness period is more prolonged, encouraging disease sporulation and infection.  Keep disease-prone ornamentals on a strict, mid-morning watering schedule to reduce leaf wetness periods and you will notice that the next flush of growth is much nicer.  Rhapsody is a newer biological fungicide that can be used to protect nursery crops from diseases.  There are several fungicides registered to manage leaf diseases on ornamentals.

Downy mildew continues to be an issue on herbaceous perennials and deciduous shrubs (e.g. Rosa, Cornus, Prunus etc.).  The fungus causes reddish-purplish splotches (whose margins are denoted by leaf veins) on the tops of leaves.  Downy mildew can be easily mid-diagnosed.  Right after irrigation, you can often see ¡°downy¡± fuzz (sporulation) on the bottom of the leaf (but it disappears as soon as the leaves dry).  You can also put symptomatic leaves in a sealed plastic bag with a moist paper towel, check for ¡°downy¡± fuzz the next day.  This disease is exacerbated by long leaf wetness periods.  Make sure you irrigate susceptible crops early-to-mid morning to minimize the leaf wetness period.  Acrobat 50WP is registered for greenhouse ornamentals and works as a PREVENTATIVE fungicide.

Take a close look at the foliage of Norway, silver and red maples for subtle yellow halos.  These yellow halos are the beginnings of tar spot lesions.  Monitor these lesions over the next few weeks as they fill in with tar-like spots (these are the fruiting structures that will send up 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.

Powdery mildew is evident on highly susceptible ornamentals (Amelanchier, Physocarpus, Rosa, Syringa etc.) right now.  Look for powdery, while 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 fungicides include Banner MAXX, Compass, Nova, MilStop, Rhapsody (B. subtilis) etc.

Fall webworm nests are becoming more noticeable on deciduous trees (e.g. Fraxinus).  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 since there are multiple generations of this pest.  Chemical pesticides may give some reduction in webworm populations (webworms hide in the tents during the day and feed at night).  Keep in mind that many predators, parasites and pathogens attack fall webworm.  Damage from the fall webworm is usuallyinsignificant to tree health, late in the season.  Telescoping pruners can be an excellent tool for IPM.

Magnolia scale is maturing on the undersides of young magnolia twigs at this time.  They are quite tolerant of many insecticides this late in their life cycle but if you have a small infestation and they haven¡¯t laid their eggs yet, you can pick them off and destroy them.  Once they turn that orangy-pink colour, they start laying their eggs (tiny, white grains similar to salt).  Crawlers start to hatch around the 2nd week of August in south-central Ontario but we are a little behind this year.  If you want to try insecticides for the crawlers, make sure you are making at least 3 repeat 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.

Beech Scale crawlers will be hatching soon (from mid-late August to mid-late 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 applications of dormant oil may also reduce beech scale populations.

Scale insects are pretty bad in some areas.  Monitor evergreen Euonymus for the second generation of Euonymus scale crawlers in the next couple of weeks.  Also, monitor for the second generation of Pine needle scale crawlers on Austrian, Mugo and Scots pine.  Repeated applications of insecticides will be necessary as emergence is staggered, especially with the 2nd generation.

Japanese beetle adults are still flying.  Look for large, coppery-green metallic beetles (13mm long) with distinctive white tufts of hairs around the sides of their abdomen.  I¡¯ve had a few people report groups of JB¡¯s forming small balls on the ground (males swarming newly emerged females). They are very attracted to floral lures and Japanese beetle sex pheromones and can be easily trapped 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 plants.  If adult populations become economically threatening, applications of Imidan, Sevin and Malathion may be warranted.  Growers: if you think a drench of Intercept will be needed to allow shipping of nursery stock outside your JB zone, the deadline for Intercept applications is August 22, 2009.

We have seen significant leafhopper populations in nursery crops (watch your Caragana, Ptelea, Acer-especially red-leaved cultivars of A. platanoides) especially after forage crops are cut.  Each year I receive calls of injury on Acer in the mid-summer and quite often, late spring leafhopper injury is to blame.  Leafhoppers (and aphids) that feed on expanding foliage will cause it to twist and become shrunken and distorted, often with blackened leaf edges.  Leafhoppers injury also appears as bronzing or stippling to mature leaves.  Monitor populations and treat with pesticides before damage becomes economically threatening.  Leafhoppers are very mobile, tiny, pale coloured jumping insects that are easily disturbed when you approach infested foliage. Leafhoppers are also attracted to yellow sticky cards, for monitoring.  Registered insecticides include Tristar and Sevin XLR.

We¡¯ve noticed quite a significant population of aphids in the landscape and on outdoor nursery stock this year.  There are several species that can be found feeding on the stems and leaves of woody and herbaceous plants.  Insecticidal soap may help reduce populations of aphid, repeat applications at least weekly to give good knockdown.  In the nursery, several insecticides are registered to manage aphids on ornamental crops.

The honeylocust plant bug has taken it¡¯s toll on honeylocust foliage this year, insecticidal application need to be made during leaf emergence to suppress this plant bug, too late now.  Their feeding caused twisting, mottled and defoliated stems. Honeylocust leafhoppers have also become more of a problem as the summer progresses.  Time insecticide applications (e.g. Tristar for leafhoppers in the nursery) where monitoring reveals significant populations and injury. Also, take a close look for Honeylocust spider mite on the lower leaf surfaces.  This tiny, orange mite can cause a lot of late season injury (bronzing) on foliage, contributing to premature leaf drop (along with all of the other insects we¡¯ve already mentioned!).

We found spider mites on leaves of Quercus a few weeks ago.  Check for teeny-tiny mites that are orange with black backs (visible with magnification).  They are causing bronzing on the foliage.  It looks like they are in the genus Oligonynchus (spruce spider mite, maple spider mite) and they look very similar to the maple spider mites we find on red-silver hybrids this time of year.

Two-spotted spider mites (TSSM, Tetranychus urticae) are quite active on field grown ornamentals (woody and herbaceous).  We¡¯ve seen them on several species, most recently on Norway maple (¡®Harlequin¡¯).  Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs. These mites are small but the damage is significant so catch them early. TSSM overwinter as adult mites in the soil and crawl up on host plants and start feeing in late spring.  Where the egg stage is present, Apollo (an ovicide) is available to help reduce populations of eggs and newly hatched nymphs. Miticides registered for this mite in the nursery include: Apollo, DynoMite, Forbid, Kanemite, Kelthane and Vendex.

Emerald ash borer adults may still be flying.  TreeAzin (azadirachtin, neem) has an emergency use registration (until August 31) for emerald ash borer on ash.  This is an injectable insecticide that is delivered though BioForest¡¯s Ecoject system, to inject insecticides to protect ash trees from this borer.  For more information contact BioForest (http://www.bioforest.ca/). The regulated areas for Emerald Ash Borer have been updated (it has most recently been found in Welland). The movement of potentially infested material is restricted in new areas that are regulated under Ministerial Orders. Check out:http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/survenqe.shtml

EVERGREENS:

White pine weevil larvae (Pissodes strobi) are feeding and PUPATING from inside the shoots (terminals) on pine and spruce.  Terminal shoots become brown, flagged or crooked right about now.  PRUNE OUT infested shoots down to the original bud and DESTROY them to prevent the successful emergence of the next generation.

Spruce spider mites (Oligonychus ununguis) can be found feeding on new growth of conifers (Abies, Picea, Pinus, Thuja etc.).  Use lots of water and pressure, try to coat undersides of twigs and foliage.  Kanemite, Floramite and Vendex are registered for use against spruce spider mite.  If you are using Kelthane, treat water if pH > 7.0 as alkaline water will decrease efficacy of Kelthane.

Taxus or Fletcher Scale (Parthenolecanium fletcheri) NYMPHS are feeding on foliage of Thuja and Taxus.  Look for honeydew and small, flat, light brown oval scales on foliage.  Applications of insecticides are most effective against newly hatched crawlers and repeated applications will be necessary since egg hatch and crawler emergence is staggered.

Cedar leaf miner (Argyresthia sp) larvae are starting to feed inside tips of Eastern white cedar.  Foliar applications of systemic insecticides can be effective when applied to the young larvae (mid-late August).  A light sheering of foliage in late August will also help reduce the number of larvae that successfully overwinter.

Galls of Eastern and Cooley Spruce Gall Adelgid will become more noticeable over the next few weeks as they turn brown.  The immature adelgids that feed inside the galls are pupating and winged adults will be emerging soon out of the tiny openings in the gall.  Once insects leave the gall, it turns brown and becomes more noticeable.  If you have the time, pruning out and destroying green galls can help reduce the population for the next generation of adelgids and also improve the look of the tree.  A fall application of horticultural oil to the undersides of branches will help smother the overwintering stage.

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