Nursery and Landscape Report for July 30, 2009

Environment Canada is calling for warm, humid conditions to continue.  Showers are expected on Sunday.  Highs will be in the mid-20’s and winds will be from the SW or W at about 10-15 km/hr.

Growing Degree Day summaries are from Environment Canada (base temperature 10oC) (July 20).

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”.  The larval bags can be found on foliage and branch tips and resemble killed branches or small spruce cones.  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.  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 youirrigate 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.

Euonymus anthracnose is sporulating and infecting the second flush of growth on container grown euonymus.  Ensure good fungicide coverage before warm, humid nights or after pruning.  Daconil is registered for this disease.  Anthracnose appears as a leaf spot (usually late summer) and stem canker and can be quite serious on variegated cultivars of Euonymus fortunei.

Powdery mildew is becoming 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.

Magnolia scale is becoming quite noticeable on the undersides of young magnolia twigs at this time.  The scale are large, white, powdery looking bumps that squish and are quite watery.  They are quite tolerant of many insecticides this late in their life cycle but if you have a small infestation, you can rub them off (that will kill them).  Once they turn that orangy-pink colour, they start laying their eggs and are impossible to kill.  Crawlers start to hatch around the 2nd week of August in south-central Ontario (earlier in the SW, later in the East).  If you want to try insecticides for the crawlers, make sure you are making at least 2 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.

Japanese beetle adults are 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.

Viburnum leaf beetle adults have emerged.  They too will feed on the interveinal tissue of leaves, causing skeletonising of the second flush.

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!).

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.

We found spider mites on leaves of Quercus this week.  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 greenhouse include: DynoMite, Vendex, Floramite, Forbid and Kelthane.

Peach tree borer (Synanthedon exitosa) adults may still be flying in Prunus blocks. Look for cankered regions and chewed bark/wood in the lower stems of Prunus x cistena (and other Prunus spp.) 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 (approximately 390 GDD Base 10oC, ‘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.  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 are also starting to emerge in container production at this time.  To purchase pheromones, try ordering from IPM suppliers such as www.greatlakesipm.com and www.naturalinsectcontrol.com.

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 four new areas that are regulated under Ministerial Orders. Check out:http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/survenqe.shtml

EVERGREENS:

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 closely at 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, 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.

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.

Pine false webworm (Acantholyda erythrocephala) larvae may still be snipping off foliage and making 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.

Red-headed pine sawfly may still be feeding on new growth of pine.  When threatened, the larvae will simultaneously rear up on their end and form an “S” shape.  Small infestations can be removed manually.  Contact insecticides are registered for this pest (e.g. Success 480 SC).

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 have pupated and tiny, grey adult moths may still be found fluttering around foliage.  Foliar applications of systemic insecticides are much more effective when applied to the next generation of young larvae (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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