Nursery and Landscape Report for July 16, 2010

You have reached Jen Llewellyn for the 14th edition of the 2010 OMAFRA Nursery and Landscape Report, updated on Friday, July 16th.

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Environment Canada is calling for continued hot, humid weather for the next several days.  Highs will be in the range of 28-31^oC in most areas.  There is a chance of showers and T-storms tonight and over the weekend.  Winds will be out of the west or southwest at 20km/hr.

Growing Degree Days are to the end of Thursday, July 15 (GDD 10^oC / GDD 50^oF).  These numbers are only a guide for monitoring purposes. The temperatures at your production facility can vary significantly from the nearest weather station.   Check out: https://climate.weather.gc.ca/?url=http%3A%2F%2Fclimate.weather.gc.ca

Weed ID Online:  http://www.weedinfo.ca/home.php

PLEASE NOTE: 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. There is exception from the ban for the use of pesticides to maintain the health of TREES, if certain conditions are met.  For more info, you can go to the Ministry of the Environment’s website at http://www.ontario.ca/pesticides

VARIOUS ORNAMENTALS:

If you are growing ornamentals in containers, now is a good time to check EC and pH.  Where pH is creeping up to 7.0 and above, you may want to do some monitoring for chlorosis (yellowing) and interveinal chlorosis on woody and herbaceous crops.  Many nursery ornamentals cannot get needed micronutrients at high pH and suffer deficiencies of Iron (Fe) and Manganese (Mn), [not Magnesium (Mg)].  If you are seeing chlorosis and media pH is alkaline, try supplementing with chelated Fe/Mn products that are formulated for greenhouse and nursery crops.  2-3 foliar applications should help crops green up quickly.  Drenches are longer lasting but a lot more labour intensive.  Chlorosis on Syringa and Hydrangea is often an indication of high pH in the media.  Also, test your irrigation water for pH and level of bicarbonates at a commercial lab.  The bicarbonates in your irrigation water are driving the pH up in the container media – you need to know what level those bicarbonates are at.

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, mid-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).

Check for adults of black vine weevil and strawberry root weevil hiding under crops such as Picea, Rhododendron, Taxus, Thuja and Euonymus in field and container (woody and herbaceous) production nurseries and the landscape (where Catalpa speciosa are blooming).  BVW will feed by chewing out notches in leaf margins, they are ~1.5 cm long, black, with mottled brown flecks on their backs.  SRW feed by girdling the bark of small twigs and are ~0.8 cm long, reddish brown.  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 are not effective at this time.  The next window for nematodes to target the next generation larvae in soil will be late summer.

White grubs adults may still be flying, such as European chafer.  A preventative application of Intercept (imidacloprid) is registered for white grubs in nursery production.  In the field, the application period is June to July (to coincide with egg-laying).  Nematode applications for white grubs (e.g. European chafer) are not effective at this time.  Try timing nematode applications for late August/early September to catch early-instar larvae.

Japanese beetle adults are quite 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 turf.  If adult populations become economically threatening, applications of Sevin, Malathion or Imidan may be warranted.  Growers: to help qualify for the Japanese beetle certification program, an application of Intercept on container or field stock should be made some time between June and July (notify your inspector first).  The cut-off period for Intercept applications to comply with the CFIA JB Certification program this year may be as early as July 31^st this year.

DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:  

Sudden leaf drop has been reported on deciduous trees in the landscape and also on some crops in the nursery (e.g. Euonymus).  Some of the leaf drop is likely in response to extreme heat, humidity and those areas not receiving as much precipitation.  In some cases, spring diseases such as anthracnose have been linked to the dropped leaves.  It is a survival mechanism of the plant and in most cases, does not lead to dieback.

Fireblight is quite active in field production this summer.  Look for sudden dieback of branches with persistent, dark-brown leaves.  Often, the branch tips become curled like a Shepherd’s crook.  You can try removing the trees carefully, during hot/dry weather only, bagging symptomatic tissue and destroying it immediately to try reducing disease spread.  Copper products should help to protect healthy foliage in the remainder of the field.  This is a very virulent disease.  Bloomtime, Blightban and Serenade Max may help give some disease suppression.

We are seeing dieback of Syringa reticulata ‘Ivory Silk’ in field production nurseries.  Those trees growing on heavier, not-as-well draining soils with clay in them are holding too much water/insufficient aeration and the fine feeder roots of the trees are dying.  In the canopy, we are seeing wilting, tissue browning, brown leaves persisting on the trees.  If you slice into the cambium on the stem at the soil line, you will see brown lesions in the tissue.  Previous lab reports have come back with Fusarium root and stem wilt.  The underlying cause is poorly-drained soils and ‘Ivory Silk’ intolerance of heavy soils.

Powdery mildew is an issue on highly susceptible ornamentals (Amelanchier, Rosa, Syringa) with this hot, dry weather.  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 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 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.  Acrobat fungicide was recently registered to help combat downy mildew on ornamentals.  Reducing leaf wetness periods will also go a long way.  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.  Bacterial diseases may be suppressed with copper fungicides and reduced leaf wetness periods.

We saw black spot on rose last week in the landscape.  The disease looks like dark lesions with fuzzy edges and quite often causes infected foliage to turn yellow and premature leaf drop.  Black spot can also cause a purplish cane blight.  The disease is most common on older rose cultivars that are under overhead irrigation.  Rogue out severely affected plants in the nursery.  Where disease pressure is still low in the nursery, some protection may be achieved with the use of Banner Maxx, Daconil, Nova, Senator etc.

Pear trellis rust (Gymnosporangium fuscum) is starting to become evident on pear trees this year in the landscape.  Look for small, bright orange 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).

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 with a dusting of white powder.  They will be starting to lay their eggs pretty soon.  Pick off scale insect and look at the underside: if it is still fleshy, they haven’t matured yet.  If tiny, white grains can be seen (like salt grains), they have started laying their eggs.  Crawler hatch usually starts late July to early August (~1200 GDD 10^oC).  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.

Leafhoppers: nymphs and adults are feeding on crops.  Monitor for leafhoppers (such as potato leafhopper) on nursery crops such as Caragana, and Acer, especially after forage crops have been cut on neighbouring farms.  Leafhopper 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. Adults blow in from the south and prefer to feed and lay their eggs on newly expanding leaf tissue, especially the 2^nd flush in June.  Leafhopper nymphs are tiny, flightless, yellow-green insects that move sideways, very rapidly across the leaf. Leafhoppers suck plant sap from expanding foliage and cause foliage to wilt, become off-coloured and eventually curl and become stunted with brown-black margins (“hopper burn”). Leafhopper injury also appears as bronzing or stippling on more mature leaves.  Monitor populations and treat with insecticides before damage becomes economically threatening.  Leafhoppers are also attracted to yellow sticky cards, for monitoring.  Registered insecticides include Tristar and Sevin XLR.

I know it’s early but Fall webworm nests may be starting to form on trees.  I’ve seen them in early summer on Betula (birch) before, they are also common on Fraxinus (ash) and Juglans (esp. black walnut).  Look for webbed tents on the ends of branches with fuzzy, crème-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.  Chemical pesticides may give some reduction in webworm populations but it is very difficult to get past that 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.

European fruit Lecanium scale crawlers are active.  Look for adults: reddish brown bumps on the twigs of deciduous trees such as Quercus, Fraxinus and Acer.  Crawlers are tiny, pale tan and emerge slowly over several days, multiple applications of insecticides may be warranted.  For a low toxicity alternative, try insecticidal soap and the summer rate of horticultural oil where appropriate.

Woolly beech aphid can be found feeding on European beech (Fagus sylvatica) leaves.  The aphids overwinter as eggs, hatch at bud bread and give birth to live young as leaves have expanded.  They secrete a white, waxy substance that covers their body and makes it appear “woolly”.  Insecticidal soap or a strong stream of water can help reduce numbers of woolly aphids before they coat the undersides of the leaves.  Infestation does not reduce host vigour, but honeydew production attracts other insects (ants, bees, wasps) and sooty mould.

Emerald ash borer adults are active in south western Ontario.  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 help protect ash trees from this borer.  For more information contact BioForest (https://bioforest.ca/en/canada/products/).   The regulated areas for Emerald Ash Borer have been updated. Check out: http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/survenqe.shtml

Honeylocust plant bugs and honeylocust leafhoppers can be found feeding on new foliage (nymphs are 3-4 mm long, green, fast crawling plant bugs and tapered leafhoppers).  The plant bugs have really caused a lot of injury on mature honeylocusts in Wellington County this year.  This was a significant pest in the last couple of years, treat where there is a history of damage and a high population, where appropriate.  There are multiple generations throughout the growing season.

Peach tree borer (Synanthedon exitosa) adults may still be active in container and field production. 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. Applications of insecticides for egg hatch/newly-hatched larvae should be finishing up soon.

Gypsy moth larvae have pupated and adults are emerging.  We haven’t seen many gypsy moth larvae this year, much of the larvae were killed by naturally-occurring diseases in June, 2009. Sticky bands around trunks should be placed out now to help intercept flightless adult females and prevent them from laying eggs in the canopy above (and to attract and trap adult males on the sticky surface to interrupt their mating plans).  Pheromone traps for adult males can also be placed out and are available from IPM suppliers such as Natural Insect Control in Niagara.

We found spider mites on leaves of Quercus this time last year in nursery production.  Check for teeny-tiny mites that are orange with black backs (visible with magnification).  They have caused bronzing on the foliage in past years.  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) are active on greenhouse and field grown ornamentals (woody and herbaceous).  They love this hot, dry 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.  In the greenhouse, biocontrol agents should be brought in to coincide with the first sign of TSSM.  Phytoseiulus persimilis and Amblyseius californicus are two good choices for predatory mites when temperatures are below 26^oC.  Wait until this heat wave is over and re-introduce.

EVERGREENS & CONIFERS:

Look for yellow-headed spruce sawfly on current season’s needles of spruce (they have more of a reddish-brown head actually).  Sawfly larvae are very susceptible to chemical control when they are still young.

Red-headed pine sawfly is 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.  Several contact insecticides are registered for conifer sawflies, try Success 480 SC as a low toxicity alternative.

White pine weevil larvae (Pissodes strobi) are feeding from inside the shoots (terminals) on pine (white, Scots) and spruce (Norway, Serbian).  Terminal shoots become yellow, droopy or flagged like a Shephard’s crook right about now (we are seeing this in field production).  By cutting cross-sections of wilting terminals, you will see the small white legless larvae just inside the shoot.  Prune out infested shoots down to the original bud and destroy them to prevent the successful emergence of the next generation.  You will have to train a new leader.

Pine false webworm larvae are feeding on the foliage of white pine. 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 (Parthenolecanium fletcheri) crawlers are active on foliage and twigs of Thuja and Taxus.  Look for honeydew, black sooty mould and small, brown bumps on foliage (dead adult females). Applications of insecticides are most effective against crawlers in late June/early July this year.  Repeated applications (2-3 times) will be necessary since egg hatch is staggered.   Try insecticidal soap and the summer rate of horticultural oil where appropriate.

There were some pockets of Striped Pine scale on Scots pine last year in the landscape and nursery.  Look for reddish brownish “bumps” along the undersides of twigs and copius amounts of honeydew and black sooty mould.  It is advised to flag infested trees and treat them in early July to target the newly hatched crawlers.  Try insecticidal soap and the summer rate of horticultural oil where appropriate.

Cedar leaf miner larval populations were very damaging this spring.  The next generation of larvae are just starting to hatch.  Applications of 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.  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.  In field production, SSM populations usually go dormant (egg stage) in the heat of the summer.  However in container production, SSM may stay active all summer (probably due to cooling effect of overhead irrigation).

– See more at: https://lawnsavers.com/nursery-and-landscape-report-2010/nursery-and-landscape-report-for-july-16-2010.html#sthash.1wDjvTx4.dpuf