Nursery and Landscape Report for September 24, 2010

You have reached Jen Llewellyn for the 21st edition of the 2010 OMAFRA Nursery and Landscape Report, updated on Friday, September 24th.

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The 32nd annual Canadian Greenhouse Conference is coming to the International Centre (near Pearson / Toronto airport) October 6 and 7th. The program includes pre-conference tours, sessions related to the production of greenhouse ornamentals and vegetables and there is also a trade show. For more information please check out their web site at

Growing Degree Days are to the end of Thursday, September 23 (GDD 10oC / GDD 50oF).  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:

Peterborough: 1187 / 2137 Hamilton RBG:    1422 / 2560
Vineland Stn:   1383 / 2489 London CS:   1380 / 2484 Windsor:   1701 / 3062

Weed ID Online:

Up to half of the annual fertilizer requirement may be applied to field and landscape plants, after top growth ceases (mid-September to mid-October).  Autumn is a major root growth period for woody and herbaceous perennials.  Roots will grow and absorb nutrients whenever soil temperatures remain above 5¡ãC (conifers will grow at even lower temperatures).  Environmental cues like temperature, day length and light intensity will stimulate plants to prepare for dormancy – late season root growth and storage is part of that process.  It is not advisable to apply fertilizer in late fall or winter¡ªabsorption will be limited due to cold soil temperatures and fertilizer can be lost through runoff.

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

Rodent bait for vole control in the nursery and landscape should be placed out by now (especially where container plants are pot tight).  With all the seeds and fruit available this time of year, rodents are breeding heavily and build up their numbers.  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 torotate 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.

With autumn mowing practices you have the opportunity for the cultural control of many tree diseases (and help discourage voles and mice from nesting near your trees). All those infected leaves dropping from the maples, oaks and crabapples are carrying fruiting structures that will be a source of disease next spring.  Research has shown that mowing/mulching fallen leaves regularly (e.g. weekly) and applying a light irrigation (and some water soluble nitrogen that is part of your fall fertilizer program) will help accelerate the breakdown of those diseased leaves over the autumn months.  This means a significant reduction in the amount of fruiting structures that can start off the disease cycle next spring.  Kevin Frank of Michigan State University suggests keeping mower blades sharp since leaves can be tougher than grass.  Raise the mower height up and mow leaves when they are lightly wet (e.g. morning dew).  This will keep the leaves from blowing all over and will prevent the mower from getting bogged down in wet leaves.  The decomposing leaf litter is an excellent source of slow release nutrients and organic matter for your lawn or cover crop.


Check for tiny, white, legless larvae of black vine weevil and strawberry root weevil feeding on roots of plants such as Picea, Rhododendron, Taxus, Thuja and Euonymus in field and container (woody and herbaceous perennials) production nurseries and the landscape.  Applications of beneficial nematodes (e.g. Heterohabditis bacteriophora) should have been applied by now, while soil temperatures are still warm enough.  In the landscape, Steinernema kraussei can be used as it has some activity in cooler temperatures and may infect BVW larvae in the soil over the next several weeks.  Nematodes are much more effective in containers where soil moisture can be maintained.  Met52 is also available and is another biological option for managing black vine weevil in nursery production.  Met52 comes in a granular form and is meant to be incorporated to the container media at the time of potting.  Met 52 is available through Plant Products.

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 feeding damage on cedar, spruce, and several different deciduous hosts including honeylocust and crabapple.  Foliage will turn brown and become quite sparse.  The larval stage is finished feeding in most areas.  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.


Fireblight was bad in some production areas this summer. Given the warm, wet season, it¡¯s no surprise that this was a fairly significant year for this disease We noticed fireblight on sprout-free understock and also newly budded understock.  Carefully remove, bag and destroy infested plants on dry days.  For landscape trees, you may want to hold off on pruning.  Pruning during warm autumn weather could still lead to new infections.  Wait until plants go dormant and prune well below the symptomatic tissue.  Better still, prune in late winter when the disease and plants are dormant.

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).

Viburnum leaf beetle adults have laid their eggs on the twigs of Viburnum.  Look for holes and skeletonised foliage on Viburnum leaves.  Turn the new twigs upside down and you will see rows of brown, bumpy caps on the underside of the green twig.  Pick off the bumpy caps and you¡¯ll see the tiny yellow eggs tucked down inside the twig.  By pruning out infested twigs, you can reduce the population of hatching larvae next spring.

This is a great time of year to monitor for Eastern tent caterpillar egg masses.  Monitor Prunus, Malus and Crataegus on sunny days once the leaves have dropped.  Look for shiny, silver thickened bands around current season¡¯s twigs.  Prune out and destroy to prevent all those messy larval tents and defoliation next spring!

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 large, black spots.  This is tar spot on maple, named after the large, circular black lesions formed by the fruiting structures.  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, you can still see some of the dead adult female magnolia scales: large, pinkish-orange scales.  Crawlers are settling on permanent feeding sites on the undersides of twigs and developing into dark, nymphs. Insecticide applications should be completed by now.  You may want to try an application of dormant oil in mid October, to smother the overwintering nymphs.

Beech Scale crawlers may still be active (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.  Fall (October) and spring dormant applications of horticultural oil may also reduce overwintering beech scale nymphs.

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 are empty and the larvae are finished feeding and are overwintering as pupae in the soil.  Damage from the fall webworm is usually insignificant to tree health, late in the season.

Emerald ash borer larvae are feeding inside the cambium of ash trees at this time.  The application period for TreeAzin (azadirachtin, neem) finished August 31st.  There have been new finds of Emerald Ash Borer in Ontario.  The latest information can be found at:


Cedar leaf miner larval populations were very damaging this spring.  The newest 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.  These mites are very active because of the cool, wet weather we¡¯ve been having.  Spruce spider mites do a lot of feeding 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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