Nursery and Landscape Report for October 10, 2008

You have reached Jen Llewellyn for the 22nd and LAST EDITION of the 2008 OMAFRA Nursery and Landscape Report, updated on Friday, October 10th.

Environment Canada (http://www.weatheroffice.gc.ca/forecast/canada/index_e.html?id=ON) is calling for a gorgeous Thanksgiving weekend.  We can expect sunshine and high¡¯s of 20-23^oC.  Night-time lows will be in the range of 5-12^oC (a little cooler in the East and North). Intellicast¡¯s radar (http://www.intellicast.com/National/Radar/Current.aspx) is a clear slate for southern Ontario today.

Growing Degree Day accumulations to the end of Thursday, October 9th (GDD 10^oC / GDD 50^oF).(Courtesy of those nice folks at the Weather INnovations Incorporated (WIN): http://www.weatherinnovations.com/index.cfm).  These numbers are only a guide for monitoring purposes. The temperatures at your production facility can vary significantly from the nearest WIN weather station.

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.

With autumn mowing practices you have the opportunity to intergrate with 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.

Rodent bait for vole control should be placed out by now 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.

The presence of wasps, ants and ladybird beetles may be a good indicator that there is a significant population of sucking insects (e.g. mealybugs, scales, aphids).  Most scale insect crawlers have settled as nymphs and are developing a waxy, protective layer.  Applications of dormant oil/landscape oil will give good knockdown of populations this fall and next spring.

DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:  

Take a close look at the foliage of Norway (also silver and red maples) for large, black spots.  These are tar spot lesions.  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 and may be associated with premature leaf drop.   Rake up and destroy infested foliage to reduce the amount of spores available during leaf emergence next spring.  Otherwise, mowing fallen leaves will help accelerate they microbial breakdown, which will also reduce spore load next spring.

Where Gymnosporangium rust was detected on ornamental Pyrus in the landscape this summer, look for bright orange-red lesions on the tops of leaves and tan swellings on the undersides.  Tiny, cr¨¨me-coloured ¡°strings¡± appear on the swellings to signal sporulation.  Spores will be sent out to infect the alternate host, Juniperus.  This is Pear Trellis Rust and it has been confirmed on several ornamental Pear trees in the Toronto area last year and is likely the species present in many other areas as well.  This disease does not overwinter on Pyrus, it overwinters on the Juniperus host.

I¡¯ve had a few inquiries about fireblight this summer.  It¡¯s no surprise that this was a really bad year for this disease.  A lot of people are wondering what they can do to improve the look of the trees.  Science says to hold off on pruning.  Because of the warm weather, pruning could still lead to new infections.  Wait until plants go dormant and prune well below the symptomatic tissue.  Better still, prune in late winter.

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.   http://www.extension.umn.edu/distribution/housingandclothing/M1181.html

Are you seeing mite injury on Acer rubrum, Acer x freemanii (e.g. ¡®Autumn Blaze¡¯, ¡®Jeffersred¡¯)?  Mite injury appears as bronzing and flecking on the top sides of leaves.  Look at the bottom leaf surface and check for tiny, pinpoints or specks.  You¡¯ll need to get your hand lens out.  Recently we have discovered populations of ¡°maple spider mite¡± in at least 2 areas of southern Ontario.  Maple spider mite (Oligonychus aceris) looks exactly like spruce spider mite: black backs, brown legs and head and they lay red, spherical eggs but it feeds on maple leaves.  They can cause major leaf stippling and sometimes the injury results in leaf drop and poor fall colour.  Maple spider mite overwinters as tiny (you¡¯ll need a hand lens to see them) red eggs next to the leaf scar.  Applications of horticultural oil this fall and next spring may help reduce mite populations next summer.  Be careful, silver maples can be sensitive to oils.

Fall webworm nests are very common on deciduous trees (e.g. Juglans, Fraxinus, Prunus, Malus) in the landscape this year.  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).  Chemical pesticides aren¡¯t going to help much (webworms stay in their protective tents and only come out to make a new tent).  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.

Magnolia scale adults are dead but are still clinging to twigs as orangy-pink bumps.  If you pick them off, you will see tiny white grains (empty egg cases).  Crawlers are small, black specks and have settled at permanent feeding sites on twig undersides.  Fall applications of horticultural oil can help smother this scale and help knock down populations.  Avoid horticultural oil applications when high temperatures (e.g. >28^oC) or freezing temperatures are in the forecast.

Beech Scale crawlers have settled. 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.  Applications of insecticidal soap and Landscape Oil or other registered chemical insecticides should be finishing up.  Dormant applications of horticultural oil may cause some phytotoxicity reactions to beech.

There are several more sites for Emerald ash borer infestation in Ontario, most recently in Vaughan and Sault Ste. Marie,  http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/survenqe.shtml

Viburnum leaf beetle adults have laid their eggs on the twigs of Viburnum.  Look for holes and skeletonised foliage on Viburnum.  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!

VARIOUS HOSTS:

Black vine weevil and Strawberry root weevil adults are still feeding on evergreens and perennials in the field and landscape. Adulticides registered for root weevils include Pounce, Sevin and Thiodan. Where black vine weevil larvae are a problem in container production (e.g. perennials, evergreens), you can still treat with Heterohabditis bacteriophora (BGreen) or Heterohabditis megidis (NemasysH).  Any time the media temperatures are above 10-12oC and it is kept moist for 2 weeks, Heterohabditis nematodes will be active.  When used according to the label, nematode applications should result in a significant reduction of larval populations in containers and in the landscape.

There are still some distinct areas around Lake Ontario where Gypsy moth populations are high.  Blue Colorado spruce seemed to be a significant host in the landscape again this year (a sign that the insect is over populated).  Some of this year¡¯s larvae fell victim to fungal and viral diseases with the cool, wet weather we received in late spring.  Manual removal of GM egg masses can help reduce populations for next spring, but many of these egg masses are also laid quite high on the tree trunk, out of reach.  (Something to consider if you are thinking of an egg mass removal program).

EVERGREENS:

The next generation of larvae of the cedar leaf miner are feeding inside the current season¡¯s foliage.  Foliar applications of systemic insecticides (to target mining larvae) are becoming less effective as larvae are preparing for winter diapause.  Where insecticide applications are not possible, try a light sheering (pruning) of branch tips to help prevent the young larvae from completing their life cycle.

Spruce spider mites are feeding on conifers (Abies, Picea, Pinus, Thuja etc.).  You will require a hand lens to see them better.  Adults are tan brown with black backs, nymphs are more orange.  When it gets cold, the adults will turn a reddish colour.  Use lots of water and pressure, try to coat undersides of twigs and foliage.  If you don¡¯t see much activity, monitor in September/October when temperatures cool down¡­.fall is a major feeding period for this mite.  Kanemite (Shuttle) and Vendex are registered for use against spruce spider mite.  If you are usingKelthane, treat water if pH > 7.0 as alkaline water will decrease efficacy of Kelthane.  Floramite can be used for SSM on Christmas trees in Canada.

THIS IS THE FINAL EDITION for the 2008 growing season.

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