Nursery and Landscape Report for August 28, 2008

You have reached Jen Llewellyn for the 19th edition of the 2008 OMAFRA Nursery and Landscape Report, updated on Thursday, August 28th.

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Environment Canada (https://weather.gc.ca/forecast/canada/index_e.html?id=ON) is calling for showers and cloudy conditions for much of Thursday and Friday BUT¡­.they are actually forecasting sunshine and warm weather for the last long weekend of the summer!  High¡¯s will be in the mid-high 20¡¯s and night-time lows will be in the mid-teens (a little cooler in Eastern Ontario).  Intellicast¡¯s radar (http://www.intellicast.com/National/Radar/Current.aspx) is showing some patches of precipitation over southern Ontario today.

Growing Degree Day accumulations to the end of Wednesday, August 27 (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.

DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:  

Given the weather, it¡¯s no surprise that plant diseases are significant in susceptible crops this year.  Monitor for common leaf diseases such as leaf spot, downy mildew, powdery mildew and anthracnose on herbaceous perennials and deciduous shrubs (Rosa, Prunus, Cornus).  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 and you will notice that the next flush of growth is much nicer.  Rhapsody is a biological fungicide that has some PREVENTATIVE efficacy against leaf diseases on ornamentals.

Take a close look at the foliage of Norway (also 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 and may be associated with premature leaf drop.

Where Gymnosporangium rust was detected on ornamental Pyrus in the landscape this summer, look for bright orange-red lesions on leaves.  Cr¨¨me-coloured sporulation on the undersides of leaf lesions will appear in the next few weeks or so and will send out spores to infect Juniperus.  Pear Trellis Rust 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.

Honeylocust spider mite is starting to ramp up on Gleditsia in production nurseries and in the landscape.  Mites are very tiny (similar to TSSM) with clear-tan bodies.  We have seen this mite in production nurseries in previous years, especially in hot, dry summers.  Where populations are high, mite injury could cause significant stippling, bronzing and defoliation may result.  Try repeated applications of the summer rate of horticultural oil or insecticidal soap.  Otherwise, Orthene and Kelthane are registered for this mite.  Repeat applications may be necessary (remember Kelthane can only be used 1x per year).  http://www.forestryimages.org/browse/detail.cfm?imgnum=1325012

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.  Where injury and populations are threatening marketability and crop health, horticultural oil, insecticidal soap and registered miticides will help reduce populations.  Dormant oil applications this fall and next spring can also reduce populations of maple spider mite eggs that overwinter on buds of small twigs.  http://www.ca.uky.edu/HLA/Dunwell/KHC/NurseryUpdate20_2004.html

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 are orangy-pink and they have laid their eggs and are resistant to insecticides.  Crawlers have hatched and now is the time when they are the MOST susceptible to insecticides.  Crawlers are small (0.5-1mm) flattened and mobile, usually on the undersides of young twigs.  They will hide under the protective cover of the female for a few days first.  If you want to try insecticides for the crawlers, make sure you are making at least 2-3 repeat applications, 7-10 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.

Leafhopper populations are significant in some areas, they are infesting outdoor ornamentals in many parts of the province (watch your Caragana, Ptelea, Acer) where forage crops are receiving a cut.  Leafhoppers are also attracted to yellow sticky cards, for monitoring.  Leafhoppers are very mobile, tiny, pale coloured jumping insects that are easily disturbed when you approach infested foliage. Pesticides are often not warranted this late in the season.  Registered insecticides include Tristar and Sevin XLR.

Aphid populations usually start to build this time of year.  Aphids love to feed on the soft, succulent new leaves.  Quite often they hide on the leaf undersides or inside coiled up leaves.  A sure sign of aphid infestation is the presence of ants and ladybird beetles.  Injury is not as significant this late in the season.  Several insecticides will knock down aphids, some newer products include Endeavor and Tristar.  Some softer alternatives include insecticidal soap.

There are several more sites for Emerald ash borer infestation in Ontario: http://www.inspection.gc.ca/english/plaveg/pestrava/agrpla/survenqe.shtml

In Ontario, TREEAZIN is registered for use as an injectable insecticide (using the Eco-Ject system, BioForest Technologies) to help protect ash trees against Emerald ash borer attack (until August 31^st).  Treat trees in July and August, on sunny days; this will facilitate rapid uptake and help protect the tree from larval attack.

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.

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), wait until the next generation of larvae in September and treat with Heterohabditis bacteriophora (BGreen) or Heterohabditis megidis (NemasysH) then.  This should result in a significant reduction of populations in late summer.

EVERGREENS:

Look for defoliation of last year¡¯s needles on pines (Scots, Austrian, red) as a sign of Lophodermium needlecast.  Affected foliage is found primarily at the base of the tree.  Fallen, diseased needles will be brown with football-shaped black fruiting structures on them.  These fruiting structures will produce spores that infect the newest growth from now until the beginning of autumn.  Protect new growth with applications of Copper Spray, Daconil and Dithane starting now until the end of September.  Sporulation takes place when conditions are warm and wet.     http://www.plantpath.cornell.edu/Trees/LophNcst.html

Where Fletcher scale was a problem on evergreens last year, monitor for small, brown scale adults on evergreens such as Taxus, Thuja. These scales can be found on the undersides of foliage and twigs.  The adults are dead, if you pick them off, you will see the tiny white egg cases (empty) underneath.  Fletcher scale crawlers are settling as nymphs and are still susceptible to many pesticides (including summer rate of horticultural oils and insecticidal soap).  Fletcher scale nymphs are light tan, very tiny and very flat (use a hand lens to monitor).  If they are alive, they will be watery if you poke them with a pin.  If they are dead, they will flake away easily.  Egg hatch is staggered so apply insecticides weekly and repeat to get optimal control.

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 effective when applied to these young larvae in the next week or two.  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.

Look for the second generation of pine needle scale crawlers in the next couple of weeks (Rose-of-Sharon and Bottlebrush Buckeye are blooming).  Adult scales appear as white flecks on the needles and crawlers are a dark reddish/purple and are quite mobile.  Newly hatched crawlers are the most susceptible to chemical control.

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.  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 using Kelthane, 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 MESSAGE WILL BE UPDATED the week of September 2nd.

– See more at: https://lawnsavers.com/nursery-and-landscape-report-2008/nursery-and-landscape-report-for-august-28-2008.html#sthash.vAMx7kRV.dpuf