Nursery and Landscape Report for August 12, 2008

You have reached Jen Llewellyn for the 17th edition of the 2008 OMAFRA Nursery and Landscape Report, updated on Tuesday, August 12th.

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Environment Canada (http://www.weatheroffice.gc.ca/forecast/canada/index_e.html?id=ON) is calling for the chance of showers with sun and cloud expected for the next few days.  High¡¯s will be in the low-mid 20¡¯s and winds out of the NW this afternoon but will be changing quite a lot over the next few days.  Night-time lows will be in the mid-teens for the rest of the week.  Intellicast¡¯s radar (http://www.intellicast.com/National/Radar/Current.aspx) is showing rain-free conditions for southern Ontario today.

Growing Degree Day accumulations to the end of Monday, August 11 (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 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.

Downy mildew is rearing it¡¯s ugly head on some 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.  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).  Downy mildew can therefore be easily mid-diagnosed.  This disease is exacerbated by long leaf wetness periods.  Make sure you irrigate 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.

LEAF BLISTER can be found rampant on decidous trees this year.  It causes large, black blister-like spots on the foliage (reminiscent of low temperature injury).  So far we¡¯ve noticed fungal leaf blister on red oak in the nursery and landscape.  Arborists are also reporting this disease on Siberian elm in the landscape.  The fungus overwinters on the shoots and sporulates in the spring to infect emerging leaves.  Fungicides will not help this late in the season.

Powdery mildew is evident on many outdoor ornamentals.  It appears as a white-grey powder on the tops of leaves.  This fungus is unique in that it does not require water to grow and infect host tissue.  Powdery mildew takes off when days are hot and dry (spore dispersal) and nights are cool and damp (spore production).  Early detection is the key to managing this disease.  Always start monitoring for powdery mildew based on historical hot spots or crops (e.g. Amelanchier, Prunus, Rosa etc.).  Treat with a fungicide, like Nova or Banner Maxx (same family), Compass, sulphur and Rhapsody when symptoms first appear and repeat every 5 to 10 days.  Rhapsody ASO is a new biological control that has good preventative efficacy against powdery mildew.  Be aware that sulfur will damage many Viburnum spp and almost any species under temperatures of 27^oC or more.  Always consult the label.

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.

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.

Fall webworm nests are becoming more noticeable on deciduous trees (e.g. Fraxinus).  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 may give some reduction in webworm populations (webworms hide in the tents during the day and feed at night).  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.

Magnolia scale is becoming quite noticeable on the undersides of young magnolia twigs at this time.  They are orangy-pink and they have started laying their eggs and are resistant to insecticides.  Crawlers start to hatch around the 2^nd week of August in south-central Ontario (earlier in the SW, later in the East) but the cooler temperatures likely set their development back this year.  Crawlers are small (0.5-1mm) flattened and mobile, usually hanging out 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.

Poplar-Willow borer adults are emerging from the stems of Salix (willow) at this time.  Take a look at the bark of top-grafted Salix for subtle sawdust and frass clinging to the bark.  If you scrape the area with a knife, you will find their tunnel and if you work your way up the tunnel, you might still find a pupa.  We found them on Salix understock (standards) plant symptoms ranged from ¡°none¡± to those Salix that were dying back.  Remove infested plants to prevent the next generation of adults from emerging and laying their eggs in your production blocks.  Check your understock mother blocks as well.  Some growers may want to treat bark to prevent successful egg laying/hatch, once adults have emerged (Endosulfan, Pyrate, Thiodan).

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.  I often get 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.  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.

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.

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 to confirm it is a spider mite (8 legs, two body regions) and to view physical characteristics.  Usually, two-spotted spider mite is the culprit that causes so much injury on deciduous trees this time of year, but 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

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.  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 August or 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:

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 whitish-clear, very tiny and very flat (use a hand lens to monitor).  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 oliage.  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.

Galls of Eastern and Cooley Spruce Gall Adelgid have become more noticeable as they are turning brown.  The immature adelgids that feed inside the galls have pupated and winged adults are emerging out of the tiny openings in the gall.  Once insects leave the gall, the gall 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.

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.  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 Monday, August 18th.

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