Nursery and Landscape Report for July 24, 2008

You have reached Jen Llewellyn for the 16th edition of the 2008 OMAFRA Nursery and Landscape Report, updated on Thursday, July 25th.  The report will be updated in 2 weeks.

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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 and there is, yet another, SEVERE THUNDERSTRORM WATCH for many parts of southern Ontario this afternoon.  It will be sunny on Friday, with high’s in the mid 20’s and winds out of the SW, but the rain may return for the weekend.  Intellicast’s radar (http://www.intellicast.com/National/Radar/Current.aspx) is showing current radar conditions for our area.

Growing Degree Day accumulations to the end of Wednesday, July 23rd (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.

Reminder: Alkaline water (>pH 7.0) that has a high concentration of bicarbonates can actually reduce the action of many pesticide products including: *Cygon*, Dipel, Dylox, Furadan, Imidan, Kelthane, Malathion, Orthene, Pounce, Pyrate, Sevin.  It helps to mix the pesticides as close to the application period as possible and to mix only the amount needed for that application (ie. Avoid using tank mixes that have been sitting around for several hours).  Ground water sources in southern Ontario can contain high levels of bicarbonates.   Try using acidified water or rain water (cistern water) for you sprayer tank.

DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:  

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 starting to rear it’s ugly head on 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 becoming 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.

Magnolia scale is becoming quite noticeable on the undersides of young magnolia twigs at this time.  The scale are large, white, powdery looking bumps that squish and are quite watery.  They are quite tolerant of many insecticides this late in their life cycle but if you have a small infestation, you can rub them off (that will kill them).  Once they turn that orangy-pink colour, they start laying their eggs and are impossible to kill.  Crawlers start to hatch around the 2^nd week of August in south-central Ontario (earlier in the SW, later in the East).  If you want to try insecticides for the crawlers, make sure you are making at least 2 repeat 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.

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 in a couple of weeks, once adults have emerged (Endosulfan, Pyrate, Thiodan).

Japanese beetle adults have emerged.  Look for large, coppery-green metallic beetles (13mm long) with distinctive white tufts of hairs around the sides of their abdomen.  They are very attracted to floral lures and Japanese beetle sex pheromones and can be easily trapped 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 plants.  If adult populations become economically threatening, applications of Imidan, Sevin and Malathion may be warranted.

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 their first 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.

Lecanium scale (Parthenolecanium corni) crawlers are settling into the nymph stage and permanent feeding sites.  Monitor deciduous trees (e.g. Quercus, Fraxinus) and look for small, rounded, dark brown bumps on the undersides of small twigs.  Pick off these adult female scales and look for tiny, white grains underneath….those are the egg cases.  Crawlers are fast-moving, white insects with 6 legs.  Treat at weekly intervals with the summer rate of Landscape Oil or insecticidal soap.  Population of scale insects on and landscape trees that have southwest exposure will be further advanced in their development (i.e. the eggs will hatch sooner than on other trees).

Golden oak scale crawlers may still active (450-700 GDD Base 10^oC).  Treat at peak egg hatch and repeat at least 2 x to catch their staggered emergence.  Golden oak scale is most commonly found on our English oaks, especially on stressful sites.

Cottony maple scale crawlers are starting to settle.  Adult females lay their eggs in those cottony masses, they look like a piece of popcorn.  They are often found on silver maples that are under stress.  Despite their name, I’ve seen them on a broad range of woody plants.  Monitor for peak egg hatch before attempting pesticide applications.

You won’t have trouble finding aphids infesting herbaceous and woody nursery stock 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.  Several insecticides will knock down aphids, some newer products include Endeavor and Tristar.  Some softer alternatives include insecticidal soap.

Two-spotted spider mites are infesting container grown ornamentals (woody and herbaceous) in the greenhouse and in outdoor production.  Use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs. These mites are small but the damage is significant so catch them early.  Miticides registered for this mite include: Dyno-Mite, Vendex, Kanemite, Forbid and Kelthane.  TSSM on field grown nursery stock have emerged. TSSM overwinter as adults on the ground, in polyhouses and in greenhouses.  After they emerge and lay their first clutch of eggs, try applying Apollo (an ovicide) at the FIRST sign of egg hatch.  This will help reduce viability of eggs and newly hatched motiles.  Do not make more than one application of Apollo per season.  Predatory mites, such as Phytoseiulus persimilis or Amblyseius californicus are also quite effective against two-spotted spider mites although these predatory mites aren’t as active when temperatures exceed 30^oCBiological control:  http://www.omafra.gov.on.ca/english/crops/hort/news/grower/2008/01gn08a1.htm

Gypsy moth adults are flying.  Males are very mobile, dusky-brown that fly erratically near the ground.  Females are more robust, white, flightless that crawl up trunks to lay their eggs.  We have seen many cases of larval mortality in the nursery and in the landscape.  The frequent rains have been ideal for the spread of pathogenic fungi that infect GM larvae and kill them.  Look for dead carcasses of larvae stuck to tree trunks or littering the ground.  We are seeing about 30-50% kill from natural borne fungi (pretty cool eh?).  Sticky bands around trunks (above pupation sites where possible) will help prevent adult females from laying eggs above those bands, and will attract males to the sticky surface.

Swarms of brown, buzzing insects at dusk around trees and shrubs are probably European chafers.  They are late this year, but they are flying once the sun goes down.  They fly in giant mating swarms, feed on foliage and come down to the ground to lay their eggs.  Preventative applications of Intercept will hopefully help reduce the number of successfully hatching larvae.

There are more sites for Emerald ash borer infestation in Ontario: http://www.inspection.gc.ca/english/corpaffr/newcom/2008/20080716e.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 emerged.  They too will feed on the interveinal tissue of leaves, causing skeletonising of the second flush.

VARIOUS HOSTS:

Black vine weevil and Strawberry root weevil adults have emerged 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.

Look for long-legged, bronze coloured beetles feeding on roses, crabapples and other woody ornamentals in the coming weeks, these are Rose chafers (Photo: http://www.uwex.edu/ces/wihort/flowers/RoseChafers.htm).  Try shaking beetles into a bucket of soapy water, this will smother them.  Contact insecticides (e.g. Sevin) will reduce populations but control may not be acceptable.

EVERGREENS:

If you are bringing in SOD (Sudden Oak Death, Phytophthora ramorum) host nursery stock from high risk areas, you may want to monitor for SOD symptoms.  Camellia, Rhododendron, Viburnum, Pieris, Kalmia and Syringa are considered to be high risk host genera, as they are most common genera found positive for SOD in retail and wholesale nurseries.  For a complete list of SOD regulated hosts, check out:        http://www.inspection.gc.ca/english/plaveg/protect/dir/sodspe.shtml

The California Oak Mortality Taskforce (COMTF) is a great place to find photographs and the latest info on this disease:    http://www.suddenoakdeath.org/

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 will become more noticeable over the next few weeks as they turn brown.  The immature adelgids that feed inside the galls are pupating and winged adults will be emerging soon out of the tiny openings in the gall.  Once insects leave the gall, it 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.

Look for yellow headed spruce sawfly on spruce.  Sawfly larvae are very susceptible to chemical control when they are still young.  Try Success (spinosad) as a lower toxicity alternative.

Red-headed pine sawfly will feed 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.  Contact insecticides are registered for this pest (e.g. Success 480 SC).

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.

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.  They have completed their life cycle and if you pick them off, you will see the tiny white egg cases (empty) underneath.  Fletcher scale CRAWLERS have hatched and are susceptible to many pesticides (including summer rate of horticultural oils and insecticidal soap).  Egg hatch is staggered so apply insecticides weekly and repeat to get optimal control.

THIS MESSAGE WILL BE UPDATED Monday, August 11th.

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