August 15, 2009
By Jen Llewellyn
OMAFRA Nursery Crops Specialist

Growers need to be aware of the cut-off date for drench applications of Intercept (imidacloprid) to treat outdoor-grown ornamental nursery stock for Japanese beetle (Popillia japonica) larvae. All Intercept insecticide applications (greenhouse and outdoors) will need to be made by Aug. 22, 2009 for plants that are not otherwise eligible for shipment because of the Japanese beetle (JB). This date will be enforced for Ontario and Quebec this year, and will change in future years, depending on seasonal temperatures.  
For the purposes of Japanese beetle infestation, zone 1 is considered JB-free (B.C.), zone 2 is an area of low JB prevalence (Nfld.), zone 3 is partially or generally infested (Ont., Que., N.B., N.S., P.E.I.), and zone 4 is not known to be infested (Alta., Sask., Man., Yukon, Nunavut, N.W.T.). If the nursery stock is not eligible for shipping to a different JB zone and it is after Aug. 22, Dursban (chlorpyrifos) will be the only other CFIA-approved insecticidal treatment. Intercept can be used as an additional measure to a JB certification program to ensure JB-free nursery stock. Intercept can also be used where nursery stock does not meet the requirements of a JB certification program (e.g. vegetation-free buffer zone could not be maintained), or where nursery stock is not grown under a JB certification program.

Intercept has the added benefit of being active against European chafer larvae, though early summer applications would be more effective at targeting European chafer since the adults mate and lay their eggs earlier than JB.  

It should be noted that only plants grown during the JB flight period, under the JB Greenhouse/Screenhouse, or JB Greenhouse Plant Program, will be eligible for shipping from a zone 3 to a zone 1 area.  Otherwise, the plants will require treatment with the appropriate insecticide. That means that nursery stock grown in Ontario (zone 3) under the JB Nursery Management Program, or the JB Containerized Nursery Stock Program is not eligible for shipping to British Columbia (zone 1), but it is eligible for shipping to all other Canadian provinces.  Usually there are very few shipments of rooted nursery stock that would be destined for British Columbia and many of the JB-free states (California, Arizona, Hawaii, Idaho, Montana, Nevada, Oregon, Utah, Washington). There is more of a chance for greenhouse-grown plants to be marketable in the JB-free regions of North America and this is where the JB greenhouse certification programs come in, and/or the use of CFIA approved insecticides.   

The last days of summer

Take a look around the landscape this time of year and you will probably see the results of several chewing, sucking and mining insects. We really got hit hard by aphids this year. I have never seen so many species in such large numbers. Honeydew and sooty mound can be found on several species of trees. We’ve noticed a significant increase in linden aphid this year and the lindens in many parts of southern Ontario are off-colour and showing some leaf distortion.  

European chafer and Japanese beetle adults have done a decent amount of skeletonizing on deciduous trees and shrubs so far this season (linden being one of their favourite hosts). Wooly aphids seemed to have produced an extra couple of generations this year, especially on beech. Scale insects of many species are settlled and producing a protective, waxy coating that makes them quite tolerant to insecticides. However, magnolia scale crawlers are starting to hatch and this insect can be suppressed with two or three applications of summer oil (e.g. landscape oil) to the undersides of the twigs and foliage.

Cedar leafminer was quite prevalent on eastern white cedar this summer. There’s a pretty significant population of larvae feeding inside the foliage at this time. Although there are no systemic insecticides that are allowed under the pesticide ban, a late-Aug. trimming of foliar tips should help reduce the population of leafmining larvae. The trade-off may be a bit more winter burn on those tips if we get an early winter.  Leafhoppers and plant bugs are mature and easy to see in nursery crops and the landscape.  Injury this late in the season is inconsequential. The most destructive period for feeding was in June and early July.  

Tar spot, powdery mildew, Gymnosporangium rusts and several leaf spots and blights continue to plague ornamentals in the landscape and nursery. Fungicide applications in late spring/early summer are much more effective for leaf blights than they are when applied this late in the season. Beware that for many diseases (except Gymnosporangium), overwintering leaves will harbour pathogens and be a source of innoculum next spring. Where possible, collect and destroy diseased foliage and remove. In the landscape, regular mowing can accelerate the microbial breakdown of diseased tissue and can significantly reduce the innoculum load for next spring.

Don’t forget about new landscape plantings this month. Trees and shrubs that were planted this year, and even those planted last year, are still working hard to establish a bigger root system to help collect much needed water and nutrients. Newly-planted nursery stock can really suffer during extended hot, dry conditions in August and September. Trickle, irrigation, soaker hoses, even just putting the hose on low to allow a slow dribble of water to soak into the root zone can really help these plants to establish before the onset of winter.  

More and more we are seeing the use of irrigation bags. These mobile rings hold water and release it slowly through tiny holes into the soil around the trunk of new transplants. The bags are fantastic for achieving consistent wetting down past the top few inches of soil and can save a lot of water and energy. The most common product I’ve seen on the market is TreeGator. It will need to be moved from tree to tree once they are emptied, but they are quite durable and a real lifesaver for our newly planted trees. There you go, “Lifesaver,” now we’re talking.  That would be an excellent product name for an irrigation bag, don’t you think?   

Pest and disease watch for mid-Aug. to mid-Sept.

For more information on pest management, phenology indicators and growing degree day summaries, check out publication 383, OMAFRA Nursery-Landscape Plant Production and IPM.  2007.  Refer to the tables starting on page 39. To order call: 1-800-668-9938.

Growing Degree Day Accumulations (1100-1300 GDD Base 10oC)
Hydrangea paniculata ‘Grandifora’, white flowers to pink
Solidago canadensis late bloom
Sorbus aucuparia fruit orange

Monitor for the following pests and diseases:
ash fall webworm (larvae), emerald ash borer (larvae, pupae)
birch   bronze birch borer (larvae)
cedar     cedar leafminer (larvae)
cherry (Prunus) peach tree borer (larvae)
crabapple, pear, serviceberry Gymnosporangium rustssporulating
deciduous trees plant bugs, aphids, leafhoppers
deciduous plants (roses, lilacs, honeysuckle) powdery mildew
euonymus euonymus scale (2nd nymphs), black vine weevil (adults, eggs, larvae)
evergreens spruce spider mite (eggs, nymphs)
honeylocust honeylocust mite
larch larch casebearer (larvae)
magnolia magnolia scale (crawlers, nymphs)
maple tar spot
oak, beech etc. gypsy moth (eggs)
pine pine needle scale (2nd nymphs), Zimmerman pine moth (adult, egg, larvae)
rhododendron, yew black vine weevil (larvae)
rose two-spotted spider mite, Japanese beetle (eggs, larvae)
viburnum viburnum leaf beetle (egg masses)
Contact Jen Llewellyn at 519-824-4120, ext. 52671, fax: 519-767-0755, or e-mail :  See the Nursery-Landscape Report at