of the 2005 Ontario vegetable season
By Marg Land
This past growing season will stand out in many Ontario growers’ minds as one of the hottest and the driest in recent memory.
This past growing season will stand out in many Ontario growers’ minds as one of the hottest and the driest in recent memory. And while these weather conditions might have brought some welcome relief from disease pressure, it brought on many close encounters of the insect kind in the province’s vegetable patches.
Photo courtesy of ARS Photo Service
|An example of cabbage looper larvae. The top specimen is diseased while the looper on the bottom is healthy. |
Photo courtesy of Clemson University – the USDA Cooperative Extension Slide Series, www.insectimages.org.
|An infestation of spider mites on a plant showing both the web and plant injury. Photo courtesy of Clemson University – USDA Cooperative Extension Slide Series, www.insectimages.org.|
The cabbage looper decided to move away from its traditional food source and aimed its sights on tomato plants this past season, munching on the leaves and acting as a defoliator. “It’s not usually a pest of tomato but we were facing high population pressures this year,” explained Ontario Ministry of Agriculture, Food and Rural Affairs vegetable specialist Jennifer Allen.
For future reference, she explained the pest has a threshold population of 15 larvae per 30 plants before control sprays should be used. Dipel 2X, Thurcide, Bioprotec, Pounce and Matador are all registered for use against cabbage looper. “You want to use the highest rates and lots of water,” explained Allen. “You want good coverage.”
Also attacking tomatoes this past season were spider mites. Symptoms included yellow mottling of the leaves and a web-like substance covering the underside of the leaves. Spider mites also work as defoliators, causing tomato plants to weaken and not fruit. Allen said there are no threshold levels for spider mite, which can easily spread from field to field by attaching to clothes. She advises using miticides Kelthane, Lagon or Cygon to control the pest. “You should also scout all uninfected fields before moving to infected fields to help avoid spread,” she said.
Thrips infections were very high in the province this past season with some local growing areas, such as New York State, reporting control failures, resulting in unharvestable fields. Onion thrips infect the plant by sucking the chlorophyll from the leaves, causing them to brown and limiting bulb formation and/or bulb sizing. The pest has varying threshold points, ranging from three onion thrips per leaf in dry onions to one onion thrip per leaf in Spanish production. Allen said Ripcord, Matador, Decis, Dibrom and Diazinon are all registered for use against onion thrips but warned that there is extensive resistance to all of these pyrethroid and organophosphate products. She suggests varying your spray program, using a pyrethroid first before moving to an organophosphate and then shifting back to a second type of pyrethroid.
“You need to be able to get the spray into the leaf axis,” she added, urging growers to use lots of water and surfactants with the sprays to improve coverage.
Swede midge was very busy this past summer increasing its territory in Ontario, Quebec and New York State. Ontario had four more counties placed under the seedling quarantine while Quebec had 14 growing regions quarantined. New York State also has four more counties where the pest has been discovered.
Five generations of the pest were observed in Ontario this past season. “Growers got hit from the beginning of the season all the way to the end,” said Allen, adding she didn’t bring in pheromone monitoring traps until the beginning of November.
Swede midge loves to munch on cole crops, resulting in numerous symptoms, such as brown scarring in cauliflower, the formation of multiple heads in cabbage plus the formation of blind heads in broccoli, just to name a few.
There is no threshold point for control of swede midge. Both Matador and Assail have been registered for use against the pest.
While disease pressure may have been down in 2005, viruses were still a factor, especially in cucurbits where pests such as aphids and cucumber beetle have no problem spreading the infections from plant to plant. Cucumber mosaic virus, squash mosaic virus and zucchini mosaic virus were all present this past growing season, causing mottled leaves and warty fruit. While infected seed can also spark mosaic virus outbreaks, it’s fairly certain insects played a role in the infections’ spread in 2005.
There is no cure or spray program for mosaic viruses; instead, growers are urged to rogue out infected plants and try to keep insect populations under control. “Insecticides don’t work quick enough to control transmission,” explained Allen. “You need to have overall control of the populations.”