Bertha armyworms invading canola
Alberta Agriculture crop specialist offers some thoughts to keep in mind
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Reports of bertha army worms feasting on canola have cropped up in northeast Alberta, according to the Lakeland Agriculture Research Association (LARA) and Alberta Agriculture.
“Canola looks real good but just in the last week to week and a half there has been a real surge in bertha armyworms,” explained Janet Montgomery, crop specialist at the Lakeland Agriculture Research Association (LARA), in Fort Kent.
Mark Cutts, a crop specialist with Alberta Agriculture, says that there are areas of the province including Two Hills, Minburn, Provost and Vermilion, that are seeing high enough numbers of bertha army worms that farmers are taking control measures, such as aerial spraying.
Bertha armyworm start off as little green larvae, an inch and a half and bigger, said Cutts. It is at this stage that they cause crop damage, feeding on the underside of leaves or directly on the seed pods. Commonly, they chew holes in the pods and eat the seeds, or at high numbers, consume the entire seed pod.
He recommended scouting for these worms in the morning or evening, as they lie low in hot weather. Alberta Agriculture recommends that to get accurate larval estimates in a crop, farmers should sample at least three locations a minimum of 50 metres apart. The average number of larvae at the sites surveyed can help determine if the economic threshold has been exceeded and if an insecticide is necessary.
Farmers should weigh the variables of the value of their canola and the cost of insecticide applications, Cutts noted. Alberta Agriculture recommends insecticide applications when bertha armyworm larvae are abundant enough that the value of the crop they consume is greater than the cost of controlling them.
“Late in season, the one thing that producers need to be concerned about right now, is the pre-harvest interval of these insecticides,” added Cutts. The pre-harvest interval refers to the number of days that must pass between application of an insecticide and the time when crops are swathed or straight cut. The shortest pre-harvest interval for insecticides that deal with this problem is seven days, for products such as Decis or Matador, to a lengthier pre-harvest interval of 21 days for Lorsban/Pyrinex/Nufos/Clorex or 30 days for a product such as Ripcord.
Another insect that is causing damage are Lygus bugs, but their populations don’t necessarily overlap with bertha army worms, he said. Lygus bugs are generally being seen west of Highway 2, while bertha armyworms are generally being seen as more of an issue in northeast Alberta.
Whatever people may be spraying to control, he suggested there should be good communication between farmers and their neighbours. “Giving a warning about spraying an insecticide is probably a good idea,” he said. Residents in the St. Paul area may have noted that spraying is taking place in the early morning or late evening, due to the fact that the worms are not out during the hotter daytime hours.
Matt Janz, director of agriculture services for the MD of Bonnyville, says that this area deals with the bertha armyworm regularly, but it is on about a five to seven year cycle that the numbers reach the economic threshold. Janz said he is not exactly sure what could have brought the increased number of bertha armyworms into the area but it may have something to do with the air currents. He speculates these currents may have also brought in another pest in the form of a fungus called aster yellow, caused by the aster leafhopper.
The leafhoppers transport the aster yellow’s phytoplasma, a type of bacteria, from plant to plant. This causes the fungus to develop, which can stunt crop growth.
Unlike the bertha armyworm though, the aster yellow can’t be sprayed and is difficult to predict. Fortunately, Janz said the fungus is minimal in the area and won’t result in a huge yield loss.
“I think the loss is minimal, I think maybe a 10 per cent yield reduction. Not a huge reduction but still a little bit of reduction depending on how bad the disease is in the field but I haven’t seen any terrible, terrible fields with it. There’s just a hint here and there of it.”
Besides the presence of pests though, crops in the area have been in relatively good shape, according to Montgomery. Besides the trouble rain causes when bringing in hay, the amount of moisture the area has had this summer has kept everything in good standing order.
“It was a dry spring, but then once the rain started we’ve had quite a bit of it. It’s been a challenge in terms of getting hay in because lots of people have had their hay rained on but for standing crops that much moisture is really good.”
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