Each winter, Alberta Agriculture and Forestry entomologist Scott Meers and Alberta Agriculture and Forestry insect research technologist Shelley Barkley host #ABbugchat on Twitter, drawing the attention of growers across the province. This year, the pair released forecast maps for three pests: grasshopper, bertha armyworm and cabbage seedpod weevil. Here’s what you missed.
The forecast for 2019 is based on the grasshopper count from the previous August. The map, which is available online at Alberta Agriculture, shows a risk in the western part of southern Alberta. If spring is dry, Meers warns that there is a major risk of outbreaks. He also notes that while the forecast for Peace is very low, they are investigating the possibility that the 2017 survey is more predictive of the 2019 situation.
“I have very strong suspicions that we could see high grasshopper populations in the Peace and in northern central Alberta,” said Meers. “We can’t change the forecasting model until the research is done however.”
Uncertainty in the forecast for the Peace and northern central Alberta stems from the presence of a population of Melanoplus bruneri, which appears to be following a two-year cycle.
In 2018, bertha armyworm was monitored using a network of pheromone-baited traps placed in 290 locations throughout the province. The traps show a very strong increasing trend in parts of central Alberta, centred around Camrose, but also into Vermilion River. “I fully expect an outbreak in 2019, but I hope I am wrong,” said Meers.
Last year, growers in east-central Peace were also spraying for bertha armyworm. Meers expects the outbreaks to be larger in 2019.
The outlook for bertha armyworm, he said, can be modified by cold weather with no snow cover. “That’s true for parts of the at-risk areas, but most of the risk area has significant snow cover,” he said.
Growers are reminded that many parasitoids attack bertha arm worm, including several tachinid flies and many different wasps. Bertha armyworm can also fall victim to viral and fungal diseases if conditions are right.
Cabbage seedpod weevil
Cabbage seedpod weevil numbers have been lower the past couple of years, and range has contracted back to more traditional areas, said Meers.
“My bottom line for cabbage seedpod weevil for 2019 is this,” he said. “South of A line from Red Deer to Provost scout early canola; south of Highway 1 expect threshold levels in early canola.
“A milder winter may fuel a resurgence of the range extension in 2019,” he added.
Scouting four locations per quarter should be enough if done well. Be sure to include both the field edge, as well as farther in the field. “Ten locations would be better, but may not be practical,” Meers added.
Meers suggests 25 sweeps per location, rather than 10, but 10 is easier math. Threshold is at least 2.5 per sweep.
“Below that we don’t recommend spraying,” said Meers. “It doesn’t pay below that.
“There are very few parasitoids that attack cabbage seedpod weevil in Alberta, that’s why we have to spray so often,” he added.