The 2018 pest survey results for Saskatchewan look like good news for the 2019 season. Grasshopper, pea leaf weevil and diamondback moth populations were all low in 2018. Large numbers of Bertha armyworm moths were caught in the Outlook and Watrous areas, but these do not necessarily predict 2019 populations. Saskatchewan Ministry of Agriculture integrated pest management agrologist Carter Peru, who is responsible for co-ordinating pest surveys in the province, shared the 2018 survey results.
Bertha armyworm populations raise some concern. In 2018, 238 sites were monitored for the pest, and the results show higher numbers than 2017.
“A large amount of moths were caught in the Outlook and Watrous areas,” said Peru. “We think the cycle might be coming out of the low end and we could see higher numbers next year.”
Bertha armyworm normally follows a cycle of outbreaks that ranges from five to eight years. The last major outbreak was in 2013.
“It’s also important to note that the maps we produce weekly from early June until early August, monitor the adult male moths, which actually don’t cause the damage to crops,” said Peru. “It’s the larval stage that has to be scouted before producers decide to spray an insecticide.”
Pea leaf weevil
Pea leaf weevil populations in 2018 were a lot lower than they were in 2017. There was some higher feeding damage in the southwest corner of the province, but it was not significant in other areas of the province. The lower number in 2018 compared to 2017 might be due to environmental conditions, said Peru. Dry conditions can reduce pea leaf weevil populations due to the negative impact on eggs and larvae.
The pest survey map also shows very low populations of grasshopper for 2019. Some 1,200 sites were monitored for the survey in 2018.
“For the grasshopper survey map, the techniques used to smooth transition lines can affect values in localized areas,” Peru added. “Therefore, the map should be used for regional analysis only.”
Diamondback is another insect to monitor for in 2019. Diamondback moths arrive in Saskatchewan on southern U.S. winds, but the pest does not overwinter in significant numbers in the province.
“This means that diamondback moth populations cannot be predicted based on past years of surveillance,” said Peru.
To help monitor, the Ministry sets up pheromone traps and counts moth population arrival and abundance. Updates are provided on the Ministry’s website regularly, so this is a tool that producers can use to be more aware of diamondback populations and risk of crop damage.
Scout for diamondback larvae regularly, said Peru, especially in July and August when larvae can cause the most damage to crops. Count the number of larvae per square metre. In immature and flowering canola, the economic threshold is reached at 100 to 150 larvae per metre squared. At the pod stage, it’s between 200 to 300 larvae per square metre.
“Economic thresholds depend on a variety of factors, including the cost of spraying and the price of canola,” said Peru.
Peru cautions growers to scout regularly and often for all insect pests, said Peru. Environmental greatly impacts populations, so be sure to pay attention to changing conditions.
“Bertha armyworm, diamondback moth, pea leaf weevil and grasshopper populations are no exception to this,” said Peru. “There’s always potential for localized outbreaks.”
“Even though our results show lower risk, it’s still very important to scout,” he concluded.
For survey maps and weekly updates throughout the growing season, visit the Saskatchewan Agriculture website.