There could be a bertha army worm outbreak in parts of the province this year, but cabbage seedpod weevil survey numbers are down, and, save in the south, grasshoppers aren’t a big worry, according to new provincial pest forecasts.
Bertha army worm
Keep watch is the take-away from last year’s survey, which consisted of 350 sites with pheromone-baited traps for capturing moths, set up and monitored by a network of agronomists, agricultural fieldmen, farmers and other co-operators.
“In 2020, the bertha army worm population increased in many locations in Alberta,” states the survey and forecast report from Alberta Agriculture and Forestry.
“While it is difficult to accurately predict the 2021 bertha army worm populations based on the 2020 moth catch, it appears the outbreak in the Peace is declining while in central and southern Alberta a population increase is entirely possible.”
Weather (including snow cover) has a big impact on bertha army worm numbers, as do the populations of their natural enemies, which can greatly reduce bertha larval populations.
“It will be critical to have very good coverage of pheromone traps in 2021 to develop an early warning of potential problems during the coming season,” the survey states.
But the system is only intended “to increase the awareness of canola producers to the damage potential of bertha army worm” and growers need to carefully scout their fields.
“Experience from previous outbreaks has shown us that adjacent fields or even different parts of the same field can have greatly different bertha army worm numbers,” the report states. “Producers growing peas and fababean also need to pay close attention to the bertha monitoring system as bertha army worm has been known to feed on both those crops.”
This and other pest reports, and their accompanying survey maps, can be found at alberta.ca (search for ‘pest monitoring’).
Cabbage seedpod weevil
For the fourth straight year, the numbers for this pest were lower than normal.
Since weevils were first found in canola fields in southern Alberta, it has moved north and also crossed the Saskatchewan border.
“Predictive models based on climate data indicate that this pest will eventually disperse to all regions of canola production in Western Canada, including the Peace region,” says this year’s report.
But last year’s survey — sampling was done in 236 fields in 50 municipalities in the south and central Alberta — found the pests weren’t as far north. In 2019, weevils were found (“in very low numbers”) as far north as Edmonton, while last year the northern limit seemed to be Red Deer.
“But this insect still requires monitoring in 2021,” the report states. “Any producers who grow canola in southern Alberta and into the south portion of central Alberta will have to check their canola crops as they come into flower. The earliest-flowering canola crops tend to have the highest risk from cabbage seedpod weevil and should be monitored very closely.”
This survey is conducted by agriculture fieldmen across the province and last year, many (thankfully) had little to report.
“Surveyors were hard pressed to find grasshoppers in the Peace and northern portions of central Alberta.”
That may be because of grasshopper species that have a “biennial life cycle,” in which “a low grasshopper year (is) followed by a higher population,” the report states.
But in the south, dry summers are resulting in higher numbers.
“Portions of southern Alberta indicating moderate to severe risk could experience problems with grasshoppers if environmental conditions favour grasshopper hatching and development in late May through June. Localized factors such as light soils or south-facing slopes result in an elevated risk of grasshopper infestations.”
When scouting, producers should pay close attention to areas such as field margins and fencelines where there is green growth in the fall, as these are where grasshoppers like to lay their eggs.