Insect update: Bertha, diamondback and weevil counts

July 11, 2018 - Issue 15

Insect trap counts are generally low across the Prairies, but bertha counts keep rising. Here are the latest provincial survey results.

Bertha armyworm

Counts are climbing for bertha armyworm moths.
Alberta: Most sites are low so far. As of July 11, a handful (7) are into the medium range with accumulation of 300-900. One site is high (900-1200). That is Camrose. See the map.
Saskatchewan: Counts so far are low across Saskatchewan. See the latest map.
Manitoba: Higher cumulative counts so far are in the western part of Manitoba, with four traps in the 300-900 range, which in Manitoba is called “uncertain risk”. Tilston has the highest count, with 714 as of July 4. All other traps are currently in the low risk category. Find the latest Manitoba Insect and Disease Update here.

Scott Meers with Alberta Agriculture provides the following information on how to interpret bertha trap results:

“When an area starts to get a mixture of traps near 300 moths, some over 300 and the odd one even over 900 moths then we are into potential outbreak territory. We are on the verge of this in Camrose/Beaver counties this year. In addition there is a smattering of traps that have gone over 300 throughout southern and central Alberta. This is still fairly low overall level risk but one that can not be ignored. It means we need to be scouting canola fields in the vicinity of the elevated trap catches.” Read Scott’s full report.

Cabbage seedpod weevil

Some areas are above thresholds but, in general, counts seem to be lower this year than last year. This may be due to dry conditions, but that weather effect on CSPW is not confirmed. For canola fields past 20-30% bloom, the most yield-damaging egg-laying has probably already occurred. But 30% bloom is far too early to consider abandoning control if CSPW are still above thresholds. See the Alberta cabbage seedpod weevil map. How to use a sweep net, including video links.
Diamondback moth

Adult moth surveying is over for 2018, so the focus now is on looking for larvae, especially as canola starts to produce pods. Thresholds and scouting.
Alberta: Only one location had counts above “no risk” (0 to 25 count). That was at Lamont, which had an accumulated trap count of 29 adults when surveying ended. That puts it just into the elevated risk range (26 to 200 count). See the map.
Saskatchewan: Only one location was “elevated risk”. That is Regina, with an accumulated count of 50. See the results.
Manitoba: Highest adults counts were in the Central region and Interlake, but overall levels are generally low. So far no economic populations of diamondback moth larvae have been reported.

Canola Watch