Weevils pressure healthy seed alfalfa crop

Pesticide resistance has been found in Alberta, but other good control options continue to be available to producers

Seed alfalfa crops in southern Alberta and southern Saskatchewan are starting to flower, and growers are preparing to put their leafcutter bees in place, ready to do their pollination work.

Alfalfa weevils are also making their presence known and in some parts of southern Alberta have already reached spraying thresholds.

“There’s definitely weevil pressure coming out,” said Brad Alexander, research and extension manager with the Alfalfa Seed Commission in Alberta. Weevil resistance to synthetic pyrethroids was identified in the Rosemary, Alta., area several years ago, and Alexander said resistant weevils are also being found further afield.

However, there are other control options including organophosphates and Coragen, a Group 28 pesticide.

The latter is labelled for suppression, but Alexander said it has been added to a study undertaken in conjunction with Olds College to test its efficacy and better identify why the systemic pesticide is labelled for suppression rather than control.

Commission president Brian Slenders, who farms in the Brooks, Alta., area, said he has found good weevil control with Coragen in combination with other options.

Alexander has been keeping a close eye on weevil development in part because of extra insect collection needs. Agriculture Canada researchers are unable to do field work due to COVID-19 restrictions so he has stepped into the breach.

“It just so happens that we’re in the third year of a five-year insect collection study so I have put on my masters student’s pants again and I’ve been out there doing hundreds of sweeps in all the fields,” he said. “It’s actually been kind of fun, getting back doing a lot of field work, a lot of sweeping.”

Alfalfa seed crops in southern Alberta are looking healthy due to recent rain. However, Slenders said there was considerable winterkill and acreage is down from previous years. A harsh winter with low snow cover and saturated conditions caused ice build-up on plant crowns, particularly in low spots.

“It’s hard to gauge,” he said about acres affected.

“Some fields are 10 percent, some fields are less, some fields have been taken out, so that would be more than 25 percent, I would guess.”

After a slow start, alfalfa seed crops have caught up to their normal pace and leafcutter bees will be placed in fields soon.

Slenders said research projects have been affected by the pandemic, including those involving pesticides.

“We’re seeing a lot of delays in our research there. On the flip side, it has made guys very conscious of what they’re doing and very careful with their spray applications. I think that’s the entire alfalfa seed industry wide.

“We’re seeing a real conscientious effort to do the best possible job out there, when they’re doing their spraying now. Not that there wasn’t before, but now it’s even more so.”

A surplus of alfalfa seed has dampened interest in expanding acres, said Slenders, so an increase isn’t likely until the excess is used.

For now, the recipe for a good alfalfa seed crop in his region requires major doses of sunshine.

“We need heat now. We’ve got lots of water. We can irrigate now and we’ve got a good amount of moisture in the ground. So we just need some heat now. We need some temperatures so those bees can get to work. Over 25 C is ideal for the month of July. That will set us up for a good crop.”

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