The heat is back in the forecast, and so are the flea beetles.
Manitoba Agriculture reported that the beetles were, “aggressively feeding in pockets,” and that some farmers were spraying for flea beetles in the last week of May.
Lionel Kaskiw, farm production adviser with the province, says beetle pressure may get worse as the calendar flips into June and temperatures rebound from the widespread overnight frost reported May 26.
Why it matters: Canola first struggled with cool, dry seeding conditions, followed by a sudden frost event, and now the annual battle with flea beetles has begun.
Temperatures jumped to near 30 C only days after the frost event and remained high into the first week of June.
That’s good news for the heat-loving pest, agronomist Justine Cornelsen of the Canola Council of Canada said, although she noted that she has not had an alarming amount of flea beetle complaints just yet.
“What I’ve seen hasn’t been bad,” she said. “Of course, with flea beetles, it can be very isolated. It’s not generally a region; it kind of varies from field to field. The main piece is that we need to be following threshold numbers. Feeding damage always looks way worse than it actually is.”
The Canola Council of Canada recommends farmers spray once feeding damage reaches 25 per cent of the leaf surface. Economic injury, the point where cost from flea beetle damage breaks even with the cost of insecticide, actually sits closer to 50 per cent leaf, but experts argue that the lower 25 per cent threshold gives more time for a producer to act, since damage can accumulate so quickly.
Provincial entomologist John Gavloski has also warned producers not to overestimate.
“Your eyes are always drawn to the damage and it often will look horrible when it’s at 25 per cent, but really, there is a lot of green still left,” he said during one of the province’s Crop Talk webinars in mid-May.
Eric McLean of Blanshard, Man., is among those hard-hit farmers this year. Despite spraying, the western Manitoba farmer expects he will have to reseed at least two fields due to a combination of frost, flea beetle damage on those weakened plants, and hot winds in the meantime.
“The problem this year is between the dry conditions and the crazy winds and the frost and cold nights and all of a sudden hot days and everything else, the crop isn’t actively growing as much as it should be,” he said.
The farmer noted that other environmental conditions have seemed to exaggerate any feeding damage this year. Even in his own area, however, he says damage reports are patchy and his seed business hasn’t had any huge upswing in calls from farmers needing to reseed.
The unabated dry conditions are unlikely to help. While the province’s dry spell broke along the Assiniboine River in the last weekend of May, storms dropped little rain in areas of the northwest, Interlake and far southwest.
“With the temperatures we’re going to be seeing, we could see some real action on (flea beetles) and with some areas not receiving as much rainfall, the canola is still growing fairly slowly, so I think those producers in those areas are definitely going to need to be watching,” Kaskiw said May 27.
Lack of rainfall still dominated the agricultural issues in western Manitoba, Kaskiw went on. With the exception of Killarney, the region still sat at below-average precipitation. Multiple areas reported less than 30 per cent of normal rain as of May 27.
Angela Brackenreed, agronomist with the Canola Council of Canada, noted that flea beetle feeding might compound any frost stress.
“Now we have a plant that has less leaf area and is growing slower and the flea beetles will certainly take advantage of that, so we really need to be watching these crops closely,” she said.
The multiple stress points are nothing new, Cornelsen pointed out, and flea beetle damage must usually be considered in light of other stand establishment concerns.
Canola stands can still yield well with two plants per square foot, she said, but those stands must then be carefully managed and diligently scouted to avoid future loss, compared to a stand with the council’s recommended five to eight plants per square foot.
The renewed heat may push slow-to-emerge canola quickly through its vulnerable stage, Cornelsen said.
The Canola Council of Canada maintains that canola is most at risk between emergence and the third true leaf.
Moisture, however, is still an unanswered question if farmers are hoping crops will speed past their vulnerable stage.
The rains in the last weekend of May helped, Cornelsen said, but many areas are still looking for more. Fields were starved for moisture coming into the season already, she said, and the forecast in the last week of May promised high temperatures, without any additional rainfall.
“It’s definitely dry in areas and we would take more rain, especially now that the crops are in now,” she said.
“Thankfully, a lot of the crops were seeded into moisture, so they got that first initial top-up getting out of the ground, but we will take more.”