Crop diseases, pests | Herbicide resistance is also a threat of poor agronomic practices
ST. JEAN BAPTISTE, Man. — Dangerous cropland problems are coming home to roost after years of prairie farmers pushing rotations and overusing key tools, agronomy experts said during St. Jean Farm Days.
Clubroot, blackleg, multiple herbicide resistant weeds and chemical resistant insects are all nibbling at the edges of Manitoba’s cropland productivity, threatening to become major management issues.
“It’s likely in Manitoba now, and it’s something you are going to have to look out for,” Manitoba Agriculture farm production adviser Ingrid Kristjanson said about glyphosate and multiple herbicide resistant kochia.
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As well, multiple herbicide resistant giant ragweed and palmer amaranth are moving toward southern Manitoba, carried on rivers and streams and spread wide by floods.
Other production specialists voiced the same note of caution about the threat of clubroot to canola fields, the danger of overusing neonicotinoids against insect pests and the host of problems created by pushing agronomic practices.
Years of high returns for soybeans and canola have encouraged farmers to tighten their rotations to levels many advisers consider dangerous.
Soybean-on-soybean and canola-on-canola rotations have occurred, and many farmers have employed two-year rotations for their biggest money-making crops.
It has created a fertile ground for crop diseases and pests, which find homes in the roots, trash and soil that linger for more than a year after a crop has been harvested.
Farmers have also relied heavily on glyphosate for pre-seeding, in-crop and post-harvest weed control, creating ideal conditions for glyphosate resistance to naturally develop. Farmers often use glyphosate on every field every year at least once, and sometimes numerous times.
As well, farmers have sometimes used seed treatments and other tools to compensate for the risks they’re taking with tight rotations, allowing the treatments to begin to lose effectiveness by repeated exposure to diseases and pests.
Dennis Lange of Manitoba Agriculture warned farmers that seed treatments aren’t silver bullets or bulletproof armour and won’t entirely make up for pushing rotations or taking other obvious risks.
Experts also noted a risk that many farmers might be unaware of: using resistant crop varieties or control products when problems have not yet appeared. They said this can ruin the effectiveness of those controls and be counterproductive.
Manitoba Agriculture oilseeds specialist Anastasia Kubinec said re-search has shown that resistant crop varieties can lose their clubroot-fighting powers after being grown two or three times.
“If you are not finding clubroot, you can stay with the canola variety that you have,” said Kubinec.
Kristjanson said fighting multiple resistant weeds can demand a tool most farmers have little experience with these days: hand-and-glove.
“It’s worth (hand) picking the straggler,” he said about lone weeds in a field surviving a chemical treatment.
