When the Weed Society of America challenged its members to evaluate weed pressure on field crops, Peter Sikkema found that in Ontario edible beans were most challenged by weed pressure.
“The crop I work on that is most affected by weed interference is dry beans,” the professor at University of Guelph’s Ridgetown campus said at the Ontario Bean Growers annual research day near Exeter.
That means that Sikkema pays good attention to new potential weed control options for edible beans.
He screens old and new herbicides each year to see if any will work on edible beans.
The option he is most encouraged by right now is the potential to manage glyphosate-resistant Canada fleabane with 2,4-D, which isn’t normally used much in dry beans because of the potential for crop injury.
Canada fleabane resistant to glyphosate is especially a challenge for farmers trying to grow edible beans in a strip till or notill system.
He and his research assistants applied the 2,4-D ester in different plots two weeks before planting, a week before planting, one day before planting and then pre-emergence or five days after planting.
The researchers found there is less crop injury the further out before planting the field is sprayed.
Interestingly, Sikkema found that there was less injury when the 2,4-D was applied pre-emergence compared to the application one day before planting.
“We think the reason is that when you are planting the beans, you are disturbing the soil, you’re moving the 2,4-D into the seed zone of the dry beans. You’re getting greater uptake when you are applying preplant than if you apply it preemergence and leave it on the soil,” he said.
He showed a plot of white beans to farmers during field tours at the research day that had been sprayed at double the usual rate, preemergence. The beans were thriving.
“That’s amazing for an unregistered treatment in Ontario,” he said.
“I’m confident that there’s an adequate margin of crop safety in dry beans with 2,4-D applied preemergence. If you had asked me that two years ago, I would have almost definitively said no you wouldn’t have an adequate margin of crop safety in dry beans.”
With three years of data, Sikkema said the treatment is an option for management of glyphosate-resistant Canada fleabane in dry beans and he said he would be comfortable that registration for the use could be pursued.
“I think dry beans have almost the same level of tolerance as soybeans,” he said, and 2,4-D is a registered treatment in soybeans.
However, he also said, “I don’t want anyone leaving here thinking I think 2,4-D doesn’t cause injury in dry beans.”
The positive is that under certain application options, like preemergent application, the beans will grow out of 2,4-D injury, while giving farmers a control option for glyphosate-resistant Canada fleabane.
Sikkema looked at white, small red kidney and adzuki beans in the study and found that the adzuki beans had the greatest tolerance to 2,4-D.
No to Fluridone on edible beans
Sikkema also has looked at using Fluridone, used mostly as a herbicide in peanuts, in edible beans. However, he found that there was too much injury to justify pursuing registration.
Seven days after emergence the beans he tested had nine per cent injury. At the two times normal rate there was 20 per cent crop injury.
Interestingly, Sikkema said the real challenge was the fact that injury got worse as the crop grew. Normally beans will grow out of some herbicide injury, but at 56 days after crop emergence the injury was continuing to worsen.
Putting Dual with Permit depends on weed pressure
Sikkema has also been testing how herbicides Dual and Permit work when tank mixed and applied preemergence in white beans.
Dual is strong on grasses such as barnyard grass and green foxtail, so it makes little sense to add Permit if that’s what you’re trying to control, said Sikkema. His trial found no change in control by adding Permit when trying to manage those weeds. However, Dual is weak on wild mustard, so in the case of trying to control that weed, the addition of Permit to the tank mix makes sense.
The trial found that when applied together Dual and Permit showed a modest increase in redroot pigweed control and a “dramatic” improvement in control of lambsquarters, wild mustard, common ragweed and velvetleaf.
The yield from the plots was highest when Dual was mixed with Permit, but still lower than the weed-free control plot.