More seeds help control weeds

If knowledge is power, organic farmers may soon find themselves winning the battle against weeds.

Steve Shirtliffe, an assistant professor with the department of plant sciences at the University of Saskatchewan, and Eric Johnson, a weed biologist at the Agriculture Canada research farm in Scott, Sask., are both working on organic weed control methods.

“One of the things we found out is that oats will tolerate harrowing. There was some recommendations in the past that said you should not harrow oats, but we did a collaborative study and we found oats to be even slightly more tolerant than wheat,” said Johnson.

The researchers presented their recent individual work at an organic workshop last month in Saskatoon.

Shirtliffe’s talk focused on using increased seeding rates in peas and lentils to choke out weeds, while Johnson talked about mechanical methods of control.

To test his theory, Shirtliffe increased conventional seeding rates between 50 and 100 percent. This reduced weed growth by about a quarter in lentils and a third in peas.

“In peas, the effect on weeds is actually more apparent, because peas are more competitive to start with,” said Shirtliffe in a later interview.

“Essentially, by having more plants growing … you’re suppressing the weeds, because they’re taking up more space.”

Although higher seeding rates are more effective with peas overall, it is less costly with lentils because of their smaller size. Shirtliffe said it also gives lentil crops, which tend to be uncompetitive, an advantage they wouldn’t have normally.

“In order to increase your crop’s competition with the weeds, increasing the seeding rate is the big hammer,” said Shirtliffe. “Using what people would consider normal, conventional seeding rates is not enough under organic conditions.”

More seeds also mean more yield. Shirtliffe found that increasing the seeding rate increased yields by 35 to 40 percent.

Johnson told producers that post-emergent tillage may be a more effective treatment than previously believed.

“Certainly not much post-emergence harrowing is being done, because it is variable and it’s time consuming,” said Johnson in an interview. “My data would suggest that there’s some benefits to doing this, but I can understand why growers are reluctant to.”

Using both pre- and post-emergent tillage produced yields between 60 and 85 percent of what a herbicide-treated crop could. But Johnson didn’t think this is the answer in every situation.

“Most pre- and post-emergence tillage, you’ll cause too much crop damage in crops like flax and canola, so you can’t really use it in those crops. They’re just too small-seeded and not well anchored enough and you’ll cause too much injury.”

For small-seeded oilseed crops, Johnson recommended organic farmers delay seeding so that they can use tillage before the seeds are in the ground.

“That’s the only strategy you can really use on those crops.”

Now that Johnson and Shirtliffe have laid the groundwork in their individual research, they will collaborate in future research.

“We’re going to look at whether physical weed control offers anything over cultural weed control, or is cultural weed control enough?” said Johnson, referring to his own tillage experiments and Shirtliffe’s work in increased seeding rates. A study is expected to start sometime this year and will continue for three years.

“I guess we’re a pretty natural combination,” said Shirtliffe. “Lennon and McCartney, Shirtliffe and Johnson.”

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