If you go organic, you’re going have weeds – but they shouldn’t overrun your fields.
That was the message organic extension specialist Brenda Frick had for attendees at the recent Go Organic conference.
“The theory of organic weed control is pretty simple, but the reality is fairly different,” said Frick, who teaches weed control in organic agriculture in an online course at the University of Saskatchewan.
“You need to build a system with only a few weeds to manage so that the weeds become part of that system and are not devastating.”
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Be careful not to bring in weeds to your farm by, for example, bringing in hay infested with new weeds.
“Due diligence is important in not bringing in more weeds,” said Frick. “If you’re bringing in seeds from far away, you want to make sure they’re clean.”
The first time a producer sees a weed growing in the field, they should get rid of it as “the first invaders are really important,” said Frick.
“Once you’ve got a hundred million wild mustard plants, there’s not a lot you can do,” she said. “But if you’ve got three of something, you can deal with it. If it is a small problem, producers can till it or remove it. But if it is a big problem, organic producers may want to consider using green manure.”
In the latter case, be cautious because “I’ve also seen really good crops under a bunch of weeds,” she said.
Farmers switching to organic production tend to be nervous about weeds the first couple of years but eventually learn to relax, she said.
Diversity
Building diversity in your cropping system, stepping up weed control at key times (such as at harvest when the weed canopy is gone but weeds are still growing), and changing rotations (which should incorporate nitrogen-fixing legumes) will help in weed control, she said.
“In order to build appropriate diversity, you need a rotation that puts something different in there,” said Frick.
Fall cropping, incorporating livestock, and growing different crops or varieties together at the same time increase diversity. Frick used the example of growing flowers in vegetable gardens as a way to attract insects which are beneficial in weed control.
“Anything that benefits the crop will put weeds at a disadvantage,” said Frick.
Weeds grow in areas where crops aren’t doing very well, she noted.
“Often when you see weeds, you’re seeing areas of missed opportunity for your crop,” said Frick. “Often, the best control you have against a weed is the crop. Part of that is using all the space you can, so that might go into intercropping.”
If weeds are established before a crop, they will take up many of the resources that the crop can use, she said.
When seeding into a field of perennial weeds, consider fall tillage, followed by another tilling during seeding. Another option is to do a surface till after planting. The ability of a particular crop to compete against certain types of weeds should also be considered.
“There’s something to be said for picking the right varieties for your area,” said Frick.
Organic farmers often use different varieties than conventional producers do, and heavy seeding of well-cleaned seed is often critical. If weeds are established, rotary hoeing or harrowing can be used to kill weeds, especially when they are young and small.
“Harrowing is a bit of an art because you are trying to do little damage to your crop while damaging your weeds. It takes a bit of finesse,” she said.
A Noble blade can be used in the fall. The machine cuts off bits of the roots while leaving the canopy of the plants. It’s good in a no-till system, and should not be used in an intercropping situation.
If a field is really bad in an organic system, producers may want to consider it for green manure, Frisk said.
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“Thetheoryoforganicweedcontrolisprettysimple,buttherealityisfairlydifferent.”
BRENDA FRICK
UNIVERSITY OF SASKATCHEWAN
