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CUBA CITY, Wis. - Weeds can be especially challenging on organic farms. A recent field day at Pleasant View Dairy Farm, Cuba City, Wis., helped approximately 50 people hear an expert's advice on the topic.
Former dairy farmer Kevin Kiehnau of Jacksonport, Wis., in Door County, outlined practices that can control weeds without the need for chemical herbicides. The field day was sponsored by Southwest Wisconsin Technical College, USDA Risk Management Agency, and Organic Valley. Kiehnau is the east-central division manager for Organic Valley. As such, he assists farmers in several states.
He began his talk by cautioning against seeking one, seemingly magical, antidote to weed woes.
"There's no silver bullet," Kiehnau said. "If someone comes along who's selling a silver bullet for your weed control problems, he's probably blowing smoke."
Instead, weeds in row crops can be organically controlled using crop rotations. And, there's a place for mechanical means and burning, or flaming, weeds. Certain systems of weed control can also work.
Kiehnau, who milked cows 27 years and has had his farm certified organic the past 20, said weed control in row crops, such as corn, really begins in the fall, well before the next crop is planted. Proper soil preparation in the autumn, along with planting a cover crop, all affect what happens the next growing season, he said.
A key to controlling weeds is to not let so many of them get started in field. An important practice is to apply manure in the fall - not in spring, Kiehnau said.
That's because manure contains a great deal of soluble nutrients that can spur weed growth. Those nutrients, along with spring tillage, give weed seeds what they need to germinate.
"You're just begging for a weed burst when you apply manure in the spring," he said. "Weed seeds are very opportunistic. They like to germinate in the top half inch of soil," so tilling shallowly only helps them.
On his farm, Kiehnau built storage for an entire year's worth of manure. That lets him apply 95 to 98 percent of it in the fall.
The organic specialist suggested farmers conduct tests on their own farms. Apply a strip of manure in the fall and another one the next spring. Then make note of the weeds in each. "You can see exactly where the spring manure went on," he said.
If it's not possible to get all or most of a farm's manure applied in the fall, composting it can help. The heating that goes on inside the windrows will kill many weed seeds.
Planting a small grain as a cover crop or green manure crop after manure goes on in the fall ties up nutrients in the growing plants, and keeps them from being used by weeds, he noted.
Kiehnau took a moment to differentiate between a cover crop and a green manure crop. A cover crop, he explained, is planted to hold the soil over winter and tilled the next spring. A green manure crop, by contrast, gets tilled under while it's still green, and is intended to add nutrients to the soil.
Be careful with green manure crops. Kiehnau said a newly tilled green manure can heat, so much so that the germination of newly planted seeds can be harmed. He advocated waiting a few days before planting.
Fall is the time to begin controlling grasses, such as foxtail, according to Kiehnau. Plowing can work, as can using a field cultivator or a rotovator. The idea is to get the weeds' roots on top of the soil, where they will dry and die.
"If you haven't controlled your grass in the fall," he said, "you're not going to be able to control it in the spring, either."
He also said he likes to build fertility in a cover crop or green manure in the fall. But then he likes to see the soil fertility decline a bit.
When it comes to tillage, Kiehnau said he likes to have the ground almost ready to plant the fall before. For corn, one fairly deep pass with a disk can be all that's needed before planting.
"Try to work the seedbed as little as possible," he said. "A disk leaves a nice, soft seedbed that corn likes."
For small grains sown in the spring, using a field cultivator very shallowly can prepare the seedbed. Don't shoot for a soft seedbed, since small grains do better in firm soil, especially when they are being used as nurse crops.
Whatever tillage is done, it should not include rolling the field, the organic specialist said. That's because weed seeds germinate best when they have tight seed-to-soil contact.
On corn planters, Kiehnau reminded that they need to be maintained and adjusted correctly to perform optimally. That will help prevent doubles, triples and skips.
Plant at the right speed. Don't be in a hurry, he suggested.
"I never see a person planting corn driving too slow. But I see about 80 percent of them driving too fast," Kiehnau said.
Especially with older planters, limit the speed to about 4.5 miles per hour, he said. Planting too fast can lower yields 25 to 30 bushels per acre, he added.
It's also a good idea, Kiehnau said, to plant corn in 30-inch rows. That row spacing will let the corn plants shade out weeds between the rows.
Know which weeds are especially troublesome and a farmer can change the soil. For example, if grasses are a problem, adjust the soil's pH by applying calcium in the fall, Kiehnau said. Calcium helps loosen the soil, and grasses don't do as well in loose soil.
Different farms have different weed problems. Improving the fertility of the soil can lessen weeds problems, "But they don't go away," Kiehnau said.
Weeds can offer insight into the soil. Pigweed and lamb's quarters, for example, indicate good soil, while the presence of others - like knapweed - indicates poorer soil.
In the constant battle against weeds, he reminded the farmers that they need to constantly assess their farms' weed situations and be willing to make changes in the way they address them. Things like the weather, the type of soil, and planting conditions can all affect weeds and crops.
"One thing I can tell you for sure about farming," said Kiehnau, "is that practices change almost daily."
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