Controlling Weeds Takes a Whole Systems Approach
Published: Friday, March 22, 2019
When it comes to organic crop production, it is all about interacting with nature and making the most of every interaction.
"Everything you do is a dance," said Joel Gruver, associate professor of soil science, Western Illinois University.
Gruver provided two keynote presentations during the 2019 Organic Seminar during Ag and Natural Resources Week at Michigan State University.
"It's a combination of all the different practices you do that create the context of success or failure in organic crop production. You need a whole systems approach that integrates lots of small tactics together to achieve small benefits from each one that adds up to a high level of successful weed control."
The foundation of a good weed control program is soil fertility. However, Gruver's definition of fertility isn't the correct levels of N, P and K in the soil per a standard soil test required for a specific crop, but rather the correct amount of organic matter to feed the living biome in the soil. Cover crops and perennials on the soil provide plants that can utilize photosynthesis for longer periods each year in order to feed soil biome.
Gruver suggests sampling a fence row to determine the soil organic matter potential and compare it to the actual organic matter in the field, then strive to add organic matter to build up to the soil's potential.
Give the crop as much competitive advantage as possible, starting with a clean seed bed. No-till, conventional till and cover crop residues all demand different practices to achieve a clean starting point. Blind tillage practice allows a good flush of weeds to green up after the crop is planted, then destroys the white-rooted weed seedlings at their weakest time post-emergence with a rotary hoe or other light tillage, disturbing only surface weeds and leaving deeper planted, germinating crop seed undisturbed.
Blind tillage, along with the first row-tillage pass should be taken seriously and timed properly. Mid-summer tillage during summer's high heat paves the way for weeds to self-destruct.
"Once weeds are disturbed, they will put all their energy back into regrowth, but in the heat of summer, they spend all their energy and don't have enough to regenerate because the heat exhausts those efforts," Gruver said.
Soil temperatures must be warm enough to promote rapid seed germination. This may mean delaying planting until the soil is sufficiently warm.
Select well adapted varieties that promote maximum leafiness and rapid canopy closure. That may mean having to increase plant populations and adjust row spacing.
"It's not always which piece of equipment you use, but how well you use it," Gruver explained, saying that most farmers have similar sets of equipment, but some are better at optimizing performance than others.
Seed treatment and banded fertilizer application can help hasten growth and canopy development. Non-composted manure can be a source of weed seed and should be used sparingly.
"Weeds are very responsive to nutrients, and overapplication of manure can mean weed pressure that is heavier than necessary," Gruver said.
Weed seed dormancy is nature's way of seed control, and dormancy can be promoted by burying weed seed deeply through tillage.
Cropping strategies for the organic producer involve a big picture of targeted, strategic practices to control weeds. A toolbox for weed control that contains numerous small tools to achieve a big picture of success will help organic growers enter the 2019 crop season with confidence.
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