No-Till Notes - “Weed Control”

By Mark Watson, Panhandle No-till Educator 

Last week I had a producer call to visit about weed control in continuous no-till crop production systems. The conversation started with what herbicides we use to produce our crops. I explained to the producer that herbicide selection is very important, but not the whole story when it comes to controlling problematic weeds.

I’ve always felt that the place to start with good weed control is with solid management strategies. Implement good management practices on your farm and use herbicides to control the weeds your management strategies may have missed. 

The first management decision is to minimize soil disturbance. Low soil disturbance when planting in a no-till crop production system will close the window on many weed seed germinations by not allowing any weed seed buried below the germination zone to move to an area where the weed seed can germinate.

Think of the top 2-3 inches of your soil as the weed seed bank. As long as you can control the weed seed in the top few inches, no other weed seed will be in a viable germination zone. You simply have to control the weeds within this zone.

Leaving the previous crops residues on the soil surface will also prevent weed seed germination. Mulching your flower bed or garden is an effective way to control weeds and conserve water around your house. The same holds true in your fields. A heavy layer of residues on the soil surface will discourage weed seed germination due to lack of sunlight.

I really like narrow row spacing when seeding my crops. If I can achieve a good plant population of the crop I’m seeding in narrow rows weed control is much better. A rapid developing crop canopy with a heavy layer of residues on the soil surface does wonders for competing with weeds in the growing crop. Shading the soil surface to prevent sunlight from reaching the soil surface really discourages weed seed germination during the growing season.

Diverse crop rotations will also be very effective in breaking up persistent weed problems. Use diverse crop rotations to maximize competition of problematic weeds. You need to understand the life cycle of the weed you are trying to control and plant a crop that will develop and provide competition against the specific weed.

Diverse crop rotations also allow for use of diverse herbicide combinations. Varying modes of action within the herbicides you choose goes a long way in controlling weeds and preventing the development of weed resistance to herbicides. Research at Dakota Lakes has shown approximately 95% weed control if you can prevent any weed from producing seed for 2 years. 

An example would be downy brome or cheat grass in our winter wheat crop. Cheat grass has long been a problem in winter wheat production in our region. We use a winter wheat, corn, field pea crop rotation on our dry land acres. During the corn and field pea portion of the rotation we have a two year window for controlling downy brome and not allowing any downy brome to go to seed. This has proven over the years to be very effective in controlling downy brome in our winter wheat crop.

We also plan to add field peas to our irrigated crop rotation. One reason is to help control palmer amaranth which has shown up on our farm in the past couple of years. Palmer amaranth is a warm season broadleaf weed in the pig weed family. We feel the field peas, a cool season broadleaf will provide good competition by developing a crop canopy before the palmer amaranth has a chance to germinate. 

Our rotation will be corn, field peas, winter wheat, and then edible beans. We feel we can control palmer amaranth pretty well in the corn, field peas, and winter wheat for three consecutive years before we plant edible beans. The edible bean is the crop where palmer amaranth will be competitive due to similar life cycles.

Through the use of these management strategies we can greatly enhance our chances for good weed control. We then use herbicides to help control the weed populations that our sound management practices have missed. This strategy has helped maintain good weed control in our continuous no-till crop production system.

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