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Why you should attack weeds in the fall

Agriculture.com Staff 07/06/2010 @ 5:21pm

Attacking winter annuals and simple perennials and biennials in the fall, rather than waiting until spring, is the most effective way to control the weeds.

Fall herbicide treatments are most effective under no-till production but growers who till their fields may also benefit from the practice. I've seen some growers who have built up their seed banks so much that they could not till the soil properly in the spring. So even if you are practicing tillage, there may be a need to apply fall herbicides.

You will get a better kill with a fall program. With winter annuals, it's easier to kill them in the fall when they are young and smaller than when they are much bigger in the spring and stressed from the winter weather. And with biennials and simple perennials, any translocating product will go with the nutrients down to the root systems and kill the plant.

Winter annuals, such as purple deadnettle, common chickweed, and marestail or horseweed, pop up in August and grow until June --with the exception of marestail, which grows until October. Simple perennials, such as dandelion and curly dock, and biennials, like wild carrot and poison hemlock, can survive during winter by redirecting nutrients to the roots before cold weather sets in.

A fall treatment of such weeds is effective for several reasons:

Weeds, such as marestail and dandelion, are much harder to kill in the spring than in the fall. And fall treatments require a smaller herbicide rate because the overall size of the weed can be much smaller.

Some weeds, like shepherd's-purse, can be effectively killed in the spring but they must be controlled before setting seed. By treating in the fall, a grower can reduce the amount of seed production of winter annuals.

A fall treatment affords a grower bare soil in the spring. Bare soil allows for more sunlight, which results in higher soil temperatures, faster drying times and an earlier planting date.

Some weeds are hosts for insects. Purple deadnettle, for example, is host for soybean cyst nematode. Purple deadnettle has come in early enough already this fall to help create another generation of nematodes. So with that alone, nematode populations could increase. Chickweed is a good host for cutworm moth, which can reduce corn stands in the spring.

Do you have an agronomy question? Email cheryl.rainford@meredith.com. We'll send some of the most common questions to professionals in the industry and see what they say. Look for answers in upcoming Agro-Connect Ask the Experts columns.

Attacking winter annuals and simple perennials and biennials in the fall, rather than waiting until spring, is the most effective way to control the weeds.

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