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Weather Offers Extended Opportunity for Fall Weed Control

Fall can be an excellent time to control many winter annuals like penny cress, shepherds purse, prickly lettuce, downy brome and marestail. Most years the window for applying herbicides in South Dakota is finished by early November. This year, however, climatologists are suggesting that we may not have a hard freeze in South Dakota for another couple of weeks. This weather will give winter annuals the opportunity to continue to germinate and grow. However this weather will also provide SD producers with an extended opportunity to control those difficult winter annuals.

Problems with spring applications
Spring weather is often not favorable for herbicides applications. Cool, wet conditions can make timely herbicide applications a challenge, especially when targeting winter annuals that already have a jump on the season. Herbicide applications need to be made early to provide effective control on winter annuals.

Benefits of fall applications
Another benefit to fall herbicide applications is that most herbicides used to control downy brome in winter wheat have some fairly long crop rotation restrictions. When applied in the fall, the rotation restriction is much less of a concern for the crop after the winter wheat.

Fall herbicide applications also work better on marestail as it germinates in the fall. Research has shown that marestail is much easier to control in the fall when it is in the seedling stage than in the spring. Marestail can be resistant to glyphosate. Applications of 2, 4-D provide the most effective control in the fall.

Considerations before applying
Producers should be sure to carefully scout fields prior to any herbicide applications. When considering fall herbicide applications weeds should be healthy. Most herbicides work best when temperatures are in the upper 50’s and 60’s. A hard frost will limit the effectiveness of the herbicide on many weeds.

Source: South Dakota State University 

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