Effective weed management is a yearlong process that begins well before planting time.
In this interview, Dallas Peterson, Ph.D., an extension weed specialist at Kansas State University, discusses which weed-management strategies soybean farmers should be implementing this spring both before and during planting time.
Q: With planting season coming up, what are your biggest tips for weed-management?
A: The time before planting season is critical for weed control. Farmers should implement a diversified weed management plan that includes the integration of many different practices. Farmers should always apply the full labeled herbicide rate, time the application effectively and rotate the herbicide modes of action they are using. In the long term, crop rotation is also one of the most important weed-management strategies.
Q: Why is herbicide application timing so important for weed control?
A: A large part of herbicide effectiveness can be attributed to timing. If farmers don’t catch weed problems early, they are going to be in trouble. Weeds emerge and grow very quickly, and once they reach a certain stage of growth, they can become very difficult to control. That’s why farmers should be proactive with their weed control before planting season and regularly scout and treat their fields for weed problems throughout the year.
Q: Many farmers use pre-emergence herbicides as their first defense against weeds in the spring. What are your recommendations?
A: Application of pre-emerge herbicides depends largely on the biology of the target weed. When dealing with summer annuals, for example, it is ideal to apply herbicide before the weed germinates in the spring. If farmers wait until the weed germinates at planting time, they are going to be behind. However, applying herbicides too early can also be detrimental because they degrade rapidly and can become ineffective.
Q: So when is the best time to apply pre-emergence herbicides?
A: If your primary target weeds are waterhemp or Palmer amaranth, it is better to wait until closer to planting because they usually don’t begin to germinate until May and then will continue to germinate through the summer. Sequential applications of residual herbicides may be the best approach to control a broad spectrum of weeds and for an extended period of time.
Q: Farmers are often concerned about herbicide carryover during planting time. What factors contribute to herbicide carryover?
A: Weather and precipitation patterns are important factors. Last spring, we had the perfect conditions for herbicide-carryover issues. Fall herbicide treatments applied in 2013 had little moisture for breakdown to occur in the spring. That lack of moisture left farmers planting into fields with herbicide residues, which caused problems with the next crop.
Q: Should farmers be concerned about herbicide carryover this year?
A: I wouldn’t expect it to be much of a problem this year because we’ve had better moisture throughout the fall and winter this past year. However, if farmers plan to use dicamba as a pre-plant treatment for control of spring weeds like marestail, kochia and ragweeds they need to check waiting intervals and note precipitation patterns after planting to ensure they don’t experience short-term carryover issues. Reading herbicide labels carefully and keeping good records of crop rotations and herbicide usage from year to year can also prevent potential herbicide carryover problems in the future.