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Be on the Lookout for Waterhemp in Drowned Out Areas (08/01/19)

Most of the Valley seems to have finally dried out from the heavy rainfall events in the first half of July.

Most of the Valley seems to have finally dried out from the heavy rainfall events in the first half of July. Unfortunately, the receding water has revealed a lot of acres of drowned out crops. To add insult to injury, many of the acres are now susceptible to late season weed flushes. Waterhemp is the most problematic weed to think about in these drowned out areas. Waterhemp can still germinate throughout August and produce more seed before the end of the growing season. In fact, we have already observed new flushes of waterhemp in our research plots in Fargo that spent 14 days under water.

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The main goal in these drowned out areas will be the prevention of additional seed production. Tillage is a viable control option. Mowing can help reduce seed production but will not completely eliminate it. Herbicides can be useful in these drowned out areas. Herbicide choice will probably be driven on a field to field basis depending on the weeds in these areas, the remaining crops in fields with drowned out areas, and the crops surrounding these fields.  The remaining crops in these fields are likely well past the growth stage cut-offs of most herbicides, however, these drowned out areas can practically be treated as fallow or prevent plant ground. Group 4 herbicides like 2,4-D or dicamba will be effective on broadleaf weeds. However, extreme caution should be practiced if using those herbicides since nearby sensitive crops will be well into reproductive growth stages where damage from off-target movement is more likely to cause yield loss. Paraquat (Gramoxone, others) and glufosinate (Liberty, others) can offer non-selective control of emerged weeds, but can also cause issues if drift onto sensitive crops occur. Overall, preventing additional weed seed production in these problem areas will give us a leg up on weed control in 2020 and future years.

 

Joe Ikley

Extension Weed Specialist

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