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Weed Control With Your Cover Crop
GARRET MONTGOMERY
JACKSON, TENN.
With planting just around the corner, there are a few management considerations of cover crops that are being used for weed control. There is no single best way to manage all cover crops prior to any given cash crop. Tailoring the cover crop to best fit your cash crop can make a difference in the ultimate success of your weed control program. Recommendations below are in reference to weed control cover crops (wheat, cereal rye, other common cereals, and/or vetch, crimson clover, Austrian winter peas, other common legumes):
Corn: Termination of a cover crop prior to planting should begin at least 10-14 days before corn planting. Our research has consistently shown that although corn can be planted into a green cover crop, the advantages do not yet outweigh the disadvantages.
• Advantages to delaying termination: Increased cover crop biomass, though it is not enough to provide good weed suppression. The reason for this is the majority of biomass provided by covers is produced through April. This is obviously too late to timely plant corn.
• Disadvantages to delaying termination: Increased insect pressure: Any time termination is delayed within two weeks of planting, the probability of above and below ground insect problems increases.
Cotton: Provided you can get good cotton seed to soil contact, our research has shown that termination of a cover crop should be can be done 14 days before or after planting cotton, without negative impacts on yield. A cover crop that produces good biomass will likely remove one in-season herbicide application.
Soybeans: Termination of cover crops will be dependent on herbicide tolerances of the soybean variety planted. However as a generality, if the cover crop being planted into, will not lay down when the soybeans are planted (cereal rye, wheat), measures should be taken to ‘roll’ the cover crop as some yield loss has been observed from soybeans trying to grow through a dead but standing cover crop. Additionally, if termination is < 2 weeks prior to planting, expect to use an insecticide seed treatment + a pyrethroid insecticide near planting. However, in contrast to corn, the weed control benefits can actually outweigh the impacts of the added cost for controlling insects depending on your situation.
• Conventional, Liberty Link, Rou-ndup Ready: Termination should consist of Roundup (32oz) 7-10 days before planting, followed by Gramoxone + a residual immediately behind the planter.
• Xtend Soybeans: If the cover crop is a cereal+legume mix Roundup+Xtendimax/Engenia has provided excellent control, and in this system, termination can be delayed all the way until 14 days after planting. Our research has indicated that in this system, termination conducted 10-14 days after planting will maximize control of Palmer amaranth in soybeans.
Lastly, cover crops DO NOT eliminate the need for PREs or residual herbicides. With that being said, cover crops can also effect the efficacy of residual herbicides. In our research, products that have been effective as residuals in cover crops have been Warrant, the PPOs (Reflex, Valor…), and Metribuzin (atrazine, Caparol, and Cotoran should work also). ∆
GARRET MONTGOMERY: Department of Plant Sciences, University of Tennessee
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