Early-season rains and major flooding of bottom ground has significantly impacted planting decisions by some corn and soybean producers. As a result there are likely to be cropland in Kentucky that will not be planted this season.
However, a successful weed control program may still be a needed to keep weed pressure down and reduce the introduction of more weed seed into the soil seed bank which can impact future crops.
Although tillage and mowing are mechanical control methods that can be used on fallow fields, herbicide applications can be one of the most cost effective methods to combat weeds.
For broad-spectrum weed control herbicide products that contain glyphosate (eg. Roundup, etc.) would be one of the chemical control options to consider. Glyphosate has little or no soil residual activity and will not limit the planting of a subsequent crop next season; whereas, herbicides with soil residual activity may delay planting of certain rotational crops.
Depending on the size and type of the weeds the application rate suggested would be equivalent to 0.75 to 1.5 lb ae/A [2 to 4 pt/A of a Glyphosate product (containing 3 lb ae/gal) or 1.3 to 2.67 pt/A of Roundup PowerMax (4.5 lb ae/gal)].
Use equivalent rates of other products. With herbicides such as glyphosate, a second application may be needed before the end of the season. A potential drawback of using glyphosate as the primary means of weed control in these fields is that it may aid in selecting for glyphosate-resistant weeds, such as marestail (also known as horseweed), palmer amaranth, and waterhemp.
The use of 2,4-D or dicamba can be tank mixed with glyphosate to provide added control to some broadleaf plants and may be desired in fields with concerns for herbicide-resistant weeds.
Other broad-spectrum, non-residual herbicide products may also be used such as paraquat (eg. Gramoxone) or glufosinate (eg. Ignite 280SL) to cause a quicker "burndown" of vegetation, but may be less effective on certain weeds.
Application timing may be the most important decision. Sufficient weed growth should occur before making the first herbicide application, however, larger weeds can be more difficult to control.
Allowing weeds to emerge can also serve as a vegetative cover throughout the season. After the weeds are sprayed, the dead plant material that remains can also be beneficial as a ground cover.
Another option to deal with fallow fields is to plant a desirable cover crop. When cover crops become well established they can aid in weed suppression. Factors to consider when planting cover crops are the additional cost of seed, weed control options for establishment, and the potential uses of the crop at the end of the season.
In summary, herbicide applications can be an effective method to combat weeds on fallow ground. Be sure to read and follow the label directions and precautions when applying herbicides to fallow fields and consult product labels when using tank mix combinations.