With flood, cold, and wet conditions in March/April, many producers are facing a smaller than expected window for making their burndown herbicide applications before planting crops. This makes timely applications now even more important to provide for a proper interval before planting.

For more on burndown herbicide options in row crops, listen to this month's CropWatch podcast when host and Extension Educator Michael Sindelar talks with the author, Amit Jhala.

Dicamba and 2,4-D are commonly used burndown herbicides for control of winter annual broadleaf weeds such as dandelion, field pennycress, henbit, tansy mustard, and marestail.

Additionally, several summer annual weeds in Nebraska emerge early in the season, prior to planting corn and soybean, and need to be controlled before they grow too large to be effectively controlled. Of particular concern are giant ragweed, kochia, and marestail. We believe there are numerous populations of these species in Nebraska that cannot be controlled by glyphosate because they have evolved resistance to glyphosate. Therefore, use of 2,4-D/dicamba has increased in recent years, particularly for control of glyphosate-resistant marestail and giant ragweed. Based on observations in our giant ragweed research studies, we have had success controlling glyphosate-resistant giant ragweed with any herbicide program containing 2,4-D as a component of a burndown program.

If you apply 2,4-D prior to planting, be sure to adhere to the planting interval specified on the label. The planting interval for 2,4-D products used prior to soybeans varies, often between 7 and 30 days, depending on application rate.

As a general guideline, the following planting intervals should be maintained for corn, soybean, and sorghum after applying 2,4-D/dicamba

• We recommend NOT applying dicamba in pre-plant burndown applications unless you are planting Roundup Ready 2 Xtend soybean. FeXapan, Engenia, or XtendiMax are labeled dicamba products that can be applied in burndown before planting Roundup Ready 2 Xtend Soybean.
• If 2,4-D (4 lb/gal product) is applied at 16 fl oz/acre in a burndown program, the planting interval should be seven days for corn and soybean.
• If 2,4-D (4 lb/gal product) is applied at a rate above 16 fl oz/acre in a burndown program, the planting interval should be 14 days for corn and 30 days for soybean. 
• If dicamba is applied at 4 oz/acre or less in a burndown program, the planting interval for corn should be five days. If dicamba is applied at 8 oz/acre, the planting interval for corn should be seven days.
• DiFlexx and DiFlexx DUO are dicamba products with CSI safener; therefore, corn can be planted any time after application of these products, which may be particularly helpful in a replant situation. Care should be taken, however, so that corn seed does not contact the herbicide.
• If dicamba is applied at 4 oz/acre in a burndown program, the planting interval for sorghum should be five days. If dicamba is applied at 8 oz/acre, the planting interval for sorghum should be 10 days. Certain products may have a longer planting interval. For example, Clarity applied up to 8 fl oz/acre requires 15 days of planting interval to sorghum.
• If 2,4-D is applied at 16 oz/acre or less in a burndown program, the planting interval for sorghum should be 10 days. If 2,4-D is applied at more than 16 oz/acre, the planting interval for sorghum should be 21 days.