Now is the time to start thinking about the establishment of a cover crop. If herbicides such as glyphosate, paraquat, Liberty, 2,4-D, or dicamba are being used to control problem weeds prior to cover crop establishment, remember to consider the replanting interval.

  • Glyphosate and paraquat – most cover crops can be planted any time after application.
  • Liberty – according to a recent label update, Liberty can be applied 7 days before cover crop establishment. Planting of cover crops for conservation purposes may be planted in fields previously treated with Liberty as long as these cover crops are not grazed by livestock or harvested for feed. For best results, do not plant cover crops less than 7 days after an application of Liberty nor before 1/2 inch of rainfall or irrigation has occurred. Planting sooner than this may result in stand reduction.
  • 2,4-D – depending on the rate of 2,4-D applied, at least a week to four-weeks waiting period is necessary before establishing cover crops. If small grain covers are being established, some research suggests a minimum delay of 7-10 days after application at rates of 1 pint/acre of 2,4-D ester. Also, other studies have shown that certain clovers (e.g., red and crimson) and alfalfa may be established within the same constraints with 2,4-D ester. To be certain, a longer waiting period and rainfall help to reduce the potential for injury.
  • Dicamba – usually requires at least a couple weeks or more before certain cover crops can be planted and this also is directly related to the amount applied. Some have asked about the use of Sharpen and Elevore as a burndown prior to cover crop planting. According to their labels, some suggestions can be made.
  • Sharpen (1 fl oz) – no restrictions for small grains but has a 1-month wait period for other cover crops (species not specified; but some may be more sensitive). Keep in mind, once Sharpen has been applied, the cover crop cannot be harvested or grazed for livestock feed.
  • Elevore – small grains, ryegrass, and canola can be planted after 14 days but there is a 9-month wait for clover and mustard species.

Penn State research.We conducted a field study in 2020 at Rock Springs to examine the effects of commonly used burndown herbicides prior to fall cover crop establishment. In summary, the use of Group 4 (auxin) herbicides as a burndown treatment prior to fall cover crop establishment tends to be risky. However, depending on what species is selected (e.g., cereal rye or ryegrass) and when it will be planted (>7 days after application) some Group 4 herbicide options could still be useful. Furthermore, from our preliminary data, other herbicides such as Sharpen and Liberty might have a fit since they are generally safe to many cover crop species and can control problematic weeds such as glyphosate-resistant marestail/horseweed and Palmer amaranth. These could be tank-mixed with glyphosate for broad-spectrum burndown prior to cover crop establishment.

Related Content:

Cover Crop Burndown Considerations,

Tips For An Effective Cover Crop Burndown,

Late Fall Herbicide Treatments for Cover Crops?