Burndown Herbicides Before Forage Crop Establishment

Now is the time to start thinking about the establishment of a forage crop. However, there are certain aspects that need to be considered including herbicide carryover from previous crop and weed management prior to cover crop establishment.

Herbicide carryover from corn herbicides?

Depending on where you are located in the region, the likelihood of herbicide carryover injury to fall-seeded forage crops due to dry conditions during the growing season might be an issue. If you are in a region that was droughty, the potential for herbicide carryover will be highest when seeding small-seeded broadleaf forage crops (i.e., alfalfa, clover species, etc.) on production fields that received applications containing mesotrione or clopyralid, particularly when applied in POST applications. Misapplications or overlapping spray patterns are often an additional contributing factor that increases the likelihood of herbicide carryover.

Burndown herbicides for establishing fall-seeded forage crops?

In addition to rotation interval restrictions, it is important to understand the potential for burndown products to impact forage crop establishment due to soil residual activity. The simplest and most risk-free approach is to use only glyphosate or paraquat to start clean prior to crop seedings. These broad-spectrum products have no soil residual activity. However, additional products are often needed to control glyphosate-resistant species (marestail, Palmer amaranth, waterhemp) as well as certain other weeds. Here are several burndown herbicide options and their restrictions to consider:

• Glyphosate and paraquat – most forage crops can be planted any time after application.
• Glufosinate (e.g., Liberty Ultra) – must wait to plant any forage crop (both legume and grass) until 180 days after the last application. Failure to comply with these restrictions may result in illegal herbicide residues in the forage crops.
• 2,4-D and dicamba – in general, it is best to wait 3 months to plant alfalfa and clover for 2,4-D and 4 months for dicamba. Also, neither of these herbicides are recommended immediately prior to (i.e., at least 3 weeks) grass forage establishment since they can interfere with seedling germination and establishment. However, in pure grass stands, they can be applied postemergence once the seedling forage has 5 leaves and a well-established root system.
• Sharpen – must wait 4 months to plant alfalfa or clover if Sharpen is applied at 1 fl oz/acre. However, in pure grass seedings, Sharpen (1-4 fl oz) can be applied to assist with burndown and forage grass can be planted immediately afterwards.
• NovaGraz and PastureGard HL – in forage grass systems only, these products could be used as a burndown prior to establishment. NovaGraz must be applied 14 days before planting and PastureGard HL, 21 days before. These will severely injure or kill legumes. Other products such as Crossbow, GrazonNext HL, Starane Ultra, Metsulfuron, Harmony Extra and others are not labeled for use prior to forage establishment.