Emergency Forages and Herbicide Issues

Posted: July 20, 2016

With the spotty rains over the past few weeks, some growers might be thinking about abandoning the current crop and planting an emergency forage crop.

Here are a few things to consider before harvesting the main crop for forage or planting an emergency forage crop.

Harvest restrictions:

A number of herbicides have restrictions when harvesting corn or soybean for silage or forage. Harvest restrictions are based on the potential for illegal herbicide residues in the feed or forage. Although not generally a problem, early harvested corn may fall under some of these restrictions. Some pre-emergence corn herbicides such as atrazine, Acuron, Anthem, and Sharpen have intervals from 60 to 90 days; while other pre-emergence herbicides can be less than 45 days. For example, post-emergence applied products such as Steadfast Q and Resolve Q have a 30 day, Status a 32 day, Liberty a 70 day, Roundup a 50 day, and Impact/Armezon a 45 day harvest restriction for silage following herbicide application. Many of the pre and post applied soybean herbicides are not labeled for soybean forage but some that are include BroadAxe/Authority Elite-30 days, Boundary and metribuzin-40 days, FirstRate-14 days, and Liberty-40 days. Fortunately, in-crop applications of Roundup have only a 14-day harvest restriction. The Touchdown Total label does not allow harvest for forage, while other glyphosate products vary regarding their harvest restrictions.

Crop rotation:

Herbicide labels also restrict when rotational crops such as sorghum, winter wheat or spring oats may be planted. Re-cropping restrictions may be based on either potential crop injury from herbicide residues in soil or the potential for illegal pesticide residues in the rotational crop. Rotation restrictions range from none to at least 26 months, so be sure to check a current herbicide label or other reliable information source before planting a rotational crop this late summer or fall. Most atrazine containing treatments have at least a 10-month restriction before planting small grains. Forage sorghum or sorghum-sudan grass may be better alternatives for atrazine-treated corn fields. You can find both harvest restriction information and re-crop information on the herbicide labels and in the 2015-16 Penn State Agronomy Guide or the 2016 Mid-Atlantic Field Crop Weed Management Guide.

Contact Information

Dwight Lingenfelter
  • Program Development Specialist
Phone: 814-865-2242
William S. Curran
  • Professor of Weed Science
Phone: 814-863-1014