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Managing herbicides in ditch forages

Clopyralid and picloram herbicides are commonly used to control weeds in road ditches. Herbicide residues in forages can contaminate livestock manure and lead to crop injury during application. To prevent crop injury,

  • Always follow herbicide harvest or grazing restrictions

  • Test soil or forage for residues

  • Work with local, county or state transportation agencies

Harvesting grass and legumes along roadways is common, especially in western Minnesota. Ditch hay provides suitable forage for beef cattle, dairy heifers and horses. But ditch hay treated with picloram or clopyralid can lead to broadleaf crop injury via manure application.

This injury has reduced grain yields, and in some cases, resulted in total yield loss.

Common roadside herbicides

Picloram and clopyralid are herbicides that control unwanted broadleaf weeds in the following areas

  • Croplands

  • Rangelands

  • Pastures

  • Along roadways

These herbicides control hard-to-kill noxious weeds like thistles, without harming beneficial or planted grasses. As a result, local, county and state highway departments commonly use them along roadways.

Herbicides with aminopyralid are starting to replace picloram and clopyralid because they better control Canada thistle. But they pose the same risk to broadleaf crops from contaminated manure. Such cases haven’t been reported yet in Minnesota.

These products cause injury to sensitive crops, but there’s no documented history of human or livestock toxicity by picloram or clopyralid.

Crop injury from contaminated manure

When animals eat picloram- or clopyralid-treated hay, the chemicals pass through the animal and end up in their manure usually within a day or two.

In agricultural production, applying manure to fields is beneficial and common. Manure contaminated with picloram or clopyralid can harm or kill sensitive crops including:

  • Soybeans

  • Lentils

  • Peas

  • Legumes

  • Potatoes

  • Tomatoes

  • Peppers

Injured plants can exhibit twisting, leaf cupping, and loss of apical dominance. This results in short plants and abnormal side shoots.

Soybean field affected by picloram
Soybean field affected by picloram contaminated manure. PC: Brett Potter
Soybean injury
Soybean injury as a result of picloram contaminated manure applications. PC: Bruce Potter

Avoiding crop injury

Labels of many products containing picloram and clopyralid list restrictions important for those harvesting ditch hay.

  • Manure and urine containing these herbicides may cause injury to sensitive broadleaf plants

  • Don’t use treated plant material in compost.

  • Don’t spread picloram and/or clopyralid contaminated manure and/or compost on land used for growing susceptible crops. Contaminated manure may be spread onto fields that will be planted to grass crops (i.e. corn, small grains, or sorghum sudan forage).

Always read and follow warnings and recommendations on herbicide labels. These will vary between products. Some examples may include:

  • Don’t allow lactating dairy animals to graze treated areas within 7 days after application

  • Withdraw meat animals from treated fields at least 3 days before slaughter

  • Don’t harvest or cut the forage within 30 days after application

  • Don’t plant sensitive broadleaf crops in treated areas until a sensitive bioassay shows no detectable herbicide is present in the soil

If you carefully follow all the directions on the herbicide label, sensitive crop injury from manure applications should not occur.

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Working with local, county and state agencies

If you harvest, feed and sell ditch hay, work with the local, county and state highway departments.

  • Identify which herbicides are used in the roadside weed control program

  • Determine which roadsides are spot treated and if some areas have broadcast treatments

  • Find out when roadsides will be treated

Working with local, county, and state agencies can reduce the risk of harvesting forages with unwanted herbicide residues. If you know and follow the herbicide’s harvest or grazing restrictions, you can harvest and feed the forage to livestock without contaminating manure.

Permitting

You need a permit if you plan to hay highway areas owned by the Minnesota Department of Transportation (MnDOT). You don’t need a permit on roadways where MnDOT only owns an easement.

You can get a permit by contacting MnDOT. The permit is free and MnDOT will notify you of any cutting restrictions due to herbicide use, wildlife habitat designation or calendar date restrictions.

Visit MnDOT’s website for more information on permits. Roadways owned by county and local governments have their own regulations, and farmers should contact their County or Township to obtain any cutting restriction information prior to harvest.

Author: Krishona Martinson, Extension equine specialist

Reviewed in 2021

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