We have received a number of phone calls recently concerning crop damage in peas treated with herbicides containing the active ingredient clethodim. Clethodim is an ACCase inhibitor (Group 1) used to control grass weeds in broadleaf crops. There is no clethodim activity on broadleaf crops like peas. So why is there sometimes injury to peas?
Clethodim products containing 26.4% or 2 pounds of clethodim per gallon (for example, Arrow 2 EC, Clethodim 2 EC, and Select 2 EC) contain as much as 70% petroleum distillates. This high level of petroleum distillates, combined with the required crop oil concentrate and liquid fertilizer additives, can act as a sprayer cleaner, dislodging old herbicide residues that are embedded in tank walls or hoses, resulting in unwanted herbicide residue in the sprayer liquid. It is these residues, and not the clethodim, that are injuring the peas.
This type of damage, which is not unique to clethodim products, can be avoided by properly cleaning sprayers between applications, particularly when changing what crop is being treated. While proper sprayer cleanouts are time-consuming, it can save a lot of money and misery. Removing Herbicide Residues from Agricultural Application Equipment is an excellent publication by Purdue Extension that can help you do a good job of sprayer cleanout and possibly save you headaches and dollars down the road.