Codistillation is when a herbicide evaporates or changes from a liquid to a vapor with water. This can occur from soil, water or plant surfaces and can be responsible for substantial loss of some herbicides. When codistillation occurs with Oxyflurofen (GoalTender, Goal 2XL and others), the concern is not herbicide loss but crop injury. Codistillation can occur with several herbicides. It is affected by many factors including temperature, moisture, organic matter, soil pH and other variables. In general, codisillation is greatest when temperatures, moisture and pH are high and organic matter is low. One of the herbicides used in this region that is most affected by codistillation is Eptam (EPTC). A study conducted several years ago in Brawley California found that more than 80% of the Eptam that was applied in irrigation water was lost by codistillation. Most of this was from the soil after it had reached the field. In our trials, we have found that codistillation may help GoalTender and Goal 2XL (oxyfluorfen, also sold as Galligan, Oxi Flo and others) kill weeds but it also can increase crop injury. Goal can move into plants in the vapor phase once it has lifted off and both weed control and crop injury are enhanced. We have seen this when Goal is Chemigated through sprinklers. Goal is primarily a contact type herbicide and moves little in the plant. It works preemergence by killing weeds as they emerge from the soil and contact the herbicide. It is rare for contact type herbicides to work better when overhead water is applied but this seems to be the case with this herbicide. In many cases this potential is exaggerated. Lift-Off of Goal differs from the usual off target drift that can occur with other herbicides. In this case it is movement of the herbicide with water vapor. Moisture must be present and this moisture must evaporate. The vapor normally stays in the field and it is common for a band application to the furrows, for instance, to move across the bed top. Significant movement out of the field normally only occurs with wind. GoalTender is not as volatile as Goal 2XL and is less prone to codistillation but it occurs with both. The picture below is of GoalTender that was applied to the furrows only but it lifted off and covered the entire bed. The crop grew out of this in 2 weeks.

Tickes/J.Pena

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.