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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. Lift-Off or codistillation of Goal lift off injury
seems to be worse this season because of rain. 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.
To contact Barry Tickes go to: btickes@ag.arizona.edu.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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