The three leading causes of 2,4-D injury are: volatilization (or vapor drift), spray drift, and sprayer contamination. The potential for injury from each of these causes can be greatly reduced by adhering to best management practices as described in the following paragraphs.
Another way in which 2,4-D injury can occur is by spray drift. Spray drift means physical movement of spray droplets by wind. As opposed to vapor drift (previously described), spray drift can occur with any formulation of 2,4-D (or any herbicide). Spraying during windy conditions and using nozzles and pressures that result in the creation of fine spray droplets increase the risk of spray drift.
Except in extreme cases, such as spraying in very windy conditions and using nozzles and pressures that create very fine droplets, spray drift normally is observed only over short distances. A buffer of 200 feet or more between the area being sprayed and the susceptible crop usually is adequate to prevent injury from spray droplet drift unless it is very windy. If there is no wind or if the wind is blowing away from the cotton field, a shorter buffer is acceptable.
Vapor Drift (Volitilization)
Most cases of 2,4-D injury to cotton result from vapor drift of an ester-containing formulation of 2,4-D. Vapor drift injury results when the herbicide volatilizes and the vapors move to a susceptible crop such as cotton. Injury from vapor drift can occur at rather long distances from the sprayed area.
Hot temperatures, moist soils, and temperature inversions all increase the potential for vapor drift. Vapor drift is not movement of material caused by wind. In fact, calm or no wind may lead to inversions that could result in vapor drift. Vapor drift can be avoided by simply refraining from the use of ester-containing formulations of 2,4-D. Ester formulations of 2,4-D should not be used within a mile of any cotton field during the months that cotton is in the field. Most commercially available ester formulations are considered "low volatile." These formulations are still volatile, and their use can lead to cotton injury. Formulations containing a mixture of 2,4-D ester and 2,4-D acid, i.e., Weedone 638, should also be avoided in cotton-producing areas. Vapor drift is not a problem with amine formulations of 2,4-D.
Ester and ester-acid formulations of 2,4-D are popular because they mix well with liquid nitrogen. Amine formulations also can be mixed with liquid nitrogen if the 2,4-D is premixed with water before adding it to the liquid nitrogen. The type of spray nozzles that a farmer uses does not reduce the potential of vapor drift.Stolen and adapted from: "Mr. Cotton Doesn't Like Miss Ester: A Practical Guide to Significantly Reducing 2,4-D Injury to Cotton" produced by the 2,4-D Ester Stewardship Program.
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