Herbicide Injury in Horticultural Crops, Part I
Throughout my career with University of Missouri Extension, there have been many occasions where I have seen herbicide injury on horticultural crops. Some of these were slight, but many were very serious, with significant crop loss.
There are several types of herbicide injury. One is carryover. In this case, the herbicide that was applied to a crop the previous season does not break down completely, and causes damage to the crop you have planted this year.
You can also see herbicide injury if your spray equipment is not cleaned out completely. Some chemicals have a notorious reputation for being hard to clean from equipment, and yes, I have seen that kind of damage on several occasions as well.
Occasionally, you can see damage with labeled applications of herbicides… chemicals being used on the crop that they were designed and labeled for…. but for some reason things go wrong and they still cause injury. That is rare, but it still happens. Just follow the label to the letter and that will usually keep you from problems.
I have also seen damage on crops from herbicides that washed downhill into a pond used for irrigation. While the herbicide was labeled for the plant being sprayed (usually brush), it was not labeled for the crop that was being irrigated. Not a good situation, needless to say, and the crop was damaged.
Another situation is where a pasture was sprayed with a herbicide that was labeled for such situations, but livestock eating in the pasture also ate the herbicide, which carried through in the manure. When the manure was used with a crop, damage occurred. I also saw this once with soil that was brought into a greenhouse from a pasture that had been sprayed with a herbicide which was not labeled for the greenhouse crop.
But the most common type of herbicide damage is off-target drift. If the wind is blowing the wrong direction, there can be damage over long distances. Be sure to follow label directions, and watch the wind speed. This can occur with any herbicide.
Many herbicides are quite volatile, and can drift for many miles, injuring crops and gardens. This can occur well after the time of application, and even under conditions where there is little wind. Drift from 2,4-D applications is a good example of this kind of problem. The latest problems with this have resulted from improper use of synthetic auxins, such as Dicamba and related herbicides.
Unfortunately, I see drift/volatilization problems too frequently as I work with horticultural producers. Last year, for example, I saw a tomato greenhouse that was exposed several times to non-labeled herbicides, causing damage. This reduced the grower’s crop yields. It also may delay the first fruit set, if it damages flowers. The first ripe fruits are the most valuable, and command the best prices at the market.
In my next column, I will outline some measures that a grower might consider to avoid drift and volatilization problems. I will also discuss some resources that applicators might want to utilize to avoid damage to non-target crops.
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