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Herbicide Damage on Tomato Plants

Posted by Kim Ellson - Gardening

I was carrying out a site visit when I was asked to inspect some tomato plants growing in a high tunnel that were displaying symptoms of distorted growth. The damage looked much like that which could be caused by herbicide drift (probably vapor drift) from some kind of a plant growth regulator such as 2,4-D or Dicamba. These herbicides would first affect the new growth, causing leaf curling, twisting, and epinasty (increased growth on upper surface). Under the right conditions (especially very warm/hot weather) the vapor can drift great distances, sometimes more than a mile. Also, these products can be found in many broadleaf lawn herbicides and brush killers. Vapor drift is often worse on very warm days, which is also when high tunnels are opened to vent excess heat.

Pesticide applicators should avoid the use of highly volatile pesticides during high temperatures to reduce the potential for vapor drift. It would be considerate for the pesticide applicators to warn the neighbors of their spraying intentions, however growers might not be able to keep tunnels sealed on hot days without suffering heat damage. In addition, never use mowed grass to which a herbicide has been applied for mulching the tomato crop. The residual activity of 2,4-D within the soil or on plastic is variable; it is therefore up to the grower's discretion whether to replace crop plants. Determining factors include but are not limited to; extent of damage, maturity of crop, assessment of new growth, and availability of replacement plants. Damaged plants can remain unproductive depending on severity of exposure. If damage happens early in the season, a new planting can often overtake and exceed those stunted plants. Tomatoes grown in high tunnels are susceptible on hot days when the sides are opened for ventilation and temperature control.



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