Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Each year, there are cases where vegetables in high tunnels and greenhouses are injured by herbicides. Drift from herbicide applications near greenhouses and high tunnels can cause major losses.
Small spray particles can move long distances with wind. This is called particle drift which is commonly associated with herbicides such as paraquat. Vapor drift occurs when the herbicide volatilizes and then moves in the air, which is common with ester formulations of 2,4-D
Growth regulator herbicides are often of most concern for drift damage to high tunnel and greenhouse crops. This group includes dicamba, 2,4-D, MCPA, MCPP, triclopyr, picloram, clopyralid, aminopyralid, and quinclorac. Drift from these herbicides can occur over one mile from where they were applied.
Sources for drift can be crop field, turf and lawn care, right of way, and other applications. Another issue is with applications to control weeds around greenhouse or high tunnel structures themselves.
Tomatoes and other solanaceous crops such as potato and eggplant are particularly susceptible to damage from these growth regulator type herbicides. The most common symptom of this injury is the twisting of petioles and deformed leaflets. Stem and petiole elongation, downward cupping or rolling of new leaves, stem splitting, vein yellowing, and stunting may also be observed.
The most susceptible period for greenhouses and high tunnels is when the sides or ends are fully open. In areas surrounding high tunnels or greenhouses, do not use herbicides that might contaminate the greenhouse or environment by volatilization or movement in water. Do not use growth regulator type herbicides, such as those labeled for broadleaf weed control in turf, near greenhouses or high tunnels. Do not use soil sterilant herbicides such as Picloram, Arsenal, Oust, or Casoron around greenhouses or high tunnels.
Growth regulator herbicide damage to high tunnel tomatoes. Injury was most severe along open sidewalls. This high tunnel was next to crops fields where the drift likely came from. Note the deformation of the leaves.