By: Darren Robinson, University of Guelph, Ridgetown Campus; Janice LeBoeuf, OMAFRA, Ridgetown
Herbicides are useful tools for the management of weeds. The herbicides registered for use in tomatoes are selective in their activity, injuring or killing weeds while being safe to use on the crop. Crop injury may occur, generally when a crop is stressed beyond its ability to adequately deal with a herbicide application. Injury due to herbicides can arise as a result of several factors, including weather-related stress, soil factors such as light soil texture and low soil organic matter, shallow planting and sensitive crop varieties. The pages in this section contain information on herbicide injury for several products registered on tomatoes in Canada. Injury to a crop can also result from factors other than herbicides, such as drought, frost, nutrient deficiencies, insects, nematodes or diseases. These factors should also be considered when diagnosing an injury scenario, since the symptoms caused by these factors may look very similar to and be mistaken for herbicide damage.
Sencor (PPI or POST) injury: Sencor moves upward in the plant in the transpiration stream, so injury symptoms are typically seen in older leaf tissues. The leaves will show chlorosis (yellowing or whitening) between the leaf veins, and burning around the leaf margins.
Conditions that increase the chance of injury: cool, wet weather, high pH (>7.5), cloudy weather prior to application
Dual II Magnum
Dual Magnum (PPI) injury: Dual does not translocate far in the plant, and injury symptoms occur only in stressed plants in cold, wet weather. If injury does occur, symptoms will include yellowing and curling of the new leaves and petioles.
Conditions that increase the chance of injury: cool, wet weather, low soil organic matter (<2%)
Treflan (PPI) injury: Tomatoes are particularly susceptible to Treflan injury on low organic matter soils, or if transplants have been placed too shallow in the soil. Injury symptoms include club roots, stunting and occasionally purpling of leaves.
Conditions that increase the chance of injury: cool, wet weather, shallow planting (<4”), low organic matter (<2%)
Conditions that increase the chance of injury: low organic matter (<2%), low CEC (<12)
Pinnacle (POST) injury: Pinnacle translocates in the phloem to new developing tissues, so injury symptoms will be seen in the ‘heart’ of the plants at the growing points. Injured plants will cease growth and turn chlorotic within days of application, especially if the herbicide is applied in hot weather to sensitive varieties. Check for variety sensitivity with processing representatives.
Conditions that increase the chance of injury: hot, humid weather (>30oC), sensitive varieties (eg. H9909, N1069)
Prism or Sandea
Prism or Sandea (POST) injury: Injury symptoms may be observed in hot, humid weather, and will appear in the youngest leaves. Symptoms include chlorosis and slight stunting. Variety sensitivity to Prism or Sandea is not as prevalent as to Pinnacle.
Conditions that increase the chance of injury: hot, humid weather