Tomato and Pasture Herbicides

Tomato is very sensitive to pasture and right-of-way herbicides. The extent of off-target herbicide damage depends on level and timing of exposure and management practices.     
Management aids are available to help prevent and diagnose off-target herbicide injury in tomato.
Preventing Herbicide Injury in Tomato
Herbicide selection- follow label use directions and precautions, understand herbicide characteristics such as volatility, water solubility, persistence, and efficacy.
Drift prevention- know weather conditions for minimizing drift potential, proximity to sensitive crops, proper application timing, nozzle selection, and sprayer set-up.
Sprayer contamination- to best avoid injury from contamination, dedicate a sprayer for pasture-use only.
Field selection- risk assessment based on topography, surface water, field history, and future plans for field.
Movement of cattle and handling of manure- rotational grazing in line with fields targeted for rotation to tomato, proper waiting periods, manure application and storage.
Handling of treated hay- purchased or produced on site, origin and herbicide treatment history, bale segregation, storage, and feeding.
Monitoring results- field number or name, date and rate of application, weather conditions.
Diagnosing Herbicide Injury in Tomato

Many herbicides used in pastures and hay fields are growth regulators that mimic the plant hormone auxin. When observing herbicide damage in tomato, it is often difficult to distinguish between these herbicides. The symptoms below can help to identify certain characteristics of each of these herbicides in tomato. The following are descriptions of commonly observed symptoms resulting from tomato exposure to synthetic auxin herbicides:

Curling- folding of edge of leaf margins.
Epinasty- twisting, bending and/or elongation of stems and leaf petioles.
Blistering- appearance of raised surfaces on leaf tissue.
Chlorosis- yellowing or whitening of leaves resulting from loss of chlorophyll.
Necrosis- browning of tissue resulting from cell death.
Herbicides Evaluated for Symptomology on Tomato
Common Name
Chemical Family Trade Names
aminocyclopyrachlor* Pyrimidine-carboxylic acid Not registered for use in pastures and hay fields
aminopyralid Pyridine-carboxylic acid Milestone, ForeFront R&P, ForeFront HL, GrazonNext
picloram Pyridine-carboxylic acid Tordon, Surmount, Grazon P+D
2,4-D** Phenoxyacetic acid Various names and mixtures
dicamba Benzoic acid Banvel, Clarity, Oracle, Rifle, Brash, Rangestar, Weedmaster
*Products containing aminocyclopyrachlor are registered for non-cropland use, but are not yet registered for use in pastures. 
**Picloram, aminopyralid, and dicamba are often sprayed in combination with 2,4-D.  
Time Lapse Videos
Tomato plants were grown in a greenhouse and treated with simulated drift rates for aminocyclopyrachlor, aminopyralid, picloram, dicamba and 2,4-D.  Plants were allowed to dry and moved indoors under artificial light. Photographs were captured every hour for ten days. Images were then compiled to create a time-lapse video showing the development of symptoms.
Get Microsoft Silverlight
Description: All plants exhibited leaf curling and petiole drooping shortly after exposure. By day 2, all plants were bending horizontally at the main stem. At day 5, aminocyclopyrachlor (MAT28) and picloram plants were compact, while the aminopyralid plant was elongated and slightly more upright. By day 7, new growth had ceased and swelling in stems was evident.

Get Microsoft Silverlight

Description: 2,4-D and dicamba plants exhibited leaf curling, petiole twisting, and stem bending one day after exposure. By day 5, apical growth ceased and leaves began to wither. At day 10, the 2,4-D plant was yellowed and necrosis was evident in the dicamba plant.

Symtomatic Still Images

Stem bending and leaf curling
Stem bent horizontally

Stunted new leaves and petioles twisting
Leaf curling and petiole drooping
Yellowing and advanced epinasty

Lesions on main drooping stem
Leaf curling and petiole
Severe epinasty

Stem cracking, blistering, and drooping
Upper stem bending
Reddish brown lesions on main stem

Strapping and toothed margins on young leave
Stem bending, petiole and leaf curling
White bumps on main stem

Early necrosis and drooping, loss of apical growth