Photo by Joe Beeler 

Tobacco and Pasture Herbicides


Tobacco is extremely sensitive to auxin or growth regulator herbicides. Even minute doses can seriously injure the crop. Off-target damage to tobacco often results in expensive fines and/or lawsuits, lost productivity for growers, and bad publicity for the industry. Herbicide damage can lead to poor leaf quality, reduced yield, and possible rejection by buyers.

Preventing Herbicide Injury in Tobacco

 
 
 

 

Most of the tobacco growers in Tennessee are also cattle producers or their neighbors are cattle producers. When using pasture herbicides near tobacco fields, there are several things to consider:

Herbicide Selection- label use directions and precautions, volatility, water solubility, persistence, and efficacy.
 

Drift Prevention- weather, proximity, nozzle selection, and sprayer set-up.

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 tobacco, manure application, storage, etc.

Handling of Treated Hay- purchased or produced on site, origin and herbicide treatment history, bale segregation and feeding.

Accurate Record Keeping- field number or name, date and rate of application, weather conditions.



Diagnosing Herbicide Injury in Tobacco


Diagnosing herbicide injury in tobacco can be difficult because many pasture herbicides mimic the plant hormone auxin, and symptoms can be quite similar. The images and descriptions seen here are intended to highlight characteristic symptomology of each of these broadleaf herbicides on tobacco. The following are descriptions of commonly observed symptoms resulting from exposure to synthetic auxin herbicides:

Hooding- downward folding and cupping of entire leaves.
Curling- folding of edge of leaf margins
Epinasty- twisting, bending, and/or elongation of stems and leaf petioles.
Chlorosis- yellowing or whitening of leaves resulting from loss of chlorophyll.
Necrosis- browning of tissue resulting from cell death.


Herbicides Evaluated for Symptomology on Tobacco


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 (MAT28) 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



Burley and flue-cured tobacco 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 2 weeks. Images were then compiled to create a time-lapse video showing the development of symptoms.
Get Microsoft SilverlightAminocylopyrachlor, aminopyralid, and picloram

Description: Picloram symptoms appeared first, as mature leaves were drooping at petioles and young leaves were hooded at one day after exposure. At day 7, aminocyclopyrachlor (MAT28) and aminopyralid plants exhibited hooding in young leaves while the picloram plant had severely limited apical growth and “pigtailing” of youngest leaves. By day 14, newly formed leaves of aminocyclopyrachlor and aminopyralid plants were cupped upwards and the picloram plant had ceased apical growth.

Get Microsoft Silverlight2,4-D and dicamba

Description
: The leaves on the dicamba plant started to droop within a day after exposure. Hooding appeared in both plants within three days after exposure. By one week, new leaves on the dicamba plant were severely curled downward from the leaf margins. By day 10, the dicamba plant had severely limited apical growth while the 2,4-D stalk was elongated above the untreated plant. Near the end of the video, young leaves on the 2,4-D plant were elongated and pointed, while the meristem of the dicamba plant was aborted.

Symptomatic Still Images


aminocyclopyrachlor 
Downward cupping at 3 days
Upward cupping at 10 days

Reduced lateral expansion in new leaves
aminopyralid 
Hooding at 3 days
U Upward cupping of new leaves

Clustering of bud leaves at 1 month
picloram
Initial Hooding
Initial Hooding

Initial Hooding
2,4-D 
Stalk elongation and inversion of young leaves at 10 days
Wrinkled older leaves, pointed new leaves at 1 month

Wrinkled older leaves, pointed new leaves at 1 month
 
 
dicamba 
Leaf curling from base at 3 days
Hooding and prominent veins

Hooding and prominent veins