Cotton and Pasture Herbicides
 
 Cotton is sensitive to auxin-type herbicides. Off-target damage can lead to delayed harvests, reduced productivity for growers, and bad publicity for the industry. 
 
The extent of damage depends on level and timing of exposure, crop cultivar, and management practices. Management aids are available to help prevent and diagnose off-target herbicide injury to cotton. 
 
   
Preventing Herbicide Injury in Cotton
Herbicide selection- label use directions and precautions, volatility, water solubility, persistence, and efficacy.
Drift prevention- weather, proximity, application timing, nozzle selection, and sprayer set-up.
Sprayer contamination- dedicating a sprayer for pasture-use only
Field selection- risk assessment based on topography, surface water, field history, and future plans for field.
Monitoring results- field number or name, date and rate of application, weather conditions.
 
Diagnosing Herbicide Injury in Cotton
Many herbicides used in pastures and hay fields mimic the plant hormone auxin. When observing herbicide damage in cotton, it is often difficult to distinguish between these herbicides. The symptoms below can help to identify certain characteristics of each of these herbicides in cotton. The following are descriptions of commonly observed symptoms resulting from cotton 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 Cotton
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 Video
Cotton plants were grown in a greenhouse and treated with simulated drift rates for aminocyclopyrachlor (MAT28), 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 SilverlightFive Herbicide Drift
 
Description: At day 1, symptoms of leaves drooping at petioles appeared in 2,4-D and dicamba plants, soon followed by picloram. New leaves were folded at the margins by the fourth day. Growth was stunted and petioles continued to twist and become epinastic by day 7. Aminocyclopyrachlor (MAT28) and aminopyralid plants had new leaves folded at the margins and older leaves drooping slightly at the petioles by day 7. Also at day 7, all plants had well developed blisters on younger leaves. By day 14, picloram, 2,4-D, and dicamba plants had essentially ceased apical growth, while the aminocyclopyrachlor and aminopyralid plants had blistered and chlorotic new growth.
Symptomatic Still Images
aminocyclopyrachlor 
Slight petiole bending, leaf curling
Petiole bending and inital blistering at one week

Severe blistering and curling on youngest leaves at two weeks
aminopyralid 
Initial curling and slight petiole epinasty
Older leaf petioles drooping blisters forming on leaf margins

Severe blistering and main stem twisting
picloram
Leaf curling and petiole twisting
Severe downward bending of petioles and blistering on new leaves

Severe stunting in apical growth
 
2,4-D 
Petiole twisting at three days
Leaf curling, some reddeing on petioles

Severe leaf curling, lobe elongation
 
 
dicamba 
Severe epinasty at three days
Blisters along leaf veins

S-shaped petioles and los of apical growth