|BUOL, JOHN - Mississippi State University|
|REYNOLDS, DANIEL - Mississippi State University|
|DODDS, DARRIN - Mississippi State University|
|MILLS, J - Monsanto Corporation|
|NICHOLS, ROBERT - Cotton, Inc|
|BOND, JASON - Mississippi State University|
|DUBIEN, JANICE - Mississippi State University|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2018
Publication Date: N/A
Interpretive Summary: The introduction of auxin herbicides weed control systems has led to increased occurrence of crop injury in susceptible soybeans and cotton. Off-target exposure to sub-lethal concentrations of dicamba can occur at varying growth stages, which may affect crop response. Field experiments were conducted for three years in Mississippi to characterize cotton response to a sub-lethal concentration of dicamba equivalent to 1/16 of the labeled rate. Weekly applications of dicamba at this rate were made to separate plots from one week after emergence to 14 weeks after emergence. Visual injury, crop maturity, shifts in where bolls were set on plants, and fiber quality were determined and varied according to when the exposure occurred. Exposure from one to nine weeks after emergence resulted in 32% visual injury and exposure from seven to ten weeks after emergence delayed crop maturity. Exposure from eight to ten weeks after emergence led to increased cotton height, and exposure at seven weeks after emergence reduced yield by 18%. Where the bolls were produce on the plant varied depending upon when the exposure happened, and this affected crop maturity. Minimal effects on fiber quality occurred, except fiber-length-uniformity was reduced when plants were exposed at nine or ten weeks after emergence. Thus, the effects on visible injury, boll distribution, crop maturity, yield, and fiber quality, presents a complex picture of effects from a very low rate off-target exposure of cotton to dicamba. These damages varied depending when the exposure occurred.
Technical Abstract: The introduction of auxin herbicide weed control systems has led to increased occurrence of crop injury in susceptible soybeans and cotton. Off-target exposure to sub-lethal concentrations of dicamba can occur at varying growth stages, which may affect crop response. Field experiments were conducted in Mississippi in 2014, 2015, and 2016 to characterize cotton response to a sub-lethal concentration of dicamba equivalent to 1/16x the labeled rate. Weekly applications of 35 g ae ha-1 dicamba were made to separate sets of replicated plots immediately following planting until 14 w after emergence (WAE). Exposure to dicamba from one to nine WAE resulted in up to 32% visible injury and exposure from seven to ten WAE led to increased cotton ht while a reduction in total yield resulted from exposure at seven WAE (18%). Cotton exposure from three to eight WAE reduced the yield partitioned to position one fruiting sites, while exposure at three to six WAE also reduced yield in position two fruiting sites. Exposure at two and three WAE increased vegetative branches and exposure at three to seven WAE increased yield partitioned to plants with aborted terminals. However, increased yield partitioned to plants with aborted terminals corresponded with reciprocal decreases in yield partitioned to older fruiting structures. Minimal effects were observed on fiber quality, except for decreases in fiber length uniformity resulting from exposure at nine and ten WAE.