Cotton stage of growth determines sensitivityto 2,4-D

Authors: BYRD, SETH - University Of Georgia; COLLINS, GUY - North Carolina State University; CULPEPPER, A - University Of Georgia; DODDS, DARRIN - Mississippi State University; EDMISTEN, KEITH - North Carolina State University; WRIGHT, DAVID - University Of Florida; MORGAN, GAYLON - Texas A&M University; BAUMANN, PAUL - Texas A&M University; DOTRAY, PETER - Texas Tech University; MANUCHEHRI, MISA - Texas Tech University; JONES, ANDREA - University Of Missouri; GREY, TIMOTHY - University Of Georgia; Webster, Theodore; DAVIS, JERRY - University Of Georgia; WHITAKER, JARED - University Of Georgia; ROBERTS, PHILLIP - University Of Georgia; SNIDER, JOHN - University Of Georgia; PORTER, WESLEY - University Of Georgia

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2016
Publication Date: 4/1/2016
Citation: Byrd, S.A., Collins, G.D., Culpepper, A.S., Dodds, D.M., Edmisten, K.L., Wright, D.L., Morgan, G.D., Baumann, P.A., Dotray, P.A., Manuchehri, M.R., Jones, A., Grey, T.L., Webster, T.M., Davis, J.W., Whitaker, J.R., Roberts, P.M., Snider, J.L., Porter, W.M. 2016. Cotton stage of growth determines sensitivityto 2,4-D . Weed Technology. 30:601-610.

Interpretive Summary: The level of visual cotton injury, plant maturity effect, boll abortion, and yield loss from potential 2,4-D drift, volatility and drift, or tank contaminations will be influenced by 2,4-D rate, stage of cotton maturity, and environmental conditions that occur after the incident. Crop injury, primarily epinasty, is far more pronounced when cotton is damaged by 2,4-D in a vegetative stage of growth and lessens as the cotton becomes more mature. Often with visual epinasty, the peak level of injury for vegetatively growing plants does not appear until 4 to 5 wk after exposure. In contrast, more mature cotton containing a significant boll set will display minimal epinasty, with maximum levels of injury often observed by 1 wk after application. Importantly, yield loss does not correlate with visual estimates of cotton injury, but rather with boll population and retention on the plant, reflected in plant mapping data. Drift or contamination occurring between 9-lf and FB+2 wk has the greatest likelihood to reduce the number of fruit per plant, which correlates with greatest potential for yield loss. Injury from 2,4-D nearly always influences plant maturity, but a delay in maturity does not always result in yield loss; rather the environment, cultivar, and harvest procedures late in the season can often overcome this effect. The results from this study do contrast some of the previous literature. For example, yield loss was reported to be most severe when drift injury occurred during early growth stages, particularly those prior to bloom. In a meta-analysis incorporating 20 studies on the yield effect from 2,4-D drift in cotton concluded that yield losses are most severe during the vegetative and squaring stages, while the detrimental effect on yield lessens when cotton is exposed during the later flowering and boll stages. It is unclear why conflicting differences exist in regards to stage of growth sensitivity when comparing results from this research to the literature. However, it is apparent that more work needs to be done in developing a method for evaluating 2,4-D injury on cotton during later, reproductive growth stages and predicting the corresponding effect on yield. Furthermore, the influence of cultivar maturity on the response to sub-lethal rates of 2,4-D should also be evaluated. A full season cultivar with fairly vigorous vegetative growth was utilized in the current study, while an earlier maturing cultivar may respond differently in regards to the effect on reproductive development and yield.

Technical Abstract: The impending release of EnlistTM cotton and soybean cultivars likely will increase the use of 2,4-D, which has raised concerns over potential injury to susceptible cotton. An experiment was conducted at 12 locations across the cotton belt during 2013 and 2014 to determine the impact of a simulated 2,4-D drift application (2 g ae ha-1) or tank contamination application (40 g ae ha-1) on cotton during six different growth stages. Cotton growth stages at the drift or tank contamination application included 4 leaf (4-lf), 9 leaf (9 lf), first bloom (FB), FB+2wk, FB+4wk, and FB+6wk. Epinasty from 2,4-D was far more pronounced with applications during vegetative growth stages; injury exceeded 50% at 7 of the 8 locations where visual injury was evaluated when either rate of 2,4-D was applied to 4- or 9-lf cotton. As cotton matured beyond the FB+2wk stage, plant vegetative injury from the drift application was less than 10% at 7 of 8 locations; for the contamination rate, injury was less than 25% at 7 of 8 locations. The maximum level of epinasty from vegetatively treated plants occurred 4 to 5 wk after application while the mature cotton displayed maximum epinasty within a week. Importantly, yield loss did not correlate with visual symptomology, but rather more closely followed effects on cotton boll set. The contamination rate of 2,4-D applied to 9-lf, FB, or FB+2wk cotton had the greatest effect across locations reducing the number of bolls per plant when compared to the control. This was likely a response to cavitation of bolls noted with these treatments. The contamination rate of 2,4-D applied at FB+4 wk or later did not influence the number of bolls per plant and only at 4 locations did the application reduce the number of bolls per plant when applied at the 4-lf stage. A reduction of boll number per plant was not detectable with the drift rate of 2,4-D except at 4 locations when applied only at the FB stage of growth. Similar to boll set, yield was influenced by 2,4-D rate and stage of cotton growth. Loss in yield of greater than 20% occurred at 5 of 12 locations when the drift rate was applied between 4-lf and FB+2wk (highest impact at FB). For the contamination rate, yield loss was observed at all 12 locations; averaged over these locations yield was 45, 58, 66, 45, 16, and 7% below that noted in the control when applied at 4-lf, 9-lf, FB, FB+2 wk, FB+4 wk, and FB+6 wk, respectively. Results suggest the greatest yield impact from 2,4-D would occur between 9-lf and FB+2wk and the level of impact will be influenced by 2,4-D rate and environmental conditions post application as they influence the progress toward boll development and plant recovery.