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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #324844
Title: Impact of irrigation rate on pre-emergence herbicide activity

Author
item SMITH, HUNTER - UNIVERSITY OF FLORIDA
item FERRELL, JASON - UNIVERSITY OF FLORIDA
item WEBSTER, THEODORE
item FERNANDEZ, JOSE - UNIVERSITY OF FLORIDA
item DITTMAR, PETER - UNIVERSITY OF FLORIDA
item MUNOZ, PATRICO - UNIVERSITY OF FLORIDA

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2016
Publication Date: 7/1/2016
Citation: Smith, H.C., Ferrell, J.A., Webster, T.M., Fernandez, J.V., Dittmar, P., Munoz, P. 2016. Impact of irrigation rate on pre-emergence herbicide activity. Weed Technology. 30:793-800.

Interpretive Summary: Cotton producers rely on irrigation to incorporate residual herbicides, however the necessary rate of irrigation can vary depending on herbicide chemistry and soil type. In sandy soils, there is often little organic matter to influence the mobility and dissipation of preemergence herbicides, so herbicide movement is more predictable. Herbicide solubility becomes the critical factor for determining the optimal irrigation rate for soil incorporation in sandy soils. Moderately soluble herbicides like s-metolachlor and acetochlor have soil movement that is highly correlated to irrigation rate. Herbicidal efficacy of s-metolachlor was highest in plots receiving 6.4 or 12.7 mm of irrigation and no significant differences were detected between these incorporation rates in any data collected. Significant differences in irrigation rate were apparent for incorporation of acetochlor but there were no differences between the 3.2-12.7 mm irrigation rates. Rainfall and additional irrigation 7 days after treatment (DAT) facilitated the slow release of acetochlor and prevented new Palmer amaranth from emerging. Insufficient incorporation of acetochlor at the 0-1.6 mm irrigation rates, allowed for the emergence of Palmer amaranth 7 DAT and plants were still present at harvest (35 DAT). Across all herbicides and irrigation rates, fomesafen treated plots provided the most consistent control of Palmer amaranth. Fomesafen plots that did not receive incorporating irrigation allowed for the emergence of Palmer amaranth 7 DAT, but many of these plants were controlled later with additional irrigation or rainfall. There appeared to be no adverse effects on weed control for leaving fomesafen on the soil surface for 7 days before incorporating it into the soil. Dicamba provided the least and most inconsistent control of Palmer amaranth compared to all other preemergence herbicides tested. The high solubility and rapid mobility allow inconsistent activity and reinforce the fact that dicamba should likely be used in tandem with other soil active herbicides for optimum Palmer amaranth control.

Technical Abstract: The importance of preemergence herbicide applications in cotton has increased since the development of glyphosate-resistant Palmer amaranth (Amaranthus palmeri). Cotton producers are relying on residual herbicides for control of Palmer amaranth, as postemergence options are limited or ineffective. S-metolachlor, acetochlor, fomesafen, and dicamba all provide preemergence activity on Palmer amaranth, but little is known about the effect of irrigation rate on incorporation and herbicidal efficacy. In 2015, an experiment was conducted on fine sand and loamy sand soils to evaluate the influence of irrigation rate on preemergence herbicide control of Palmer amaranth. Irrigation rate was significant for the incorporation of both s-metolachlor and acetochlor. Herbicidal efficacy of s-metolachlor was greatest in plots receiving 6.4 and 12.7 mm of irrigation where Palmer amaranth biomass was reduced to 4.0 and 2.1% of non-treated control (NTC), respectively, compared to 61.3% in plots that did not receive incorporating irrigation. Acetochlor incorporated at 3.2-12.7 mm irrigation rates were not significantly different but did significantly reduce Palmer amaranth biomass compared to the 1.6 mm irrigation rate. Irrigation rate was not significant for the incorporation of fomesafen or dicamba. Across all herbicides, fomesafen treated plots provided the most consistent control of Palmer amaranth. Fomesafen reduced Palmer amaranth biomass to < 2.5% of NTC at all irrigation rates. Dicamba provided the least and most inconsistent control of Palmer amaranth producing 16.6-51.4% of NTC biomass.