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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #310182
Title: Adsorption, desorption, and degradation of fomesafen in soil

Author
item LI, XIAO - University Of Georgia
item GREY, TIMOTHY - University Of Georgia
item PRICE, KATILYN - Auburn University
item VENCILL, WILLIAM - University Of Georgia
item Webster, Theodore

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Glyphosate resistant (GR) and acetolactate synthase (ALS) inhibitor resistant Palmer amaranth in the southeast USA have increased the use of herbicides with soil activity for weed control in cotton production. These soil-active herbicides are considered crucial components in cotton weed control programs due to the lack of effective topical herbicide against resistant weeds. Fomesafen is a residual herbicide that provides excellent control of GR and ALS inhibitor resistant Palmer amaranth in cotton. It is registered in cotton and soybean at rates of 280 to 420 g/ha and belongs to the diphenylether herbicide family; the mechanism of action of this family is inhibition of protoporphyrinogen oxidase (PPO), which causes failure in chlorophyll production and accumulation of radical oxygen species in plant cells. Fomesafen application in cotton production areas has increased significantly in the past several years because of the rapid expansion of resistant Palmer amaranth. Total usage of fomesafen in all cotton producing states increased by 4.92-fold from 2007 to 2010, and applied on 221,000 ha in 2010. Despite large increase in usage, fomesafen may possess greater mobility and bioavailability to crops if applied to soils with high sand fraction, high pH and low OM. In this scenario, fomesafen concentration in soil solution is high due to less adsorption. And the possibility of crop injury by fomesafen during seed germination is greater as compared to in soils with low pH, high OM and high clay content. Growers need to be cautious about crop injury in soils that show less adsorption to fomesafen, especially when fomesafen is applied PRE. Biological degradation was not the major pathway of fomesafen dissipation in two GA soils investigated under aerobic condition. This suggests other processes, such as photolysis, irreversible binding, lateral and vertical movement, could be more important during fomesafen dissipation from surface soil. Fomesafen residue persisted over 120 d in Cecil sandy loam but was not detectable in Tifton loamy sand 28 DAT. Higher fomesafen adsorption to Cecil sandy loam may account for the greater DT50 and longer retention in this soil as compared to the Tifton loamy sand. Based on the results of these research data, it is likely that long fomesafen persistence and greater possibility of carryover injury to sensitive crops may occur in soils showing high affinity to fomesafen, particularly when environmental conditions are dry and not favorable for this herbicide to move out of the surface soil.

Technical Abstract: Fomesafen provides excellent control of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in cotton, but limited information is available regarding its soil behavior and degradation. Freundlich distribution coefficient (Kf) for fomesafen on seven soils varied from 1.3 to 9.3. Four soils had a desorption rate of 11 to 29%, while others showed greater desorption rates of 26 to 81%. There was a positive correlation between soil clay content and Kf, as compared to soil pH, which was negatively correlated to Kf. Soil pH and sand content were positively correlated to fomesafen desorption. Soil organic matter (OM), and both clay and silt contents were inversely correlated to fomesafen desorption. Soil pH had the largest impact on Kf, while OM content had the greatest effect on fomesafen desorption. Cecil sandy loam and Tifton loamy sand treated with fomesafen was incubated aerobically under 20 C and ambient soil moisture for 90 d. No significant reduction in fomesafen concentration was observed during the experiment. Fomesafen adsorption and desorption were affected by multiple soil properties, such as pH, silt, clay, and OM. Fomesafen was not susceptible to biological degradation in soils under aerobic conditions.