Physiological Bases of Sugarbeet (Beta vulgaris) Tolerance to Foliar Application of Ethofumesate

Abstract

Absorption, translocation, and metabolism of foliar-applied ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulphonate] were studied to explain field observations showing differences in susceptibility among sugarbeet (Beta vulgarisL.), common ragweed (Ambrosia artemisiifoliaL.), redroot pigweed (Amaranthus retroflexusL.), and common lambsquarters (Chenopodium albumL.). In laboratory studies, two- to four-leaf seedlings of the highly susceptible species, redroot pigweed and common lambsquarter, absorbed greater amounts of14C-ethofumesate from foliar application than the moderately susceptible common ragweed and tolerant sugarbeet. Sugarbeet translocated very little14C from treated foliage to untreated plant tissue. All weed species translocated14C-ethofumesate to untreated leaf tissue when14C-ethofumesate was applied to seedlings at the two-leaf stage. Ethofumesate was translocated basipetally to the stem and root of two-leaf redroot pigweed and common lambsquarter seedlings. A high percentage of the14C was found in the water-soluble fraction in sugarbeet seedlings, indicating inactivation. The amount of metabolites recovered in the non-polar fraction depended on the stage of plant growth. Total photosynthesis and respiration in redroot pigweed was inhibited 4 h after foliar application and did not recover after 96 h. Uptake and evolution of CO2were also inhibited in sugarbeet leaves, but they recovered rapidly, depending on age of plant at treatment. The stage of plant development was the key factor determining species response to foliar treatments of ethofumesate in terms of absorption, metabolism, and total photosynthesis and respiration.