Physiological effects of temperature on turfgrass injury to amicarbazone.  J. Yu and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Amicarbazone effectively controls annual bluegrass (Poa annua L.) in cool-season grasses with spring applications but summer applications are too injurious for selective control.  Experiments were conducted to evaluate uptake, translocation, and metabolism of ¹⁴C-amicarbzone in hybrid bermudagrass (Cynodon dactylon x C. transvaalensis), tall fescue (Festuca arundinacea), and annual bluegrass.  Grasses were grown in growth chambers set for 25/20 C (day/night) or 40/35 C.  At the cool temperature, annual bluegrass absorbed more foliar applied amicarbazone than tall fescue and bermudagrass after 72 hours.  Foliar absorption increased at 40/35 in all species, compared to 25/20, and tall fescue had similar absorption to annual bluegrass at the high temperature.  Bermudagrass had less foliar absorption than annual bluegrass at both temperatures and less absorption than tall fescue at the high temperature only.  Annual bluegrass and tall fescue had approximately twofold greater root absorption of ¹⁴C-amicarbazone than bermudagrass after 72 hours. Annual bluegrass had less metabolism of amicarbazone than tall fescue at 25/20 but both species recovered similar levels of parent herbicide at the high temperature. Bermudagrass had more metabolism of amicarbazone than annual bluegrass and tall fescue at the high temperature but metabolism was similar to annual bluegrass at the low temperature.  Results suggest bermudagrass tolerance to amicarbazone is attributed to less absorption than cool-season grasses while increased sensitivity of tall fescue to amicarbazone at high temperatures results from greater foliar and root absorption.