Ecology and herbicidal control of selected perennial range weeds of South Texas

Abstract

Three species of perennial range weeds, common goldenweed (Isocoma coronopifolia (Gray) Greene), Drummond's goldenweed (Isocoma Drummondii (T.&G.) Greene), and spiny aster (Aster spinosus Benth.) were studied relative to ecological adaptation and factors influencing their control with herbicides. Germination of Drummond's goldenweed achenes occurred at continuous temperatures from 5 to 35C, with optimum germination at 20 and 25C. Both germination and seedling vigor were relatively tolerant of extremes of pH, but germination was reduced when achenes were exposed to NaCl concentrations in excess of 1000 ppm. Germination and seedling vigor of common and Drummond's goldenweed were sensitive to simulated moisture stress of -6 to -8 bars. Seed viability remained high for only 6 months. In the field, vegetative growth of established Drummond's goldenweed occurred from February until flowering in November. Elongation rates of individual stems of young weeds growing on a site with deep, productive soil varied directly with extractable soil water. Growth rates of young plants on sites characterized by poor drainage, high salinity, and low soil fertility were suppressed and not highly correlated with soil moisture. Over the entire growing season, mean stem elongation rates of young Drummond's goldenweed averaged 0.49 mm/day, while stem elongation rates of mature weeds averaged 0.77 mm/day..