Dynamics of seedling emergence and control of Urochloa panicoides P. Beauv resistant to glyphosate in Tucumán (Argentina)

Abstract

Urochloa panidoides P. Beauv is a problematic weed in the Argentine Northwest and glyphosate resistant biotypes have been detected. This study characterized the dynamics of emergency in relation to environmental conditions and evaluated alternatives of chemical control on populations resistant to glyphosate. For two consecutive growing seasons 2015-2016 and 2016-2017, in crop areas, two studies were conducted. In the first study, every 15 days destructive seedling counts were carried out in six plots of 1m2. Temperature and rainfall were recorded. With the temperature, the calculation of the accumulated degree days (GDDA) was carried out. In the second study, in a randomized block 
experimental design, the efficacy of six pre-emergent residual herbicide treatments was visually evaluated at 30, 45 and 60 days after application (DDA). In both campaigns, the emergence dynamics of seeds that broke dormancy adjusted to the temperature, however, rainfall played a crucial role in triggering the germination process. This is evidenced by observing that in Tucumán, U. panicoides emerges from the spring rains. Regarding pre-emergent residual herbicide treatments, Imazethapyr, sulfometuron + chlorimuron and clomazone had a control efficiency greater than 80% up to 60 DAA. S-metolachlor and diclosulam showed acceptable controls (above 88%) up to 30 DAA and after 45 DAA, 
and after 45 ADD, their controls were unsatisfactory. It is concluded that the herbicides Imazetapir, sulfometuron + chlorimuron (inhibitors of the enzyme acetolactate synthetase) and clomazone (inhibitor of dioxy-D-xylulose phosphate synthase) are useful residual chemical alternatives for the management of U. panicoides in previous fallows for soybean and corn crops.