Efecto de la dureza del agua y del sulfato de amonio sobre la eficacia de herbicidas de barbecho químico en Carduus acanthoides y Conyza bonariensis

A study was conducted to evaluate the efficacy of different herbicides with two water qualities, with and without addition of amonium sulfate in C. acanthoides and C. bonariensis in a fallow plot near to soybean planting. A randomized block design with 3 replicates was used. Treatment efficacy was evaluated visually as percentage of control relative to the weedy check, 30 days after application.Analysis of variance procedures were conducted on data and means were separated using LSD test at the 0.05 significance level. In both species, control of the majority of the treatments was lower in 2008 than in 2009. In 2008 control was lower with hard than with soft water for both weed species. Efficacy increased with hard water by the addition of ammonium sulfate with glyphosate alone and in some mixtures with glyphosate. Glyphosate in mixture with clopyralid showed the highest control of both weeds. In 2009 all treatments provided adequate control indicating that adding herbicides or ammonium sulfate was not necessary. It is concluded that adding glyphosate to clopyralid, 2,4-D or ammonium suphate may be usefull tools to control C. acanthoides and C. bonariensis in unfavorable conditions such as the presence of hard water or low precipitations.