Pablo Calviño

Use of non-selective herbicides for wheat physiological and harvest maturity acceleration

Abstract Double cropping of wheat (Triticum aestivum L.) and soybean (Glycine max (L.) Merr.) in the southeast of Buenos Aires Province, Argentina, is risky because of the short frost-free period after wheat harvest and the probability of water deficits during the soybean cropping period. Soybean yield declines rapidly with delays in the sowing date. The objective of this work is to evaluate the potential to anticipate wheat harvest through the application of non-selective herbicides prior to physiological maturity. Two experiments were carried out in Tandil during the 1997 (wet year) and 1998 (dry year) growing seasons. Treatments consisted of herbicide (Glyphosate and Paraquat) applications to two wheat cultivars at different moments prior to physiological maturity. Herbicide applications produced greater grain moisture decreases than in the checks. The contact product exhibited greater drying rates than the systemic one in the water-deficient year. No differences in herbicide effect were observed between cultivars. Grains continued to accumulate dry weight after herbicide applications. In 1997, herbicide applications with grain moisture of 45% produced grain weight decreases close to 9% and a 7 days anticipation in harvest time. In the same year, herbicide applications with grain moisture of 40% decreased grain weight non-significantly and anticipation in harvest time was close to 5 days. In 1998, applications with both 40 and 45% grain moisture, did not significantly decrease grain weight and the anticipation in harvest time was close to 3 days. Considering both years and cultivars, harvest anticipation and grain dry weight decreases due to herbicide applications were better associated with the current rates of grain filling (r=0.87 and 0.76 for harvest anticipation and grain dry weight decrease, respectively, on the basis of chronological time, and r=0.85 and 0.79, respectively, on the basis of thermal time) than with grain moisture during that time.