The objective of this work was to evaluate the effect of cover crops and fallow duration on the onion crop planted in direct sowing in trials carried out for three years. In the year 2013, two field trials were carried out in two sites. Two cover crops (oats and millet) and one uncovered control were evaluated at three planting dates. The studied variables were crop establishment and dry matter of the cover. In the field trials performed in 2014 and 2015 the effect of the length of the chemical fallow of oats on the establishment of onion was evaluated. The effect of the duration of the chemical fallow of oats was also evaluated in laboratory in 2015 in Petri dishes. In 2013, the greatest establishment was obtained in the treatments without cover in both sites. In 2014 the greater the duration was of the chemical fallow of the cover, the greater the onion establishment. In the field trial in 2015, no effects of fallow duration on crop establishment were observed, a result attributable to the intense rainfall recorded. In the laboratory, germination was higher in treatments with longer fallow periods. Based on the results, evidence was obtained of the negative effect of the cover crops in the establishment of the onion crop. These effects were inversely related to the duration of chemical fallow and may be attributable to allelopathic effects.
Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs, is a serious constraint on wheat yields in the Southern Cone region of South America. A 2-year experiment was conducted to evaluate fungicide deposition, disease development and grain yield. Three spray nozzles were evaluated: an air-induction flat fan (AI), a wide-angle flat fan (TT), and an extended-range flat fan (XR). A systemic fungicide containing azoxystrobin and cyproconazole was used in both years. Tan spot severity and the area under non-green leaf area disease progress curve (AUNGLA) were analysed. There were no significant differences in deposition among nozzles, and no significant interactions between nozzles and leaf layers in the first year. In both years, AUNGLAs were similar for the three nozzles types, and the tan spot severity in untreated plots was significantly higher than in fungicide-applied plots. Grain yield was higher in the fungicide-applied plots, and there were no significant differences among nozzles in both years. Droplet size had no effect on the fungicide’s efficacy for tan spot control in Uruguay across three susceptible wheat cultivars. The use of drift-reducing nozzles and a systemic fungicide in these trials led to satisfactory performance for spray deposition, canopy penetration and control of the tan spot disease of wheat in the same way as expected from conventional nozzles.
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