In Mexico, the production of barley (Hordeum vulgare L.) is affected by various diseases including leaf rust (LR) caused by Puccinia hordei Otth. In the spring-summer/2018 cycle, under rainfed conditions and natural incidence of HR, a factorial test was established under a randomized complete block design, in the municipalities of Texcoco and Temascalapa, State of Mexico and Tlaxco, Tlaxcala, to evaluate the effect of two fungicides (Azoxistrobin 11.1% + Tebuconazole 18.4% and Tebuconazole 25%) on the LR control in six varieties of barley. The variables measured were day to heading and maturity (DE, DM), Plant height (PH), Test weight (TW), grain yield (Yield) and final severity of the disease (FDS). Highly significant differences were found for TW, Yield and FDS for varieties, fungicides and localities (Tukey, p≤ 0.05). The most effective fungicide was Azoxistrobin 11.1% + Tebuconazole 18.4% taking FDS of 2% and yield (REND) of 2,757.2 kg ha-1 compared to the non-fungicide check which had 23% FDS and yield of 2,262.7 kg ha-1. The variety with the greatest resistance was ABI Voyager (10MS) and the most susceptible, Doña Josefa (40S). Disease control influenced performance, there were losses of 31% in Apizaco; 20% in Esmeralda; 19% for Doña Josefa and ABI Voyager; Maravilla with 16% and AC Metcalfe 9%. Resistance levels observed together with the use of fungicides will allow a comprehensive control of the disease.

Foliar diseases affecting rainfed barley in Mexico are mainly net blotch, spot blotch and leaf scald, which demerit the physical quality of grains. Current varieties are not resistant; thus, chemical control is an option to complement genetic control. This study aimed to determine the biological effectivity of fungicides to control foliar diseases and their effect on grain yield. The locations and crop seasons to conduct the study were in Tlaxcala and Puebla in 2019, respectively. The experimental design was a randomized complete block design in a split-plot arrangement with four reps. The main plot consisted of two varieties (Esmeralda and Doña Josefa), while sub-plots were two fungicides (Azoxistrobin 7.07 % plus Propiconazole 11.79 % and Propiconazole 25.64 %). Field measurements included days to heading and maturity, grain yield, test weight, and final disease severity (a visual score for disease control). The analysis of variance indicated significant differences (p≤0.01) between varieties, grain yield, and final disease severity. Disease control was more effective due to Azoxistrobin 7.07 % plus Propiconazole 11.79 %. Grain yield was more significant with fungicide application, overall Doña Josefa with Propiconazole 25.64 % (5972.38 kg ha-1). Field observations indicated that the application of Azoxistrobin lengthens the cropping season delaying the senescence (stay-green). Results suggested that chemical control of foliar diseases in barley is a suitable option.