Field Efficacy of Two Benzothiadiazole-Based Systemic Acquired Resistance Inducers in Spring Barley

Foliar diseases reduce barley productivity and may impair physical grain quality, while repeated activation of plant defense can impose metabolic costs. This two-year field study evaluated whether two previously characterized benzothiadiazole-based systemic acquired resistance (SAR) inducers—N-methoxy-N-methylbenzo[1,2,3]thiadiazole-7-carboxamide (BTHWA) and didecyldimethylammonium benzo[1,2,3]thiadiazole-7-carboxylate ([N111010][BTHCOO])—could suppress foliar diseases without compromising crop yield. Each year, the experiment was established as a randomized complete block design with four blocks, with all six treatments represented once per block. Both compounds were applied six times at 5 or 10 g a.i. ha−1 per application; an untreated control and a two-application fungicide program served as references. Disease severity was assessed at BBCH 59 and 77, while grain yield, thousand-grain weight, hectolitre weight, and moisture were determined at harvest. Both compounds reduced disease severity relative to the untreated control, although statistical significance depended on compound, application rate, pathogen, and assessment date. The 10 g a.i. ha−1 treatments generally provided stronger disease suppression than the corresponding 5 g a.i. ha−1 treatment of the same compound and resulted in significantly higher grain yield than the untreated control and the corresponding lower-dose treatments. The fungicide program generally provided the strongest disease control and highest yield. Neither compound adversely affected thousand-grain weight or hectolitre weight. These findings support development of benzothiadiazole-based SAR inducers in integrated barley protection, with optimization focused on application timing, frequency, and reduced-fungicide programs.