Benzothiadiazole induces resistance to Plasmopara helianthi in sunflower plants

A novel synthetic chemical CGA 245704 (benzo (1,2,3) thiadiazole-7-carbothioic acid S methyl ester (aci-benzolar-S-methyl) (BTH) applied as a soil drench and foliar spray was shown to provide good protection against Plasmopara helianthi in sunflower plants. Soil drenches at the rates of 150 and 200 mg/Kg soil, were applied 3 days before the inoculation and induced high levels of protection (80-82%) against downy mildew. At the highest concentration (up to 300 mg/Kg soil) about 90% protection was observed but at these rates phytotoxic symptoms were notd. This compound also provided good protection against P.helianthi when applied 1 day post-inoculation. The chemical had no antifungal activity in vitro against P.helianthi. In addition the combination of CGA 245704 and metalaxyl, as a seed dressing at low rates, provided a high level of control against the disease; however, the activity of this combination was not significantly different from metalaxyl alone. CGA 245704 applied as a soil drench and foliar spray also protected sunflower plants from P.helianthi foliar infection