Control of early blight and bacterial spot in tomato by Rosmarinus officinalis extract

ABSTRACT Aiming to develop new measures of plant protection against diseases, the objective of this study was to verify the control of early blight (Alternaria solani) and bacterial spot (Xanthomonas vesicatoria) in tomato plants, as well as the antimicrobial activity against their causal agents, using soluble powder of rosemary (Rosmarinus officinalis). For the stability test, the soluble powder was kept at 40 oC during 0, 60, 120 and 180 days and assayed at five concentrations (0, 50, 100, 150 and 200 mg L-1). When the shelf life and the best concentration were defined, the application intervals of seven, 14 and 21 days were evaluated. As control treatments, the following fungicides were used: Azoxystrobin (200 mg active ingredient – a.i mL-1) for early blight and Copper Oxychloride (400 mg a.i. mL-1) for bacterial spot. There was no in vitro antimicrobial activity of the extract against A. solani and X. vesicatoria. The calculated concentration of rosemary extract that resulted in the least severity of diseases was 130 mg L-1, with 24 months of shelf life of the soluble powder. The extract provided the same control level for early blight and bacterial spot as that of the used fungicides, showing efficiency of up to 75% at a seven-day application interval. These results show the efficiency of rosemary soluble powder in controlling early blight and bacterial spot in tomato plants.