Evaluation of thiophanate-methyl in controlling Verticillium wilt of potato and artichoke

Verticillium dahliae is a soil-borne vascular pathogen difficult to control, especially after the phasing out of several fumigants. Where resistant varieties are not available, Verticillium wilt (VW) is controlled through an integrated approach. Chemical control has been extensively studied, but often does not provide a satisfactory protection level. Recently, thiophanate-methyl (TM), the sole benzimidazole currently on the market, has been registered for the use in soil applications. We evaluated the efficacy of TM against V. dahliae in in vitro, greenhouse and field experiments. We confirmed that TM is one of the most effective fungicides against V. dahliae in in vitro tests (EC50 = 0.006 ?g mL-1). In a greenhouse experiment, soil drenching with TM (0.073 or 0.146 mL plant-1, corresponding to 0.65 or 1.3 L ha-1) reduced the incidence of VW of artichoke, but not the symptoms severity or vascular browning. In pot-grown potato, TM (at 5.6 or 11.2 mg plant-1) completely suppressed the disease and promoted plant growth. In one field trial, a high dose of TM (2.1 L ha-1) only delayed VW progress, but did not affect yield losses. In a second field trial, with a more severe V. dahliae attack, no significant disease control was observed following TM applications, neither by foliar spray nor by chemigation. We concluded that TM is effective against V. dahliae, but it can provide only a partial VW control when the disease pressure is not too high. However, the results obtained in the field trial emphasize the need for further trials under different levels of inoculum pressure and with different application protocols.