Efficacy of Commercial Biocontrol Products and Fungicides Against Verticillium dahliae Isolates from Michigan Potato Fields

Potato is a key commodity in Michigan, but profitability is hindered by Verticillium wilt caused by Verticillium dahliae. Although pre-plant fumigation with metam-sodium is effective, environmental concerns may limit its use, necessitating alternative methods such as biological control agents (BCAs). Few BCAs are registered in the United States for controlling Verticillium wilt in potatoes, and their effectiveness against Michigan isolates lacks peer-reviewed evidence. This study involved two sets of experiments. In the first set of experiments, pure cultures of each BCA were tested for direct antagonism against Michigan V. dahliae isolates in vitro. In the second, the most effective BCAs were evaluated in their commercial formulation to validate disease suppression efficacy in planta under greenhouse conditions. Our in vitro growth inhibition experiment showed that Trichoderma asperellum and T. gamsii (Tenet) and Streptomyces lydicus (Actinovate) showed over 60% antagonism against V. dahliae isolates. In greenhouse trials with potato cultivar Russet Norkotah, Actinovate reduced disease caused by V. dahliae isolate 1 by 68% and by V. dahliae isolate 2 by 33%, compared with the inoculated/nontreated control. In conclusion, this study provides the first comprehensive evaluation of commercial BCA products and the fungicides Elatus and Quadris against V. dahliae isolates from Michigan. Our findings highlight the potential of S. lydicus as an effective post-planting treatment and demonstrate that BCA efficacy is influenced by the V. dahliae isolate. Integrated pest management strategies that incorporate BCAs, targeted fungicide use, and cultural practices could enhance Verticillium wilt management in potato production.