Synergistic and antagonistic interactions between biological and DMI fungicides for management of blossom blight and brown rot of nectarine

Peach brown rot and blossom blight are caused by Monilinia fructicola in the southeastern United States. Management is primarily achieved with synthetic fungicides, and little is known about the potential for biologicals to serve as alternatives. Recent studies found that the biorational fungicide Howler EVO (Pseudomonas chlororaphis AFS009) + the demethylation inhibitor (DMI) fungicide propiconazole reduced lesion development synergistically under lab conditions. This study evaluated the field efficacy of Howler EVO and another biological fungicide, Theia (Bacillus subtilis AFS032321), in combination with Propi-Star EC (propiconazole) or Cevya (mefentrifluconazole) to control of blossom blight and brown rot in nectarines over multiple years at the Clemson University Musser Fruit Research Center, Seneca, SC. Results showed that Howler EVO + the half label rate of Propi-Star EC (1/2 Propi-Star EC) synergistically reduced blossom blight incidence. Postharvest brown rot incidence was also reduced by Howler EVO + 1/2 Propi-Star EC. Both Howler EVO + 1/2 Propi-Star EC and Howler EVO + the full rate of Propi-Star EC (Propi-Star EC) revealed synergistic interactions. Theia + the half label rate of Cevya (1/2 Cevya) was as effective as Cevya in postharvest evaluations, with synergism observed in one of the experimental years. A discriminatory dose assay confirmed that the M. fructicola population at the research station was largely sensitive to DMI fungicides. This study illustrates that biologicals have the potential to be integrated into management programs to reduce chemical input in commercial nectarines and peach orchards.