Tank Mixing Fungicides for Effectiveness Against Eastern Filbert Blight of Hazelnut.

Hazelnut (Corylus avellana) production in Oregon primarily occurs on cultivars susceptible to Anisogramma anomala, the causal agent of eastern filbert blight (EFB). Management of EFB involves planting resistant cultivars, removal of cankered limbs, and the application of fungicides. Tank mixes of demethylation-inhibiting (DMI; Fungicide Resistance Action Committee [FRAC] group 3) or quinone outside inhibitor (QoI; FRAC group 11) fungicides with chlorothalonil (FRAC group M5) at full or reduced rates were evaluated for effectiveness against A. anomala. The use of chlorothalonil in a mix with a DMI or QoI fungicide was an effective treatment for EFB even if each component of the mix was at half the labeled rate. Different liquid or dry formulations of chlorothalonil were equally effective in a tank mix for EFB control. The combination of propiconazole (FRAC group 3) tank mixed with trifloxystrobin (FRAC group 11) was not effective, whereas trees treated with propiconazole tank mixed with pyraclostrobin (FRAC group 11) resulted in significantly fewer EFB cankers compared with nontreated trees. When using tank mixes for EFB management, DMI fungicides should remain at full rates while mixing with a half-rate of chlorothalonil. In contrast, QoI fungicides and chlorothalonil could both be used at half-rates and still maintain acceptable EFB control. Tank mixing chlorothalonil with fungicides at risk of resistance development can help maintain consistent EFB control and should help prevent or delay the emergence of fungicide-resistant A. anomala isolates.