Monilinia vaccinii-corymbosi Apothecial Development Associated With Mulch Depth and Timing of Application

Pseudosclerotia of Monilinia vaccinii-corymbosi overwinter on the soil surface and develop apothecia in early spring, supplying primary inoculum for mummy berry disease of blueberry. Burial of pseudosclerotia in soil and incubation in the dark have previously been identified as critical factors inhibiting M. vaccinii-corymbosi apothecial development. Mulches of Douglas-fir (Pseudotsuga menziesii) sawdust at 2.5 or 5 cm depths, blueberry leaves (Vaccinium corymbosum cv. Bluetta) at a 2.5 cm depth, and a bare ground (no mulch) control were assessed for an effect on apothecial development in the spring for 2 years. Mulches were applied corresponding to pseudosclerotial overwintering stages. Loss of mulch depth was also assessed throughout the overwintering season. A 5 cm depth of Douglas-fir sawdust was associated with greater apothecial suppression in comparison with bare ground. Douglas-fir sawdust at a 2.5 cm depth varied in effectiveness, while 2.5 cm of blueberry leaves was not more effective at suppressing apothecial development than the bare ground treatment. Application timing did not affect apothecial development, but mulches lost significantly more depth when applied at the beginning of the overwintering season as compared with late winter mulches. Therefore, loss of mulch thickness due to weathering and/or decomposition may also affect apothecial development.