Mulching to Manage Mummy Berry of Blueberry

Graduation date: 2016Monilinia vaccinii-corymbosi pseudosclerotia overwinter on the soil surface and produce apothecia in early spring, providing primary inoculum for Mummy Berry Disease of blueberry. Burial under 2.5 cm of soil or the absence of light have previously been identified as critical factors preventing the development of apothecia. Mulches were applied to overwintering pseudosclerotia at different developmental stages in outdoor conditions over a two-year period. Douglas-fir (Pseudotsuga menziesii) sawdust applied at depths of 2.5 or 5 cm, blueberry leaves cv. 'Bluetta' at a depth of 2.5 cm, and a bare ground (or no mulch) control, in combination with application timing, were assessed for their effect on apothecial development. Application timings corresponding to visible stages of pseudosclerotial overwintering development included maturation, dormancy, germination/emergence, and differentiation. Mulches were tested at the OSU Botany and Plant Pathology Field Lab, Corvallis, OR and at two collaborator field sites in the Willamette Valley. Mulch depth loss was also assessed at the end of the overwintering period.\ud A mulch depth of 5 cm of Douglas-fir sawdust was associated with more instances of complete apothecial suppression than the bare ground treatment. Mulch application timing did not have an effect on apothecial development. A significant change in Douglas-fir sawdust mulch depth was observed when applied in October as compared to a February application. Therefore, it is recommended that mulches be applied in late winter to decrease mulch depth loss due to decomposition and/or weathering.\ud In the laboratory, apothecial development under various light qualities and the effects of burial depth on light intensity were assessed. Vials, containing a pseudosclerotium, were capped with a clear, red, or blue filter, and placed into one of two photosynthetrons in a completely randomized design. Pseudosclerotia were incubated at 9-10°C on a 12-hr photoperiod with 80 μmol m⁻² s⁻¹ intensity for 14 days and monitored for apothecial development. In addition, two additional light exclusion trials were performed in a dark room at 5x10⁻⁵ μmol m⁻² s⁻¹ intensity. Light intensity was measured under increasing depths of soil or Douglas-fir sawdust. Clear filtered (full spectrum) or red filtered light stimulated more apothecia in comparison to blue filtered light. There was no difference in apothecial stimulation between the red or clear filtered light environments. Light was required for apothecium development, as zero apothecia developed in the dark environment, confirming previous reports. When light intensity was measured under increasing depths of soil or Douglas-fir sawdust, light conditions favorable to apothecial development was detected at a 0.5 cm depth but not at a 2.5 cm depth. \ud An annual application of at least 5 cm (2 inches) of Douglas-fir sawdust either in late winter (prior to sporulation) or anytime during the fall and winter months, if maintained at or above the 5 cm minimum depth, can help reduce the likelihood of apothecial development in the spring