Factors affecting Neofuscicoccum ribis infection and disease progression in blueberry

Botryosphaeria stem blight is an economically important disease of blueberry worldwide. In this study, factors affecting inoculum production, infection and disease progression of Neofusicoccum spp. in blueberries were investigated. Under laboratory conditions conidia of the main three Neofusicoccum species (N. australe, N. parvum and N. ribis) were released from pycnidia at 15–30 °C and under relative humidities (RHs) of 80–100%, with greatest numbers released by N. parvum. The greatest numbers of oozing pycnidia and conidial release occurred at higher temperatures (25–30 °C) and RHs (92–100%). Inoculation of green shoots with different N. parvum and N. ribis conidial concentrations (50 μL of 5 × 10⁴−5 × 10⁶ conidia/ mL) caused 100% incidence but lesion lengths increased with increasing concentrations. Wound age affected N. ribis lesion development, with lesions only observed for 0–7-day-old wounds in soft green shoots and 0–4-day-old wounds for both hard green shoots and trunks. Colonisation length decreased with increasing wound age. Lesions developed on wounded shoots when plants were exposed to 20 or 25 °C and 90 or 100% RH during the early infection processes; and in non-wounded shoots spot-like lesions were observed although N. ribis colonised the stem tissue. Seasons (summer, autumn and winter) had no effect on susceptibility of wounded plants to N. ribis. External lesions only developed in summer-inoculated plants and colonisation length was lower in winter-inoculated plants. Information on host and environmental factors that affect disease development determined by the study will be used to inform the development of control strategies

Evaluation of fungicide efficacy against Neofusicoccum species causing dieback disease of blueberries in New Zealand

Several Botryosphaeriaceae species have been reported to cause stem canker, twig blight and dieback of blueberries, with different species being reported in different parts of the world. Pruning wounds are regarded as primary infection sites for these pathogens. This research evaluated in vitro and in vivo efficacy of fungicides against the main Neofusicoccum species associated with blueberry dieback in New Zealand. In vitro evaluation showed that four out of the nine fungicides tested were effective at reducing mycelial growth and/or conidial germination and germ tube growth of three pathogenic isolates each of N. australe, N. luteum, N. parvum and N. ribis. In vivo evaluation carried out with fungicides on wounded and non-wounded plant tissues on potted and field blueberry plants showed that carbendazim and tebuconazole were the most effective for protecting blueberry plants from infection by Neofusicoccum species. This research showed the importance of protecting both wounded and non-wounded tissues, with more than one application of fungicides likely to be required to provide effective control of the disease under natural inoculum levels