Can plant shaking reduce the incidence of Botrytis?

Abstract

Wine production is expanding in Scandinavia with a focus on organic growing, and Solaris becoming the signature grape of the region. However, despite the robustness of Solaris, methods for reduction of disease pressures are still needed. A new project has been initiated in Denmark on disease control in organic growing. The main focus is on Botrytis cinerea the cause of bunch rot, the disease creating most challenges when growing Solaris. Three different methods are tested. 1) Shaking the plants with a portal harvester shortly after fruit set, to remove flower debris being a nutrient source that facilitates early stages of infection. 2) Spraying after flowering with the chitosan-based product ‘Botryless’ (Lallemand). 3) Spray treatments with ‘AquaHort’, providing micro-doses of copper. For the shaking method net bags were placed on 60 clusters prior to shaking and the amount of tissues shaken off (ovaries, anthers, caps) was quantified and B. cinerea growth from the flower parts was studied on potato dextrose agar (PDA) plates. From two different shaking intensities an average of 30 and 47mg flower parts/cluster was removed by shaking. Sclerotia (resting structures of the pathogen) was produced after 8 weeks of culture in 41 out of 60 petri dishes. Later – at pea size – latent infections of B. cinerea were investigated. Surface sterilized berries were cut in half and placed cut-side up on PDA. Based on morphological assessment, two B. cinerea infected fruits were found in the control and non from the shaking treatment. In addition, growth of Alternaria, Cladosporium and Fusarium species was identified, but also several unidentified fungal species developed. Further identification will be made based on ITS sequencing, but the initial results indicate a reduced level of latent infections. Shortly before harvest incidence of botrytis was scored based on a 12-level scale (1% – 90%) showing a clear reduction by shaking and by ‘AquaHort’, while only a tendency to fewer clusters with high levels of infection (>50%) was found in the ‘Botryless’ treatment. Finally, the effect of ‘AquaHort’ on the level of leaf necroses (hyperreactions to downy mildew attacks) was assessed shortly after harvest. The percentage necrotic tissue was assessed on the upper 30-40 cm of the canopy on all shoos on every 10th plant in 4 treated rows and 4 untreated (100 plants/row). The average disease score was significantly reduced from 10,6% in the control to 3,8 % necroses for ‘AquaHort’.