Management of raspberry and strawberry grey mould in open field and under protection. A review

Grey mould, caused by Botrytis cinerea, is one of the most important diseases of strawberry and raspberry. In the UK, the majority of raspberry and strawberry production has recently switched to cropping under polythene tunnels. Although the risk of grey mould is greatly reduced under protection, a similar strategy is still adopted to manage grey mould on these crops. We first reviewed published studies on the epidemiology of grey mould on raspberry and strawberry, most of which are for crops grown in open field: (1) inoculum source comprises sclerotia on plant debris, plant organs and weeds, and resting mycelia on plant tissues. (2) Infection of flowers and the establishment of quiescent mycelium in floral parts is one of the main avenues for the rotting of ripe fruits. Thus, control of grey mould in open-field crops relies heavily on the scheduled application of fungicides during the flowering and early fruiting periods. (3) Recent research suggested possibility of B. cinerea as an endophyte. We carried out studies to understand the infection of flowers and fruit by B. cinerea on raspberry and strawberry crops grown under protection in order to assess whether management strategies developed for open crops are appropriate for crops grown under protections. Our main findings are: (1) covering crops early in the season did not significantly affect the incidence of raspberry fruit with latent infection by B. cinerea at harvest but reduced latent infection in strawberry. (2) Models developed for strawberry crops grown in the open did not give reliable predictions of flower infections on both strawberry and raspberry grown under protection. It was not possible to develop a predictive model for flower infection on raspberry grown under protection. (3) The level of ripe fruit with visual symptoms at harvest was low, usually close to zero. (4) Nearly all fruits from both sprayed and unsprayed crops were colonised by several fungi, including B. cinerea, within 7 days of harvest when stored at room temperatures. Based on these results, we question the value of scheduled fungicide applications to flowers and fruit for grey mould control under protection, and suggest that post-harvest fruit management, e. g. rapid cooling, is the key to prevent fruit from developing fungal rots before consumption.