How can grey mould be prevented on raspberries?
Grey mould can soften ripe raspberries and cover them with grey spores. Prevention involves more than removing mouldy berries at harvest: flowering conditions, cane arrangement and postharvest handling all matter.
Following infection and symptom development
1. Separate softening from grey growth Fruit rot associated with Botrytis cinerea may begin with softening and discolouration, followed by grey, fuzzy or dusty spore growth under humid conditions. Not every soft raspberry has Botrytis. Overripeness, crushing and other rots can look similar initially. Note whether deterioration starts on the plant or only after fruit enters a container. Comparing several sound and affected berries is useful, but do not attempt diagnosis by closely smelling mouldy fruit. The appearance, timing and handling history together provide better evidence than softness alone. 2. Remember the flowering period Damage seen on fruit may not have begun the day before harvest. Botrytis can infect flower tissues, with the problem becoming obvious as fruit ripens. Record prolonged damp weather during flowering as well as at picking. Dense canes may slow drying, making the duration of wetness around blossoms and fruit clusters important after rain. A dry harvest day does not rule out earlier infection. Symptom appearance and the pathogen’s entry into the plant should not be treated as the same event when reviewing management. 3. Cultivar and cropping-season differences Summer-bearing raspberries and those producing an autumn crop on current-season canes require different pruning systems. Before thinning for disease prevention, establish which canes will carry the next crop. Risk also changes when harvest coincides with a region’s wet season. Low losses from a cultivar elsewhere do not guarantee equivalent performance locally. Plant spacing, training and row orientation should suit the cultivar’s vigour. Cutting every raspberry planting in the same way can remove productive wood or leave unnecessary density, depending on its cropping system.
Reducing losses in the row and at harvest
4. Air movement and irrigation Orderly training on suitable supports can reduce crowded clusters and poorly ventilated pockets. Remove spent fruiting canes at a time appropriate to the cropping system. Where possible, direct irrigation to roots rather than keeping berries wet overnight with overhead watering. Withholding needed root-zone water is not a treatment for mould. Weeds filling the row and dense growth encouraged by excessive nitrogen can also delay drying. Include these factors in management instead of considering disease prevention solely as a decision about whether to spray. 5. Frequent, gentle picking Avoid leaving overripe fruit on plants; pick regularly and separate rotten berries from sound ones. Unnecessary handling of wet fruit and crushing in deep containers can increase losses. Use clean shallow containers and keep harvested berries out of direct sun. Prompt appropriate cooling preserves quality but does not make existing mould safe to eat. Discard mouldy raspberries. Contact between a diseased berry and sound fruit in a container can alter the distribution of subsequent deterioration, so postharvest appearance does not always reflect where initial infection occurred. 6. A local plan for recurrent problems Have the diagnosis checked if substantial rot returns each season, and review records from flowering through harvest. A commercial planting and a home garden may not need the same protective programme. Consider only products locally authorised for the relevant raspberry use, following label instructions and harvest intervals. Avoid homemade mixtures on fruit. At season’s end, compare disease levels, harvest frequency and cane density to identify which changes helped. One rainy day rarely explains the full pattern; infection history and handling conditions both contribute to the final loss.