Beginner

Scientific Name: Botrytis cinerea

Identification

• Infected, ripe berries are covered by a grey, fuzzy mould.
• Disease is most pronounced during cool and moist conditions.
• Infections usually occur during bloom, and symptoms usually develop during harvest or after harvest on picked fruit.
• Open blossoms may show signs of blight, brown and dry up.
• Mouldy berries that are not removed from the cane become mummified.

Often Confused With
Fire Blight
Anthracnose

Period of Activity
Temperatures around 22°C -25°C, high relative humidity, and plant surface wetness caused by rain, overhead irrigation, fog or dew provide an ideal environment for Botrytis. Raspberry plants are susceptible during bloom and again as the fruits ripen. Symptoms may appear prior to harvest, or after fruit has been picked and packaged.

Scouting Notes
In early spring, look for mummified berries and overwintering sclerotia on old fruiting canes.  During bloom, check for browning or drying on petals of open blossoms. As the fruit ripens, check for signs of fruit infection.  Look in sheltered areas and the centre of rows where relative humidity is highest. Older plantings where crop debris has built up over time are more at risk.  Plants injured by harvest machinery, wind or insects are more prone to infections.

Thresholds
None established.  

Advanced

Scientific Name: Botrytis cinerea

Identification
Botrytis grey mould, also known as botrytis fruit rot, is caused by Botrytis cinerea, the same fungal pathogen that causes cane botrytis.

This fungus causes a common and serious fruit disease in raspberries worldwide. The disease is most severe during cool and moist conditions, such as long rainy and cloudy periods. Because Botrytis typically infects through wounds or weakened tissue, physical damage caused by wind, insects and harvest machinery can favour this disease.

While infections usually occur during bloom, symptoms develop mainly during harvest or after harvest on picked fruit. Infected, ripe berries are covered by a grey, fuzzy mould. Botrytis also infects open blossoms, causing them to turn brown and dried. The receptacle, which remains after fruit is harvested, may also become infected. If mouldy berries are not removed from the cane, they remain attached and become mummified.

Often Confused With
Fire Blight
Both diseases can cause dry, hard, mummified fruit. In the case of fire blight, leaf and cane tissue may be affected as well.  Active fire blight infections often exude an amber or milky ooze in humid conditions.

Anthracnose
Lesions on fruit caused by anthracnose may appear similar to those caused by B. cinerea. However, anthracnose lesions are not covered by a dusty or fluffy grey mould.

Biology
The fungus B. cinerea survives on a wide range of hosts on both living and dead tissues. It overwinters as small black sclerotia in cane lesions, and as mycelium in plant debris. In spring, conidia are produced and dispersed by wind, splashing rain, and overhead irrigation. The risk of infection increases at moderate temperatures, high relative humidity and when plants are wet during bloom. As flower buds open and blossoms mature, they become susceptible to Botrytis infections. After infection, the fungus remains dormant in developing fruit.  If environmental conditions are favourable close to harvest, the fungus will reactivate and symptoms of the disease will develop quickly. Early symptoms include transitory, watery pockets on individual drupelets that were infected in the spring. Eventually the infected ripe fruit becomes covered with rapidly growing fungal mycelium and conidia. Secondary infection can occur when the styles and stamens attached to immature fruit produce conidia. These conidia infect fruit close to harvest. Because the disease can be dormant in the fruit, it sometimes develops on stored or packaged fruit that did not have symptoms at the time of picking.

Period of Activity
Temperatures around 22°C -25°C, high relative humidity, and plant surface wetness caused by rain, overhead irrigation, fog or dew provide an ideal environment for Botrytis. Raspberry plants are susceptible during bloom and again as the fruits ripen. Symptoms may appear prior to harvest, or after fruit has been picked and packaged.

Scouting Notes
In early spring, look for mummified berries and overwintering sclerotia on old fruiting canes.  During bloom, check for browning or drying on petals of open blossoms. As the fruit ripens, check for signs of fruit infection.  Look in sheltered areas and the centre of rows where relative humidity is highest. Older plantings where crop debris has built up over time are more at risk.  Plants injured by harvest machinery, wind or insects are more prone to infections.

Thresholds
None established.  

Management Notes

• Ensure adequate air circulation to promote drying of plant tissues by pruning out old canes, and controlling weed growth. Use trellises to hold plants erect.
• Keep rows narrow by removing excess primocanes at the edges of the row in May and June.
• Avoid excessive use of nitrogen fertilizer as it promotes lush growth that prevents good air circulation and retains moisture.
• Remove old and diseased canes and destroy them.
• Bloom is the most important time to control botrytis grey mould, however, pre-harvest sprays are also required if the weather is wet. Begin spraying at 5-10% bloom and repeat every 7-10 days if the weather is wet. Choose fungicides from different fungicide groups to reduce the development of resistant strains. For a list of registered fungicides in Ontario, refer to the Raspberry Calendar in OMAFRA Publication #360: Guide to Fruit Production.
• Botrytis grey mould affects all raspberry varieties, but Tulameen and Jewel are especially susceptible.  Polka exhibits a high tolerance of B. cinerea.
• Harvest berries when they are red and ripe, yet still firm. Pick berries directly into the containers sold to customers to minimize handling. Ensure containers are shallow enough to avoid crushing of bottom berries.
• Immediately after harvest, cool fruit to near 0°C to slow fungal growth.