Integrated Management of Bramble Diseases

Bramble Fruit Rots

Figure 49: Botrytis fruit rot (gray mold) on raspberry fruit.

Disease Development

The gray mold fungus is capable of infecting a great number of different plants. It overwinters as minute, black fungus bodies (sclerotia) on infected plant debris including dead raspberry leaves and canes. In early spring, these fungal bodies produce large numbers of microscopic spores (conidia). Spores are spread by wind where they are deposited on blossoms and fruits. They germinate when moisture is present and infection occurs within a few hours. The fungus usually enters the fruit through flower parts, where it remains inactive (latent) within the tissues of infected green fruits. As the fruit matures, the fungus becomes active and rots the fruit. Thus, while infection actually occurs during bloom, symptoms are usually not observed until harvest. This is important to remember when one considers control. Temperatures between 70 and 80°F and moisture on the foliage from rain, dew, fog, or irrigation create ideal conditions for disease development. The disease can develop at lower temperatures if foliage remains wet for long periods.

Vast numbers of conidia are produced on the surface of infected plant parts, especially fruit. One infected fruit may be covered by millions of spores, which are carried by wind to cause additional infections on flowers and ripe fruit.