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Botrytis Fruit Rot

Botrytis fruit rot or gray mold is the most common and most serious disease of Rubus species worldwide.

The disease is caused by the fungus Botrytis cinerea. This pathogen has a wide host range and can survive on either living or dead tissue. It can overwinter on dead leaves, plant debris, and on the stems. The fungus rots fruit in the field before harvest, especially if rain occurs during blossoming. Most overripe and bruised fruit are susceptible, especially red raspberries. Aging leaves also are attacked, giving rise to cane infections.

Symptoms

Infections in the spring can be observed on canes, appearing as bleached-out, whitish areas. Infected berries become covered with masses of fungal spores, which give the disease its characteristic name "gray mold." If not harvested, infected berries become mummified, remain attached to the plant, and can serve as additional sources of inoculum in the planting. Botrytis can also cause a cane blight and leaf spotting.

Disease Management

Cultural practices that create an open plant canopy, improve air circulation, increase light penetration, and speed the drying of plant surfaces after rain aid in the control of the disease. Avoiding excess nitrogen fertilizer and eliminating weeds help maintain an environment less susceptible to gray mold. It is also important to harvest fruit before it is overripe. If fungicides are necessary, they should be applied during bloom, with additional applications made during harvest if needed. Refer to Table 7.5 for pesticide recommendations.

The important insects and diseases to be controlled, except for viruses, are listed in the right-hand column of this spray schedule. Always consult the label before making pesticide applications. Labels vary greatly among commercial products of the same material. It is important to refer to the label for the best timing and application rates when applying pesticides. Also read the text for information on cultural practices to minimize the application of pesticides. Due to a wide array of various products containing the same active ingredient, for insecticide recommendations, when appropriate, the active ingredient is listed instead of the name of the formulated product.

Table 7.5. Pesticide recommendations for brambles. (Follow all instructions and application rates listed on pesticide labels.
Time to Spray
Suggested Materials
Pests to be Controlled
Dormant (blackberries) - before buds open
Lime sulfur
Anthracnose, cane blight, powdery mildew, rust
Delayed Dormant - just as buds begin to open
Lime sulfur Anthracnose; spur blight on raspberries; powdery mildew, rust, and cane blight on blackberries
New shoots 8 inches long
Sulfur; Malathion; Esvenvalerate
Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; plant bugs
Petal Fall
Sulfur; Carbaryl plus Rotenone or Pyrethrum
Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; rose chafer; aphids; mites; plant bugs
Preharvest Sulfur Fruit rots
Midharvest Sulfur Fruit rots
Postharvest Malathion plus Carbaryl
Aphids, if present; Japanese beetles

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Botrytis Fruit Rot

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