In extremely overgrown and weedy plantings, the disease can cause a loss in yields, especially if excessive nitrogen is applied.
Symptoms and Disease Cycle
Spur blight is caused by the fungus Didymella applanata, which overwinters in infected canes. Symptoms appear in late spring or early summer as chocolate-brown, dark-blue, or purplish spots or bands on new canes and petioles. These lesions enlarge until the cane is girdled. By late summer, canes may crack and split lengthwise, at which time the reproductive, pimple-like, black fruiting structures of the fungus can be seen. These structures overwinter and the following spring discharge spores into the air or may ooze to the surface of the stem during wet periods. Symptoms on leaves appear as chocolate-brown, angular, or wedge-shaped areas. The effects of spur blight are increased plant susceptibility to winter injury and reduced yield as a result of the withering and eventual death of infected laterals. Leaflets also wither and drop prematurely.
Suggested controls are the same as those for cane blight, botrytis blight, and anthracnose. Keeping the plant canopy open to ensure that leaves and canes dry rapidly after rain will help in controlling this disease. Thorough pruning, including the removal of pruned canes from the planting, is helpful. Lime sulfur and sanitation are useful, and keeping row width narrow to increase air movement is particularly effective. Producing only the fall crop on primocane bearers has greatly reduced the incidence of the disease. Several fungicides can be used during the season. 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|
|Postharvest||Malathion plus Carbaryl||Aphids, if present; Japanese beetles|