Gardening Articles: Edibles :: Small Fruits & Berries
Blackcap Brambles (page 3 of 3)
by Lee Reich
Pruning Black Raspberries
1. Raspberry canes are biennial, growing stems the first season, then fruiting and dying in the second season. So the first step in pruning is to cut the canes to the ground right after they finish fruiting. They'll soon die anyway, and removing them admits more sunshine to the new canes growing from the base of the plant. Finish pruning old canes before plants leaf out in spring.
2. In the summer, when the new canes reach about 20 inches tall, pinch out the top two inches to keep them at 18 inches. Do this weekly for several weeks until all the new canes (primocanes) have reached the desired height and been pinched back.
3. The summer topping described in step 2 stimulates growth of side branches, which will fruit the following season. Pinching back at 18 inches keeps the plants stocky enough that you won't need a trellis. (Alternatively, you could run a single wire above the row at about three feet. Delay pinching until the canes are tall enough to be tied to the wire.)
4. In the dormant season, preferably just before growth begins in spring, thin out canes, removing any that are diseased, damaged or spindly. On remaining canes, shorten the side branches proportionally to their vigor. The largest side shoots can be 18 inches long, and the thinnest about six inches long.
Black raspberries fall prey to a number of diseases. Orange rust is a fungus that produces decorative but deadly splotches of orange spores on the leaves. Anthracnose fungus can also be debilitating, attacking black raspberries more readily than red raspberries. The weakened canes, spotted with purple-margined gray lesions, are susc to winter cold damage and produce dried-up fruits. Black raspberries also are very susceptible to mosaic virus. In its advanced stages, mosaic causes mottled leaves as well as stunting, and even death, of a plant.
Disease problems of black raspberries vary from site to site. "Some plantings get rust, while others do not," says Dr. Harry Swartz, a breeder of black raspberries at the University of Maryland. "I could not get infection in my test plots on young or old plants even after dusting them with the contents of a one-ounce bottle of spores that I had collected."
In a test planting of black and red raspberries during two wet years, Pennsylvania State University's Dr. Barbara Goulart found that the blacks outyielded the reds, in spite of the blacks' higher susceptibility to anthracnose. Even mosaic infection is unpredictable. Some commercial plantings in New York become unproductive within three years because of mosaic virus while other plantings seem unaffected. Farther south and in the Pacific Northwest, mosaic is less common. The Pacific Northwest does have its share of Verticillium, though.
The first line of defense is to obtain clean plants from a nursery. Then select a site with the good drainage and the ample sunlight that raspberries like. Prune to encourage air circulation and remove diseased canes.
If anthracnose becomes a problem, spray the plants with lime-sulfur solution at budbreak and, if needed, during the growing season. Always keep an eye out for orange rust and mosaic virus. Pull up and burn any plants you suspect carry either disease. Even with clean plants and a clean site, a black raspberry planting will eventually decline from a buildup of pests, so don't be surprised if you need to replant at a new site in 5 to 10 years.