At this time of year, we tend to see more virus problems on woody plants. Viruses can cause a wide range of symptoms, but if you learn to recognize viruses on one host, you will know what to look for on others. Virus diseases of brambles also cause a range of symptoms. Low vigor is a major symptom, as would be the case with most viruses. The leaves may be yellowish, mottled light and dark green on the same leaf, blistered or puckered, dwarfed, curled, wrinkled, and cupped downward with the mosaic types. The leaf curl viruses generally cause slight stunting and “bushy” growth with small, dark green, bunchy, stiff, tightly curled leaves. These symptoms are also very similar to those caused by some of the growth regulator herbicides. Look closely at the pattern in the patch. Herbicide injury is more intense near the source of the herbicide and progressively less intense as you move away from the source. Other broadleaf plants will likely show symptoms as well, and all at about the same time. Viruses are more likely to occur on scattered plants and to spread slowly during the season. They also tend to be fairly specific to one type of plant species.
Virus diseases reduce the yield and fruit quality of bramble fruits more than they do for most other fruit crops. Once infected, plants remain so for life. The virus particle needs a live plant cell in which to multiply and spread. It cannot be cultured, extracted, or induced to sporulate in a lab. The bramble viruses are spread by aphid feeding, but not by pruning or other mechanical injuries.
You cannot kill or inhibit virus particles with sprays. Control involves destroying all infected cultivated and wild brambles within 1,000 feet, if possible. Start new plantings with certified, virusfree plants. If you are growing both black and red raspberries, separate them by at least 150 feet to reduce virus cross-infection. Maintain strict aphid control at all times. For more information read Report on Plant Disease No. 710, “Virus Diseases of Brambles.” This publication is also available on VISTA, the University of Illinois Extension publications site, under horticulture publications. Access the site at http://www.ag.uiuc.edu/~vista/horticul.htm.