Verticillium Wilt

Verticillium Wilt is caused by the fungus Verticillium albo-atrum. It infects raspberries and blackberries, and a wide range of plants, including members of the nightshade family (e.g., tomato, eggplant, pepper). It also infects squash, stone fruits, blueberry, and strawberry, and many weeds, such as pigweed, horse nettle, ground cherry, and lambsquarters. In the brambles, it is most serious on black raspberries, but can also occur on red and purple raspberries. Blackberries vary in how susceptible they are to this disease. Loganberry is highly resistant and boysenberry is highly susceptible. It is common in the northern half of the United States and on the Pacific Coast.

Symptoms. Symptoms are most noticeable in hot, dry weather, and plants may look better in cool, fall weather. Symptoms begin at the bottom of the canes and work up. Leaves on new canes become pale green, then yellow in midsummer. Leaves may drop early. On second-year canes, fewer leaves are made. Beginning at the bottom of the cane and progressing upwards, the leaves become yellow, wilt, and fall off. Symptoms may be on only one side of the cane. If the canes are cut open, the water-conducting vessels are usually reddish. Infected canes may die in one to three years.

Infected raspberry canes may have a purple or blue streak that begins near the soil line and extends upward. On red raspberries, the individual leaflets may fall, leaving the petiole attached to the plant. On blackberries, the canes wilt, and the leaves turn yellow, then brown, and then die. The canes do not turn blue. If infected canes survive the winter, they may set fruit, but usually collapse as the fruit is ripening.

Prevention. Use disease-free planting stock. Do not plant raspberries after the above host plants for at least three to four years. Planting raspberries after at least two years of corn or wheat may help reduce the amount of fungus in the soil. Control weeds. Resistance is not available for this disease. See current recommendations for chemical control measures.

Phytophthora Root Rot

Phytophthora Root Rot of raspberries is caused by several Phytophthora species including P.megasperma, P. cactorum, P.citriocola, P cryptogea and others. This disease was first reported on red raspberries in Scotland in 1937. It has been in North America since 1958 and has been a widespread problem since the mid 1980s. It is primarily a red and purple raspberry disease, but can infect black raspberries and blackberries as well. It usually affects plants in wet or heavy soils. Infection can occur in patches in the planting, which corresponds to the low or soggy areas. These patches can become larger with time, as the amount of the fungus in the soil increases. The symptoms are most noticeable in the spring.

Symptoms. Both first year and second year canes may be affected. Generally, fewer first year canes are produced than normal. First year canes may develop a dark, water-soaked spot at the base and may then wilt rapidly and collapse. Symptoms may also develop more slowly, with yellowing, wilting, and dying of infected canes. Second-year canes are weak and stunted with small off-color leaves. They may produce weak side shoots. Leaves may turn yellow all over or turn brown around the edges or between the veins. Leaves, or even entire canes, may wilt. The entire cane may die in warm weather.

To diagnose this disease, the roots of a dying, but not yet dead, plant must be examined. If the bark is scraped from the main roots and crown, the layer underneath should be white on a healthy plant. On Phytophthora-infected plants, this layer is red-brown, and will later become dark brown. Often there is a distinct line where the infected and healthy tissue meet.

Some symptoms of this disease are similar to winter injury, but winter injury does not affect the number of first-year canes produced.

Prevention. Plant disease-free nursery stock. Plant in well-drained sites, preferably where brambles have not been grown before. The fungus spreads from plant to plant by swimming spores, so it is important to prevent flooding or puddling around the plants. It is better to prevent this disease by planting in an appropriate site. In questionable sites, plant on raised beds. Discourage water and soil movement from one field to another. Resistant varieties are available, such as Latham, Boyne, Killarney, and Nordic. See current recommendations for chemical control measures.

References.

Ellis, M.A. 1991. Verticillium Wilt. pp. 36-37 in Compendium of Raspberry and Blackberry Diseases and Insects. M.A. Ellis, R.H. Converse, R.N. Williams, and B. Williamson, eds. APS Press, St. Paul, MN.

New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.

Wilcox, W.F. 1991. Phytophthora Root Rot. pp. 34-36 in Compendium of Raspberry and Blackberry Diseases and Insects. M.A. Ellis, R.H. Converse, R.N. Williams, and B. Williamson, eds. APS Press, St. Paul, MN.

Wilcox, W. 1989. Disease Scouting and Management. Chapter 8 in Bramble Production Guide. NRAES-35. M. Pritts and D. Handley, eds. Cooperative Extension, Ithaca, NY.

By: Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998

Updated by: Mary Concklin, UConn IPM. 2012.

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.