There are two vascular wilt diseases of potato and they are difficult to tell apart. Both can cause the entire plant to die and cause the potatoes to become discolored inside. Although fusarium wilt is considered a warm weather disease, and verticillium wilt is considered a cool weather disease, they can overlap, and frequently do.

Fusarium Wilt

Fusarium wilt is caused by several species of the fungus Fusarium. Although there are species of Fusarium that can cause disease in many plants, this species causes disease only in

s progresses much faster under wet soil conditions.

Symptoms. The most noticeable symptom is wilting, which may or may not be more obvious on one side of the plant. Other symptoms may occur long before the plant wilts, however. The first symptom often is the plant’s pale appearance. The lower leaves turn yellow. Later they become more yellow or bronzed, and eventually die, dry up and hang on the plant. This begins on the lower leaves and progresses up the plant. The entire shoot may look purplish. The stems may fail to elongate, giving the leaves a “rosette” appearance. Leaves may be rolled. In the axils of the leaf, small tubers may appear. The roots and lower stems decay, and when the stems are cut open lengthwise, a browning can be seen in the vascular region in the lower stem. This is especially evident at the nodes. Brown flecks can be seen in the central portion of the inside of the stem.

On the tubers, there can be surface blemishes and decay. Browning often occurs at the stem end, and decay often sets in where the tuber attaches to the stolon. When the potato is sliced open, the ring of the vascular tissue is often brown. This browning may be darker than that found in verticillium wilt. The discolored area is firm, and does not ooze.

Prevention.

• Resistance is not available for this disease, although some varieties are somewhat more tolerant than others.
• Use disease-free seed potatoes that are fungicide treated.
• Do not plant potatoes in fields known to be infested with this fungus.
• A long rotation is considered important for disease prevention. Fungus can survive in the soil for a long time.
• Do not over-irrigate fields.

Verticillium Wilt

Verticillium wilts are caused by Verticillium albo-atrum, and V. dahliae. V. dahliae is more important in Connecticut than V. albo-atrum. Both fungi infect potato and many other plant species, including tomato, eggplant, strawberry, many trees and many common weeds. Grasses, corn, other grains, and certain legumes are not hosts of either fungus. This disease is serious, especially in cool climates. It was first reported in 1914 in Germany, but was not given a lot of attention until the 1950s, mostly due to the difficulty in telling it apart from fusarium wilt.

Symptoms. Plants infected with this fungus are often described as having “early maturity”. Symptoms usually begin at about flowering time. Plants wilt; especially on hot, sunny days. The wilt may occur on only one stem of a plant, or only on the leaves on one side of a stem. Generally, the lower leaves wilt first and the wilt progresses up the plant over time.

When temperatures are cooler and the soil is moist, the plants may not wilt. In this case, the major symptoms will be a yellowing of the lower leaves, which will later wither and die. These symptoms, too, will progress up the plant. If the stem is cut upwards at an angle, starting near the soil line, the vascular tissue appears tan to light brown. Occasionally, brown streaks may be seen running up the outside of a stem.

Some tubers will have a light brown ring of vascular discoloration when cut open, especially near the stem end. There may also be pink or tan discoloration around the eyes or on the surface of the tubers. If the tubers are stored under dry conditions, these will simply dry up. If the tubers are stored under wet conditions, secondary rot organisms may invade at these points and cause rotting of the tubers. Cavities may be formed inside severely affected tubers of susceptible varieties.

Similar Diseases. Blotches on tubers are sometimes mistaken for late blight, especially after the rot starts. Look for the ring of vascular browning. Also, look at the inside of the lower stem for vascular browning. If the disease is late blight, there is usually fluffy white fungal growth on the undersides of the leaves.

Prevention.

• Plant disease-free and treated seed tubers.
• Resistance is available for this disease.
• Rotate with grasses, grains, or legumes for more than 5 years.
• Planting potatoes following sudangrass or corn in the rotation has been shown to decrease disease, especially if the corn or sudangrass has been planted for several years.
• Avoid tomato, eggplant, and other members of the potato family in the rotations.
• Control susceptible weeds.
• Control nematodes, if present.

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

Updated by: T. Jude Boucher, IPM, University of Connecticut. 2012

References.

• Davis, J.R., O.C. Huisman, D.T. Westermann, S.L. Hafez, D.O. Everson, L.H. Sorensen, A.T. Schneider. 1996. Effects of Green Manures on Verticillium Wilt of Potato. Phytopath  86:444-453.
• Huguelet, J.E. and Hooker, W.J. Fusarium Wilts. 1981 in Compendium of Potato Diseases. W. J. Hooker, ed. APS Press, St. Paul, MN. pp 60-62
• Rich, A.E. 1981. Verticillium Wilt in Compendium of Potato Diseases. W. J. Hooker, ed. APS Press, St. Paul, MN. pp 62-63
• Rich, A.E. 1983. Potato Diseases. Academic Press. New York.

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

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