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Fusarium and Verticillium Wilt Diseases in Vegetables
The vascular wilt diseases are common, destructive to many vegetables in Utah. They cause severe problems in commercial plantings and in home gardens. Wilts are usually caused by species of the Verticillium fungus but may be caused by Fusarium fungus. Many vegetables re affected including potatoes, tomatoes, peppers, squash, melons and others.
Vascular wilt disease first appears as premature yellowing or other discoloration of the leaves. The stems and leaf petioles remain green. Infected plants may wilt during the day and revive at night, but eventually the vine wilts permanently and dies prematurely.
The wilt is caused by the plugging of the water conducting or vascular tissues. As the fungus grows inside the plant, it fills the conducting tissue and make it impossible to get water to the leaves. These symptoms often occur only on one side of the plant, with other portions of the plant remaining healthy.
In addition to the wilting symptom, both fungi can cause discoloration in the vascular system in the lower stems of the plants where they enter the soil. This is most easily seen by slicing through the stem vertically and looking for streaking.
Plants infected by Fusarium often show bunching of upper leaves and shortening of stem internodes, creating a rosetting symptom.
This vascular discoloration in both diseases can extend into potato tubers but is more common and pronounced when Fusarium causes the disease. In addition, some species of Fusarium cause rot of the underground stem, tuber blemishes, and decay, especially at the stem end.
All of these fungi live in the soil. They are capable of living saprophytically, in the absence of a host plant, and persist in the soil for many years. The fungi usually infect through wounds in roots,
Because the fungi are present in soil, anything that moves soil, such as water or wind, farm equipment or transplants, can spread the fungi. Additionally, the disease is introduced to new areas in infected seed potatoes. The fungi are added to the soil when infected plant debris is tilled in after harvest.
Control of Fusarium and Verticillium depends heavily upon cultural methods. If an area is known to be contaminated with either of these fungi, avoid planting susceptible crops in that area.
Crop rotations are not especially effective in reducing the fungi, since they can live saprophytically in the absence of a host.
Many weeds are fungal hosts so good weed control is important in reducing this disease.
Resistant varieties are extremely important. Always look for VF resistant varieties when selecting varieties for infested soils. There are no potato varieties resistant to Fusarium wilt, but some commercial varieties show resistance to Verticillium wilt such as Russet Burbank.
Resistance does not mean immunity and it is dependent on location, fungus population and the strain of the fungus. On some plants, nitrogen is side-dressed in mid-season to reduce stress to the plant. Avoid drought stress to the plants and avoid any injury to the plants that may allow the diseases to enter the plants.
