Verticillium Wilt

Extension Bulletin 1908

PLANT DISEASE

VERTICILLIUM WILT

Verticillium wilt, a disease of a from one host plant to another, Cankers and bleeding are not plant’s vascular system, occurs but commonly, the leaves wilt, usually associated with Verticil- worldwide, but is most impor- drop (Figure 1), eventually turn lium wilt, but on Russian olive tant in temperate regions. In the yellow, and die prematurely. and cherry there may be con- Pacific Northwest, 50 genera of Wilting usually begins with the siderable gum production on plants have been reported as lower leaves and spreads the trunk and larger branches. susceptible to this disease, upward. For most types of which is caused by a fungus. In plants, severe disease may Certain plants develop addi- Washington State, verticillium darken the water-conducting tional symptoms: wilt is especially common in tissues, especially in the lower irrigated areas and is particu- stem. This can be seen by • Alfalfa. V-shaped necrotic larly severe on mint, potato, cutting the stem lengthwise. lesions develop at the apex of cherry, eggplant, melon, and the leaflets and shoots die such ornamentals as rose and without prominent crooking. catalpa. Mint wilt is especially • Cherry. The spurs may die devastating; if a mint planting and the leaves drop. Gener- becomes infected, production ally, one side of the tree may become uneconomic within 3 to 5 years. In the late 1940s, growers moved most of the mint production from mid- western to western states in an effort to escape from Verticil- lium wilt. Unfortunately, they carried it with them on infected mint roots.

Symptoms. The fungus invades plant roots and plugs the water- conducting tissues, which prevents water from reaching the leaves. Symptoms may vary Figure 1. Verticillium wilt on cherry. Figure 2. Verticillium wilt on mint. becomes infected and the tubers are commonly infected Until recently, V. dahliae iso- leaves eventually turn a flame with V. dahliae and spread the lates were thought to have a or yellow color. In addition, pathogen. wide variety of hosts, but recent the woody tissue may have research showed that certain spots or extensive brown V. dahliae produces small, isolates differ in aggressiveness discoloration. black, resting structures called on various hosts. Isolates of V. • Melons. A portion or all of the microsclerotia. Under favorable dahliae obtained from mint plant yellows and usually conditions, the microsclerotia plants were significantly more wilts just before the fruit is sprout to produce small, thread- aggressive on mint than isolates mature. like strands (hyphae) that invade obtained from other host plants. • Mint. There is a characteristic the roots of susceptible plants. Also, certain isolates (VCG 4A) bronzing and twisting of the These infection threads invade from mint and potato were top leaves, which gives them the water-conducting cells of more aggressive on potato than a half-moon appearance the plant and cause wilt symp- were other isolates (VCG 2B (Figure 2). toms by destroying the ability of and VCG 4B). Further evidence • Raspberry. Especially in black the plant cells to conduct water. for host adaptation or specific- raspberry, the lower portion of Microsclerotia can be produced ity comes from studies regard- diseased canes may have a in large numbers in some host ing synergistic associations blue or purple color. The plants, such as potato, and can between V. dahliae isolates and disease is often called “blue survive in the soil for up to nematodes. When a mint or stem” in this case. fifteen years. This makes crop potato plant becomes infected rotation both a high-risk prac- with both Verticillium dahliae Pathogens. Verticillium wilt is tice and an ineffective control and the root-lesion nematode caused primarily by two species measure. For example, heavy Pratylenchus penetrans, the of Verticillium. damage can occur on suscep- plant may develop earlier and tible hosts, such as cherry and more severe symptoms of (1) Verticillium dahliae is the strawberry, when they are verticillium wilt than a plant most common species and planted in soil previously infected only by V. dahliae. This attacks a wide range of plants. It cropped to potato. happened on potato with V. is a major problem in many dahliae isolates from VCG 4A ornamentals in addition to There are at least four groups, or and on mint with isolates from many crop plants including strains, of V. dahliae that can VCG 2B, but not vice versa, mint, potato, cherry, and vary from each other in many and isolates from VCG 4B strawberry. It can also attack characteristics including patho- showed weak or no interaction hops, but is usually only serious genicity and aggressiveness. on potato with the nematode. when the hop plants are grown These strains are called vegeta- Currently, isolates of the follow- in soil treated with the insecti- tive compatibility groups ing groups of V. dahliae are cide heptachlor. This chemical (VCGs). VCGs are genetically considered to be host-adapted: seems to predispose hops to isolated from each other, mean- VCG 4A (potato), 2B (mint). more serious damage. V. ing that an individual from one Research on host adaptation dahliae readily infects potato group (for example, VCG 2) can and aggressiveness is being and causes potato early dying fuse with another individual conducted to develop better (PED), which is a serious from the same group (VCG 2), disease management practices. problem in the Midwest and but not with an individual from Pacific Northwest. PED is a different group (for example, (2) Verticillium albo-atrum is marked by premature vine VCG 4). Isolates of V. dahliae most notable for causing alfalfa death and reduction in tuber can be identified in the labora- wilt and is less common than V. yield by as much as 30 percent. tory by pairing known and dahliae in relatively warm Commercial certified seed unknown isolates. temperate climates. It is further distinguished because it does the soil and potentially infect survive in the soil for up to 15 not produce microsclerotia and new plantings. years as microsclerotia. its threadlike strands (hyphae) • Maintain a balanced fertilizer • Prune infected and diseased have thick, dark walls. It is schedule to avoid excessive limbs of cherry and ornamen- called the “dark mycelial type.” succulent growth in young tal trees. Cherry trees usually plants. recover from wilt. Disease control. Controlling • Provide adequate water verticillium wilt is difficult and during warm weather to Additional tips: can be expensive, but several prevent or delay the onset of means of avoiding the disease wilt symptoms. • Soil fumigation can reduce and reducing losses are avail- • Always use planting stock the amount of fungus present, able: certified to be verticillium- but this method of control is free and to have been grown expensive and recontamina- • Avoid planting susceptible in verticillium-free soil when tion is always possible. trees and other plants in soil planting susceptible crops in • Disease-resistant cultivars are previously cropped to sus- soil known to be free from the not available for most crop ceptible herbaceous plants fungus. Keep in mind the plants, but some plant species such as potato, tomato, accidental introduction of are more resistant or tolerant eggplant, etc. verticillium wilt to the Pacific than others and should be • Eliminate susceptible weed Northwest when infected considered when the disease hosts such as pigweed, mint plants from the Midwest is known to be a serious nightshade, and lamb’s- were brought here. problem. quarter from plantings. These • Prevent movement of soil • Crop rotation is of little value are hosts of the fungus and from infested fields into clean because, once again, the will enable it to build up in fields since V. dahliae can fungus can survive in the soil for many years. COOPERATIVE EXTENSION

By Matthew Sunseri and Dennis A. Johnson, Department of Plant Pathology, WSU Pullman

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Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, sex, religion, age, color, creed, national or ethnic origin; physical, mental or sensory disability; marital status, sexual orientation, and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published December 2001. Subject code 356. C. EB1908