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SYMPTOMSFusarium wilt, caused by Fusarium oxysporum f. sp. niveum is one of the most important diseases of watermelon. The host range of this pathogen is thought to be restricted to watermelon, although artificial inoculations indicate that summer squash also may be susceptible. A distinct race of the fungus (Fusarium oxysporum f. sp. melonis), causes a similar type of wilting on muskmelon. The disease may affect plants in all stages of growth. Damping-off is common on young seedlings. Young plants may develop a soft, cortical rot which results in chlorotic leaves and stunting. The most common symptom on older plants is wilting. Generally, the wilting process begins in one or more lateral vines of the plant. The leaves become flaccid, wither, and turn brown. Gradually, the wilting progresses until the entire plant is killed. Vascular discoloration often is associated with wilted vines. This is best seen by slicing vertically through a vine near the soil surface. Look for a yellow-brown discoloration in tissue directly beneath the outer layer of the vine. A white fungal growth also may be formed at the base of the dead vines. DISEASE CYCLEThe disease-causing fungus may be introduced into a field on contaminated seed. Once established, the fungus can survive in the soil for many years. The fungus penetrates the fibrous root system of the host and moves within the vascular system of the plant causing blockage of the water-conducting tissue. CONTROLBecause the fungus can survive in soil for periods as long as 10 years, it is often impractical to control the disease through crop rotation. The most satisfactory means of controlling Fusarium wilt is the use of resistant varieties. Use only those cultivars with resistance in fields where wilt has been a problem. The following table indicates the relative susceptibility of various watermelon cultivars.
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| CULTIVAR | RESISTANCE |
CULTIVAR |
RESISTANCE |
|---|---|---|---|
| BABY FUN | (R) | PEACOCK | MR-SR |
| BLUE BELLE | (R)S | TENDERGOLD | MR-SR |
| SWEET MEAT | (R) |
SUNSHADE |
MR-SR |
| DIXIE LEE | HR-MR |
GARRISONIAN |
S(AN) |
| SMOKEYLEE | HR | PETITE SWEET | (R)-S(AN) |
| CALHOUN GRAY | HR-MR |
SUGARBABY |
(R)-S |
| ALLSWEET MR | (AN) |
TOP YIELD |
S |
| CRIMSON SWEET | MR(AN) |
TENDERSWEET |
S |
| CHARLESTON 76 | MR-SR(AN) |
TRI X-313 |
S |
| CHARLESTON GRAY | MR-SR |
KLONDIKE BLUE RIBBON |
S |
| PRINCE CHARLES | MR | CONGO S | (AN) |
| LOUISIANA QUEEN | MR | BLACK DIAMOND | S |
| SWEET PRINCESS | SR |
IOWA PRIDE |
? (AN) |
| JUBILEE | SR-S(AN) |
OASIS |
? (AN) |
| KLONDIKE R7 | SR |
MIRAGE |
S |
| SUMMERFIELD | SR |
CARNIVAL |
R |
| FIESTA | R |
REGENCY |
R |
| ROYAL JUBILEE | R |
ROYAL SWEET |
R |
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SANGRIA |
R |
| HR = highly resistant, MR = moderately resistant, SR = slightly resistant, and S = susceptible to Fusarium wilt (based on information from Martyn and Mclaughlin, Plant Disease 67:493-495 and Midwest Vegetable Production Guide). (R) indicates company claims for resistance to Fusarium wilt and (AN) indicates resistance to anthracnose. |
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Web updated 9/01/06 |