Watermelon Fusarium Treatment: Managing Fusarium Wilt On Watermelons

Watermelon Fusarium Treatment: Managing Fusarium Wilt On Watermelons

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By: Mary H. Dyer, Credentialed Garden Writer

Fusarium wilt of watermelon is an aggressive fungal disease that spreads from spores in the soil. Infected seeds are often initially to blame, but once fusarium wilt is established, it can be transmitted by anything that moves the soil, including wind, water, animals, and people. What can you do about watermelons with fusarium wilt? Can the disease be controlled or treated? Let’s consider how to manage fusarium wilt on watermelons.

Symptoms of Fusarium Wilt on Watermelons

Fusarium wilt of watermelon is a specific disease that can’t be transmitted to other plants, including cantaloupe, cucumbers, or others in the same plant family.

Although infection occurs when spring weather is cool and damp, fusarium wilt can show up on the plant at any stage of growth, any time during the growing season. Mature plants are better able to handle the disease than seedlings, which often collapse.

In its early stages, fusarium wilt of watermelon is evidenced by stunted growth and wilting that shows up during the heat of the afternoon, rebounding in the cool of evening. As the disease progresses, wilt becomes permanent.

Diseased leaves turn yellow or dull green, often becoming brown, dry, and brittle. The infection, which enters through the roots, usually takes over entire plants but may be limited to one side. If you break or cut a stem, fusarium is easy to spot by the brown vascular tissues within. After the plant wilts, you’ll see masses of tiny spores on the dead vines.

In some cases, you may not notice watermelons with fusarium wilt until the hot days of summer, especially when plants are stressed by drought. Any melons that develop are abnormally small.

Watermelon Fusarium Treatment

Watermelon fusarium wilt is difficult to manage and, currently, there are no effective fungicides for watermelon fusarium. Treatment involves careful prevention, sanitation, and maintenance, including the following:

  • Plant disease-free seeds or transplants.
  • Look for fusarium-resistant tomato varieties. No variety is 100 percent free of risk, but some are more resistant than others.
  • Practice crop rotation. Don’t plant watermelon in an infected area for at least five to 10 years; the disease can live in the soil indefinitely.
  • Clean garden tools before moving to an uninfected area.
  • Destroy infected plant matter by burning or discarding in sealed plastic bags. Never place infected debris in your compost bin.

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Read more about Watermelons

What causes watermelon plants to wilt?

If watermelons are wilting, this might indicate that there's a fungal problem coming from the soil. Fusarium wilt of watermelon causes plants to wilt, and it may begin in one or more vines. Pull out a plant and look for any browning or discoloration at the base or on the roots.

Similarly, what's wrong with my watermelon plant? Watermelon affected with down mildew exhibit symptoms such as leaves that curl inward, turn brown and die along with irregular-shaped fruit. Fusarium wilt is another fungus that attacks the root first and travels up the plant stems. Affected plants exhibit symptoms of wilting and stunted growth before dying.

Similarly, you may ask, how do you control wilt in watermelon?

The best control for Fusarium wilt of watermelons is the use of resistant varieties coupled with crop rotation. Long rotations (five years or more) may lessen the survival rate of the fungus spores in the soil and decrease the severity of symptoms.

Why are my watermelons turning black and dying?

When a watermelon plant is deficient in calcium or suffering from drought or excessive nitrogen, it may develop blossom end rot, which shows as a pale green to brown to black discoloration on the end of the fruit where the flower was.


Watermelon yield loss due to Fusarium wilt is increasing in the U.S., due in part to the emergence of the virulent race 2 of Fusarium oxysporum f. sp. niveum, and to the shift in production to triploid cultivars, which generally have less host resistance than previously grown diploid cultivars. One potential management strategy is the use of soil-applied fungicides to reduce Fusarium wilt. The U.S. national program, interregional project 4 (IR-4) supported multistate trials of soil-applied chemicals to manage Fusarium wilt of watermelon. Greenhouse trials were conducted in Maryland, Indiana and Georgia to test the efficacy of 14 chemicals on Fusarium wilt. Based on the performance of these chemicals in the greenhouse, six in Maryland and Delaware and eight in Indiana were selected for subsequent field evaluations. These chemicals were applied once, as a drench at planting, in field trials in Maryland, Indiana, and Delaware in 2008. The fungicides prothioconazole, acibenzolar-S-methyl, and thiophanate-methyl resulted in the greatest reduction in Fusarium wilt, and caused no phytotoxicity. In Maryland and Indiana in 2009, these chemicals were applied through the drip irrigation line alone and in combination, at 0, 2 and 4 weeks after planting. The experiment was repeated in 2010 in Maryland. Prothioconazole alone and in combination with acibenzolar-S-methyl or/and thiophanate-methyl resulted in the greatest decrease in the area under the disease progress curve (AUDPC) of Fusarium wilt of watermelon in Maryland in 2009. The same trend was observed in 2010 in Maryland where three of the prothioconazole treatments ranked the lowest of all treatments and prothioconazole in combination with thiophanate-methyl had significantly lower Fusarium wilt AUDPC compared to the non-treated control. All chemical applications except for acibenzolar-S-methyl in combination with prothioconazole reduced Fusarium wilt AUDPC in Indiana in 2009. Prothioconazole alone and prothioconazole in combination with thiophanate-methyl ranked lowest in Fusarium wilt AUDPC, although not significantly lower than most other treatments. These studies are the first to demonstrate that the soil-applied fungicides prothioconazole and thiophanate-methyl may provide an additional field management option for Fusarium wilt of watermelon.

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Fusarium Wilt

Fusarium wilt affects many plant types, but tomato gardeners know this deadly, soil-borne disease especially well. Also known as stem rot, it's a common tomato wilt disease, which moves into plants through their roots. From there, it clogs the plant's passageways, blocking the flow of water, nutrients and vital juices until wilting and eventually resulting in death.

Tomatoes and close relatives such as eggplant, peppers and potatoes all suffer the same fusarium types. Other fusarium pathogens attack different plants, from brassicas such as cabbage, broccoli and kale to tropical plants, including bananas and palms. Warm summer temperatures favor the disease, which often spreads through infected garden transplants and soil.

Fusarium Wilt Identification/Symptoms: Unlike other wilt diseases, fusarium wilt often shows up only on one side of a plant, branch or leaf. Bottom leaves show symptoms first. As the disease progresses upward, the plant wilts, turns brown and drops its leaves. If cut, affected stems near the base show clogged vascular pathways and dark brown streaks. In the early stages, roots look healthy, but they eventually rot, too.

How to Control Fusarium Wilt: Once fusarium wilt infects a plant, there is no effective treatment. Remove and dispose of affected plants immediately don't compost this garden refuse. Whenever possible, remove and replace fusarium-infected garden soil.

For tomato growers, one of the best defenses against this long-lived disease is using varieties with known fusarium resistance. Look for plant tags that include F, FF or FFF — these letters indicate resistant to the three main fusarium "races." Unfortunately, fusarium-resistant varieties aren't available for many plant types.

If fusarium wilt hits your garden, don't plant the same or related plant types in that area for at least four years.

Depending on your climate, it may be possible to control fusarium wilt by "solarizing" your soil. This involves covering it with plastic so it reaches very high temperatures over a long period. Your local extension agent can help with information on whether soil solarization is practical and effective for fusarium wilt in your area.

Fusarium Wilt Tip: Keep your garden tools and boots clean and free from soil. Contaminated tools and soles can spread fusarium pathogens to fresh soil.

Always read product labels thoroughly and follow instructions, including guidelines for treatable diseases and plants.

Protect Watermelon Plantings From Wrath of Fusarium Wilt

By Gene McAvoy | March 19, 2018

Fusarium wilt of Watermelon
Photo by Cheng-Fang Hong

Fusarium wilt of watermelon is common problem in Florida where resistant varieties are not used, but it might occur to some extent even when resistant varieties are used. Fusarium wilt is cased by the fungus Fusarium oxysporum fsp. Niveum.

Typically, the first noticeable symptom is that one side of a plant wilts. This one-sided wilt commonly occurs three to four weeks after transplanting. In older plants, there is marginal, progressing to a general yellowing of the older leaves and wilting of one or more runners. In some cases, sudden collapse occurs without any yellowing of the foliage.

On stems near the crown of the plant, a linear necrotic lesion may develop, extending up the plant and usually on one side of the vine. Infected plants have white, healthy roots, but the vascular tissue is brown and discolored. Slicing the tap root lengthwise into two equal halves will reveal two streaks of vascular tissue that are dark yellow-brown, orange brown or reddish brown. In Florida, Fusarium wilt is likely to occur prior to fruit set.

In the field, infected plants often appear in clusters.

Survival and Spread
The fungus that causes Fusarium wilt in watermelon is very specific and cannot infect even closely related plants such as cucumber and muskmelon. Fusarium forms resilient spores (chlamydospores) that can remain viable in the soil for many years. This means Fusarium wilt may appear in a field that may not have had a suitable host for several seasons.

It also means the disease will not spread from plant to plant, only from spores in the soil. Therefore, any process that moves soil may be responsible for spreading this disease between or within fields. The optimum temperature for infection is near 80°F, with little infection occurring above 86°F.

Fusarium has been found to be associated with seed, but the main importance here would be the potential of introducing a new race into the field from other areas of the world.

Management Methods
Fusarium wilt is difficult to manage. The best control for Fusarium wilt of watermelons is the use of resistant varieties coupled with crop rotation. Long rotations (five years or more) may lessen the survival rate of the fungus spores in the soil and decrease the severity of symptoms. Crop rotation is generally not totally effective because chlamydospores survive so long in the soil and the pathogen can survive in or on the roots of symptomless host plants.

Although no commercial watermelon varieties are completely resistant to Fusarium wilt, some varieties offer partial resistance, which can lessen the impact of this disease.

Fumigation can reduce the incidence and severity of Fusarium wilt but recolonization of the soil occurs very quickly.

Few fungicides are available for fusarium wilt control, but a soil application at transplant with prothioconazole (Proline 480SC, Bayer CropScience) may reduce disease in the field.

Liming the soil to pH 6.0-7.0, as well as reducing nitrogen levels in the soil, may help reduce the incidence of fusarium wilt.

Watch the video: A Few Quick Tips on Starting Watermelons. Read Below