• Watermelon wilt is caused by Fusarium oxysporum f. sp. niveum (FON), which infects only watermelon.
• Races of FON
• There are four known races worldwide:
  1. o Race 0: Earliest, many old varieties were susceptible.
  2. o Race 1: Common observed pathogen, some varieties show resistance.
  3. o Race 2: More aggressive, overcomes resistance to race 1.
  4. o Race 3: Most virulent among all races.
• In India, Race 1 and Race 2 have been reported infecting watermelon.

• Fusarium oxysporum f. sp. niveum becomes more severe in light, sandy soils low in organic matter, especially at slightly acidic pH (5.5–6.5) and optimal soil temperature of 25–27 °C.
• When drought is followed by sudden irrigation/rain, stressed roots get minor damage and release more exudates, making them more prone to Fusarium infection.
• Continuous cultivation of watermelon in successive seasons allows fusarium to persist and accumulate in the soil over the years.
• In the presence of the Root-knot nematode, watermelon roots are damaged, which forms galls, and reduces water and nutrient uptake. The wounds they create make roots more vulnerable, allowing Fusarium to enter easily. Together, nematodes and Fusarium impose a combined stress that greatly increases wilt severity.

• Fusarium wilt in watermelon (caused by FON) begins with early symptoms such as sudden wilting or damping-off in seedlings, where young plants may collapse and die.
• In older plants, the first signs include temporary daytime wilting and yellowing of older leaves, with partial recovery in the morning.
• As infection advances, wilting becomes permanent, one or more runners die, and symptoms often start on one side of the plant, giving a unilateral wilt pattern before full collapse.
• Internally, characteristic reddish-brown vascular discolouration appears in the xylem.
• Stems may show cracks or crown lesions with brownish gum.
• Affected plants become stunted, fruit set declines, and fruits that develop are usually smaller and poor in quality, leading to major yield loss.

Because FON is soil-borne, persistent, and may have multiple races (including aggressive ones), management requires an integrated strategy combining cultural, biological, and (as needed) chemical approaches

Cultural Management

• Avoid planting watermelon (or other cucurbits) in the same field repeatedly. Rotation with non-susceptible crops helps reduce inoculum build-up.
• Since light sandy soils, low organic matter and slightly acidic or sub-optimal pH favour FON wilt, improving soil with organic amendments, maintaining good drainage, and avoiding waterlogging or prolonged moisture stress helps.
• Avoid physical root injuries or damage, which can facilitate root invasion by a pathogen.
• Excessive nitrogen fertilisation (especially ammonium-N) may exacerbate wilt severity.

Biological Management

• For fields with a history of Fusarium wilt, apply 150 kg of Multiplex Annapurna as a basal dose to strengthen soil health and reduce disease risk.
• Using bio agents such as Multiplex Nisarga aat 4 Kg/ acre, Multiplex Bio-Jodi at 5 Kg/ acre and Multiplex Safe Root at 5 kg/acre helps in limiting pathogen and root-knot nematode activity, reducing disease progress.

Chemical Management

• Soil drenching with fungicides such as Multiplex Nagcarzim at 2 g/l, Multiplex Jodi at 2 g/l, or Multiplex Vishesh at 2 g/l (which can be used for both foliar spray and drenching) provides effective control of the disease.
• Additionally, Multiplex Duo Care at 1 ml/l may be applied as an early-season foliar spray for better protection.