Causal Agent: 

Fungus (Fusarium oxysporum f.sp. niveum)

Characteristic Symptoms:
 
Affected plants show general leaf yellowing starting with the older leaves that eventually wilt.
   
Once wilting occurs, the foliage becomes desiccated and necrotic and the plant may die within 2-3 days.
   
Vascular discoloration of infected stem and roots are important diagnostic symptoms.
   
One-sided wilt may also occur.
   
Conditions for Disease Development:
 
The pathogen is soil-borne and is host-specific (i.e., infects only watermelon).
   
The pathogen is disseminated primarily by movement of infested soil or diseased plant parts and contaminated seed.
   
Infection occurs through the root, primarily in the area of elongation, and is aided by wounds created by insect/nematode feeding.
   
The disease is most severe in light, sandy soils with pH 5.5-6.5), high nitrogen content and available soil moisture of less than 25%.
   
Disease incidence and severity is high when temperature is around 25-27°C.
   
The pathogen may be seed-borne.
   
Management and Control:
 
Avoid planting in contaminated land or area with previous history of high FW incidence or do not plant watermelon on the same area for a minimum of 5-7 years.
   
Remove wilted plants including roots as soon as symptoms are observed to minimize spread of disease.
   
Control root-knot nematode and root-feeding insects since they may help in disease establishment and spread.
   
Use resistant/moderately resistant varieties, if available.
   
Use resistant rootstock in grafted seedlings.
   
Increase the soil pH by liming and reduce nitrogen level in the soil.
   
Biofumigation of soil using chopped mustard leaves can help reduce inoculum level in the soil.
   
References:
Compendium of Cucurbit Diseases (1996) by the American Phytopathological Society
   

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