Fusarium wilt symptoms include damping off of plants in fields with high infection, or wilting at later stages. The wilting symptom can start on one side of the plant (unilateral).
Symptoms of Fusarium wilt that can be seen are yellowing and wilting on transplants. This may be due to the use of contaminated seed, seedling trays, potting media or equipment.
In the pathogen population is in high numbers in the soil and cool weather conditions, symptoms of wilting can show within a short period of a week to 2 weeks after transplanting.
Stunting and wilting of plants. Infected watermelon vines stay behind and remain green for a short period, then turn yellow and progressively desiccate until wilted plant is completely brown.
Vascular discoloration of the stem at the base of the plant is a characteristic symptom of Fusarium wilt. However other soil-borne vascular pathogens can also cause this symptom.
Sometimes, gummosis can be observed protruding from split stems of affected plants. This symptom is often observed when plants are infected with gummy stem blight.
Characteristic of many Fusarium oxysporum f. sp. niveum isolates is pink coloration of mycelia (fungal strands), but rarely seen is pink discoloration of the vasculature.
Older runners often succumb to the disease (unilateral infection). Eventually, wilted runners at the base of the plant are covered by the survivor runners or other plants.
Moderate wilting gives the watermelon plant a dull-green appearance in the field. Wilting leaves are soft to the touch while healthy leaves feel crunchy and look bright green.
Stunted plants and patchy growth from Fusarium wilt can result in poor ground coverage as seen in a watermelon field in Florida. This pattern can vary from field to field.
Under cool conditions and the presence of the pathogen in the soil, Fusarium wilt can cause wilting of plants, but tends to be randomly present or in certain sections of the field than the entire field.
Affected plants with non-symptomatic, and symptomatic leaves. Plants may recover from wilting as soil temperature increases, but the infection could delay fruit maturity and reduce yield.
A hotspot of Fusarium wilt in a field. Vine thinning and wilting leave fruits exposed to sunburn. This has a direct impact in reducing total marketable yield of watermelon.
Cut sections of the watermelon stem can be placed on an agar medium for checking for the growth of the fungal pathogen which will indicate growth of the fungus in the vasculature.