Not known to transmit any human or animal pathogens.

Fusarium oxysporum f. sp. cubense is associated with banana root borer (Cosmopolites sordidus), which can carry the fungus to new places in and on its body. Cane weevil (Metamasius hemipterus) damage is also associated with Fusarium wilt of banana. 

Surveys for tropical race 4 should occur in banana and plantain. 

Because symptoms are similar for all races of Fusarium oxysporum f. sp. cubense, surveys in more susceptible varieties (i.e., not "Cavendish" types) are likely to detect non-targets, including non-TR4 strains already established in Florida, Hawaii, and Puerto Rico. 

No specific signs are present.

On plants that are more than four months old, yellow and wilted leaves are typical symptoms of Fusarium wilt of banana. The yellowing typically progresses from the older to the younger leaves. The yellow leaves may remain erect, split longitudinally, or collapse at the petiole and hang down along the pseudostem. The base of the pseudostem may also split. Symptoms become most obvious during formation of fruit bunches.

Banana suckers that are less than four months old are unlikely to show visible symptoms. Banana fruit do not show any specific disease symptoms.

The major way to differentiate Fusarium wilt from other causes of yellowing and wilting is by cutting into the banana pseudostem. There, the major internal symptom is a reddish-brown discoloration of the xylem, which may be restricted to one or a few columns or present in a partial ring. TR4 does not produce sporulation that would be externally visible to surveyors.

There is not a specific time for survey in established plantations. However, symptoms may become most apparent when a new pseudostem is established as the leader, or during bunch formation, which is 9-13 months after planting. If pathogen load is high in soil, new banana plantlets will die after a few weeks or months.

On the field scale, banana plants may develop symptoms in groups. Banana farms with poor biosecurity practices, such as frequent imports of international planting material and those with high non-worker foot traffic, may be good targets for survey.

Visual Survey
Visually inspect host plants throughout the survey site for yellowing banana plants with yellowing and wilting leaves. Wilted plants infected with F. oxysporum f. sp. cubense Tropical race 4 will have reddish-brown internal discoloration in cut pseudostem tissue.

Survey for symptoms of Fusarium oxysporum f. sp. cubense Tropical race 4 in banana planted in the United States.

Non-TR4 strains may occur in plantings of varieties other than "Cavendish" types.

Collect 3 to 5 pseudostem samples of at least one square inch from plants with internal vascular discoloration. Ensure tissue is fresh, not soft and rotted.

Place samples in paper bags, envelopes, or glass vials (NOT plastic bags). Spray samples with 1-2% ascorbic acid (vitamin c) solution to prevent further tissue darkening that may mask original symptoms.  

Carvalhais, L.C., Henderson, J., Rincon-Florez, V.A., O"Dwyer, C., Czislowski, E., Aitken, E.A.B. and Drenth, A., 2019. Molecular diagnostics of banana Fusarium wilt targeting Secreted-in-Xylem genes. Frontiers in Plant Science, Volume 10 - 2019.

Li, M., Jinxiu, S., Xiaoling, X., Yueqiang, L., Hongfei, W., Pinggen, X., Jianuan, Z., Shaobin, Z. and and Jiang, Z., 2013. Identification and application of a unique genetic locus in diagnosis of Fusarium oxysporum f. sp. cubense tropical race 4. Canadian Journal of Plant Pathology, 35(4): 482-493.
 

This fungus causes nonspecific yellowing and wilting symptoms, which are similar to several different bacterial diseases of banana. In the United States, leaf yellowing may most likely be caused by abiotic factors, including water stress, nutrient deficiencies, or herbicide damage. To increase the likelihood of identifying Fusarium spp., symptomatic plants should be examined for internal symptoms, especially vascular discoloration in the lower pseudostem.