New Work On Chemical Management Of Fusarium Wilt In Watermelon

Nathan Kleczewski Ph.D
Extension Specialist- Plant Pathology
Assistant ProfessorDepartment of Plant and Soil Sciences

Fusarium wilt of watermelon, caused by Fusarium oxysporum f.sp. niveum (FON), is the most important and severe soilborne disease of watermelons.  As growers know, this plant pathogen, once established in a field, is battled yearly.  This is because the fungus produces special overwintering structures that are resistant to environmental stress and persist in the soil for upwards of 10 years.  FON infects seedling roots, eventually moving into the vascular system.  The activity of the fungus eventually disrupts the function of the vascular system, resulting in wilt of vines.  Although single runners can be affected, it is not uncommon to see entire plants wilted and dead as a result of FON.  Plants that are able to survive infection often are stunted and produce fewer or smaller fruit.  For more information on Fusarium wilt of watermelons, see my article in Plant Health Progress.

Growers have limited options for managing Fusarium wilt.  The most common practice is to utilize diploid varieties with resistance/tolerance to FON race 1, the most commonly found pathogenic race; however, race 2 and 3, which are highly aggressive, are found at high levels in watermelon fields in Delaware and Maryland, as well as other areas where watermelons are produced.  These races can overcome resistance to FON race 1.  In addition, an increase in seedless watermelon production has resulted in more outbreaks of Fusarium wilt in watermelon.  This is because most of our seedless watermelon varieties lack resistance to FON race 1.  Other practices such as increasing the organic matter in soils through cover crops, avoiding excessive use of nitrate, and scouting transplants and fields can also help to reduce the impacts of Fusarium wilt on watermelon.

Research presented in a new paper published in the journal Crop Protection examined the efficacy and utility of Actigard and several fungicides in the greenhouse and field in several locations throughout the United States over a 3 year period.  A total of 13 fungicides were evaluated  on the FON susceptible cultivar Sugar Baby.  Fungicides with the greatest performance in greenhouse trials were evaluated in the field using different techniques, rates, and number of applications.  Overall, the study showed that prothioconazole and thiophanate-methyl were the most effective fungicides and that severity of Fusarium wilt can be significantly reduced when fungicides are applied through the drip.  The study indicates that three applications through the drip are likely to result in the greatest amount of disease suppression.  A supplemental label was recently recieved for Proline (prothioconazole) for use through the drip in some states, including Maryland and Delaware.  This gives growers an additional tool for managing Fusarium wilt in watermelon.

Source : udel.edu