From Clemson Plant Pathologist Tony Keinath and Extension Agent Rob Last.
Watermelon growers may find new plants with symptoms of Fusarium wilt as the plants start to set fruit or as fruit sizes up. In the infested field at Coastal REC, 3-5% of the plants previously rated as healthy showed symptoms in the past 2 weeks. A few plants collapsed completely (see below), while most plants had only one wilted vine. The heat during the week of May 15 also may have brought on symptoms if plants were water-stressed.
Extra fertilizer and water will not suppress Fusarium wilt. Plants in the CREC field received excess water and fertilizer the past 2 weeks due to a misfunctioning valve. More plants showed symptoms during this period (3-5% symptomatic plants) than before the mishap (2% symptomatic plants). Overfertilization is expensive due to current fertilizer costs and may actually harm the vines, leading to additional symptoms and yield loss.
Proper fertility might help the “good” vines on diseased plants be more productive, but that study has not been done as far as we know.
At this point in the growing season, there is nothing growers with Fusarium wilt problems can do to minimize the damage. All effective control measures require pre-plant action. Growers are encouraged to review their options for next year.