Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu, Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu and Karen Rane, Extension Specialist Entomology, University of Maryland rane@umd.edu
Fusarium crown rot on watermelon, caused by Fusarium solani, was observed this past week in one field on Delmarva and is suspected in others. The first sign of an affected plant is leaf wilt, which is eventually followed by vine wilt and plant death. However, unlike Fusarium wilt caused by F. oxysporum f. sp. niveum, the vascular system in crown rot infected plants is not discolored. Examination of the stems reveals dark reddish to brown surface discoloration and a restriction of growth at the soil line. (The external stem discoloration is not diagnostic though, as several diseases and non pathogenic causes can lead to similar symptoms). Fusarium crown rot is more common on squash and pumpkin than watermelon and muskmelon, but all cucurbits are susceptible. However stress can lead to high disease levels in watermelon some years. For example the disease was prevalent on watermelon in 2008. The pathogen that causes Fusarium crown rot will not survive more than three years in soil. Fields with confirmed crown rot should not be planted to any cucurbit for four years.
Figure 1. Fusarium crown rot on a watermelon plant.