Fusarium Wilt of Watermelon in the Southern US in 2013

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I have been receiving reports of severe watermelon Fusarium wilt from states south of us. A small part of the increase has been due to infected transplants. However, most cannot be traced to transplants. Severe wilt has occurred in fields that have not had watermelon in them for 5, 7, or even 10 years. In one field, a cultivar that was resistant to race 1 of Fusarium oxysporum f. sp. niveum, had severe wilt.

There are several reasons why this may be occurring. For many years growers applied MeBr or other fumigants, there were good genetics in most diploid (seeded) cultivars, and race 1 was likely the predominant race. It is still a little early, and cold to see high Fusarium wilt incidence here on Delmarva. That could change rapidly in the next few weeks. Be on the lookout for symptoms – and remember that other pathogens such as Pythium can cause similar symptoms. Get a diagnosis if you are unsure of the cause.

Fusarium wilt must be managed with multiple tactics. The following are recommendations to minimize the disease:

● Use resistant watermelon cultivars (even if they only have resistance to race 1). Also, use resistant pollenizers.

● Rotate fields at least 5 years between watermelon crops.

● Fumigate if economically feasible.

● Fertilizer can impact wilt: lime to maintain a pH of 7.0, and use nitrate instead of ammonium nitrogen.

● Avoid diseased transplants.

● Consider planting a hairy vetch or crimson clover cover crop in the fall before your watermelon crop and incorporating it as a green manure in the spring. Both cover crop species have suppressed Fusarium wilt in our trials.