A bacterial disease called watermelon fruit blotch has appeared occasionally in Iowa. Symptoms often appear at midseason as water-soaked or coffee- colored stains on fruit. The stains develop cracks, and secondary microorganisms can then invade and rot the fruit. In some cases, infected fruit actually split open. Economic losses in an infected field can be very high; even fruit that show only the staining are unsaleable. The seedborne nature of the disease means that can it can be brought into a field on infected seed or transplants.
Watermelon fruit blotch symptoms were found on seedlings this spring by transplant producers in the southeastern U.S. The source of the outbreak is apparently seed of a Harris-Moran variety, "Millionaire." Some suspect transplants found their way to Iowa fields. However, tests of the transplants, which had blackening at the leaf margins, were negative for the pathogen, and the symptoms were not characteristic of the seedling phase of watermelon fruit blotch, which is typified by watersoaked areas on the foliage and abundant bacterial streaming under the microscope. With any luck, we have dodged the bullet. Needless to say, "Millionaire" seed and transplants have been withdrawn from sale. No other varieties have been implicated at this time.
This article originally appeared in the May 25, 1994 issue, p. 80.