Bacterial fruit blotch (BFB) is a disease caused by the pathogen Acidovorax avenae subsp. citrulli. Most cucurbit crops are affected by this disease, although watermelon cultivars are commonly more susceptible. However, this summer, I received cantaloupe samples (Figures 1 and 2) that tested positive for BFB using serological tests.
Figure 1. Immature cantaloupe fruit showing circular water-soaked and sunken lesions (Photo by Cesar Escalante).
Figure 2. Mature cantaloupe affected by bacterial fruit blotch. Note flesh rot caused by bacterial infection (Photo by Cesar Escalante).
When environmental conditions are conducive, BFB can be a serious problem during the seedling stage, causing collapse of the foliage after development of water-soaked spots on lower surface of cotyledons and leaves. However, symptoms caused by BFB are more distinctive in the fruits, where they initiate as small water-soaked spots. When the disease is more advanced, symptoms in watermelon are usually different from those in cantaloupes. In watermelon, the water-soaked lesions are bigger, with irregular shapes, enlarged, and occasionally accompanied by cracking (Figure 3), whereas in cantaloupe, small and circular water-soaked lesions and sunken spots persist (Figure 1). Fruits affected by this bacterium are unmarketable due to flesh rot (Figure 2).
Figure 3. Watermelon fruit with enlarged and irregular water-soaked lesions and cracking (Courtesy of Dan Egel; originally published in the Southwest Purdue Ag Program website, Vegetable Disease Photos).
The causal agent of BFB is transmitted through seed; therefore, planting certified and clean seed is crucial. Use sanitized equipment during greenhouse handling activities. Inspect seedling lots for BFB symptoms before transplanting them in the field. The pathogen causing BFB can survive in the soil for a long period. Therefore, allow a 3- to 5-year rotation with non-cucurbit crops. Bactericides such as copper-based products and Actigard – 0.5WDG (acibenzolar-s-methyl) can be applied in the field. Consult the 2024 Midwest Vegetable Production Guide to learn more about product application recommendations.