The gram-negative bacterium Acidovorax citrulli causes bacterial fruit blotch (BFB) disease of cucurbits, which represents a serious threat to melon and watermelon production worldwide. To date, there are no efficient means to manage the disease, and reliable resistance sources for cucurbit germplasm are lacking. Mineral nutrition markedly affects plant diseases. Recently, we reported that disease severity on melon foliage and A. citrulli growth in the leaf tissue were significantly influenced by the form of nitrogen supply. In the present study, we investigated the influence of potassium nutrition on BFB severity and A. citrulli establishment in the foliage of melon plants. Fertilization with relatively low concentrations of potassium increased these variables compared with higher potassium concentrations. Since establishment of A. citrulli during the growing season is assumed to increase the incidence of fruit infection, the fact that mineral nutrition influences BFB incidence in the plant foliage is of particular importance.