Roots often appear black and infected plants may die before flowering. The bacteria persist in plant debris in the soil and can infect nasturtiums through the roots. Control strategies are aimed at prevention. However, removing and roguing of diseased plants is critical. It is also important to avoid overhead irrigation since these bacteria are easily spread in splashing water.
Crop rotation is also effective since planting in clean soil gives best control.
It is therefore helpful to avoid planting in areas used for other plants that are susceptible to the same disease, i.e., tomatoes, potatoes, eggplants, zinnias, dahlias, chrysanthemums, and marigolds. Bacterial leaf spot, Pseudomonas sp. Small brown to black spots appear on the leaves. These may have water-soaked margins. This disease can be minimized by improving air circulation by thinning the plants and by avoiding overhead irrigation since these bacteria are easily spread in splashing water.