This bacterial disease occurs wherever cucurbits are grown, but is especially troublesome in humid areas. Cucumbers, muskmelons, and summer squash are most susceptible. Infection appears first as watersoaked lesions on the undersides of leaves. The spots grow between veins, taking on an angular shape. Spots turn straw-colored or brown, and eventually dry up and fall out, leaving ragged holes in leaves. Spots may exude a milky fluid that dries on leaf surfaces. Fruit and stems may also be affected. The disease overwinters on seed and plant residues. Splashing water spreads bacteria among plants.
Use at least a 2-year rotation. Grow resistant varieties and use seed stock grown in arid climates. Use drip irrigation rather than overhead watering. Avoid working in garden when plants are wet. Destroy infected plants and those adjacent to them to prevent spread.
Photo courtesy of Howard F. Schwartz, Colorado State University, Bugwood.org