Pacific Pests, Pathogens and Weeds

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Summary

• Worldwide distribution. On watermelon (and squash), and other members of the cucumber family, including weeds. A minor disease, worse under shade.
• Small, about 5 mm, round spots with grey centres, brown margins, and sometimes yellow halos. Centres may fall out, spots merge, resulting in black areas, and leaf fall.
• Spores on the underside of the leaves are spread in wind and rain.
• Cultural control: do not plant new crops next to old; use 3-4-year rotation; weed; do not grow watermelon under shade; collect and burn trash after harvest. Chemical control: copper, chlorothalonil, or mancozeb.