Diseases That Affect Watermelon Plants

• For many people, freshly picked watermelon is one of the highlights of summer. Unfortunately, watermelons, which belong to the cucurbitaceae plant family of gourds, are vulnerable to a number of blights. Citrullus lanatus, one of the few plants classified as both fruit and vegetable, needs some protection against the diseases that commonly afflict it to make it makes it to the picnic table.
  
  

Downy Mildew

• Downy mildew begins as irregular, yellow areas on the upper surface of leaves. As the mildew progress, the center of these areas turn brown, and fuzzy gray areas may appear on the underside of the leaf. Cool temperatures combined with high humidity can result in rapid spread of this disease. The South Texas Vegetable Web recommends mefanoxam to combat mildew. A Louisiana State University Agriculture Center study suggests reducing canopy density.
  
  

Anthracnose

• Long, shallow, tan stem lesions combined with brown or black leaf spots signal the presence of anthracnose. Sunken, water-soaked lesions on the fruit may turn black. Like gummy stem blight, anthracnose can survive on infected plant residue. Deep burrowing is recommended to prevent recurrence of the disease, as well as rotating away from members of the curcubit family.
  
  

Gummy Stem Blight

• The fungus Didymella bryoniae causes large, circular dark brown spots on leaves and gummy brown cankers on the stems, as well as water-soaked lesions on the fruit itself. In some cases, tiny, round, black structures (pycnidia) may be visible within the lesions. The LSU Agriculture Center advises suggests avoiding this blight by using treated seeds, thoroughly cleaning any infected plants out of your garden and rotating crops every two to three years.