Managing Diseases in Greenhouse Grown Melon Transplants

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Examine greenhouse transplants daily. Below are pictures of common diseases that show up on transplants and some advice on how to manage each disease. Additional information is available in the links.

Bacterial Fruit Blotch

The first symptoms of bacterial fruit blotch in the greenhouse is water-soaking on the undersurface of cotyledons.

Bacterial fruit blotch in watermelon transplants. Note the yellow halos around the necrotic lesions.

  • If a bacterial pathogen is present, conditions in greenhouse transplant houses are highly favorable for the development of disease.
  • Separate different seedlots, in order to reduce lot-to-lot spread if disease occurs.
  • The two most prevalent bacterial diseases on watermelon or cantaloupe are bacterial fruit blotch (BFB) or angular leaf spot.
  • Both can cause significant yield loss in the field. BFB has caused extremely high losses in the recent past.
  • If either bacterial disease is suspected, collect a sample and submit it to your extension educator, specialist, or UD or UMD plant diagnostician.
  • If BFB is confirmed, destroy all trays with symptomatic plants, and the trays that were immediately adjacent to them (this should include those that were adjoining when symptoms were first observed).
  • Some fungal diseases also can show up in transplant production: gummy stem blight, Alternaria leaf blight, anthracnose, and Fusarium wilt.

Angular Leaf Spot

Angular leaf spot on cantaloupe looks similar to bacterial fruit blotch.

Upper and lower surface of leaf with symptoms of angular leaf spot.

Links to more information:
Managing bacterial fruit blotch in the greenhouse

Managing bacterial fruit blotch in the field

Comprehensive article including disease cycle, epidemiology and management