P&PDL Picture of the Week for
July 15, 2013

What’s Wrong with These Watermelons?

John Orick Purdue Master Gardener State Coordinator, Department of Horticulture and Landscape Architecture, Purdue University

Diagnosing plant problems can be very tricky! Being a plant problem “sleuth” requires asking a lot of questions in order to learn about the plant, its growth habits, its growth environment, the gardener’s past care of the plant, the history of the problem, and any other information that might be helpful. Here are some good questions to ask as you attempt to diagnose plant problems:

  • How long has this plant looked like this?
  • When did you plant it?
  • What’s the soil type? Does it hold water or is it well-drained?
  • Were any other plants affected?
  • Did you apply any fertilizer or pesticides? What products did you apply and how much?
  • What plant species is this? What is the variety?
  • Is the damage random or uniform?
  • What is normal growth for this plant?

These are all great questions to ask, but the first strategy for diagnosing a plant problem is to recognize normal growth for that plant species, variety or cultivar. Sometimes, what we don’t know about the plant in question can lead to a false diagnosis. Plant problem “sleuths” must ask questions and know what normal growth looks like for that specific plant species, variety or cultivar before determining if the plant even has a problem.

So, I haven’t answered the question, “What’s wrong with these watermelons?” Well, there is nothing wrong with these plants. The photos show the normal visual characteristics for the heirloom watermelon variety, Moons and Stars. The primary characteristic of this variety are the yellow spots of various sizes which appear on the leaves. At first look and without more information, a gardener might think a fungal disease is attacking their prize watermelons. In this case, asking for information about the species variety and knowing what normal growth looks like for this plant answers the question and puts a gardener’s mind at ease.

Click image to enlarge

Wide view of Moons and Stars watermelon leaves

Closeup of Moons and Stars watermelon leaves

Closeup view of Moons and Stars watermelon leaves

All Heirloom watermelon 'Moons and Stars' photos were taken by John Orick at the Master Gardener Association of Tippecanoe County demonstration gardens in Lafayette, IN.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service