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Pests & Diseases
Cucumber beetles attack plants, feeding on leaves and stems, but should not be confused with lady beetles, a beneficial insect. Both striped and spotted beetles can cause damage; striped cucumber beetles can transmit diseases like bacterial wilt. The best prevention is to remove weeds or planting a “trap crop” to attract the insects away from melon plants.

Aphids cause leaves to curl and can prevent plants from growing to full size. Melon aphids, specifically, can be identified by their long legs, antennae, and range of color from yellow-green to greenish-black.

Honeydew waste secretions can cause fungal growth and attract other insects. Natural aphid enemies—such as parasitic wasps or lady beetles—can help lower populations.

Rindworms include several caterpillar species such as beet armyworm, cabbage lopper, cutworms, and tobacco budworms. They feed on stems and foliage but the more costly damage is to rinds, which may be difficult to spot. Other insect dangers include leafminers, spider mites, squash bugs, stink bugs, thrips, vine borers, and whiteflies.

Anthracnose creates small, brown-black spots on leaves and fruit. Prevention includes seed treatment, crop rotation, and fungicide applications.

Downy mildew is caused by an airborne fungus and exacerbated by heavy rains. Yellow-brown spots appear on the leaf surfaces with a brown to grey fungus on the underside.

Fusarium wilt can survive for years in sandy soils, like rootknot nematodes. As the name implies, it can be identified by wilting leaves and a yellow color on the underside of leaflets that spread to the rest of the plant. Crop rotation, avoiding excessive use of nitrogen, and eliminating debris can help with prevention. Other diseases include gummy stem blight, bacterial fruit blotch, rind necrosis, and watermelon mosaic virus.

Storage & Packaging
At 59°F to 60°F watermelon can be stored for about 2 weeks; lower temperatures (below 55°F) may add another week. Chilling injury can occur if temperatures fall below 45°F for any period of time and can cause pitting, flesh discoloration, loss of flavor, and increased decay upon return to room temperature.

In terms of shipping, various packaging options exist, but all should provide adequate cushioning and be thoroughly inspected for cleanliness and structural integrity.

References: Alabama Cooperative Extension, National Watermelon Promotion Board, NC State University Cooperative Extension, Texas A&M AgriLife Extension, University of Florida/IFAS Extension, University of Georgia Cooperative Extension, USDA.


Grades are divided into U.S. Fancy, U.S. No. 1, and U.S. No. 2; for all grades, watermelon with good external quality will be mature, well-formed, not overripe, and free from anthracnose, decay, and sunscald. Size and shape, as well as factors such as discoloration and bruising will also affect grades.

Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the USDA or CFIA inspection was timely; and (3) the entire lot was inspected.

U.S. Grade Standards Days Since Shipment % of Defects Allowed Optimum Transit Temp. (°F)
10-5-2 5

There are no good arrival guidelines for this commodity specific to Canada; U.S. guidelines apply to shipments unless otherwise agreed by contract.

References: DRC, PACA, USDA.


• Anthracnose is a free-from defect and always scored against the serious damage tolerance
• If present, anthracnose is scored against the decay tolerance when penetrating the rind or when spots are large and soft enough to give way with finger pressure
• Seedless watermelons with seeds are scored as a defect when they have more than 10 mature seeds (not to include pips or caplets) visible when cut into four equal sections (one lengthwise cut and one crosswise cut)
• Melons, being pale red or lighter in color are scored as ‘immature’ against the 5% tolerance for serious damage.

Source: Tom Yawman, International Produce Training,

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This information is for your personal, noncommercial use only.