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Melon Growing Problems: Troubleshooting

Melon watermelon1
Melon problems
Melon Growing Problems: Melons thrive in very warm weather and need consistent moisture to grow to maturity.

Muskmelons, cantaloupes, winter melons, and watermelons: they all thrive under the same cultural conditions and they all share similar growing problems.

Cantaloupes are muskmelons: these melons have pumpkin-like ribbing, a skin covered with a netting of shallow veins, and most varieties have a musk smell.

Winter melons (which are a type of muskmelon) ripen at the very end of summer as the weather turns cool: honeydews, crenshaws, casabas, and Persians.

Watermelons–which are a different botanical family than muskmelons and winter melons–share all of the growing requirements.

Melon Problems and Solutions:

Leaves curl under and become deformed and yellowish. Aphids are tiny, oval, and yellowish to greenish pear-shaped insects that colonize on the undersides of leaves. They leave behind sticky excrement called honeydew which can turn into a black sooty mold. Use insecticidal soap.

Leaves turn pale green, yellow, or brown; dusty silver webs on undersides of leaves and between vines. Spider mites suck plant juices causing stippling. Spray with water or use insecticidal soap or rotenone. Ladybugs and lacewings eat mites.

Leaves yellow; tiny white winged insects around plants. Whiteflies will congregate on the undersides of leaves and fly up when disturbed. Remove infested leaves and the whole plant if infestation is serious. Introduce beneficial insects into the garden.

Coarse white speckling or stippling on upper surface of leaves; leaves may brown. Leafhoppers are green, brown, or yellow bugs with wedge-shaped wings. They suck the juices from leaves and stems. Use floating row covers to exclude bugs; spray with insecticidal soap.

Trails and tunnels in leaves. The leafminer larvae tunnel inside leaves. Destroy infected leaves and cultivate the garden to destroy larvae and keep adult flies from laying eggs. Cover crops with floating row covers.

Water-soaked blotches on leaves–not enlarging past leaf veins; water-soaked spot can appear on fruits Angular leaf spot or bacterial spot is a waterborne bacterium which causes irregular geometric patterns on leaves. Spots may turn yellow and crisp. Avoid wetting foliage with irrigation. Prune off infected leaves and stems. Clean up garden. Plant disease-resistant varieties. Rotate crops up to 2 years.

Knots, galls, or swollen beads on roots; plants wilt; poor yield. Nematodes are microscopic worm-like animals that live in the film of water that coats soil particles; some are pests, some are not. Root-knot nematodes feed in the roots and stunt plant growth. Most common in sandy soils. Rotate crops. Solarize the soil with clear plastic in mid-summer.

Holes chewed in leaves, leaves skeletonized; runners and young fruit scarred. Spotted cucumber beetle is greenish, yellowish, ¼ inch (7mm) long with black spots and black head. Striped cucumber beetle has wide black stripes on wing covers. Hand pick; mulch around plants; plant resistant varieties; dust with wood ashes.

Leaves have yellow specks that turn brown, then black; vines wilt from point of attack. Squash bug is a flat, shield-shaped black or brownish bug with a triangle on its back; it sucks juices from plants. Trap adults beneath boards in spring, hand pick and destroy.

Round white powdery spots and coating on leaves. Powdery mildew is caused by fungal spores. Spores germinate on dry leaf surfaces when the humidity is high; spores do not germinate on wet leaves. Common in late summer or fall but does not result in loss of plant. Avoid water stress. Pick off infected leaves.

Irregular yellowish to brownish spots on upper leaf surfaces; grayish powder or mold on undersides. Downy mildew is caused by a fungus. Improve air circulation. Plant resistant varieties. Rotate crops. Keep garden free of plant debris.

Mottled, distorted leaves. Mosaic virus causes leaves to become thickened, brittle, easily broken from plant; plants are stunted and yields are poor. The virus is spread from plant to plant by aphids and leafhoppers. Remove diseased plants. Remove broadleaf weeds that serve as virus reservoir.

Early flowers don’t set fruit. A couple of possible reasons: (1) There may not be enough pollinators, mostly bees. Hand-pollinate using artist’s paintbrush. Bee activity may be low because of cool weather or insecticides.

Fruit is misshapen or flavor is bitter. Several possible reasons: (1) Inadequate pollination: be sure bees and pollinators can get to flowers; (2) dry soil: keep the soil evenly moist while melons are developing; use drip or trickle irrigation in drought and mulch to retain soil moisture; (3) high temperatures: temperature swings of 20° or more can cause bitter flavor; keep soil mulched; (4) poor soil fertility: add aged compost to planting beds and side dress melons with aged compost.

Plants wilt and die beginning with crown or older topmost leaves. Verticillium wilt is a soilborne fungus. Light brown streaks can be seen in stem split lengthwise. Rotate crops. Avoid soil previously planted in cucumbers and family members, potatoes, peppers, eggplant, and tomatoes.

Vines wilt suddenly and die starting with one or two leaves. Bacterial wilt clogs the circulatory system of plants. It is caused by bacteria that is transmitted by cucumber beetles and is seen often where the soil stays moist. Remove and destroy infected plants before the disease spreads. Control cucumber beetles with rotenone or sabadilla. Wash hands and clean tools with a bleach solution.

Plants are stunted and yellow; runners turn yellow and wilt gradually die. Entire plant collapses. One-sided brown lesion may form on affected runner for 1-2 feet. Fusarium wilt is a fungal disease which infects plant vascular tissues. Fungal spores live in the soil and can be carried by cucumber beetles. Plant disease-resistant varieties. Rotate crops. Remove and destroy infected plants. Fungicides are not effective

Water-soaked spots–sunken, brown or black–on fruit. Belly rot, bacterial spot or blight, blossom end rot. Remove and destroy infected fruits. Remove all plants and plant debris at the end of the season. Promote good drainage adding organic materials to planting beds. Keep the soil evenly moist; mulch to retain soil moisture. Avoid over-head watering. Rotate crops.

Plants produce few fruits, mostly foliage. Plants are likely spaced too close together. Space plants at recommended distances, 8 to 12 inches apart. Plant spaced too close or too far apart yield fewer fruits as a result of poor pollination.

Melon Growing Success Tips:

Planting time. All melons require a growing season of at least 100 frost-free days. Plant melons when the soil has warmed to 70° to 80°F. To jump start the season start seed indoors 2 to 4 weeks before transplanting into the garden.

Planting. Grow melons in full sun with plenty of air circulation. Melons must stay warm and dry to prevent disease and grow quickly and uninterrupted. Grow melons in loose, well-drained soil rich in organic matter. Prepare planting beds with aged compost and side dress with compost during the growing season. Grow melons on raised hills: 4 to 6 feet apart for muskmelons, 6 to 12 feet apart for watermelons. Thin to 2 to 3 melons per hill or fewer.

Care. Mulch to keep down weeds. Water to keep melons evenly moist; do not let the soil dry after transplanting or as fruits develop. Male flowers will appear first followed by female flowers. Give melons manure tea when fruit sets and again about two weeks later. Don’t allow new flowers to develop after midsummer; let the plant concentrate it growing efforts on fruit that can mature before the end of warm weather.

Harvest. Muskmelons and cantaloupes that smell ripe are ripe. They shoud come away clean from the vine little pressure. Thump a watermelons to determine if it is ready for picking: a ripe watermelon will make a dull thump.

More tips: How to Grow Muskmelons and Cantaloupe and How to Grow Winter Melons.

 

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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  1. We gave the horse some seedless watermelon and got a vine to grow. The first watermelon fell off the vine, but it is white inside, and sort of cucumber/watermelony water flavored. Most of the fruit was beautiful, but it did sort of have a higher pitched thump.

    Will this continue to ripen, or is it just “wild watermelon” like they say, and flavorless ?

    • Most seedless watermelons are hybrids–check out the seed packet to see; hybrids generally do not grow true to the seed from the parent. It is likely, you will not again see the melon that the original hybrid spawned.

    • True cantaloupes–sometimes called European cantaloupes–mature with gray-green skins that are not netted. Their botanical name is Cucumis melo cantalupensis. The fruits Americans call cantaloupes are muskmelons; they have netting. Check your seed packet to be sure which type you planted; then check the days to maturity to know if your fruit is near or past maturity. Gently lift the melons; if the fruit naturally slips off the plant, it’s ready. You can also sniff the blossom end of the fruit, which will smell fruity when ripe; the blossom end will also be slightly soft when ripe.

  2. I have a lot of luck growing pumpkins, squash, and cucumbers. But I cannot seem to grow watermelons or cantaloupe. This year I had some good starts I planted around May 15th; and the plants died. The story of my melon experience. The pumpkin plants I planted at the same time are doing good.

    • Depending on your USDA Zone, May 15 may be a tad early for melons. We are in Zone 9a and set melons out in early June. Be certain nights are staying warm before setting melons in the garden. You can help melons by placing aluminum foil or another reflective material around the plants–especially early in the season; black plastic or stones near the plants will also absorb solar heat and release the warmth at night. When setting out melons, give the transplants a dose of B1 vitamin (get it at the garden center) to guard against transplant shock.

    • You can use leaves as long as they are not infested with insect pests or diseases. Any organic mulch across the garden surface will slow soil moisture evaporation and keep the soil from growing too warm. Melons like heat; the heat will speed ripening. Be sure to keep the soil evenly moist so that the melons can uptake water without interruption.

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