Pests & Diseases Affecting Home Grown Melons
Melons are closely related toand suffer from many of the same . Disease flourishes particularly in moist conditions and the worst problems usually occur in cold years when the air has been continually damp around the melons because no ventilation has been given. If you are forced to use a chemical spray, be careful. Melons, like most members of the Cucurbitaceae family, are sensitive to some chemicals. Check the label before you spray.
Red spider mite: melons do not escape the attentions of this common pest. The small red mites can just be seen on the underside of the leaves which become grey-brown speckled, and yellow in bad attacks. In very serious attacks the plants themselves wilt. Unlike most melon diseases, however, the mites dislike damp, cold conditions and are unlikely to be a problem in coldish years. In hot weather, prevent attack by spraying with water.
Greenfly: the only other pest which is likely to be a serious problem on melons is greenfly. These little green insects collect on the growing point and on the undersides of leaves, where their attacks result in curled, discoloured leaves and stunted plants. They may also spread virus disease. Spray with derris, or bioresmethrin.
Collar rot: probably the most serious disease affecting melons. Soil borne bacteria attack the base of the stem, causing it to decay and become soft and messy. The leaves wilt and the plants die. Prevention is better than cure with collar rot, and the most important point is to keep thearound the base of the stem fairly dry. Do this by planting on mounds and by watering through pots buried in the mounds. Lightly infected plants may be saved by watering with Cheshunt compound, but it is not worth trying to save badly infected plants. Pull these up and dust the soil around adjacent plants with benomyl or captan.
Wilt: the symptoms of wilt are similar to those of collar rot but with wilt the base of the stem is not infected. Instead, wilt is the result of soil-borne fungi which rot the root. There are two different fungi which cause wilt and they respond differently to temperature. Plants attacked by the fungus Fusarium may recover if the temperature is raised. Try raising it to at least 24 C (74°F). If they continue to wilt, the other wilt fungus, Verticillium, is likely to be responsible and high temperature will make them worse. In this case, shade the plants and decrease the temperature, with improved ventilation. Watering with Cheshunt compound may also help against both wilt diseases. Little can be done for serious attacks, however. In these cases pull up and burn the plants.
Botrytis cinerea (Grey mould): a fluffy grey mould on the stem, fruits and leaves is a sign of attack by this fungus. It likes damp stuffy conditions so give extra ventilation. Spray infected plants with captan or benomyl.
Powdery mildew: this thrives where plants are kept short of water, especially in poor ventilation. The disease appears as a whitish powder on the surface of the leaves and in severe cases the leaves turn yellow. Stems and fruit may also be affected. Spray with sulphur or dinocap.
Leaf blotch: this disease starts as small, pale spots on the leaves. The spots rapidly increase in size and number and destroy the leaves. Leaf blotch is serious and cannot be easily controlled, though sometimes dusting with flowers of sulphur may help. Pull up and destroy infected plants and if possible sterilise the soil.
Virus: melon virus produces a yellow mottling on the leaves, which occasionally also produce wart-like outgrowths. The fruit may also be discoloured. As with all viruses, there is no cure but as the virus is normally spread by greenfly, the best protection is to control these pests. Infested plants should be lifted and destroyed.
Watermelons are completely different. They belong to a totally different species. Citrullus vulgaris, and in temperate regions can only be successfully grown in greenhouses.