Resistant Varieties

Resistant or tolerant varieties of most species are available, and should be used where powdery mildew is likely to be a problem. Several safe chemicals are effective against powdery mildew.

Scab is caused by a fungus which attacks the fruit, particularly cucumber, but it may occasionally damage young squash fruits. Sunken, dark brown, irregular spots appear on the fruits from which a gummy substance is extruded. The young fruits become malformed and cannot be used.

The disease spreads rapidly in cool, moist weather. It is most serious on cucumbers in the northern tier of States (Wisconsin, Michigan, Minnesota, New York and Maine). Good garden sanitation and use of resistant varieties should successfully solve this problem for the home gardener.

Mosaic caused by virus is one of the most widespread and serious diseases of cucurbits. Characteristic symptoms are light-green mottling of the leaves, and the younger leaves are malformed, dwarfed, and slightly curled. With late infection, the symptoms are mild and little harm is done to the crop. Vines infected in early stages of development normally are dwarfed, the leaves and flowers malformed, and they do not produce acceptable fruit.

There are roughly two classes of virus that attack cucurbits. (1) Watermelon mosaic viruses which are not seed-borne, and are spread by sucking insects chiefly aphids. (2) Squash mosaic viruses, which are seed-borne and are spread by chewing insects chiefly cucumber beetles.

The watermelon mosaic viruses are destructive pests of cucurbits because they are spread by aphids, and it is almost impossible to deny aphids access to home gardens. Apparently the virus is carried by several widely grown ornamentals, so sources of the virus are always present. Control is difficult, although there are resistant or tolerant varieties of cucumber, but resistance breeding programs in other species are not well-developed.

Control of the squash mosaic viruses can be established by planting virus-free seed. Also, controlling cucumber beetles and other chewing insects prevents dissemination of the virus.

Root knot disease is caused by minute eelworms or nematodes which enter the roots where they feed and breed. Feeding causes the root tissues to swell, producing nodules or galls on the roots. Some galls are small, others may be the size of a walnut. Plants become dwarfed, unthrifty, and often turn yellow and die. Soil heavily infested with nematodes should be fumigated, using one of the several nematocides that are effective when properly applied. Fumigation will reduce the population of nematodes to a point where good crops can be grown for at least 1 to 2 years. Some control can be obtained by crop rotation, that is, by not planting susceptible crops in the same soil for 3 to 5 years. Much research has been done, but resistant varieties are not yet available.

Cucumber beetles, both striped and 12-spotted, are common pests in most gardens. It is important to control them because the adults seriously damage or totally destroy the plants,

and their activities also spread certain diseases of cucurbits (bacterial wilt, squash mosaic). Additionally, the larvae bore into roots and stems below the soil line, often causing the plants to suddenly wilt and die. There are satisfactory chemicals that will control these insects, but they must be applied at the first appearance of the beetles for acceptable control.

Aphids----small, fragile, soft-bodied insects with sucking mouth parts can be a problem on cucurbits during the course of the growing season. Aphids come in several colors, such as black, green, yellow, or pink. They feed on the undersides of leaves, causing a curling or cupping. With severe infection, the leaves become sticky, lose color, and the, plant dies. Winged females fly from plant to plant, establishing new colonies. Aphids can be controlled by chemicals, but be sure to use those insecticides that are least harmful to aphid predators.

Banded cucumber beetle.

The squash bug is a troublesome pest of squash and pumpkins, and Occasionally attacks gourds. Adults and the immature forms (nymphs) suck the sap from leaves and stems,

causing the plant to wilt and die. The adult bug is about a half inch long, and dirty brownish, or black. The nymphs are much smaller and steel-grey. The female deposits the relatively large and brownish eggs in regularly arranged masses on the underside of the leaves.

Good plant sanitation helps control this pest. Promptly remove and destroy debris from cucurbit vines and fruit. You can trap the bugs by placing a shingle or board at the base of the plants. The bugs collect here during the night, and can be destroyed the following morning before they become active. Also, searching out the egg masses and destroying them can be helpful. Insecticides are effective against heavy infestations.