Plant Health Problems
Cucumber is the most common member of the Cucurbit family. See Cucurbit for a detailed discussion of the other common diseases of this host.
Diseases caused by Bacteria:
Bacterial wilt, Erwinia tracheiphila.
Plants with this disease wilt quickly and may dry up so fast that the leaves remain green. When the stem is cut across, a sticky, white ooze may be seen. Bacterial wilt is not seedborne. The bacteria are carried from plant to plant by the feeding of the two-spotted and striped cucumber beetles.
Controlling the cucumber beetles will slow the spread of the bacterial wilt. Backyard gardeners may wish to cover their plants with spun-bonded polyester or floating row covers to keep out beetles. Planting extra seeds so that diseased plants may be removed at once will leave sufficient plants for a crop. Also, succession planting is helpful. Certain commercial varieties of cucumbers are somewhat resistant to bacterial wilt.
Melon aphid, Aphis gossypii.
This aphid infests many different kinds of plants both in the field and in greenhouses, but it is particularly troublesome on cucurbits. It generally makes its appearance in scattered places in the field late in the summer and may become abundant on the undersides of the leaves. When aphids are abundant, they may cause a downward twisting or cupping of the affected leaves. Honeydew from the aphids may cause the fruit to be sticky, and aphids may also transmit viral pathogens. See Aphid fact sheet.
Melonworm, Diaphania hyalinata.
On occasion, cucumber may be injured by slender, active greenish caterpillars with two narrow white stripes running the full length of their bodies. They feed mostly on the foliage, but may burrow into the fruit. They are rare, however, and no specific control measures have been needed.
Pickleworm, Diaphania nitidalis.
This insect occasionally causes damage to late maturing crops. The white, yellowish or greenish larvae have yellow brown heads and are about three-fifths of an inch long when mature. They burrow in the bud, blossom, vines and fruit. Control is not generally needed.
Spotted cucumber beetle, Diabrotica undecimpunctata howardi.
This is a minor pest that occasionally causes injury. It is somewhat larger than the striped cucumber beetle, and the wing covers are greenish yellow marked with 12 black spots varying in size and arranged in three transverse rows. The life history and control is similar to that of the striped cucumber beetle. See Cucumber Beetle fact sheet.
Striped cucumber beetle, Acalymma vittatum.
This is the most destructive insect pest of cucumbers. The beetles hibernate under trash or in the ground, and appear upon the plants as soon as the seed germinates. The greatest injury occurs to the young plants, and the beetles feed usually on the underside of the leaves.
The beetles are one-fourth of an inch or less in length, with thorax and wing covers yellow, with three black longitudinal stripes that extend to the tips of the wing covers, and with a black head and abdomen. It should be distinguished from the similarly striped female western corn rootworms, which have yellow abdomens and are not important pests of cucurbits. The adults can transmit the organisms that cause bacterial wilt. Cucumbers and muskmelons are generally susceptible to this disease, although watermelons and some varieties of squash and pumpkin are not. The eggs are laid the last of June on the surface of the ground or in crevices in the soil, and oviposition continues for about a month. The eggs hatch in about a week and the young larvae work their way downward along the main stem, where they burrow into it, causing much injury. A full grown larva is one-third of an inch long, slender and white with brown head and thorax. The adults appear again in early to mid-August. There is only one generation annually. See Cucumber Beetle fact sheet.