What is a Cucumber Worm?

A cucumber worm is a white worm that tunnels its way into cucumbers and other fruits and vegetables, leaving waste or “frass” at the entry point. Other affected fruits and vegetables include squash, cantaloupe, pumpkins, and watermelon. The cucumber worm is the larva of the cucumber beetle. The cucumber beetle, also “striped cucumber beetle” flies from its hibernating location early in the crop season. Before plants have a chance to fully emerge, the cucumber beetle eat off the stems, which eventually kills the plant. Later, the adults feed on the leaves, vines, and the actual fruits of plants that manage to survive. The beetles will make deep pits in the rinds of fruits and vegetables making it impossible to sell them on the market.

Adult cucumber beetles will also feed on peas, corn, beans, and other plants. They will feed on host plant as well. Mush like the human immune system, this weakens the plants defenses, making it susceptible to a host of other problems. The cucumber worm and beetle also carry a number of viruses such as “squash mosaic virus” and “cucumber mosaic virus (CMV).”

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Cornell University, Department of Plant Pathology offers the following descriptions of both viruses:

Squash mosaic virus (SqMV) can cause an important disease of melons and squash crop. The virus is seedborne in muskmelon and is spread in nature principally by the spotted and striped cucumber beetles. The virus is carried within the seed and cannot be eliminated by hot water or chemical treatment with tusodium phosphate.

Symptoms consist of pronounced chlorotic mottle, green veinbanding, and distortion of leaves of young seedlings. On mature plants, leaves show intense dark green mosaic, blistering, and hardening, suggestive of a hormonal herbicide effect (fig. 1). Infected fruit coming from such plants show a strong mottled pattern with a lack of netting on melons (fig. 2). Control measures include selection of disease-free seed and cucumber beetle control.

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Cucumber mosaic virus (CMV) is probably the most widely distributed and important virus disease of cucurbits. The virus overwinters in many perennial weed sources especially attractive to aphids when weed growth resumes in the spring. Early infection of squash and melons is particularly common. Aphids are the main and most efficient method of virus spread. Summer squash displays severe downward cupping along the midvein and leaf reduction from which the plants fail to recover (fig. 3). Color breaking of squash fruit is usually seen, but is not unique for this virus; other viruses causing this symptom include watermelon mosaic viruses 1 and 2, squash mosaic virus, and zucchini yellow mosaic virus. Early decline of muskmelon vines is usually attributed to CMV infection and should not be confused with collapse or “sudden wilt,” which is a more complex disease and a plant-stress-related syndrome. CMV may be seedborne to a limited extent in some crops and weeds such as common chickweed (Stellaria media). Good CMV-resistant (actually tolerant since plants are infected by the virus) cucumber varieties are commercially available and produce a high percentage of unmottled fruit. All other commercially grown cucurbits are susceptible to CMV, although in yellow summer squash varieties that also carry a “precocious yellow gene,” this gene serves to mask the color breaking common with cucurbit viruses (see discussion under WMV-2).

Unfortunately, once the fruit or vegetable becomes infected with a virus, there is no way to control it. There are ways to prevent cucumber worm infestations and treat infestations. According to the American Gourd Society and Ohio State University Extension the following methods may be effective in prevention and control.

Prevention
Inspect plants frequency for beetle infestations. Row covers can provide protection, but during blossoming time, tile covers must be removed for several hours each day, to allow pollination. Plant wilt-resistant varieties and use trap crops, if appropriate.

Insecticides
Although there are several insecticides that control the beetle, only a few chemicals can be used on cucurbit plants because of their sensitivity to chemical injury. Application of an insecticide is usually recommended as soon as the plants begin to emerge through the soil. For prevention of bacterial wilt, it is often advisable to spray at 5-day intervals, beginning when seedlings emerge or after transplanting and continuing spray schedule until vines run. If rain occurs within the 5-day period, repeat the treatment promptly and then return to the regular 5-day treatment interval.

Sprays prepared from wettable powders are less phytotoxic than sprays prepared from emulsifiable concentrates. Dusts are likewise effective if plants are Thoroughly covered. Rotenone 1% dust gives good beede control. Malathion may cause injury to plants if applied before they start to vine. Malathion may cause some foliar burning and should not be applied when plants are wet. Do not combine Malathion and Sevin for application to cucumbers due to possible phytotoxicity.

Recommended chemicals include rotenone, methoxychlor, malathion and carbaryl (Sevin) applied according to label directions and safety precautions.

Predators and Parasites
Natural predators include soldier beetles, tachinid flies, braconid wasps and certain nematodes.

Good luck!

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