Insects attack vine crops


Vine crops (cantaloupes, cucumbers, watermelons, and squash) can be attacked by two kinds of insects that cause a rapid wilting and in most cases, death of the plants. The first insect is the squash vine borer and it will also attack cucumbers and melons to a lesser degree.

Damage first appears as a sudden wilting of a long runner or an entire plant. Closer examination reveals masses of coarse, greenish-yellow excrement, which the borer has pushed out from the stem. Splitting the stem cap may reveal a thick, white, wrinkled, brown-headed caterpillar up to 1 inch long and almost 1/4 inch thick. In commercial squash plantings 25 percent or more of the crop can be damaged.

Home plantings suffer even greater losses, as infested vines are often completely girdled and usually become rotten and die. Small borers may enter leaf stems but are most often found toward the base of the plant. Later on they may be found throughout the stem and even in the fruit. Sometimes vines are almost severed.

The adult is a “clear-winged” moth with metallic greenish-black scales on the front wings. The hind wings are transparent like those of a wasp. Moths have a wing expanse of 1/2 inch. The abdomen is ringed with orange and black. They fly swiftly and noisily about plants during the daytime. Female moths lay their small, oval, somewhat flattened, brownish eggs on stems in May or early June. Young borers hatch in about a week, tunnel into stems, feed and are full grown in about four weeks. They have a brownish head, six short slender legs on the thorax (body) and five pairs of short prolegs (false legs) on the abdomen. Each proleg bears two transverse rows of crochets (curved spines). Larvae leave their burrows and make a cocoon in the soil.

Two or three weeks later, adults emerge, giving rise to a second generation of larvae in North Carolina during early August. The insect overwinters an inch or two below the soil surface inside a tough, dirt-covered, silk-lined, black cocoon about 3/4 inch long, in either the larval or pupal stage.

Once borers have gained entrance into stems, little control is possible; hence, early detection is critical. Excrement should be watched for around the bases of plants, and when first noticed, insecticide sprays should begin. Success of any insecticidal treatment depends on early and repeated treatment. Apply a liquid spray of Thiodan or pyrellin to the stems near the base of the plant and repeat weekly during egg laying periods (early June and early August). As most insecticides are toxic to honey bees and other pollinating insects, applications should be made in late evening and directed to the base of plants.

If only a few vines are present, keep a close check on them. Should any wilting occur, check the base of plants for signs of excrement and borer damage.

If there is evidence of borer activity, remove the borer by slitting the vine with a sharp knife and removing the larva. Then cover the injured area with moist soil. Some gardeners put a shovelful of soil at one or more locations along each vine. This is to encourage the plant to develop a supplementary root system and thus overcome squash vine borer attacks at the base.

The other destructive insects of vine crops include the striped and spotted cucumber beetle. The adults feed on foliage and stems of young cucurbit seedlings all season long, causing a rapid wilt and collapse of the entire plant, due to the introduction of the bacteria into the plant which plugs up the “plumbing system” of the plant. Plants cannot take up water due to a plugged up vascular system so the plants die. First generation adults emerge from late June to early July. A complete life cycle requires from six to nine weeks. There are two and sometimes a partial third generation each year.

The adult spotted cucumber beetle is about 1/4 inch long with a bright yellowish-green body. The head, legs and antennae are black, and 12 black spots appear on the wings. Adult striped cucumber beetles are about 3/16 inche long, black and yellow in color, and have three longitudinal black stripes on the wing covers. Both have beaded antennae about 1/16 inch long.

Adult striped cucumber beetles prefer cucumbers, cantaloupes, winter squash, pumpkins, gourds, summer squash and watermelons. They also feed on beans, peas, corn and blossoms of several wild and cultivated plants. Larvae develop on these and related cucurbits. The spotted cucumber beetle has a wider host range and, in addition to cucurbits, may be found on beans, peas, potato, beet, tomato, eggplant and cabbage. The larva is the well-known southern corn rootworm, which feeds on the roots of corn, peanuts, small grains and many wild grasses.

Several cultural measures discourage cucumber beetles. Early plowing-disking removes vegetation and discourages egg laying. Delayed planting (more favorable germinating conditions) and heavy seeding rates ensure a good stand. These pests are usually not as troublesome in sandy soils. Wire or cloth screen protectors shaped like cones or row covers will keep beetles off home plantings until plants get established.

A foliar insecticide, such as Sevin, or pyrellin, applied as soon as seedlings emerge from the soil, will retard cucumber beetle feeding and encourage plant establishment. Where insects are abundant, additional foliar applications may be needed to prevent beetles from spreading bacterial wilt and cucumber mosaic so constant vigil is required.

Proper watering

Many people, when asked, “How much do you water garden?” The main answer is, “I let the hose run slowly, for about an hour, once a week.” How do you know if you are putting on to much or too little water? It depends on what kind of soil you have. Sandy soils drain faster than clay soils. So it would take less time to water down to a 6 inch depth in a sandy soil than in a clay soil.

A good way to determine when and how much water you should add is to get a long-handled screwdriver and push it into the soil before it becomes hard to push. Then pull it up and you can measure how deep the soil is wet. Most crops and plants need a good 6-8 inches of wetted soil, so that plants do not suffer from moisture stress.

Water until you reach a 6-8 inch wetted depth, by using the screwdriver method. When the soil surface feels dry to the touch, then water deeply to maintain that 6-8 inch wetted depth. By doing this several times, you will learn how much time it takes to keep the soil moist, down to 6-8 inches, and you can keep your plants from stressing in the hot summer months.

Do not water based on a set amount of time or a certain day of the week. If you do that, you will end up giving your plants either too little or too much water and you will constantly be guessing if your plants are getting enough water.

Calendar of events

June 12 Lunch ‘N Learn- “Saving face”

June 13
4-H Summer Fun – Gardening with Johnny

June 14 4-H Summer Fun – Goods from the woods

June 17 4-H Summer Fun- Cloverbuds: Goods from the woods

June 18 4-H Summer Fun – 4-H Investigates

June 20 Beekeepers meeting

June 25 4-H Summer Fun – Pollinator nation

June 26 4-H Summer Fun – Take me out to the Bball game

June 27 4-H Summer Fun – Where does your water go?


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