Feb 22, 2011

To preserve sales, control pumpkin pests

Pumpkin sales in late September and October are often the key to profitability. As a result, pest management is essential to ensure an adequate supply of pumpkins is available during this critical period. Several insects attack pumpkins in the Midwest. Table 1 shows the frequency and severity of several of these pests.

Squash bug

The squash bug is usually the most consistent pest of pumpkins in the Midwest, and is relatively difficult to control. Consistent monitoring and early detection is the key to proper management. Adults become active in late April or early May. Adults are about five-eighths of an inch long and gray or black. Eggs use laid-in clusters of up to 20, usually in the angle formed by two veins on the underside of leaves. Newly laid eggs are yellowish but become bronze-colored after a couple of days. Nymphs look much like adults, except they are smaller and lighter in color. Nymphs will usually congregate in groups, so they are relatively easy to find if they are present.

Both adults and nymphs feed with their sucking mouthparts to remove sap from the plant. Later in the season, squash bugs will feed directly on the fruit, sometimes to the point of causing the fruit to collapse.
Cucurbit Yellow Vine Decline appears to be vectored by squash bugs. The causal agent of this disease is a bacterium that colonizes the phloem. It takes four weeks after infection for symptom to appear, but once they do the entire vine may decline in just a few days. The aboveground symptoms look similar to what you might expect from squash vine borers or a root disease. Research has shown that the only way to avoid this disease problem is to successfully control the squash bug.

Seedling plants should be inspected frequently for the presence of squash bugs or wilting symptoms. Insecticides should be applied whenever wilting is observed and squash bugs are present. When plants reach the early flowering stage, they should be scouted for the presence of squash bug eggs. Fields that average more than one egg mass per plant need to be treated.

You will achieve maximum control when you time your sprays to coincide with egg hatch. You should begin your spray program early in the hatching period. The pyrethroid insecticides (Asana, Brigade, Mustang Max, Pounce and Warrior) provide the best levels of control.

Cucumber beetles

The spotted cucumber beetle appears later in the season because it overwinters in Southern states and must migrate to the Midwest. Cucumber beetles have black legs and bellies, while the rootworm beetles have yellow.

Cucumber beetles damage pumpkins by feeding on stems, leaves and fruit and can vector bacterial wilt of cucurbits. While this disease can be devastating to cantaloupes and cucumbers, pumpkins are only vulnerable to bacterial wilt when the plants are young. Once the plants have been in the field two to three weeks, they are unlikely to contract the disease.

When plants are young, fields should be scouted frequently because the beetles can rapidly build up to very large numbers. At the seedling stage, treatment is justified when populations average one beetle per plant.

There are three strategies for chemical control: seed treatments, in-furrow treatments and foliar sprays. The FarMore DI400 seed treatment contains three fungicides and the insecticide thiamethoxam, and has been shown to provide control at the two-leaf stage – comparable to in-furrow treatment with Admire Pro.

Foliar sprays should be used only when populations exceed five beetles per plant, because excessive sprays will reduce natural enemy populations and may result in outbreaks of aphids or mites. The pyrethroid insecticides generally provide the most effective and economical control. However, these insecticides are harsh against natural enemies and don’t provide much control of either aphids or mites.

Squash vine borer

Squash vine borer is a greater concern in small plantings and backyard gardens than in larger commercial production. Growers who have had problems with squash vine borer will often have problems year after year, while other growers may never have serious problems.

The adult squash vine borer is a clear-winged moth that looks like a wasp. The female will lay eggs singly on the vines, often near the crown. The newly hatched larva will eat its way into the vine and start consuming the vascular tissue. At times, one borer feeding in the crown of a plant can kill the entire plant, but more commonly a borer will cause wilting.

There will often be frass (insect poop) coming out of the hole where the borer entered the plant. If you find the frass, cut open the vine to confirm that a borer is causing the problem. If you find borer damage, make two insecticide applications spaced five to seven days apart, directed at the base of the plants.

Aphids

There are a number of aphid species that will attack pumpkins, but they all cause similar damage. The direct damage usually is insignificant. However, many species of aphids carry viruses that reduce pumpkin yields. In addition, when aphid populations are high close to harvest, their feces, known as honeydew, act as a substrate for the growth of black sooty mold.

Aphids reproduce without mating and produce live young. Aphids are usually kept at reasonably low numbers by a variety of natural enemies, including parasitic wasps, lady beetles, lacewings and syrphid fly larvae. Outbreaks often occur when natural enemies are killed by insecticides.

Later-planted pumpkins often have considerably more yield loss due to viruses. It is generally thought that insecticides are not an effective way of stopping aphids from transmitting viruses to pumpkin plants. Even if the insecticide kills the aphid, the plant is still infected. However, keeping aphid populations low can help to reduce the secondary spread of virus throughout the field. In years when soybean aphids are numerous, pumpkins are especially vulnerable because the migrating soybean aphids infect plants with viruses when they pause to determine if they are on a good host plant.

Mites

Mites can increase rapidly to high populations when weather conditions are favorable, namely during hot, dry weather with few heavy rainstorms. Mites can also be more severe near a dusty road. Look on the underside of leaves for the colonies, which will often be accompanied by webbing. It’s important to discover the infestations before you start to see wilting, because much of the damage will already be done at that point.

Mite infestations are often localized, so it’s possible only a portion of the field will require treatment. Acramite, Agri-Mek, Epi-mek and Oberon will provide good to excellent control.

– By Rick Foster, Purdue University