The Dirty Half Dozen: Six Insects That Are Harmful To Vegetable Gardens
(Editor's Note: This article was originally published on July 9, 2008.)
In a previous article, Nature's Ninjas, I listed some Good Guy Bugs that are welcome additions to any garden. They are predators, and help eliminate the pests that will rob you of your harvest. New gardeners are sometimes confused about insects, and run for the nearest weapon upon seeing any creature with over four legs. The trick is to encourage the beneficials, but to eliminate the harmful insects safely without killing the Good Guys. Here at Dave's Garden we have an Insect Identification Forum. If an unfamiliar insect lands on your vegetables, post there for help with its identity.
One of the most destructive insects in my area is the Spotted Cucumber Beetle, Diabrotica undecimpunctata howardi. Many gardeners have no idea how harmful this insect is, and simply think it is a green Ladybug. This benign looking little creature can lay waste to a nicely tended vegetable garden, even if there are no cucumbers planted. It carries a virus called Bacterial Wilt that attacks many types of vining vegetables. Once your plants are weakened by it, the harvest is in jeopardy, or the plants might die. Your plants are most susceptible when they are very young. Adult Cucumber Beetles chew the leaves and stems. Larvae chew the roots. In my area, the physical damage caused by actual chewing is minimal. The virus that is introduced into the plants will cause the entire plant to wilt and die. After a plant is infected, there is no cure. Row covers are an effective organic control, while applying an approved pesticide for your area in the evening will control them chemically.
Aphids are another common pest. They come in many shapes, sizes, and colors. Aphids belong to the family Aphidiae. Many gardeners who grow roses are quite familiar with them. They come in various colors and shapes, but are all similar enough to be recognized quickly. These little soft bodied creatures live in colonies, and suck the juices from whatever plant they are on. They thrive in humid conditions where the air does not circulate well. My worst problem with aphids seems to be on my tomato plants. The foliage tends to grow lush and thick, giving them many places and opportunities to establish themselves. They can also be problematic on peppers, beans, and eggplants. Controlling aphids organically with a predator insect simple and effective. Most populations can be eliminated with ladybugs or lacewings. The adults and larvae can consume great numbers of them. Insecticidal soap is another safe way of eliminating aphids.
The Striped Blister Beetle, Epicauta vittata (Fabricius) arrives in mid to late summer. Seemingly overnight a great colony can attack, and any type of vegetable is in jeopardy. They eat tomatoes, squash, beans, melons and peppers with much enthusiasm. They are called Army Beetles because they tend to travel in large groups. They are extremely destructive, and can ruin a carefully tended garden in short order. These insects can be responsible for nasty burn-like lesions on the skin of humans if they are crushed. The name, Blister Beetle is not just for show, they actually do cause blisters. While the beetles are very destructive, the larvae are a beneficial predator. The larvae of the Striped Blister Beetle feed on grasshopper eggs. Destroying the beetles while keeping the larvae can be problematic. One method that my Grandmother used was to sprinkle flour on the adults. The flour gums the beetle's legs and wings up, and they fall to the ground and die. This was an organic method of pest control decades before anyone even knew the term. An approved insecticide for your area can also be applied.
Tomato Hornworms, Manduca quinquemaculata are large green caterpillars of the Five Spotted Hawk Moth. They feed on members of the Solanaceae family. That includes tomatoes, peppers, eggplants, potatoes and the decorative plant Brugmansia. They have voracious appetites, and can strip a tomato plant of its foliage almost overnight. The small white things hanging off of the hornworm in this image are the pupae of a small parasitic bracnoid wasp. If you find a hornworm in this condition, it is already doomed. The wasp larvae that were using it for a host have consumed much of its insides. The pupae will hatch, and the new wasps will fly away to find new hornworms to infect. I simply move the hornworm to a non-food source when I find them in this condition to allow the wasps time to mature. Handpicking is an effective control, but one can apply Bt (Bacillus thuringiensis) which is considered an effective organic pesticide. These caterpillars can do great damage to a garden. The best treatment is to find them before they grow to their full size of nearly three inches. Bare stems in the tomato patch are a sure sign that they are feasting on your precious plants. Leave no leaf unturned until you find the culprits. Where there is one, chances are excellent there are more.
Grasshoppers are a common sight in meadows, flowerbeds and vegetable gardens. They are of the Order Orthopetera. These are eating machines, and will strip the foliage bare from most any living plant. They hatch in spring as nymphs, and begin to enjoy a season-long buffet in your gardens if left unchecked. They will consume corn, beans, peppers, peas, broccoli and squash with gusto. They can travel in great numbers, and will eat their way through gardens and across the countryside. A handful of these can be an annoyance, clouds of them are devastating. Organic bait containing Nosema locustae can be purchased. This sickens the grasshoppers, and healthy ones eat the sick ones, in turn becoming sick themselves. Several mild winters followed by hot summers will allow grasshopper populations to flourish. A few grasshoppers here and there can be an expected annoyance. When the population increases to the point where they are starting to destroy gardens, measures should be taken to get them under control, they will destroy vegetables and ornamentals with equal enthusiasm.
Leaf-footed Bugs are of the Family Coreidae and can be identified by the wide spot on each hind leg resembling a small leaf. They suck the sap and juices from a great number of plants. Fruit crops are favorites, but they are not very picky and will happily settle on nearly any vegetable plant. They tend to be found in groups, and sometimes there will be individuals with different levels of maturity within the crowd. The young Leaf-footed Bugs are small red or orange creatures with black legs. Each time that the nymphs molt into another version it is known as an instar. Control can be difficult if large populations are in your gardens. The only Organic control that I know of is hand picking. As they move slowly and are not disturbed easily, this can be accomplished. The pesticide Sevin can be applied if infestation occurs far enough from the projected harvest date. Please read all instructions before applying poisons.
Learning to identify the insects that visit your garden is an important and responsible thing that all gardeners should do. Educating yourself on proper controls for the harmful insects lets you garden in safety while protecting your crops from damage. Understanding the difference can help you maintain a healthy balance of predators which will decrease the need for pesticides. Be alert for The Dirty Half Dozen in your vegetable garden. Quick identification will help in a fast removal of these villains, leaving more vegetables for you and your family.
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