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Silent Invaders of the Garden

by Gerry Oliver

Despite our best efforts, insect pests invade the garden each year. While reducing the vigor of garden fruit and vegetables, they cause great frustration to the gardener. Familiarizing yourself with their appearance as well as understanding their habits will be the best way to control damage in the garden.

The most commonly found pest is the aphid. It is a small soft-bodied, pear-shaped insect with long antennae and a pair of conicles (tube-like appendages that project from the back end). They can be green, brown or black in color.

Aphids damage plants by sucking sap, causing withered foliage and loss of plant vigor. The insect secretes excess fluid, called "honey dew", which makes the leaf sticky and susceptible to black mold. It also attracts ants, which "farm" the aphids, protecting them and extracting the honey dew. The aphids carry disease such as "yellows" and mosaic virus to tomatoes.

Cultural practices such as fertilization have a direct effect on aphid populations. Increased nitrogen levels in the plants cause a rapid increase in aphid numbers. Once the population reaches a certain density, flying aphids develop and will go off to another plant to start a new colony. Aphids can produce both live young and those hatched from eggs.

Control of aphids is two-step - cultural and active treatment. Cultural practices such as removal of host plants, such as plantain and lamb's quarters as well as maintaining a black zone around the garden will reduce the chance of infection.

A strong jet of water sprayed on the plants every few days will dislodge the aphids as well as damage or crush their soft bodies. Insecticidal soaps will kill them while remaining non-toxic to most plants or animals.

Spider mites are difficult to see but do considerable damage to plants. These members of the Arachnida family (which includes spiders and ticks) cause loss of vigor, discoloration of leaves and slow growth as they suck juices from the plant. With large infestations, the leaves wither and fall off the plant.

The webs can be seen on the underside of the leaves, and in severe infestations the webs will extend from leaf to stem or leaf to leaf. With magnification, the spider mites can be seen in the web. Look for webs if the leaves begin to turn brown.

Nitrogen-rich fertilizer used on the plants can cause rapid increases in aphid numbers. Hot, dry weather will also stimulate production of young.

Treating for spider mites requires great diligence. At least three applications of an insecticide are required spaced seven to 10 days apart. If the weather is hot and dry, the applications must be made more frequently, as young will be hatching faster.

Maintaining moister conditions around the plants will help slow down reproduction rates of the mite. Many predatory insects, such as lady bugs and green lacewing, will be attracted to your garden and should be encouraged.

Thrips are small, slender insects which have feathery wings. They are quite small, but do considerable damage by sucking juices, rasping and stinging plant tissues. The plant tissues will turn a silvery-white color before dying. Other indicators of infestation by thrips are buds that die before opening or show distortion of the petals when the bud opens. Plants such as roses, chrysanthemums, dahlias and gladiolus show these symptoms readily.

Cutworms attack just about everything in the garden, weed or cultivated plant. They eat the young plants off at the surface level or just below. These plump, half-inch long, gray-colored larvae are best dealt with using solid barriers such as milk cartons, Styrofoam, or plastic cups with the bottoms cut out, pushed about two inches into the soil.

These barriers should be placed around transplants when they are planted into the garden. For seed grown plants, sprinkle cornmeal along the row and carefully work into the top layer of soil. It is supposed to give the larvae a case of terminal indigestion.

Control of weeds and grass in and around the garden will discourage the adult moth from laying eggs. Generous working of the soils in spring will dislodge the larvae.

Slugs and snails are becoming a major problem in many gardens. They are appearing in areas they have traditionally not been found.

Slugs are grayish, worm-like, legless insects that travel on a slimy secretion. This secretion is a tell-tale sign of their presence. Snails have a hard shell that offers them protection from the elements and predators. They rip large holes in leaves during their feeding as well as eating young plants and seedlings.

During dry, hot periods, both slugs and snails retreat to cool, shady, moist places such as underneath plants, on the underside of objects laying on the soil surface or near a source of moisture. Mulched gardens are a prime attractant to both insects.

Control is difficult. We do know however that they dislike rough surfaces, so modifying some areas in the garden will make it less attractive to both slugs and snails. Coarse sand, wood ashes and diatomaceous earth can cause damage to the skin of the insect. Placed around the plants or between garden rows, these will provide greater protection.

With a better understanding of the garden pests we can approach controls more easily, and with greater success.

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