Plant problems can be prevented with appropriate preparation and attention. The American Horticultural Society’s New Encyclopedia of Gardening Techniques (Mitchell Beazley, 2009) gives a detailed look into planting from preparation to harvest. This discussion of garden pests is an excerpt from Chapter 4, “Growing Vegetables & Herbs: Common Problems.”
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It can seem at first that vegetables are vulnerable to a host of pests and diseases, and that growing them will be an unrelenting and unwinnable struggle. It is true that there are many creatures poised to enjoy your harvest before you do, and each year some plants will be lost or damaged by disease, but the problems are not really so great. With good cultivation techniques and some defensive measures, losses will be minimal. The key is to watch plants carefully, spot potential problems early, and act promptly, ideally before any damage is done. In the vegetable garden, as everywhere else, prevention is better than cure.
Some pests, such as slugs, will attack almost any plant in the garden and are familiar to every gardener; these are discussed in Chapter One. Other pests are specific to certain crops, or even a single crop.
Adult beetles are about 1⁄4in. long with yellow wing covers, each with three black stripes or eleven black spots. The adults lay eggs in the soil and the slender, whitish larvae, with black or brown heads, burrow into the soil and feed on the roots of cucumber, squash, melon, and potato plants. The larvae pupate in the soil, the adults emerging in spring to lay their eggs. Predators such as praying mantis and ladybeetles are effective, as are some insecticides.
Flat-backed, grayish or black bugs, 1⁄2–1in. long, suck sap from cucumbers, melons, pumpkins, and squashes. Their activities can be recognized by the plants being marked with brown or yellow dots; in the worst cases, plants become stunted, and the leaves turn black and die. The best protections are using floating row covers until flowering begins, good sanitation, and crop rotation.
These small insects cluster under brassica leaves and suck sap. Direct damage is minor, but their sugary excrement, called honeydew, encourages sooty molds. Whiteflies are difficult to control; remove all old plants in spring before planting anew to limit reinfection. Spraying with an appropriate treatment will reduce infestations, but the effect may be short lived. Damage is mainly confined to outer leaves, so this pest can often be tolerated.
Brassicas and allied plants, such as radish, turnip, and arugula, as well as eggplants are prone to attack from these tiny beetles. They are black, sometimes with yellow stripes, and jump from plants when disturbed. They eat small holes in leaves in spring and late summer. Seedlings can be killed or retarded; keep them watered so they quickly grow through the vulnerable stage. If necessary, spray with an appropriate treatment.
Carrot rust fly
This pest attacks carrots and, to a lesser extent, parsnip, celery, and parsley. The maggots, up to 1⁄2in. long, leave brown tunnels in roots. Most damage occurs in late summer. Grow under row covers or in a 30in. tall enclosure (see page 196) to prevent the low-flying females from laying eggs, or try less susceptible varieties.
Brassicas are host plants for several caterpillars, worms, and loopers. They can be a serious problem on young plants, retarding establishment and reducing vigor, as well as damaging maturing plants and reducing their appeal by their damage and their droppings. Remove them by hand on frequent regular patrols, or grow plants under floating row covers or insect-proof net to prevent eggs being laid. Organic control with Bacillus thuringiensis (Bt) is also effective.
Pea & bean weevil
Grayish brown adults, 1/5 in. long, eat U-shaped notches in leaf edges of peas and fava beans in early summer and feed on pollen. The larvae burrow into the pods and feed on the developing seeds inside, ruining the crop. The holes where the larvae enter often close up, disguising their entry. Sprays and predators can deal with the adults, but once the larvae are inside the pods there is no control.
A paperback edition of New Encyclopedia of Gardening Techniques will be released in April 2013.
This excerpt has been reprinted with permission from The New Encyclopedia of Gardening Techniquesby the American Horticultural Society, published by Mitchell Beazley, 2009.