By the staff of National Gardening magazine Even in the best managed vegetable gardens -- with soil rich in compost, and a diversity of plant species that encourage natural predators -- certain pests will get out of hand. There is a nugget of truth in the old maxim that insects are most likely to gang up on plants that are already unhealthy because of a soil nutrient imbalance or drought. This is the case, for example, with some aphid outbreaks. Unfortunately, the maxim doesn't come close to explaining all our pest problems. For instance, vegetables are bred largely for yield and flavor, often at the expense of natural resistance to pests. Furthermore, all vegetables are tender and nutritious, and this fact is not lost on a wide array of insects. With cabbage worms, horn worms, bean beetles and Colorado potato beetles, the better you've made the soil, the more they like your vegetables. If these or similar insects are in your neighborhood and you are growing their favorite crops, you are almost certain to have a pest outbreak. Given these realities, what should you do? Most likely you will consider using some kind of insecticide. Here we summarize the latest experience and expert advice about the sprays and dusts used to control pests in vegetable gardens. Also described are two promising new insecticides. Integrated Pest Management Vegetable garden pest control begins with basic good gardening common sense, such as choosing varieties that are resistant to pests in your region, preparing the soil well and providing regular irrigation. It helps to have in your garden a diversity of plants and many kinds of habitats. Water, even a very small pond, is very attractive to many insects and other creatures. Likewise, an abundance of flowering, nectar-bearing plants will encourage and sustain parasitic and predatory insects. The next step in least a toxic-pest control strategy is to employ barriers, such as row covers, to exclude pests altogether. Using a pesticide, any pesticide, is always the measure of last resort. You spray or dust late in the game, when the pest insect is clearly way out of control and an important crop is at risk. When a pest first arrives, or when prior experience tells you it soon will, the best approach is to develop a strategy of control. Integrated pest management (IPM) is a pest problem-solving process that includes considerations such as pesticide resistance, natural biological controls and pollution in addition to problems caused by the pest. IPM integrates many pest control methods and minimizes insecticide use, particularly the more toxic, broad spectrum kinds. When a problem does occur, it is essential to correctly identify the cause. The beetle you see near a hole in a leaf may be a predator. But if it is damaging your plants, simply pick it off. Also consider that doing nothing at all -- letting nature take its course -- is often the best approach. Always use simple, noninvasive remedies first.
Sensible Insecticides Used Responsibly Remember, too, that just because an insecticide has a botanical origin or is considered acceptable to organic gardeners, it still contains a toxin and is not automatically safe for humans.
Eleven Vegetable Pest Remedies
Adios (Sevin plus bait).
Bt. Bt exits naturally in most soils. Different strains of Bt occur that produce protein crystals toxic to certain insects. The strain for most caterpillars is Bt. var. kurstaki. Commercially prepared Bt spray or powder has no effect on adult butterflies or moths. Remember, however, that not all caterpillars are pests. Strains of Bt are developed for a few other pests. Some leaf-feeding beetles (including Colorado potato beetle) are susceptible to B. t. tenebrionis , for example. Because Bt is a near-perfect insecticide there is danger of overuse. Any overused insecticide will gradually become less effective as insects evolve defenses to it. Some insect pests, such as the diamondback moth and Indian meal moth, were once susceptible and are now at least partially immune to Bt.
Diatomaceous earth (DE) Dust DE onto leaves and stems to control pests such as aphids, Colorado potato beetle, immature forms of squash bug, Mexican bean beetle or white fly. Or spread it as a barrier to slugs and snails. It works best in dry situations. It is not selective and kills spiders and beneficials as well as pests. Don't overuse it. DE is available in two different forms. One form is used primarily in swimming pool filters. It is not an effective insecticide and is dangerous to inhale (it can cause a lung disease called silicosis). In your garden, use only the natural grade of DE. Still, it is wise to wear goggles and a dust mask during application. Dust DE onto leaves and stems to control pests such as aphids, Colorado potato beetle, immature forms of squash bug, Mexican bean beetle or white fly. Or spread it as a barrier to slugs and snails. It works best in dry situations. It is not selective and kills spiders and beneficials as well as pests. Don't overuse it.
Horticultural oils. Oils kill insects by plugging the pores through which they breathe. Oils can damage plants if applied at excessive rates or on particularly hot (above 100 degrees) or cold (below 40 degrees) days. Spray oils in vegetable gardens to kill aphids, leafhoppers, spider mites and white flies. A few drops of oil in the ear tips of corn controls corn earworm.
Insecticidal soaps. Advantages of soaps to home gardeners include safety to both the applicator and non-target insects. They are selective, so easily incorporated with other, natural biological controls. Some plants, such as peas, are readily burned by soaps, and their effectiveness is greatly reduced if mixed with hard water. Don't use liquid dishwashing detergents or hand soaps. Though many will kill insects, they might hurt the plants too. Some fatty acids are toxic to plants, the reason a soap-based weed killer is now available. Dish soap manufacturers change the oils used in their formulations regularly, based on cost and availability, so the brand that worked fine for your neighbor last year might severely stunt your Brussels sprouts this year.
Malathion. Neem works both as an insecticide and as an antifeedant. It kills insects in the juvenile stage by thwarting their development, and is most effective against aphids, thrips and white flies. There is no quick "knock-down" with neem, but a week or so after application, you'll notice a steady decline in the number of pests. It is not effective against adult insects (though it may interfere with egg production), and has little impact on beneficial insects. As an antifeedant, neem is effective against Japanese beetles. Apply neem before the beetles appear and reapply after rainfall. Once beetle numbers build up on the plant, neem no longer discourages them. Neem sprays degrade very quickly in water. Mix only the amount you need and apply all of it immediately. On the plant neem retains its activity against juvenile insects pests for about one week.
Pyrethrins. The terminology can be confusing. Pyrethrum, discovered around 1800 in the Transcaucasian region of Asia, is the ground-up flowers of the daisy. Pyrethrins (most always plural) are the insecticidal components of the flowers. Pyrethroids , such as cypermethrin, permethrin and resmethrin, are synthetic compounds that resemble pyrethrins. They are more toxic and more persistent than pyrethrins so much more toxic to beneficials. Though increasingly popular in commercially, home gardeners should avoid using them. Often, pure pyrethrins only stuns insects. This is why they are often combined with a synergist, piperonyl but toned, chemicals that enhance the effectiveness of the active ingredients, thus enabling formulations with less pyrethrin to kill insects.
Rotenone. Apply rotenone in the early evening when bees are not active. Like Bt, it is more effective in a pH-balanced solution. Use a buffer solution if your water is strongly alkaline. Rotenone is a broad-spectrum insecticide and should be reserved as a last resort against the hardest to control pests such as cabbageworms, Colorado potato beetles, flea beetles, fruit worms, Japanese beetles, loopers, Mexican bean beetles and weevils.
Sabadilla.
Sevin (carbaryl). Reporting by Deborah Wechsler. Technical review by Whitney Cranshaw, Colorado State University.
Copyright NGA
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