NGA Articles: Summer's Bad Guys

Summer's Bad Guys (cont)

By: Charlie Nardozzi

Broad-spectrum Sprays

These poisons should be your last resort against an invading insect population. They tend to act broadly, killing some beneficials as well as target pests, and must be used according to instructions, since they can also harm plant leaves. As with any pesticide, read the label carefully to determine the best timing and application.

Garlic spray and hot pepper spray are two newer products that act primarily as repellents. They are most effective in greenhouses against soft-bodied insects such as aphids, spider mites, and whiteflies. They don't impart their flavor to vegetables. Researchers are testing their effectiveness on a broader range of pests in the field. Gardeners may want to experiment with these.

Synthesized chemical sprays such as phosmet (Imidan) are the most effective on tough pests such as curculios. Some botanical sprays such as rotenone are losing favor because of their toxicity, and manufacturers are considering not reregistering these pesticides for some uses. Currently certain formulations of rotenone are not sold in Colorado and California.

Diatomaceous earth (DE). These fossilized shells of water-dwelling diatoms have sharp edges that pierce and dessicate the bodies of many insects such as slugs, earwigs, and flea beetles upon contact. Sprinkle it around or on plants, and reapply after a rain.

Horticultural oil. Years ago, most gardeners were familiar with dormant oil spray which could only be applied on dormant deciduous plants to smother insects (especially at the larval stage) and eggs. New, refined petroleum-based formulations can be sprayed any time of year on most plants.

Vegetable oil-based products are also available, but these are best used as a dormant spray to kill overwintering eggs. Always check for any harmful effects by test-spraying a few leaves first. Don't spray on drought-stressed plants, when temperatures are above 90&degF, or when humidity is high. Don't mix sulfur with the spray.

Phosmet (Imidan). This is a synthesized chemical that controls curculio and many other insects. It works best sprayed on fruit trees when flower petals fall and 14 days later. Use it with extreme caution: it is toxic to bees, fish, and wildlife.

Insecticidal soap. Soaps have become the mainstay pesticide spray for organic gardeners. Better formulations and added stickers improve their effectiveness. They kill or repel a wide variety of insects, including aphids, leafhoppers, and spider mites. Cover plants well with the spray, but don't spray if temperatures are above 90&degF. Check the label for plants that should not be sprayed.

Neem. The latest in plant-based insecticides, this extract from the seeds of a tropical tree comes in two formulations: extract and oil. The extract's active ingredient is azadirachtin, which repels some insects, suppresses feeding, disrupts mating, and kills a wide range of insects including aphids, Japanese beetles, and leafhoppers. The oil form is mainly used to suffocate soft-bodied insects and beetle larvae. Both are most effective used as a preventive spray or when insect populations are low. Neem is probably the safest botanical for animals and humans, but some research has shown it can harm some beneficials such as ladybugs.

Pyrethrins. Derived from the crushed flowers of African daisies, pyrethrin is an effective spray that works quickly on many adult insects. Although it is harmful to bees and some beneficials, such as ladybugs, it's safe for animals and humans.


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