园丁如何控制有害昆虫，保护有益昆虫

Most gardeners know this story.

They have planted beautiful gardens and they are happy to see helpful insects like bees and butterflies surrounding the flowers. But as they take a closer look, the tomato plants are covered in black dots and filled with harmful insects like aphids.

Some gardeners may immediately reach for chemicals like pesticide. But this is not wise. Although it may stop the aphid problem, it will also threaten bees and butterflies. They help plants reproduce and keep harmful insects, or pests, under control.

Instead, take a series of small steps to control the harmful insects.

The process starts with the idea that having some pests is acceptable. Only when there are too many pests should a pest control be considered. The first defense should always be the safest method available.

Also remember that helpful insects like butterflies start out as caterpillars. And all caterpillars eat plants. So, some plants will have at least some holes, which is good for the ecosystem.

But how do you deal with the aphids on tomato plants? You want to wash aphids off with a strong current of water. It usually works. But if they continue to return after several attempts, and you believe it is time to take stronger actions, take another small step.

In this case, the next step would be to use a pest control called insecticidal soap. It is nontoxic and safe for people, helpful insects (when dry), and most plants. Make sure your plant is not one of the few that is sensitive to the product.

Prevention

As a rule, prevention is the best treatment. Inspect plants closely, including under their leaves, before bringing them home from the store. Do not bring any home that show signs of disease or the presence of harmful insects.

When planting, space plants out to permit them to grow to their full size. Plants too close together can grow harmful organisms like mold, mildew, and fungus.

Keep your garden clear of fallen leaves, fruit, and other waste. They invite insects and other harmful pests if permitted to remain on the ground.

When you do see pests like aphids, wash them away. Use rubbing alcohol for removing some insects or pick them off the plants. Traps can be used to capture insects like slugs.

Pesticides

If you decide a pesticide is necessary, choose it carefully and follow the directions and warnings on the product. Avoid using any pesticides in extreme heat, on windy days, or when plants are wet.

Treat the plants early in the morning or at night, when helpful insects, like bees and butterflies, are inactive. It might hurt, but consider removing flowers from the plant to lessen the risk that helpful insects will come in contact with the pesticide. In most cases, more flowers will come.

Pesticides like insecticidal soap and horticultural oil work by suffocating pests rather than poisoning. They must come in direct contact with the pests, and they become safe for helpful insects once they have dried.

I'm Gregory Stachel.

Jessica Damiano reported this story for The Associated Press. Gregory Stachel adapted it for VOA Learning English.

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pesticide – n. a chemical that is used to kill animals or insects that damage plants or crops

garden – n. an area of ground where plants (such as flowers or vegetables) are grown

nontoxic – adj. not poisonous

rubbing alcohol – n. a liquid that contains alcohol and water and that is used to clean wounds or skin

suffocate – v. to kill (someone) by making breathing impossible

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