CORVALLIS, Ore. – What to do about garden pests, including insects, plant diseases and weeds, can be a challenge for gardeners who want to effectively manage the pests without damage to the environment and human health.
The question-and-answer series below illustrates a strategy called Integrated Pest Management, a systematic approach to identify pests and use tactics that are cultural, physical, biological or chemical.
The least toxic and effective methods are always considered first, according to Oregon State University researchers Andy Hulting, a weed control specialist, and Gail Langellotto, an entomologist.
Q: How do I know if I have pest problems in my garden?
A: Check your plants regularly for pest damage such as missing leaves, flowers or fruit or changes in color, texture or size. Most plant problems in home gardens are caused by poor growing conditions, temperature extremes, poor water management or compacted soil. Look under leaves and use a flashlight after dark, which is when many insects are active.
Q: How do I identify what is causing the problem?
A: Often it's not a pest, but another problem such as sun scald or nutrient deficiencies. "Don't apply pesticides without understanding the problem you are trying to solve," Langellotto advised. "Many insects are beneficial and actually help gardens grow better. Others do no damage." Some insect pests can be dislodged with simple methods such as shaking the plant or spraying with a high-pressure stream of water.
Your local OSU Extension office and its Master Gardeners can help correctly identify the culprit and at what point in the pest's life cycle it is most susceptible to control measures.
Q: What pest management tool should I use?
A: Integrated Pest Management utilizes a combination of methods to keep pest populations at an acceptable level, with the least toxic and effective first.
- Cultural methods: Choose healthy plants that are not prone to pest problems, plant them where they will grow well and rotate where annuals are planted to avoid buildup of disease populations.
- Physical methods: Pull or dig weeds and hand-pick or trap insect pests off of plants. Row covers designed to extend the gardening season have been found to also keep insect pests away from plants.
- Biological methods: Garden plants can attract beneficial insects, such as parasitic wasps and green lacewings, to help keep pests at bay. Some of the more common ones are alyssum, coreopsis and sunflower. The flowers of plants in the Apiaceae family (including carrots, parsnips, celery, parsnip, cilantro and dill) are known to be especially good at attracting parasitic wasps and other beneficial insects.
Q: When and how should I use chemical methods?
A: Some pest problems are difficult to manage without chemical pesticides. However, chemicals can affect human health and be toxic to other organisms. Thus, use them judiciously and only after you are confident you have identified the pest, have chosen an appropriate pesticide, and that other methods are not likely to provide acceptable levels of control. Read all label directions before choosing and using pesticides in the garden.
"If you want to utilize biological controls in the garden, avoid broad-spectrum insecticides whenever possible," Langellotto said. "They may help you manage your insect pests, but they also kill other insects they contact, including beneficial ones."
Q: What precautions should I take with chemical pesticides?
A: If you decide to use a chemical, check the label to make sure your intended use or site is included on the label. Then choose one that is least harmful to the environment and to the applicator, specific to the pest and least harmful to beneficial organisms.
Pesticides labeled "Caution" are the least toxic to humans, "Warning" are more toxic, and "Danger-Poison" (with a skull and crossbones), are the most toxic. The law requires that you read the label. Be sure to wear protective clothing, especially eye protection, gloves and long pants.
Pesticides are more concentrated than they used to be, according to Hulting, and are made for very specific uses. "You might need only a fraction of an ounce to treat a large area or number of plants, perhaps less than in previous years," he said. "Don't use more product than the label specifies. More is not better."
Q: Where can I get more specific information?
A: For fact sheets, frequently asked questions and podcasts on pesticide use, call the National Pesticide Information Center at OSU at 1-800-858-7378.