Managing Pests and Diseases

How to Work With Nature to Control Garden Problems

An organic approach to pest control can be safe and effective.

Start With Prevention

• Choose disease-resistant varieties. Many ornamental plants and vegetables have proven resistance to diseases such as canker, mildew, and rust.
• Don't overcrowd your plants. Good air circulation prevents the damp conditions that promote the growth of fungi and other disease organisms.
• Watch moisture levels. Notice if the soil is too wet or too dry and correct these conditions. Try to keep foliage dry.
• Practice crop rotation. Even more than insects, disease pathogens can persist in the soil from one season to the next. Moving susceptible crops from year to year is excellent preventive medicine.
• Inspect your plants. Regularly prune leaves or stems that you suspect may be diseased. Destroy the cuttings.
• Be sanitary. Humans are effective, if innocent, spreaders of plant disease. Pathogens can be spread by your footwear, hands, and clothes. Wash your hands before and after working with your plants, and clean your clothes if you think you have come in contact with sick plants.
• Clean your tools. Soil clinging to tools may harbor disease organisms. Similarly, clean out pots and flats before reusing them. A 10 percent bleach solution (1 part bleach to nine parts water) makes a good disinfectant.

Insect pests and plant pathogens are a challenge for every gardener and the temptation to wipe them out is strong. We encourage you to resist the urge to reach for an arsenal of chemical weapons. In the short term they may provide a quick knock-down to the attackers, but they may also kill beneficial organisms. In the long term, you expose yourself and the landscape to toxic chemicals, and risk disrupting the natural ecosystem that you and your garden inhabit.

All things considered, an organic approach is both safer and more effective. Here's how you can work with nature to control pests and diseases, and enjoy a healthier garden and harvest.

Organic methods of pest and disease control mean a healthier garden for you, your plants and the insects, birds and animals around you. Organic pest controls do not try to eradicate all insects—that would upset the natural balance of life in your garden, and perhaps endanger birds and other animals by exposing them to poisons and depriving them of an important food source.

Instead, the organic approach requires that you spend a bit more time in your garden, take extra good care of your plants, and keep an eye out for early signs of insect attack or disease symptoms. As gardeners, we can learn to tolerate some damage to our plants, and we should use such damage as a signal that our plants need more attention.

Not every insect is an enemy. Some are pollinators, some break down organic matter, and some are beneficial predators that feed on the real enemies. You want to be able to identify your friends and foes, and then encourage the friends and frustrate the foes. Effective and appropriate technologies, such as physical barriers, traps, and specific biological agents, are available to assist in your efforts to protect your garden and at the same time maintain a safe, harmonious natural environment.

Insects and diseases usually attack unhealthy plants, so the key to preventive control is taking good care of your plants. That means paying close attention to them and providing them with the conditions they need for healthy, vigorous growth. Those steps include the following:

Grow your plants in healthy soil. Add organic matter to your garden every year to improve nutrient levels, soil structure, and water-holding capacity. Make sure your plants are getting the right amount of water and all the nutrients they need, supplemented with organic fertilizers if necessary. Don't force plants to compete with masses of weeds for water and nutrients. Use mulches, such as landscape fabric or plastic, and pull a few weeds every time you visit the garden. Thin your seedlings so the plants are not overcrowded and there is good air circulation between them; check seed packets for thinning instructions.

Make annual garden cleanup part of your routine. Leaving old squash vines, tomato plants, and similar debris in your garden after the harvest ends is like putting out a welcome mat for pests and pathogens. Many insects overwinter in such debris, and they will get an early start nibbling on your plants the following spring. Many plant pathogens also live in the soil year-round.

Remove and dispose of any diseased or infested plants. Till other debris into the soil or put it in your compost pile. Then cultivate the soil so that any remaining eggs, larvae, or pupae will be exposed to birds and cold temperatures. Keep on top of the weeds around your garden, since they can also harbor insect pests.

Rotate your crops. Many insects and disease-causing organisms overwinter in the soil near their host plants. If you grow the same plant (or a related one) in the same place the next year, you give those pests a big head start. Crop rotation can thus reduce insect damage and minimize exposure to soilborne disease organisms. Wait at least two years before you plant the same or related crops, such as broccoli and cauliflower, in the same spot. Brassicas, potatoes, tomatoes, and onions are particularly vulnerable to problems when planted in the same place year after year.

Crop rotation also helps keep soil nutrients in balance over time. Heavy feeders, such as tomatoes and lettuce, can be followed the next year by legumes, such as peas and beans, which actually return nitrogen to the soil through microorganisms on their roots. The third year, you could let the soil "rest" by planting light feeders in that spot, such as carrots or beets.

Practice companion planting. This technique takes advantage of the various ways different plants complement or protect one another, thereby promoting each others' healthy growth. Marigolds, for example, have a natural resistance to insects, and planting marigolds as a border around the garden, or among vegetables, seems to discourage both insect and animal pests in colorful fashion.

More information: Companion Planting in the Kitchen Garden Planner

Mixed cropping: If you place smaller groups of plants throughout the garden, rather than planting all of your potatoes, say, in one place, it will be more difficult for pests to converge on the whole lot. Mixing marigolds and strong-smelling herbs in among your plants can deter insect pests by masking the smell of the plants they want to eat.

Interplanting herbs and flowers that attract beneficial insects, such as dill or fennel, is another effective way to give the "good guys" an edge.

Timed planting: Insects usually appear at about the same time every year, so you can schedule your plantings to avoid the heaviest feeding stages. An excellent chart of some common insect emergence times can be found in The Encyclopedia of Natural Insect and Disease Control. You could also keep records to gain familiarity with these patterns in your own region and microclimate.

Resistant varieties: Sometimes certain varieties or cultivars show a strong natural resistance to pests and/or disease. Seed catalogs are a good guide for selecting these resistant varieties. Why not experiment and try some along with your old favorites.