Take care of your plants
Identifying the pest
Predators, traps and deterrents
Organic insecticides
Pathogens and disease
Resources

Take care of your plants
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.

Your Garden Is an Ecosystem
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.

Care of Your Plants
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.

Garden Cleanup:
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.

Make garden clean-up a part of your yearly routine.

Crop Rotation
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.

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.

Basil is said to be beneficial to tomatoes; carrots grow well with leaf lettuce, and their roots exude a substance that helps peas; and members of the allium family, such as onions and garlic, effectively deter pests that attack roses. You also need to be aware of certain plants that hate each other and inhibit each other's growth. For example, tomatoes and members of the brassica family (broccoli, cabbage, etc.) do not grow well when planted together.

Consider planting an assortment of flowers or wildflowers in the fields, meadows, or formal beds that surround or adjoin your vegetable garden. Ornamental alliums, such as nodding onion (Allium cernuum), make especially good insectary plants, as do most members of the Apiaceae (Celery Family), Asteraceae (Aster Family), and Lamiaceae (Mint Family). Growing insectary plants near the garden provides habitat for many beneficial insects, which in turn help control pest populations around your other plants.

Try intercropping based on growth characteristics. Deep-rooted plants and shallow-rooted plants grow well together in a group, because they draw water and nutrients from different layers of soil. Examples include Swiss chard and beans, or lettuce and carrots. Corn and cucumbers have another symbiotic relationship: both like heat and well-drained soil, but cukes like the shade provided by corn plants.

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 standby favorites!

Even when you take good care of your plants, you will still encounter some insect problems.

Identifying the pest
Your first job when you discover a problem is to identify the pest and/or the damage it causes. This will allow you to determine the least toxic, yet most effective solution. There are two types of insect pests.

Sucking Insects
Aphids, leafhoppers, and harlequin bugs insert their long mouth parts into plants and suck out the juices. As they feed, some of these insects can also transmit plant viruses. Typical signs of sucking damage include a weakening of the plant; yellowed, brown or wilted leaves; and a sticky substance or sooty black mold covering the leaves (this is especially common with aphids). Unlike most insect pests, these look like adults as soon as they hatch from the egg.

Chewing Insects
This group includes caterpillars and beetle larvae, such as the Colorado potato beetle, cabbage worms, and tomato hornworms. They are voracious feeders that tear and mash plant tissue, -nibbling on leaf margins or making holes through leaves, and they are capable of completely defoliating a plant. Most chewing insects go through a complete metamorphosis, from eggs to larvae to pupae to adults, changing appearance at each stage. Different insects cause damage at different points in this cycle, sometimes in more than one stage (the Colorado potato beetle, for example, is destructive as a grub and as an adult).

In general, insects are easiest to control during the egg stage. Simply remove the eggs from the underside of leaves and dispose of them. Since many insects reproduce more than once during a season, you should keep your eyes open for eggs all summer long. Larvae and nymphs often overwinter in the soil or in plant debris, so garden cleanup in the fall is a good means of prevention.

Consult the recommended books for tips on how to recognize the symptoms of various insect attacks, and for detailed information on the life cycles of your problem pests.

Predators, traps and deterrents
Many types of pests can effectively be deterred with physical barriers and traps. You can protect young seedlings form cutworms by making a simple collar. Just cut out a three-inch strip of cardboard or ring of plastic from a simple yogurt container, encircle the stem and push it an inch or two into the soil.

Row covers are an effective deterrent to flying insects that want to lay eggs on your plants. If you use row covers, you may need to remove them to allow pollination to occur, and then replace them after the flowers have disappearted. You should also be aware of the life cycle of the insect you are trying to control: be careful not to trap overwintering larvae inside a row cover!

You can also buy traps that attract insects by using color, taste and sex hormones. Examples include traps for aphids, whiteflies, thrips and Japanese beetles. Slugs have a particular affection for stale beer and will drown in a shallow saucer of it placed in your garden.

Our animal friends can be pests too. The Golden Rule here is: don't harm them, just make them want to leave your garden alone. A simple fence will keep out dogs and possibly cats. Deer are great jumpers, and it generally takes a seven-foot fence to deter them (unless it's an electric fence!). Repellents can be quite effective for deer, especially if you periodically change the location of the repellent. Deer become bolder when something becomes familiar.

Electric fence systems can prevent rabbits, woodchucks, deer, and perhaps your own chickens from getting into the garden. Burrowing animals, such as moles, voles, mice and gophers can be repelled by devices that create harmless sounds or vibrations they don't like. Deer, raccoons and skunks can also be deterred with sonic devices.

You can try to keep birds away from your vegetables with scarecrows and other homemade noise and commotion-makers. Netting can also protect plants from birds, especially fruits and berries.

Organic insecticides
No matter how well you care for your plants and maintain your garden, you will inevitably have to deal with pest problems at some point.

Biological Insect Control
Many very effective biological pest controls have become available during the past twenty years. These naturally occurring pathogens destroy specific insects but do not harm other creatures that inhabit the same environment.

The biological control most commonly used in gardens is Bacillus thuringiensis (Bt). This bacterium kills many kinds of insect larvae by paralyzing the digestive system. Bt is sold as a dust or liquid under such trade names as Dipel and Thuricide. A new strain that is effective against Colorado potato beetle larvae (Bt "San Diego") is sold under trade names such as Beetle Beater.

Milky spore (Bacillus popillae) is another example of a biological pest control. Once the bacterium becomes established in the soil, it can effectively control the Japanese beetle population in your yard for up to twenty years.

Natural Insecticides
Most natural insecticides are less toxic than synthetic chemicals. They don't accumulate in the environment or in animal tissues, and most insects don't readily develop resistance to them. Still, they can upset the ecological balance in your garden because some of them will also kill beneficial insects and honeybees. They should be used with caution and care.

Be aware of any specific toxicities indicated on the label, and spray late in the day when honeybees have returned to their hives. Always wear a mask and remove contact lenses when applying dusts, and wear gloves and protective clothing when applying any kind of insecticide. Follow label directions carefully.

Diatomaceous Earth (DE)
This is made from the fossilized skeletons of marine creatures known as diatoms. The razor-sharp particles pierce soft-bodied creatures such as slugs, beetles, aphids, spider mites, cabbage loopers, and hornworms (but not earthworms), killing them by dehydration. The trace minerals found in diatomaceous earth also enhance soil fertility. However, DE is not selective and will also kill some beneficial insects, such as ladybug larvae.

Insecticidal Soaps
Like DE, these work by inducing dehydration, but they are less toxic to bees and other beneficials. They are made from potassium salts of fatty acids. Some plants are sensitive to insecticidal soaps, so test a small area first, and avoid spraying on a hot, sunny day.

Botanical Insecticides
These products, which are derived from plants, include pyrethrum, rotenone, nicotine, sabadilla and ryania. These substances break down easily when exposed to light, heat or water, so they are less likely to contaminate soil or groundwater. Most states allow certified organic farmers to use these agents. However, they are some of the most toxic substances used in organic pest control, so use them as a last resort, and with discretion.

As with other insecticides, take proper precautions when applying botanical pest controls. Wear gloves and protective clothing, and avoid using any insecticides near waterways, because they could be harmful to fish.

Pathogens and disease
Blight. Rust. Fusarium wilt. Botrytis. Smut. Scab. The names we give to plant diseases are unpleasant and downright ominous. But then again, so are their consequences. Diseases often appear very suddenly, and can severely weaken or kill a plant within days. Plant diseases can be caused by fungi, bacteria, viruses or nematodes, which can be soilborne, carried through the air, transmitted by insects or lodged within dead plant cells.

As with insect pests, as soon as you notice a disease problem your first job is to make a diagnosis and identify the culprit. Treatment usually involves removing the infected parts of a plant, or the whole plant, and destroying them.

The same good cultural practices that prevent insect pest infestations are the first line of defense against disease-causing plant pathogens. Build healthy soil, use compost, keep your flowers and vegetables appropriately watered, and clean up garden debris.

Ways to prevent disease problems:
* 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 and regularly prune leaves or stems that you suspect may be diseased. Destroy the cuttings.

* Be sanitary. Humans are effective, if innocent, vectors 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.

Sometimes what looks like disease is really a nutritional problem. Improper pH, deficiencies or excesses of certain micro- or macronutrients in the soil, or temperature extremes can cause plants to appear diseased, and in a sense they are. Always check your reference books first to rule out nutritional problems. Often, such problems can easily be addressed by adding lime, compost, fertilizer or specific soil amendments. Foliar feeding, especially with organics like seaweed and fish emulsion, can be very helpful for boosting your plants' general health.

As you continue year by year to build healthy soil in your garden, to understand the nuances of your own ecosystem, and to learn more about insects, animal pests, disease pathogens, and their habits, organic prevention and control will become second nature. You'll find that you have fewer and fewer pest and disease problems, and it will become easier every year to control them without chemicals.

Resources
Favorite Books
The Organic Gardener's Handbook of Natural Insect and Disease Control eds. Barbara W. Ellis and Fern Marshall Bradley (Rodale, 1996).

The Gardener's Bug Book by Barbara D. Pleasant (Storey, 1994).

Rodale's Flower Garden Problem Solver by Jeff and Liz Ball (Rodale, 1990).

Bugs, Slugs, and Other Thugs by Rhonda Massingham Hart (Storey, 1991).

Natural Insect Control ed. Warren Schultz (Brooklyn Botanic Garden, 1994).

Carrots Love Tomatoes by Louise Riotte (Garden Way Publishing, 1975).

Web Sites
Iowa State Entomology Index of Internet Resources

Biological Control: A Guide to Natural Enemies in North America