Use natural disease control
Using natural disease control can be an inexpensive, effective method of ridding your lawn, garden, and landscape of common plant diseases without the use of harmful synthetic chemicals.
How to use natural disease control
Diseases affect all living things, including plants. Most plant diseases are fungal, bacterial, or viral. A plant disease prevents the plant from performing the functions it needs to thrive and grow. Some fungal or bacterial diseases, for example, use up the plant's food supply, inhibiting it's growth, while other bacterial infections can block pathways, restricting the plant’s intake of water and nutrients. Viruses can also stunt a plant's growth or disfigure its foliage. Most common plant diseases are fungal.
Fungal diseases are found on lawns, in vegetable gardens, and on landscape plants. Since fungi lack chlorophyll and can’t manufacture their own nutrients by photosynthesis as plants do, they must get their food from other living organisms. Not all fungi are bad. The majority of fungi feed on decaying and dead matter, helping it decompose and return to the soil, supplying it with minerals and other nutrients. Mycorrhizal fungi are found on the roots of most plants, and create a symbiotic relationship that helps the plants absorb phosphorus and other nutrients as well as survive a drought.
Other fungi are harmful, however, causing fungal diseases such as blights, botrytis, clubroot, damping off, mildews, rusts, spots, and wilts. Lawns may suffer from fungal diseases such as dollar spot, brown patch, and a variety of rusts, smuts, and blights.
Plants can get diseases from bacteria and viruses just like people do. Unlike insects and many fungi, which can be seen with the naked eye, you can’t see bacteria and viruses. Recognizing and treating these diseases can be challenging.
Bacteria are single-celled microorganisms which often secrete a sticky or slimy substance. A plant usually only gets a bacterial disease if it has a wound or cut through which the bacteria can enter (from insect damage, for example). Bacterial diseases are not as prevalent on plants as fungal diseases or viruses. Common bacterial diseases include bacterial wilt and scab.
Some bacteria are actually good for plants. Just as the bacteria used to make yogurt is beneficial to people, the nitrogen-fixing bacteria on the roots of legumes are good for plants, helping them absorb nitrogen from the air.
Viruses are microscopic bits of genetic material (RNA or DNA) encased in a protein coating. Viruses infect other living things in order to reproduce: Plants, animals, people—even fungi and bacteria—can be infected with viruses. A virus attaches itself to a host and reproduces inside the plant’s cells. A single plant may host millions of virus particles.
Viruses are often the most difficult plant diseases to diagnose. They may attack brassicas, lettuce, potatoes, and tomatoes. A blotchy, mottled, light green-and-yellow “mosaic” pattern often appears on infected leaves, which also may be crinkled or curled.
Common plant viruses include bean mosaic, cauliflower mosaic, and cucumber mosaic. Viruses are named after the plant they were first discovered on; just because a virus is called cucumber mosaic doesn’t mean it only infects cucumber plants.
There are no cures for plant viruses, and they are difficult to eradicate. Viruses are often spread by infected insects which carry the disease, called vectors. Common vectors include aphids, thrips, whiteflies, and leafhoppers. Hands or garden tools that come in contact with infected plants can also spread viruses. The best remedy for viruses is prevention. Insect infestations such as aphids should be treated as soon as they are discovered. A few “healthy” aphids feeding on your plants won’t hurt them much, but if the aphids carry a mosaic virus, the virus may kill your plants.
Tips to prevent and manage plant diseases
- Learn how to identify common plant pests and diseases. Prompt action can help you treat an infection before it gets out of control.
- Don’t water too late in the day—make sure plant foliage is dry by dusk. Water spreads fungal diseases. Try not to work in the garden when it’s wet. Allow enough space in between plants for good air circulation.
- Wash soil off garden tools after using. Wash your hands if you've handled diseased plant material to keep from infecting healthy plants. Clean tools and plant pots with hot water and detergent at the end of the season.
- Use natural pest control to manage insect infestations.
- Practice crop rotation, which can help slow down the proliferation of clubroot spores, for example.
- Check plants and seedlings to make sure they’re free of pests and disease before you buy them.
- Dispose of diseased plants in the trash, don't add them to the compost. If you make your own compost and the pile has an internal temperature of at least 160°F, it will kill nearly all pathogenic fungi, bacteria, and nematodes, but why take the risk? Also, plant diseases may overwinter, so don’t bury diseased plant material in your yard.
- Plant seed and plant varieties that are disease resistant. The letters after the name tell you what the variety is resistant to. For example, the tomato “Roma VF”, is resistant to vericillium wilt (V) and fusarium wilt (F). Plants may be bred for resistance to nematodes (N), tobacco mosaic virus (T), alternaria (A), and other pests and diseases.
- Use organic biofungicides to eliminate fungi and bioinsecticides to control insects that spread bacteria and viruses.
- Try baking soda spray for fungal diseases: mix 1 teaspoon of baking soda dissolved in one quart of water.
Common fungal diseases
- Blights flourish in warm, wet weather affecting vegetable crops such as potatoes and tomatoes. The Irish Potato Famine in the 1840s was the result of potato blight. The first sign of blight is dark spots, progressing to wilting, yellow leaves, and rotting fruit. Cane blight affects cane fruits, especially blackberries. Remedies: Only purchase certified seed potatoes, which are free of disease. Destroy diseased foliage and discard infected potatoes (potato blight can overwinter on affected tubers). Practice crop rotation. For blackberries, thin to improve air flow, cut diseased canes to ground level.
- Botrytis (gray mold) is a common plant disease that affects vegetable crops such as lettuces and tomatoes; flowers such as peonies; and fruit such as strawberries and grapes. Botrytis likes cold, damp conditions. Brown spots or blotches on leaves are early indications, followed by a fluffy gray mold that kills the plant tissue underneath. Too much nitrogen fertilizer can lead to botrytis. Remedies: Keep foliage dry, clear garden debris at the end of the season, and destroy infected plant material and fruit. Maintain good air circulation.
- Clubroot is a fungal disease found in the vegetable garden. It affects brassicas such as broccoli, cauliflower, and cabbage. Clubroot occurs in acid soil. Once in the soil, it can survive for up to 20 years. Remedies: Grow plants from seed or purchase seedlings from a reputable grower. If your soil is infected with clubroot, raise the pH level above 7.2 to get rid of the disease, using organic soil amendments.
- Damping off is caused by soil-or water-borne fungi that causes seedlings to collapse and die or fail to emerge at all. The disease may result from infected plant pots, inadequate ventilation, or overcrowding. Remedies: Clean pots and flats, don't sow seeds too thickly, and avoid overwatering.
- Downy mildew causes leaves to turn yellow with a grayish or white mold underneath. Older leaves may have small black spots and die slowly in the fall. Lettuce, onions, peas, and spinach may be affected. Wet foliage can cause downy mildew. Remedies: Use drip irrigation or container watering. Don’t water with an overhead sprinkler.
- Powdery mildew looks like a powdery white dust (or raised "webbing" on apples) and takes hold in hot, dry conditions when plants are overcrowded. Plants affected include grapes, lilacs, phlox, squash, and zinnias. Remedies: Water sufficiently. Destroy infected leaves to keep it from spreading to other plants. Use baking soda spray.
- Dollar spot appears as small spots of bleached-looking grass and white cottony threads of fungus on the lawn in the morning. Causes include thatch and nitrogen deficiency. Dollar spot often occurs in spring and fall, when days are warm, nights are cool, and there's too much moisture. Remedies: Aerate the soil, add nitrogen, or improve drainage.
- Leaf and pod spots (anthracnose) affect the vegetable garden, causing sunken brown spots on beans, brassicas, cucumbers, peppers, and tomatoes. Anthracnose also attacks trees, especially maples, sycamores, and dogwoods. Remedies: For vegetables, buy disease-resistant cultivars and dispose of infected plants. For trees, keep well-watered and mulched. Destroy infected leaves.
- Black spot appears on roses. Spots are often surrounded with a yellow ring. Remedies: Spray once a week with fungicidal soap or baking soda spray.
- Fusarium wilt and verticillium wilt cause leaves of vegetable plants to yellow and wilt, eventually turning brown. The disease starts from the base of the plant and works its way up, eventually killing it. Fusarium wilt is more prevalent in warm climates and verticillium wilt in more common in cool climates. Both can be spread by cucumber beetles and squash vine borers. Fusarium and verticillium fungi can survive in soil for several years without a host plant, so crop rotation as little effect. Remedies: Grow disease-resistant varieties. Destroy infected plant matter.
Common Bacterial Diseases
- Bacterial wilt, which is carried by insects such as cucumber beetles, causes plants to suddenly wilt and die. Cucumbers, melons, and squash are prime targets. If you cut the stem of the plant open and see slimy threads, the plant most likely has bacterial wilt. Remedy: Control beetles early in the season using natural pest control. Try floating row covers. Destroy affected plants to prevent spread.
- Scab produces rough, brown, corky spots on roots or tubers such as potatoes, beets, and radishes. Scab also affects apples. The defect is cosmetic only, and the produce is safe to eat. Scab is more prevalent in highly alkaline, sandy soil. Remedies: For vegetables, keep foliage dry, and don’t overcrowd plants, and providing adequate air circulation. Avoid liming soil prior to planting potatoes. For apple trees, plant resistant cultivars and rake up and dispose of infected leaves, as spores will overwinter.
Common viral diseases
- Cucumber mosaic affects tomatoes, peppers, squash, spinach, celery, and beets, as well as cucumbers. The cucumber mosaic virus is carried by aphids. Remedies: Plant mosaic-resistant varieties. Control aphids using natural pest control. Remove and discard diseased plant material.
- Tobacco mosaic can be spread by cigars, cigarettes, pipe tobacco, or chewing tobacco that is infected with the virus. Vegetable plants in the nightshade family, including tomatoes and peppers can be infected with tobacco mosaic. Remedies: If you use tobacco, keep these products away from the garden. Wash your hands before gardening, as touching tobacco infected with the mosaic virus can spread it to your garden plants.
Find it! Natural disease control
Buy Shield-All II Neem Fungicide for fungal diseases on vegetables, trees, shrubs, houseplants, roses, and ornamentals. Choose Plant Guardian Biofungicide (wettable powder or liquid concentrate) to prevent and fight especially challenging fungal diseases.
Using natural disease control helps you go green because…
- It prevents the use of cancer-causing synthetic chemical fungicides.
- It prevents the use of synthetic chemical fungicides which kill other beneficial organisms.
- It keeps your soil healthy.
The US is the world's largest manufacturer of pesticides, followed by Germany and Japan. In 2001, US shipments of pesticides and other agricultural chemicals totaled $8.9 billion, with nearly 25 percent of pesticides shipped used for lawn, garden, and other noncrop household and institutional purposes.
Though pesticides were in use since before World War I, it was not until 1954 that public health concerns were addressed. Congress amended the Federal Food, Drug, and Cosmetic Act (FDC Act) requiring the US Food and Drug Administration (FDA) to set residue tolerance levels (maximum allowable pesticide residue) for pesticides used on raw produce. These tolerance levels were determined using a risk/benefit analysis—public health risks were weighed against benefits to the food supply.
Initial legislation focused on preventing pesticides from entering the food supply via food grown commercially and in home vegetable gardens. Health risks, however are not limited to ingestion—pesticides can be absorbed through the skin or inhaled. Exposure may come from contact with chemical pesticides on treated grass or from mists or sprays during insecticide application. Exposures can also come indirectly from food, drink, or household items contaminated by pesticide application. Pets are also at risk from pesticide exposure, and may contribute to human exposure by tracking lawn and garden pesticides into the house.
In 1970, the newly created US Environmental Protection Agency (EPA) was tasked with setting residue tolerances, and two years later Congress created the Federal Environmental Pesticides Control Act, requiring all pesticides manufactured in the United States to be registered with the EPA. In the 1990s, the Clinton administration introduced a program to reduce the use of agricultural pesticides in the United States, and to prevent the export of banned pesticides for use on foreign crops, which are then imported back into the US In 1996, President Clinton signed the Food Quality Protection Act, which stated that all exposures to pesticides must be shown to be safe for infants and children, who are especially at risk when exposed to these chemicals. A 1998 study by the Environmental Working Group, however, found that 77,000 infants consume unsafe levels of pesticides every day.
Although copper is a valuable trace mineral in soil, copper-based fungicides can cause a severe toxicity if overused. Therefore, copper fungicides are often not recommended, even though they are approved as organic.
Related health issues
Mancozeb and chlorothalonil, popular lawn fungicides used by homeowners and commercial lawn care companies, cause cancer in animals and are classified by the EPA as probable cancer-causing chemicals in humans.  Popular products that contain chlorothalonil include Bonide Liquid Fungicide, Daconil 2787, Dragon Daconil 2787, Fungi-Shield, Ornamental and Vegetable Fungicide, Pennington's Pride Multi-Purpose Spray, and Security Fungicide.
Mancozeb also reacts with sunlight to form a new compound the EPA categorizes as a known human carcinogen.  Mancozeb is a broad spectrum protectant fungicide used on vegetable and ornamental plants for many common diseases including anthracnose, leaf spots, downy mildew, blights, scab, rusts, and smuts. Some brands are labeled for common fungal lawn diseases.  Popular products that contain mancozeb include Bonide Mancozeb Plant Fungicide with zinc, Dithane T/O and WF, Dithane-45, Dragon Lawn and Vegetable Disease Control, Dragon Mancozeb Disease Control, Green Light broad spectrum Mancozeb, Hi-Yield Maneb Lawn and Garden Fungicide, and Maneb.
Tests show that commonly used agricultural and lawn fungicides, such as Maneb-80, can cause hyperactivity in animals after a single dose. The researchers state that there is little investigation of the toxicity of herbicides and fungicides, even though their yearly growth and production outpace that of insecticides.
- acidic: A pH of 1.0 to 7.0.
- bacteria: single-celled microorganisms.
- biofungicide: A fungicide derived from natural materials such as animals, plants, bacteria, and certain minerals.
- bioinsecticide: An insecticide derived from natural materials such as animals, plants, bacteria, and certain minerals.
- brassicas: Members of the mustard family (of the genus Brassica) including brussels sprouts, broccoli, cabbage, cauliflower, and turnips.
- compost: A mixture of decayed organic matter that is used for fertilizing and conditioning soil.
- crop rotation: The practice of growing different crops in succession on the same land chiefly to preserve the productive capacity of the soil.
- fungus: An organism which produces spores and cannot manufacture chlorophyll, including molds, mildews, rusts, smuts, mushrooms, and yeast.
- fungicide: An agent that kills fungi.
- legume: A member of the Fabaceae or Leguminosae family of plants, including peas, beans, peanuts, lentils, chickpeas, and soybeans.
- nitrogen fixing: The process by which bacteria that live in root nodules take nitrogen from the air and convert it to a form that plants can absorb.
- pathogenic: Causing or capable of causing disease.
- pH: The measured acidity of soil
- vector: An organism, such as an insect, that transmits a pathogen.
- virus: A simple microorganism (or complex molecule) that must infect another living thing in order to reproduce.
- BBC - Pest and Disease Identifier Use the BBC's database which asks a series of questions about plant symptoms, tells you which disease it might be, and suggests treatments.
- University of Georgia College of Agricultural & Environmental Sciences - Plant Pathology Find out which diseases may affect your lawn, ornamentals, vegetables, fruits, nuts, and farm crops using this illustrated database.
- US Environmental Protection Agency - What are Biopesticides? Learn what biopesticides are from the EPA.
- Tukey, Paul (2006) The Organic Lawn Care Manual. North Adams, Massachusetts: Storey Publishing
- Answers.com - Pesticides and agricultural chemicals, not elsewhere classified (SIC 2879)
- Office of New York State Attorney General Andrew M. Cuomo - Home and Garden Pesticides: Questions and Answers about Safety and Alternatives
- The Dirt Doctor - Organic Products and Their Recommended Uses
- Chemical Pesticides - Health Effects Research
- University of Georgia - Homeowner Fungicide Guide
- University of Georgia - Homeowner Fungicide Guide: Mancozeb