Many fungicides are registered for use on plants, but only a few are readily available to gardeners. They are not restricted in use or categorized as highly toxic. Often they are difficult for the average gardener to obtain in small quantities. Several companies cater to the backyard grower by packaging in small quantities and selling through local variety stores or garden centers. Some of these labels, however, do not specify for “home owners only” and therefore cannot be recommended by Washington master gardeners. These products can still be used by home gardeners. In the Host and Disease Descriptions section of this book, materials available in homeowner formulations and packaging are identified with the symbol H.
Some of the fungicides, such as the sulfur and copper products, can be used for growing organic produce. Others, such as captan, triforine, and chlorothalonil, are synthetically produced and not used for organic gardening.
Fungicide names can be very confusing at first. Plant pathologists usually refer to them by their general or common name such as chlorothalonil. Manufacturers and retailers use trade names. For example, chlorothalonil is packaged as Fungonil, or Multi-Purpose Fungicide for the home market, and as Bravo or Exotherm Termil for commercial markets. The differences are in the formulation (such as a liquid or powder), in how much active ingredient there is per unit of weight (10%, 50%, etc.) and in how it is used (as a spray or drench, for example). Some products, such as a generic flower or fruit spray, may contain more than one type of chemical, usually an insecticide and a fungicide together. The ingredient list on the label will tell you what is in the product.
The label is the law. No matter what anyone else says, always follow label directions. To do otherwise is against the law. However, there are some specific exceptions. If the label says to use a certain amount of product, you cannot use more of it. You can use less, but only if it is still effective at the lower rate. Sometimes a rate range is given so use the higher rate when disease pressure is high and the lower rate when you expect disease pressure to be low. Never use a product on a plant that is not listed on the label. You can use a product to control a disease that is not listed on the label as long as it is effective and the plant is on the label.
Some fungicides work better (stay on the plant longer or spread over the leaf surface) if a spreader sticker is mixed with the solution. It is usually a good idea to add these materials to powders or dusts to be sprayed on plants. Liquid fungicide formulations usually already include such compounds.
Understanding the disease cycle, proper timing, coverage and selection of the right fungicide are needed to get good control using fungicides. Many fungicides work by protecting healthy plant tissues. Captan, copper products, chlorothalonil, and sulfurs must be present before fungi begin the infection process. Although myclobutanil and triforine are locally systemic, they must be applied soon after (or before) infection for maximum benefit. None of these fungicides can revive heavily diseased plants.
The following chemicals are listed first by their common name, then by trade names used for the homeowner market. The chemical and its uses are then described.
Captan (Hi-Yield Captan Fungicide)—One of the best all-around, general-purpose fungicides to control a huge variety of plant diseases, but it is not very good against powdery mildews and rusts. Captan is labeled for ornamentals, lawns, vegetables, and fruit, sometimes alone or in mixes with other pesticides. It works well to control leaf spots, blights, and fruit and vegetable rots. It is compatible with many other fungicides but cannot be mixed with oils, lime, or strongly alkaline (soapy-feeling) materials.
Chlorothalonil (Ortho MAX Garden Disease Control, Bonide Fung-onil, GardenTech Daconil)—This is another good, general-purpose fungicide for many fungal diseases. It is best as a foliar treatment as it breaks down rapidly in soil. It is one of the longer lasting fungicides available so you do not have to spray as often, as with other products. Some people are allergic to it and may develop skin rashes if repeatedly exposed. It is labeled for vegetables, fruits, and many ornamentals including shade trees.
Copper-based compounds (Monterey Liqui-Cop)—There are many copper products, but fixed copper sulfate is the one most gardeners will find. Bordeaux mixture, made by adding copper sulfate and calcium hydroxide to water, was the first fungicide. It still is used extensively in France to control downy mildew on grapes. It is a highly effective fungicide that stays on the plant surface even after several rains. Usually it is used as a dormant spray as it may burn young tissues. The copper most commonly obtained is labeled for use on many fruits, nuts, ornamentals, and a few vegetables. It controls many fungal and bacterial cankers, galls, blights, and leaf spots. Experts recommend copper for many plants and diseases not listed on labels because the federal agencies have decided that no tolerance levels need to be established due to copper’s low toxicity and insolubility in water.
DMI-type fungicides such as Myclobutanil (Spectracide Immunox), Propiconazole (ferti-lome Systemic Fungicide, Fungi Fighter Lawn Fungicide, Infuse), and Tebuconazole (Bayer Advanced Disease Control)—These fungicides have been around in commercial agriculture for some time and are now available in home packaging. They are very effective against powdery mildews, rusts and many leaf spots. Best used when green foliage is on the plant since they move into plant tissues. Be careful not to overuse these materials as fungi can develop resistance resulting in poor disease control. You may also find other active ingredients in this same class mixed with insecticides (Amdro Rose and Flower Care or Ortho Rose and Flower Insect and Disease Control).
Horticultural and Botanical Oils (Neem Oils such as Concern Garden Defense or Green Light Rose Defense, R-T-U Year-Round Spray Oil, Jojoba Oils such as E-Rase)—Some of these are petroleum derived oils while others are from plants. These are effective when powdery mildew has gotten away on you. These products are good eradicants of the fungus if you get excellent coverage of the plant surfaces. Do not use when plants are wet from rain, irrigation or dew. Some oils such as neem oil have a lot of paraffin and may freeze up at low (less than 40°F) temperatures. Just use warm water to get it back in solution. Overall, the neem oils have not done as well for disease management as other horticultural oils in western Oregon.
Lime sulfur or calcium polysulfide (Bonide Lime Sulfur, Hi-Yield Improved Lime Sulfur)—Lime and sulfur boiled together create calcium polysulfide, a foul-smelling but effective fungicide. It is primarily used as a dormant spray because it can burn young foliage. However, it can be safely used on some crops when diluted with a larger amount of water. It is labeled for several ornamentals and fruits and controls powdery mildew, scab, brown rot, peach leaf curl, rusts, and mites.
Soaps (Safer’s Insect Killing Soap)—These are effective on powdery mildew if you use them often and get excellent coverage of the plant surfaces. Also has activity on soft-bodied insects.
Sodium or Potassium Bicarbonates (Bi-Carb Old-Fashioned Fungicide)—Yes sodium bicarbonate is just plain old baking soda. The potassium bicarbonates were developed to prevent salt build up from the sodium form. No, not as good as many of the other products already listed but better than doing nothing. Research data is usually based on adding in oils, which are effective by themselves. Absolutely will not control black spot of rose.
Streptomycin (ferti-lome Fire Blight Spray)—An antibiotic produced from a common soil inhabiting, filamentous bacterium. There is a home label from ferti-lome for use on apples, pears and pyracantha to manage fire blight. Needs to go on at bloom when the weather is expected to be warm and wet. Although it is labeled for rose crown gall you most likely will be better off getting a new rose than following instructions on the label.
Sulfur (Safer Garden Fungicide, Bonide Sulfur Plant Fungicide and many other names with the word sulfur in them)—Elemental sulfur alone is active against powdery mildews, some rusts, leaf blights, and fruit rots. It also is active against mites. It is labeled for fruits, beans, and many ornamentals. Shorter application intervals are needed with sulfur when compared to other products. Sulfur is active as a vapor only within a certain temperature range. If the temperature is over 85 to 90°F at the time of application, some foliage may burn. At low temperatures, no fungicidal activity will occur. Some plants, like ‘Concord’ grapes or apricots, are sensitive to sulfur and will burn at any temperature.
Thiophanate methyl (ferti-lome Halt Systemic Fungicide)—A close relative to benomyl (Benlate) and sometimes can be found at garden centers or nurseries. Use of Benomyl on ornamentals was pulled in the early 1990’s. This is the next best thing and can be used on ornamentals as well as lawns and some fruit trees. If you had fungi resistant to Benlate then they will be resistant to this product also. Tank-mix this product with another fungicide for better management of diseases.
Triforine (Ortho Orthenex, Ortho RosePride Disease Control)—Another locally systemic fungicide to control powdery mildew, rusts, and some leaf spots or blights. It is labeled for use on several ornamental plants and has been used for years to control all of the important rose diseases. Some gardeners may find that it does not work as well as it has in the past due to the build-up of fungi resistant to the chemical.
Compared to nematicides and insecticides, these fungicides have low toxicity. One would have to eat, drink, or breathe very large quantities to have any immediate or short-term effect on one’s health. Some fungicides, however, have been shown to cause tumors in laboratory animals. When using any pesticide, toxic or not, take several precautions. These are always outlined clearly on each label. Wear protective clothing (gloves, long-sleeve shirt, and long-leg trousers) while mixing or applying the product, keep it out of reach of children and animals, apply it when weather is calm, and clean all equipment, clothes, and yourself after application.
One last point. Many diseases can be controlled using several nonchemical control techniques. A combination of techniques, both cultural and chemical, usually works quite well for control of most diseases.