Many fungicides are registered for use on commercially produced plants, but only a few are readily available to home gardeners. Most fungicides are not restricted in use or categorized as highly toxic. Yet many of these fungicides are difficult for the average home gardener to obtain in small quantities. Several companies cater to the home gardener 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 or for residential use 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 home garden formulations and packaging are identified with the symbol H.
Some of the fungicides, such as the sulfur and copper-based products, can be used for growing organic produce. Others, such as captan, tebuconazole, 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 Fung-onil, 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.), or in how it is applied (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-based products, chlorothalonil, and sulfurs must be present before fungi begin the infection process. Although myclobutanil and tebuconazole are locally systemic, they must be applied soon after (or before) infection for maximum benefit. None of these fungicides can cure heavily diseased plants.
These products may help control diseases but are not a replacement for cultural practices such as crop rotation and the use of resistant varieties. Use fungicides as part of an integrated program for disease management.
Please read and follow the precautionary and safety statements on all pesticide labels including those listed as organic. Some of the products below may be dangerous in their concentrated form to humans, domestic animals, and/or aquatic organisms such as fish. Many products can be toxic if accidently splashed into the eyes, inhaled, swallowed or absorbed through the skin. Some people can develop skin rashes if repeatedly exposed to some products.
The following chemicals are listed first by their common name (in bold), then by trade names used for the home garden market (in parentheses). The chemical and its uses are then described.
Bicarbonate (Bi-Carb Old Fashioned Fungicide)—Can be used on a number of crops for powdery mildew management but take care. These are a potassium-based and not the sodium-based material you find in the kitchen. Although these materials get a lot of press they are NOT effective when used after infection. Do not use for black spot management on rose either, as it will not work.
Captan (Hi-Yield Captan Fungicide, Bonide Captan Fruit and Ornamental)—One of the best all-around, general-purpose fungicides to manage 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 manage 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. If you use the powdered formulation you will need to agitate (shake, swirl, etc.) the tank to keep it mixed up.
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. It is labeled for vegetables, fruits, and many ornamentals including shade trees.
Copper-based compounds (Monterey Liqui-Cop and many other names with the word copper in them)—There are many copper products available including copper sulfate, copper octanoate, and copper-ammonium complex. Bordeaux mixture, made by adding copper sulfate and calcium hydroxide to water, was the first fungicide. It still is used in France to manage doznd a few vegetables. It controls many fungal and bacterial cankers, galls, blights, and leaf spots.
DMI-type fungicides such as myclobutanil (Spectracide Immunox), propiconazole (ferti-lome Systemic Fungicide, Infuse Systemic Disease Control), tebuconazole (BioAdvanced Disease Control) and triticonazole (Ortho Rose & Flower Disease Control)—These products are labeled for use on several ornamental plants and have been used for years to manage all of the important rose diseases. 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.
Horticultural, essential and botanical oils (Neem oils such as R-T-U Year-Round Spray Oil, Essential oils such as Dr Earth Final Stop)—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 otherwise you get poor coverage (since oil and water do not mix). 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. Never mix oils with sulfur products as it can be toxic to plants and some labels warn of using either product within 2 weeks of each other.
Phosphorus acid (Monterey Garden Phos, Organocide Plant Doctor)—These materials are good for the control of oomycete diseases such as Sudden Oak Death, late blight of potato and tomato, downy mildews, root rots, and similar diseases. Apply them on the ground at the start of root growth or on the foliage in autumn before leaves fall for root rots. These are not fertilizers as the P is unavailable to the plant. That property also makes them systemic and move throughout the plant. Do not apply too close to a copper spray since the acid will make too much copper available and hurt the plant. Depending on the disease they are also labeled as basal bark sprays or for injection into trees.
Soaps (Safer’s Insect Killing Soap and many others)—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. If the temperature is over 85°F to 90°F at the time of application, some foliage may burn. Some plants, like ‘Concord’ grapes or apricots, are sensitive to sulfur and will burn at any temperature. Never mix sulfur with oil products as it can also be toxic to plants and some labels warn of using either product within 2 weeks of each other. Some people can develop skin irritation when frequently handling plants parts treated with sulfur.
Thiophanate methyl (Bonide Infuse Systemic Disease Control Lawn and Landscape)—This granular form of the chemical is labeled for lawn care but there are only a few diseases that might benefit from its use. It can also be used to manage some root diseases on ornamentals. It needs to be watered within 24 hours after application to move it down into the root zone. From there the roots will pick it up and distribute it through the plant.
Biological Control (Serenade Garden Disease Control {Bacillus subtilis strain QST 713} and Monterey Complete Disease Control {Bacillus amyloliquefaciens strain D747})—Several companies are marketing the use of microorganisms (Bacillus spp.) to combat plant disease pathogens. They make some wide claims about how many different diseases they can control. In general, you will get good management of powdery mildew diseases with these products. These products may suppress some of the soilborne pathogens but are not a replacement for cultural practices such as crop rotation and the use of resistant varieties; use as part of an integrated program for disease management. In many cases the active ingredient organism need not be alive to get disease control. There may be a protein that the organism produces that is active against pathogens or it may just stimulate plant defense mechanisms.
Biological Control (Actinovate Lawn and Garden {Streptomyces lydicus strain WYEC 108})—This soilborne, filamentous bacterium has many claims but scant research to back it up. Has been used successfully on blueberry mummy berry, grape powdery mildew, and some control of strawberry gray mold. This product may suppress some of the soilborne pathogens such as Fusarium diseases but are not a replacement for cultural practices such as crop rotation and the use of resistant varieties; use as part of an integrated program for disease management.
You may also find other fungicide active ingredients mixed together and/or with insecticides. Many of these are labeled for various crops for more complete management of several problems at the same time. They are good when you have multiple pest problems but not if you have only one problem. (Ortho Rose and Flower Insect and Disease Control or Bonide Fruit Tree and Plant Guard).
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, acutely 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 managed using several non-chemical management techniques. A combination of techniques, both cultural and chemical, usually works quite well for management of most diseases.