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Fungicides can be an important component of a disease management program. However, it is important to remember that their use should be integrated with the use of sound cultural practices, a knowledge of pathogen and disease biology, and disease resistance whenever possible.
Fungicides are only effective when infectious plant diseases that are caused by fungi are truly the cause of the problem. In many cases, pests and diseases follow other environmental imbalances and may not be the major problem. In cases such as these, a fungicide may help but is often not the total answer. Also, it is important to remember that fungicides are only effective if several rules are followed. First, the correct material must be selected. This depends on correct diagnosis and identification of the pathogen. Second, the chemical must be applied at the right time of year and frequently enough to protect plant material adequately. Third, fungicides must be applied properly over plant surfaces. These three rules depend on making correct decisions based on correct knowledge. Too many people simply ?EUR??,,????'??spray and pray,?EUR??,,????'?? and are often disappointed with the results.
You must be sure of what the problem is before proceeding. The most effective fungicides in use today have been developed for specific situations and specific diseases. To use these chemicals, you must spend time making a correct diagnosis.
Your state Extension specialists, plant disease diagnostic clinic, and county Extension agents can assist you with the proper diagnosis.
Diagnosis leads to selection of the right material to do the job. Usually, several materials are effective against the type of disease you are dealing with. For instance, triforine, sulfur or triadimefon all control powdery mildews. Before selecting any chemical, read the label. Can you carry out the instructions? Is the plant type listed on the label? If so, the chemical is registered for use on the plant, and should be effective in providing disease control if used properly. If not, it is illegal to use that particular pesticide.
Foliar application fungicide sprays usually work in controlling infectious diseases because they act as a chemical barrier on leaf, stem or flower surfaces. When the pathogen arrives on the plant surface, it encounters this barrier and is unable to infect the plant. Effective fungicide use requires that this barrier be as complete as possible. A spray method must provide the best combination of practical usefulness and good coverage. For many diseases, special attention must be given to undersurfaces of leaves, especially on the lower leaves of the plant.
The completeness of the barrier depends on how well the spray spreads and sticks to the plant surfaces. For this reason, spreader-stickers or spray adjuvants can be added to many sprays. Sometimes the product label alerts the user to these problems. However, observing the spray deposit after you have finished some of the job may be the best way to decide if an adjuvant should be used. Hairy or waxy foliage is especially difficult to cover properly without a spreader-sticker.
Timing refers to when and how often the spray must be applied to effectively control a disease. The first application usually is made at a time close to but before the pathogen arrives on the plant surface. This information is often provided on the pesticide label or is available in Extension literature from your local county Extension agent. In most situations, fungicides are not effective in controlling the disease if the pathogen has already entered (infected) the plant tissues. In many cases, specific information about the disease cycle may be needed to time the first application correctly.
After the first application is made, the pesticide barrier is established on the plant surfaces. Effective use involves keeping this barrier active and complete throughout the time that the pathogen can arrive on and infect the plant. Modern fungicides are developed so that they do not persist in the environment for long periods of time. Rainwater, sunlight, microbial action and oxidation decrease effectiveness of the fungicide. Reapplication of the spray is needed in many cases to keep the fungicide barrier active.
Plant growth also affects the completeness of the barrier. As new leaves and shoots appear, they are unprotected and may be subject to infection. If so, they must be recovered with the barrier.
The fungicide label gives reapplication guidelines, usually in ranges of 7-14 day intervals. If excessive rainfall or rapid growth of the plant occurs, the shorter interval between sprays should be used. If not, use the longer interval.
This information was prepared by Charles C. Powell, Extension Plant Pathologist (retired), The Ohio State University.
Turf diseases and the use of fungicides is a broad topic, so let?EUR??,,????'???s focus on one common problem?EUR??,,????'??+brown patch?EUR??,,????'??+and one common cool season turfgrass?EUR??,,????'??+tall fescue. Brown patch is a turf disease that tends to become active when a dry spell of weather is followed by a period of warm and wet weather.
Before getting out the fungicides, let?EUR??,,????'???s talk cultural practices that can keep brown patch from developing and spreading. Summer management includes reducing the amount of time the fescue is wet and keeping the soil from being excessively damp.
Irrigate tall fescue deeply, but infrequently. Apply enough water to wet the root zone, then reapply when the turf begins to wilt.1 With this in mind, when you water is important. Early morning irrigation, between midnight and 6 a.m., is recommended, as it washes the large droplets of dew and guttation from the foliage. This allows the turf to dry quicker after sunrise. (Note: guttation water, the second component of dew, is exuded out the plant through the hydathodes?EUR??,,????'??+the small opening normally at the tip of the leaf. This moisture is high in organic compounds (amino acids) that are food for fungi.2
Irrigation before or after sunrise will extend leaf wetness and speed brown patch development.
Tall fescue should be mowed to a height of 3 to 3.5 inches during summer, which helps keep the canopy open and dry and slow the spread of brown patch.
In shady areas, prune the shrubs and trees to let more sun on the turf. Again, this will help reduce brown patch growth, while improving the overall health of the turf. Note: If the turf still gets too much shade, a shade-tolerant turfgrass (hard fescue or strong creeping red fescue) is a better choice than tall fescue.
Poor soil drainage will only encourage brown patch, so install drainage tile, reduce soil compaction, and/or modify the soil profile to increase drainage. If drainage is still poor, forget the turf and install other landscape features.
?EUR??,,????'??With a broad spectrum product ?EUR??,,????'??? you are pretty much sure of getting everything that could be a serious problem in a lawn care situation,?EUR??,,????'???EUR??,,????'??+Rich Hanrahan, a product development manager for fungicides.
Excessive nitrogen levels of nitrogen fertilizer enhance the severity of brown patch. High nitrogen levels produce soft, lush leaf tissue that is easily invaded by the brown patch fungus. To help slow the spread of brown patch nitrogen fertilizer should not be applied to tall fescue after May 1. If small amounts of nitrogen (>0.25 lb N/1000ft.2) are applied during the summer to maintain color, then a preventative fungicide program is recommended.
A preventative fungicide program should be undertaken where brown patch has been a problem in the past. Products containing the active ingredient thiophanate-methyl will provide good control, but must be reapplied every 14 days when the disease is active.1
Here are a few outstanding brown patch fungicides (with application amount per a 1,000 sq. ft. area):2
Each provide about 28 days of control. Should be applied every 21 days for best results.
Note: A fungicide like Armada is a full-spectrum fungicide that combines the active ingredients in Compass (Trifloxystrobin) and Bayleton (Triadimefon) to prevent and control not only brown patch, but these other cool-season turf diseases: dollar spot, leaf spot, anthracnose, summer patch, gray leaf spot, rapid blight, red thread, pink patch rust, southern blight, stripe smut, fusarium patch and pink snow mold.3
References
7 to 14: Day intervals, the usual range reapplication rates of fungicides. If excessive rainfall or rapid growth of the plant occurs, the shorter interval between sprays should be used. If not, use the longer interval. Source: Ohio State University Extension Service
1945: The year scientists began the process of synthesizing organic salts of iron, zinc and mercury as fungicides.
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
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