- Do your homework. Learn what disease organisms are most likely to infest the types of turfgrasses you’re growing. Then, study the symptoms of potential activity of those organisms on your grasses so you can be watching for them.
- Disease issues are among the most difficult turfgrass problems to identify. The symptoms of multiple attack organisms can be similar, making diagnosis of what you discover tricky. In some cases, it may take laboratory analysis for exact identification. Early detection is extremely important.
- Monitor your fields. Refer to your site map and turfgrass quality records as the first step in identifying areas most susceptible to disease activity.
- Records from previous years make this step even easier, as disease activity typically returns to the same spots if you haven’t been able to change physical elements or cultural practices to avoid it.
- Once you know the what and the where, focus on the why.
Learning the Triggers
- Track the weather. Like weeds and insects, disease organisms become active when climatic conditions are favorable for them. With diseases, daytime and nighttime temperatures and humidity levels in the right combination often are triggers that activate the organisms. Look ahead to short- and long-term weather forecasts as well as monitoring the conditions you’re currently experiencing, to identify the thresholds of potential activity.
- While you can’t change the weather, you can manipulate certain growing conditions to reduce the grass plant’s susceptibility to specific disease organisms. Study the triggers for the fungal activity you anticipate, such as high nitrogen levels or excessive thatch, and be proactive in addressing them.
- Explore the options in grass varieties that are less susceptible to the disease organisms you’ve identified. With cool-season grasses, such as bluegrass, perennial ryegrass or turf-type tall fescue, you may be able to reduce disease pressure by overseeding with less-susceptible varieties that blend in well with your existing grasses.
- Because fields of warm-season grasses, such a bermudagrass or zoysiagrass, are typically a single variety, changing to another variety would require removal of the existing turfgrass and installation of the new.
Even with careful monitoring and the use of best management practices, disease pressure can occur and reach damaging levels. Research available fungicide options to incorporate into your disease management program.
- Even with careful monitoring and the use of best management practices, disease pressure can occur and reach damaging levels. Research the fungicide options to incorporate into your disease management program.
- One of the best resources to define fungicides and how they work and to assist in the critical step of selecting a product to combat fungal disease outbreaks is “Chemical Control of Turfgrass Diseases 2017,” developed by researchers at the University of Kentucky and Rutgers University.
- Commercial fungicides are never one-size-fits-all. This document clearly states their limitations: “They are effective only against specific turfgrass diseases. They must be applied at the right time to be effective. They have to be applied at the right rate to be safe and effective. They often must be applied repeatedly.”
Contact or Systemic
- Typically, fungicides are grouped into two general types: contact and systemic. Contact fungicides, sometimes called protectant fungicides, remain on the surface to which they’re applied and don’t enter the plant tissue. Once in place, they provide a barrier between the plant and disease organism. Just like sunscreen when applied to human skin, the barrier is active only on the specific area that it covers.
- Systemic fungicides are absorbed by the plant, moving from the surface to which they’re applied into the internal plant tissue.
- Within the broad category of systemic fungicides are subcategories which describe how the fungicide moves within the plant. These are described in scientific terms within the “Contact and Systemic Fungicide” section of “Chemical Control of Turfgrass Diseases 2017.” (The descriptions below are derived from that section.)
- Locally systemic fungicides don’t move far from the point at which they’re absorbed. Locally systemic fungicides that only move from one side of the turfgrass leaf blade to the other side are further classified as translaminar fungicides.
- Some systemic fungicides move within the plant’s xylem (water-conducting tissue), traveling upward in the transpiration stream but with little downward movement. These are called xylem-mobile or acropetal systemic fungicides. Within this group, some are termed “moderately mobile” while others are “highly mobile.”
- The last subcategory within the systemic fungicides is termed phloem-mobile. Phloem is the tissue that moves food from the leaves and other photosynthetic tissues to other plant parts. Phloem-mobile fungicides can move up and down within the plant, from the leaves to the roots and from the roots to the leaves.
- As the document states, “Systemic fungicides sometimes can suppress the fungus after it has infected the plant, whereas contact fungicide must be present on the plant’s surfaces before infection begins to be effective.”
- All of these descriptions about how a fungicide works are called its Mode of Action (MOA).
Preventive or Curative
- Fungicide applications are used in two specific categories: preventive and curative.
- Preventive applications are most effective. They should be used if an unacceptable level of disease activity has been present in a specific area previously, when both turfgrass vigor and climatic conditions closely match the current situation but the disease symptoms haven’t yet appeared.
- For the most damaging of turfgrass diseases, many turf managers opt to begin preventive treatment when the triggering climatic conditions are forecast and highly likely to occur.
- Curative applications should be used when an unacceptable level of disease activity is present. When this has occurred previously in a specific area, when both turfgrass vigor and climatic conditions closely match the current situation, and those conditions are likely to continue, curative applications should be made when disease symptoms first appear.
- Though the word curative implies the restoration of disease-impacted turfgrass tissues, in reality curative applications only protect uninfected tissues, including new growth, from becoming infected.
- Thus, if all the turfgrass tissues that might be infected are already showing evidence of disease activity and conditions aren’t favorable for further turfgrass growth, there will be no benefit – and no reason to make – a curative application.
- A change in climatic conditions to those that significantly reduce or eliminate the potential for activity of that infectious disease also would also make a curative application impractical and unnecessary.
- Typically, preventive application rates are lower than curative rates and the interval between applications is longer.
- Where preventive applications are effective, they’re not only good for your turfgrass in terms of plant health, overall aesthetics and playability, they’re good for your bottom line. They reduce both product and labor costs.
Be aware of resistance
- While contact fungicides have no risk of developing resistance, many of the systemic fungicides do.
- As “Chemical Control of Turfgrass Diseases 2017” states, “Infectious fungi sometimes develop resistance to particular fungicides, especially when a product is used repeatedly without alternating with chemically unrelated fungicides and without reducing disease pressure through cultural practices.”
- “When fungicide resistance develops, use of that product or other chemically similar products no longer control the disease effectively.”
- To avoid resistance when multiple systemic fungicide applications will be needed, you’ll want to alternate products. To help with that, the Fungicide Resistance Action Committee (FRAC) provides fungicide resistance management guidelines in the form of FRAC codes.
- These classify products in fungicide groups according to the different MOA. FRAC codes are included on product labels.
- The 2017 version of the FRAC code list is available here.
Selecting the Product
- “Chemical Control of Turfgrass Diseases 2017” also lists a wide range of plant diseases by common name; gives the scientific name for the pathogen and its proper pronunciation; lists the principal hosts (types of turfgrass, both cool- and warm-season) affected by the disease; and the season(s) in which the disease is likely to occur.
- The document goes beyond that to describe in detail the climatic conditions specific to the development of that disease, the range of cultural practices to discourage that development and tips on gaining the most effective treatment with various fungicide product applications.
- You can use all this – or a similar current regional guide – as your starting point in determining your fungicide application strategy. Then, tap into your best local and regional resources. Check out blogs, email alerts and tweets of extension turfgrass specialists and turfgrass pathologists. In addition, read reports and advice from your peer network of other sports turf managers with similar climatic conditions, turfgrass venues and budgets.
Making the Application
- When chemical control will be needed, choose the product or products that best match your fungal control strategy in the formulation most suited to the type of equipment available.
- If you’ll be spraying systemic products, consider all the options of individual product application or tank-mixing either two systemic products with different MOA, or one systemic product with a contact product. As always, read the product labels and follow the directions precisely, including carrying out any pre- or post-application procedures.
- The information on the label will alert you to potential issues of product incompatibility and ways to avoid phytotoxicity (a damaging effect on plant growth).
- Make sure you’re using the correct nozzle type and size for the application and the sprayer is operating properly. With contact fungicides, either used alone or in a tank mix, thorough coverage of all plant surfaces is essential. Systemic fungicides must reach the proper area of absorption, either the plant leaf tissue or the root zone.
- Monitor results closely to determine the application’s effectiveness and plot the next step in your fungal control strategy.