Of all the pests that cause turf damage, fungal diseases are the most mysterious. This characterization stems from the issue of not being visible like weeds and insects. The symptoms may be fairly clear, such as lesions and pustules on leaves, but the pests themselves are microscopic.
Correct ID of the disease
The most important factor in disease control is correct identification of the causal pathogen. Unfortunately, many diseases are difficult to identify. Diagnosis often involves the discovery of several causal agents, not just the fungus.
Proficiency in turf disease diagnosis is a skill that can be learned. It involves exposure to facts, photographs and actual diseased plant material under the tutelage of a seasoned veteran, as well as regular practice. Each is equally important for success.
To learn the specifics of each disease that may arise on your clients’ properties, immerse yourself in instructional classes conducted by nearby land grant universities and extension offices. Literature distributed by these entities is also quite helpful. Then, practice diagnosis on a regular basis. Make it a point to be a part of the identification of every disease problem your company encounters, as well as ones that you cooperate with.
Timing is important for turfgrass disease control. Each of the organisms that cause damage has a life cycle that contains vulnerable stages. If a fungicide is applied too late, the disease is not suppressed, and time and money is wasted. The training classes and literature referenced above will also provide key information about the vulnerability of various life cycle stages. Bottom line: it’s important to catch the disease in the most vulnerable stage.
When choosing fungicides, it’s common to find both liquid and dry formulations of the same product available. Manufacturers formulate these products in more than one form in order to give the end user more choices, which can sometimes be helpful in maximizing control. In all cases, however, the choice comes down to liquid or dry.
In general, if the disease is mostly leaf blade active, such as dollar spot and Bipolaris leaf spot, liquid formulations are best. These products are applied in such a way as to place the active ingredients into contact with the germinating spores of the fungus. If the disease is mostly rootzone active, such as summer patch, granular formulations may facilitate better penetration to the area of infection.
It can be confusing at times to know which to choose because some diseases, such as Pythium blight, initially infect the grass plant on the leafy surfaces, but quickly work their way into the root system. In either case, it’s important to be aware of factors that degrade or limit the effectiveness of applied fungicides, such as adsorption, absorption, excessive thatch, temperature, slope, photodecomposition, irrigation interactions, drift, leaching, sprayer calibration and volatilization.
Like most things we do in life, weather plays a big role. It’s difficult to overstate the importance of weather when it comes to disease control.
Wind is your enemy when applying fungicides. Because most are applied with a boom sprayer, with the nozzles located 18 inches or so from the turf surface, drift is not a huge factor, but certainly not to be overlooked. Loss of applied product due to excessive wind is not an issue as when applying herbicides, where nearby ornamentals can be injured, but the loss of effectiveness remains a concern. Excessive drift means that less-than-optimal volume of the applied fungicide has reached the turf surface, which can result in lower efficacy.
Due to advances in formulation, many products are considered to be rain-fast in a matter of hours. A decade or so ago, the time for rainfall avoidance after an application was referred to in the number of days. On the other hand, rainfall following an application intended for the rootzone usually helps provide movement of the active ingredient downwards, resulting in improved control.
Read the label
It may be trite, but a thorough reading of the fungicide label will really help to maximize performance. The obvious piece of information to be learned from the label is the amount of product and water to add to the spray tank, or which spreader setting to use, but labels provide much more. Some fungicides are formulated to be effective only at a neutral or acid pH level. If high pH water is used, the residual of the product can be shortened from a couple of weeks to half a day.
Some fungicides are formulated “ready to go,” while others require the addition of a crop oil concentrate or surfactant. Failing to include an additive could result in lower effectiveness.
Safety factors are usually clearly spelled out on the label. One such concern is the time required for re-entry or human activity near the site of the applied fungicide. This is important for the applicator, the employees of the site and the clients themselves.
Cost is a legitimate selection and application factor, especially now when many products are priced at $200 to $400 per gallon. Take care when evaluating cost, however. A product that costs more per gallon may actually be less expensive per unit area. In most situations, several products are available for control. If so, use university test/research data to help choose the least costly, but most effective, products.
John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Roch Gaussoin is a professor of horticulture and extension turf specialist at the University of Nebraska-Lincoln.