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Tips for lawn disease management that require less reliance on fungicides.

May 31, 2011

In spite of the general worry about the current economic issues in the United States, the public remains concerned about environmental quality. A 2009 Gallup poll reported that more than 45 percent of Americans are “very worried” about the environment.

When it comes to environmental issues in the landscape industry, it can be summarized into concern over the use of fertilizer and pesticides. To that end, laws are being promulgated to restrict or ban the use of traditional pesticide chemistry. This will present significant challenges for the landscape industry.

Pesticide use in lawn care includes herbicides, insecticides and fungicides. Of these products, herbicides are the most widely used followed by insecticides and then fungicides for disease control. Oddly, when it comes to the severity of a problem that would lead to turf loss, the use is disproportionate. Weeds don’t kill lawns, and insects and diseases do.

Turf disease 101

Fungi that survive on living and dead organic matter in the lawn primarily cause lawn diseases. When thinking about fungal diseases, we often picture a triangle with one point being the susceptible host (turfgass plant), another point the pathogen (fungal organism) and finally the environmental conditions (leaf wetness, temperature, etc.).

Lawn care providers are often handed a lawn that may not have the best turfgrass species or variety, i.e., susceptible to many turfgrass diseases. Of course the pathogen is usually always present, or there might be a site with particular history of disease problems. Therefore, with two strikes against you, the only determining factor is the weather.

Persistent leaf wetness and warm temperatures are ideal conditions for foliar pathogens (diseases that infect leaves). Poor soil conditions, such as persistently wet or compacted soils often lead to severe root diseases. In fact, the 2010 growing season throughout the northern U.S. presented both these weather patterns and many lawns suffered, especially the irrigated ones.

In the end, fungicide use for lawn diseases is often fighting against the odds. Fungicides attack one aspect of the triangle, the pathogen. This is an uphill battle, as most products do not kill the organism, rather they simply slow and stop growth and infection. If conditions persist the organism will likely reinvade.

The question remains that if our lawn diseases can be so devastating and fungicides may only be of limited value, how can we improve our chances in controlling lawn diseases?

Host resistance

In my judgment, if we are not using lawn grasses developed in the last five to 10 years with improved disease resistance, we are not servicing our client properly. This is not absolute, as sometimes a lawn grass adapts to growing environment and thrives; however, improved varieties may often lead to enhanced water and fertilizer use efficiency.

I often wonder why we don’t develop regular renovation plans that work to introduce improved grasses into our lawns. This is especially true for lawn pest problems where we have had a history of insect or disease pests. For example, if lawns have struggled with surface feeding insects, why wouldn’t we plant endophyte-enhanced grasses we know provide natural resistance?

The National Turfgrass Evaluation Program has been conducting trials with all the major turfgrasses for the last 30 years. In those years, we have seen enormous increases in disease resistance. For example, let’s take gray leafspot.
Gray leaf spot was such a devastating disease of lawn height turfgrass that many university personnel were simply not recommending the use of tall fescues and perennial ryegrasses. Breeders began to investigate resistant ecotypes from around the world, and within five years of research there was a palette of resistant varieties available that have made this problem almost obsolete.

It is time we start investigating this avenue for enhanced turf performance. We may also find that if our customer’s lawn improves, we find a new revenue stream, and, in the end, we use fewer fungicides. Maybe you could call it “lawn refresh” or “shifting to sustainable”?

“Climate” change

I know what you are thinking, and while there is evidence that the climate is changing and often leads to more disease, the climate here refers to the growing environment.

Simply put any limitation you have to ideal growing environment, i.e., low light, poor drainage, compacted soil, excessive traffic, the more susceptible your lawn will be to turf disease. Imagining the triangle again, the growing environment on one point has a strong influence on the host and the organism.

Therefore, as with “lawn refresh,” the idea of improving the site to improve efficiency goes hand in hand. Modifying the growing environment can be a source of revenue as well as allowing improved varieties to thrive. In either case, modifying the “climate” that the lawn is in is the second leg on the stool for supporting reductions in fungicide use.

Cultural shift

Often the only aspects of lawn management we can control directly are the cultural practices. How we mow, water and feed can have profound influences on lawn disease management. The same principles apply as did for the growing environment, in that maximizing plant health will help reduce the need for fungicides.

Mowing with a sharp blade and at the proper height that allows for good turf density and excellent rooting are the first steps. However one factor is known but often unable to be adjusted and that is mowing frequency.

As we strive to reduce our fuel use, often by reducing mowing frequency, the grass leaves can remain wet for longer periods of time. This persistent leaf wetness, especially with warm temperatures into the evening hours, creates ideal environments for foliar diseases such as dollar spot, brown patch and Pythium.

In this case, mowing may not solve the problem, but air movement will. It is well established in research that air movement across a turf that leads to disruption of the leaf surface will reduce foliar diseases. This may require some brush removal to create “alleys” for air to move through.

Interestingly, there is some research that suggests early morning irrigation that knocks the dew and condensation off the leaves may reduce certain foliar diseases. However, in 2010 most of the disease problems I observed with lawns were because of lawn irrigation, not in spite of lawn irrigation.

Most lawns are overwatered, as many statistics will show. But worse yet is the lack of uniformity of the irrigation systems. Most systems do not apply the water uniformly over the lawn. This means there are persistent wet and dry spots.

Often the lawn is irrigated to the dry spots to avoid overwatering the wet spots. This leaves the dry spots wanting for more water. In 2010, with prolonged periods of dry weather, many areas relied on irrigation in the absence of rain and this lead to persistently overwatered and disease-susceptible turf.

There is no question that drier turf is often less disease susceptible. However it cannot be extreme. Therefore we recommend that water be supplied for most turfgrasses to supply between 60- 80 percent of water lost to evaopotranspiration (ET) in a deep and infrequent pattern to keep plants healthy and reduce need for fungicides.

Turf nutrient management is vital for plant health, yet the primary nutrient often involved in disease management is nitrogen. Nitrogen should be the focus of our programs as we strive to avoid excessive growth leading to lush, disease-susceptible turf. Yet under-supplying the plant with nitrogen will reduce leaf growth and allow for certain diseases to persist, such as red thread and leaf spot.

Reduced risk and bio-fungicides

The EPA classifies fungicides that are applied at low rates, with low toxicity, low chance for resistance and limited non-target effects as reduced risk. These types of products with active ingredients, such as boscalid for dollar spot control, polyoxin D zinc salt for brown patch control and phosphite materials for Pythium, should be the cornerstones for disease management.

These products show excellent performance under low to moderate disease pressure. Most of the time for lawns, these products will meet your needs for disease management on their own; however, when disease pressure is great, they can still be used to reduce the use of traditional fungicide chemistry.

Our research at Cornell University has shown that integrating reduced risk and bio-fungicides with traditional materials will allow for reduced rates and extended intervals of traditional products. If you are considering fungicide reduction simply from a product perspective, you have three options: don’t apply anything, apply lower rates or apply at longer intervals.

In most cases, we see 50-75 percent reduction of traditional fungicide use for most turf areas under the highest disease pressure when recued risk or bio-fungicides are incorporated in the program. If you start to calculate disease management on a cost- per-day-of-control, some products that seem expensive might be less when you extend the intervals or apply them at reduced rates.

Integrated management

In the end, disease management, as with most lawn pests, is best done on an integrated basis. A resistant turf in a good growing environment and properly managed will require less fungicide use. Furthermore, when a fungicide is needed, start with the least toxic option under most conditions. If pressure gets high, integrate a traditional material at low rates.

Over time, as you grow comfortable with this approach to managing diseases, you will find this to be translatable to other pest problems. The more you rely on fungicides as your primary means of managing disease, the less likely any reduction will be possible. This should be an easy sell to a customer interested in a high quality lawn that is sustainable, environmentally and economically.

The author is an associate professor at Cornell University.