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Features - Lawn Care

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

May 9, 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.

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”?

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 evapotranspiration (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.

The author is an associate professor at Cornell University.