Common Lawn Diseases

How and when do lawn diseases strike?

Fungi-microscopic organisms that are found everywhere and are spread by water, air, animals, etc.-usually cause plant diseases. Certain varieties of turf are more susceptible to certain diseases than others, and they are under different cultural practices. That is why one lawn may have a disease problem while another next-door may be fine. Most diseases we see are warm-weather diseases that are more severe during high rainfall and high humidity. May and June are the months when most turf diseases do their damage. During the summer months, the humidity levels are generally lower, unless a homeowner is irrigating excessively. Fall provides another opportunity for fungi to infect turf, especially during rainy periods.

Spring Dead Spot

Spring dead spot is one of the most troublesome diseases of bermudagrass. It is caused by a fungus that infects the turf in the fall. However, symptoms do not appear until the following spring with large circular dead spots, which do not green-up with the rest of the bermudagrass. As the season progresses, the grass from the outer edges will fill in, but it sometimes takes well into the summer to do so.

Spring dead spot seems to be most severe on lawns that were sodded within the past 3-8 years. Certain varieties of bermudagrass, such as tiff varieties, are also more susceptible. As the lawn matures after about 10 years, it usually seems that the disease is no longer much of a problem. The severity of the winter also plays an important role, with more spots present after hard winters. If bermudagrass is over-fertilized with nitrogen late in the fall, the disease will typically increase. At LawnAmerica, we gradually cut back on the nitrogen level in September to help with this issue, and also to send the turf into winter dormancy in a fairly lean state, which is the proper thing to do.

Inconsistent Control of the Disease

Oklahoma State University now recommends that two fall fungicide treatments be done for best control of spring dead spot. We can apply a special fungicide in the fall called Vilista, which is a new product with good research showing promise to help prevent the disease, with a follow-up about 4 weeks later with a different type of fungicide. This should help, but it is not a sure cure in all situations. We have experienced a decrease in the number and severity of the spots the following spring, with a faster fill-in of healthy bermudagrass.

Fungicides are expensive. However, if your problem is severe, we do recommend this service. We can provide this special treatment for 2.1x your normal treatment cost, which will be invoiced with your initial treatment in late September or early October. The follow-up treatment is included, so you will not be invoiced with the second treatment.

Maintaining good soil fertility, irrigation, and aeration are cultural practices that will help dead spots fill in faster during the summer. You can also rake a thin layer of black topsoil into the areas in spring to help speed up the fill in. Or, you can even just dig the dead area out and replace the soil and sod for an instant fix. Only do this if you have a free weekend and a lot of energy, though!

Other Common Turf Diseases

Here are a few other common turf diseases, as well as the cultural practices you can use to lessen the chance and severity of these diseases:

  • Brown patch - Brown patch is a problem disease we see from about mid-May through July. This disease typically causes damage to fescue and St. Augustine lawns. Look for brown spots that are a few inches to several feet in diameter with a yellowish "smoke ring" around the perimeter of the patch (especially early in the morning). It is recommended to apply a turf fungicide to avoid losing turf, if the conditions merit such treatment.
  • Dollar spot - Dollar spot is a summer disease of bermudagrass and zoysiagrass. Small silver dollar-shaped brown spots appear, sometimes coalescing together to form larger brown patches. This disease is favored under low soil fertility and low soil moisture conditions, along with excessive dew or frequent irrigation. Fungicides are usually not recommended for this disease, as a good nitrogen fertilization will eliminate the problem.
  • Large Patch - Large patch is a mid-spring and mid-fall disease mainly infecting zoysiagrass, but that can also infect bermudagrass during extreme damp conditions and mild temperatures. These yellow to brown somewhat circular areas can be quite large, up to several feet in diameter. An orange ring around the expanding border is sometime present as the spot moves into healthy turf. If the disease is moderate to severe, we recommend fungicide treatments mid-spring and again mid-fall to help prevent the disease.
  • Winterkill - Winterkill refers to any severe damage or death sustained by the turf during the winter months. This can sometimes be mistaken for turf disease. For the most part, well-cared-for turf is resilient, but winter weather can be unforgiving to even the best lawns.

Maintain Proper Soil Fertility

As long as you are on one of our full programs, preferably the 6- or 7-step program, we'll take care of any diseases that attack your lawn. Inadequate nitrogen and potassium are especially known for increasing disease problems. Too much nitrogen fertilization can also lead to disease problems. That's why we only apply the proper amount of fertilizer each time-not too much and not too little-in order to green-up your lawn. On some types of grass that are more susceptible to diseases in the summertime, we apply slow-release organic fertilizers, which are safer and better to use during periods of high disease pressure.

Irrigate Properly

Disease problems are more severe when the turf stays constantly moist. Sometimes, Mother Nature takes care of that for us, especially during spring. Sometimes homeowners can make the problem more severe by watering every day and at the wrong time of day. We recommend deep, infrequent irrigation so that the water can get down deep into the root zone. We want the topsoil to dry out a little in-between waterings. Do not water every day. Also, do not water in the evenings so that the turf stays damp all night. Finish your irrigation as the sun comes up early in the morning so the grass blades will dry out quickly.

Mow Properly

Mowing with a dull blade will damage the grass blades, leading to more infestation from fungus pathogens. Not mowing frequently enough and leaving excessive clippings on the turf can also lead to increased vulnerability to disease. We do offer a turf disease service with applications of certain turf fungicides. These are liquid applications, which not only kill the disease pathogens, but also will provide about 3 weeks of systemic control of re-infestation. We can do this on an as-needed basis, or we can set you up on a semi-preventative program with 1 or 2 treatments of fungicide every year during the peak disease periods (from about April through early July).

Additional Resources

Here are a few educational resources that can provide you with additional information about turf diseases:

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