Preventing Lawn Diseases

The easiest way to prevent fungal disease on turf is to maintain a healthy lawn.

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Incredibly, there are over 400 species of fungi that are known to inhabit lawns. Many fungal diseases that affect lawns are seasonal and don't do any permanent damage.

Roughly 100 fungal diseases are potentially harmful, quickly turning a green and vibrant lawn into a brown, decaying, ugly patch.

Unfortunately, zeroing in on which fungus is causing a problem can be tricky, and symptoms range from rust to mold to brown spots and rings. Both diagnosis and control are especially difficult. By far, the easier thing to do is prevent fungal diseases in the first place.

Figure A

  • Have your soil tested (figure A). Nutrient deficiencies and pH problems can not only create conditions that mimic fungal diseases but also invite fungal diseases.

    With a clean trowel or large spoon--preferably one made of stainless steel--take samples of dry soil in the lawn. Take at least four or five samples at various locations, to a depth of four inches, and combine them in a clean, unused plastic bag with an airtight seal.

    Take the soil sample to your local Cooperative Extension office or to a nursery that offers soil sampling services. Fees for basic testing are usually less than $10.

    If the test results indicate a nutrient deficiency--say of nitrogen, phosphorous or potassium or perhaps even iron--take the necessary steps to correct it using a natural fertilizer. If pH is a problem, increase it with agricultural lime or decrease it using sulfur, both according to package instructions.

  • Figure B

  • Test for adequate drainage (figure B). Dig a few holes in the lawn roughly six inches deep. Fill the holes with water, and monitor the time it takes for the water to drain from the holes.

    Poor drainage can invite fungal diseases, so if the water doesn't drain from the holes within an hour, chances are you've got a drainage problem, and solving it may require any number of different approaches--from simple aeration and the addition of compost to a full-blown French drain.

  • Figure C

  • Water early in the day (figure C). Grasses that remain moist, especially overnight, are extremely susceptible to fungal diseases. Water early in the morning so that grass blades have a chance to dry out during the day.

  • Figure D

  • Make sure your mower blades are sharp. Dull blades leave ragged cuts that provide an easy invasion site for fungal spores. Keep the grass mowed high--at least 2-1/2 inches high. Short cuts lead to an increase in fungal disease.

  • Figure E

  • Routine aeration (figure E)--say once or twice a year--will also help prevent fungal diseases. The same is true of dethatching, since many fungal organisms colonize in thatch.

  • If you have a lawn service mow your grass, insist that they disinfect the undersides of their mowers with a solution of one part bleach to nine parts water (figure D) before mowing your lawn. This simple step will destroy infectious fungal spores that may have hitched a ride from the previous lawn.

  • Avoid the use of synthetic fertilizers, herbicides, even fungicides. All are potentially toxic to soil organisms, including earthworms. And those organisms are very often the first line of defense against fungal diseases.

  • A number of insects can cause damage to lawns, including grubs, mole crickets and various caterpillars, and the damage they cause can mimic the damage caused by fungal disease.

    So in areas of your lawn that appear damaged, verify first that insects aren't the problem by examining the area carefully.


    So what if, despite your efforts to prevent fungal diseases from attacking your lawn, you suspect that your lawn has nevertheless been invaded? You'll need to collect a sample for diagnosis.

  • Figure F

    Cut a section of diseased turf roughly one foot square and include about two inches of soil (figure F). Wrap the sample in newspaper, and place it in a box for mailing. Include in the box a note with as much information as possible--type of grass, date collected, overall symptoms--anything and everything that will help the pathologist make an accurate diagnosis. And again, take or mail the sample to a Cooperative Extension Service office.

    An important tip: Mail the sample on a Monday so it doesn't sit around unopened all weekend at the post office or lab. When it comes to diagnosing fungal diseases, fresher is better.

    If the report indicates that you do indeed have a fungal disease in your lawn, don't panic. Instead, either use the type of product recommended by the lab, which will almost certainly be a synthetic control, or fight back using any number of different all-natural strategies:

    Figure G

    Compost, for example, spread over the infected area (figure G), can be extremely effective in fighting fungal pathogens. Compost tea sprayed over the lawn works well too. Neem oil is another knockout product, and it too has awesome anti-fungal properties. Fungicide soaps also work well and are easy to apply.

    And a solution containing either sodium or potassium bicarbonate--baking soda mixed at the rate of two tablespoons per gallon of water--will control a number of fungal diseases in the lawn.

    But as is the case with all plant diseases--and many human ones as well--the best offense is a good defense. In other words, consider prevention as your first line of defense, all of which are aimed at promoting healthy turf, and you may never have to deal with offensive fungal diseases in your lawn.

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