University of Vermont
Department of Plant and Soil Science

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LAWNS: AVOIDING DISEASE DISASTERS

Leonard Perry, Horticulture Professor
University of Vermont

If you have a home, chances are you have a lawn.  The master groundskeeper at Boston’s Fenway Park, David Mellor, provides some tips and advice in his book The Lawn Bible on how to avoid disease disasters in your lawn.
    
Almost all lawn diseases are caused by harmful fungal pathogen organisms.  These are present everywhere, along with beneficial fungi.  These good fungi help keep the bad ones in check, and help to break down that layer of thatch in lawns.  This, in turn, returns nutrients back to the soil.  Proper lawn maintenance helps to promote these beneficial fungi.  It also helps to prevent fungal disease by keeping grass plants healthy, and conditions not good for fungal growth.  So proper lawn maintenance is the main key to avoiding lawn diseases.  Prevention of these is much easier than trying to cure a diseased lawn.
   
Proper lawn care involves:
--Proper grass selection.  Even before starting a lawn, or renovating one, choose grass varieties appropriate for your area, light conditions, and soil type.  Otherwise they’ll be weak, and more susceptible to diseases.
--Proper mowing.  This means not mowing grass too short (for most grasses 3-inch high works well), as this will stress grass.  Taller grass plants are more tolerant to heat and drought stresses.  Similarly, to not stress grass plants, don’t mow more than one-third off at a time, and make sure mowing blades are sharp.
--Proper watering.  Water established lawns deeply and infrequently, if needed at all.  Water in the morning so grass can dry during the day and not go into the night wet.  Improve drainage with an aerator (available from rental stores) if soils are compacted.
--Proper fertilizing.  Only add what is needed, according to a soil test.  Too little, and plants will be stressed.  Too much, and plants are weakened either from excess thatch build up, too much top growth for the root growth, and excess nutrients washed away, possibly into watersheds.
--Proper chemical use, or none.  Improper use of insecticides, fungicides, and herbicides can weaken grass, and kill beneficial organisms that help grasses to thrive and be strong.  Use only what is needed, according to label directions, and only if there aren’t other options.
  
In spite of your best attempts at good lawn care, problems may develop.  They may not be caused by a disease, but by drought, pest-damage, improper chemical use, or other.  So the first step is to determine the cause of the lawn problem.  Since this can be difficult, with similar symptoms from several diseases, look closely at the grass blades, patterns overall in the lawn, and note any recent changes in culture or climate. 

If any doubt as to the cause, check with your state Extension Plant Diagnostic Clinic which you can locate through the Northeast Plant Diagnostic Network (www.npdn.org/nepdn/regional_contacts).  Also check lawn problems with local full-service garden stores (seasonal stores and chain stores often are of little help), or a local professional lawn care company (not ones that merely mow). 
  
Here are ten main lawn diseases and cultural ways to help prevent or control them.
>Snow Mold.  Patches of dead grass, either pink or gray, show up in spring after snow melts.  To avoid this disease, mow in fall until grass stops growing, and avoid excess nitrogen in fall.
>Dollar Spot.  Small dead spots a few inches across may appear in spring and fall with warm days and cool nights.  Don’t overwater if this problem is present, give proper nitrogen fertility, and reduce thatch if present.
>Stripe Smut.  With this pathogen, leaves curl up and die, appearing shredded at leaf tips.  You’ll see it mainly in the cool of spring or fall.  Water and fertilize properly, and reduce excess thatch.
>Brown Patch.  Circular patches of brown grass appear in summer during hot, humid weather.  Allow grass to dry between watering, and water early in the day.
>Leaf Spot.  With this disease, grass blades have elongated spots with brown centers and purple edges.  Improper watering and too low mowing during cool, wet weather can lead to leaf spot.
>Powdery Mildew.  A white powdery substance on leaves, resembling a dusting with flour, indicates this disease which loves high humidity and warmth during summer, particularly in shady areas.  Many Kentucky bluegrass varieties get this disease.  If a shady area, improve light conditions if possible, choose shade-tolerant varieties, and don’t overfertilize or overwater.
>Rust. With rust, affected areas take on a rusty color; leaf blades start with yellow spots that develop rusty lumps of spores.  You’ll see it on stressed grass, particularly Kentucky bluegrass or ryegrass during warm, moist weather.  A properly maintained lawn with proper or high mowing and good fertility, is the way to avoid rust.
>Red Thread. Patches of lawn appear reddish, and a closer look shows tangles of red fungal threads at the tips of grass blades.  Cool, moist weather favors this pathogen, particularly on fine fescue and perennial ryegrass, or lawns that are poorly fertilized.
>Fusarium Blight. This disease starts as small light to reddish brown circular spots which, as they enlarge, have characteristic live green grass in their centers.  Drought-stressed grass with shallow roots is particularly prone to fusarium.  Water properly, don’t overfertilize, aerate if excessive thatch is present, mow at the proper height, and reseed with resistant varieties.
>Pythium Blight. This also is known as “grease spot”, as small patches of grass look slimy when wet.  Dry, they’ll be light to reddish brown.  Use proper watering, particularly during warm, humid weather, and correct a too high soil pH (too alkaline).
   
Keep in mind through the season that for a lawn disease you need the pathogen (often present), a vulnerable grass plant (i.e. stressed or weak from improper culture), and the right conditions for the fungus to thrive.  Unless you have all three, your lawn won’t get diseased.  You’ll find many more tips on growing and caring for lawns in David Mellor’s book.


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