Every year, during both fall and spring, I must get asked the same question a hundred times, "Why are patches of my yard dying?" When the conditions are right, it is most likely turf fungus that is damaging your yard.
How do I know if it is turf fungus?
First off, turf fungus only does well during the following conditions:
Usually turf fungus will form a more circular or rounded damaged area, there are exceptions to this. There will be an inch border where the grass is yellowing and the center is brown, as if there was a fire that started in the middle and is burning outward. The turf should feel rotten, almost squishy, like old produce. Sometimes people mistake insect damage for fungus damage. Usually insect damage will have bite marks on either the leaves or the roots of the grass. A lot of time you can actually pull up on the yellowing grass and it will come up as if it is not attached to the root. Also insect damage will follow more of a trail and be more sporadic.
how do I fix it turf fungus?
The best practice is to have good cultural controls. Water your turf for longer periods and more infrequently throughout the year. Be sure your yard does not have areas of standing water. Do not cut your grass when it is wet. It will stress your grass and make more entryways for fungus. Use a core aerator twice a year to reduce thatch. Absolutely do not apply any nitrogen rich fertilizer late summer through early spring. To ensure a healthy lawn, apply a preventative fungicide just before the temperatures begin to drop.
If you are in a new home, you should look for areas of your yard that have a heavy weed infestation. Usually this is an area where there has either been heavy insect damage, fungus damage or sitting water. Once the turf has died, weeds are quicker growers and will naturally take over.
If you can see the damage, unfortunately you are too late to treat what has already been damaged. Your choices for the dead turf are to let it grow back in or to cut out the dead area and lay down some sod. I would recommend using sod since it is quicker and will not leave a barren area for weeds to infest. You can treat the area to prevent it from spreading further with a fungicide. Be sure to reevaluate your yard for cultural controls as well.
Which fungicide should I use?
There should be a good selection at your local hardware store. Be sure to pick one that is labeled for turf and the type of fungus you are targeting. Some fungicides can get pretty expensive, so pick the most cost effective one that targets your problem fungi for the longest period of time. Also, some fungicide are labeled to work only before the fungus has emerged, some are labeled for after the fungus has emerged and some for both. Be sure to read the label and choose correctly.
I have found propiconazole, myclobutanil and triflozstrobin to all work very well in treating brown patch and take-all patch. I seem to see these two pop up more often than anything else.