Reddish brown patches, pock marked areas of tan grass and yellowing. These are lawn issues we are seeing now and have been expecting given environmental conditions this year.
Roughly circular patches of reddish-brown grass, especially in tall fescue lawns, are symptoms of brown patch disease. Kentucky bluegrass is also affected but symptoms are less prominent.
To confirm brown patch, closely inspect individual grass blades in the affected area. Look for irregularly shaped, tan-colored lesions surrounded by a dark brown margin. It is best to do this just before mowing rather than right after mowing or lesions may be removed.
While brown patch will not kill a lawn, and affected areas often recover by spring, good cultural practices should be used to reduce disease. For example, avoid fast release nitrogen applications during summer and avoid evening or night irrigation. There’s not much we can do about rainfall and cloudy weather.
If brown patch causes thinning of an area, overseed with cultivars resistant to brown patch. Seeding is best done by mid-September and lawns should be core aerated prior to seeding to provide seed to soil contact. Without aeration, overseeding will not be as successful.
Fungicides, although not recommended this late in the season, also provide control. If fungicides are used, apply them at the first sign of disease, usually late June into July. Remember, fungicides do not kill the fungus or cure infections. They work best by preventing infections early in the growing season.
I’m often asked if grass clippings should be collected when there is an active disease. Research is not showing much benefit to doing this and the fungus can be spread by the mower itself. It would be wise to follow the recommendation of mowing often enough so that no more than one-third of the grass blade is removed during any one mowing.
Pock-marked areas of tan grass, especially in full sun locations, could be summer patch disease. This is a root rot disease, so dead grass in the affected area can easily be pulled from the roots. On close inspection, no lesions or leaf spots will be seen on individual grass blades.
Summer patch is mostly found on Kentucky bluegrass and is a difficult disease to control. While fungicides can be applied as a soil drench in May when the roots are being infected, they have not proven to be very effective. Once this disease is established, reseeding or overseeding the area with improved cultivars or changing the turfgrass species to tall fescue may be needed.
Yellowing of turfgrass at this time of year has almost become so the norm so I don’t receive near as many questions related to it. As you may know, lawn yellowing is caused by a combination of hot soil temperatures, too wet of soil, and high pH soils.
Hot soil temperatures and wet soils, often due to irrigation systems that are rarely turned off, lead to root dysfunction that reduces the root systems ability to take up iron. A nutrient that is not as readily available to plants in high pH soils.
Once soil temperatures cool off and irrigation systems are turned off, lawns typically come out of grass yellowing and green up.
If needed, an application of iron (no nitrogen) can be made to mask the yellowing. It is best to apply a liquid application of ferrous or iron sulfate, or other iron source, and do not water it in.