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Winterkill, NOT DISEASE is causing June problems for warm-season turfgrasses

June 19, 2009
by Grady Miller and Lee Butler

Mother Nature seems to be causing problems with many warm season grasses in NC, particularly the zoysiagrasses in the piedmont.

The NC State Turf Diagnostics Lab has received an unusually high number of calls, emails, and samples related to irregularly damaged zoysiagrass that have led growers to believe a disease is causing widespread problems. The overwhelming majority of the samples evaluated have come back negative for diseases and insects.  Also, some growers have submitted soil and nematode assays to the NCDA with negative results.

The most common disease of zoysiagrass in the spring is large patch.  The complaints we have received do not match the field symptoms caused by this disease.  More information about large patch can be found at the following link:

http://www.turffiles.ncsu.edu/diseases/large-patch

Another disease that can be found on ‘Meyer’ and ‘El Toro’ zoysiagrass this time of year is spring dead spot. Once again, the complaints do not match the field symptoms. More information about spring dead spot can be found at the following link:

http://www.turffiles.ncsu.edu/diseases/spring-dead-spot

It seems that the colder than normal winter combined with the lingering cool spring increased winterkill more than typical seen on zoysiagrass. The problem seems to be worse on turf installed within the last two years.

Any condition that resulted in a turf area going into the fall/winter stressed may worsen winterkill. So, a dry area (perhaps due to poor irrigation coverage), compacted soil, excessively saturated soils, or site previously weakened by disease or insects may have caused the damage to be worse.

Winterkill is often erratic with total devastation in one area and minor injury in nearby areas. In addition to previously mentioned stresses, damage may be variable due to fertilization practices, amount of shade, soil type, thatch levels, elevation, and north-facing versus south-facing slope.

By mid June, if regrowth is absent or sporadic, then some degree of damage was sustained. If the damaged area is relatively small, the turf may fill in from stolon and rhizome growth from around the edges. If the damaged area is extensive, then it will require taking plugs from healthy areas of the landscape and transplanting within the damaged turf or re-sodding.

Plugging can be very effective to jumpstart turf fill. It is also very desirable since turf is used from the same site, preventing the opportunity of mistakenly introducing a different grass. Sodding will require the normal soil preparations used with new turf establishment. It is very important to note that if a preemergence herbicide has been applied within the last several months that sodding may not be successful due to root pruning caused by the herbicide.