Thursday, April 3, 2014


Nick Christians
April 2, 2014

 Winter damage at turf research (prior year)

 Desiccation on bentgrass (prior year)

Winter damage to turf can occur from a variety of causes.  These include diseases such as snow mold, ice cover, traffic, frost heaving, desiccation, and direct low temperature damage.  In recent years, desiccation due to mild conditions, lack of snow cover and drying winds late in the winter have been the biggest reason for winter damage in Iowa (see my blog on this site from January 2, 2012).  Snow mold is sometimes a problem (see blogs from March 11, 2010, Sept. 10, 2010, Nov. 27, 2012 and Dec 8, 2012).  The biggest concern this spring, however,  is likely to be direct low temperature damage.

This past winter has been one of the coldest in recent memory for most of us in the Midwest.  As Ryan mentioned in his last blog, the average temperature over the past 3 months was 14.7 degrees F as compared to a normal average of 22.1 F.  We also hit some very low temperatures during the last 3 months, with low temperatures on some days dropping below -20 F.  Records in Ames show that this winter was the ninth coldest in the last 141 years. The question as to how much winter damage we will see as the turf emerges from dormancy depends on the species grown on the site and on a series of complicated, interacting conditions that occurred during the winter.

Kentucky bluegrass (Poa pratensis) and creepging bentgrass (Agrostis stolonifera) tend to be quite tolerant of cold temperatures.  The fine fescues as well have proven to be quite tolerant in my experience.  Perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea), and Annual bluegrass (Poa annua) are more likely to be damaged by low temperature.  The warm-season grasses are generally more susceptible to cold temperature damage.  Bermudagrass (Cynodon spp) is easily damaged, whereas Zoysiagrass (Zoysia japonica) and buffalograss (Buchloe dactyloides) are more tolerant.  It will be on the perennial rye, tall fescue, and annual bluegrass that I expect the most damage as the grass emerges from dormancy in this area.  Creeping bentgrass is very susceptible to winter desiccation, but the continual snow cover that we have had in most regions of the Midwest should prevent this from being a major problem this year.

An even more important determining factor in direct low temperature kill is the condition of the grass going into the winter and the conditions that occur in the localized area during the winter.  Seedling ryegrass and seedling tall fescue that were established late in the fall are particularly susceptible to cold temperature damage.  It is not unusual to loose late seedings of these species in years with less severe winters that occurred this year. Mature stands of these species survive cold temperatures much better if they harden off properly before extremely cold temperatures occur.  Snow cover during the winter tends to be a good thing, and I rarely see damage in cold winters when snow lasts most of the winter as it did this year. 

If there has been intermittent melting, allowing water to settle in low areas, followed by a hard freeze, damage is more likely to occur.  This is particularly true of perennial ryegrass and annual bluegrass damage.  I have observed this type of damage a number of times over the years and I expect to see some of it this spring.

Damage to annual bluegrass is hard to predict.  This species is more sensitive to direct low temperature kill than is either Kentucky bluegrass or creeping bentgrass.  However I have seen years where I expected to see a lot of annual bluegrass damage and didn’t.  There have also been years when I didn’t expect damage and a lot of it occurred.  Again, it is a series of other factors that determine annual bluegrass damage.  These include the condition of the grass going into the dormancy and the combination of weather conditions that develop during the winter.  As cold as it was this winter, I am anticipating quite a bit of damage.  I am getting early indications from the Chicago that quite a bit of damage has occurred on greens and fairways where annual bluegrass is the primary species.  I’ll keep you informed on that as the spring progresses.  Winter damage to annual bluegrass is often quite localized due to variations in winter conditions.  Here in central Iowa, the annual bluegrass seems to be emerging from dormancy in good shape.

In the last two years, I have done a number of blogs on bermudagrass showing up in Iowa turf areas (Aug. 2, 2012, Sept 18, 2013, July 29, 2013, and June 17, 2013).  Another warm-season grass that has become a problem because of the series of mild winters in recent years is Windmill grass  (Chloris verticullata) (Sept. 19, 2013, July 3, 2012, Aug. 6, 2012).  Neither of these species was a problem up to about 5 years ago.  Both species are quite sensitive to cold temperatures.  It will be interesting to see if they survive this severe winter.  Windmill grass is a perennial, but it is also a very good seed producer.  I suspect that this grass is here to stay, even if a lot of the existing plants died during the winter because of the amount of seed in the soil.

Windmill grass in lawn.

Windmill grass seedhead.

Bermudagrass on Iowa State campus in the summer of 2013.

Let me know what you are seeing as the season progresses.  I would appreciate any pictures that might be of interest to others in the industry.

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