LAWN/GOLF: When do you first schedule N applications on zoysia?

mid April
late April
early May
mid May
late May

Update (05/02/2016)

No Large Patch Leap Caused by Late Spring N

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April ends warm

  1. Most areas of Missouri had above normal temperatures for April, despite a cool start.. - Source: Pat Guinan
  2. April was particularly dry in Missouri, with many areas ending 0.5 to 2 inches below normal. - Source: NOAA


April temperatures turned around quickly in the latter half of the month.  Despite the cool start, most of Missouri ended at + 1.5 to + 3 degrees above normal for the month.  The temperature increase caused a soar into pest pressures like Poa annua seedhead emergence, and through temperature thresholds for pesticide applications including fairy ring and annual summer weed preemergents.  May has started cool, but forecasts indicate a rise back into the 80s this weekend and into next week, with the formation of an “omega block” or bubbled pattern to the jet stream, with Missouri being in the bubble.         

Despite last week’s widespread thunderstorms, total April rainfall was much below normal in many parts of the state, except for localized areas around Springfield, St. Louis, and the complete washout in Kansas City.  This spring rainfall pattern has been the yin: with the middle portion of the state in an abnormally dry or moderate drought stage (, and the yang: with excessive rainfall in Kansas City and northeast Missouri causing potential flood issues to stream down the Missouri river.  May is the wettest month on average in Missouri with nearly 5 inches of precipitation expected to fall in the month.  Although the rest of this week appears to be dry, the 6-10 day outlook a return to above average chances for precipitation, particularly again for the western portion of the state.      

6-10 Day Outlook: Cool May not expected to last.

  1. Temperatures are expected to rise into middle May. - Source: NOAA CPS
  2. More precipitation expected next week. - Source: NOAA CPS

Quick Hits

Soil Temperatures Rise Quickly Into Late Spring Form

  1. Springfield soil temperatures climbed quickly in the latter part of April.
  2. Columbia soil temperatures are well above the soil temperature threshold since mid April.
  3. St. Louis soil temperatures similar to Columbia.
  4. Kansas City soil temperatures dropped substantially in late April, but eclipsed the zone in mid April.

  • Window for Spring Prevention Eclipsed:  A quick rise in temperatures through the latter half of April launched the region well past the soil temperature threshold for prevention of soilborne diseases on golf putting greens.  This shouldn’t be much of a surprise as the blooms are gone on daffodils, forsythia, and redbud, crabgrass and knotweed are early leafing, Poa seedheads are out en masse, and about every other phonological indicator has gone past.  The growing degree day tracker ( agrees as most pests are in their “done” or mid to late season stages.   

Billbug Adults Prowling

  1. Billbug adults, like this one, are resuming activity and egg-laying after a short winter nap.
  2. Both zoysia and Kentucky bluegrass managers should be wary. Symptoms are drought-like.

  • Billbug Warning: On sites with previous history, scouting and preventive control of billbugs on zoysia should be considered now.  Curative control is challenging, and a preventive strategy targeted towards control of adults is suggested.  ‘Meyer’ zoysiagrass covers the Missouri landscape due to its exceptional cold tolerance, but is also unfortunately the most susceptible cultivar to billbug damage.   Previous research at U. of Arkansas found hunting billbugs were most active in late March and April, but some activity was observed throughout the whole year.  Complicating matters, several billbug species are present and may feed on zoysiagrass in Missouri, and their peak periods of activity and egg laying may be different.  Our best current model is on the growing degree day tracker website which predicts the bluegrass billbug life cycle with a base 50 degree day model.  The model currently indicates most of Missouri well within the range of first activity of overwintering adults (

Late Spring Nitrogen Doesn’t Spark Large Patch

Large Patch Fertility

  1. Large patch extremely active in plots now. Orange margins in non-fungicide treated plot.
  2. Nitrogen fertilizer applications in spring (5-d ST average = 65 F) does not seem to increase large patch.

Large patch remains the topic of discussion in this update.  As shown in the picture above, large patch is extremely active and prevalent now.  We’ve observed the disease throughout the state on zoysiagrass, and even on a bermudagrass sports field in SW Missouri.  As noted in the previous update, fungicide applications are often necessary in spring, and can be made even to dormant turf in early April to prevent infection.

Little is known on cultural practices to reduce large patch severity.  Nitrogen fertilization during large patch development in fall and spring has been discouraged since brown patch in cool season turfgrasses, caused by a different R. solani anastomosis group, is more severe in over-fertilized turf. Previous research from Kansas State University, however, found fertilization with urea during the spring and fall did not consistently result in higher amounts of large patch.  This research was expanded further with a collaborative project with KSU, examining the impacts of three different nitrogen sources (calcium nitrate, ammonium sulfate, and urea) applied at 0.5 lb N/1000 sq ft at three different timings (5-day 2 inch soil temperatures of 60°F & 70°F in the spring and 70°F in the fall) vs. a summer standard program.  All treatments had 1.5 lb N/1000 sq ft per annum.  The study will be published in the upcoming issue of Crop, Forage and Turfgrass Management, with an overarching result that during the spring of 2014, which had the highest large patch severity, we observed no increase in large patch severity from spring fertilizer treatments. 

We currently are conducting a similar, but expanded field experiment with various nitrogen sources (urea, calcium nitrate, ammonium sulfate, and Duration 120-day) applied at the medium 5-day average soil temperature of65°F in spring and fall, and a slightly higher per annum rate of 2.0 lb/1000 sq ft.  As shown in the figure above, we are seeing similar results to the previous research, with no observable impact on large patch severity and more green turf in plots treated in the spring during the large patch infection period. 

A small shot of nitrogen (0.5 lb N/1000 sq ft or less) later this week to zoysiagrass when temperatures rise into the 80s may be a good idea, particularly in shaded or other areas prone to mild dollar spot outbreaks.  Our ongoing research is investigating which nitrogen source may be best for the late spring application, so stay tuned.


Lee Miller
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Extension Turfgrass Pathologist
University of Missouri