LAWN: Are you seeing a link between nitrogen fertility and winterkill on zoysiagrass lawns?

Yes - more on overfertilized lawns
Yes - more on underfertilized lawns
No connection
No - tied to disease or insect activity
Haven't noticed any winterkill

Update (05/24/2018)

First Summer Sip From a Fire Hose

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Unprecedented May temperatures

  1. Every May day in 2018 has had above average temperatures. - Source: Missouri Climate Center
  2. The whole region has experienced hot May days. - Source: Midwest Regional Climate Center

By far, the weather story of May is the well above average temperatures. Missouri is on track to have the warmest May in recorded weather history (since 1895), with areas of the state ranging 7-10 degrees above normal. In Columbia and many other areas, every single day in May has had above average temperatures (see graph above) and this trend is forecasted to continue (see below). This quick snap to summer has been echoed throughout the region and transition zone. Recall that April in MO was the second coldest on record, which prompted me to ask our state climatologist Dr. Pat Guinan if this huge swing has ever happened before in back-to-back months. At the time, December 1989 was the second coldest at 22.6 F (now third) and January 1990 was the second warmest at 39.3 F (now third). This is the only similar occurrence since 1895, and at those cool temperatures, not much mowing or plant care was going on.

Will this warm May foreshadow June - August temperatures or precipitation? Historically speaking no. Dr. Guinan ran the numbers and neither warmer than normal (shown below) or cooler than normal Mays are indicative of the type of summer weather that occurs thereafter. The only constant indicator is the amount of precipitation in May often relates to the rainfall that occurs in the upcoming summer months. So, as usual in this portion of the country expect anything.

Warm Mays Haven't Historically = Summer Trend
Top 10 warmest Mays in Missouri and what happened the following summer (June - August)

Welcome rains occurred over the past seven days in the middle portion of the state, with perhaps a bit too much around Joplin, Springfield, and the Bootheel. Regions in mid Missouri received 1-2" depending on location, while there was a report of nearly 5 inches occurring near Cape Girardeau. Over the next three days, expect spotty thundershowers with 0.5 – 1 inch of precipitation expected, mainly in the central and western portion of Missouri, and potentially much more in northwest Arkansas. Dr. Guinan says the forecast after this is extremely unsettled, particularly with models showing some threat for an early tropical low pressure Gulf system (now called Invest 90L) to migrate its way into the region.

6-10 day outlook - Warmth Remains Through May

  1. Central Missouri is in a large rain deficit over the last 30 d. - Midwest Regional Climate Center
  2. Uncertainty exists on the amount of rain to expect in mid May. - Source: NOAA CPS

Quick Hits

Bermuda and Zoysia Winterkill Symptoms Remain

  1. Bermuda not fertilized with N (outside our fraze plots) sustained the worst damage.
  2. In some plots, fraze mowing did increase winterkill. Fraze as early as possible in summer.

  • Winterkill Lingers - May warmth promoted complete greenup of both zoysia and bermudagrass, and allowed for a thorough assessment of winterkill from this past winter/spring season… and it's extensive. Last week on Twitter (@muturfpath) several pictures were posted in a winterkill week, much in the same vein as Shark Week on the Discovery Channel. We have observed quite a bit on our bermudagrass trial areas at the research farm, and the diagnostic lab has received numerous phone calls and samples of zoysiagrass lawns in St. Louis that just never greened up. A few things have been obvious in many of these situations. If the areas were not fertilized with at least nitrogen in the previous year, winterkill was very severe. We observed this in a 'Patriot' bermudagrass area just outside of a fraze-fertilizer study that did not receive N in 2017. While potassium is often thought of as the "winterizer", in reality without sustainable levels of nitrogen, potassium might not be taken up in significant quantities from soils with sufficient levels. This effect may have also occurred in zoysia home lawns, that may not have received enough N the year (or in some cases years) prior. Normal areas with higher winterkill damage, such as excessively low areas that might hold water, and excessively exposed areas that might be prone to lower temperatures. Notably, our most recently frazed bermudagrass plots at five and eight mm also incurred increased winterkill compared to non-frazed. Fraze mowing occurred on July 7, 2017 and perhaps there was not enough recovery time prior to fall to allow for enough mat development to protect susceptible rhizomes, stolons, and crowns. Fraze mowing in this region should be done as early as possible in the upper transition zone to allow for complete recovery prior to fall dormancy.

Red Thread Prevalent on Fine Fescue/Perennial Ryegrass

  1. Red thread symptoms on a susceptible fine fescue variety.
  2. Pink tufts of mycelium characterize this disease on perennial ryegrass.

  • Red Thread/Pink Patch – Red thread is a curiously conspicuous disease that occurs most severely on perennial ryegrass and fine fescue, but can also occur in tall fescue and Kentucky bluegrass under low fertility conditions. Red thread is caused by Laetisaria fuciformis which produces sclerotia that look like red strands (hence the disease name). During wet conditions or in early morning dew, pink tufts of mycelium may be observed on infected leaf blades. Fungicides are normally not required for control, particularly in home lawns, but the disease is a sign that nitrogen may be necessary, or the soil should be tested for other nutrient deficiencies.

Rhizoctonia disease pressure begins

  1. This arc of diseased bentgrass is infected with a Rhizoctonia spp.
  2. After incubation, tufts of right-angled branched mycelium emerged from infected tissue.

  • Rhizoctonia diseases – A few rings caused by a Rhizoctonia spp. (most likely zeae) were observed earlier this week on our "disease green" at the MU turfgrass research farm. Upon some close inspection, brown patch lesions could be found sporadically in tall fescue swards. Warm temperatures and rainfall should have us well in the range for Rhizoctonia infection, leading to brown patch on creeping bentgrass putting greens and fairways, and as the Achilles heel of tall fescue. Creeping bentgrass is normally covered, but on lawns with a history of severe infection applications of azoxystrobin or other QoIs may be necessary to prevent density lawns. Shaded or overirrigated lawns are more susceptible to the disease. Overfertilized lawns are also more susceptible, so limit all use of fast release nitrogen sources on tall fescue lawns until milder temperatures resume in the fall. For more information on brown patch control on home lawns, see this previous report.

Foliar and some basal rot anthracnose active

  1. On bentgrass, foliar anthracnose can affect older leaves, and cause an orange mottled look.
  2. When anthracnose infects at the base (yellow arrow) decline can occur quickly.

  • Anthracnose on creeping bentgrass putting greens – The disease story of 2017 is occurring now, right on schedule with the first outbreaks observed last year (see last year's report here). The same tenets apply. Keep the nitrogen at sufficient levels. Keep topdressing. Rotate fungicides from many different classes since pathogen populations are known to develop resistance. When curative control is necessary, apply a contact with a systemic, and/or apply a strong combination of two actives (i.e. Briskway, Lexicon). Last, apply fungicides in high enough carrier volume to reach the base of the plant. Two gallons of water carrier per 1000 sq ft is good, three may be better.

Smith-Kerns Model for Dollar Spot Prediction*
Probability for dollar spot occurrence soared above the model threshold at all four modeled sites in MO (Springfield, CoMo, STL, and KC). A considerable dollar spot outbreak occurred on May 17 in Columbia (denoted by explosion on graph).
*Model based on 5-day rolling averages of air temperature and relative humidity.

  • Dollar Spot – Definitely not wanting to be left out, the research farm experienced its first major outbreak of dollar spot on creeping bentgrasslate last week. This coincided quite nicely with the newly minted Smith-Kerns dollar spot model as shown above, with the model going above 20% on March 13 and the extreme outbreak observed on March 17. All areas are well in the environmental zone of dollar spot activity. As we track forward into summer, it will be interesting how the model responds to our high temperatures, which normally lower dollar spot severity.

  • Pythium Root Rot & Nematodes on Bentgrass Putting Greens – Don't forget. These recent rains and higher temperatures should promote Pythium root rot infection and symptom development. Previous problems should prevent. When in doubt, test and assess. A good article on nematodes was published recently and can be accessed here.



Lee Miller
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Extension Turfgrass Pathologist
University of Missouri