GOLF: Have you applied a preventive application for Pythium root disease yet?

In the next week
In June
Not planning to

Update (05/10/2018)

From Freezer to Grill Grate

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Out of a Cannon

  1. Summer-like temperatures welcome May. - Source: Missouri Climate Center
  2. Warm temps expected to continue, perhaps flirting with records this weekend. - Source: NOAA

Out of the freezer and directly on to the grill grate is no way to prepare a steak, but that is exactly what we’re getting this spring season. April in Missouri was the 2nd coldest on record, only second to 1907, averaging 7+ degrees below normal across the state.  Now, the region has gone into the fryer with temps 5-10 degrees above normal for the region in the first week of May. Temperatures are forecasted to rise even higher into this weekend, perhaps flirting with near record highs in many cities. The season is here, and has been shot out of a cannon in a very short time.

Heavy 2+ inch rains occurred over the first week of May in the southeast and northwest portion of Missouri, southern Iowa and northern Arkansas. Most areas have received some rainfall in May, but May is historically and crucially our wettest month, with an inch of rain expected every week.  As demonstrated in the graphic below, central and west Missouri is extremely dry. Here in Columbia we expect 4+ inches of rain in April and only received 0.4. Additionally, our May evapotranspiration rates have been abnormally high for this time of year in May, anywhere from 0.2 – 0.25 inches/day. We need the rain here in central MO badly. Dr. Pat Guinan, the Missouri state climatologist, notes some inconsistency in the short term 5-day forecast for rain, with a front that could either settle over I-80 in Iowa or I-70 in Missouri. We could use its company on I-70 for sure. The below graphic (panel B) from the NOAA is encouraging and hopefully accurate, because it’s starting to feel like 2012 around here.

A Hole with No Rain

  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

  • Several more zoysia lawn cases in St. Louis have been called in over the last two weeks. If injury occurred in 2017, it is fairly difficult, nay impossible, to determine the cause in 2018. This being said, the weather has not been conducive for zoysia overwintering or spring growth. As demonstrated by this article by Dr. Jim Brosnan at U of Tennessee, the weather data doesn’t lie, and this past winter and spring were intense for most across the middle belt of the U.S. My recommendation is that as zoysia recovers and slowly greens, fertilize it with 0.5 – 0.75 lb N/1000 sq ft. This will allow a good assessment of the damage and determination of whether to begin renovation in early June or bank on recovery from the outside in. Remember from previous updates, fertilizing has been demonstrated to not increase large patch. For homeowners considering a switch to cool-season tall fescue and/or Kentucky bluegrass and the advantage of annual fall overseeding to rebuild density, renovation should wait until late August – mid September when seed will be most likely to germinate and thrive disease free. 

New Smith-Kerns Model for Dollar Spot Prediction*

  1. Springfield: Only region to experience a few events over the 20% estimated threshold.
  2. C. D. Columbia, STL and KC have been too dry (low humidity) and cool in April to promote spikes in predicted pressure.
    *Model based on 5-day rolling averages of air temperature and relative humidity.

  • On creeping bentgrass and Kentucky bluegrass, dollar spot is late for most of us in Missouri, but should be just around the corner. A new model for predicting dollar spot development and application timing was created by Dr. Damon Smith and Dr. Jim Kerns and is aptly named the Smith-Kerns Dollar Spot Prediction Model. The model was tested extensively in Wisconsin, Oklahoma, Pennsylvania, Mississippi, Tennessee, Connecticut, and New Jersey and the results are published here. Huge kudos to all of those involved.

    Dr. Paul Koch at Wisconsin has published a comprehensive webpage explaining the specifics of the model, how it can be used, and various resources to allow for easily implementing it into your program. Their research shows a 20% probability threshold as calculated by the model for applications to provide effective disease suppression. This is a starting point since many factors are variable from one site to the next, so turfgrass managers should work with the model to get a feel for what works best for their management situation. Four locations in Missouri are shown above, and only Springfield has hit the 20% mark. Please let me know if you are using this model in your management program, and hopefully it will help you shave off an application or two or three…

Pest Management for Home Lawns Booklet
This pocket-sized booklet covers the most common weed, disease, and insect problems in home lawns. Information includes identification and management tips, with emphasis on both cultural practices and pesticide recommendations for control.

  • Pest Management for Home Lawns is a resource for managing lawns in Missouri, including all of the common weeds, diseases and insects. This pocket-sized book is authored by three specialists in each of the three pest types (including myself). The main goal of this guide is for use as a communication aid with homeowners regarding their current pest problems, and methods in which to control them. For more information, go to

Soil Gremlins Teaming Up on Golf Greens

Pythium root rot hampering spring root growth

  1. Just like Gremlins, don't keep roots too wet after midnight.
  2. The reduction in root growth is obvious on areas + PRR.

In the last week, four courses in St Louis and mid Missouri had significant Pythium infection in root and crown tissue. How could this be? The season has just barely begun and the weather has been dry? Below are a few key points about Pythium root rot that should be recognized.

  • Pythium root-infecting and disease-causing species are diverse, and do not require warm +90 temperatures to infect. Several studies out of Canada including this one have found Pythium spp. that are more virulent at lower temperatures than at high ones. Symptoms may be more prevalent when warmer temperatures arrive, but this is an artifact of a compromised root system, not an indication of when the damage was done.
  • As stated above, Pythium spp. in the soil are very diverse. Abad et al. 1994 isolated 33 species from 56 different golf courses in North Carolina. These species are different morphologically and more importantly in environmental conditions in which they infect.
  • Rain did fall. February was the wettest on record in Missouri, and March followed suit, particularly in the St. Louis area. New roots were more than likely attempting to “bud out” then and were initially infected.
  • Water continued to fall... through irrigation. When left to irrigation alone, we can often over irrigate, particularly if…
  • There is a good amount of organic matter to keep water in the top portion of the profile, and...
  • The water has nowhere to go, due to poor drainage, or perhaps a long and mild freeze thaw cycle that kept the upper portion of the profile wet but not considerably cold.
  • Last but not least, in some of these cases, we’ve detected an accomplice that isn’t so much driving the getaway car, but unlocking the front door. Significant numbers of ring nematodes were found at one site (>1,000/100 cc soil), lance at one site (144/100 cc soil) and stunt at three sites (105 - 702/100 cc soil). Perhaps most troubling, root-knot nematodes were observed in high numbers (90 - 1,404/100 cc soil) at four sites, and observed in the roots at a fifth (analysis forthcoming). These numbers are only going to go up, and nematodes and their mouth daggers open perfect sites for secondary pathogen infection by greedy opportunists like Pythium spp.

Two by Two

  1. Pythium oospores (black arrows) in a bentgrass root downstream from…
  2. Meloidogyne root-knot females (red arrows).


If you are having trouble with root development now,

1. Dig and rinse the root profile to observe root formation and color with a 10x lens.

2. Get a sample to a diagnostic lab to check for root pathogens.

3. Send a sample in for nematode analysis. For information on this service at MU, see

4. If on a site with a history of Pythium root disease, consider making a watered-in application of Segway at the half rate (0.45 oz/1000 sq ft) tankmixed with a QoI fungicide (i.e. Heritage, Insignia, Fame). Water in with at least 1/8 inch of post-application irrigation. Throughout the summer, make preventive watered in applications every 14-21 days rotating the low rate of Segway with other effective chemistries such as Banol, Signature, Stellar, Subdue, the QoIs, etc. This rotation should help mitigate fungicide resistance development and knock back the different Pythium spp. likely infecting the roots.



Lee Miller
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Extension Turfgrass Pathologist
University of Missouri