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Update (7/24/2012)

School's Not Out for Summer Patch

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Extraordinarily hot and dry weather conditions impacting crops throughout Missouri.

Good weather news has been hard to come by this summer in Missouri and other parts of the Midwest.  We are in the firm grip of a widespread drought, which unfortunately has a bad habit of perpetuating itself.  Lack of water in plants and on the ground doesn’t drive humidity, which in turn does not result in a return of water vapor to clouds for storm activity.  It’s advisable to have some liquid in the bottom of the crock pot even when set to low, but the region has simply been dry searing for an exceptionally long time.  Add in the high heat of the 5th warmest July so far, and the 6th driest June and the pot roast is going to be real tough at dinner. 

Water use has been astronomical to keep high amenity lawn and sports areas in working condition.  I’ve heard the figure “250k- 300k gallons of water a day” several times over the last two weeks from golf course water usage, which got me to thinking how this may relate to our observed evapotranspiration rates.  In the span from 7/8 - 7/22, it was calculated that plants lost a total of 3.467” of water to our hot and dry atmosphere.  This equates to 94,143 gallons per acre, or 9.4 million gallons per 100 acre golf course. At a rate of 300k gallons/day, the 14-day total for replacement that courses are adding back is only 4.2 million gallons, or ~44% replacement.  A 70% replacement rate is recommended, which may be practically impossible for irrigation systems or water supplies over large acreages to adequately handle.  With this being said, it is amazing the beautiful shape that some of our local courses are still in despite this brutal stretch.  Although not easy by any means, this is proof that hot and dry is oftentimes much better for turfgrasses than hot and saturated.

Not many disease samples in the last two weeks have been submitted into the lab, but rather most samples have been affected by physiological decline. As indicated above, golf greens with too much organic matter in the soil profile and carrying too much water are having issues with a lack of root depth.  This situation is predisposing the weakened roots to opportunistic pathogens that are preying on a severely heat stressed plant.  

Quick Hits

Pythium blight on tall fescue in excessively watered lawns.
  • Two severe cases of Pythium blight on tall fescue were brought into the lab over the last week.  Unbelievably, both lawns were severely over-watered during the heat of the day.  One was a grow-in of tall fescue sod (not advisable in a 100 + degree drought condition) that was left with standing water. Pythium blight infects the turfgrass leaves and crowns in high 90+ temperatures.  The pathogen is also known as a water mold, and requires long periods of leaf wetness or total saturation to spark zoospore release and initiate the infection cycle.  In both cases, reducing the duration of leaf wetness by watering less (can’t believe I’m saying that) and watering early in the morning would greatly reduce the incidence of this disease.  In these cases, a curative fungicide such as Subdue or Banol may be necessary to halt disease progress. Note that Pythium is not a true fungus, so different classes of “fungicides” are necessary for control.     

Summer Patch - Enjoying Its Season

Summer patch infecting creeping bentgrass as well as bluegrasses.

A bentgrass putting green sample came in last week from southwest Missouri that had odd patch symptoms despite an extensive 4-6” root system.  Patches were 2-5 feet in diameter with some being solid, and others having a more ring-like or “frog-eyed” appearance.  Stand symptoms were similar to those I’ve observed for Pythium root dysfunction in the Southeast U.S., but the root morphology was very different as affected roots had a darkened vascular cylinder and abundant root hairs.  In this case, the sample was affected with summer patch. 

Take-all patch is the most diagnosed patch disease on creeping bentgrass, but normally symptoms occur much earlier in late spring or later in autumn.  Roots in this sample also had growth cessation structures (Photo - B above), which is a characteristic indicating a summer patch infection instead of take-all patch.  You’ll also note two large structures in the image, which look very much like Pythium oospores, but are actually spores of a Glomus spp.  Glomus is a genus of vesicular-arbuscular mycorrhizae, and is normally beneficial to plants allowing for increased nutrient uptake. 

Start of story time…  In a similar droughty year of 2005 in Chicago, Dr. Randy Kane, (a mentor of mine), noted these mycorrhizae going wild, busting out of roots and causing some damage on golf greens.  The levels seen in this sample were much lower than those observed in Chicago, and in the current case are not causing the turf decline.   However, it’s worth noting how the similar weather patterns between Chicago summer 2005 and Missouri summer 2012 may be driving these similar cycles of soil microbial activity.  In a presentation given in 2005 by Dr. Kane, I found that he also was observing summer patch infecting creeping bentgrass in 2005, much like this year.  Now back to the original story…   

Summer patch is a root-infecting soil borne disease that is normally attributed to the bluegrasses (both annual and Kentucky).  In the case of annual bluegrass, this disease is normally a welcome “death blow” to this nuisance weed in high temperatures, but in Kentucky bluegrass this disease can cause considerable problems in lawns, sports turf, and golf course roughs and surrounds.  Since it’s a root disease, it is important to manage it preventively.  For areas with a history of the disease, preventive fungicide applications should be initiated in the late spring when 2” soil temperatures reach 65°F for 3 consecutive days.  In areas of high infestation, 2-3 applications are necessary on a 28 day interval to obtain adequate control.  Fungicides should be watered-in with 1/8-1/4” of irrigation to deliver the fungicide to the target area (i.e. root zone).  Fungicides in the QoI (strobilurin) or DMI class are most effective in controlling summer patch. In a curative situation, particularly on golf putting greens, a QoI such as Heritage or Insignia or a benzimidazole such as thiophanate-methyl should be applied due to the potential for phytotoxicity of the DMIs in this current period of high heat stress.      

Cultural management of this disease may be difficult in this area, particularly on golf putting greens.  Research out of Rutgers University showed good suppression of summer patch on Kentucky bluegrass with acidifying fertilizers such as ammonium sulfate.  Even in a curative situation, a light application of ammonium sulfate (0.2 lb N/1000 ft2) may be applied and lightly watered-in to encourage recovery.  The problem in this region is the extremely high pH irrigation water that some courses are using, which may negate the positive acidifying effect of the fertilizer on the rhizosphere in a sand-based golf green root zone.  Manganese sulfate applications  (2 lbs/A) have also been utilized by some to suppress summer patch in Kentucky bluegrass .  Research again out of Rutgers University showed the summer patch pathogen (Magnaporthe poae) caused a change in the manganese element that rendered it unavailable to the plant.  This change was found necessary in the infection process, and supplemental manganese applications have resulted in lower disease expression.  It is unknown if manganese sulfate applications on golf greens would work in the same manner.      

Missouri Turf & Ornamental Research Field Day

Just a quick thank you to all of those who came out to attend the field day and for your support of the program.  Attendees may have noticed the impressive helicopter fly over that began the proceedings, (wish I could take credit for that), and I hope that was just a start of a memorable and worthwhile day for you.  If you missed field day (and the incredible fly over), or want a refresher, I’ll be providing a short recap of some of the events in following updates.

Lee Miller
Follow on Twitter!  @muturfpath
Extension Turfgrass Pathologist
University of Missouri