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Update (6/22/2012)

Shorter Days, Shorter Roots, & Root Rot

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June is only a few degrees above normal for Missouri, but hot temperatures lie ahead.

Not the most upbeat update title I’ve come up with, but it is truthful.  We have passed the summer solstice, our longest day of sunlight for the year, and are now starting a very gradual photoperiod decline until December 21st.  Evidently, this winter solstice is the subject of some doomsday scenarios including a major motion picture -  Oh, the Mayans and their zeros, maybe this is affecting my normally optimistic demeanor…     

Drought conditions prevail across Missouri.

Temperatures have been relatively mild so far this June, but are set to boil for this weekend and again later next week.  With our current drought situation, this will have a dramatic impact on cool season turfgrasses.  Tall fescue, and especially Kentucky bluegrass and fine fescue lawns that aren’t irrigated are either in or heading back into drought dormancy.  Creeping bentgrass and Poa annua roots on golf putting greens are now shrinking after an extended spring growing season (thanks to a record breaking March). 

Water management is always important, but is now critical for all cool season turf species.  Lawns are requiring nearly an inch a week of supplemental irrigation during this period to remain green.  Water management on golf putting greens is now on that fine line of keeping the soil wet but not saturated (see below).  Dr. Brad Fresenburg and I wrote an article detailing irrigation and evapotranspiration, which can be found here -   As you can see in the article, the ET numbers have been off the charts in late spring and early summer.  I also have some irrigation tips below that I first wrote about in the June 5th update.

As you can read in the Quick Hits, most turf diseases have not been prevalent with the dry conditions.  Brown patch on tall fescue, in particular, has not been observed in the diagnostic lab (good for Missouri) nor in my research plots (bad for me).  Insect damage has replaced disease as the major lawn pest so far, and is propelling my current foray into entomology.  Dr. Wayne Bailey, our extension entomologist on the crop side, stated he too is observing insect pests that he has never witnessed in the state before. 

Quick Hits

  • Dollar Spot:  Fueled by a few cool nights and constant irrigation on putting greens, dollar spot is causing more damage now at the turf farm than any other disease.  We have observed numerous new infection centers in the last week in our research plots. 

  • Drought Stress: As if I haven’t said enough about it already, non-irrigated turfgrass is in drought survival mode.  This has led to some homeowners believing they have a disease, when in reality tall fescue and Kentucky bluegrass are in an extreme water stress situation.  Even more drought tolerant zoysia and bermudagrass species are feeling the extreme pinch.  If this is combined with a nitrogen application, (horribly miss-timed in the case of cool season turf) the plants are trying to cash leaf growth checks that their roots and low soil water conditions can’t afford. 

    Remember the early bird accomplishes the best irrigation.  Watering in the early morning hours is always preferred, because it rinses dew and guttation fluid off the leaf blade and disrupts the turf disease cycle.  In addition, the plant is rested and can take up the water, and winds are lighter in early morning to allow for more even irrigation distribution.  Watering lawns and landscapes during the heat of the day can cool the plant briefly, but is inefficient and can spark significant disease outbreaks.  Two – three deep ¼” – ?” irrigation events a week will be necessary to keep growing turf healthy during this extreme period.

  • Localized Dry Spot:  In this extreme period, golf course greens with water repellant soils have been a struggle if not impossible to manage.  Golf greens afflicted with this problem should apply wetting agents or penetrants on a routine basis to combat the problem.
Hunting billbugs are causing severe damage to zoysia across the state.
  • Billbugs: The current billbug outbreak (particularly hunting billbug on zoysia) is complicating matters, as turf symptoms typically resemble drought stress.  I wrote about this pest in detail last week (click here to view), and we are noticing early symptoms on zoysia at our turf research farm – see above.  These early symptoms appear as spots of turf 2-4” in diameter scattered throughout the turf stand.  These spots coalesce in high infestations to result in uniformly necrotic turf areas. 

Japanese beetle adults captured in high numbers
  • Japanese beetles peaking: Captain Obvious here, reporting large numbers of Japanese beetles.  I believe the reported catch numbers indicate they are currently at their peak.  This pest is feeding heavily on ornamentals and untreated crops (particularly corn silks), and is laying eggs in turf.  This peak signals the time to apply preventive annual white grub insecticide treatment in susceptible areas.  Like the motto has been all season long: about 3 weeks earlier than normal. 

Mealybug feeding damage on zoysiagrass
  • Mealybugs in Zoysia:  I believed this pest was reserved for the zoysia in our greenhouse, but I was mistaken.  In a first, a homeowner in Jefferson City sent a recently sprigged zoysia sample that was loaded with mealybugs.  These insects create white cottony masses near the turf crown that resembles fungal mycelium.  Within white masses, mealybugs, which look like swollen ticks, pierce into plant tissues and withdraw plant sap.  Early symptoms can include a “buggy whip” appearance, or curved leaf blades, and chlorosis up one side of the leaves.  Large infestations can cause drought-like symptoms.  In most cases, natural insect predators such as lady beetles and wasps maintain mealybugs below damaging levels.  Several control methods should be attempted before using an insecticide as a last resort.  These include a high pressure spray of water to knock bugs from leaf stems or using a drench of an insecticidal soap or diluted Ivory/Dawn dish soap.      

Pythium Crown/Root Rot – In a Drought??

Pythium root rot occurring on golf greens in the region

Much to some golf superintendents dismay, Pythium root rot has reared its ugly head in the region.  Over the last week, three samples from Missouri and Kansas have come in to the diagnostic lab exhibiting Pythium crown and root rot.  In all cases, symptoms occurred shortly after our last rain event a week ago, which dropped 0.5” up on most areas.  Even a short window of soil saturation can spark Pythium spp. to produce zoospores in abundance, and rapidly infect heat stressed bentgrass or Poa annua.  It is also important to note that unlike Pythium foliar blight, root rots don’t need extreme >90°F temperatures to flourish and infect.   Temperatures from 70°F on up will work just fine as long as the pathogen has a pool to swiw in, making poorly drained or shaded areas an obvious area for disease occurrence.

As noted in a previous update, this disease takes advantage of a hole in many greens fungicide programs.  Not many superintendents apply a watered in fungicide that targets Pythium.  Remember that most fungicides are apoplastic, so they move up in the plant not down.  One notable exception is fosetyl-Al (i.e. Signature), which may help suppress symptoms of this disease when used on a frequent basis.  Curative root rot recommendations center on ethazole (Koban or Terrazole), an older fungicide chemistry that in most cases is not easy to find.  This fungicide can cause phytotoxicity and should be watered into the soil profile to rinse off the leaf blade and deliver to the target zone where the pathogen resides.  Subsequent application of Subdue, Segway, or Banol 10-14 days later is often needed to sustain control and recovery.  Before a rain or soil saturation event, preventive application of one of these three fungicides should be applied in areas with a history of the disease.        

Much is still not known about Pythium root rot and the many species that cause it.  Adding to the confusion is another disease caused by Pythium species termed Pythium root dysfunction. Pythium root dysfunction has been recently characterized in North Carolina on newly constructed (< 5-7 years old) creeping bentgrass putting greens.  This symptom breaks the Pythium rules, and routinely occurs in drier areas of a putting greens and infects roots during lower spring temperatures. In current cases, the soil profile was wet and roots and crowns were notably rotted, so root dysfunction is not believed to be the cause.  Our newest graduate student, John (JB) Workman, is focusing his dissertation research on investigation of the biology and control of this disease.  Read more about JB and Pythium root diseases in the 6/5 Update.   

Save the Date: Missouri Turf & Ornamental Field Day – July 10th

-  Want to see Dr. Starbuck discuss evergreen trees for the last time before his retirement? 
-  Want to meet JB in person and hear more about the Pythium project? 
-  Want to find out about the latest and greatest methods for turf and ornamental management?
-  Want to meet local vendors interested in providing management solutions?
-  Or, do you just want to eat a great lunch among your colleagues and research scientists?

Well then, come on over to the research farm on July 10th for all kinds of interesting lessons and information on how to effectively manage turf and ornamentals in Missouri.  Our outstanding lineup of presentations and displays is set, and our research teams look forward to meeting and discussing your plant management practices.  Look forward to seeing you there!!

Click here to see the event flyer.
Click here to see the full schedule.
Click here to register.

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