March 5, 2009
 
1. MSMA use continues in the short run with new directions for use
2. Fungicide synergism for dollar spot control on golf course putting greens
3. Buffalograss in Arkansas?
4. New extension publication on Pythium diseases of turfgrass

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1. MSMA use continues in the short run with new directions for use

On January 16, 2009, the MAA Research Task Force (Task Force) signed an agreement with the U.S. Environmental Protection Agency (EPA), which permits the continued use of MSMA on sod farms (as well as golf courses) through 2012.  Use of existing stocks would be permitted until the end of 2013.  The directions for use of MSMA will be revised on future labels.  A brief summary of the affects of this agreement on turfgrass managers is as follows:

a.   MSMA use on golf courses will be continued until December 31, 2013.        
-  One broadcast application on newly constructed courses.
-  Application on existing courses limited to spot treatment only.
     
b.  MSMA use on sod farms will be continued until December 31, 2013.
-  Two broadcast applications will be allowed per crop.
-  25 foot buffer strip around permanent water bodies.

c.  MSMA use on highway rights of way will be continued until December 31, 2013.
-  Two broadcast applications will be allowed per year.
-   100 foot buffer strip around permanent water bodies.

d.  Other MSMA uses, such as residential turf, forestry, non-bearing fruit and nuts, , railroad, pipeline and utility rights of way, fence rows, storage yards and similar non-crop areas will not be permitted after December 31, 2010.

e.  Uses of the related products DSMA, CAMA and cacodylic acid and its sodium salt, 
will not be permitted after December 31, 2010.

During 2012, EPA will have a committee of scientists review the scientific information that will be gathered by then on the cancer risk posed by inorganic arsenic.  If that scientific review concludes the risk of exposure to inorganic arsenic does not exceed acceptable levels (as the registrants believe it should be able to conclude), the continued use of MSMA for sod farms could be extended or a determination made that MSMA can be re-registered for use.

Contact info for the MAA Research Task Force is: MAA Research Task Force (MAATF),·P.O. Box 33856,  Washington, D.C. 20033-0856. 800-890-3301.

The news release from MAA is also available at: http://www.maatf.com/docs/pdf/28_090127_Anouncement%20of%20MAATF%20Agreement%20with%20EPA.pdf

 

2. Fungicide synergism for dollar spot control on golf course putting greens

The term “synergy” is defined as “the interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects.”   

You might think about synergistic effects in people, where several people acting together can sometimes accomplish more than the sum of everyone working independently.  Sometimes the phrase “1 + 1 = 3” is used.  Of course, antagonism is also possible, where working together is NOT efficient and 1 + 1 = 1.5.

The term synergy has also been used to describe pesticide interactions.  That is, certain pesticide combinations may lead to better control than would be expected based on the performance of each pesticide alone.  In contrast, antagonism occurs when pesticides interfere with each-other’s efficacy and results are worse than expected.

To test for synergy, it is necessary to do replicated tests of the components alone and in combination, then use statistical analyses to determine whether the effects are merely additive (1 + 1 = 2) or if true synergy is occurring (1 + 1 = 3).  (For the math fans out there, part of that method is explained below.)

In the well-known text Diseases of Turfgrasses, Third Edition, by Houston Couch, several synergistic fungicide interactions are reported.  In particular, synergistic effects were reported from several particular mixtures of low-rates of fungicides.  That is, effective disease control was reported to be possible using reduced rates of each component of the mix, giving better-than-expected control.

Recently, Dr. Rick Latin (Purdue University) and Dr. Lee Burpee (University of Georgia) conducted a thorough set of field experiments (two sites over 3 field seasons) to re-examine fungicide synergy for dollar spot control for some of these mixtures.  The results were published in both the academic journal Plant Disease as well as in the trade publication Golf Course Management. The tests included four combinations:

In 92 comparisons based on these four mixes, 84 showed simple additive effects (1+1=2), 5 showed antagonistic effects (1 + 1 = 1.5), and 3 showed synergy (1 + 1 = 3).  Thus, the authors concluded that synergistic effects are unlikely to be observed with these products. 

Why the discrepancies with prior reports?  Of course, the pathogen populations can shift over time to respond differently to fungicides, and pathogen populations can vary from site to site.  And, fungicide formulations can change.  This could account for some discrepancies.  In addition, some of the prior reports were not “peer-reviewed” in academic journals, leading to some skepticism.

There are other good reasons for tank-mixing, of course.  Additive effects are helpful.  Combining materials can expand the number of diseases controlled.  And, some pesticide labels recommend tank-mixes as part of a fungicide resistance strategy.

Testing for synergy:

Example:
When applied alone, fungicide A provides 50% disease control and fungicide B provides 75% disease control.  When applied
together (using the same rates), disease control = 85%.  Is this synergy, or just additive effects?

If fungicides interact additively (1 + 1 = 2), we expect that the % control of the mixture will be as follows:

Expected (A + B) = A + [B(100-A)]/100

where A = observed control in A-alone and B = observed control in B-alone

In our example:

Expected = 50 + [75(100-50)]/100 = 87.5

The expected 87.5% disease control is pretty close to what we observed.  That is, this does not appear to by synergy.  The next step is to repeat the experiment several times, get the averages, and use statistics to determine whether the observed control is equivalent to what we expect based on additive effects. 

If the observed disease control is statistically higher than expected, than a synergistic effect is occurring.  For example, if the combined disease control was more like 99%, we would suspect synergy the statistical analysis would probably confirm it.

Anyone still reading?  If so, here is some obscure trivia for you.  The word “Synergy” is also the name of the holographic computer from the 1980’s carton “Jem.”  Type “Showtime, Synergy!” into google.com and see for yourself.  It’s pretty bad.
Hey, just because I remember it, doesn’t mean I was actually a fan.  I only watched it a few times. Honest.  I just remembered the Synergy part because it is kind of a cool word.

Megan Kennelly, Kansas State University, Extension Plant Pathology

References:
Couch, H 1995. Diseases of Turfgrasses. Third Edition. Krieger Publishing Company, Malabar FL.

Burpee, L, and Latin, R. 2008. Reassessment of fungicide synergism for control of dollar spot.  Plant Disease 92:601-606.

Latin, R., and Burpee, L. 2008. Re-examining fungicide synergism for dollar spot control. Golf Course Management, July.  p. 84-87


3. Buffalograss in Arkansas?

I have received many calls recently about using buffalograss (Buchloe dactyloides) in Arkansas for everything from home lawns to college campuses. Buffalograss is a cold hardy, native, warm-season grass well adapted to western Oklahoma, Kansas, and Nebraska. It requires little fertilization and has excellent drought tolerance.

Although there is some buffalograss in Northwest Arkansas, it does not compete well with weeds in Arkansas because of our higher rainfall and more humid conditions compared to western OK, KS, and NE. As a result, several herbicide applications would be needed to produce a good quality buffalograss turf in Arkansas. In most situations in Arkansas where buffalograss is planted, the turf will become very weedy and infested with bermudagrass in the long run. Therefore, buffalograss is not recommended as a sustainable turf for Arkansas except in some unirrigated, full-sun lawns where aesthetics is not a principal concern.

Aaron Patton

 

4. New extension publication on Pythium diseases of turfgrass

This publication address the most common Pythium diseases (blight, root dysfunction, and root rot) and provides information about the pathogens, host grasses, disease symptoms, fungal signs, seasonal occurrence, and management options.

This publication (FSA7565 – Pythium Diseases of Turfgrass) is available at http://turf.uark.edu/publications/pub.html  and http://www.uaex.edu .

Aaron Patton and Steve Vann

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