Golfdom, May 2014

plant uptake biotic degradation microbial metabolism abiotic degradation photodegradation are governed by temperature We wanted to examine the influence of temperature on the persistence of iprodione and chlorothalonil to see if fungicide indeed breaks down faster as temperatures increase We followed a similar protocol as Dr Latins experiment where we applied both fungicides to field plots and collected cores for sampling We used commercially available ELISA enzyme linked immunosorbant assay kits for each fungicide to determine fungicide concentration on the leaf surface in response to the following temperatures 50 68 and 86 degrees F We collected tissue at zero seven 14 21 and 35 days after the initial fungicide application and this data allowed us to calculate half life values for each fungicide within each temperature treatment For iprodione we found average half life values of 39 86 and 44 days at 50 68 and 86 degrees F respectively For chlorothalonil we determined that half life values were 948 85 40 days at 50 68 and 86 degrees F respectively These values are averaged across two or three experiments we conducted in 2010 and 2011 Koch 2012 Clearly temperature has a profound influence on the persistence of these two fungicides and most of the fungicides we use in turf With these experiments cores were removed from the field and placed in growth chambers without mowing When we collected cores from the field at each of the sampling dates above without incubation at a specific temperature half life values for iprodione and chlorothalonil were 176 and 21 days respectively Not only does temperature influence depletion of fungicide but so does physical removal due to mowing Koch 2012 SCIENCE OF RE APPLICATION Most fungicide failures occur during the summer months when most FIGHTING THE GOOD FIGHT Fairy ring is shown on an ultradwarf bermudagrass putting green turf pathogens are highly active and fungicides are readily depleted With certain diseases it may be necessary to use high rates and short intervals in order to maintain adequate protection regardless of the status of fungicide resistance within the population On the other hand when pathogens are not as active and fungicide depletion is minor extended residual control can be expected The two extremes are Pythium blight or Pythium root rot and snow mold When Pythium blight or Pythium root rot develop many times shortened application intervals and potentially high rates are recommended in order to maintain disease suppression However with snow molds one or two properly timed fungicide applications protect turf plants for many months Turf managers should not expect protection well after snow melts in the spring Our research shows that fungicides deplete readily as snow melts in the spring Re application of fungicide will be required to protect turf against Microdochium patch The science behind re application intervals is not exact Most of the recommendations come from fungicide efficacy testing at universities I think these are solid but they can fail too We do not have a handle on how many fungal cells are killed with an application and then how long it takes for the fungus to recover in every situation For example Dr Latin conducted another experiment investigating the residual efficacy of fungicides for brown patch control Again he found that fungicide residues were not sufficient on the leaf surface to protect against brown patch beyond seven to 10 days after the initial application Latin 2011 This study was conducted in a similar fashion to his dollar spot study mentioned above Yet we routinely see 21 to 28 days of control with some of the products he used in his study azoxystrobin and flutolanil So why do we see extended control of brown patch in many cases but not with dollar spot or Pythium blight It could be that fungicides that are superior for brown patch may be ultra toxic to Rhizoctonia solani and many more fungal cells are killed when applying fungicides for preventative control of brown patch Another possible explanation could be that these fungicides persist longer in thatch and soil where the brown patch fungus resides Dr Gail Schumann investigated the fate of fungicides in a Kentucky bluegrass sward in 2000 She found that propiconazole was not detectable seven days after application on the leaves similar to the findings of Dr Latin and our results mentioned above However her work examined more components of the turf systems such as roots soil and thatch She found almost no propiconazole in the soil or roots rather most of the residue persisted for 28 days in the Continued on page 44 May 2014 Golfdom 43 Golfdom com PHOTO BY JIM KERNS