Golfdom, May 2014

Super Science FIGHTING THE GOOD FIGHT Factors affecting fungicide performance Part 3 of 3 Depletion factors By Jim Kerns Ph D Editors note This is third of three articles by Dr Kerns on disease management and control I n the two previous articles we discussed the importance of fungicide selection application rate application timing disease pressure and fungicide resistance All of these factors help turfgrass managers develop solid disease management programs but what happens to the product once it is applied Six processes affect the persistence of fungicides in an environment volatilization plant uptake biotic degradation microbial metabolism abiotic degradation photodegradation or pH activity solubility based movement in water and sorption and desorption to plant and soil surfaces After application of a fungicide there are many different fates for the product FUNGICIDES ARE FUNGISTATIC Dr Rick Latin conducted an interesting experiment investigating the depletion of commonly used dollar spot fungicides Fungicides were applied in the field cores were collected and inoculated at zero three seven 10 14 17 and 21 days after the initial fungicide application The fungicides he used were Banner MAXX propiconazole Chipco 26 GT iprodione 3336 4F thiophanate methyl Daconil Ultrex chlorothalonil and Fore mancozeb Figure 1 shows his results nicely yet notice that in almost every case protection of the foliage started to break down around seven to 10 days after the initial fungicide application Although many of these products may provide 14 days of dollar spot suppression this FIGURE 1 Depletion of five fungicides commonly used for dollar spot control in creeping bentgrass turf 0 21 10 3 17 7 14 Days after fungicide application 100 75 50 25 0 Dollar spot severity The study was a bioassay in which fungicides were applied to field plots and cores were removed and inoculated with the dollar spot fungus at zero three seven 10 14 17 and 21 days after fungicide application Figure was adapted from Latin 2011 work clearly shows that these products were depleted fairly rapidly from the leaf surface Latin 2011 Please do not view this as justification to apply fungicides every seven days We know that fungicides are really fungistatic Fungistatic means that fungal cells are killed but the entire fungal body is not destroyed in response to a fungicide application Therefore once the fungus overcomes the shock of cell death growth can resume if conditions are favorable The current suite of fungicides is effective but they only kill small portions of the fungal body Keep in mind that once we see disease develop the amount of fungal tissue required to induce that reaction is large Fungi are extremely prolific organisms and even the absolute best fungicides cannot kill all the fungal cells present in the tissue So depending on the current environment it may take the fungus a few days or weeks to recover from the fungicide applications For example our research with dollar spot clearly shows that the fungus needs four or five days of colonization before inducing plant symptoms If we apply one of the fungicides above and assume eight to 10 days of protection of the foliage another four or five days of conducive conditions for fungal re growth then 12 to 15 days of dollar spot suppression should be expected In some cases the disease may break through the common re application interval for a fungicide but that does not necessarily mean fungicide resistance has developed in the population Under certain circumstances we may be fighting an active pathogen population and active depletion of the fungicides as well TEMPERATURE TREATMENTS Of the six processes that affect fungicide persistence in the environment the first four mentioned above volatilization 42 Golfdom May 2014 Golfdom com