Golfdom, March 2017

Super Science TABLE 2 Follow up Trial 2014 2015 Timing Date Nitrogen Source fall 14 16 Sept AMS CN U spring 15 6 May AMS CN U D fall 14 spring 15 16 Sept 6 May AMS CN U summer 15 only 20 June 15 July AMS CN U 18 Aug Application dates for fall spring and summer fertilizer treatments of ammonium sulfate AMS calcium nitrate CN urea U or Duration D for the follow up trial All timings are based on a 65 degree F five day average soil temperature threshold measured at a 2 inch depth All spring and fall applications of ammonium sulfate calcium nitrate and urea received 05 lbs N 1000 sq ft on the listed date s All ammonium sulfate calcium nitrate and urea plots received a total of 20 lbs N 1000 sq ft per year Torque was applied once to duplicates of all plots on this date at a rate of 06 fl oz 1000 sq ft A singular application Duration CR 120 day was applied at a rate of 3 lbs N 1000 sq ft Continued from page 31 State University and in Columbia Mo The University of Missouri Treatments included ammonium sulfate calcium nitrate or urea applied in spring or fall when soil temperatures at a 2 inch depth averaged 60 degrees F or 70 degrees F over a five day period and a standard summer nitrogen application schedule Table 1 A follow up and ongoing study at the University of Missouri combines several factors including nitrogen application timing nitrogen source and a single spring fungicide application in an effort to develop an integrated strategy for large patch management Table 2 NO THREAT IN SPRING OR FALL N In both studies nitrogen was applied just prior to or during visible large patch outbreaks in both the spring and fall A previous mantra was that nitrogen applications made during the infection period would encourage lush leaf growth and predispose zoysia to more severe infection and symptom development Another fear was that fall nitrogen applications would predispose zoysiagrass to winterkill Results from both field studies do not demonstrate either assertion to be true No increase in large patch severity was observed with spring or fall nitrogen applications compared to summer applications in Kansas or Missouri In addition Missouri plots receiving a late spring nitrogen application 70 degrees F soil temperature threshold had lower large patch severity and higher percent green cover compared with those receiving a standard summer program on several rating dates in 2014 This finding was not consistent with results at the Kansas location The details of this study were published in the peer reviewed scientific journal Crop Forage Turfgrass Management The second follow up study is yielding similar results regarding spring fertility applications Plots without fungicide applications that received summer only and fall nitrogen applications had greater large patch severity in the spring than those receiving spring or combined fall plus spring nitrogen applications Figure 2 In fact any plot receiving nitrogen applications in the spring without fungicide statistically had similar large patch severity compared with their identically fertilized plots treated with a single spring tebuconazole application Figure 3 There were no interactions between fungicide applications and nitrogen timing Plots receiving fall nitrogen applications in both trials had longer sustained green turf in the fall with no increase in fall large patch symptoms and no winterkill damage the following spring These findings go against previous notions that nitrogen applications during large patch outbreaks increase disease severity and suggest that spring nitrogen applications may encourage zoysiagrass to outgrow large patch infection SOURCE OF CHOICE Although urea is the cheapest nitrogen source other nitrogen sources such as ammonium sulfate may negatively affect the FIGURE 2 Large patch development on plots receiving nitrogen at different periods of time in Missouri Summer A Spring B Fall C Fall plus Spring D No fungicide was applied to these plots 32 Golfdom March 2017 Golfdom com