Golfdom, October 2012

www turfgrasstrends com October 2012 TURFGRASS TRENDS 35 of 7 8 See Table 1 The results showed that several factors affected the level of annual bluegrass control from mesotrione The good news was several treatment regimes provided consistently high levels of annual bluegrass control The bad news was these treatment regimes required a significant number of frequent low rate applications Upon closer examination of the data we saw temperature during the treatments had a large effect on the results For most treatment regimes the higher the temperature the better the results Note that the trial with the highest average daily air temperature was the trial conducted in July 2010 In this trial five treatment regimes gave more than 80 percent annual bluegrass control Some regimes that provided poor control in other trials provided respectable annual bluegrass control in this trial For example applying 01 lbs active ingredient per acre weekly for a total of five applications resulted in control ranging from 15 to 57 percent in the other five trials but in the July trial annual bluegrass control was 92 percent Similarly 017 lbs a i acre applied three times on a Monday Thursday Monday schedule showed control levels of 3 20 and 23 percent in the other trials conducted in 2010 but 70 percent in the July trial The higher temperatures increase the activity of Tenacity dramatically probably because higher temperatures result in greater production of oxygen radicals and without the carotenoids to quench them the oxygen radicals wreak havoc on the plants So when temperatures are hot control is excellent and good control can be achieved with less frequent applications Excellent control was achieved from 01 lbs a i acre applied once a week for five applications or twice a week for five applications Conversely when temperatures are cool but not cold activity is reduced In the May 2010 trial only two treatments provided control above 40 percent The May 2009 trial saw several treatments provide greater than 80 percent control even though the average temperature of the trial was comparable to the 2010 trial Looking more closely at the temperature data we saw that in 2010 temperatures dropped right after the first application reaching a low average daily air temperature of 46 F at four days after the initial treatment Day 5 experienced a low of 34 F and an average of 48 F Beginning at 17 days after the initial treatment the air temperatures in 2010 exceeded the ones in 2009 and helped push the averages close together But my guess is that drop in temperature after the initial application Continued on page 36 PHOTO COURTESY BRUCE BRANHAM PH D Mesotrione selectivity derives from differential rates of metabolism in plants The bleached annual bluegrass on the left half of the photo has been treated with Tenacity