Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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INTERACTION OF BENSULIDE AND CARFENTRAZONE FOR MOSS CONTROL ON
GOLF PUTTING GREENS. J.B. Willis, S.D. Askew, Virginia Tech, Blacksburg and J.S.
McElroy, Univ. of Tennessee, Knoxville.
ABSTRACT
Carfentrazone was recently registered for moss control on creeping bentgrass
(Agrostis stolonifera) putting greens. Previous results indicate that carfentrazone does
not injure creeping bentgrass, however, reports from NC, TN, and VA blame
carfentrazone for temporary injury to bentgrass putting greens. Putting greens had been
previously treated with bensulide prior to carfentrazone treatment in several of these
injury cases. Studies were conducted in Blacksburg, VA and Knoxville, TN to evaluate
bensulide with carfentrazone applied in sequence to creeping bentgrass on USGA
specification sand-based putting greens. The VA experiment is summarized below.
A split plot experimental design was used with three replications and a 3 by 8
factorial arrangement of treatments. Main plots were: bensulide at 6.25 lbs ai/A followed
by bensulide at 6.25 lbs ai/A at a 14-day interval, bensulide at 12.5 lbs ai/A, and no
bensulide. Subplots were carfentrazone applied 0, 1, 3, 7, 14, 21, and 28 days after
bensulide (DAB), and no carfentrazone application. Bensulide applications were
incorporated with irrigation immediately after application and all carfentrazone
applications included 0.25% nonionic surfactant.
Although creeping bentgrass in plots treated with bensulide alone was not injured,
bensulide increased severity and duration of creeping bentgrass injury when
carfentrazone was applied at 0, 1, and 3 days later. For example, carfentrazone applied
0, 1, and 3 days after either rate of bensulide injured creeping bentgrass on average 80,
91, and 18%, respectively 3 days after carfentrazone treatment (DAT) and 74, 82, and
34%, respectively 7 DAT. Creeping bentgrass injury was not greater than 12% 14 DAT
from any treatment except carfentrazone applied 0 and 1 DAB, which injured creeping
bentgrass 22 and 20%, respectively. Carfentrazone applied beyond 3 DAB did not
significantly injure creeping bentgrass. Thus, from this single experiment we can
tentatively conclude that carfentrazone treatment should be separated from bensulide
treatment by at least 7 days.
An unexpected result of this experiment was creeping bentgrass injury by
carfentrazone alone. When applied at 0 and 1 d after bensulide was applied to other
plots, carfentrazone alone injured creeping bentgrass 53 and 78%, respectively 3 DAT
and 32 and 60%, respectively, 7 DAT. These treatments did not significantly injure
creeping bentgrass at 14 DAT or beyond and no other timing of carfentrazone alone
injured creeping bentgrass. The general trend of more injury earlier in the study is
suspicious, especially since no previous researchers had observed significant injury to
creeping bentgrass from carfentrazone alone. All injury in this experiment consisted of a
rapid desiccation that is similar in appearance to sun scorch. A rain event of 0.75 inches
occurred 3 days prior to the 0 DAB carfentrazone treatment and the green was irrigated to
incorporate the bensulide treatment 4 hours prior to the 0 DAB carfentrazone treatment.
Consequently, the root zone was more saturated than normal at the 0 and 1 DAB timings
and days were clear and sunny. We plan to continue this work by evaluating moisture
and creeping bentgrass cultivar influence on injury due to carfentrazone.
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