Annual Bluegrass (Poa annua L.) Control In Creeping Bentgrass (Agrostis stolonifera) Putting Greens with Various Combinations of Amicarbazone and Paclobutrazol.

Annual bluegrass (Poa annua L.) is a problematic weed in creeping bentgrass (Agrostis stolonifera L.) putting greens due to its ability to survive at low mowing heights and inadequate control options from pre- and postemergent herbicides.  To date, annual bluegrass control on creeping bentgrass greens is best achieved through the repeated usage of plant growth regulators (PGRs).  Paclobutrazol, a gibberellin biosynthesis inhibitor, is currently the most effective PGR labeled for annual bluegrass suppression in creeping bentgrass putting greens.  Although PGRs are effective choices for suppression of annual bluegrass growth and seedhead production, they do not provide acceptable long-term control.  Amicarbazone (70WG, Arysta LifeScience) is a postemergent photosystem II inhibitor herbicide belonging to the triazolinone family.  Amicarbazone has shown potential for annual bluegrass control in cool-season turf, including creeping bentgrass greens. Research was conducted to determine the efficacy of various amicarbazone and paclobutrazol treatment regimes for annual bluegrass control in creeping bentgrass greens.  Bentgrass tolerance trials on ‘A1’, ‘A4’, ‘Crenshaw’, ‘L-93’, and ‘Penncross’ varieties and annual bluegrass control trials on ‘Crenshaw’ and ‘Penncross’ greens were initiated Spring, 2010.  All plots were arranged in a randomized complete block design with plots measuring 1 x 2 m.  Treatments included amicarbazone (49 and 65 g ai/ha) and paclobutrazol (70, 140, and 280 g ai/ha) standalone treatments, tank-mixtures, and the usage of both chemistries at varying rates and sequential timings.  All amicarbazone treatments included a non-ionic surfactant (0.25% v/v).  Visual bentgrass quality and annual bluegrass percent cover ratings revealed positive results from the incorporation of both products in an annual bluegrass control program.  Results indicated three monthly applications of amicarbazone (65 g ai/ha) tank-mixed with paclobutrazol (280g ai/ha) enhanced creeping bentgrass quality and annual bluegrass control, compared to each applied alone.