An Integrated Nutritional and Chemical Approach to Poa Annua Suppression in Creeping Bentgrass Greens.

Creeping bentgrass (Agrostis stolonifera L.) provides an ideal putting surface for golf courses located in temperate climates but is invaded by annual bluegrass (Poa annua L.) and silvery-thread moss (Bryum argenteum Hedw.). There are no currently registered herbicides for annual bluegrass control in bentgrass greens. Paclobutrazol and FeSO4 will suppress one or both of these pests, but research on the effectiveness of the two together has not been reported. Our objectives were to determine the effects of repeated high rates of FeSO4 and paclobutrazol on transitioning annual bluegrass out of a creeping bentgrass green and determine if seaweed extract (SWE) aids the transition. An unanticipated objective was to assess treatment effects on moss incidence. The effects of all combinations of FeSO4 (0.0, 12.2, 24.4, or 48.8 kg ha-1), paclobutrazol (0.18-0.36 kg a.i. ha-1), and SWE (12.8 L ha-1) on control of these pests were investigated over 2 yr on a 'Penneagle' green. All FeSO4 rates decreased annual bluegrass to 21% when averaged over 2 yr. The paclobutrazol program reduced annual bluegrass to 5% regardless of FeSO4 rate. Repeated use of SWE had no effect on annual bluegrass or moss populations. An 8% decline in annual bluegrass occurred in untreated plots, possibly due to creeping bentgrass competition being favored by biweekly application of ammonium sulfate and exclusion of phosphorus and potassium fertilizers. Treatment with FeSO4 decreased moss, regardless of paclobutrazol or SWE. Paclobutrazol increased moss when FeSO4 was not applied. Season-long applications of FeSO4 (24.4 kg ha-1) plus high rates of paclobutrazol controlled annual bluegrass and silvery-thread moss while providing a putting surface of acceptable quality. [ABSTRACT FROM AUTHOR]