Role of phosphorus in suppression of Poa annua on bentgrass greens

June 25, 2005

Summary: The lack of Poa annua on the five-year-old A4 greens at Talega suggest that low soil phosphorus might play a role in limiting invasion by poa. This report summarizes the findings of a study conducted by George Kenny at Talega that reveals the approximate minimum level of phosphorus that is needed to maintain healthy bentgrass with the target of suppressing poa invasion.

• In order to continue the poa control strategy of low phosphorus management, do not apply excessive phosphorus. The target is between 20 and 30 ppm Mehlich III P to maintain adequate bentgrass growth at the lowest phosphorus levels possible. For increased accuracy in phosphorus testing, use the Olsen test for phosphorus and target a minimum of 5 ppm in the soil for adequate growth of bentgrass. Olsen P values above 5 ppm may be needed if iron levels are increased or the turf begins to display the purple symptoms of phosphorus deficiency.
• Do not apply more than ½ lb P₂O₅/1000 sq ft in a single application. MAP is a good source but monopotassium phosphate 0-52-34 will also do a good job while applying potassium at the same time without the added nitrogen.
• Apply 2 lbs 0-0-50/1000 sq ft monthly throughout the year to provide needed potassium. Irrigate following application.

Full print version of report (471Kb)

Investigators: Larry Stowell (PACE Turfgrass Research Institute), George Kenny (Talega Golf Club)