Phosphorus influences annual bluegrass competitiveness at seeding in perennial ryegrass and creeping bentgrass

Annual bluegrass (AB; Poa annua L.) infestation is aided by phosphorus (P), but there is no information evaluating the effect of P on AB encroachment into turfgrass at seeded establishment. We hypothesized AB seedling survival and vigor will increase with P rates, compromising establishment of desired turfgrass species. Greenhouse pot studies evaluated the effect of P application rate on AB establishment or cover when seeded with perennial ryegrass (Lolium perenne L.) or creeping bentgrass (Agrostis stolonifera L. '007'). Two experimental runs were repeated in time. In perennial ryegrass, five P rates (0, 25, 50, 100, and 200 kg P ha(-1)) and two cultivars ('Black Cat II' and 'Home Run LS') were tested in sand media (11 mg kg(-1) Mehlich-3 extractable P). In creeping bentgrass, five P rates (0, 12.5, 25, 50, and 100 kg P ha(-1)), which were modified in the second run (0, 6.25, 12.5, 25, and 50 kg P ha(-1)), were tested in sand media (3 mg kg(-1) Mehlich-3 extractable P). Regardless of cultivar, AB establishment in perennial ryegrass improved when P was applied and was 90% of maximum at 1.7 kg P ha(-1). In creeping bentgrass, both AB and creeping bentgrass cover increased when P was applied and AB was 90% of maximum at 12.1 kg P ha(-1). Creeping bentgrass cover was not compromised by P application rates as low as 6.25 kg ha(-1). Phosphorus enhances AB cover from seed when sown with perennial ryegrass or creeping bentgrass seed in low P soils.