Phosphorus Fertilization Effects On Annual Bluegrass.

Annual bluegrass (Poa anna L.) is a common and persistent winter annual weed in southern landscapes.  Control of this weed often depends on the effectiveness of preemergent herbicides.  However, previous research has indicated that soil variables such as phosphorus (P) or pH may affect populations of annual bluegrass.  Typically, previous work was performed on Poa annua/bentgrass swards, with emphasis placed on the dual management of those grasses, rather than the elimination of Poa annua.  Thus, the objective of this work was to evaluate the effect of P rate on various growth parameters of Poa anna, seeking management methods for reduction of Poa annua.   Conducted two times in the greenhouse, this study evaluated rates of P (0, 56, 112, 224 and 448 kg P ha^-1) applied to 3 soil types (sandy clay, loamy sand and a sand/peat mix), with 5 replications.  Poa annua was seeded into each pot, and collected data included number of germinated seedlings, plant height, days to first seedhead, panicles per seedhead and viability and weight of produced seed.  In general, as P rate increased plant size and seed production also increased.  Poa annua grown in soil with lower rates of added P were shorter and less vigorous.