Ingress of Poa Annua Into Perennial Ryegrass Stands.

Annual bluegrass (Poa annua L.) is an opportunistic grassy weed that invades turfgrass stands under thinning caused by traffic, disease and other biotic and abiotic stresses. Good density is important to minimizing the ingress of weeds such as annual bluegrass (POAAN). To that end planting of adapted species and cultivars is one of several strategies for maintaining turfgrass function. The objective of this study was to assess the ingress of POAAN into 120 genotypes of perennial ryegrass (Lolium perenne L.) over a 5-year period as part of the 2004 National Turfgrass Evaluation Program (NTEP) test. The NTEP cultivars were planted in the fall of 2004 at the Joseph Troll Turf Research and Education Center, South Deerfield MA. Plots were mowed at 3.75 cm and fertilized with 196 kg N ha^-1 yr^-1. Percent POAAN was assessed visually each year following the first full after establishment in 2006. Encroachment of POAAN was assessed in relationship to other factors such as disease incidence and turfgrass density. No interaction was detected between genotype (G) and year (Y) according to ANOVA of POAAN. Further analysis of GY interaction using Additive Main Effect and Multiplicative Interaction (AMMI) model indicated that the AMMI0 model (main effect means) was 6.31 times as accurate as the raw data (AMMIF) in predicting POAAN ingress in future years. POAAN increased in each year from 12.6% (2006) to 17.6% (2009). Entries including D04-1667, DP 17-9788, Citation Fore, Line Drive GLS, and LCK exhibited less than 5% POAAN. Less ingress of POAAN was closely associated with greater fall cover and less pythium blight in 2005 as well as faster spring green-up and better wear tolerance in 2006.