Effect of Dogfennel Removal on Bahiagrass Production.

Dogfennel (Eupatorium capillifolium) is the most common broadleaf weed in Florida pastures.  Many ranchers do not realize the impact of dogfennel on bahiagrass (Paspalum notatum) production, because forage is not limited during the rainy season to warrant timely removal.  Therefore, the objective of this research was to evaluate the impact of dogfennel on bahiagrass production.  Plots were established near Ona, Florida with dogfennel densities of 0, 25% cover, 50% cover, and ³ 75% cover in April, 2007.  Additionally, one-half of the plots were fertilized with 56 kg/ha nitrogen in April, 2007.  Dogfennel and bahiagrass were removed monthly beginning in May.  Biomass was dried at 60 ^oC for 4 days.  The factorial arrangement of treatments was completely randomized in a split-block design, with nitrogen fertilization as the block factor.  Each density was replicated four times in each fertility regime.  There was no density by fertility interaction for dogfennel or bahiagrass biomass at any harvest time.  Dogfennel biomass at low densities increased 23-fold from May to September.  A 10-fold increase in dogfennel biomass was observed at the medium density from May to September.  At the high density, dogfennel biomass increased from 872 kg/ha to over 12,000 kg/ha in September, which was a 14-fold increase.  Monthly bahiagrass yield was at least 1.4- and 1.7-fold greater when dogfennel was not present compared to medium and high dogfennel densities, respectively.  Bahiagrass biomass from low dogfennel densities was not different from plots without dogfennel except in August and September where bahiagrass biomass was 1.2 and 1.5 times lower, respectively.  When dogfennel ground cover is less than 25%, dogfennel should be removed prior to August to prevent significant yield reductions.  In contrast, dogfennel should be removed if groundcover is greater than 25% as early as possible to prevent yield reductions.