Organic Mulch and Halosulfuron Placement Affect Yellow Nutsedge Control and Ornamental Plant Quality in Landscape Beds

Abstract

Halosulfuron (SedgeHammer™) applied above or below pine nugget, pine straw, or shredded cypress mulch at 0, 0.038, or 0.075 kg ai·ha−1 (0.034 or 0.067 lb ai·A−1) was evaluated for postemergence control of yellow nutsedge in two field experiments. Tolerance of ‘Mystery’ gardenia (Gardenia jasminoides Ellis), ‘Stella de Oro’ daylily (Hemerocallis x), and ‘Big Blue’ liriope (Liriope muscari L.H. Bailey) to overtop applications of halosulfuron was also evaluated. Without halosulfuron, mulching with pine nugget, pine straw, and shredded cypress provided about 51 to 62% yellow nutsedge control at 4 weeks after treatments (WAT) compared with non-sprayed bare soil plots. At the infestation level of 167 tubers per m2 (15 tubers per ft2) in both experiments, halosulfuron application at the lower rate resulted in similar control as the higher rate regardless of mulch type and herbicide placement. Applications prior to mulching provided equal or, in some cases, better control than applications after mulching. Overall, halosulfuron resulted in greater control in Experiment 2 than Experiment 1, possibly because of smaller yellow nutsedge shoots in the second trial. Over-the-top application of halosulfuron at the higher rate caused transient leaf injury and reduced aboveground biomass in liriope. However, mulching improved gardenia transplant quality as indicated by reduced leaf chlorosis and increased number of flowers.