Mississippi State University’s South Mississippi Branch Experiment Station works with the IR-4 project to conduct trials and collect data to facilitate EPA registration of pest management products important in production of specialty crops. During the 2024 growing season, Gemini Granular was evaluated for phytotoxicity and pre-emergent weed control for Eupatorium purpureum ‘Gateway’. Height, percent flowering, and flower number was also recorded. Gemini Granular is 0.40% Prodiamine 0.25% Isoxaben. Eupatorium purpureum ‘Gateway’ liners were transplanted from 50-cell trays into an aged/screened pine bark based medium in 11.4 L containers on June 28, 2024. Medium was amended with sphagnum peat, perlite, a starter dose of 12-6-6 and 15-9-12 controlled release fertilizers. Containers received drip irrigation. Herbicide was applied twice during the season at 6-week intervals with a hand shaker (July 8 and August 20, 2024). Herbicide rates were control (0 lbs./A), 1x (200 lbs./A), 2x (400 lbs./A), or 4x (800 lbs./A). Experimental design was completely random with 10 replications. Data were analyzed in SAS version 9.4 (SAS Institute, Inc., Cary, NC) using PROC GLIMMIX with mean separation using Tukey’s HSD at α = 0.05. Plants exhibited no phytotoxicity, regardless of herbicide rate. Plants receiving Gemini Granular at 200 lbs./A had greater heights compared to the heights of control plants or plants receiving the 2x or 4x herbicide rate. Flower numbers were only reduced for plants receiving the 2x herbicide rate. Flowering percentages ranged from 16.6% for control plants to 5.1% for plants receiving the 2x herbicide rate. In general, weed pressure was low, and there were no differences between treatments for weed number. Gemini Granular applied at 200 lbs./A, the 1x rate, provided effective and safe weed control for Eupatorium purpureum ‘Gateway’.
