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Research Project: Utilizing Herbicide Tolerant and Competitive Cultivars and Innovative Cultural Practices to Enhance Weed Management in Vegetable Crops

Location: Vegetable Research

Title: Differences in tolerance of broccoli and cabbage cultivars to clomazone herbicide

item Harrison, Howard
item Farnham, Mark

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2012
Publication Date: 2/1/2013
Citation: Harrison Jr, H.F., Farnham, M.W. 2013. Differences in tolerance of broccoli and cabbage cultivars to clomazone herbicide. HortTechnology. 23(1):6-11.

Interpretive Summary: Command 3ME herbicide (clomazone) controls a number of annual grass and broadleaf weeds that are important pests in broccoli fields. It is used extensively for weed management in cabbage (Brassica oleracea) and other vegetable crops, but clomazone is not registered for other cultivar groups within B. oleracea which include broccoli, brussels sprouts, cauliflower, collards, kale and others. The objective of this study was to assess clomazone response of broccoli varieties in comparison to cabbage varieties to determine if it can be safely used on broccoli. Four broccoli and four cabbage varieties were included in greenhouse and field studies to assess the relative tolerance of the two crop groups. Both greenhouse and field experiments indicated that varieties of both crop groups varied in clomazone tolerance. The most tolerant broccoli variety, Green Magic, was injured less that the most susceptible cabbage variety, Bravo. None of the broccoli cultivars were severely injured by clomazone at the rates that are recommended for cabbage, and broccoli yields were not affected. The results of this study indicate that clomazone can be safely used for weed control in broccoli at rates that are recommended for cabbage. As with cabbage, care should be taken to avoid clomazone injury when growing susceptible cultivars. Registration of clomazone for use in broccoli would provide eastern broccoli growers with a valuable component for their weed management programs.

Technical Abstract: Clomazone herbicide is registered for cabbage in the U.S., but not for other cultivar groups within Brassica oleracea. Greenhouse and field experiments were designed to compare the tolerance of broccoli and cabbage cultivars to clomazone and assess its potential for weed management in broccoli. Four broccoli (Captain, Green Magic, Legacy, and Patron) and four cabbage (Bravo, SC 100, Stone Head, and Vantage Point) cultivars were evaluated in all experiments. In a greenhouse experiment, ‘Bravo’ cabbage was most susceptible, and its injury ratings and shoot weight reduction at 0.5 mg active ingredient/kg potting medium were similar to ratings and shoot weight reduction for the other cabbage cultivars at 2.0 mg/kg. Among the broccoli cultivars, ‘Patron’ was highly susceptible, exhibiting injury and shoot weight reduction similar to ‘Bravo’. ‘Green Magic’ was the most tolerant broccoli cultivar, and it exhibited injury and growth reduction similar to the tolerant cabbage cultivars. In a field experiment, clomazone at 0.28 kg/ha caused only minor chlorosis to the susceptible cultivars, ‘Bravo’ and ‘Patron’. At 0.56 and 1.12 kg/ha most cultivars exhibited chlorosis at two weeks after transplanting (WAT); however, tolerant cultivars recovered and injury was often not observed at 6 WAT. At 1.12 kg/ha, chlorosis persisted until maturity on ‘Bravo’ and ‘Patron’ foliage. Clomazone did not reduce mean broccoli head weight or the percentage of plants producing market-size heads. Mean cabbage head weight for ‘Bravo’ was reduced by clomazone at 1.1 kg/ha. This study indicates that the variability in clomazone tolerance among broccoli cultivars may be similar to that among cabbage cultivars and that the herbicide can be used safely on tolerant broccoli cultivars at rates that are recommended for cabbage.