Sweet corn (Zea mays L.) is an important field-grown vegetable crop in Ontario; nearly 170,000 t of sweet corn are produced on 14,000 ha with a farm-gate value of $22.8 million (Mailvaganam, 2006). Effective weed control is important for the production of sweet corn. The only herbicides registered for postemergence (POST) broadleaf weed control in sweet corn in Ontario are atrazine, bentazon, and bromoxynil (OMAFRA, 2006). More research is needed to identify POST herbicides that can effectively control emerged problem broadleaf and grass weeds in sweet corn production.
Topramezone is a newly introduced pyrazolone postemergence herbicide. Topramezone inhibits the activity of the 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzyme, which in susceptible weeds disrupts carotenoid synthesis, causing leaf bleaching, necrosis, and plant death (Anonymous, 2006). In field corn, topramezone can be applied in tank mixes with atrazine to control several broadleaf and grass weeds such as palmer amaranth (Amaranthus palmeri), common lambsquarters (Chenopdium album), velvetleaf (Abutilon theophrasti), kochia (Kochia scoparia), Amaranthus spp., Polygonum spp., Sinapis spp., Solanum spp., barnyardgrass (Echinochloa crus-galli), Digitaria spp., Setaria spp., fall panicum (Panicum dichotomiflorum), proso-millet (Panicum miliaceum), and goosegrass (Eleucine indica), including ALS, glyphosate, and triazine-resistant biotypes (Anonymous, 2006).
The currently registered POST herbicides in sweet corn do not satisfactorily control late-emerging velvetleaf and triazine-resistant redroot pigweed (Amaranthus retroflexus). Atrazine suppresses velvetleaf and does not control the triazine-resistant biotypes, and bromoxynil provides only fair control of Amaranthus spp. Bentazon is weak on pigweed and ragweed (Ambrosia artemisiifolia) and can significantly injure some sweet corn hybrids (Diebold et al., 2004). Mesotrione can also injure some sweet corn hybrids (O'Sullivan et al., 2002) and does not control many annual grass weeds, including Setaria spp., fall panicum, and witchgrass (Panicum capillare). Topramezone controls many of these troublesome weeds (Anonymous, 2006; OMAFRA, 2006) and therefore would be of benefit to sweet corn growers in Ontario.
Sensitivity of sweet corn to herbicides is dependent on the application rate, hybrid, and environmental conditions. Some of the commonly grown sweet corn hybrids in Ontario such as Calico Belle, Delmonte 2038, and GH2684 have shown sensitivity to other herbicides such as AE F130360 (foramsulfuron), bentazon, CGA152005 (prosulfuron), mesotrione, nicosulfuron, primisulfuron, and RPA201772 (isoxaflutole) (Diebold et al., 2003, 2004; O'Sullivan and Sikkema 2001, 2002; O'Sullivan et al., 1999, 2000, 2002; Robinson et al., 1993). Hybrid sensitivity is an important factor for registration of herbicides in sweet corn. To our knowledge, there is no published information on the sensitivity of sweet corn hybrids to POST applications of topramezone. The objective of this study was to determine the tolerance of eight commonly grown processing sweet corn hybrids—Calico Belle, CNS 710, Delmonte 2038, FTF 222, FTF 246, GH 2684, Reveille, and Rival—to topramezone.
Anonymous 2006 Impact Herbicide, technical information and use guide for field corn, sweet corn and popcorn AMVAC Los Angeles, Calif
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