Sweet corn (Zea mays L.) production is important to the economy of Ontario where nearly 113,000 t of sweet corn are produced on nearly 10,000 ha annually [Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA), 2013]. In 2012, sweet corn had a farm-gate value of $33 million and ranked as the second largest field-grown vegetable crop after tomato in Ontario in terms of farm-gate value (OMAFRA, 2013). Effective weed control is important for sweet corn production. The number of herbicides labeled for sweet corn lags behind that of field corn in Ontario mainly as a result of tolerance concerns for some sweet corn hybrids. More research is needed to identify preemergence (PRE) and postemergence (POST) herbicides that provide broad-spectrum weed control in sweet corn production.
Isoxaflutole is a soil and postemergence-applied isoxazole herbicide in field corn that inhibits p-hydroxyphenyl pyruvate dioxygenase (HPPD), an important enzyme involved in the biosynthesis of carotene pigments in plants (Senseman, 2007). Isoxaflutole provides residual control of grass and broadleaf weeds such as wild proso millet (Panicum miliaceum L.), giant foxtail (Setaria faberii Herrm.), green foxtail [Setaria viridis (L.) Beauv.], yellow foxtail [Setaria glauca (L.) Beauv.], barnyard grass [Echinochloa crusgalli (L.) Beauv.], fall panicum (Panicum dichotomiflorum Michx.), common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), smartweed (Polygonum spp.), annual nightshades (Solanum spp.), and velvetleaf (Abutilon theophrasti Medic.) (Bhowmik et al., 1996, 1999; Clarke et al., 2001; Luscombe et al., 1995; OMAFRA, 2012; Taylor-Lovell and Wax, 2001; Vrabel et al., 1997, 1998).
Earlier studies with isoxaflutole have shown unacceptable crop injury in some sweet corn hybrids in Ontario and other geographic areas (O’Sullivan et al., 2001; Van Wychen et al., 1999; Wicks et al., 2007). The manufacturer of isoxaflutole (Bayer® Inc.) has recently introduced isoxaflutole in combination with a safener, cyprosulfamide, thus allowing PRE and early POST application through the V2 stage (two leaves with visible leaf collars) of field corn (Owen, 2011). The registration of isoxaflutole plus cyprosulfamide would provide Ontario sweet corn producers with a new, broad-spectrum herbicide that controls selected annual grass and broadleaf weed species.
Determining sensitivity of sweet corn hybrids to new herbicides is critical to sweet corn growers to minimize the potential for crop injury and yield losses (Morton and Harvey, 1992). Sweet corn hybrid sensitivity has been documented for isoxaflutole (O’Sullivan et al., 2001), but this work was done before the safener was available. Before isoxaflutole plus cyprosulfamide can be registered for use in sweet corn, hybrid sensitivity must be determined. On the basis of work by O’Sullivan et al. (2001) and Pataky et al. (2008), the hybrids in our study were categorized as sensitive (‘Merit’), as having intermediate sensitivity (‘GH 4927’ and ‘BSS 5362’), and tolerant (‘GG 741’). We hypothesized that cyprosulfamide improves tolerance of sweet corn to isoxaflutole (PRE and POST) in the hybrids with intermediate sensitivity but not in the sensitive or tolerant hybrids. The objective of this study was to determine the sensitivity of four commonly grown sweet corn hybrids to isoxaflutole alone or in combination with cyprosulfamide.
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