Experiments were conducted to determine the efficacy of glyphosate on four common lambsquarters populations collected from Kansas, Nebraska, North Dakota, and Ohio. Glyphosate dose-response studies for common lambsquarters treated at 2.5-, 7.5-, and 15-cm heights showed that glyphosate at 1.1 kg ae ha−1caused more than 80% injury to 2.5-cm plants but less than 55% injury to 7.5- and 15-cm plants. All populations were susceptible to glyphosate at the 2.5-cm height. The glyphosate rate required to cause 50% injury (GR50) was 430, 500, 500, and 560 g ha−1for the Kansas, North Dakota, Ohio, and Nebraska populations, respectively. Differential response of common lambsquarters populations was evident with 15-cm plants where the GR50was glyphosate at 1,010, 1,230, 1,650, and 2,770 g ha−1for the Kansas, North Dakota, Nebraska, and Ohio populations, respectively. Reduced injury on 15-cm common lambsquarters plants by glyphosate may be partly attributed to reduced glyphosate accumulation per unit of plant tissues and enhanced calcium content in more-developed plants. All four common lambsquarters populations at the early seedling stage were susceptible to glyphosate, but tolerance increased as the plant developed and the extent of tolerance differed among populations.

Studies were conducted to determine if altered absorption, translocation, or metabolism were the basis for the reduction in sulfonylurea herbicide efficacy on foxtail species when mesotrione was mixed with a sulfonylurea herbicide. Green foxtail and yellow foxtail plants were grown in the greenhouse and treated at the four-leaf stage with14C-labeled nicosulfuron or rimsulfuron, applied alone or with mesotrione or mesotrione + atrazine. Absorption of nicosulfuron was greater in green foxtail and yellow foxtail 7 d after treatment (DAT) when applied alone, compared with absorption when mixing the herbicide with mesotrione or mesotrione + atrazine. When nicosulfuron was applied alone, 9% more of the nicosulfuron in green foxtail was translocated at 7 DAT, as compared with when nicosulfuron was applied in combination with mesotrione or mesotrione + atrazine. Translocation of nicosulfuron in yellow foxtail, however, was similar when nicosulfuron was applied alone or in combination with mesotrione or mesotrione + atrazine. The addition of mixing rimsulfuron with mesotrione did not reduce the absorption of rimsulfuron in green foxtail 7 DAT, but the addition of mesotrione + atrazine resulted in a 20% decrease in rimsulfuron absorption 7 DAT compared with absorption of rimsulfuron applied alone. Yellow foxtail absorption of rimsulfuron at 7 DAT was decreased by 11 or 20% when mixed with mesotrione or mesotrione + atrazine, respectively. Application of rimsulfuron alone resulted in 6% more herbicide being translocated to the treated tiller in green foxtail at 7 DAT, compared with an application of mesotrione + atrazine and rimsulfuron. Translocation of rimsulfuron in yellow foxtail was similar when applied alone or in combination with mesotrione or mesotrione + atrazine. Nicosulfuron and rimsulfuron metabolism in foxtail species was similar when applied alone or in combination with mesotrione or mesotrione + atrazine.

The Roundup hybridization system (RHS) is a novel process for hybrid seed production based on glyphosate-mediated male sterility. RHS replaces mechanical detasseling with glyphosate spray and greatly simplifies the process of hybrid seed corn production.

Experiments were conducted in the greenhouse and the field to evaluate the efficacy of various sulfonylurea herbicides applied with mesotrione or mesotrione + atrazine. The addition of mesotrione or mesotrione + atrazine to sulfonylurea herbicides had no adverse effects on the control of large crabgrass or velvetleaf in a controlled environment. Tank mixing mesotrione or mesotrione + atrazine with nicosulfuron or foramsulfuron, however, antagonized nicosulfuron and foramsulfuron control of green foxtail and shattercane. Field experiments conducted in 2004 and 2005 also indicated that addition of mesotrione + atrazine to a sulfonylurea herbicide decreased herbicidal efficacy on green foxtail, yellow foxtail, and shattercane, compared with the sulfonylurea herbicide applied alone. In addition, increasing mesotrione application from 53 to 105 g/ha decreased efficacy of sulfonylurea herbicide in the tank mix on selected grass species. This research showed that the addition of mesotrione to sulfonylurea herbicides resulted in decreased efficacy of sulfonylurea herbicides on green foxtail, yellow foxtail, and shattercane. The addition of atrazine to the tank mix or an increased mesotrione rate will further decrease herbicide efficacy of sulfonylurea herbicides on shattercane and foxtail species.

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