Effect of New Auxin Herbicide Formulations on Control of Herbicide Resistant Weeds and on Microbial Activities in the Rhizosphere

Widespread distribution of glyphosate-resistant weeds in soybean-growing areas across Mississippi has economically affected soybean planting and follow-up crop management operations. New multiple herbicide-resistant crop (including soybean) technologies with associated formulations will soon be commercialized. The objectives of this research were to determine the efficacy of new 2,4-D + glyphosate and dicamba formulations on herbicide resistant weeds, and to determine the impact of the new 2,4-D + glyphosate formulation on microbial communities in the soybean rhizosphere involved in nutrient cycling. New 2,4-D + glyphosate and dicamba formulations registered for use on 2,4-D and dicamba-resistant soybean, respectively, adequately controlled glyphosate resistant and susceptible pigweeds (Palmer amaranth and tall waterhemp) and common ragweed. The 2,4-D + glyphosate formulation did not significantly impact soil microbial activities linked to nutrient cycling in the soybean rhizosphere. These results indicate these new 2,4-D + glyphosate and dicamba formulations can be effective in controlling glyphosate resistant and other herbicide resistant weeds while not having adverse effects on the activities of beneficial soil microorganisms.

Microencapsulated chlorpyrifos: Degradation in soil and influence on soil microbial community structures

Degradation kinetics of microencapsulated chlorpyrifos （CPF-MC） in soil and its influence on soil microbial community structures were investigated by comparing with emulsifiable concentration of chlorpyrifos （CPF-EC） in laboratory. The residual periods of CPF-MC with fortification levels of 5 and 20 mg/kg reached 120 days in soil, both of the degradation curves did not fit the first-order model, and out-capsule residues of chlorpyrifos in soil were maintained at 1.76 （±0.33） and 5.92 （±1.20） mg/kg in the period between 15 and 60 days, respectively. The degradation kinetics of CPF-EC fit the first-order model, and the residual periods of 5 and 20 mg/kg treatments were 60 days. Bacterial community structures in soil treated with two concentrations of CPF-MC showed similarity to those of the control during the test period, as seen in the band number and relative intensities of the individual band on DGGE gels （p 〉 0.05）. Fungal community structures were slightly affected in the 5 mg/kg treatments and returned to the control levels after 30 days, but initially differed significantly from control in the 20 mg/kg treatments （p 〈 0.05） and did not recover to control levels until 90 days later. The CPF-EC significantly altered microbial community structures （p 〈 0.05） and effects did not disappear until 240 days later. The results indicated that the microcapsule technology prolonged the residue periods of chlorpyrifos in soil whereas it decreased its side-effects on soil microbes as compared with the emulsifiable concentration formulation.