The Influence of Pendimethalin and Trifluralin Herbicides on the Soybean-Bradyrhizobium Japonicum Symbiosis (Nitrogen Fixation, Dinitroaniline, Glycine Max, Nodulation).

Laboratory, greenhouse, and field investigations were conducted to determine the influence of pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine), trifluralin (2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine), and other selected herbicides on the Bradyrhizobium japonicum (3I1B110)-soybean (Glycine max, (L.) merr.) symbiosis. Bradyrhizobium japonicum, strain 110 growth on yeast extract mannitol (YEM) agar was not inhibited by most herbicides in direct contact with cells when applied at 10 to 2000 mg L(\u27-1). Pendimethalin and trifluralin inhibited B. japonicum growth at levels over 2000 mg L(\u27-1). Bradyrhizobium japonicum growth in YEM broth was not inhibited by pendimethalin or trifluralin at 100 mg L(\u27-1). Metolachlor (2-chloro-N-(2-ethyl-6-methylphehyl)-N-(2-methoxy-1-methylethyl)acetamide at 10 mg L(\u27-1) increased growth in YEM broth during the first four days of a 13-day incubation period. Respiration by B. japonicum was decreased by pendimethalin at 100 mg L(\u27-1), even when arabinose or glucose was added to the inoculated media. Evolution of CO(,2) was higher when arabinose was included as the carbon source. Nodule number, dry weight of nodules, roots, and plants, and N(,2)(C(,2)H(,4)) fixation per plant of Forrest cv. soybeans were significantly decreased by trifluralin at 0.90 and 1.80 kg ha(\u27-1) equivalent in the greenhouse. Linuron (N\u27-(3,4-dichlorophenyl)-N-methoxy-N-methylurea) inhibited nodule number, and nodule and plant dry weight. Pendimethalin decreased nodule dry weight and C(,2)H(,4) production per plant of Centennial cv. soybeans at 0.75, 1.00, and 1.25 kg ha(\u27-1) in the greenhouse. Plant dry weight was decreased at 1.25 kg ha(\u27-1). Trifluralin decreased nodule and plant dry weight at 1.00 and 1.25 kg ha(\u27-1), and C(,2)H(,4) production per plant at 0.75, 1.00, and 1.25 kg ha(\u27-1). Pendimethalin and trifluralin injured Centennial cultivar soybeans at 1.12, 1.68, and 2.24 kg ha(\u27-1) when grown on an Olivier silt loam. Nodule number and dry weight, and C(,2)H(,4) production were decreased during vegetative growth at all rates in 1984. Seedling injury caused by pendimethalin and trifluralin was not as severe in 1985, with most injury occurring at 1.68 and 2.24 kg ha(\u27-1). Nodule number and dry weight were decreased up to the R3 growth stage. Occasional inhibition of C(,2)H(,4) producton was found. Inhibitory effects were not present at seed formation, and seed yield was not affected in either year

23 rd Annual Southern Conservation Tillage Conference for Sustainable Agriculture Agricultural Water Quality and Quantity: Issues for the 21 st Century

Proceedings of th

Identification of rice cultivars resistant to Lissorhoptrus oryzophilus (Coleoptera: Curculionidae), and their use in an integrated management program

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States and is a particularly severe pest in Louisiana The current management program for this insect in Louisiana relies heavily on insecticides, most notably the seed treatment fipronil (Icon). Diversification of the management program by incorporation of alternative strategies is needed to improve the effectiveness and long-term stability of the program. In the three experiments reported here, three components of a diversified management program for the rice water weevil in Louisiana - host plant resistance, treatment of seeds with Icon, and the cultural practice of delayed flooding - were investigated. Comparison of the densities of weevil larvae on the roots of several commercial cultivars indicated that the long-grain cultivar \u27Jefferson\u27 was more resistant to infestation by the rice water weevil than the other cultivars. The medium-grain cultivars \u27Bengal\u27, \u27Earl\u27 and \u27Mars\u27 and the long-grain variety \u27Cocodrie\u27 were the most susceptible to infestation. Comparison of yield data from untreated plots and plots treated with Icon indicated that the long-grain cultivars Cocodrie, Lemont, and Jefferson were more tolerant of weevil injury than the other cultivars. A 2-wk delay in flooding was associated with yield benefits in plots not treated with Icon. Treatment of seeds with Icon controlled weevils in all three screening experiments. The implications of these results for the development of an integrated management program for the rice water weevil are discussed. © 2001 Entomological Society of America

Southern Conservation Tillage

Improving tropical maize (Zea mays L.) tolerance for drought stress was initiated in 1991 in a fullsib recurrent selection program. This breeding program was initiated to compare two selection environments and to improve the yield stability of tropical maize under the north Florida drought-prone environments. Rainfed and irrigated plots were used to evaluate 140 fullsib families, along with four checks in a 12 X 12 partially balanced lattice design with four replications. Relative grain yield, plant and ear height leaf area, flower delay, canopy temperature, tassel weight, and drought index were used to select the fullsibs for the recombination phase. Yield reductions, ranging from 2 to 40% in the stress site, were mild due to appreciable rainfall. High variability existed among the fullsibs tested for grain yield. Irrigated grain yield ranged from 3987 to 8039 kg ha , and rainfed grain yield from 3066 to 7124 kg ha . A 15% selection pressureresulted in the advancement of 21 fullsibs from either site to the recombination process