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item Ortiz Ribbing, Loretta
item Williams, Martin

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 9/24/2005
Publication Date: 2/7/2005
Citation: Ortiz-Ribbing, L.M., Williams, M. 2005. Two fungal organisms infect several weedy amaranthus species [abstract]. Weed Science Society of America Meeting Abstracts. 60(1):16.

Interpretive Summary:

Technical Abstract: Several plants in the genus Amaranthus are weeds in cropping systems throughout the world and some biotypes have developed resistance to a number of herbicide families. In an effort to develop alternative, biologically-based weed management tactics, studies were initiated to quantify the selectivity of two fungal organisms as mycoherbicides. Response of Amaranthus spp. seedlings to Microsphaeropsis amaranthi (3 x 10-6, Phomopsis amaranthicola (1 x 10-7 and a mixture of the two organisms (1.5 x 10-6 + 4 x 10-6, M. amaranthi and P. amaranthicola, respectively) was tested under controlled and field conditions at Urbana, IL in 2004. Weeds included Amaranthus retroflexus, A. hybridus, A. spinosus, A. albus, A. blitoides, A. rudis, A. palmeri, and A. albus. Seeds of each species were sown in the greenhouse, conidial suspensions were applied at the 2- to 4-leaf stage, and then pots were placed either in a dew chamber 24 h)and back in the greenhouse, or in the field between two rows of soybean. Treatment with fungal organisms infected most weeds,reducing growth and survivorship, although weed responses in the greenhouse were less than those observed in the field. Percent mortality for A. albus and A. blitoides were between 80 and 100% 14 to 15 DAT for the mixture or M. amaranthi alone, in greenhouse and field trials. In the greenhouse, the mixture of the two organisms significantly reduced A. rudis height and caused 33% seedling mortality compared to control or either fungal organism alone. This synergistic effect was not observed in the field between the mixture and M. amaranthi alone, however, the mixture had a synergistic effect compared to treatment with P.amaranthicola alone. In field experiments, height of A. rudis, A. hybridus, and A. albus was significantly reduced by fungal treatments. The fungal treatments caused significant reduction in biomass of A. rudis, A. hybridus, A. retroflexus, A. albus, A.spinosus, and A. blitoides. All eight weed species treated with M.amaranthi or the mixture had disease severity ratings of 4.4 to 5(scale 5 0 to 5, 55dead weed) 15 DAT, and mortality ranged from 74 to 100%. This research indicates seedlings of several Amaranthus species are susceptible to conidial suspensions of P. maranthicola and M. amaranthi in both controlled and field environments.