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United States Department of Agriculture

Agricultural Research Service

Title: Potential of Phomopsis Amaranthicola and Microsphaeropsis Amaranthi, As Bioherbicides for Several Weedy Amaranthus Species

Authors
item Ortiz Ribbing, Loretta
item Williams, Martin

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2005
Publication Date: January 1, 2006
Citation: Ortiz Ribbing, L.M., Williams, M. 2006. Potential of Phomopsis amaranthicola and Microsphaeropsis amaranthi, as bioherbicides for several weedy amaranthus species. Crop Protection. 25(1):39-46.

Interpretive Summary: Species of the Amaranthus genus are troublesome weeds found growing in many agronomic and horticultural crops throughout the world, and some biotypes have developed resistance to a number of herbicide families used for their control. In an effort to develop alternative, biologically-based weed management tactics, studies were initiated to quantify the weed selective ability of two fungal organisms to eight Amaranthus species. Response of weed seedlings to Microsphaeropsis amaranthi, Phomopsis amaranthicola, and a mixture of the two organisms were tested under controlled and field conditions at Urbana, IL in 2004. Weeds included common waterhemp, (Amaranthus rudis); Palmer amaranth, (A. palmeri); Powell amaranth, (A. powellii); redroot pigweed, (A. retroflexus); spiny amaranth, (A. spinosus); smooth pigweed, (A. hybridus); tumble pigweed, (A. albus); and prostrate pigweed, (A. blitoides). 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 inter-row of a soybean field. Treatment with fungal organisms infected most weeds, reducing growth and survivorship. Percent seedling mortality for tumble and prostrate pigweed 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 two organisms and M. amaranthi alone significantly reduced tumble and prostrate pigweed height. Fungal treatments reduced biomass of Powell amaranth and prostrate pigweed. In field experiments, seedling mortality for all eight weed species treated with M. amaranthi alone or with the mixture of both organisms ranged from 74 to 100%. In addition, these treatments reduced biomass of common waterhemp, redroot pigweed, spiny amaranth, smooth pigweed, and tumble pigweed. Height of common waterhemp, smooth pigweed, and tumble pigweed was reduced by all fungal treatments. This research indicates seedlings of several Amaranthus species are susceptible to conidial suspensions of P. amaranthicola and M. amaranthi in both controlled and field environments, and that they could potentially provide an alternative biologically-based method for managing weeds in the genus Amaranthus. Benefits of using a mixture of both organisms include enhanced activity on more weed Amaranthus species and a greater likelihood of infection under variable environmental conditions.

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 weed selective ability of two fungal organisms to several Amaranthus species. Response of weed seedlings to Microsphaeropsis amaranthi (3 x 106 conidia.ml-1), Phomopsis amaranthicola (1 x 107 conidia.ml-1), and a mixture of the two organisms (1.5 x 106 + 4 x 106 conidia.ml-1, M. amaranthi and P. amaranthicola, respectively) were tested under controlled and field conditions at Urbana, IL in 2004. Weeds included common waterhemp, (Amaranthus rudis); Palmer amaranth, (A. palmeri); Powell amaranth, (A. powellii); redroot pigweed, (A. retroflexus); spiny amaranth, (A. spinosus); smooth pigweed, (A. hybridus); tumble pigweed, (A. albus); and prostrate pigweed, (A. blitoides). 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 inter-row of a soybean field. 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 seedling mortality for tumble and prostrate pigweed 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 two organisms and M. amaranthi alone significantly reduced tumble and prostrate pigweed height. Fungal treatments reduced biomass of Powell amaranth and prostrate pigweed. In field experiments, all eight weed species treated with M. amaranthi or the mixture of both organisms had disease severity ratings of 4.4 to 5 (scale = 0 to 5, 5=dead weed) 15 DAT, and mortality ranged from 74 to 100%. In addition, these treatments reduced biomass of common waterhemp, redroot pigweed, spiny amaranth, smooth pigweed, and tumble pigweed. Height of common waterhemp, smooth pigweed, and tumble pigweed was reduced by all fungal treatments. This research indicates seedlings of several Amaranthus species are susceptible to conidial suspensions of P. amaranthicola and M. amaranthi in both controlled and field environments.

Last Modified: 11/28/2014
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