|Wyss, G. S.|
Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2004
Publication Date: 6/1/2004
Citation: Wyss, G., Rosskopf, E.N., Charudattan, R., Littell, R. 2004. Effects of selected pesticides and adjuvants on germination and vegetative growth of Phomopsis amaranthicola, a biocontrol agent for amaranthus spp. Weed Research. 44:1-14. Interpretive Summary: Phomopsis amaranthicola is a fungal biological control agent under development for control of Amaranthus spp. A number of insecticides, herbicides, and fungicides that could be used in a crop production system were evaluated for their effect on the fungus. This is performed to determine if the fungus could be used in combination with the pesticides or if the pesticide use would have to be avoided if the fungus is used for weed control. Many of the tested materials inhibited the growth of the fungus and it is concluded that a case-by-case selection of application methods, such as tank-mix or sequential application, along with proper timing of applications of the fungus and the chemical agents will be necessary.
Technical Abstract: Phomopsis amaranthicola, a bioherbicide agent for Amaranthus spp., was tested in vitro for its compatibility with commercial formulations of 16 adjuvants, 24 herbicides, 9 fungicides, and 4 insecticides at 2X, 1X (highest labelled rate), 0.75X, 0.5X, and 0.25X concentrations. These chemicals were tested for their effects on spore germination. Selected herbicides and fungicides at 1X were also tested for their influence on colony growth. The herbicides atrazine, bentazon, metribuzin, and imazethapyr did not affect spore germination at any concentration, whereas, napropamide, prodiamide, and simzine inhibited germination at 2X. Spore germination was barely affected at 1X and weakly affected at 2X HR with ametryn, DCPA, imazapyr, naptalam, and pendimethalin. Glyphosate, oxyfluorfen, paraquat, trifluralin, clethodim, sethoxydim, metolachlor, and pebulate were highly toxic and highly inhibited germination at 1X. The protective fungicides chlorothalonil, copper hydroxide, iprodione, mancozeb, and maneb totally inhibited spore germination at all concentrations. Vinclozolin allowed spore germination only at 0.25X. Among the systemic fungicides, mefenoxam and benomyl affected spore germination at all concentrations, whereas fosethyl-Al was toxic at 0.75X and above. The insecticides dimethoate and malathion had an LD50 value below 0.5X, and dicofol was toxic at all concentrations tested. Cyromazine inhibited spore germination at 2X only. It is possible to integrate the use of P. amaranthicola with some herbicides, fungicides, insecticides, and adjuvants, but not others. A case-by-case selection of application methods, such as tank-mix or sequential application, along with proper timing of applications of the fungus and the chemical agents will be necessary.