A host-specific fungus Colletotrichum truncatum strain 00-3B1 (Ct) was mixed with herbicides to improve the control of scentless chamomile, a noxious weed in western Canada. The compatibility of Ct conidia (spores) with herbicides was evaluated in vitro, and varying effects were observed with different products on spore germination. Clodinafop, glufosinate, MCPA, and 2,4-D ester were relatively benign and delayed the germination slightly, whereas dicamba, imazethapyr, metribuzin, and 2,4-D amine were noticeably more inhibitive. Bromoxynil, glyphosate, sethoxydim, and Merge® (spray adjuvant) were most inhibitive, showing >50% inhibition after 24 h. To determine potential synergy, Ct was applied at 7 × 106 spores/ml in tank mixtures with selected herbicides at 1× and 0.1× registered rates under greenhouse conditions. Combining Ct with MCPA, 2,4-D ester, clopyralid, or metribuzin at 1× rate resulted in synergistic or additive interaction on scentless chamomile, increasing weed control significantly when compared to Ct or herbicides applied alone. Similar applications of Ct with imazethapyr, 2,4-D amine, dicamba, or glyphosate were antagonistic. Treatments with Ct plus 1× metribuzin killed scentless chamomile completely, whereas neither Ct nor the herbicide alone caused plant death, suggesting the value of this tank mixture.
Nomenclature: Bromoxynil; clodinafop; clopyralid; dicamba; 2,4-D; glufosinate; glyphosate; imazethapyr; MCPA; metribuzin; sethoxydim; scentless chamomile, Matricaria perforata Mérat, #3 MATIN; causal agent of anthracnose, Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore.
Additional index words: Biocontrol, bioherbicide, synergy.
Abbreviations: Ct, Colletotrichum truncatum strain 00-3B1 (from scentless chamomile).