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Biological Control of the Weed Sesbania exaltata Using a Microsclerotia Formulation of the Bioherbicide Colletotrichum truncatum

Clyde D. Boyette, Hamed K. Abbas, Bobbie Johnson, Robert E. Hoagland, Mark A. Weaver
American journal of plant sciences 2014 v.5 no.18 pp. 2672-2685
Colletotrichum truncatum, Sesbania exaltata, biological control, biopesticides, conidia, corn oil, environmental factors, field experimentation, fungi, greenhouse experimentation, greenhouses, hemp, mortality, pesticide formulations, planting date, rice, sclerotia, soil, surfactants, weed control, weeds
Colletotrichum truncatum, grown on rice grain (3 to 4 weeks, 22˚C to 24˚C) produced a fungus-infested rice mixture of microsclerotia and conidia (spores) in a ratio of ~9:1, respectively. Greenhouse tests of this formulation (0.4 to 50 mg finely-ground fungus-rice product) which applied pre-emergence to 5 cm2 of soil surface, caused 22% to 96% hemp sesbania plant mortality, after 14 days. Post-emergence treatment (fungus-rice aqueous formulation; 2.4 × 10^5 microsclerotia ml−1, 30% unrefined corn oil and 0.2% Silwet L-77 surfactant) of weeds surviving the pre-emergence application, resulted in 93% mortality, after 14 days. Based on greenhouse results, field tests were undertaken: 1) pre-emergence treatment (fungus-rice formulation at 2.4 × 10^5 microsclerotia cm−2), 2) post-emergence (fungus-rice product in 30% unrefined corn oil, 0.2% Silwet) only treatment, applied 15 days after planting and 3) pre-emergence treatment followed by post-emergence treatment (fungus-rice product in 30% unrefined corn oil, 0.2% Silwet) applied 15 days after planting to surviving weeds. Control treatments were: 1) autoclaved rice product sans fungus, 2) unrefined corn oil (30% unrefined corn oil, 0.2% Silwet in water) and 3) untreated plants. Planting dates were: early season (April-May), early-mid season (June-July), late-mid season (July-August), and late season (September-October). Weed mortality was recorded at 15 days for the pre-plus post-treatment, and at 30 days after planting for the pre-emergence only and the post-treatment only. The early season, pre-emergence treatment caused 67% hemp sesbania mortality (3-yr average) within 15 days and the post-emergence treatment caused 91% mortality of the surviving weeds. In the late-mid-season, pre-emergence treatment caused minimal (<5%) mortality at 15 days, but mortality in the post-emergence treatment was >80%. Results suggest that seasonal environmental conditions are important in the efficacy of this C. truncatum-rice product formulation when applied pre- or post-emergence to this onerous weed.