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Influence of epidemiological factors on the bioherbicidal efficacy of Phomopsis amaranthicola on Amaranthus hybridus

Rosskopf, E.N., Yandoc, C.B., Charudattan, R., DeValerio, J.T.
Plant disease 2005 v.89 no.12 pp. 1295
Phomopsis, plant pathogenic fungi, biological control agents, conidia, Amaranthus hybridus, host plants, herbaceous plants, weeds, weed control, biological control, plant age, epidemiological studies, dew
Greenhouse experiments were performed to determine the effect of dew period temperature and duration, plant growth stage, conidial concentration, and the addition of adjuvants on the bioherbicidal efficacy of Phomopsis amaranthicola on Amaranthus spp., using Amaranthus hybridus as test plant. P. amaranthicola infected A. hybridus at 20, 25, 30, and 35 degrees C but the disease level achieved at 20 degrees C may not be sufficient to cause high plant mortality. Plant mortality was also significantly lower in plants that were exposed to 4 h of dew. Plants at less than two- to two- to four-leaf stage were more easily killed than older plants, and increasing conidial concentration from 10(5) to 10(6) or 10(7) conidia ml(-1) did not result in higher mortality levels. Among the adjuvants tested, polyalkyleneoxide-modified heptamethyltrisiloxane, algal polysaccharide, hyrdroxyethyl cellulose, and octylphenoxy polyethoxyethanol reduced conidial germination. Conidia applied with invert emulsion caused the highest plant mortality (74%) but invert emulsion alone caused 33% plant death due to phytotoxicity. Results indicate that P. amaranthicola can infect and kill Amaranthus spp. under a range of temperature, dew period, and inoculum levels and, therefore, has good potential as a bioherbicide agent.