Outdoor Studies of the Efficacy of Alternaria alternata in Controlling Amaranthus retroflexus

Abstract

Application of 250 L ha -1 containing 10 7 Alternaria alternata conidia ml -1 caused 61% reduction in dry weight and a 45% mortality in Amaranthus retroflexus plants growing in a wheat crop. However, only 10-22% of the applied conidia were retained on the leaf. In one experiment, conidia remained viable for 4 days on the leaf surface until conditions were favourable for germination. Competition from the wheat crop, as well as its creation of a moist micro-climate, improved the control of Am. retroflexus by A. alternata . Total control of Am. retroflexus may be difficult to achieve with A. alternata , but suppression to reduce or eliminate its competitive effect on crops is possible.