Efficacy of Trematophoma lignicola petrak as a biological control agent for Amaranthus retroflexus L.

The pathogenicity of Trematophoma lignicola on Amaranthus retroflexus was i ncreased when its conidia were formulated in oilseed rape emulsion. However , this formulation did not reduce the dew period required to allow conidial germination and infection of the host, nor did it protect the conidia from desiccation before the onset of dew. The fungus gave effective control of A. retroflexus plants up to the 4-true-leaf stage. Plants with 5 to 6-true- leaves were infected and their dry weight reduced, but plants with more tha n 6-true-leaves were unaffected. Plants grown in warm conditions (18-21 deg reesC/12-15 degrees, day/night) were more likely to be successfully control led than those grown in the cold (10-12 degreesC/7-8 degreesC; day/night). Significant dry weight loss of A. retroflexus plants were achieved at appli cation volumes down to 100 l ha(-1) at 5 x 10(6) conidia ml(-1). More effec tive control was achieved by application of conidia of T. lignicola than my celial or pycnidial applications.