Latent infections and residues of the bioherbicide agentColletotrichum gloeosporioidesf.sp.malvae

Latent infections of Colletotrichum gloeosporioides f.sp. malvae ( C. g. malvae ) in plants and seed were determined in several crops under field conditions after application of C. g. malvae conidia at 12 times the recommended rate. Colletotrichum g. malvae was isolated in trace amounts from Brassica napus/campestris, Linum usitatissimum, Lens culinaris, Brassica juncea/hirta, Helianthus annuus , and Triticum spp. only at the 2-wk isolation. Colletotrichum g. malvae was never isolated from Beta vulgaris. After 5 wk, C. g. malvae was not detected in any of the crops, except for Carthamus tinctorius at harvest, and was not detected from wash water of plant tissue or seed after 72 h. Colletotrichum g. malvae recovery in the field, as in controlled environmental conditions, decreased with time, which indicates that buildup of inoculum did not occur. Fungi other than C. g. malvae and bacteria isolated from seed and from wash water of plant tissue increased with time throughout the growing season. Colletotrichum g. malvae was not recovered from seed or crowns of any of the crop cultivars at either location in either growing season, except for C. tinctorius. Only one seed of the C. tinctorius cultivar ‘S-208’ out of 17,280 C. tinctorius seed analyzed over three growing seasons tested positive for C. g. malvae. Colletotrichum g. malvae was found only on the seed coat; the germinated seedling was not infected. Colletotrichum g. malvae was not recovered from any of the wash water from seed. These results should alleviate any of the concerns regarding the fate of the millions of conidia applied during a normal spray operation on nontarget plants, the potential infectivity of nontarget plants, the potential buildup of C. g. malvae in the field, and the utilization of any of the C. g. malvae- treated crops for food or feed.