Field tests of Trichoderma harzianum Rifai aggr. as a biocontrol agent of seedling disease in several crops and Rhizoctonia root rot of sugar beet

In field studies, mean stands of crops of snapbean, field corn, pea, soybean, and squash in New York were somewhat greater from seeds treated with conidia of Trichoderma harzianum applied in a Methocel slurry than from non-treated controls; however, stands were generally poorer than those from captan-treated seed. The biocontrol agent and captan had little effect on kidney bean and sweet corn since these crops are only slightly susceptible to seedling disease caused by Pythium spp. which were present in the field. In Colorado fields also infested with Pythium spp., stands of sugar beet from T. harzianum-treated seed (Pelgel slurry) tended to be greater than those from non-treated seed and equal to those from maneb-treated seed, but differences were not significant. In Colorado, Rhizoctonia solani, cause of root rot, was also present in the soil. A combined analysis of variance of treatments across 2 years showed that a preplanting-incorporated in-row application of T. harzianum in a wheat-bran carrier or a maneb seed treatment slightly, but significantly, reduced the severity of Rhizoctonia root rot in sugar beet as compared with the non-treated control. Seed treatments with T. harzianum had little or no effect. In plots where the agent was applied to the soil, numbers of Trichoderma propagules increased 600-fold by harvest; where maneb seed treatment was used, they increased only fivefold. Densities of the agent remained the same or decreased in plots where Trichoderma was used as a seed treatment.