Abstract

Commercial strains of Trichoderma harzianum ( Th) and/or T. virens (Tv) were used as seed treatments to protect 'Marketmore 76' cucumber against damping-off caused by Pythium aphanidermatum (Edson) Fitzp. ( Pa) in soilless media. Slurry-coating osmotically or osmomatrically primed seeds with Th, Tv or ThTv (applied at half-rates each) was less effective than slurry-coating non-primed seeds in managing damping-off. The combination coating eliminated damping-off only in non-primed seeds, and tended to reduce damping-off in primed seeds compared to coating with Th or Tv alone. Using only non-primed seeds, slurry coatings with technical grade mefenoxam fungicide, Th, Tv and/or ThTv decreased total damping-off to 2.6%, 7.4%, 2.0% and 0%, respectively, from the 30.1% occurring in non-coated seeds. Th, Tv, or ThTv applied to growth media at the same rate as the seed coating (1 mg per seed) were generally as effective as the seed coatings, and only the ThTv growth medium application eliminated damping-off. It was further established that Th and/or Tv can be stored on seeds up to 4 weeks at either 4 or 21°C with no loss of colony forming units.

In a second study the effectiveness of ThTv in protecting 'Early Wonder Tall Top' table beet (Beta vulgaris L.), a microgreen crop, against damping-off caused by Pa was investigated. Seed-balls were incubated for 2 days at 21°C in moist exfoliated grade 3 vermiculite containing ThTv at 0, 0.25, 0.50, 0.75 or 1.00 mg per seed-ball. Four days before planting, the peat-lite was inoculated with 0, 0.5 or 1.0X the Pa rate used in the cucumber experiments. Increasing ThTv per seed ball decreased percentage damping-off. At 1 mg per seed ball, damping-off was 5 and 19% in the 0.5 and 1.0 Pa levels, respectively. Including Agro-lig UF with the incubating seed-ball-ThTv mixtures resulted in a further decrease in damping-off percentage. Increasing ThTv per seed ball applied as a growth medium drench decreased percentage damping-off, but not to the extent achieved with seed-ball treatment. At 1 mg ThTv per seed ball as a drench, damping-off was 20% and 55% in the 0.5 and 1.0 Pa levels, respectively.