Compatibility of a Trichoderma atroviride biocontrol agent with management practices of Allium crops

Trichoderma atroviride Karsten strain C52 populations were measured in agronomic soils in combination with soil organic amendments, a nitrogen fertiliser, fungicides and diallyl disulphide (DADS) (a Sclerotium cepivorum sclerotial germination stimulant). Trichoderma atroviride C52 populations did not proliferate 2 weeks after inoculation in sandy soils (4.7 × 102 cfu/g soil) compared with silt loam soils (1.1 × 106–5.7 × 107 cfu/g soil), however, the addition of two blended pellet products containing poultry manure and other organic nutrients or humic acid plus organic matter to the sandy soil enabled populations to proliferate well (1.1–1.3 × 105 cfu/g soil). In vitro, twice field rate applications of urea reduced in vitro Trichoderma atroviride C52 growth (spore germination, germ tube length and mycelial growth), however, T. atroviride C52 populations were less sensitive to field rate applications of urea in field soil. Overall, T. atroviride C52 populations were not adversely affected when exposed to any of the fungicide soil treatments tested (populations ranged from 1.7 × 105–1.1 × 108 cfu/g soil). Volatiles of DADS reduced T. atroviride C52 mycelial growth in vitro when DADS was applied to the medium at standard and twice recommended field rates but not at half field rate. No spore germination occurred under any of the DADS in vitro treatments compared with 100% spore germination in the control. However, when DADS was applied to soil 4, 6 and 8 weeks before application of T. atroviride C52, populations were unaffected. Based on these data, an application strategy for the use of a commercial formulation of T. atroviride C52 in an integrated white rot management programme for onions is proposed.

► An integrated disease management strategy for control of onion white rot (Sclerotium cepivorum) is proposed.
► Organic matter was needed to achieve the high Trichoderma atroviride populations levels required for biocontrol in sandy soil.
► T. atroviride populations were unaffected with field rate fungicides and diallyl disulphide.
► Nitrogen restricted fungal proliferation but applications of nitrogen can be modified to minimise detrimental impacts.