Biological Control: Disease management in organic brassica seed and transplants FV 352 John Clarkson Warwick Crop Centre Steve Roberts Plant Health Solutions Warwick Crop Centre www.warwick.ac.uk/go/wcc
Background To evaluate organically acceptable brassica seed and transplant treatments for disease control Pressure to reduce chemical inputs Potential pathogens from companion planting (e.g. birdsfoot trefoil) Disease targets: Soilborne: Pythium and Rhizoctonia damping-off (Warwick) Seedborne: Phoma, Alternaria (PHS) Growing conditions Bulrush organic modular compost Cauliflower cv. Belot (soilborne diseases) 345 module trays
Biological Control Treatments Trianum (Trichoderma harzianum T22) Prestop (Gliocladium catenulatum) Mycostop (Streptomyces griseoviridis) Subtilex (Bacillus subtilis) Revive P (Bacillus subtilis) Trichoderma viride S17A (Warwick) Composted green waste + Trianum + T. viride S17A Compared with: fungicide treated seed (thiram)
Examples of claimed activity Product Claimed Activity Trianum P. ultimum and P. aphanidermatum in tomato P. ultimum in lettuce P. ultimum in pelargonium Prestop P. aphanidermatum in cucumbers P. ultimum in bedding plants Phytophthora cryptogea on bedding plants Mycostop Pythium spp. in cucumber P. ultimum in basil Phytophthora sp. on gerbera and campanula Subtilex Pythium spp.
How do biological control agents work? Antibiosis Production of antibiotics and other anti-fungal compounds Competition for space and nutrients Efficient root colonisation and nutrient scavenging Parasitism Direct attack and colonisation of pathogen Induced resistance Stimulation of defence reactions of the plant Plant growth promotion Increased root system
Testing biological control agents against Pythium Must have a reproducible system for pathogen inoculation and disease development BCAs must be applied at correct time and in appropriate formulation Viability of BCAs must be checked so that correct dose is applied Ideally monitor BCA survival in soil
Getting pathogen dose correct Emergence 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 0.1 0.5 1 5 10 15 % Pythium inoculum
Number of healthy seedlings BCAs against Pythium 40 Pythium 1 35 30 25 20 15 10 5 0 Uninoc control Inoc control Fungicide Trianum Prestop Mycostop Subtilex Agralan
Number of healthy seedlings BCAs and green waste compost against Pythium 40 Pythium 2 35 30 25 20 15 10 5 0
MSc Project Plant mini system More controlled environment Different timings of adding BCAs Other treatments added Trianum as a seed treatment Serenade Endofine Trichoderma T34
BCAs added before Pythium
proportion survived Greenwaste and BCAs 1.0 0.8 0.6 0.4 0.2 0.0
Summary BCAs were ineffective against Pythium damping-off when applied at sowing. BCAs Prestop and Endofine (and Trianum G in one experiment) significantly reduced Pythium if added to the growing medium two weeks before sowing. Green waste compost treatments significantly reduced damping off caused by Pythium with or without BCAs added. BCAs can be inconsistent and often this is associated with pathogen inoculum levels / disease pressure.
Discussion Points How do we get BCAs to work? Identify most appropriate products and timings If it doesn t work why doesn t it work? Define important environmental factors including substrate / temp / moisture Formulation seed treatments or granule application? Which Pythium or other oomycete species are important? 250 Pythium species; many are soil inhabitants and are saprophytic; some show promise as BCAs. The main species causing damping-off is probably P. ultimum but others may be more important depending on crop e.g. P. aphanidermatum. What is prevalence of Phytophthora or Rhizoctonia which can also cause damping off symptoms?