Clubroot management strategies for brassica production Aaron Heinrich and Alex Stone Dept. of Horticulture

It’s called clubroot for a reason…

Hosts And more… Susceptibility varies by species and cultivar

Clubroot’s impact “In the past 3 years [ ] we have had a 25% loss in our brassica crops due to clubroot, costing us between $60-80K/year. We are running out of clubroot free ground on which to rotate brassica crops.” “In 2013 we experienced a 30 to 50% loss in 5 of our highest yielding brassica crops this year totaling $20K. Three years ago we played out this scenario knowing that our future looked quite bleak... We need to figure out a way to grow brassicas in fields that have a high clubroot population.”

Is incidence increasing? 1.Increase in radish and turnip cover crop seed 2.More farms with 15+ year history of short rotations (<4 yrs) 3.Increased brassica production to meet demand 4.More overwintering brassica crops

Disease cycle Disease severity affected by: 1.Moisture 2.Temperature 3.Low soil pH 4.Spore density

Management strategies 1.Rotation – 5 to 7 years out of brassicas 2.Sanitation 3.pH manipulation – lime to pH ≥7.0 4.Boron? 5.Biologic controls? 6.Resistant cultivars? 7.Water management Control not eradication is the goal

Management strategies 1.Rotation – 5 to 7 years out of brassicas 2.Sanitation 3.pH manipulation – lime to pH ≥7.0 4.Boron? 5.Biologic controls? 6.Resistant cultivars? 7.Water management Control not eradication is the goal

Liming success in California 1978 clubroot first identified Started aggressive liming program Still present but controlled

2012 clubroot survey Response from 19 of 37 farmers 83% had used lime as a control – 21% aimed for pH ≥6.8 – 52% verified if target pH reached – 26% said liming helped Is liming effective in western Oregon? Are farmers liming “correctly”?

2014 Greenhouse study: Cauliflower Control pH= 5.7 Infection rate: 100% Avg plant wt: 0.3 g Limed pH ≥ 7.1 Infection rate: <4% Avg plant wt: 0.8 g

2014 Greenhouse studies: cauliflower Dead/ dying Minor clubs on laterals 1.Serenade not effective 2.Boron reduced severity but not infection rate 3.Increasing pH from 5.7 to 6.3 slightly effective 4.pH >7.0 highly effective pH

2014 Field studies: broccoli & kale

2014 Field studies pH 6.7 pH 7.3

2014 Field studies: Lacinato Kale In 3 field trials: 44-77% reduction in infection rate 74-90% reduction in disease severity Serenade and B (4 and 8 lb/A) not effective in these studies >50% clubbed <50% clubbed clubs on laterals pH

Why is there a difference between greenhouse and field studies? TreatmentpH Infected plants (%) Control6.091 Limed (field mixed)7.034 Limed (sieved/mixed) 7.06 (Adapted from Dobson et al., 1983) Clubroot field trial: western WA Same pH, different infection rate

Importance of uniform soil mixing TreatmentpH Infected plants (%) Microscale pH variability (pH unit) Control Limed (field mixed) Limed (sieved/mixed) (Adapted from Dobson et al, 1983) Clubroot greenhouse trial Under field conditions, 100% clubroot control highly unlikely with liming.

Implementing a successful clubroot liming program Steps: 1.Estimate lime requirement 2.Choose lime material 3.Apply at correct time 4.Incorporate thoroughly 5.Measure soil pH Target pH ≥ 7.0

Step 1: Estimate lime requirement 1.Use SMP buffer test and OSU pub. EM 9057 to raise pH to ~6.7 (6” incorporation depth) 2.Multiply SMP buffer rate by to increase pH >6.7 SMP Buffer x SMP Buffer

Step 2: Choose lime material ProductFormCost material only ($/ton) Microna Ag-H 2 OPowder210 Microna AccessPowder105 Ash Grove Ag limePowder60 CalPrilPrilled260 Microna Garden PearlsPrilled392 Most reactive Least reactive Most economical, similar performance

Using pelleted lime Advantages – Easy to handle Disadvantages – Expensive – Less reactive (i.e. requires higher rates) – Requires additional steps

Using pelleted lime efficiently If incorporated too soon, the pellets will not disperse! Option 1: – Broadcast – Apply irrigation (or wait for rain) – Till Option 2: – Broadcast – 1 st tillage – If sufficient moisture, no irrigation needed – 2 nd tillage 1.5 minutes

Step 3: Apply at correct time Apply 1 wk minimum before planting

Step 4: Incorporate thoroughly TreatmentpH Infected plants (%) Microscale pH variability (pH unit) Control Limed (field mixed) Limed (sieved/mixed) Clubroot greenhouse trial (Adapted from Dobson et al., 1983)

Step 5: Measure soil pH Soil sample! Verify if target pH reached Caution: if you can see unreacted lime, the soil test pH may be higher than what the plants are experiencing!

Integrated Clubroot Management Scouting Rotation (4-5+ yrs) Maintain soil pH ≥6.8 Plant resistant varieties Irrigation management No one strategy is enough!

Acknowledgements We thank our farmer partners for their collaboration as well as the following organizations for funding this project: The Agriculture Research Foundation Oregon Processed Vegetable Commission