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

Clubroot management strategies for brassica production

Aaron Heinrich and Alex StoneDept. 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 [2009-12] 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 seed2. More farms with 15+ year history of short

rotations (<4 yrs)3. Increased brassica production to meet

demand4. More overwintering brassica crops

Disease cycle

Disease severity affected by:1. Moisture2. Temperature3. Low soil pH4. Spore density

Management strategies

1. Rotation– 5 to 7 years out of brassicas

2. Sanitation3. 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. Sanitation3. 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

ControlpH= 5.7Infection rate: 100%Avg plant wt: 0.3 g

LimedpH ≥ 7.1Infection rate: <4%Avg plant wt: 0.8 g

2014 Greenhouse studies: cauliflower

Control Serenade Boron (10 lb/A)

Lime Lime

5.7 5.7 5.7 6.3 7.1

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5 rating

4 rating

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1 rating

Infe

ctio

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Dead/dying

Minor clubs on laterals

1. Serenade not effective 2. Boron reduced severity but not infection rate3. Increasing pH from 5.7 to 6.3 slightly effective4. pH >7.0 highly effective

pH

2014 Field studies: broccoli & kale

2014 Field studiespH 6.7

pH 7.3

2014 Field studies: Lacinato Kale

No lime Lime6.7 7.3

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Rating 3

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ction

rate

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No lime lime0

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t wt (

g)

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% clubbedclubs on laterals

pH

Why is there a difference between greenhouse and field studies?

Treatment pHInfected

plants (%)Control 6.0 91Limed (field mixed) 7.0 34Limed (sieved/mixed) 7.0 6

(Adapted from Dobson et al., 1983)

Clubroot field trial: western WA

Same pH, different infection rate

Importance of uniform soil mixing

Treatment pHInfected

plants (%)

Microscale pH variability

(pH unit)Control 5.9 100 0.7Limed (field mixed) 6.4 86 1.1Limed (sieved/mixed) 6.5 25 0.3

(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 requirement2. Choose lime material3. Apply at correct time4. Incorporate thoroughly 5. Measure soil pH

Target pH ≥ 7.0

Step 1: Estimate lime requirement1. Use SMP buffer test and OSU pub. EM 9057 to

raise pH to ~6.7 (6” incorporation depth)2. Multiply SMP buffer rate by 1.5-2.0 to increase pH

>6.7

0 1 2 3 4 5 6 75.96.16.36.56.76.97.17.37.5

ton lime/acre

SMP Buffer

1.5-2.0 x SMP Buffer

Step 2: Choose lime material

Product Form Cost material only ($/ton)

Microna Ag-H2O Powder 210

Microna Access Powder 105

Ash Grove Ag lime Powder 60

CalPril Prilled 260

Microna Garden Pearls Prilled 392

Most reactive

Least reactive

Most economical, similar performance

Using pelleted limeAdvantages– 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 – 1st tillage – If sufficient moisture, no irrigation needed– 2nd tillage

1.5 minutes

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

0 1 2 3 45.6

5.8

6.0

6.2

6.4

6.6

6.8

7.0

7.2

Ash Grove (3 t/a)Microna Ag H2O (3.1 t/a)Microna Access (3.0 t/a)Cal Pril (3.3 t/a)Garden Pearls (3.6 t/a)

Weeks after application

pH

Step 4: Incorporate thoroughly

Treatment pHInfected

plants (%)

Microscale pH variability

(pH unit)Control 5.9 100 0.7Limed (field mixed) 6.4 86 1.1Limed (sieved/mixed) 6.5 25 0.3

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 FoundationOregon Processed Vegetable Commission