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 [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 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
Control not eradication is the goal
1. Rotation
–
5 to 7 years out of brassicas
2. Sanitation
3. pH manipulation
–
4.
5.
6.
7.
lime to pH ≥7.0
Boron?
Biologic controls?
Resistant cultivars?
Water management
Management strategies
Control not eradication is the goal
1. Rotation
–
5 to 7 years out of brassicas
2. Sanitation
3. pH manipulation
–
4.
5.
6.
7.
lime to pH ≥7.0
Boron?
Biologic controls?
Resistant cultivars?
Water management
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
Infection rate and
severity (%)
100
80
5 rating Dead/
60
4 rating
dying
3 rating
40
2 rating
20
Minor clubs
1 rating on laterals
0
Control
pH 5.7
1.
2.
3.
4.
Serenade
Boron (10
lb/A)
Lime
Lime
5.7
5.7
6.3
7.1
Serenade not effective
Boron reduced severity but not infection rate
Increasing pH from 5.7 to 6.3 slightly effective
pH >7.0 highly effective
2014 Field studies: broccoli & kale
2014 Field studies
pH 6.7
pH 7.3
2014 Field studies: Lacinato Kale
450
90
400
Rating 3
>50% clubbed
Rating 2
<50% clubbed
Rating
1 on laterals
clubs
80
70
60
50
40
30
20
Plant wt (g)
Infection rate and
severity (%)
100
350
300
250
200
150
100
10
50
0
No lime
pH 6.7
Lime
0
No lime
lime
7.3
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
Why is there a difference between
greenhouse and field studies?
Clubroot field trial: western WA
Treatment
Control
Limed (field mixed)
Limed (sieved/mixed)
pH
6.0
7.0
7.0
Infected
plants (%)
91
34
Same pH,
6
different
infection rate
(Adapted from Dobson et al., 1983)
Importance of uniform soil mixing
Clubroot greenhouse trial
Treatment
Control
Limed (field mixed)
Limed (sieved/mixed)
Microscale
Infected pH variability
pH plants (%) (pH unit)
5.9
100
0.7
6.4
86
1.1
6.5
25
0.3
Under field conditions, 100% clubroot
control highly unlikely with liming.
(Adapted from Dobson et al, 1983)
Implementing a successful clubroot
liming program
Target pH ≥ 7.0
Steps:
1.
2.
3.
4.
5.
Estimate lime requirement
Choose lime material
Apply at correct time
Incorporate thoroughly
Measure soil pH
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 1.5-2.0 to increase pH
>6.7
7.5
7.3
7.1
6.9
6.7
6.5
6.3
6.1
5.9
SMP
Buffer
1.5-2.0 x
SMP
Buffer
0
2
4
ton lime/acre
6
Step 2: Choose lime material
Product
Most
reactive
Least
reactive
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 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
1st tillage
If sufficient moisture, no irrigation needed
2nd tillage
1.5 minutes
Step 3: Apply at correct time
Apply 1 wk minimum before planting
7.2
7.0
pH
6.8
6.6
6.4
Ash Grove (3 t/a)
6.2
Microna Ag H2O (3.1 t/a)
6.0
Microna Access (3.0 t/a)
5.8
Garden Pearls (3.6 t/a)
Cal Pril (3.3 t/a)
5.6
0
1
2
3
Weeks after application
4
Step 4: Incorporate thoroughly
Clubroot greenhouse trial
Treatment
Control
Limed (field mixed)
Limed (sieved/mixed)
Microscale
Infected pH variability
pH plants (%) (pH unit)
5.9
100
0.7
6.4
86
1.1
6.5
25
0.3
(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