Walnut Blight
Management Using
Xanthomonas arboricola pv
juglandis Dormant Bud
Population Sampling
5
101
Sa c ra m e nto
Rive r
80
Sacramento
YOSEMITE
NATIONAL
San Francisco
Oakland
Stockton PARK
580
680
Sunnyvale
San Jose
Sa n Jo a q uin
Rive r
KINGS CANYON
NATIONAL
PARK
Fresno
101
5
SEQUOIA
NATIONAL
PARK
DEATH VALLEY
NATIONAL
MONUMENT
CALIFORNIA
15
40
101
Pasadena
C o lo ra d o
Rive r
San Bernardino
Los Angeles
Riverside
Long Beach
San Diego
Richard P. Buchner – UC Farm Advisor, Tehama County
William H. Olson – UC Farm Advisor Emeritus Butte County
Dr. Steven E. Lindow – Plant Pathology UC Berkeley
Dr. James E. Adaskaveg – Plant Pathology UC Riverside
Cyndi K. Gilles – Research Assistant Tehama County
Renee Koutsoukis – Research Assistant UC Berkeley
10
8
Walnut Blight infestation in Northern California
Xanthomonas arboricola pv juglandis
Blight History – Vina Variety
Tehama County, California
Location
2011 %
pathogen
2011 %
Blight
2012 %
pathogen
2012
Spray
Schedule
2012 %
Blight
South
16
1.49
30
4/16 & 5/2
3.50
Middle
23
1.23
10
4/16 & 5/2
6.49
North
6
2.00
16
4/16 & 5/2
2.42
2011 Spray Schedule: 6.74 Kg/Ha Kocide 2000 + 2.7 Kg/Ha Pro-Stick 4/12, 4/26 and 5/5
2012 Spray Schedule: 4.49 Kg/Ha Badge + 2.7 Kg/Ha Manzate 4/16 and 5/2
2012 Vina Walnut in Tehama County, California
Log (Cfu/bud)
Rating
M
L
L
M
M
L
L
L
L
Replant
L
M
L
L
0
L
L
L
Replant
0
0
0
L
0
L
0
0
0
0
L
L
Replant
0
0
10% infested buds
4.0
3.0
2.0
(no nut drop)
1.0
0.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Bud #
Xaj Histogram for Low Blight Rating
40% infested buds
6.0
5.0
Log (Cfu/bud)
Tree #
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
4.0
3.0
2.0
(0 to 30 nuts)
1.0
0.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Bud #
Xaj Histogram for Medium Blight Rating
67% infested buds
6.0
5.0
Log (Cfu/bud)
Rating
L
M
L
L
M
L
H
H
H
H
H
H
H
H
M
M
L
L
M
0
M
L
M
M
M
L
M
H
Replant
L
0
M
L
L
L
4.0
3.0
2.0
(30 to(30
100
tonuts)
100 nuts)
1.0
0.0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Bud #
Xaj Histogram for High Blight Rating
50% infested buds
6.0
Log (Cfu/bud)
Tree #
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
Xaj Histogram for Zero Blight Rating
5.0
5.0
4.0
3.0
2.0
(over 100 nuts)
1.0
0.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Bud #
2011
%
Pathogen
60
3
2011%
Blight
2.60
.52
2012
%
Pathogen
2012
%
Blight
Vina 2012 Spray Schedule
Butte County, California
43
4/2
(A)
B,M,S,
Z
4/9
(GH)
B,M,S,
Z
4/16
(A)
B,M,S
4/24
(GH)
B,M,S,
Z
5/25
(GH)
B,M
16.17
3
4/2
(A)
B,M,S
4/9
(GH)
B,M,S,
Z
4/16
(A)
B,M,S
4/24
(GH)
B,M,S,
Z
5/25
(GH)
B,M
.87
(G) or (A) indicates ground or air applications. (H) indicates half sprays every
other row alternating. B=Badge at 4.49 Kg/Ha, M=Manzate at 2.7 Kg/Ha,
S=Freeway at 292.30 ml/Ha and Z=Zinc Sulfate 36% at 1.12 Kg/Ha.
3
Tehama County, Northern California
% Blight
2.5
2
1.5
1
0.5
0
2010
2011
2012
2013
Walnut Blight damage for 14 walnut orchards in Tehama County from 2010 to 2013. Blight
damage is increasing in one orchard with a history of high initial inoculum.
20
Butte County, Northern California
18
16
% Blight
14
12
10
8
6
4
2
0
2011
2012
2013
Walnut Blight damage for 15 walnut orchards from 2011 to 2013. Improved spray programs
plus a low disease pressure year resulted in much better disease control in 2013.
Relationship of % buds with pathogen and the associated bud population. Very strong correlation
of incidence of bud infestation with average population size of pathogen – disease prediction can
be made based on more easily measured incidence of infestation rather than average population
size. The lines drawn represent the linear regressions Y=0.0308X + 0.055 (R2=0.967) (2012); and
Y=0.0398x + 0.067 (R2=0.626) (2013).
Relationship between the % buds infested with pathogen and the % walnut blight damage for 30
orchards in Butte and Tehama counties for 2012. The lines drawn represent the linear regression
Y=0.218x – 0.28 (R2=0.56); and Y=0.001x + 0.14 (R2=0.001) for orchards in Butte and Tehama
counties, respectively.
Relationship between the % buds infested with pathogen and the % walnut blight damage for 30
orchards in Butte and Tehama counties for 2013. The lines drawn represent the linear
regressions Y=0.039x + 0.067 (R2=0.626); and Y=0.032x – 0.096 (R2=0.58) for orchards in
Butte and Tehama counties, respectively.
Walnut Bud Sampling Methodology

Sample buds in December, January,
February, March or early April for late
leafing varieties. Buds can be sampled to
the time they start to open. Early samples
will allow more time to design disease
control strategies.

Select 100 dormant walnut spurs with nice
fat terminal buds. Cut off about a 3 inch
length. Spurs reachable from the ground
are easy to collect and represent a good
sample location because bacteria sprinkle
down through the tree canopy.

Walk the entire area collecting a random
sample. One or two buds per tree should
spread the sample adequately. Deciding
how many samples to collect will depend
upon experience on an orchard by orchard
basis. One sample could easily represent
50 acres if experience suggests reasonable
uniformity.

Save spurs in a paper bag and store in a
cool dry place. The paper bag will allow
samples to breathe and eliminate
condensation. Mail or transport buds to a
lab. The lab will select a 30 terminal bud
subsample to plate on agar and save the
remaining buds as a backup sample.

Walnut orchards can be highly variable. Try
to achieve as representative sample as
possible.

In California, samples can be analyzed at
the California Seed and Plant Lab.
www.calspl.com 916-655-1581
Tehama County Bud (Low % Infested)
Avg. log cfu = 0.23
6.0% infested buds
30
# of samples
25
20
15
10
5
0
0
3
3.5
4
4.5
More
Log Cfu/sample
Incidence of populations of X. juglandis on walnut buds sampled following
harvest on 12/1/10. This is a histogram typical for a low population sample.
Notice that over 25 buds had zero pathogen.
Tehama County Bud Samples (High % Infested)
Avg. log cfu = 2.92
73.3 % infested buds
9
# of samples
8
7
6
5
4
3
2
1
0
0
2.5
3
3.5
4
4.5
More
Log Cfu/sample
Incidence of populations of X. juglandis on walnut buds sampled following
harvest on 12/1/10. This is a histogram for a high population sample. Notice that
only 8 buds had no detectable pathogen and most of the buds were in the ten to
the fourth (10,000 colony forming units) or more range. This would be an
example of a high risk orchard.
Additional Information
cetehama@ucanr.edu (Buchner website)
walnutresearch.ucanr.edu (California Walnut Research Reports)
www.calspl.com (California Seed and Plant Lab)
Thank you