1. health and fitness
2. disease

An Overview of Bacterial Spot Disease
and Management in Peaches
Three bacterial diseases we deal with:
they’re all different!
•  Fire blight – flower surface, otherwise mostly
internal, ooze
•  Bacterial canker – favored by cool weather,
flowers, cankers especially taking out young trees
•  Bacterial spot – favored by warm weather, leaf
spots and fruit infection significant
George W. Sundin
Michigan State University
Bacterial Spot
•  Causal agent -- Xanthomonas campestris
(arboricola) pv. pruni
•  Symptoms -- spots on leaves, fruit;
cankers form on new twigs
Bacterial Spot Life Cycle
Winter
Overwinter in
twigs, terminal
buds
Spring
Black tip;
primary leaf and
fruit infections
brownish-red bark,
moist appearance
Early infections
Late infections
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Bacterial Spot Life Cycle
Disease cycle
Fruit susceptibility is
highest during 3-wk
period after shuck split
•  Tends to overwinter in twigs infected late in
the summer.
•  In spring as temperature warms, cankers
become visible and bacterial ooze is formed.
•  Bacteria spread by heavy dew, wind-driven
rain. Bacteria enter through somata, lenticels,
and wounds. Wounding can be more frequent
at sandy sites and sites adjacent to roads.
•  Bacteria then can multiply in infected tissue
and serve as inoculum throughout the season.
Bacterial Spot -- Inoculum
Considerations
There is enough inoculum
from a single leaf to infect
all of the fruit on a tree,
assuming the bacteria could
be splashed to all fruit
One objective of early copper sprays (bud
break through shuck split) is to prevent early
infections
Water congestion is
required for leaf infection
Spring
Summer
Black tip;
primary leaf and
fruit infections
Leaf and fruit
spot, defoliation
Table 4. Relative bacterial spot disease ratings for peach and nectarine varieties, SW Michigan
Research and Extension Center (Bill Shane).
Ra#ng Li$le to no leaf symptoms Up to 10% leaf area affected Peach Nectarine Sweet Breeze, Veteran, Madison, Glenglo, Nectafest PF-­‐25, PF35-­‐007, Brightstar, McKay, Risingstar, Gloria Messina, Blushingstar*, Harrow Diamond, Carene, Emeraude*, Sunhaven, PF-­‐9A-­‐007, Richhaven, Catherina#, PF11 Nectarine Redstar, Ernies Choice, Loring, Beaumont, Allstar, Canadian Harmony, Contender, Halehaven, Glowingstar, July Rose*, Flameprince, Victoria, Glohaven, Virgil#, 10 to 25% leaf PF-­‐8 Ball, Starfire, Autumn Star, PF23, Desiree, Fantasia, Zephyr*, area Summerfest, PF 5D Big, Early Redhaven, Silver Gem* affected, PF-­‐27A, Flavrburst, Newhaven, PF-­‐7A some leaf Freestone, PF28-­‐007, Vinegold#, PF-­‐24C drop Coldhardy, Earlystar, PF11 Peach, Cresthaven, Coralstar 25% or more PF Early 8 Ball, Crimson Rocket Easternglo, Ambre leaf area affected, significant defoliabon * = white flesh, # = non-melting flesh canning type.
PeenTo Tangos (NJF16), Saturn BuenOs II (NJF15) BuenOs I (NJF18) Tangos II (NJF17) Ratings July 15, 2014
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Copper Use for Bacterial Spot
Management
NC STATE UNIVERSITY
Applications of Copper Sprays
2.0-2.5 lb Cu/A
1.0-2.0 lb Cu/A
1.0 lb Cu/A
•  Copper is only toxic in its “free ion” state
[Cu2+]
–  Toxicity to bacteria and the tree
•  Quantity of free ions is determined by the pH
of the solution
–  Acidic conditions = more free ions available
•  Cool temps (50-63 F), slow-drying conditions
can increase phytoxicity
•  To reduce the risk of accumulating copper on
trees to levels that could become phytotoxic,
consecutive applications should not be made
during extended dry conditions
NC STATE UNIVERSITY
Applications of Copper Sprays
0.50 lb Cu/A
0.10-0.25 lb Cu/A (+ Mycoshield?)
Early Bud-break
Pink-Bud
Blossoms Opening
DFR – 01/04
Copper Use for Bacterial Spot
Management
•  Bottom line from Dave Ritchie, NC State:
•  “When peach foliage is present, there is no rate
of copper that has adequate activity against
bacterial spot which will not cause some leaf
injury.”
Petal-fall
Shuck-split/Shuck-off
Unacceptable Copper Phytotoxicity May Begin to Occur
DFR – 01/04
Bacterial Spot Control
•  Copper -- metal ion, broad spectrum
effects, resistance possibilities
•  Oxytetracycline -- antibiotic,
bacteriostatic, resistance possibilities
–  Mycoshield, Flame Out (not less than 0.75 lb/
A)
–  Start at late shuck split and continue on a
7-10 day schedule for 3-4 wks
Bacterial Spot Control
•  Copper -- metal ion, broad spectrum effects,
resistance possibilities
•  Oxytetracycline -- antibiotic, bacteriostatic,
resistance possibilities
•  Dodine (Syllit) -- broad spectrum effects
–  light to moderate pressure; some
phytotoxicity
•  Ziram -- zinc ion, broad spectrum effects
•  HOST RESISTANCE
–  Avoid highly-susceptible varieties
–  Reduce plantings of highly-susceptible
varieties adjacent to more resistant varieties
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What are conditions for bacterial spot infections?
What are conditions are needed for bacterial spot
infections?
Inoculate
with
bacteria
Inoculate
leaves with
bacteria
à At 76 F see symptoms in 10 to 14
days
Precondition
leaves with
48 hr high
humidity
à At 86 F see symptoms in 3 days
Post inoculation
wet period
48 hr preinoculation high
humidity
Temp
76
86
Hours wet post inoc.
0 16 24 48
1% 2% 2% 7%
5% 5% 12% 40%
Need 72 to 96 hr total high humidity / wet hr (pre + post) to
see significant disease increase.
Zehr, E.I., Shepard, D. P. and Bridges, W. C. Jr. 1996. Bacterial spot of
peach as influenced by water congestion, leaf wetness duration, and
temperature. Plant Dis. 80:339-341
Bacterial Spot Management -- SE,
USA Experiences
Zehr, E.I., Shepard, D. P. and Bridges, W. C. Jr. 1996. Bacterial spot of
peach as influenced by water congestion, leaf wetness duration, and
temperature. Plant Dis. 80:339-341
Bacterial Spot Control, Ritchie
Program
•  Trt 1 -- Kocide 2000
•  Start management early
•  Cover trees with a “blanket of copper”
–  Use a high rate (4-5 lb formulated Copper, 2 lb Cu)
• 
• 
• 
• 
Leaf surface symptoms (%)
measured 15 days later
7-10 day interval -- use a half-rate copper
1-5% bloom -- half-rate copper
Petal fall -- 1/4th-rate copper Look for signs of copper injury before EACH
application
–  3 Mar (budswell) -- 2.0 lbs metallic Cu/A
–  17 Mar (40% bloom, 1/2” leaf growth) -- 1.2 lbs
–  25 Mar (10% petal fall, 1” leaf growth) -- 0.5 lbs
–  30 Mar (petal fall) -- 0.5 lbs
–  7 Apr (1% shuck split) -- 0.2 lbs + 0.75 lbs Mycoshield
–  15 Apr (shucks off) -- 0.13 lbs + 0.75 lbs Mycoshield
–  27 Apr, 5 May -- 0.094 lbs
–  25 May, 8 Jun, 15 Jun -- 0.047 lbs
–  Will probably see some, as long as it’s not extensive, is safe for
next application
Source: Dave Ritchie, NC State Univ.
Bacterial Spot Control, Ritchie
Program
Diseased Fruit
Diseased Leaves
Copper Injury
Control
63% a
58% a
0.0 a
Copper
Program
17% b
10% b
3.0 b
Bacterial Spot Management -- SE,
USA Experiences
•  Shuck split -- Mycoshield or low rate of
TennCop (5-6 oz/acre) -- 7-10 day schedule •  Shuck split applications based on wet weather
•  Bacterial spot weather -- similar to brown rot
weather; needs rainfall, 90+% RH
•  Period between shuck split and pit hardening -fruit is most susceptible
•  After pit hardening, fruit is less susceptible, but
not immune
3.0 = shothole and 6-10% defoliation
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Cautionary note for in-season use of copper for bacterial spot
suppression on peaches and nectarines
Do fall applications of copper provide some bacterial spot control the following
season?
Rutgers study (N. Lalancette, Rutgers)
Applied 7 applications of Tenn-Cop 5E (0.5 oz copper/acre) in 200 gal water per acre, Oct 1 to Nov
21st
Growers who opt for use of copper need to be aware that the
safety margin is relatively small. Copper is toxic when the dissolved form penetrates into plant
tissue. In general, growers should avoid the use of spray additives such
as spray oils, foliar nutrients, and surfactants such as
organosilicants with penetrating characteristics when
applying coppers. Careful calibration and adjustment of spray equipment is needed
to make sure applications do not result in excessively high
deposits of copper in some areas of the trees.
Rated fruit infections next season
Fall copper applications seem to have little effect on bacterial spot severity the following year.
(modified from summary by David Ritchie, North Carolina State University)
MI Peach Sponsors
MI State Horticultural Society
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