BACTERIAL DISEASES OF STONE FRUIT: SPOTS AND CANKERS

December 16, 2015Kari Peter, Ph.D.Department of Plant Pathology and Environmental MicrobiologyPenn State University Fruit Research and Extension CenterBiglerville, PAkap22@psu.edu 717-677-6116 Ext. 223 @drtreefruit

Overview

– Predisposing factors

– Disease Cycle– Symptoms– Management

Bacterial cankerPseudomonas syringae pv. syringaePseudomonas syringae pv. morsprunorum

Bacterial spotXanthomonas arboricola pv. pruni(Xap)

G. Sundin, MSU

S. Bardsley, PSU

Bacterial Spot• Predisposing factors favoring the occurrence

of bacterial spot Cultivar susceptibility

Early bud break and early fruit ripening

Sandy soils (ring nematode) Very clay soils (drainage)

~ 86 °F temperature

Relative humidity of 100% over a period of 3 days = appearance of disease

http://www.ent.uga.edu/peach/peachhbk/pdf/stages.pdf

Forestryimages.org

Bacterial Spot Disease CycleSpring

SummerFall/Winter

Polycyclic diseaseOptimum conditions:Warm and wetDisease slows down:Hot and dry

Overwinter in cankers, infected buds, leaf scars

First infect leaves

Infect leaves and fruit

Left untreated: bacterial

populations “explode”

Bacterial Spot Symptoms - Twigs

• Cankers• Bark cracking• Black Tip

• Lack of vegetative growth• Overwintering site for bacteria

D. Ritchie, NCSU

K. Peter, PSU

Bacterial Spot Symptoms - Leaves

Bacterial Spot

Copper/Chemical Injury

• Round (like a water droplet)

• Follows spray pattern

• “Swiss cheese”

• Yellowing not always associated with lesions

• Defoliation of older leaves

• Captan and sulfur injury: similar symptoms

• Angular• Always

bordered by the veins

• Few or many lesions

• Yellowing associated with lesions

Defoliation– it does not take many lesions for this to occur

K. Peter, PSU

K. Peter, PSU

See spots? Ask yourself:• Are the spots angular?• Are the spots defined

by the small leaf veins?

Bacterial Spot Symptoms - Leaves

K. Peter, PSU

Early symptoms –light green water-soaked lesions

See spots? Ask yourself:• Are the spots angular?• Are the spots defined

by the small leaf veins?

Bacterial Spot Symptoms - Leaves

K. Peter, PSU

Bacterial Spot Symptoms - Fruit• Early Season Lesions

– 3 weeks after petal fall– Irregularly shaped– Pits extend deep into fruit

• Late Season Lesions– Shallow pits – Skin Cracking– Secondary infection: brown rot

Early season

After pit-hardening

Bill Shane, MSU

K. Peter, PSU

S. Bardsley, PSU

S. Bardsley, PSU

Japanese plum

Bacterial Spot Symptoms - FruitNot to be confused with Peach Scab

– Circular lesions– Dark olive-brown, fuzzy lesions

– Lesions form pattern– No fruit surface pitting– No foliar symptoms

BACTERIAL SPOT PEACH SCAB

S. Bardsley, PSU Bugwood.org

Bacterial Spot ManagementMain Strategies

– Prune out cankers– Resistant Cultivars

• Not immune = Still need control measures

– Chemical Control• Copper• Oxytetracycline• Biological products• Product rotation

http://njaes.rutgers.edu/peach/

Bacterial Spot ManagementCopper– Fixed vs. Bluestone– Dormant spray– Cover sprays using fixed copper

• Clean fruit vs. Leaf phytotoxicity• Defoliation: older leaves

– Avoid using copper during slow drying conditions: worsens leaf phytotoxicity

– Do not mix copper with phosphorous acid products (Rampart, ProPhyt, etc.) or foliar fertilizers

K. Peter, PSU

Bacterial Spot Management: Copper recommendations (N. Lalancette, Rutgers)

Recommended rate based on the metallic copper concentration of 0.5% = 1XCan increase concentration to 2X (1%multiply current recommended rate times 2)

** Be sure to monitor shoot s for increase in defoliation when using 2X rate**

Bacterial Spot Management

Oxytetracylcine (Mycoshield, FireLine)– Suppresses bacteria– 48 hr control window (UV degradation) – Risk of resistance– Persistent yield loss– Best when used in rotation with other products– Label limitations

Bacterial Spot ManagementA plan…

– Start applications late petal fall to early shuck split– Spray 7 – 14 days according to conditions– Rotating other products with oxytetracycline (21

day PHI) and copper (PHI varies)• Serenade Optimum (14 oz/A) or Double Nickel (1 qt/A)

– Works well in rotation– Can be tank mixed with oxytet

– For apricots, plums, etc: Cueva, Badge, Kocide, etc; Serenade Optimum, Double Nickel

– ** Always double check the label**– Phosphorous acid products ineffective

If your crop was frozen out: you still need to control for bacterial spot!

• If you don’t control the disease in no-crop years:• Build up of inoculum—issues for subsequent

years• Stress – defoliation; weakens tree making it

more susceptible to bacterial spot in coming years

Bacterial Spot Management

Overview

– Predisposing factors

– Disease Cycle– Symptoms– Management

Bacterial cankerPseudomonas syringae pv. syringaePseudomonas syringae pv. morsprunorum

Bacterial spotXanthomonas arboricola pv. pruni(Xap)

G. Sundin, MSU

S. Bardsley, PSU

Bacterial Canker

Perpendicular VVertical AxisMarchantVogel SlenderSpindleModified Central Leader Spanish Bush

Ranked in order of increasing vulnerability to canker infections Training systems

• Predisposing factors favoring the occurrence of bacterial canker

Least susceptible

Most susceptible

Source: http://nysipm.cornell.edu/grantspgm/projects/proj09/fruit/carroll5.pdf

Bacterial Canker• Predisposing factors favoring the occurrence of

bacterial canker

Cultivar susceptibility – varies by cultivar• Sweet cherry, sour cherry, plums, prunes,

peaches

Rootstock susceptibility• Gisela rootstocks highly susceptible• Mazzard more resistant

Bacterial Canker• Predisposing factors favoring the occurrence of

bacterial canker Acidic soils Sandy and clay soils Nutrient deficiency High ring nematode populations

Winter pruning Spring freezes Bacteria: Ice nucleation proteins & frost injury

• Proteins allow water to freeze at higher temperatures resulting injury to the plant

• Bacteria “feed” on the nutrients released by the injured plant tissue

Bacterial CankerFavorable conditions - susceptibility

• Mid-April (cool, wet, frost injury):– Bacteria overwintering in buds, cankers– P. syringae populations increase 10 – to 100 – fold during

bloom (blossom infection – blossom blast)• Summer:

– Humid, wet weather: symptoms on leaves and fruit– Hot and dry conditions: P. syringae populations low

• Autumn rains and cooler temperatures:– P. syringae detected at high levels prior to and during leaf fall

• *** Infection at leaf scars can be high• Early to mid-winter

– Bacteria overwinter in cankers, dead buds, healthy buds– Exposed to severe temperatures increases chance of infection

**Wind and rainstorms move the bacteria

Bacterial Canker Symptoms

Blossom – Blossom Blast

G. Sundin, MSU

• Not to be confused with blossom blight caused by the fungus causing brown rot

• No sporulation(differentiates from brown rot)

Bacterial Canker SymptomsFruit

• Sporadic• Water – soaked lesions• Chocolate – brown lesions

Leaves• Sporadic• Necrotic lesions, chlorotic rings• “Shot hole” appearance• Lesions occur along leaf margin

– curling effect

www.omafra.gov.on.ca

K. Peter, PSU

W. Turechek, USDA-ARS

Bacterial Canker SymptomsBranches and Trunk

• Facilitated by stress– Spring frost– Severe winter freezes– Water – soaking– Blossom infection– Pruning wounds– Insect injuries

• Sunken bark• Amber gummosis• Girdled branches and

trunks• Limb or tree death

• No alternating callus rings

http://commons.wikimedia.org/wiki/File:Bacterial_Canker_-_Gummosis_on_Cherry.JPG http://commons.wikimedia.org/wiki/File:Bacterial_Canker_on_Cherry.JPG

Bacterial Canker Management• Goal: reduce number of bacteria before trees

enter susceptible period

• Using Copper*– Copper alone: evidence shows limited ability to

control– Bordeaux mixture PLUS vegetable oil

• Win Cowgill – Rutgers• Described:

http://jerseyfruitagupdates.blogspot.com/2012/09/spray-cherries-for-bacterial-canker.html

– Sept, Oct, Nov, and in spring– EXAMPLE:Timing Copper sulfate Lime Water Veg. OilSept 4 lb 6 lb 100 gal 2.8 qtOct - early 5 lb 7 lb 100 gal 2.8 qtOct – late 8 lb 10 lb 100 gal 2.8 qtNov 10 lb 10 lb 100 gal 2.8 qtSpring 5 lb 7 lb 100 gal 2.8 qt

Notes: Use Powdered copper sulfate (bluestone or blue vitriol); Use FRESH hydrated lime (good quality calcium hydroxide)

Tank ½ full of water + agitation: Add copper, then lime, then the oil

K. Peter, PSU

Bacterial Canker Management

• Pruning* – Avoid large dormant cuts– Minimize impact of disease

with summer pruning– 12 inch rule: distances infection

from the main trunk– “Ugly stub”

www.extension.umd.edu

Bacterial Canker Management• Avoid tree training methods that cause

injury (limb spreaders)• Remove/Prevent tree stressors

– Plant in well drained soils– Maintain adequate nutrients– Weed control: weeds support

populations of bacteria– Control nematodes– Remove wild Prunus– Do not interplant new trees with old

trees• Old trees source of bacteria

K. Peter, PSU

Take home messages:

Bacterial spotResistant cultivarsWarm, humid temps favor high bacterial populationsDormant copper sprays; reduced rates during the seasonFavorable conditions throughout the season: Use a rotation of

products (copper, oxytetracycline, biologicals)Still need to control with or without crop

Bacterial cankerSusceptibility of rootstocks and cultivarsSpring freezes, cool fall weather promote diseaseMindful pruning – summer (low bacteria numbers)Limited control options (Bordeaux mixture in fall and early

spring)

Maintain healthy trees!

QUESTIONS?Kari Peter, Ph.D.kap22@psu.edu @drtreefruit

BACTERIAL DISEASES OF STONE FRUIT: SPOTS AND CANKERS