Fire Blight Infections Occur During Bloom

Fire Blight Infections Occur During Bloom

Risk for fire blight infections are high this weekend.  Apple are in bloom throughout most of the commonwealth, and Friday’s rain created ideal conditions for infection.

Initial infections from the fire blight bacterium occur during bloom.  The pathogen is carried to blossoms through rain or insects.  With sufficient moisture, the bacterium moves down into blossoms and infects natural openings of flower parts.  Thus, it is critical to protect apple blossoms from infections throughout bloom, especially when weather is warm and rainy.  Predictive weather models are available (http://wwwagwx.ca.uky.edu/plant_disease.html) for evaluating risk for infection.

Applications of bactericides (streptomycin or oxytetracycline) begin as the first blossoms open and continue until petal fall.  When weather conditions are conducive for infection, sprays should be repeated every 4 to 5 days.  Even when risk is low, a minimum of 2 applications is necessary to protect blossoms. 

 

Fig 1 – Blighting of shoots, also called shepherd’s crook, is the most recognized symptom of fire blight on apple.

 

More on Fire Blight

Fire blight can be a devastating bacterial disease of apple, crabapple, pear, and flowering pear, but disease epidemics are often sporadic.  In fact, optimal conditions must be met for severe disease to occur.  Our current conditions are an indication that fire blight may be severe this spring.

Erwinia amylovora infects trees through flowers.  However, large numbers of bacterial cells must be present during flowering in order for the disease to develop into an epidemic.  The fire blight pathogen favors rain and temperatures above 60˚F.  Under these conditions, bacterial cells multiply quickly.  Thus, if conditions are favorable during flowering, infection can be severe.

Predictive systems are available for growers.  University of Kentucky’s Cougarblight model evaluates the potential for infection by analyzing temperature and leaf wetness data from the previous four days in order to estimate potential risk for infection.  Trees must be in bloom for this predictor to be effective.  Cougarblight is an excellent decision-making tool for growers and can be accessed at http://wwwagwx.ca.uky.edu/plant_disease.html .

Most growers are familiar with shoot blight, the most obvious fire blight symptom in which infected shoots die quickly, causing branch tips to form a distinct crook (photo 1).  Shoot blight, however, does not result from infection of blossoms.  Direct penetration of bacteria into green shoots or the upper leaves of young shoots after bloom typically causes shoot blight symptoms.

Fig 2 – Initial infection by the fire blight pathogen occurs through blossoms.  Notice bacterial ooze coming from the pedicel.

 

Initial fire blight infections occur through flowers.  We call this symptom blossom blight.  Petal browning is the first sign of petal blight, but many growers do not notice it.  Browning of pedicels (stems that attach flowers to stems) follows.  Often, droplets of bacterial ooze can be seen coming from pedicels (photo 2).  Bacteria quickly travel down the spur and into the twig.  Cankers that form around the spur-attachment site girdle branches, and then branch parts above the canker also die (photo 3). 

 

Fig 3 – Bacteria can spread through flowers and spurs into twigs.  Resulting cankers can girdle entire limbs and branches.

Fire blight control measures include anti-bacterial pesticides applied during bloom.  Applications made after bloom are ineffective.  When fire blight risk is high (warm temperatures combined with rain) during bloom or if fire blight was a problem last year, the following spray schedule should be followed:

1.       Apply fixed copper at silver tip.  Homeowners should not skip this step, as it is their only tool available to combat fire blight.  Do not use copper fungicides after bud break.

2.       Apply streptomycin beginning at pink stage, repeating every 4-5 days, through petal fall.  At least 2 applications are required, but up to 4 sprays may be applied, depending on rain and temperature conditions.  Ideally, bactericides should be applied just before rains.  Pay extra attention to susceptible varieties (i.e. Gala, Jonathan, and Rome).  Utilize Cougarblight or MARYBLIGHT predictive systems for assistance.  Mycoshield (oxytetracycline) is also available for management of fire blight but is not as effective as streptomycin.  Neither product is recommended for homeowner use.

Various cultural practices may be implemented to aid in disease management.  Combine these practices with bactericide sprays above for best control.

1.       Select disease resistant or disease tolerant varieties.  Liberty, Pricilla, SirPrize, Enterprise, Gold Rush, and Sundance are recommendations from ID-21.

2.       Prune last year’s cankers and dead wood before bud break.  Burn, bury, or completely remove prunings from the orchard to eliminate the possibility of bacterial cells being carried back to healthy tissue.  Monitor predictive systems.  Know your risk.  Cool temperatures or no rainfall will result in low disease incidence.

3.       Remove flower/fruit spurs immediately after symptoms develop so bacteria cannot continue infection into branches.  Dip tools in 10% bleach, 10% Lysol concentrate, or pure rubbing alcohol after each cut to keep from spreading bacteria.

4.       Do not prune limbs or branches during the growing season.  Trees natural defenses wall off infection sites and stop disease spread.  Remove these branches during the dormant season, instead, when threat of disease spread is lowest.  Removal of all infected wood is critical to prevent spread of inoculum.

 

More information on fire blight can be found in PPFS-FR-T-12 and PPFS-FR-T-7. 

Spray recommendations for commercial growers ID-92 and homeowners ID-21 are also available online.

Peach Canker & Oozing Sap

Oozing Sap Coming from Peach Canker?  It might be a Fungal Disease.

Perennial canker of peach is a fungal infection of fruiting twigs, scaffold limbs, or trunks (Fig 1 & 2).  The disease may also be referred to as Cytospora canker, Leucostoma canker, perennial canker, valsa canker, or peach canker.  A common symptom is oozing gum from canker sites, so symptoms may also be referred to as gummosis (Fig 1). 

The causal fungi, Leucostoma spp., are weak pathogens that infect stressed or wounded plants.  Infections cause cankers, or stem lesions, that enlarge every year, creating annual rings or target-like growths.  These cankers expand until limbs become girdled and die.  Cankers often ooze gummy sap (gummosis) that eventually hardens (Fig 1).

Figure 1 – Perennial canker of peach limb, advanced symptoms with oozing sap. (Photo Penn State)

 

Gummosis can also be caused by other plant injuries such as bacterial infection (bacterial canker of peach), boring or sucking insects, and mechanical damage.  It is important to properly diagnose the cause of gummosis before considering management options. 

The fungi that cause peach canker produce spores during spring.  Fungal spores ooze from cankers during cool rainy weather.  Consequently, disease is often more severe during rainy years. 

Figure 2 – Infection of peach twigs, early symptoms.  (Photo West Virginia University)

 

Prevention of peach canker begins with vigorous plants and proper orchard sanitation. 

·        Retain plant vigor.  Maintain soil moisture, fertilize according to soil tests, and mulch properly. 

·        Avoid plant wounds such as mower damage, sunscald, winter injury, and insect injury.

·        Make clean, sharp pruning cuts that heal quickly.  Avoid jagged cuts.

·        Prune peach trees during late winter, preferably during late-February or March.

·        Prune during dry weather, only.  Fungal spores spread during wet conditions.

·        Maintain a clean orchard by pruning dead and damaged wood.  Remove cuttings from the orchard; bury, burn, or move them at least 100 yards from peach plantings.

·        Some peach cultivars are less susceptible to peach canker than others.  Use resistant or tolerant trees when possible.

 

If peach canker becomes a problem in the orchard, a strict sanitation should be implemented.  There are no fungicide treatments available for management of peach canker. 

·        Remove diseased twigs and limbs, making clean cuts at least 6 inches below cankers.  Remove diseased cuttings from the orchard.

·        Infected trunks may require “surgery.”  Using a knife or chisel, remove bark at least one inch around each disease lesion.  There is no need to cut into hardwood.  Do not paint affected area with wound dressing, paint, or oil. 

·        Prune during dry weather, only.

·        Disinfest pruners and tools between cuts using a commercial sanitizer, 10% bleach, or 10% Lysol® concentrated disinfectant.

·        Apply fungicides to open pruning wounds as a preventative.  Captan, iprodione (Rovral), and thiophanate-methyl (Topsin M) may be applied after pruning (delayed dormant phase), after petal fall, and after shuck split to prevent new infections. 

 

Sanitation and increased plant vigor are the primary disease management options for peach canker.  Growers should be aware of potential risks for infection and prevent disease outbreaks by following the guidelines above.  Once trees become infected, the pathogen can spread through orchards in just a few years.  Fungicides do not cure peach canker, and cultural practices are the primary means for disease management.

Fire Blight Season is Approaching – Preventative Copper is Recommended

As apple flowering-season approaches, growers should begin thinking about management of fire blight.  This bacterial disease can cause severe damage on apples, pears, and related ornamental plants during warm, rainy spring weather.

 

There is no single method that will provide consistent and reliable control. Management of fire blight requires an integrated approach that relies primarily on cultural practices and is supported by the judicious use of bactericides.



Fig 1 – Blossom blight phase of fire blight in which bacteria infect blossoms during bloom.

Disease Development: The fire blight bacterium overwinters primarily in cankered or diseased branches and trunks. During spring, bacteria-laden ooze is exuded from canker margins. Splashing rain and insects carry the pathogen to blossoms (Fig 1), and bees further spread the pathogen as they pollinate.

 

If weather is warm and rainy, populations of the causal bacterium (Erwinia amylovora) double every few hours, and more than a million bacterial cells can colonize a single floral stigma. Rain or dew then washes the bacteria into openings at the base of blossoms. Resulting symptoms are called blossom blight.  Infections can spread from blossoms to supporting spurs and branches, causing cankers that eventually kill entire branches (Fig 2).

 

Even if there is no blossom infection, shoot infections may occur. Bacterial cells infect externally through shoot tips, as young, succulent tissue is susceptible during periods of rapid growth. This phase of fire blight is called shoot blight or shepherd’s crook.  

 

Fig 2 – Flower and shoot infections can spread to branches, causing cankers that eventually kill entire limbs.  The fire blight bacterium overwinters in cankers and dead wood.

 

Bactericides:  During bud swell (late dormancy), an application of copper fungicide (e.g. Kocide or other fixed copper) should be applied, especially if fire blight was severe last year.  This copper application should reduce amounts of bacterium present on the surfaces of branches and spurs, reducing risk for disease development.  Do not apply copper after ¼ inch green leaf stage, as can be phytotoxic (cause foliar burn). 

 

During bloom, beginning at the first sign of open blossoms, a bactericide such as streptomycin (e.g. Agri-strep) should be applied at 4- to 5-day intervals through petal fall.  A minimum of two applications is recommended.  Another type of bactericide, oxytetracycline (e.g. Mycoshield) may be substituted, but it is not as effective as streptomycin.  Oxytetracycline may be mixed with streptomycin bactericides to help reduce the risk for resistance development.  Disease risk assessment sites (see below) may be used to improve timing and efficacy of bactericide applications.  Note:  Home orchards are usually not sprayed with antibiotics, so the preventative copper spray is critical.

 

After bloom, certain weather conditions can increase risk for shoot infections.  This shoot blight phase can be severe during rapid shoot development, especially under warm, rainy conditions.  The growth regulator prohexadione calcium (e.g. Apogee) reduces terminal growth, reducing succulent tissue that is most susceptible to infection.

 

Pruning: Growers should remove all damaged, dead, or diseased wood from trees during dormancy, before bacteria become active this spring.  This will help eliminate large amounts of infective inoculum.    

 

Disease Risk Assessment & Weather Models: Plant disease prediction models utilize weather data to analyze disease risk. The University of Kentucky maintains weather stations and incorporates this data into disease risk predictions models. Models can be found at http://wwwagwx.ca.uky.edu/plant_disease.html

  

More information:  See also our newest fact sheet Fire Blight http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-FR-T-12.pdf

Midwest Tree Fruit Spray Guide http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/MW_tree_fruit_spray_guide_ID-92_(2013)[1].pdf

Disease and Insect Control Programs for Homegrown Fruit in Kentucky http://www.ca.uky.edu/agc/pubs/id/id21/id21.pdf

White Pine Decline versus White Pine Root Decline: What's the Difference?

Decline of White Pine

Decline is common among white pine in Kentucky.  Two distinct diseases with similar names are often confused, but they are distinctly different.  Note that white pine decline is an abiotic malady that leads to slow decline, while white pine root decline is a fungal disease that causes sudden plant death.  More details follow:

White Pine Decline

Symptoms

White pine decline causes needle s to yellow and drop prematurely, causing a noticeable thinning of the canopy (Fig 1).  Other symptoms include unusually shorter needles; needle tips may become brown.  Bark of individual branches may become shriveled and needles on those branches become wilted or limp (Fig 2).

Figure 1.  White pine decline, an abiotic malady, is caused by environmental conditions.  Symptoms include thinning needles and reduced plant vigor.

Cause

White pine decline is not caused by a pathogen.  Symptoms are induced by environmental conditions such as

·         high soil pH

·         high soil clay content

·         restricted root-growth

·         compacted soil

·         mechanical disturbances that cause root injury  

Figure 2.  Wrinkled bark is common on trees suffering from white pine decline.  Needles above damaged bark become wilted and drop.

Disease Management

The best way to manage white pine decline is through prevention. Select sites with the following characteristics:

• acidic soil (pH of 5.5 and not above 6.5)
• sandy or loamy rather than clay soils
• large area for root development

·         loose soil free from soil compaction

·         sufficient soil moisture (regular irrigation and mulch)

·         vigorous plants (control insect pests and fertilize trees regularly)

Once decline begins, it may be difficult to reverse.  However, the following practices may be implemented.

·         lower soil pH by applying granular sulfur according to soil test results

·         aerate soil by vertical mulching or other means

·         fertilize and water to eliminate stress

White Pine Root Decline

Symptoms

Trees may be infected for several years without showing symptoms.  However, once symptom development begins, homeowners often notice delayed bud break and reduced candle elongation in spring.  Mature foliage then fades, droops, and turns brown rapidly (Fig 3-4).  Conversely, nearby trees may appear healthy; mortality appears quite random with a few trees dying each year. Resin flow (pitch) is visible at the tree base and is associated with a dark brown girdling canker under the bark (Fig 5).  The trunk may be flattened on the affected side.

Figure 3.  White pine root decline, a fungal disease, causes rapid wilting of white pine. 

Cause

White pine root decline, is caused by the fungus, Leptographium procerum that infects inner bark and sapwood of roots and lower trunks of white pine.  Although the disease is most serious on white pine, the fungus also can infect Scots and Austrian pines.  Losses within an infected planting range from 20 to 50%.

Figure 4.  Rapid wilting is often followed by rapid browning (needles intact) when trees are suffering from white pine root decline.

Trees planted on wet sites are more susceptible to infection, although other stresses may also cause trees to become susceptible to the disease.  Once infection occurs, the fungus may be spread from tree to tree by contaminated insects as they move from diseased trees to healthy trees nearby.  Galleries of insects such as the pine root collar weevil may be found in cankers and provide a place for the fungus to sporulate.  Weevils and other bark-infesting insects may serve as vectors for this disease.

Figure 5.  Pitch is often associated with trunk cankers caused by white pine root decline.

Disease Management

Cultural practices help reduce disease spread by insect vectors. No fungicide is available for disease management.

·         avoid  wet sites

·         do not replant eastern white pine among stumps of recently killed trees

·         remove and destroy infected trees including stumps,

·         collect samples for diagnosis by removing tissue from the canker face (bark removed) and shipping in a plastic bag.

 

Revision of original by John Hartman.