Tuesday, November 12, 2013

Recurring Pythium in the Greenhouse - Poinsettia Root Rot

One of our local greenhouse growers struggled with Pythium infections in pansy earlier this year.  Now, poinsettia are infected with the same root rotting/damping off fungus. 

So, why would Pythium be a recurring problem?  Simple.  Sanitation.

Sanitation is critical for greenhouse production, landscapes, orchards, and gardens.  In this greenhouse, fungal propagules are obviously spreading via debris, hoses, shoes, tools, drainage water, and more.  Also, Pythium favors soilless mixes, where there's no competition.  Growers should verify that potting mix is not contaminated and that containers are sterilized before reuse.

Moreover, greenhouses must be disinfested between crops, so that disease-causing propagules are not carried over from one crop to another.  

Once a greenhouse is infested with Pythium, fungicides are required for disease management.  A single fungicide application will not be sufficient to manage disease, so a regular schedule should be employed.  Rotate fungicides by FRAC group (mode of action), avoiding two consecutive applications of any particular group and observing maximum numbers of applications per season.  Fungicides effective against Pythium include: 
·         mefenoxam (Subdue MAXX) FRAC 4
·         etridiazole (Truban/Terrazole) FRAC 14
·         propamocarb (Banol) FRAC 28
·         dimethomorph (Stature) FRAC 40
·         phosphorus acids (Aliette, Alude, Vital) FRAC 33
·         etridiazole + thiophanate methyl (Banrot) FRAC 14 + 1


For more information on disease management of poinsettia or other greenhouse crops:

Fungicides for Management of Diseases in Commercial Greenhouse Ornamentals http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdf
Poinsettia Diseases  http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-2.pdf


Thursday, November 7, 2013

Stunted Pines and Brown Needles: Diplodia Tip Blight

Diplodia tip blight is a serious disease of mature Austrian, Scots (Scotch), and Mugo pines in Kentucky. The disease is caused by the fungus Sphaeropsis sapinea.  In the landscape, tip blight is normally not observed until pines reach about 12 years old and begin to bear cones. Continuous infections (3 to 5 consecutive years) can greatly weaken and eventually kill affected pines.

Infection occurs in spring; however, disease symptoms become more obvious in mid- to late-summer and fall. Needles in early stages of development stop growing as a result of shoot infections. These stunted needles eventually die and turn straw-colored (Figure 1). Infection progresses to healthy needles and cones.

Disease Management:

·         Apply fungicides (chlorothalonil, propiconazole, or thiophanate methyl) to trees just as buds swell in spring. Apply a second spray when the candles are about half elongated and a third spray as needles begin to emerge from the needle sheaths.
·         Remove and destroy dead twigs, branches, and cones as they occur. Do not prune when trees are wet.
·         Destroy all blighted needles, twigs, and cones debris as they fall to the ground.  The fungus overwinters in debris, especially infected cones and diseased needles.
·         Trees under stress tend to be more susceptible to tip blight. Fertilize and water trees as needed to promote vigor.

 For more information on tip blight or pine diseases:

Needle Cast Diseases of Conifers  http://www2.ca.uky.edu/agc/pubs/id/id85/id85.pdf

Twig, Branch, and Stem Diseases of Pine  http://www2.ca.uky.edu/agc/pubs/ppa/ppa16/ppa16.pdf

Department of Plant Pathology, Extension Publication page  http://www2.ca.uky.edu/agcollege/plantpathology/extension/pubs.html

Tuesday, September 24, 2013

Skimpy Spruce – Defoliation from the Bottom Up

Rhizosphaera needle cast, the most common disease of spruce in Kentucky, causes needle drop in lower branches, resulting in a distinct thinned appearance.  The fungal pathogen Rhizosphaera kalkhoffii primarily infects spruce but can also affect some pine species. 

Figure 1 – Needles infected with Rhizosphaera turn purplish brown during summer.
Symptoms are often noticed during summer when needles on lower branches turn purplish or brown (Figure 1).  Within a few weeks, needles fall and lower limbs are left bare (Figure 2).  Small, dark fruiting bodies called pycnidia form in stomata (pores in needles) and can be used to confirm diagnoses (Figures 3 & 4).  Pycnidia can easily be recognized with a hand lens or with the naked eye. 

Figure 2 – Needle drop and thinning of lower canopy are classic symptoms of Rhizosphaera needle cast in spruce.
The life cycle of the fungus extends over a 15-month period.   Infection takes place as spores (conidia) within these pycnidia are rain splashed from needle debris onto foliage.  This infection process occurs primarily during spring, but it can continue as long as conditions are rainy, such as this past summer.  During the winter or following spring, pycnidia develop in infected needles, plugging stomata.  Needle discoloration and needle drop occur during summer of the second season, resulting in thinning of lower canopies.  If defoliation occurs 3 to 4 consecutive years, branch death is likely.  Stressed trees are more susceptible to infection by R. kalkhoffii than healthy plants. 

Figure 3 – Fungal pycnidia are often visible without a hand lens.
Disease management should consist of good cultural practices such as improved vigor and reduced plant stress, proper spacing to improve air circulation, and most importantly, good sanitation habits.  During rainy seasons or in plantings with a history of disease, fungicides may be applied two consecutive years during spring when fungi are most active.  Fungicides that include chlorothalonil, copper, or mancozeb are effective when applied during needle emergence (mid-April) and again four weeks later.  For more information, see Homeowner’s Guide to Fungicides. 
Figure 4 – Fungal pycnidia protrude from stomata.

Saturday, August 31, 2013

Elm Yellows - a Sporadic Yet Lethal Disease of Elm

Elm Yellows, a lethal systemic disease of elm, was confirmed on two American elm (Ulmus americana) specimens in Franklin County in August 2013.  The disease can occur in isolated areas across the eastern portion of the US and can quickly devastate large plantings of native elm.  Elm yellows occurs only occasionally in Kentucky.  In fact, only one other incidence has been reported in the commonwealth during the past 30 years (Jefferson Co., 1990).

Symptoms of elm yellows usually appear during summer months and include bright yellowing that resembles early senescence (Figure 1).  Leaves can change hues with a few weeks, with petioles turning downward (epinasty) (Figure 2).  Leaves eventually turn brown and can remain attached to branches for several weeks (Figure 3). 

Figure 1.  Foliar symptoms of elm yellows disease include bright yellowing of leaves during summer.

Mature trees develop disease symptoms approximately nine months following infection, while young trees may show symptoms in as little as three months.  Trees usually die within a year or two after symptoms develop.  There is no cure. 

The causal agent of elm yellows is a phytoplasma (bacterium-like prokaryote) called ‘Candidatus Phytoplasma ulmi’. The pathogen inhabits phloem tissue of elm, and as the pathogen builds up in tissue, it becomes a metabolic sink for photosynthetic products.  Phloem then degenerates downstream from these sinks, causing root mortality in fine roots and subsequently in larger ones.  As this process ensues, tree canopies begin to show yellowing symptoms as described above. 

Figure 2.  Petioles droop and turn downward as elm yellows disease advances.
Hosts of the elm yellows bacterium are limited to elm species, particularly native elm, including the American elm (U. americana) and winged elm (U. alata).  Chinese elm (U. parvifolia) is more tolerant of infection and often remains unaffected in areas where disease has killed native elm. 

Spread of the bacterium is believed to be caused by several species of leafhoppers and possibly spittlebugs, although the white-banded elm leaf hopper has been confirmed as the primary vector.  These insects inoculate trees during summer or early autumn as they feed. 
Figure 3.  Within a few weeks of symptom development, elm yellows causes leaves to turn brown.  Leaves may fall or remain attached to trees for several weeks.

Control of elm yellows is not possible and control of insects is not practical.  Infected trees should be removed as soon as possible to prevent spread of disease.  Confirmation of elm yellows requires a molecular diagnostic test.  Non-elm or tolerant elm species, including Asian species and hybrids, should be used as replacement plants.

Thursday, July 25, 2013

Downy Mildew in Grape – Secrets to Successful Disease Management

Experienced grape growers saw it coming.  New growers hadn’t a clue.  Regardless, my crystal ball told me that with months of rain would come severe outbreaks of downy mildew in vineyards. 

Grape downy mildew has reached epidemic levels in some vineyards in Kentucky and possibly the Midwest.  The pathogen that causes the disease (Plasmopara viticola) is a water mold, which warrants special considerations for disease management.  Let’s begin with a quick overview of water molds (oomycetes, to be exact). 

Water Molds

Water molds are different from true fungi.  In fact, they are not related.  Most importantly, water molds require free water to complete their life cycles.  Initial infections often occur during rainy spring weather as temperatures begin to warm.  After infection, pathogens release large numbers of “swimming” spores (zoospores) that move in films of water (damp leaves or moist soil).  This is the repeating stage of disease that leads to epidemics if wet conditions persist.  Spores are spread by splashing water and wind-driven rain.  In addition to downy mildew pathogens, many root rotting pathogens (Phytophthora and Pythium) are water molds. 
Figure 1 - Early symptoms of grape downy mildew include yellow spots on upper sides of leaves.


Downy Mildew

Downy mildew symptoms are quite distinct.  Upper leaves are the first to develop noticeable symptoms.  Yellow circular to blotchy spots can quickly enlarge and become bright yellow (Fig 1).   As disease progresses, leaf tissue becomes reddish brown, and centers of spots becomes necrotic (dead tissue) (Fig 2).  Extreme disease conditions result in a coalescing of spots into large necrotic areas.     
Figure 2 - As downy mildew spreads, leaf tissue becomes necrotic.

The most characteristic symptom of downy mildew is the “downy” fungal masses that develop on undersides of leaves (Fig 3).  If weather remains rainy or humid/foggy, pathogens will begin producing spore capsules (sporangia) on microscopic branched structures (sporangiophores).  This branching gives the disease its fluffy, downy appearance.  Sporangia can spread to healthy plant parts by wind or rain, and then open to expose infective, swimming zoospores.  This repeating cycle is dependent upon temperature and availability of free water. 

Figure 3 - The most characteristic symptom of downy mildew is the "downy" fungal masses on undersides of leaves.

Downy mildew pathogens also produce another spore type, thick-walled overwintering spores (oospores), at the end of the season.  These spores drop to the ground and overwinter in leaf debris or in soils.  In spring, they germinate just as grape begin to bloom.  Thus, early fungicide protection is critical in order to combat the initial phase of disease.  Moreover, an effective disease management program (described below) will help eliminate some of the inoculum (oospores) that before they overwinter. 

Damage Caused by Downy Mildew

Effects of infection are two-fold.  First, diseased leaves fail to properly photosynthesize, while severely infected leaves drop, leading to inadequate energy production (Fig 4).  Secondly, grape berries may become infected, leading to yield and quality losses (Fig 5).
Figure 4 - Advanced symptom development can lead to reduced photosynthesis and leaf drop.

Fruit are susceptible to infection from bloom until 3 or 4 weeks after bloom.  After that, they become resistant to infection.  Berries may not develop symptoms until several weeks after infection.  Affected fruit become soft and brown and do not mature.  Like foliar infections, infected berries become covered with downy fungal growth when conditions are wet or humid.  While fruit become resistant to infection as they mature, cluster stems (rachis) do not.  Thus, infections in these cluster stems can spread internally to berries.  Additionally, young shoots, leaves, and tendrils remain susceptible to infections throughout the growing season.
Figure 5 - Grape berries become infected between bloom and 3 to 4 weeks after bloom.  Symptoms, however, may not develop until several weeks after infection. 

Disease Management

Growers must combine cultural and chemical practices to effectively manage downy mildew in grape vineyards. 

Cultural practices are important for both conventional and organic growers.  Maintaining dry foliage is important.  Plant spacing, pruning, tucking, and other practices that improve air circulation will help foliage dry faster, and thus, conditions become less conducive for disease development.  Surface and internal vineyard drainage can also help reduce moisture levels within canopies.  Next, sanitation should not be overlooked.  To the extent possible, remove diseased leaves, fruit, and other plant parts from vineyards.  This will help to prevent fallen debris from becoming a home for overwintering pathogens.  Some species and cultivars have some resistance to downy mildew.  See page 36 of the Midwest Small Fruit and Grape Spray Guide ID-94 for a partial listing of tolerant grapes. 

Fungicides are a vital part of management of downy mildew.  Protectant sprays should begin at bud break and continue throughout the growing season.  Keep in mind though, that fungicide applications between bud break and 3 to 4 weeks after bloom are the most critical.  When selecting fungicides, remember that the downy mildew pathogen is a water mold, not a true fungus.  Therefore, not all fungicides will be effective against infection.  Refer to Effectiveness of Grape Fungicides PPFS-FR-S-18 or the Midwest Small Fruit and Grape Spray Guide ID-94 for up to date fungicide information.

Additional information on grape production and disease management can be found online at the UK Department of Plant Pathology’s website.  http://www2.ca.uky.edu/agcollege/plantpathology/extension/pubs.html#Smallfruit

Monday, July 15, 2013

Aerial Blight Infections on Vinca and Other Herbaceous Annuals

Aerial blight (also referred to as shoot blight) has been popping up in landscapes and garden centers.  Typically, two different organisms can cause aerial blight symptoms – Rhizoctonia solani (a true fungus) and Phytophthora parasitica (a water mold).  Recent outbreaks of aerial blight in Kentucky have been reported on vinca (Figures 1-3), calibrachoa (Figure 4), and petunia, each caused by the Phytophthora pathogen.  Thus, the following information will be specific to Phytophthora aerial blight.
Fig 1 – Initial infections by the aerial blight pathogen occur on leaves of vinca.
Phytophthora species are water mold pathogens.  Briefly, that means that they must have free water to complete their life cycles (produce spores, infect, and cause disease).  During wet weather (frequent rains) or under excessive water or humidity (greenhouse conditions or heavy irrigation), water mold pathogens proliferate.  Clearly, this year’s rainy conditions are favorable for disease. 

Phytophthora aerial blight, like other water mold pathogens, is no different.  It thrives in soils of heavily irrigated or otherwise wet landscapes and in production greenhouses.  Infections occur when soilborne pathogens splash up onto stems and foliage.  Leaves become blighted (rapid collapse) (Figure 1) and then infection spreads to petioles (Fig 2) and stems (Fig 3).  Lesions on lower stems cause girdling and entire branches then fail. 
Fig 2 – Infection spreads from leaves, down petioles, and then to stems.

Once plants are infected, fungicides do not cure disease.  Affected plants should be destroyed as soon as possible to prevent diseased tissue (and the pathogen) from building up in landscape soil and greenhouse floors.  Homeowners should consider improving drainage, mulching to prevent splash, and switching to drip irrigation.  No fungicides are recommended for residential or landscape use.  Commercial growers, on the other hand, should employ a preventative program for healthy plants if nearby plants become infected.  Phosphorus acid fungicides (e.g. Aliette) are effective against water mold pathogens and are recommended for protection against Phytophthora aerial blight. 

Fig 3 – Progression of symptoms to stems.

More information for commercial greenhouse growers can be found at

Landscape and homeowner information can be found at

Fig 4 – Advanced symptoms of aerial blight on calibrachoa (million bells). 

Monday, May 20, 2013

Anthracnose Diseases of Shade Trees a Problem this Spring

Anthracnose Diseases of Shade Trees

This spring has been cool and wet, leading to slow emergence of leaves on many shade trees.  This combination of favorable weather conditions and slow leaf maturity created ideal conditions for development of anthracnose disease on several common shade trees. 

In short, the term anthracnose refers to a symptom that causes dark blotching and often leaf distortion. Defoliation (leaf drop) often occurs during severe infections.  The disease often is not fatal, and a new flush of foliar growth immediately follows.  Causal fungi may also infect twigs and branches, which develop into cankers and girdle stems. 

Anthracnose diseases are not caused by the same fungi.  In fact, causal pathogens are quite host specific, meaning that the anthracnose pathogen on dogwood will not infect ash, etc.  Symptom appearance and severity differ with each host and with climatic conditions. 

The fungal pathogens that cause anthracnose diseases have similar life cycles.  Spore production occurs in spring during periods of rain; without rain, sporulation (spore production) is reduced and spore dissemination (spread) is not possible.  Anthracnose fungi sporulate in spring as deciduous tree leaves emerge.  Mature leaves are resistant to infection, but slow emergence in spring exposes tender leaves to fungal spores for an extended period of time. 

Ash anthracnose. Common symptoms include brown blotches (Fig1) along leaf edges. Leaf drop often results, and then new leaves soon emerge. Causal fungus, Discula umbrinella.
Ash anthracnose

Dogwood anthracnose. Leaf spots, leaf blight, and lower branch dieback may occur.  The disease is most commonly observed on trees growing in shaded locations. This disease can lead to severe cankering, tree decline, and ultimately tree death.  Causal fungus, Discula destructiva.

Maple anthracnose. Symptoms begin as leaf spots (Fig 2) and may progress into shoot blight and shoot cankers. Leaf spots with brown, somewhat angular symptoms may be confused with tar spot (spots are round and black). Symptom development and susceptibility vary with tree species, but lesions often follow veins.   Causal fungi, Discula sp. and Kabatiella apocrypta.
Maple anthracnose.

Oak anthracnose.  Not commonly observed in Kentucky. Irregular brown spots develop on leaf tips and along veins.  Causal fungus, Apiognomonia quercina.

Sycamore anthracnose. Young, expanding leaves develop irregular dark, necrotic blotching centered along leaf veins or edges. These dark blotches may turn tan-colored as the diseased areas of the leaves dry out. Blighting of twigs or shoots may follow. Trees produce new foliage rather quickly, but affected branches may remain crooked (lateral shoots became dominant when terminals were killed). Also affects London plane tree.  Causal fungus, Apiognomonia veneta.   

For most trees, with the exception of dogwood, anthracnose disease is not lethal.  However, repeated defoliation can be stressful to trees.  Additionally, persistent rains and disease spread can lead to infection of twigs and branches.  Good cultural practices are important to reduce disease:

  • Anthracnose is favored by a moist environment. Select a planting site with a sunny eastern exposure to promote rapid foliage drying early in the day.
  • Rake and destroy fallen leaves, as they can be a source of inoculum (fungal spores).  Do not compost.
  • Remove dead twigs and branches, as fungi can overwinter in dead wood.  
  • Reduce plant stress when possible.    
  • Avoid wounding, such as bumping with mowing equipment and making jagged pruning cuts. The dogwood anthracnose pathogen can enter trees through wounds to branches or trunks.
  • Maintain mulch 2-3 inches thick over the root zone and beyond the drip line (not against the trunk) to help maintain soil moisture and to protect trees from lawnmower injury.
  • Protect trees from drought.  Water at least once a week during hot dry months using soakers or drip irrigation.  Avoid overhead sprinklers; wet foliage favors sporulation and infection.
  • Do not transplant dogwood trees from the wild, as they may be infected with anthracnose fungi. Purchase healthy trees from a reputable nursery.
  • Diagnose and treat insect and disease problems as soon as possible.
  • Plant disease resistant dogwoods such as C. florida 'Appalachian Spring' or oriental dogwoods (Cornus kousa) for high risk sites, such as those with heavy shade and nearby diseased trees.
  • Fungicides are often not recommended.  They can be costly and it is difficult to effectively cover large trees. Commercial nurseries, on the other hand, should protect trees with fungicides.  Dogwood that are threatened by anthracnose may benefit from early spring fungicide applications.
For more specifics on these anthracnose diseases, see
Anthracnose Diseases of Shade Trees http://www.ca.uky.edu/agc/pubs/ppa/ppa17/ppa17.pdf

Monday, May 6, 2013

Two New Strawberry Viruses Detected in Kentucky.

Two New Strawberry Viruses Detected in Kentucky. The viruses (strawberry mottle virus, abbreviated SMoV; and strawberry mild yellow edge virus, abbreviated SMYEV) originated from a plug producer in Nova Scotia. In the aforementioned case,... three growers shared a shipment of plants, but only one of the growers has seen symptoms. The other two growers have not.

We encourage strawberry growers to contact their brokers to determine the source of his/her plants. Those with high risks may need to take some of the precautionary steps outlined below.

An article describing the two viruses in more detail is available at http://extension.psu.edu/plants/tree-fruit/news. Briefly, SMoV and SMYEV are transmitted by aphids. SMYEV infects only strawberry, but SMoV can also infect the weed common lambsquarters. Therefore, we encourage high-risk growers to scout for aphids and to implement a solid weed management program.  

 Finally, remember that virus diseases cannot be cured. We recommend that symptomatic plants be destroyed to prevent spread to healthy plants. If you determine that your plants originated from the Nova Scotia area, please do not hesitate to contact me for more specific information.

Sunday, April 21, 2013

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.

Monday, March 11, 2013

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.