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

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

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.

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

Chrysanthemum Dieback – Rhizoctonia is Likely the Culprit

Dense canopies and frequent overhead irrigation of fall mums create ideal conditions for many plant pathogens, especially web blight and stem rot.  In greenhouses, plants grow under tight spacing and high humidity.  Furthermore, plant compactness creates microclimates within canopies.  These extreme conditions are conducive for growth of the web blight and stem rot pathogen, Rhizoctonia solani.  Unfortunately, some of these diseased plants make their way into retail centers and our front porches.

Figure 1– Stems and crowns infected by Rhizoctonia solani result in dieback in the upper canopy.  Photo by NC State.

 

Symptoms:  Stem or leaf dieback is often the first recognizable symptom.  This dieback is caused by infections of stems at the base of shoots and branches or by infection of roots and lower stems (Figure 1).  Opening up the canopy will often reveal stem lesions and/or webs or strands of fungal tissue (mycelia) (Figure 2).  Infected leaves appear water-soaked or necrotic, often becoming matted together with the web-like mycelia.

Figure 2– Under wet conditions, Rhizoctonia may spread to upper plant parts, inducing web blight symptoms.

 

Disease Management:  Both cultural practices and fungicides are required for proper disease management.  Keep foliage dry by avoiding overhead watering, by increasing air circulation (wider spacing, increased sunlight), and by practicing strict sanitation (remove diseased tissue and clean up fallen leaves).  Homeowners may use propiconazole (Green Light Systemic Fungicide), mancozeb (Mancozeb or Dithane), or captan (captan) fungicides.  See the Homeowner’s Guide to Fungicides.  Commercial growers and landscape professionals may take advantage of a wider array of fungicides, such as the active ingredients azoxystrobin, fludioxonil, iprodione, PCNB, pyraclostrobin, thiophanate-methyl, trifloxystrobin, and triflumizole.  Refer to the following publications for specific trade names:  Fungicides for Management of Diseases in Commercial Greenhouse Ornamentals and Fungicides for Management of Landscape Woody Ornamental Diseases.  Consult labels for specific information.

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.

Fire Blight Damage on Flowering Pear

Homeowners continue to question me concerning management of fire blight in flowering pear, crabapple, cotoneaster, hawthorn, and pyracantha.  Shepherd’s crooks and spur dieback occurred in March or April, as pathogenic bacteria infected flowers or young shoots.  Often, homeowners do not notice damage until later in the season, and inquiries continue for weeks after damage occurred.

There is no management option during this time of year, as the fire blight bacterium is not currently active.  Hot summer temperatures suppress bacterial growth, and plants are able to compartmentalize and wall off spread.  Thus, visible symptoms are the result of early infections. 

Current recommendations indicate that pruning of blighted twigs and cankered branches should be delayed until winter when risk of disease spread is lowest.  Under certain circumstances, homeowners or commercial landscape contractors may choose to prune infected branches during the growing season.  Only young, vigorous trees should be considered, and care should be taken to prevent bacterial spread.  Always avoid working with wet plants.  Cut branches at least 6 to 8 inches below cankers, disinfesting pruners between each cut (10% Lysol disinfectant, 10% bleach, or rubbing alcohol).  Ideally, winter pruning is recommended. 

Disease management includes both cultural practices and preventative bactericides.  Because the fire blight bacterium overwinters in cankered branches, removal of diseased plant tissue before bud break (mid to late winter) is critical.  Copper applied as buds swell (late dormancy or silver tip) reduces build-up of bacterial cells, especially during warm rainy spring seasons.  Streptomycin applications are only recommended for fruiting apple and are not labeled for use in the landscape. 

See earlier posts for more information on the biology of the fire blight bacterium and for management in orchards.