Untangling the Web of Copper Fungicides

Fire blight season is approaching, and delayed dormant applications of copper fungicides are commonly recommended for management of various tree fruit diseases.  But there are so many...

Below is a summary of copper formulations, their characteristics, and their limitations. 

Copper Fungicides

·       Fixed Copper

o   Safer for plant tissue than “bluestone” copper (see below)

o   May be used throughout growing season, but may cause fruit russetting

o   Low solubility in water, lower risk for phytotoxicity

o   Release copper ions slowly (with water/rain), longer residual

o   Slow drying time (rainy conditions) increases solubility, ion release, and phytotoxicity

o   Acidic conditions/additives increase solubility, ion release, and phytotoxicity

§  Adjuvants, phosphorus acid fungicides, and mancozeb lower pH

o   Use high rates during dormancy for fire blight management (until ½” green)

o   Lower rates during growing season for management of other diseases, may add lime

o   Common forms of fixed copper fungicides

§  Basic copper sulfate – Cuprofix, Basicop, Phyton, Agristar

§  Copper Hydroxide – Kocide, Champ, Badge, NuCop, CuPro

§  Copper oxychloride sulfate – C-O-C-S

§  Cuprous oxide – Nordox, ChemCopp

·       Copper sulfate pentahydrate – bluestone

o   Dormant spray, only

o   CuSO₄.5H₂O

o   Highly soluble ions, phytotoxic

o   Often combined with lime to help tie up copper ions

o   No residual activity, rapid release of copper ions

o   Common brands of copper sulfate

§  Mastercop, Magna Bon, Aquavet, Delcup

  

Tree fruit diseases managed with copper fungicides:

•                 Fire blight (spray guide recommendations: dormant – label: silver tip to green tip)
•                  Apple scab (dormant to pink)
•               Bacterial canker (after harvest and late dormant)
•                Bacterial spot (dormant/budswell, pink, and petal fall)
•                Peach leaf curl (dormant)
•                Cherry leaf spot (after petal fall)
•                Black knot (dormant)

Copper is an antimicrobial; it is not selective.  Kills any exposed plant cells, bacteria, and fungi

Large numbers of copper ions (rapid release of ions) are phytotoxic to plant tissue, especially leaf tissue

Copper fungicides are not systemic and wash off with rain.  Fixed coppers have more residual activity due to slow release of copper ions.

Metallic copper equivalent is the amount of copper available for fungicidal activity (different from active ingredient).  Basic copper sulfate usually contains the highest metallic copper equivalent.

Copper can accumulate in soils, inhibit plant growth, and is toxic to microorganisms and earthworms

More on fire blight at http://nicolewarduk.blogspot.com/2013/04/fire-blight-infections-occur-during.html

 

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 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.

Freeze Damage and Fruit Diseases: Should You Abandon Your Spray Program?

Should you maintain your fungicide program after fruit loss?

After two nights of freezing temperatures (April 10-11, 2012), many apple growers reported some level of crop loss.  Susceptibility to freeze damage results from an early season when apple bloom began as early as mid-March in some areas.  I saw few late-varieties still in bloom earlier this week, but for the most part, apple flowering was complete when cold weather set in.

According to weather reports, temperatures did not get low enough to impart severe crop damage.  However, some growers have already reported losses.  I have been receiving questions regarding fungicide spray schedules for complete and moderate-loss orchards.  Below are a few disease facts to consider before abandoning your fungicide program.

 Apple

·         Fire blight bacterium was not active during the last few weeks due to dry weather.  Now, this cool dry weather continues to suppress the pathogen. 

o   Warm wet weather can reinvigorate the bacterium and raise risk of infection.

§  Dead blossoms cannot become infected.

§  Secondary (rat tail) blossoms can become infected.  These blossoms usually develop later, so monitor bloom.  If risk is high during secondary bloom, apply streptomycin.  Remember, check CougarBlight (see below) for risk assessment in your area. 

§  Shoot/twig blight phase of the fire blight disease can occur after bloom.  Young tender growth is most susceptible. 

·        Twigs and tissue damaged by freeze, hail, etc.  can become infected, especially when temperatures are warm and rainy. 

·         Twigs and shoots are can become infected even when there is not fruit.

·         Consider the level of risk by monitoring CougarBlight. 

o   Copper is a good choice if fruit load is minimal; streptomycin is recommended for fruit-bearing apple. 

o   If orchards have a history of twig blight, Apogee provides excellent control of twig blight.

§  Chances of a 50-75% crop are high, even though some growers fear the worst.  Evaluate crop losses (and non-losses) as soon as possible.  There is a possibility of at least a moderate fruit load this year.  Consider yield when adjusting spray schedules.  Good yields should receive regular spray regimes.

§  Ideally, plant pathologists prefer that growers maintain a sufficient fungicide program, even after complete fruit loss.  However, economics influence growers’ actions, and many growers opt for a reduced-pesticide regime.  Consider the following and assess your particular situation.

·         In the case of complete fruit loss, fire blight disease management can continue with copper sprays, alone. 

·         If yield potential is moderate to high, growers should follow their regular spray program as closely as possible.  This is a decision that should be based on individual situations.   

·         Bactericides should be applied during bloom or during spans of succulent tender growth if fire blight risk is high.  When conditions are wet and temperatures are above 60˚F, fire blight can infect.  

·         Orchards with a history of fire blight should be sprayed on a regular schedule, regardless of fruit load. 

·         Highly susceptible varieties (i.e. Fugi, Gala) require a regular spray schedule, regardless of fruit load.

·         If risk is low, consider that early copper and/or streptomycin sprays should have reduced inoculum, thus far.  However, proceed with caution.

·         Scab will be active, regardless of fruit load.

o   Continue to protect trees from scab.

§  Do not abandon your scab-management spray program.  However, a low-input programs may be considered – again, from an economic standpoint, not a plant pathology standpoint. 

·         Captan is a lower cost alternative that may be considered.

·         Fungicides may be applied at wider intervals if weather is not conducive for disease.

§  A low-input fungicide program this year will probably result in higher-than-normal disease pressure next year.  Be prepared to follow a strict spray schedule in 2013.

·         Growers should consider potential yield when evaluating low-input spray programs.  This is a decision that should be based on individual situations.

Peach

o   Even in the event of fruit loss, disease management, at some level, is required.  Protection of this season's foliage will positively influence next year’s fruit.

§  Monitor foliar and twig disease outbreaks carefully.

§  A low-input, lower cost spray program can include captan + sulfur. Growers should consider orchard history and weather conditions before selecting a low-input disease management program.

§  Alternatively, wider spray intervals may be suitable if weather is not conducive for disease.

Grape

o   Good disease management programs in the past, as well as during dormant and pre-bloom fungicide applications this season, should reduce fungal inoculum. 

§  Healthy vineyards that suffered complete fruit loss should not have severe disease problems. 

§  Vineyards with high to moderate fruit loss may opt for cheaper fungicides or wider spray intervals.  See above comments for apple and peach.

§  Monitor downy mildew infections in all vineyards.  Those with complete or moderate fruit loss may opt to treat downy mildew outbreaks instead of maintaining a preventative program.  As discussed above, this is not recommended, but economics may influence growers’ decisions. 

All growers should be utilizing UK’s Cougarblight predictive system for fire blight risk in apple.

It is extremely easy to use, as growers should first click on http://wwwagwx.ca.uky.edu/plant_disease.html. Next, click “Fire Blight” on the left side of the screen. Choose the weather station that is closest to the orchard by clicking the arrow under “Station” in the center of the screen. There are a few options below, such as the history of fire blight in the orchard. Finally, click “Submit Choices.” The next screen will describe the risk of infection in the orchard.

What You May Not Know about 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).  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.

Blighting of shoots, also called shepherd's crook, is the most recognized symptom of fire blight on apple.

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).  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). 

Initial infection by the fire blight pathogen occurs through blossoms.  Notice bacterial ooze come from the pedicel.

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.  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 PPA-34 and PPFS-FR-T-7. 

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