Scab On Apple Trees: Indentifying And Treating Apple Scab Fungus

Scab On Apple Trees: Indentifying And Treating Apple Scab Fungus

By: Kristi Waterworth

Apple trees are an easy-care addition to any home garden. Beyond providing fruit, apples produce beautiful blooms and larger varieties make excellent shade trees if allowed to reach full height. Apple tree owners everywhere should read on to learn about controlling apple scab in their trees.

What Does Apple Scab Look Like?

Apple scab fungus infects developing apples early in the season but may not become visible on fruits until they’ve begun to expand. Instead, apple scab first appears on the undersides of the leaves of the blossom clusters. These fuzzy, roughly circular, brown to dark olive green lesions may cause leaves to distort or crinkle. Scabs can be small and few, or so numerous that leaf tissues are completely covered in a velvety mat.

Fruits may be infected at any time from bud set to harvest. Lesions on young fruit initially look much like those on leaves, but soon turn dark brown to black before killing surface tissues, causing a corky or scabby texture. Scabs on infected apples continue to develop even in storage.

Apple Scab Treatment

Apple scab is difficult to control if your tree is already infested, but you can protect future harvests armed with a little apple scab information. Apple scab remains dormant in fallen leaves and on fruit left attached on the tree and lying ground. Sanitation is often enough to control a mild infection; just make sure to burn or double bag all the material to prevent the disease from spreading.

When sprays are necessary, they should be applied between bud break and a month after petal fall. In rainy weather, applications every 10 to 14 days may be necessary to prevent apple scab from taking hold. Use copper soaps or neem oil when apple scab is a risk in the home orchard and keep fallen debris cleaned up at all times. If you can prevent apple scab early in the year, it’s unlikely to cause you problems as fruits develop.

In areas where apple scab is a perennial problem, you may want to consider replacing your tree with a scab-resistant variety. Apples with excellent scab resistance include:

  • Easy-Gro
  • Enterprise
  • Florina
  • Freedom
  • Goldrush
  • Jon Grimes
  • Jonafree
  • Liberty
  • Mac-free
  • Prima
  • Priscilla
  • Pristine
  • Redfree
  • Sir Prize
  • Spigold
  • Williams Pride

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Controlling Fungus & Apple Scabs on Apple Trees

Related Articles

Apple trees provide home gardeners with delicious fruit for snacks and baked goods as well as attractive foliage. Several species of apple trees fare well in U.S. Department of Agriculture hardiness zones 8 to 10. However, caring for an apple tree may mean warding off and controlling a variety of fungal diseases.


There are a few options for managing apple scab. Spraying fungicides early in the season is just one option. You can read more about products and timing here: https://www.extension.purdue.edu/extmedia/bp/bp-1-w.pdf

This article provides a list of options, but also note that general purpose fruit sprays such as “home orchard spray” or an “all purpose fruit spray" can also be used.

Information about how to apply the specific product you choose will be on the label of the product. You must follow the directions on the label - these directions are often unique to each product. I am not sure about possibility of staining siding. I would look to see if they provide any details about that on the label and do your best to be precise when spraying.

You can also use some other tactics besides fungicides to manage apple scab:

1. Plant resistant cultivars

2. Rake and remove all fallen leaves. This will reduce the amount of overwintering pathogen present to infect foliage next year.

3. Some suggest applying urea (46-0-0) to foliage before leaf drop or to fallen leaves in the spring before bud break. This essentially helps microorganisms in the soil break down infected leaves and reduces the pathogens ability to overwinter.


Fact Sheet: Apple Scab

What is apple scab?

Apple scab is a major disease of apples and crabapples worldwide. It is caused by the fungus “ Venturia inaequalis” . It causes repeated defoliation in spring and summer, resulting in fewer flowers and weakening of the tree, which leads in turn to other diseases. In addition, scab lesions on apple fruit are undesirable to the consumer, making them unsellable and resulting in significant economic loss every year.

What does apple scab look like?

  • First presents as lighter green areas that become olive green with fuzzy margins (spore production) on both sides
  • As the disease progresses, the spots develop a more prominent outline and became black and velvety
  • Leaves may became distorted and pucker and will turn yellow and drop prematurely

  • First presents as water soaked areas that turn into velvety green to olive brown lesions
  • As lesions develop they have a blistered or “scabby” appearance with a distinct margin
  • Will lead to cracking and may cause deformities and uneven growth

  • Dark green lesions at the base of flower, on sepals and on stem pedicels before and during bloom

Are there other hosts of apple scab?

In addition to apples and crabapple (Malus spp.), hawthorn (Crataegus spp.), mountain ash (Sorbus spp.), firethorn (Pyracantha spp.), loquat (Eriobotrya japonica). Different but closely related Venturia species cause scab on European and Japanese pear, cotoneaster species as well as common pear (Pyrus).

Where does apple scab come from?

The fungus Venturia inaequalis overwinters on fallen infected leaves. May overwinter in the buds in milder climates. Ascospores formed in early spring are released and carried by the wind, causing primary infections in the rainy season. Asexual conidial spores cause secondary infections throughout the spring and summer. Ideal temperatures for apple scab infection is 65-75 ° F with high humidity. Once infected, trees can continually re infect themselves and neighboring trees.

How do I prevent and control apple scab?
  • Plant resistant varieties
  • Prune for better air movement and sunlight penetration for drying /remove water sprouts
  • Remove of fallen leaves and orchard sanitation in the winter
    • Spray 5% solution of urea in the autumn to aid in the breakdown of leaf tissue (42 lb urea in 100 gallons of water). Since nitrogen is being applied in the orchard, the fertilizer program needs to be adjusted accordingly.
    • Shred leaf litter using a flail mower or remove leaf litter by raking, sweeping, or vacuuming are additional options.
  • Use fungicides as appropriate
Short animated disease fact sheet: ‘Apple Scab A Fungal Disease of Apples ’.


Overview

  • Apple scab is the most important disease of apples in New England, and if left unmanaged, will cause significant damage to fruit and leaves.
  • Infections start in the early spring, initially caused by fungal spores from leaves infected the previous year that lie in or next to an orchard. New infections produce more spores, rapidly spreading scab during wet weather in spring and early summer.
  • Management should involve both cultural and chemical control, with fungicide sprays guided by weather conditions and fungicide properties, preferably using disease forecast models and reliable weather data for the orchard site.
  • Scab-resistant cultivars have been grown commercially on a limited basis and can eliminate the need for scab fungicides, though some fungicide applications will probably be needed for other diseases.
  • Sanitation targeting apple leaves in the orchard should be done in fall or early spring to decrease scab risk.
  • Resistance to fungicides is common in apple scab. Application strategies to reduce resistance risk, such as mixing different FRAC groups, including multi-site fungicides, and limiting amounts of any one FRAC group per season should be used.

Symptoms

Apple scab infections occur on leaves, shoots, blossoms, and fruit of apple trees leaf and fruit infections are most common, and the first leaf infections may show up as early as three weeks after buds break as velvety-brown to olive-colored spots on the underside of blossom cluster leaves. New infections can develop on other leaves as they emerge. These spots turn black. Diseased leaves may turn yellow, die and drop prematurely. Early fruit infections look like leaf infections, but over time become brown and corky. Fruit infected early in the season may become misshapen and can crack as it develops. Early fruit infections often appear near the blossom (calyx) end of the fruit. Later lesions can be anywhere on the fruit. Late summer fruit infections are not visible at harvest but can develop in storage as tiny spots, “pin-point” scab. (See illustrations at the end of this fact sheet)

Disease Cycle

V. inaequalis overwinters in apple leaves infected the previous season that fell to the ground in or close to the orchard. Warming temperatures in the spring around bud-break stimulate the fungus to make ascospores in old, overwintered leaves. The first mature spores are generally available at the same time trees are first producing green tissue, green tip. Ascospores continue to be produced and released until approximately one to two weeks after petal fall, though this timing varies.

Daytime rains release mature ascospores into the air when they are mature. Those spores may land on emerging apple leaves or new fruit, causing primary infections if the tissue stays wet for long enough. The length of a wetting period needed to cause infection varies with temperature. Near freezing, leaves must be wet for 2 days to be infected. At 61ºF to 75ºF infection takes only 9 hours. After infection, it takes from 9 to 17 days from the time of infection for visible symptoms to show, again depending on temperature.

Primary infections produce conidia, spores that cause secondary infections. Several additional secondary infection cycles can occur during a growing season, depending on rain, though apple tissue becomes more resistant to scab as summer progresses. In the fall, leaves drop and a new generation of ascospores develops the next spring.

Management

A key to scab management is preventing primary infections early in the growing season. If primary scab is controlled, then there is no need to continue scab fungicide applications during the rest of the growing season. If it isn’t, keeping fruit from being infected will require several fungicide applications. Primary control greatly reduces the chance that resistance to fungicides will develop, and reduces the chance of scab in the next season.

Monitoring: To manage scab efficiently and effectively, it is highly recommended that growers either maintain a weather station at the orchard, or subscribe to a weather monitoring service. Linking weather data to a decision support system that can evaluate scab risk gives valuable management information.

The amount of scab present in an orchard after harvest will have a significant impact on scab risk in the next growing season. Significant scab damage will result in a large amount of inoculum the next spring, increasing the chances for scab infections. At the same time, no scab in an orchard greatly reduces scab risk the next year.

Control Strategies

Cultural/Resistance:

  • Eliminate wild or untended apple trees from areas adjoining the orchard.
  • Apply 5% urea to trees after harvest or to leaf litter in the fall or spring to hasten leaf decomposition and reduce primary inoculum.
  • Chop leaf litter on the orchard floor in fall or early spring to speed up leaf decay and destroy scab inoculum.
  • Prune trees to open the canopy to light, air, and spray penetration.
  • If possible, plant resistant cultivars when establishing new orchard blocks. Several good cultivars are available.

Biopesticides:

There are an increasing number of biopesticide products that have been labeled for controlling apple scab. However, while they may work reasonably well under low inoculum conditions, they are limited in their ability to manage apple scab under high disease pressure. The effectiveness of these materials can be greatly improved by carefully timing applications using an appropriate decision support system.

Chemical

There are many fungicides available to manage apple scab, including OMRI approved materials. Fungicides for a given application should be selected based on their effectiveness against scab, as well as effectiveness against other diseases. Timing fungicide applications relative to infection risk is critical, and fungicides should be applied based on timing information from weather data and decision support systems.

The apple scab fungus can become resistant to a wide range of fungicides. To decrease the risk that this will happen, use fungicides with different FRAC groups, applying them alternately, and limiting the number of times any one fungicide is used in a season.

Figure 1) Top left : apple fruitlet and leaf petiole (stem) with scab lesions. Top right: early season infections worsening and leading to corking and cracking on unripe fruit. Bottom left: ripening fruit scab lesion beginning to crack in the center. Bottom right: scab lesion on apple in storage. [Photo Credit: E. Garofalo, UMass Extension]

Figure 2) Left : many light olive-colored, young scab lesions developing on leaf. Right: expanded leaf infection detail showing two separate lesions in close proximity. These lesions will develop new spore and cause additional infection. [Photo Credit: E. Garofalo, UMass Extension]

Figure 3) Scab lesion from spore landing on lower/underside of leaf. [Photo Credit: E. Garofalo, UMass Extension]

Figure 4) Top left : scab infected leaves lie on the ground overwinter. Top right: overwintered apple leaves with scab lesions still visible. Bottom left: close up of overwintered scab infected apple leaves showing fruiting bodies that contain the spore that cause primary infections in the spring. Bottom right: ascospores ejected from fruiting bodies. When these land on leaves in the spring, they cause lesions that produce new spores, leading to additional infections. [Photo Credit: E. Garofalo, UMass Extension]

Date : March 2020
Author(s): Daniel Cooley, Elizabeth Garofalo, UMass Extension, Heather Faubert, URI Extension

Additional information available on the MYIPM app: https://apps.bugwood.org/apps/myipmseries/

Note: This information is for educational purposes only and is reviewed regularly for accuracy. References to commercial products or trade names are for the reader’s information. No endorsement is implied, nor is discrimination intended against similar products. For pesticide products please consult product labels for rates, application instructions and safety precautions. The label is the law. Users of these products assume all associated risks.

This work was supported in part by funding provided by USDA NIFA Extension Implementation Program, Award No. 2017-70006-27137


How to Get Rid of Apple Scab

Apple scab is a fungal disease that affects both edible and ornamental apple tree varieties. The fungus typically develops in late summer and causes the fruit and leaves to develop green spots that eventually turn black and cause fruit loss. The spots also have a distinctive fuzzy appearance. Once apple scab develops on a tree, it is impossible to get rid of it in the same growing season. Treatment measures typically take one full growing season to completely get rid of the apple scab fungus.

Rake up all of the leaves underneath the apple tree to prevent the apple scab fungus from spreading. Although the majority of raking will occur in the fall, you should rake leaves up regularly throughout the year. In addition, collect any diseased fruit that falls from the tree as well.

  • Apple scab is a fungal disease that affects both edible and ornamental apple tree varieties.
  • Treatment measures typically take one full growing season to completely get rid of the apple scab fungus.

Place all of the collected leaves and fruit into a trash bag and dispose of it in the trash. Do not place it in a compost area since the fungus will grow.

Wait until the early spring of the next growing season,when trees are just emerging from dormancy. Place a fungicide containing lime sulfur, or sulfur into a garden sprayer and mix it with water as directed by the packaging instructions.

Watch the tree until you notice pink buds appear. Spray the limbs and trunk of the tree with the fungicide until they are saturated.

Wait until the buds open into flower blossoms, which typically occurs within two to three weeks of bud development. Reapply the fungicide as soon as the flowers open.

  • Place all of the collected leaves and fruit into a trash bag and dispose of it in the trash.
  • Reapply the fungicide as soon as the flowers open.

Reapply the fungicide two more times during the early growing season, once when the petals fall off of the apple tree and again two weeks after that.

Cornell University notes you can also use a fungicide containing copper soap during the pink-bud stage, but you should not use it for later sprayings.

Cornell also says that sulfur can be harmful to some types of apple, so ensure the varieties you are growing are compatible with sulfur treatment.


Ways to help scabs heal

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A scab is a crusty plaque that forms over a wound. Taking steps to support the body’s healing process can help get rid of a scab.

A scab protects a wound while it heals. Keeping a wound clean and covering it with a layer of petroleum jelly, such as plain Vaseline, can retain moisture and prevent the wound from scabbing over.

When a wound dries out and a scab forms, the healing process takes longer. Also, a person may find the cosmetic outcome less appealing.

Some people find scabs unpleasant or annoying, and the area around the scab may feel itchy or uncomfortable. However, it is important not to pick a scab off.

In this article, we list eight ways to help wounds with scabs heal faster. We also describe how to reduce discomfort and the risk of scarring.

The following tips can help get rid of scabs:

Share on Pinterest A person can gently wash a scab with warm water and soap.

Always keep the scab and surrounding skin clean to avoid infection.

If the wound is exposed to dirt or sweat, gently wash the area with warm water and gentle soap, then carefully pat the skin dry.

Try not to touch the scab unless it is necessary.

Touching a scab increases the chances of bacteria and other microbes entering the wound.

When scabs become itchy, some people scratch, scrub, or pick at them.

This can feel tempting, but it delays healing and increases the risk of scarring. It may also cause bleeding or redness.

To alleviate itchiness, try gently pressing on the scab with a clean, wet or dry cloth.

Gently holding a warm compress against the area can increase circulation to the wound. More blood flow brings fresh oxygen and cells that promote healing.

Also, a cold compress can reduce inflammation and pain at the site of the scab.

The American Academy of Dermatology recommend keeping the wound moist to help the damaged skin heal. They suggest using petroleum jelly to prevent the skin from drying out, as well as to encourage healing and reduce scar formation.

Some people also find other moisturizing products helpful, such as coconut oil or emollient cream, ointment, or lotion.

Coconut oil is available for purchase online, along with emollient products.

Once a scab has formed, a person only needs to cover it if it tears, oozes, or bleeds.

However, physically active people may wish to cover scabs if there is a risk that the scabs may be damaged, during sports or exercise, for example.

To cover a scab, apply a bandage just before being physically active and remove it afterward. If it is necessary to wear the bandage for more than a few hours, make sure to change it regularly.

A range of bandages is available for purchase online.

Rest can help the body heal more quickly, while restricted sleep impairs immune function.

A study published in the Journal of Applied Physiology indicates that even relatively modest disruptions to sleep can delay wound healing.

Although the delay may not be very significant, aiming to regularly get 7–9 hours of sleep a night can help boost the healing process.

Certain nutrients play roles in the regeneration and healing of the body’s tissues. Some of the most beneficial nutrients for regeneration and healing include :

  • protein
  • selenium
  • vitamin A
  • vitamin C
  • zinc

To ensure an adequate intake of these nutrients, aim to eat a balanced diet that includes plenty of:

  • fruits and vegetables
  • sources of lean protein, such as poultry, beans, lentils, fish, and tofu
  • sources of healthy fats, such as avocado, olive oil, and nuts
  • whole grains

A study in the Journal of Wound Ostomy & Continence Nursing suggests that smoking impairs wound healing. Nicotine and other chemicals in cigarette smoke reduce oxygen flow throughout the body. Doctors call this reduction hypoxia.

According to the study, smoking also lowers the number of white blood cells that make their way to the site of the wound.

In addition, the study authors note that smoke reduces the function of lymphocytes and other cells that provide protection from infection and inflammation.

Most scabs fall away on their own. However, see a doctor if a wound with a scab has any of the following characteristics:

  • severe pain
  • continuous oozing or bleeding
  • no improvement after a few days
  • gradual worsening of symptoms
  • swelling that worsens

Also, see a doctor if a fever or chills develop.

When a person sustains an injury that is very deep or painful, they should seek medical aid.

It is also important to receive medical attention for wounds caused by a human bite or a dirty or rusty object. If a wound becomes infected, consult a healthcare provider.

Scabs are a healthy part of the healing process. They protect the wound from dirt and microbes and reduce the risk of infection. A scab will typically fall off within a few days to a few weeks.

A person can take steps to promote wound healing and reduce the risk of scarring. Some of these methods also alleviate any itching or discomfort that a scab causes.

If a scab is causing severe discomfort or if the wound does not begin to improve within a few days, see a doctor. Antibiotic treatment may be necessary.


Watch the video: How to treat Apple Scab on Crabapples