Azalea diseases leaf gall

Source(s): Laurene Hall

Azalea leaf gall is a very common and widespread fungus disease that occurs in early spring on new azalea foliage. The leaves become thickened, curled, fleshy and pale green to white in color. Fortunately, this disease is more alarming than damaging.

Caused by a fungus, Exobasidium vaccinii, which is dormant in the developing buds from one year to the next. When bud growth begins in the spring, the pathogen renews activity also, and one or more of the leaves on the shoot may develop symptoms. A spore-bearing hymenium is eventually produced which completes its development on exposed leaf surfaces. Spores are blown about by air currents, some of them lodge on the plant and finally invade leaf buds. The actual damage to plants is not nearly so important as it appears to be. However, if disease is severe, the vigor of the plant can be affected due to the loss of young leaves.

Contents

Detection

First noticed soon after leaf buds open in the spring. All or only part of the individual leaf may be affected. Part of the leaf becomes distorted with a pale green to whitish, bladder-like thickening. When young, the thickened, fleshy-like leaf is covered with a white growth. As the galls age they turn brown, dry up and fall to the ground. Occasionally, a black coating may develop on the surface of the gall, particularly during rainy weather, which results from secondary invasion of the galls by the fungus Pestalotia.

Control

  1. Handpick or prune out and destroy (burn) galls.
  2. Spray with recommended fungicides, such as Daconil 2787 or Mancozeb.
  3. Serious outbreak in large plantings: spray in early spring when leaf buds just begin to open and at two-week intervals (if spring is relatively dry) through early summer (mid-June) with Bordeaux mixture which may reduce incidence of disease in the following season. Timing of sprays is critical because the spores over-winter in the bark and bud scales.

Resource(s): Common Landscape Diseases In Georgia

Center Publication Number: 44

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Tedrow: Act fast to prevent leaf gall fungus

Question: I’ve been treating my azaleas for leaf gall. I’ve totally cut some down to ground and others hand picking, spraying and giving systemic fungicide boost. I guess it’s just a wait-and-see game to see if any treatments work – but from your experience, which do you think works better? – Cheryl L. Winterville

Answer: Azalea leaf gall, or exobasidium vaccinii, is a very interesting fungus which occurs during early spring. This pathogen creates swollen azalea leaves, which are full of spores. As the disease develops, the bottom of the leaf will eventually fall off, exposing the white, spore-covered surface.

These spores will spread on the wind to the new growth of neighboring azaleas and remain dormant until next spring.

I personally have had experience with camellia leaf gall, which is caused by another exobasidium fungus with a similar life cycle. Since the infections are extremely localized to the swollen leaves, my control method of choice is pruning.

When I located an infected branch on the plant, I prune 6 inches below the infected portion. I also spray my pruners in between cuts with a diluted alcohol solution just in case any stray spores have found the blade. Since the infections are localized, you do not need to prune the plants to the ground unless the removal of numerous infected leaves and branches causes a mis-shapen plant.

It is also helpful to remove diseased, fallen leaves and mulch if the fungus has been in the area for more than one season.

The above control measures are typically sufficient to control the fungus without using a fungicide.

Keep in mind it is extremely important to do any of these controls before the spores begin emerging. If you see the white or black spore-covered leaf surface, you have already missed the control window and you will probably have the disease again next season.

Here is more information concerning this fungus from the UGA Center for Urban Agriculture:

• Send your agricultural or natural resources questions to Amanda Tedrow, Athens-Clarke County Extension agent, at [email protected] or call (706) 613-3640.

Need help with what to do in your garden?

Q What is azalea gall?

A Azalea gall is an abnormal growth produced by some azaleas and rhododendrons in response to attack by the fungus Exobasidium vaccinii. Very little is known about how the fungus enters the plant or why some plants are more susceptible than others.

Caption: Pick off any azalea galls you find

Q Which plants are likely to be affected by azalea gall?

A As its name suggests, only rhododendrons and azaleas are affected by this disease. Certain varieties seem more susceptible than others – if a variety seems to be getting hit particularly hard in your garden, then it may be worth replacing it with a different kind. Rhododendron simsii, the Indian hybrid or indoor azalea, is particularly prone to infection.

Q What does azalea gall look like?

A Individual leaves, and occasionally flower petals, are almost entirely replaced by a growth, varying in size from pea-sized to small plum-sized. This unsightly disease affects rhododendrons and azaleas both indoors and out. However, if your plants are growing well, they should resist attack. The growth is fleshy and usually pale green, though sometimes it turns slightly reddish. As the fungus develops, a powdery white coating can be seen on the gall, which is a layer of white fungal spores. If the galls are not removed, they will finally wither and turn brown.

Q How does azalea gall spread from plant to plant?

A The spores of the fungus spread the disease from plant to plant. Spores may be carried on the air, transferred by insects or by physical contact.

Q What damage does azalea gall do to plants?

A Where only a few leaves are affected, there is little or no effect on the plant. If infection is severe, the plant’s ability to manufacture food via its leaves will be reduced and the plant will be weakened. Good growing conditions, such as adequate moisture, good drainage, free air circulation around the branches and sufficient nutrients, will help to make plants more resistant to attack and better able to cope with infection.

Q Can I reduce the chances of my azaleas being affected by azalea gall?

A The azalea gall fungus is favoured by high levels of humidity, so good ventilation indoors or in the greenhouse, even in winter, will help to reduce the incidence of this disease. Keeping insect pests under control will also reduce the chance of the fungus being transferred between plants.

Q What can I do if my plants are affected by azalea gall?

A Galls that appear on azaleas and rhododendrons should be picked off and destroyed as soon as they are seen, before they turn powdery white and spores are produced. There are no chemical controls for this fungus.

Azaleas

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How to Fertilize Encore Azaleas

Encore azaleas are crossbreeds of spring-blooming azaleas and summer-blooming rhododendrons. By crossbreeding these two shrubs, Encore azaleas bloom in the spring, summer and fall. Fertilize your Encore azaleas so that they thrive and grow large, plentiful flowers.

Wait until after the last frost (usually in March or April) to fertilize Encore azaleas. If you plant your azaleas in the spring or summer, apply fertilizer after planting. However, if you planted your bushes in the fall or winter, don’t fertilize them until after the spring.

Fertilize using azalea fertilizer or azalea feed, as marked on the packaging. There are many brands of azalea feed and fertilizer, so read dosing instructions carefully. Generally, about a tablespoon of fertilizer is needed per plant. Some granular fertilizers are sprinkled over the root area of the plants, while others must first be dissolved in water before applying.

Repeat fertilizing at specific intervals. Again, each brand of feed is different, but generally, you should reapply every one to two weeks.

Stop fertilizing your Encore azaleas after August. Fertilizer encourages new buds and you don’t want new buds forming for the approaching dormant season.

My Encore Azaleas Are Not Blooming

Sometimes after planting new Encore azaleas in the ground, the plant suffers a shock and won’t flower until the next growing season. As long as the plant is growing and looks healthy, it will adapt to its environment the first growing season and bloom the following year. These azaleas are known for skipping a flowering cycle when transplanted.

Light

Encore azaleas bloom for three seasons because of how the azalea has been bred. Because the plant can bloom for so many seasons, it needs to have at least four to six hours of direct sunlight to bloom. Plants do the best in areas where there is some afternoon shade. If azaleas are planted in areas without any shade during the day, extra care is needed to keep the soil moist.

Water

Long dry spells can reduce blooming if the soil dries out. Azaleas need moist soil to keep the plant healthy and blooming. Manually irrigate the soil during dry periods, giving the plants at least 1 inch of water once a week.

Fertilizer

Encore azaleas that are not blooming or have few blooms will benefit from an application of fertilizer. Encore azaleas don’t need fertilizer in the first year, but benefit with one application every two weeks after the first growing season. The best fertilizer is one that has a 1-3-1 nitrogen-phosphate-potassium ratio. Phosphates, the middle number, promote flowering, and nitrogen, the first number, promotes foliage growth, which you don’t want if the plant is growing healthy green foliage.

How to Care for Encore Azaleas

Keep Encore azaleas consistently moist throughout their first year. After the first year, Encore azaleas don’t need to be watered regularly unless the weather is dry for extended times. If the weather has been dry, water them well in late autumn, before the first freeze.

Step 2

Fertilize Encore azaleas immediately after the first bloom with a fertilizer formulated specifically for azaleas. This is all the fertilizer that Encore azaleas require. Never fertilize in autumn, because new growth will make the plant more susceptible to damage during cold weather.

Step 3

Prune Encore azaleas as needed to maintain a pleasant shape. Otherwise, they require no pruning, and it isn’t necessary to remove spent blooms. Any pruning should be done immediately after the first blooming, because later pruning will risk interfering with the second blooming.

Step 4

Cover Encore azaleas with an insulated garden cover their first winter. After that time, a 3 to 4-inch layer of organic mulch such as pine needles or bark chips will be enough protection to insulate the roots. Spread the mulch around the plant, but don’t pile it up against the trunk.

Encore Azalea Problems

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Reduced Flowering

For abundant flowering, azaleas need four to six hours of sun per day. If planted in a shady site, Encore azaleas will not provide repeat blooms during the year. However, too much hot summer sun will injure azaleas and cause heat stress. Select a site that receives morning sun and afternoon shade.

Pests

Many pests can damage azaleas. Lacebugs are a common insect that dine on leaf chlorophyll, leaving behind yellow speckles. Encore azalea is less vulnerable to lacebugs than other kinds of azaleas. Petal fungal blight, caused by Botrytis cinerea or Ovulinia azalea, causes a mold on flower petals.

Chlorosis

Azaleas that exhibit chlorosis or yellowing leaves may be responding to their soil environment. Azaleas require well-drained soil at a pH of 5.5. The larger Encore azaleas are more flexible regarding different soil pH levels than smaller varieties of Encore azaleas, according to Louisiana State University.

When Can Encore Azaleas Be Moved?

Azalea image by Denis Morgun from <a href=’http://www.fotolia.com’>Fotolia.com</a>

According to the Encore Azalea website, fall is the best time to transplant your Encore azaleas, but it also can be done any other time of the year. The most important thing is to water your plant thoroughly and frequently for the first few weeks after you move it.

Azaleas That Bloom Twice a Year

‘Autumn Royalty’ is a variety of Encore azalea, and actually an azalea/rhododendron hybrid. In fact, this plant was voted Azalea of the Year by the American Rhododendron Society. All Encore azaleas can bloom three times per year, depending upon your location. They are grown like standard azaleas but need just a bit more sun each day. The ‘Autumn Royalty’ blooms are large, and gorgeous shade of purple.

Autumn Starlight

Another Encore azalea, this one with 3-inch white blooms with pink freckles and an occasional pink stripe, reminiscent of some petunia varieties. The light green, narrow foliage creates a delicate backdrop for the flowers. Encore azaleas prefer a somewhat acid soil, they only need to be fertilized once a year and are hardy to USDA zones 7 through 10.

Pink Craze

This azalea, from the Bloom ’N Again® line of azaleas, is cold hardy to -10 degrees F, and needs to be planted in an area of dappled sunlight. The “Pink Craze” will bloom in September and then again in the spring. The flower is a very light, delicate shade of pink.

How to Cut Back Azaleas

Cut back azaleas with a pair of sterilized garden snips. They look like a pair of scissors and can be purchased at any home and garden store. Sterilize the snips with bleach or rubbing alcohol.

Prune the azaleas in early spring before the flowers bloom. Once the azaleas begin to flower, they will have ample time to grow to maturity and produce many blooms.

Remove the branches from your azaleas that are shaded out by the other branches. These branches will eventually die out due to a lack of sunshine. Remove these first.

Snip off the smaller branches that do not produce flowers after blooms appear. These branches will only use valuable nutrition that the blooming branches could benefit from. Removing the non-flowering branches increases the following year’s blooms.

Take off the tops of the taller branches from the inside of the plant. Cut them back to the size of the height of the outside branches. Prevent the azaleas from shock by removing only a few of the taller branches at a time.

How to Fertilize Azaleas

Prune off any dead or diseased branches, as well as faded blossoms immediately after the flowers fade in mid-spring.

Remove the mulch by pulling it away from the base of the azalea. Spread slow-release, high nitrogen granulated fertilizer around the plant, following the manufacturer’s recommended rate of application. Keep the granules of fertilizer from touching the base of the plant as it can burn the bark. Replace the mulch.

Apply granulated fertilizer that is specially formulated for azaleas around the base of the plant approximately six weeks after the first fertilizer application in the north and eight weeks in the south. Use the same method of application that you used to apply the high-nitrogen fertilizer and follow the manufacturer’s recommended rates of application. Do not fertilize after July in the north. In the south, fertilize every eight weeks until early September.

Evergreen Azaleas

Evergreen azaleas grow naturally in Asian countries and bear flowers of about 2 inches across. Evergreen azalea colors include red, pink, orange, white and purple. The plant has two sets of leaves, with one set dropping during the fall and the other in the spring. The type of variety you get depends on the color. For example, The Glen Dale azalea has chartreuse, orange, pink and red colors, while the Indica (or Indian) azalea has white, red and pink colors.

Deciduous Azaleas

Deciduous azaleas can grow large with large leaves and will grow naturally in North America and Asia. They aren’t as common as evergreen azaleas. During the fall season the leaves fall off, but during blooming season in spring the colors range from orange to magenta, yellow and white.

Species and Hybrids

Evergreen and deciduous azaleas are either species azaleas or hybrid azaleas. Species azaleas mean that it was interbred and isolated from other plants during production, whereas hybrid azaleas are a mixture of azaleas and other plant species. Species azaleas grow from seedlings from their parent plants, and hybrid azaleas must be grown from cuttings of a mother plant clone.

Azaleas With Brown Leaves

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Distressed

Most azaleas prefer partial shade to full sun. If your azaleas receive too much sun and are not adequately watered they may come distressed and turn brown. Azaleas transplanted during the heat of the day may also become distressed and start to turn brown.

Watering

Plants that are yellowed and brown may indicate a watering problem. Too little water will leave the plant parched and brown. Too much water can create root rot, which drowns the roots with excess water. Carefully check azalea roots; they should be brittle. If the roots feel mushy the plant is suffering from root rot.

Seasonal Change

Deciduous azaleas, which drop their leaves in the fall, will naturally turn brown in the fall months. Don’t worry; leaves will grow back in the spring. If the leaves fall off during the summer it may point to a problem such as a diseased plant.

Disease

Leaf gall is a fungus that affects azaleas in the spring, changing leaves from green to white and then brown. The North Carolina State University notes that the disease does not harm the plant, beyond making it look bad. Remove affected leaves by hand and discard.

Lifespan of Azaleas

Azaleas have no finite lifespan. Some azaleas in Japan are reportedly hundreds of years old. An azalea can live for many generations if they are cared for properly and are planted where they have plenty of sun and good drainage.

The Best Mulch for Azaleas

Azaleas roots are shallow and mulch is vital to protect the roots in winter and maintain moisture year-round. Four to 6 inches of decomposing oak leaves or pine needles is perfect mulches. Other options are 2 inches of hardwood or oak chips or shavings.

Azalea Plants Information

Image by Flickr.com, courtesy of Mikul

Both rhododendrons and azaleas are members of the genus Rhododendron, but azaleas usually stay smaller and have smaller leaves. Azalea flowers typically have five or six stamens, while rhododendrons typically have 10.

Flower Types

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Most azalea flowers are 2 to 3 inches wide, however they range from 1/2 inch up to 5 inches. Most flowers have five petals, but double flowers can have up to 30 petals.

Some varieties of azalea plants lose their leaves during the fall and winter and enter a dormant period. Flowering usually occurs on the bare stems in spring before the leaves sprout out.

Evergreen azaleas prefer a slightly warmer climate than deciduous types and they keep their leaves all year. It is not uncommon for them to drop some leaves during a harsh winter.

Care

Image by Flickr.com, courtesy of Margaret Anne Clarke

Azaleas prefer acidic, well-draining, moist soil with organic matter mixed in. They like moderate climates, USDA zones 6 through 8, but some varieties can take lower or higher temperatures.

The Best Place for Azaleas

Azaleas grow best in well-draining soil with a pH between 5.5 and 6. Their lighting needs depend on the variety. Most azaleas prefer shade, but some azaleas need full sun to grow. Check the specifics for your variety before choosing a planting site.

Information on the Christina Azalea Plant

Christina is an azalea hybrid created in 1966 by Vuyk van Nes Nurseries. The parent plants are the cultivars Florida crossed with Louise Gable.

Description

‘Christina’ reaches a height of 4 to 10 feet and a width of 5 to 10 feet. It has oval-shaped green leaves that are medium-sized for the Rhododendron family–about 1 1/2 inches long.

Flowers

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The red or pink flowers are hose-in-hose style, which means there is one flower inside of another. Blooming occurs in mid to late spring with two to four flowers per cluster.

They like full sun to partial shade and a slightly acidic moist-but-well-draining soil. They can planted outdoors in USDA hardiness zones 6 through 9.

Uses

Hybrid azaleas are great landscape shrubs for yards in cold climates. They are able to withstand the freezing winter temperatures and may not lose their leaves.

Azaleas Losing Leaves

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Variety

Azaleas are deciduous or evergreen. Deciduous azaleas drop or lose all their leaves in the fall. They may lose leaves earlier in the season due to dry weather. Evergreen azaleas have two sets of leaves. They lose one set of leaves in fall and keep the other set as winter foliage.

Azaleas often lose leaves due to too little or too much water. When plant roots dry out, the leaves drop off. Prompt watering may revive these azaleas and encourage foliage the following season. Too much water causes roots to rot. Over-watered azaleas lose their leaves and die from waterlogged roots.

Azaleas lose leaves when they are infected with disease. Humid weather and overhead watering encourage leaf spot and other fungus problems. Leaves develop fungus blotches and curl or fall off the plant. Fungicides applied promptly usually control serious damage.

White Fly Treatment for Azaleas

Naturally occurring predators of the whitefly include lacewings, bigeyed bugs, minute pirate bugs, certain species of lady beetles (e.g. Clitostethus arcuatus and Harmonia axyridis) and parasites of the Encarsia species.

Leaf Removal

Removing leaves that have been infested with the nymphs and pupa of whitefly can help reduce the population to an amount controllable by natural predators.

Traps

Place yellow sticky traps close to infested plants at the level of the infestation, out of direct sunlight, with the sticky part facing the plant. This strategy works best in conjunction with other anti-whitefly tactics.

Vacuum

Remove adult whiteflies with a hand-held, battery-operated vacuum early in the morning when cool temperatures make the pests sluggish. Freeze the vacuum bag inside a plastic bag overnight to kill the flies before disposal.

Soaps and Oils

Thoroughly coat plants, including the underside of leaves, with insecticidal soaps and oils such as neem oil. Don’t spray drought-stressed plants or during temperatures of 80 degrees Fahrenheit or above.

Are Azaleas Green All Year-Round?

azalea rhododendron image by Canoneer from Fotolia.com

Azaleas may be evergreen, keeping their leaves all year long, or deciduous, dropping their leaves in the fall. The green leaves on some evergreen azaleas, like ‘Delaware Valley White,’ may become yellow in winter. Some deciduous azaleas, including ‘Umpqua Queen,’ also experience foliage color changes in the fall.

Winter Care of Azaleas

Stop fertilizing by July 15. Any extra nitrogen after this point will promote new shoots of growth. These young shoots are especially susceptible to cold injury and would die in the winter climate.

Refrain from watering from September into the fall. This will help harden off the azaleas for the winter. If the fall is excessively dry, give the azaleas a good watering after the first killing frost. This will provide water for the plant over the winter and will not reduce hardiness. The ground should be wet before the cold weather sets in.

Place a thick layer of organic mulch around the base of the plant in late fall. Azaleas have shallow roots that need protection from the cold fluctuations and hard freezes. Keep the mulch from touching the trunk of the shrub.

How to Prune Native Azaleas

Prune your azaleas just after they bloom. Azaleas bloom in early spring on the previous season’s growth. If you prune azaleas after they produce a flush of summer growth, the plants will have fewer blossoms the next year.

Follow dead azalea branches back to the point where the azalea is alive. Living wood will have a green cambium layer beneath the bark. If you nick the bark with your fingernail, you will reveal the cambium layer. Cut back dead azalea branches to the living wood.

Cut back an overgrown azalea by removing the longest branches back to the central trunk of the plant.

Remove diseased branches of azaleas, branches that rub against one another or weak growth at the point where the branch meets the tree.

The Best Soil Mix for Azaleas

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General Soil Preparation

Azaleas have delicate roots and require soil that is well drained and easily penetrable. Plant azaleas in beds rather than individual holes so that prepared soil is used more efficiently. Avoid putting your azalea bed under the canopy of shallow-rooted trees such as elm, maple or ash. The feeder roots of these trees will quickly grow into the improved soil and compete with your shrubs for water and nutrients.

Soil Acidity

Azaleas must have acidic soil to thrive. The ideal soil pH for an azalea bed is between 4.5 and 6.0. If you are uncertain about the pH of your soil, obtain a soil testing kit from your local agricultural extension office and collect a sample according to directions. The soil lab will analyze your sample and send back a report detailing the pH of the soil, and offering recommendations for enriching it for optimum fertility. The most common additives used to correct soil pH are limestone and sulfur — limestone to raise pH and sulfur to lower it.

Soil Texture

One of the keys to maintaining loose, well-drained soil is to amend it with organic matter. Depending on how hard or clay-based your soil is initially, add up to 50 percent organic matter to achieve a looser texture. The Azalea Society of America recommends using fine pine bark or rotted leaves for this purpose. You may also use additional topsoil. Avoid “hot” organic materials such as mushroom compost or materials containing fresh cow manure. These additives are too alkaline and will lower the acidity of the soil.

How to Plant Azalea in B.C.

Remove your young azalea from its nursery pot. If the plant sticks, cut the pot off. Plant your azalea in the spring after any risk of frost has passed.

Dig a hole just deep enough to accommodate the root ball with the soil at the same level on the main stem as it was in the nursery pot. Azaleas have very shallow root systems, so be careful not to dig too deep.

Dig the hole about a foot wider on all sides than the root ball. This will ensure that there is enough loose soil for the roots to establish themselves in.

Place your azalea in the hole and gently fill in the soil. Pack the soil gently.

How Fast Do Azaleas Grow?

According to the Gardener’s Network, azaleas can be grown from seeds, cuttings or grafting. When grown from seed, the bush can take from two to 10 years to bloom.

Care & Feeding of Azaleas

Azalea image by fabiomarc from Fotolia.com

Pruning

Azaleas may be pruned annually to control size. This is best done in the weeks just after the blooms fade. Waiting any longer risks cutting off the origin of next year’s blooms, which are set in the fall.

Fertilize

Azaleas may require a dose of acidic fertilizer a couple of times per year. Just apply to the surface of the soil around the underneath the plant and out to the drip line. If your plant is stressed due to drought, put off fertilizing until the soil is moist and conditions are better.

The roots of an azalea plant are near the surface of the soil, making dehydration a threat during dry conditions. Make sure your plant receives adequate moisture by watering with a soaker hose or drip line to a depth of about 6 to 8 inches. Don’t over-do it, though. Water-logged plants suffer decline as well.

Pests and Diseases

Although they’re typically tough plants, a few problems can affect your azalea. Look out for powdery mildew (a fungus that looks like white powder on the leaves) and petal blight (mottled or damaged blooms in spring). You might avoid powdery mildew by choosing a sunnier location for the plant since the fungus thrives in shade. Petal blight can be alleviated with an application of fungicide just as the blooms begin to show color.

Lacebugs are among the common pests for azaleas. Look for spotted or mottled leaves as evidence of an infestation. Spraying with an insecticide may reduce or eliminate this problem.

The Size of Azaleas

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Average Height

The majority of azalea varieties grow into mature, large shrubs. The average height is typically around 4 to 8 feet, according to the Arbor Day Foundation. However, some azaleas remain closer to ground covers, reaching a mature height of about 12 inches.

Average Spread

On average, the spread of a mature azalea shrub is proportionate to its height. The tall shrub varieties reach a spread between 4 and 6 feet.

Determining Size

When purchasing azaleas from a catalog or nursery, the listed height and spread is typically the 10-year height, according to the Azalea Society of America. This is the height the azalea will reach at its mature growth.

Azalea Plant Care

Grow your azaleas in partially shady locations. Ensure your azaleas are only exposed to direct sun for 4 hours each day. Azaleas can grow in sunshine, but the blooms will not last as long.

Ensure your azaleas flourish by locating them under pine, oak or holly trees where the soil is more acidic.

Cover the roots of your azaleas with an inch of mulch created with pine bark or wood chips to prevent moisture loss and weeds. Also pile mulch between each plant to about 3 inches deep.

Prune dead wood or non-flowering shoots any time. Do major pruning right after the flowers bloom to avoid cutting off the next season’s buds.

Soak the ground around your azaleas once a week rather than a daily sprinkling. The amount of water needed depends on the time of year and the climate but generally an inch per week is sufficient.

How to Prune Louisiana Azaleas

Prune Louisiana azaleas when flowering finishes in April or May. Allow the shrub to reach the desired size before attempting to control growth.

Look through the Louisiana azalea for the tallest or widest branches. Clip them off with the pruning shears. Make the cut on the inside of the bush so that the new growth will fill in gaps within the shrub’s bulk.

Remove branches that appear to be broken, weak or diseased. These are stealing nutrients from the rest of the bush. Prune them where they meet healthy wood.

Trim branches one by one until the desired shape and size of the Louisiana azalea is accomplished. Focus more on branches in the top half of the bush. Removing them will increase sunlight and air circulation to the rest of the plant.

Prune Louisiana azaleas until late June or early July. After that, there is danger of removing flower buds.

The Best Time to Prune Azaleas

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Time Frame

Prune azaleas soon after they bloom to allow for vigorous growth and a good supply of buds the following year, reports the Texas A&M Extension.

Tools

Check plants during full bloom for any wilted, dying or infected branches, which may indicate a fungus. Remove the affected areas with sterilized cutting tools until you see clean, white wood. Use denatured alcohol to keep the tool clean as you work to help prevent the spread of fungus to clean wood, recommends the U.S. National Arborteum.

Tips

Before you begin pruning, consider which branches will be shaded and might naturally become deadwood. Remove these branches first. Avoid pruning too late in the season, as tender new growth might get damaged in cold climates.

Azalea leaf and flower gall is a disease that causes concern to many home gardeners each year. It is caused by the fungus Exobasidium vaccinii. In home landscape plantings, the disease is more alarming than damaging, but in greenhouse plants grown under very humid conditions, galls may become so abundant that they cause considerable harm if control measures are not implemented. Closely related species of Exobasidium cause similar galls on other plants, including species of Arbutus, blueberry, Camellia, Ledum, Leucothoe and rhododendron.

Fig. 1. Leaf galls on azalea caused by the fungus
Exobasidium vaccinii. Note the white
spore-producinglayer on the surface of the galls.
(Photo by R. C. Lambe)

Symptoms

Exobasidium vaccinii causes leaves and flowers to become swollen, curled, waxy and fleshy (Fig. 1). The swollen plant tissues or “galls” are made up of abnormal plant tissue. Infected leaf tissue is usually pale green in color during the early stages of the disease; infected flowers are usually pinkish. Later in the season, a white spore layer covers the infected plant parts. Galls eventually turn brown and harden as the season progresses. Lower leaves on plants are usually the most seriously damaged, but under humid conditions and in shaded locations galls may occur at the ends of upper branches.

Disease Cycle

The occurrence and intensity of the disease depends on weather conditions and on the source of the causal fungus. Spores produced in the whitish mold on the surface of galls in late spring to early summer are blown and washed to leaf and flower buds where they cause new infections. Galls form the following spring. Cool, wet weather favors dispersal of the spores.

Control

Cultural Control

When only a few plants are involved, as in a home planting or a small greenhouse area, the disease is easily controlled by hand picking the galls and burning or burying them. To prevent new infections, it is important to pick the galls before the white spore layer appears. Fungicide control is generally not warranted in home landscapes.

Chemical Control

In commercial operations, a combination of hand picking of the galls and application of a fungicide may be warranted. Two applications of a fungicide containing mancozeb (e.g. Dithane), one made just before leaves unfurl in spring and one 10 days later, will help prevent new infections. Follow label rates or refer to the current Virginia Pest Management Guide for Horticultural and Forest Crops (VCE Publication 456-017), http://www.ext.vt.edu/pubs/pmg/, for details on rates and timing of application. For information on the proper use of pesticides and fungicides, refer to any current VCE pest management guide.

Resistance

Some azalea cultivars with resistance to leaf and flower gall have been reported. Resistant and susceptible cultivars of azalea are listed in Table 1. The Purple Splendor and Roseum cultivars of rhododendron are also highly susceptible to this disease.

Table 1.
Cultivars of azalea exhibiting resistance or susceptibility to azalea leaf and flower gall

Highly Susceptible Azalea Cultivars

China Seas

Hinodeii

White Gumpo

Copperman

Mother’s Day

Herbert

Rosebud

Resistant Azalea Cultivars

Amoena

Gloria

R. Poukhanese

Aphrodite

Hampton Beauty

Sensation

Coral Bells

Kow-Ko-Ku

Thinbegen

Eikan

Mrs. G. G. Gerbing

Sunglow

Faker

Nancy

Treasure

Formosa

New White

White Jade

Glacier

Pride of Summerville

Author: Mary Ann Hansen, Extension Plant Pathologist, Department of Plant Pathology, Physiology and Weed Science, Virginia Tech

Azalea & Rhododendron Diseases

Rhododendrons and azaleas are some of the most popular spring-flowering shrubs in the landscape, and healthy plants can give years of pleasure. Many diseases and other problems can be prevented by following the recommended cultural practices for proper planting and care. More information on successfully growing azaleas and rhododendrons is available in the fact sheets HGIC 1059, Azalea Care; HGIC 1058, Azalea Planting; and HGIC 1073, Rhododendron.

Root & Crown Rot

The fungus Phytophthora species causes one of the most common disease problems in the landscape for rhododendron and azalea. This fungus is a “water mold,” and thrives in poorly drained or wet conditions. A wilted plant is usually the first sign of trouble. Rhododendron leaves will curl inward and droop. Drought can cause similar symptoms. Roots of affected plants appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion.

Crown rot causes the lower portions of the stem to have a brown discoloration of the wood near the soil line. This disease is favored in poorly drained areas or when plants are set too deeply. Plants may remain without symptoms until further stressed from drought or flooding.

Prevention & Treatment: Prevention of disease is important, because chemical controls are ineffective once symptoms appear in the landscape. Begin by purchasing disease-free plants from a reputable nursery. Avoid plants that lack normal green color, appear wilted in the morning, or have dark, discolored roots. Select resistant varieties for planting from the Table below.

Plant azaleas and rhododendrons in a well-drained and well-aerated soil. Heavier clay soils should be amended with organic matter before planting. Avoid planting in areas where water can collect around plant roots.

The following azaleas & rhododendrons have some resistance to Phytophthora root & crown rot:

Azaleas:

Resistant:

  • R. sanctum
  • R. simsii (Indian azalea)
  • R. yedoense var. poukhanense (Korean azalea)
  • ‘Corrine’
  • ‘Fakir’
  • ‘Fred Cochran’
  • ‘Glacier’
  • ‘Hampton Beauty’
  • ‘Higasa’
  • ‘Merlin’
  • ‘Polar Sea ’
  • ‘Rose Greeley’

Moderately Resistant:

  • ‘Alaska’
  • ‘Chimes’
  • ‘Eikan’
  • ‘Jan Cochran’
  • ‘Morning Glow’
  • ‘New White’
  • ‘Pink Gumpo’
  • ‘Pink Supreme’
  • ‘Rachel Cunningham’
  • ‘Red Wing’
  • ‘Shinkigen’
  • ‘Sweetheart Supreme’

Rhododendrons:

Resistant:

  • ‘Caroline’
  • ‘Martha Isaacson’
  • ‘Pink Trumpet’
  • ‘Prof. Hugo de Vries’
  • ‘Red Head’
  • R. davidsonianum
  • R. delavayi
  • R. glomerulatum
  • R. hyperythrum
  • R. lapponicum
  • R. occidentale
  • R. poukhanense
  • R. pseudochrysanthum
  • R. quinquefolium
  • R. websterianum

Do not set new plants any deeper than the original soil level. Planting in raised beds is suggested. Firm the soil slightly at the base of the planting hole to prevent the plant from settling into the bed. Do not plant azalea and rhododendron plants into sites where plants have previously died from root rot. Even resistant plants may succumb under these conditions. The fungus survives in the soil and cannot be eradicated once an area is infected.

Chemicals that are available will only suppress disease and not cure an infected plant. Fungicides available for use on azaleas and rhododendrons include metalaxyl and mefenoxam. Apply all chemicals according to directions on the label.

Petal Blight

This fungal disease, caused by Ovulinia azaleae, primarily affects the flowers of azalea, but mountain laurel and rhododendron flowers can also be infected. Indian and kurume azaleas are especially susceptible. The disease starts on the flower petals as tiny, irregularly-shaped spots, giving a “freckled” appearance. On colored flowers the spots are white, and on white flowers the spots are brown. The spots quickly enlarge and become soft and watery. Flowers rot and stick to the leaves. Infection is easily spread from flower to flower by wind, rain and insects. The fungus survives the winter in the soil.

Prevention & Treatment: The most important things that you can do to control this disease in the home landscape are to pick and destroy infected flowers and avoid overhead watering. This fungus survives in the soil, so it is important to replace the ground litter with uncontaminated mulches. Fungicides are available for cases of severe infection on azaleas. Select a product that contains captan or chlorothalonil. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

Leaf Gall

Leaf gall (Exobasidium vaccinii) is a very common fungal disease in the early spring on azaleas and occasionally on rhododendrons. Some of the native rhododendron species (azaleas) are more susceptible than hybrid rhododendrons.

In April and May leaves and buds of infected plants develop distorted growth. Leaves and possibly stems become thickened, curled, fleshy and turn pale green to white. In the later stages of the disease, the galls become covered with a white powdery substance. As the galls age, they turn brown and hard.

Leaf and flower gall (Exobasidium vaccinii) on deciduous native azalea.
Joey Williamson, ©2013 HGIC, Clemson Extension

Exobasium flower gall on Catawba Rhododendron (Rhododendron catawbiense).
Joey Williamson, ©2015 HGIC, Clemson Extension

Prevention & Treatment: This disease rarely does enough damage to require chemical control. If only a few plants are affected, pick and destroy galls. If chemical control is necessary on azaleas, mancozeb, or chlorothalonil fungicide sprays can be used according to label directions. See Table 1 for examples of products.

Dieback

Botryosphaeria rot and canker (Botryosphaeria spp.)
Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org

Dieback is an important disease of hybrid rhododendrons in the landscape and is caused by the fungus Botryosphaeria dothidea. Azaleas with similar symptoms are more likely to be infected by the fungus Phomopsis species. Typically, dying branches (stem dieback) begin to appear on an otherwise healthy plant. The leaves die and can remain attached to the plant until late summer.

Usually a single branch on an established plant is affected. Scraping away the bark with a knife reveals a reddish-brown discoloration under the bark on dying branches of rhododendron. On azaleas the discolored wood under the bark appears chocolate brown.

Prevention & Treatment: Dieback is difficult to control on rhododendrons and azaleas in the landscape. The azalea varieties that are the least susceptible include: ‘Delaware Valley White,’ ‘Hershey Red,’ ‘Pink Gumpo’ and ‘Snow.’ The following rhododendron varieties are considered resistant: ‘Boursalt,’ ‘Chionoides White,’ ‘Cunningham’s White,’ ‘English Roseum,’ ‘Le Barr’s Red,’ ‘Roseum Two’ and ‘Wissahickon.’

Reduce stress to the plants by planting in partial shade and watering during dry periods. Drought stress and freeze injury may predispose azaleas to infection. Avoid wounding the plant. Prune infected branches well below all discolored wood and dispose of dead plant material. Clean pruning tools between cuts with a dilute solution of household bleach (1 part bleach to 9 parts water) or 70% rubbing alcohol. For azaleas, fungicide sprays containing either thiophanate-methyl or mancozeb can be used. For rhododendrons apply a product containing a copper-based fungicide or chlorothalonil. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

Leaf Spots

Cercospora leaf spot (Cercospora handelii).
Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

Throughout the year, fungal spots (Cercospora species, Septoria species, Phyllosticta species and Colletotrichum species) of various colors appear on azalea and rhododendron leaves.

The diseases caused are usually minor, only affecting the aesthetic value of the plant. Cases of severe infection may result in early leaf drop, reducing the general health of the plant.

Prevention & Treatment: Remove fallen leaves. Keep leaves dry when watering plants. Fungicide sprays during periods of high humidity will prevent serious foliage damage. Fungicide sprays recommended for azaleas include copper hydroxide, copper-based fungicides, thiophanate-methyl or chlorothalonil. For Cercospora leaf spot on rhododendron use propiconazole, thiophanate-methyl, chlorothalonil or mancozeb. See Table 1 for examples of products. Apply these fungicides according to directions on the label.

Other Problems

Leaf Curl: Rhododendron leaves begin to cup and curl at the edges when temperatures drop to below 35 ºF. At 25 ºF, the leaves will be curled very tight and begin to droop. This problem is not caused by insects or disease but is a way the plant reduces water loss from its leaves during cold, dry, windy weather. Plants should recover when the weather warms again.

Table 1. Fungicide Products for Azalea and Rhododendron Disease Control in the Home Landscape.

Active Ingredient Examples of Products
Captan Southern Ag Captan Fungicide WP
Bonide Captan 50% WP
Drexel Captan 50W
Arysta Captan 50% WP
Hi-yield Captan 50 W Fungicide
Chlorothalonil Bonide Fung-onil Concentrate; & RTU1
Ferti-lome Broad Spectrum Landscape & Garden Fungicide Concentrate
GardenTech Daconil Fungicide Concentrate
Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide Concentrate
Ortho MAX Garden Disease Control Concentrate
Southern Ag Liquid Ornamental & Vegetable Fungicide Concentrate
Tiger Brand Daconil Concentrate
Copper-based Fungicides Bonide Copper Fungicide Spray or Dust
Bonide Liquid Copper Concentrate; & RTU1
Camelot Fungicide/ Bactericide Concentrate
Monterey Liqui-Cop Fungicide Concentrate
Natural Guard Copper Soap Liquid Fungicide Concentrate
Southern Ag Liquid Copper Fungicide
Mancozeb Bonide Mancozeb Flowable with Zinc Concentrate
Southern Ag Dithane M-45
Propiconazole Banner Maxx Fungicide
Bonide Infuse Systemic Disease Control Concentrate; & RTS2
Ferti-lome Liquid Systemic Fungicide II Concentrate
Thiophanate Methyl Cleary’s 3336-WP Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
1 RTU = a pre-mixed spray bottle.
2 RTS = a hose-end spray bottle.

Q: The leaves on the ends of some of my camellia branches are swollen and thicker than the rest of the leaves. They are also lighter green. I’ve seen this on azaleas but not on camellias. Is it the same thing?

A: It is indeed the same disease: camellia (or azalea) leaf gall. It is caused by the fungus Exobasidium spp.. Your plants were infected last year when spores from a similarly swollen camellia leaf were released. There is not much you can do for the problem now other than pick off and destroy the affected leaves.

Occurrence of the disease is sporadic and depends on the spring weather. Some years azaleas throughout Atlanta seem to be afflicted; some years only a few.

The disease is also called “pinkster gall” or “pinkster apple”, because it affects the wild Pinkster azalea (Rhododendron periclymenoides). I am given to understand that early pioneers would pickle the galls with spices and vinegar and enjoy them as a delicacy. Since most azalea plant parts are toxic, I wouldn’t recommend this particular snack to you.

The best treatment is to pluck off the mal-formed leaves, put them in a plastic bag and put them in the garbage. Do not simply drop them on the ground. Finish the job before the galls turn gray, the stage when new spores are produced. If you want to protect the buds for next year, spray with a just before new leaves unfurl in spring and again ten days later. Leaf galls rarely do permanent damage to the plant.

MORE INFORMATION

Azalea Leaf Gall

Pinkster apple gall

azalea leaf gall Exobasidium rhododendri

azalea leaf gall Exobasidium japonicum

camellia leaf gall Exobasidium camelliae

camellia leaf gall Exobasidium camelliae

Tags For This Article: azalea, disease, Spring

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