Source(s): Nina Eckberg
Shot-hole disease is a combination bacterial infection (Xanthomonas prunii) and fungal disease (Blumeriella gaapi and/or Cercospora sp.).
- Shot-hole Disease Identification
- Shot-hole Disease Appearance
- Shot-hole Disease Hosts
- Shot-hole Disease Season
- Shot-hole Disease Damage
- Shot-hole Disease Integrated Pest Management
- Shot Hole Fungus On Cherry Laurels
- Shot hole
- Prunus laurocerasus-Leaf Spots and Shothole
- Pests and Diseases to look out for this Autumn – check your laurels for powdery mildew and your trees, hedges and shrubs for vine weevil
- Bay Laurel Has Yellow Leaves: Why Is My Bay Laurel Turning Yellow
- Appearance of the Tree
- Bay Laurel Tree Types
- The Many Looks of the Bay Laurel Tree
- Where the Bay Laurel Grows
- Popular Uses
- Interesting Facts
- Bay Laurel Diseases
- Bay Laurel Care
- Versatile Bay Laurel Tree
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Shot-hole Disease Identification
Shot-hole disease (on a laurel in the photos) is a combination bacterial infection (Xanthomonas prunii) and fungal diseases (Blumeriella gaapi and/or Cercospora sp.)
Shot-hole Disease Appearance
Circular holes in the leaves that eventually join and make larger holes. The appearance of shooting a shotgun at the shrub and causing multiple holes.
Shot-hole Disease Hosts
Laurels (bay and Otto Luyken), camellia, ligustrum (privets), hydrangea, ivy.
Shot-hole Disease Season
April through October, peak in May and September.
Shot-hole Disease Damage
Leaves appear to be ‘eaten’ away by the disease, leaving a ragged appearance. As leaves are damaged, they begin to fall away, the plant looses its ability to make food and can become stressed.
Shot-hole Disease Integrated Pest Management
Sanitation is the best way to keep the disease from coming back. Clean up contaminated leaves from under the plant. When diseased leaves build-up under the plant, rain or watering can splash the disease back up on the plant. Spray the leaves with Mancozeb, Kocide, Kop-R-Spray or other recommended products containing copper at the first sign of a problem. Always READ THE LABEL and DIRECTIONS FOR USE section carefully when using pesticides.
Common Landscape Diseases In Georgia
Center Publication Number: 55
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- Root Rot on Evergreens – September 23, 2013
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Shot Hole Fungus On Cherry Laurels
Shot hole fungus, also known as shot hole disease, is a serious fungal disease that creates distinct BB-sized holes in leaves. With the rainy, warm weather we’ve been having this season Shot Hole Fungus is running rampant. Our Arborists report seeing Shot Hole Fungus on lots of Cherry Laurels in this area. Without treatment, this fungus will re-infect your shrubs year after year, not only ruining its aesthetic appeal but also weakening the shrubs health.
Plants Susceptible To Shot Hole Fungus:
Cherry laurel, English Laurel, Cherry Trees
Most signs of shot hole disease can be seen in spring and early summer.
- Reddish brown spots on leaves
- Holes in leaves (can look like insect feeding damage)
Most homeowners will see holes in their leaves and immediately think the issue is insects. In the case of Shot Hole Fungus, the original reddish brown damaged spots will dry up and eventually fall out leaving holes in the leaf.
Need Help With Shot Hole Fungus?
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Shot Hole Disease Treatments:
At this time of the year, the damage from shot hole fungus is already done and the disease has already taken hold of the plant. However, our Arborist suggests you sign up for a fungicide treatment plan for next year to ensure your trees/shrubs are protected from Shot Hole Fungus. In the meantime, the best thing you can do is practice proper sanitation and pruning.
Proper Pruning: By using fine hand pruning techniques (not shearing) our plant health care technicians can strategically prune your shrubs/trees to allow better air circulation. This will promote faster leaf drying and lead to less fungal issues overall.
Practice Proper Sanitation: To reduce the spread of Shot Hole Disease and lessen the chance of reinfection/the severity of the infection, proper sanitation is a must. Remove contaminated leaves around and beneath the tree/shrubs.
Proper Watering: Water the soil around the base of the plant. This type of watering will keep the shrubs leaves dry, unlike overhead watering.
Fungicides: For optimal coverage, fungicides need to be used at bud break and continued throughout the year.
Arborist Tip: If your shrubs have Shot Hole Fungus damage and are currently being treated, our Arborists recommend allowing your shrubs to grow out or fine pruning them instead of shearing them. Allowing the shrub to grow out will help hide the holes in the old growth and showcase the healthy new growth not affected by Shot Hole Disease.
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Samantha Huff is the marketing coordinator at RTEC Treecare. She enjoys learning about the technical aspects of trees and the insects and diseases that prey on them. She hopes that these articles can help homeowners gain control of their tree and shrub maintenance by being aware of the signs and symptoms of unhealthy trees.
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Tags: cherry laurelsfungifungusshot holeshot hole fungus
There are numerous reasons for holes to appear in plant leaves. These include poor growing conditions and environmental stress, insect pests feeding on the foliage and even droplets of water acting as a magnifying glass in strong sunlight. But one specific type of hole, called ‘shot hole’, is caused by plant diseases.
Shot hole is so called because it looks like the leaves have been blasted with shotgun pellets.
Small and more-or-less rounded holes are a result of plant disease infections, especially fungal leaf spots and bacterial canker. The latter attacks members of the Prunus family – such as cherries and plums, both edible and ornamental. The disease causes the part of the leaf that is affected to turn brown and die. This dead portion then falls out of the leaf leaving behind the hole.
Large and irregular shaped holes are a result of poor growing conditions and insect pests eating the foliage.
Treatment and control
For shot hole, improve the plant’s growing conditions, which will reduce stress and make the plant stronger and less likely to be attacked. Then control the fungal leaf spot disease or bacterial canker.
Similarly for the larger holes, control the insect pests eating the foliage.
Prunus laurocerasus-Leaf Spots and Shothole
Peach (Prunus persica)-Shothole
Cause Shothole symptoms are commonly observed on Prunus spp. and can be caused by a variety of factors. Development of the shothole symptom is in response to mechanical, chemical, or pathogen injury. There is the formation of meristematic tissue around the injury that becomes lignified or suberized to form a physical and biochemical barrier that, in the case of pathogens, limits the colonization of healthy tissue. The formation of an abscission layer may be dependent on temperature. In almond leaves, an abscission layer formed at 72°F but not at 59°F.
The bacteria Pseudomonas syringae pv. syringae and Xanthomonas arbicola pv. pruni as well as several fungi including Cercospora sp., Blumeriella sp., and Thyrostroma carpophilum (Coryneum blight) can cause leaf spots and shothole on cherry laurel (English laurel, Otto Luyken, or ‘Zabeliana’). Two other fungi have been reported from Germany in association with shothole symptoms. Copper spray injury and boron toxicity can also cause leaf spotting and shothole. When symptoms are advanced, it is not possible to identify the cause specifically. Some virus infections (such as Prunus necrotic ringspot virus) can cause a shothole symptom in fruiting cherries but this has not been reported for cherry laurels.
Cherry laurels (English laurel, Otto Luyken, or ‘Zabeliana’), P. laurocerasus and sometimes other Prunus spp. including cherry and plum, commonly show shothole symptoms resulting from only cultural or environmental stress. Both container- and field-grown laurel can develop symptoms. Some growers have observed that plants are more susceptible to symptom development when grown in containers. Portuguese cherry laurel (Prunus lusitanica) is nearly resistant.
Symptoms Necrotic leaf spots with circular to irregular margins. Bacterial spots are brown surrounded by a reddish border with a yellow halo. Abscission layers develop around necrotic leaf spots causing the injured tissue to drop away, leaving holes and tattered areas in the leaf (as if someone fired a shotgun at the leaf-thus the name shothole). After tissues drop, most often it is difficult to determine specifically what caused the initial injury. Observations of early symptom development, signs, and symptoms on other areas of the plant may help make an accurate diagnosis.
Cultural control No management practices have been shown to help reduce physiological shothole. For disease-induced shothole, try the following.
- Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
- Remove and destroy fallen leaves.
- Do not plant near other flowering or fruiting Prunus spp.
- One nursery reported good success with first growing in the field and then potting plants the year before sale rather than starting with containers.
- The cultivar Chestnut Hill is reported to have superior resistance to shothole when compared with Otto Luyken.
Chemical control Use only if a bacterial or fungal cause has been identified.
- Daconil Weather Stik at 1.4 pints/100 gal water is registered for fungal leaf spots. Group M5 fungicide. 12-hr reentry.
- Fixed coppers may help against both fungi and bacteria but can cause leaf injury and defoliation. Group M1 fungicides. 48-hr reentry. O
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker for fungal problems. Group 11 fungicide. 4-hr reentry.
- Junction at 1.5 to 3.5 lb/A. Can be more effective than other copper-based products when copper-resistant bacteria are present. Spray solution pH should be above 6.5. Group M1 + M3 fungicide. 48-hr reentry.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Mancozeb-based products were found useful for both fungal and bacterial causes. Group M3 fungicides. 24-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. For fungal problems. Group 1 + M5 fungicide. 12-hr reentry.
- Zyban WSB at 24 oz/100 gal water for fungal problems. Not to be confused with the smoking cessation drug. Group 1 + M3 fungicide. 24-hr reentry.
Reference Adaskaveg, J.E. 1995. Conidial morphology, host colonization, and development of shot hole of almond caused by Wilsonomyces carpophilus. Canadian Journal of Botany 73:432-444.
De Boer, S.H. 1980. Leaf spot of cherry laurel caused by Pseudomonas syringae. Canadian Journal of Plant Pathology 2:235-238.
Pests and Diseases to look out for this Autumn – check your laurels for powdery mildew and your trees, hedges and shrubs for vine weevil
Autumn is a good time of year to get ahead when it comes to treating pests and disease in the garden. It’s still warm enough for treatment to be effective and you can get any problems cleared up before winter sets in.
There are a couple of particular problems to look out for in the garden this month.
Powdery Mildew on Laurels
If your laurels are suddenly showing a white powdery film on the leaves and the newer growth is puckering up and twisting, then you have powdery mildew, which quite often appears at this time of year.
This disease is not fatal but will defoliate the newer growth. There are two ways to control this. Firstly, the non-chemical way is to prune off the infected growth and dispose of well away from the infected plants.
The second way is to spray with an approved fungicide. The Royal Horticultural Society carry an excellent up to date list of approved chemicals.
In the long term, to help prevent the disease coming back, you need to get your plants into good health for the following year by feeding them in the spring and making sure that there is good air circulation near the plants as high humidity encourages this disease.
Vine Weevil on trees, hedges and shrubs
The second and potentially more ominous pest is vine weevil. This is a naturally occurring native dull black insect approximately 9mm long with six legs and with a dirty yellow mark on the wing cases. The adult causes irregularly shaped notches in the edges of the leaves but the real damage is done to the roots by the grubs which can eat the vast majority of the root system causing the plant to wilt and die.
The adults lay the eggs in August and these hatch over winter into c-shaped white legless grubs with light brown heads and are up to 10mm long. To reduce this pest remove all dead leaves around affected plants as this is where the adults hide during the day.
Secondly encourage natural enemies of vine weevils and their grubs such as birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.
Perhaps the best method of control is to use a microscopic worm called a nematode. Nematodes can be watered onto the soil around affected plants during September and early October while the soil is still warm enough for them to be active.
These nematodes work their way through the soil searching out vine weevil grubs which they burrow into to reproduce and multiply which kills the grub. The nematodes will then move on to search out more grubs. This method of control is very effective if applied correctly, is very safe for both you and the environment, and is pest specific so it will not kill beneficial insects. Nematodes can be bought on line from a number of suppliers.
If you have any specific concerns about your plants this autumn, please get in touch.
Bay Laurel Has Yellow Leaves: Why Is My Bay Laurel Turning Yellow
Bay trees are grown all over the world for the leaves, which are used in cooking, massage therapy and for medicinal properties. Though fairly resistant to pests and disease, problems may nonetheless strike, causing the leaves to turn yellow on the bay laurel. You may be wondering why my bay laurel is turning yellow if you see yellowing of the bay laurel leaves. Bay trees are evergreen shrubs that grow beautifully in either the garden or in containers. They make wonderful topiaries shaped as balls, pyramids, or “lollipops” and may even have braided or spirally trained stems. Laurus nobilis prefers to be grown in well-drained soil in a partially shaded or protected sun exposure. Grow bay outside in warm climates or indoors or greenhouse in cooler climates.
Why is My Bay Laurel Turning Yellow?
Leaves turn yellow on bay laurel for a number of reasons, resulting from an environmental condition, pest infestation or disease. Root rot – A yellow bay laurel plant may be indicative of waterlogged roots or wet weather creating root rot, a fungal disease that does exactly what is says. This usually applies to container grown plants and symptoms also include leaf wilt and drooping as well as yellow leaves. Avoid overwatering and standing water by providing adequate drainage. You may need to repot the bay in well draining, disease-free soil after removing any infected parts. An application of fungicide may be helpful as well.
Bay sucker pest – If your bay laurel has yellow leaves, another cause may be the bay sucker (aka: jumping plant lice), a common insect marauder of bay plants. These sap suckers are most active in late spring. Early signs of these pests are yellowing of the leaves followed by thickening of the leaf tissue, and finally brown leaves that drop. Treatment for these pests is the removal of infested foliage on the yellow bay laurel plant. The damaged portions should be burned and then the bay should be treated with insecticidal soap focused on the underside of the leaves. You may need to treat more than one time. Nutrient deficiency – Lastly, if your bay laurel has yellow leaves, the root of the problem may be either an iron or a nitrogen deficiency.
A deficiency in iron is also called iron chlorosis and is a major issue in the garden that is caused by several problems, most often overly alkaline soil or damaged roots. Too little iron decreases chlorophyll, resulting in yellow leaves beginning at the edges and moving inward while the veins remain green. Treatment is dependent upon the cause. If the soil is too wet or alkaline, mix organic matter, sulfur or peat moss into the soil to correct the pH and improve drainage. A yellow bay laurel plant may be indicative of a nitrogen deficiency, which is caused by an imbalance in the pH of the soil. A uniform yellowing of the bay laurel leaves occurring in older, lower leaves first and moving upward is how a nitrogen deficiency can be diagnosed. Add a nitrate rich fertilizer to the soil, making sure to follow the directions lest you scorch the plant. A safer but slower option is to amend with decomposing organic matter to treat the nitrogen deficiency.
The Bay Laurel tree, also known as the Bay Leaf tree, true Laurel, and Grecian Laurel, is part of the genus Laurus. The small evergreen is a hardy specimen which features a multitude of uses. In addition to being an attractive specimen, the tree’s fragrant leaves are coveted by cooks who use them as an herb in a variety of recipes. Landscapers also treasure the tree for its manageable size and low maintenance.
Appearance of the Tree
Bay Laurels are easy to spot thanks to their pyramidal shape. While the tree is capable of growing to 60 feet, it is typically pruned to form a much smaller hedge or topiary.
Among the tree’s most distinguishing characteristics are:
- Bark: The tree’s shiny gray bark dulls with age.
- Leaves: The shiny green aromatic leaves are thick and leathery. The lance-shaped leaves can be harvested and used in recipes once the tree marks its second growing season.
- Flowers: Multiple clusters of tiny white and yellow flowers are produced in spring.
- Fruit: Small glossy black or purple berries appear once the flowers fall.
Bay Laurel trees are among the oldest specimens in the world. Despite its age, the tree remains as popular as ever, showing up in formal and royal gardens on all four corners of the planet.
Bay Laurel Tree Types
Bay Laurel trees are part of the genus Laurus. Its botanical name is Laurus nobilis. It joins two other evergreen specimens in the same genus:
- Laurus azorica: Commonly known as Azores Laurel, its shiny dark leaves are not edible, though its creamy white flowers are very fragrant.
- Laurus novocanariensis: Known for its leathery, deep green leaves, the shrub-like bush bears olive-shaped fruit.
The slow-growing species needs consistent pruning if it is to be kept to a manageable height.
The Many Looks of the Bay Laurel Tree
Where the Bay Laurel Grows
The Bay Laurel tree is native to the southern Mediterranean region; however, it is also grown commercially for its leaves in:
- North America
- West Indies
While the Bay Laurel can survive warm weather, it needs adequate water to prosper. The tree thrives when it is frequently watered in well-drained soil and exposed to full sunlight. It does not grow well in regions that experience cold winters or high winds. Most people plant Bay Laurel trees in herb gardens, though others use the tree as a privacy screen by cultivating a series of specimens in a single row.
Hands down the most popular feature of the Bay Laurel is its spicy, fragrant leaves. Known as the Bay Leaf, the extensively used culinary seasoning is often added to:
- Pickling brines
The leaves are also an essential ingredient in what the French call a “Bouquet Garni,” which is basically an herb bundle that also includes other herbs such as parsley and thyme. Bay leaves can be used fresh or dried, though they should be removed from recipes before serving and should never be eaten raw as the sharp edges can cut a person’s mouth or throat.
The tree’s berries are also used for a variety of medicinal purposes. In most cases, the oil from the berries is extracted and consumed to relieve stomach ailments, including flatulence. Pressed oil from the Bay Laurel’s berries is also used in perfumes, candles and soap.
The Bay Laurel tree is deeply rooted in Greek and Roman mythology. This association is clearly seen in the story in which the nymph, Daphne, is transformed into a Laurel tree by her father, Peneus, so that she could avoid the advances of Apollo. To show his undying love for Daphne, Apollo donned a wreath of Laurel on his head for all of eternity. To this day, the Laurel has symbolized success and status.
Other interesting facts about the Bay Laurel tree include:
- In some cultures the tree is credited with having magical powers to ward off evils and atrocities.
- In ancient Rome, the Laurel symbolizes victory and is the source of the word “baccalaureate.”
- Christians believe that the Laurel symbolizes Jesus’ resurrection.
- Chinese folklore states that there is a great Laurel tree growing on the moon, which is why the Chinese name for Laurel translates to “moon-laurel.”
Bay Laurel Diseases
Due to its hardy nature, the Bay Laurel is fairly disease-resistant, though it is not entirely out of the woods in terms of skirting infection. The tree is susceptible to the following:
- Root Rot: This fungal infection can attack the tree if it is exposed to excess water over a long period of time. Symptoms include mold, mildew and premature leaf drop.
- Powdery Mildew: This fungal disease typically presents itself on branches that do not get enough sunlight. The white mildew spores form on leaves and can spread to twig and branches if left untreated.
- Anthracnose: Symptoms of this fungal infection include sunken, gray, spongy patches on leaves and branches that eventually develop spore masses. In severe cases the disease can spread and the tree can die.
In addition to these diseases, insects also prey on the Bay Laurel. Sapsuckers are especially fond of the tree and cause leaves to discolor and fall prematurely.
Bay Laurel Care
Adding a Bay Laurel tree to a landscape is not as challenging as many people might think. By following these simple tips, you can get the versatile tree to grow and prosper in your own backyard:
- Plant the Bay Laurel in the early fall or mid-spring.
- Select a site that is exposed to full sunlight.
- Add compost to the well-drained soil and water generously for the first growing season, especially if drought conditions persist.
- Add fertilizer to the base of the tree in the spring.
Finally, it is necessary to prune the Bay Laurel tree in the spring in order to maintain its shape and size. Trimming is also a good idea to allow sunlight to reach the center of the tree.
Versatile Bay Laurel Tree
Historically the bay laurel tree is a valuable plant that has medicinal, ceremonial, health and even magical uses. The most common modern use is using bay leaves in cooking recipes.
Do your chokecherry or plum tree leaves look like they have been blasted with a shotgun? If the leaves are peppered with holes it is probably Shot Hole Disease. Common hosts include trees and shrubs in the plum family such as Russian almond, Mongolian cherry, Nanking cherry, chokecherry, American plum, western sand cherry, Manchurian apricot, Amur chokecherry, pin cherry, peach, nectarine and cherry. There are two possible causes of Shot Hole disease the most common is bacteria but there is also a fungus.
Shot Hole disease bacteria first appears as small, water-soaked, grayish areas on the undersides of leaves. Shot Hole disease fungi appear as small, dark purple spots. Both the bacteria and fungus caused spots become angular and are most numerous at the tip ends and along the midribs of leaves. The infected areas drop out, giving the infected leaves a shot-holed, tattered appearance. On plum, the shot-hole effect is more pronounced than on other stone fruits. Tattered leaves are still functional and normally do not cause significant harm to the tree. Severely infected leaves may eventually turn yellow and drop. Fruit is often reduced in size, sunburned, and cracked. Tree vigor and winter hardiness may also be reduced.
In severe cases, the bacteria will penetrate into branches, causing cankers. Cankers are often found along the trunk and major branch crotches. Cankers typically are dark brown and sunken in the branch; the inner tissues will turn orange-red. These pockets of bacteria will release a pus-like ooze and can plug the flow of water and nutrients, causing leaves to wilt and branch tips to die.
Shot Hole disease bacteria overwinter in the twigs, buds, and other plant tissue. In the spring the bacteria are spread by rain to leaves, shoots, and fruit. Spring infections can occur after the leaves begin to unfold. Temperatures above 65°F and warm rains are needed for the bacteria to multiply, become exposed, and be spread. After these first infections, which are rarely noticed but do initiate the disease each year, the severity of the secondary infections depends on the weather. A moderately warm season with light, frequent rains accompanied by heavy winds or recent injury to the leaves or fruit, such as wind-blown soil particles and hail, may result in severe outbreaks.
Secondary spread of Shot Hole disease can occur from oozing summer cankers and leaf and fruit lesions during warm, wet weather. The systemic movement of the bacteria from leaves and shoots contributes to the formation of cankers. These cankers can be spread during budding to healthy nursery trees.
No sprays are available to control Shot Hole disease bacteria. Rake leaves and twigs from under the tree to remove the bacteria from the area. Trim out cankers going at least 6 inches into healthy wood. Remove the infected branches and burn them. Fungicide sprays are usually not needed, especially for established trees. For young trees, a spray with products containing chlorothalonil can be used to prevent the spread of the Shot Hole disease fungus. This fungicide will not control bacteria.
Planting resistant varieties is the most effective control measure. There a quite a few varieties of peaches highly tolerant of Shot Hole disease. Resistance in plums, nectarines, and apricots is not as common. Nurserymen are well aware of the degree of susceptibility of the varieties they sell and they can provide good information for specific areas. Since trees in poor vigor are more susceptible, orchard management programs should be designed to maintain good vigor.
My sources for this news release were North Dakota State University and Penn State University Extension. If you would like more information about “Shot Hole Disease of Trees & Shrubs in the Plum Family,” contact Bob Drown at 605-244-5222 Extension 109 or by e-mail at [email protected]