Purple plum tree diseases

Plum Tree Diseases: Indentifying Common Plum Diseases

Problems with plum trees are many and diverse, resulting from wind spread virus, bacterial and fungal spores also distributed by splashing water. Plum tree diseases may slow or stop production of the fruit crop. As such, control plum disease at the first opportunity after discovery for the health of your fruit producing plum trees.

Common Plum Tree Diseases

The most common plum tree diseases include black knot, plum pocket, brown rot, plum pox virus, perennial canker and bacterial leaf spot.

Black Knot Plum Disease

Black knot is a plum tree problem that begins as a velvet green knot in spring then turns black and swollen. Black rot may girdle limbs and in severe cases form on the tree’s trunk. This plum tree problem gets progressively worse without treatment and may halt useable fruit production.

Plum Pocket Plum Disease

Swelling, discolored, hollow fruit signals the plum disease called plum pocket. Hollow fruits may be infested, itching to burst and further spread this plum tree problem. Once established, the disease returns every year. Fungicides may help, but prevention is most effective.

Brown Rot

Brown rot is another of the plum tree diseases that affects the fruit. Homeowners are often unaware of a problem until green and ripening fruits display spots of the brown rot. In worsening stages, fruits become mummified and cling to the tree. They produce spores in spring.

Plum Pox Virus

Plum pox virus is normally transmitted via aphids but can also be spread through grafting of affected plants, including peaches and cherries. Once a tree is infected, there is no treatment and the tree should be removed to prevent further infections to nearby plants. Symptoms include discolored rings on leaves and fruits. Controlling aphids is helpful too.

Perennial Canker on Plums

Plum tree diseases, such as perennial canker, are spread by a fungus, infesting wood already damaged by insect, mechanical or winter injuries. Sites with poor drainage encourage the collection of spores in damaged spots on the tree, as do excessive wounds.

Plum Tree Leaf Spot

Bacterial leaf spot attacks the leaves, often appearing unnoticed on the leaf underside. Continued infestation results in the plum tree problem of further leaf damage with holes surrounded by the red ringed bacterial indicator.

Additional Plum Problems

While not technically a disease, plum curculio is a common problem with plum trees. This snout beetle pest and its young can wreak havoc on these fruit trees, causing extensive fruit drop and decay or scabbing of the fruits. Spraying trees with suitable pesticides is your best option in combating these pests.

Various methods of control are available to the homeowner. Proper planting of resistant cultivars may be an option to correct plum tree problems. If you are putting in a new orchard, find out which cultivars perform best in you area. Your local County Extension Agent is a good source of this information. Do not plant new plum trees near older, diseased trees. Proper pruning of diseased branches is a worthwhile control.

Your plum trees versus black knot

Black knot is a fungal disease that strikes fear in the hearts of owners of plum trees. It doesn’t matter if they are edible plums or the decorative, landscaping variety, the trees could be fatally affected. Since twigs and branches are easily seen during winter, it is a good idea to check any plums for galls or swollen growths. Michigan State University Extension horticulture educators and Master Gardener hotlines receive many calls about black knot when the leaves are off the trees.

Black knot causes black, corky, swollen growths to form on branches, twigs and occasionally trunks. The nutrient and moisture flow is cut off to the branch that extends beyond the black knot. The spread of the disease has to do with suitable hosts and humid weather during the growing season.


Black knot on branches and galls. Photo credit: D. Richie, University of Georgia, Bugwood.org

Host trees are plums and occasionally cherries. Very susceptible edible plums are ‘Stanley’ and ‘Shropshire.’ For ornamentals, purple leaf plum and sand cherry are often targets. Edible plums that are moderately resistant to black knot are ‘Damson’, ‘Bluefree,’ ‘Shiro’, ‘Santa Rosa’ and ‘Formosa.’ Japanese plums are generally less susceptible. ‘President’ is the only type of edible plum that is considered highly resistant.

Black knot takes several years to develop. In the first year, small, light brown swellings are visible on the current year or last year’s twig growth, which will be towards the ends of the branches. By the next year, the swellings have grown and become olive green with a velvety appearance. During this year’s growing season, the galls swell and turn black and become misshapen. As the nutrients and moisture are cut off to the twig, the twig could become curved or bent at the location of the gall.


Black knot on flowers and galls. Photo credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org

When black knot is found, there are two choices: remove the tree or attempt to treat it. Treatment may remove a large quantity of the branches if black knot is severe. During the winter, the galls need to be pruned out. Prune at least 6 inches away from an existing gall into healthy wood. This may leave very few branches, so this may be the point when deciding whether to keep the tree needs to occur. Burn or bury the pruned black knot wood. Do not drop the pruned galls on the ground. The galls can still spread spores during the growing season. Do not prune during the growing season because the fungal spores can be spread around at this time.

Using a fungicide is recommended only for trees with severe fungal problems or valuable trees. Apply the fungicide when the trees are dormant in the spring – when there are no green buds, leaves or flowers present. Then, spray again when the flower buds color up. The fungicide is to prevent more problems; it cannot cure it. Use a fungicide that has an active ingredient of chlorothalonil or thiophanate-methyl. For many places in Michigan, it will be easier to find a fungicide with chlorothalonil. Be sure to follow the directions. The tree should be sprayed each spring following the timing given above.

Some of these plum varieties are just trouble waiting to happen. This is a very difficult fungal disease to eliminate, but for smart gardeners looking for replacement trees, they now have an idea of what not to select.

For more information on a wide variety of smart gardening articles, or to find out about smart gardening classes and events, visit www.migarden.msu.edu. You can also visit MSU Extension at the Novi Cottage and Lakefront Living Show on Feb. 21-24, or the West Michigan Home and Garden Show on Feb. 28-March 3 where we will be talking about native plants and other smart gardening options.

Plum

Prunus domestica and Prunus salicina

Bacterial Canker (bacterium – Pseudomonas syringae): Cankers develop at the base of infected buds on trunk and scaffold limbs. Cankers spread more rapidly above the point of infection than below and only slightly to the sides. This results in a long, narrow canker. Cankers develop during the fall and winter but are not visible until late winter and early spring. Damaged areas are slightly sunken and somewhat darker in color than surrounding bark. As the trees break dormancy in the spring, gum is formed and flows down the outside of the tree. Cankers have a soured smell. The bacterium is a weak pathogen and causes serious damage only when a tree is in a near dormant condition or weakened due to unfavorable growing conditions. Avoid using high fertilizer rates in late summer. Succulent, late fall growth is more easily infected. Prune when trees are fully dormant (January and February). Trees showing signs of bacterial canker should be left and pruned after all other trees have been completed.

Brown Rot (fungus – Monilinia fructicola): The brown rot fungus can cause blossom blight or fruit rot. Surface moisture and moderately warm temperatures encourage its development. Fruit damaged by wind, hail, insects, or mechanical means is more susceptible to this organism. Infected blossoms are brown and water-soaked. The fungus grows down the pedicel into the stem which may cause twig dieback. Diseased blossoms and fruit generally become covered with “tufts” of brown fungal material (See Photo). Fruit infection usually occurs near maturity. The fungal organism overwinters in mummies, stem cankers and old fruit peduncles. Control is by repeated fungicide applications (See Table Below) and sanitation.

Bacterial Spot of Plum (bacterium – Xanthomonas campestris pv. pruni): Symptoms are observed first as small, irregularly shaped lesions. The spots are pale green in contrast to the dark green surrounding tissue. In advanced stages, angular lesions are formed, surrounded by a halo of lighter colored tissue. The inner portion of the lesion turns black and drops out. This gives the leaf a “ragged” or “shot hole” appearance. Leaves heavily infected with bacterial spot turn yellow and fall. Leaf spots are concentrated toward the distal end of the leaf. Fruit infection is not as common as foliage infection. When it occurs, small spots develop and gum may flow from these spots. Highly susceptible varieties like Methley and Santa Rosa are more likely to have fruit infections than Morris, Bruce or Ozark Premier. The bacterium overwinters on infected twigs. Chemical control (See Table Below) has not been highly effective. Early and late dormant copper sprays will aid in control. Optimum nutrition is also important.

Rust (fungus – Tranzschelia discolor): Initial symptoms are minute yellow spots on the upper leaf surfaces. As the fungus develops, reddish to dark brown colored rust lesions break open on the lower leaf surfaces (See Photo). The specific rust fungus attacking plums does not attack peaches. Rust is usually a late season problem that causes rapid defoliation. If defoliation is repeatedly premature, production can be affected. Chemical control (See Table Below) is a viable option but generally not necessary. Bruce and Morris are susceptible. Methley, Santa Rosa, Ozark Premiere and Allred are tolerant or resistant.

Cherry Leaf Spot (fungus – Coccomyces hiemalis): Infected leaves have small circular purple lesions which turn brown and eventually drop out. This gives the foliage a ragged or shot hole appearance. Rainfall is necessary for disease development. Protective fungicides applied for other diseases gives economical control. This is considered a minor disease on plums.

Black Knot on Plum (fungus – Apiosporina morbosum): Affected limbs and twigs are malformed as a result of black woody growths (galls). The galls are similar to those caused by crown gall on the root system. The disease is more prevalent on the small twigs, but under severe disease conditions it may be found on large limbs. Infection of new shoots occurs from bloom until shuck split stage. Primary inoculum comes from one to two year old galls. Control of black knot is by sanitation, chemicals and resistant varieties. Prune and destroy the galled tissue. Make cuts two or three inches below the gall to insure complete removal of the fungus. Fungicides applied (See Table Below) in the early bloom periods will help reduce the occurrence of this disease.

Plum Pockets (fungus – Taphrina communis): Plum pockets are a fruit disorder of little economic importance. Infection occurs soon after bud break under cool, wet conditions. The skin of the fruit is first a reddish color and then a velvety gray. Infected fruit becomes distorted and puffy. The disease is similar to peach leaf curl except fruit rather than leaves are attacked. A fungicide program (See Table Below) used to control peach leaf curl will also control plum pockets.

Prunus Stem Pitting (virus-Tomato ringspot): (See section on Peach)

Peach Mosaic (virus): (See section on Peach)

Armillaria Root Rot (fungus – Armillaria tabescens): (See section on Armillaria Root Rot/Mushroom Root Rot)

Cotton Root Rot: (See section on Cotton Root Rot)

Root Knot: (See section on Root Knot Nematodes)

Problems of Flowering Plum

Foliage Curls, Puckers, Turns Yellow. Leaves and blooms become stunted, and ants may be visible in the tree. They are attracted to a sticky honeydew secreted by aphids.
Aphids – Aphids are soft-bodied pear-shaped insects about the size of a pinhead. Either green, brown or pink, they cluster on tender new stems and under leaves to feed. For more information see the file on Controlling Aphids
Leaves Stippled Yellow. There will be fairly obvious fine webbing on leaf stems. The webs look like tiny spider webs.
Spider Mites – Mites are tiny insects about the size of a grain of black pepper. They may be red, black, or brown. They are barely visible, but they cause brownish stippling or pale yellow spots or blotches on the leaves. As mites suck chlorophyll out of the leaves, they also inject toxins into them, discoloring and distorting them. For more information see the file on Controlling Mites
Holes In The Trunk – Visible holes in the trunk near the base of the tree from which brown frass (sawdust) and gum exude show that borers are at work.
Peachtree Borers – Adult peachtree borers are wasp-like moths. They lay eggs around the base of the plum tree trunks in late summer and early fall. These hatch into white, 1 ¼ inch long worms with brownish heads. They burrow into the tree trunk as high as a foot above the ground or several inches below the ground. Young trees can be killed during the first season of infestation. Treat minor infestations by inserting a stiff wire into each hole and killing the worms. For more information see the file on Controlling Borers
Holes In Blossoms, Stunted Tree
Weevil – Weevils are reddish brown in color. They are about ¼ inch long with black snouts. Both larvae and adults may feed on leaves and fruit of the plum tree. The larvae make zigzag paths into roots, fruit, or stems. For more information see the file on Controlling Weevils
Gray, Velvety Mold on Leaves
Powdery Mildew – A coating of white or pearly gray, velvety mold on the ends of twigs, leaves and blossoms of the plum tree indicate powdery mildew. This fungus dwarfs the twigs and kills the terminal buds, spawing the growth of numerous side shoots. For more information see the file on Controlling Fungal Disease
Wilted Leaves
Verticillium Wilt – Verticillium wilt causes leaves on plum trees to wilt and droop during midsummer or early fall. They later turn yellow, curl upward along the midrib, and drop. Leaf damage progress from the older part of the shoot to the younger growth. Prevent this problem by eliminating grasses and weeds around the plum tree. Do not plant vegetables such as tomatoes, cucumbers and peppers nearby. For more information see the file on Controlling Fungal Disease

ornamental plum tree disease

For established Prunus trees, consulting a certified arborist is worthwhile for many home owners. This allows the expert to see the full tree, interview you about symptoms, and make recommendations based on the problem or problems.
Thundercloud Purple Leaf Plum, Prunus cerasifera ‘Thundercloud’, is one of the more popular ornamental plums in our area. All of the plums are prone to pests and disease, some of which require chemical controls.
One common problem is brown rot blossom-blight. A history from you about how the trees appeared in bloom is helpful in the diagnosis.
https://pnwhandbooks.org/plantdisease/host-disease/plum-flowering-brown-rot-blossom-blight This page, “Plum-flowering Brown rot blossom blight” from the Pacific Northwest Plant Disease Handbook includes photos and descriptions. It also lists cultural controls and the boxed “H” indicates treatments available to homeowners. Leaf blights are best diagnosed when the tree is in bloom and leaf, but chemical controls must start at earliest bud-break, so a diagnosis now and a treatment plan is best.
If you hire an arborist, we recommend someone Certified. This website from ISA “Trees are Good” includes a search option for our area. http://www.treesaregood.org/

Each year blossom trees announce the arrival of spring and gaily declare that winter is over. To bring the song of spring into your garden, Don suggests a visit to your local nursery to find a blossom tree which appeals to you. Flowering plum is just one of many flowering blossom trees which burst into bloom in spring.

There are a succession of flowering blossom trees that bloom from late winter well into spring. The earliest to flower is the winter flowering peach. This is followed by the cherry plums, pears, cherries, flowering peaches and crabapples. If your garden is large enough you can arrange a succession of spring flowers that will blossom over many months.

Most of the flowering blossom trees bloom before their leaves appear, which adds to the beauty and intensity of the display.

Growing blossom trees

Although there are many different types of blossom trees, all have some basic requirements in common and are seen at their best in the temperate and cooler regions of Australia.

Climate map – Prunus x blireana

Most are at their most beautiful in flower in spring but some trees have features that make them interesting for many months of the year. The flowering plums, Prunus x lireana and Prunus cerasifera ‘Nigra’ have red new growth. The dark claret red colour persists through summer and into autumn in P. cerasifera ‘Nigra’. Although these trees have few pest and disease problems there are some that can cause problems.


Shot hole of prunus: This is a fungal disease which attacks prunus (such as almonds, flowering peaches, cherries and plums) causing the leaves to develop holes (as if peppered with shot). The leaves turn brown and drop. In severe cases the tree can become completely defoliated and will have to grow new leaves. If this cycle continues the tree will be weakened and may succumb to a secondary problem.

To overcome shot hole, spray with copper oxychloride as the trees are just coming into flower. Repeat spray in autumn after the leaves fall.

Peach leaf curl: This disfiguring disease affects the leaves of peaches and nectarines. The leaves become puckered and thickened as the fungus develops. The leaves eventually drop. It can be controlled by spraying before the leaves develop in late winter with copper oxychloride. The ideal stage at which to spray is as the leaf buds begin to swell and become plump.

Pear and cherry slug: This ugly but small dark green to black looking caterpillar (actually the larval stage of a sawfly) chews holes in leaves and can skeletonise the plant. It can be controlled by hosing the ‘slugs’ off the leaves or spraying foliage with carbaryl when the pests are discovered.

Autumn bonus

As well as looking spectacular when flowering in late winter, many of these trees also colour in autumn. The flowering cherries are particularly striking in autumn.

Care

The blossom trees all need moderately fertile soil, good drainage and protection from wind. This latter requirement is most important as blossom trees that are exposed to winds, especially while in flower, tend to only have a very short display before the wind blows the petals off the plant.

Although at their best in full sun most blossom trees will tolerate a little light shade.

These trees are grown for their flowers and rarely produce fruit however they should be checked after the main flowering time to see if any fruit has formed. If fruit has formed, clip it off. Fruit that is overlooked on ornamental trees (such as peaches) can become infected by pests such as Queensland fruit fly. So, despite it not being edible, it may still produce fruit which could in turn harbour insect pests. In addition fruit that remains on a tree can produce fungal spores which then infest other trees. Do not leave fruit lying around. Put it in a bag and into the garbage bin.

Prunus in general may make excessive growth in the central branches of the tree. To combat this, immediately after flowering each year, remove a few of the oldest stems to keep the plant youthful and vigorous and the growth open.

Shown on the segment

The main blossom tree seen on the ‘Burke’s Backyard segment was Prunus x blireana, a blossom tree which will have flowers from late August to mid-September depending on where it is growing. There is also a large flowered cultivar known as Prunus ‘Wrightsii’ available.

Availability

Flowering plum trees and other spring flowering blossom trees are available at most nurseries, especially in winter when the plants are sold bare-rooted and in spring when potted plants in flower can be purchased. Prices start at around $24.95 for a 30cm/12″ pot and $17 for a 1.5m (5′) bare rooted. Note: blossom trees tend to bloom better in their second year after planting than when newly planted in winter.

Welcome to Tagawa Gardens Nursery & Garden Center

Princess Kay Plum flowers

Princess Kay Plum flowers

(Photo courtesy of NetPS Plant Finder)

Princess Kay Plum in bloom

Princess Kay Plum in bloom

(Photo courtesy of NetPS Plant Finder)

Height: 15 feet

Spread: 10 feet

Sunlight:

Hardiness Zone: 3

Description:

A compact front yard accent tree smothered in double white flowers in early spring; a sterile variety that produces no fruit; attractive glossy black bark, upright in habit, very ornamental and hardy; needs full sun and well-drained soil

Ornamental Features

Princess Kay Plum is blanketed in stunning clusters of fragrant white flowers along the branches in early spring before the leaves. It has dark green foliage throughout the season. The pointy leaves turn an outstanding yellow in the fall. The fruit is not ornamentally significant. The smooth black bark adds an interesting dimension to the landscape.

Landscape Attributes

Princess Kay Plum is a deciduous tree with an upright spreading habit of growth. Its average texture blends into the landscape, but can be balanced by one or two finer or coarser trees or shrubs for an effective composition.

This tree will require occasional maintenance and upkeep, and is best pruned in late winter once the threat of extreme cold has passed. It is a good choice for attracting birds to your yard. Gardeners should be aware of the following characteristic(s) that may warrant special consideration;

  • Disease

Princess Kay Plum is recommended for the following landscape applications;

  • Accent

Planting & Growing

Princess Kay Plum will grow to be about 15 feet tall at maturity, with a spread of 10 feet. It has a low canopy with a typical clearance of 3 feet from the ground, and is suitable for planting under power lines. It grows at a medium rate, and under ideal conditions can be expected to live for approximately 30 years.

This tree should only be grown in full sunlight. It does best in average to evenly moist conditions, but will not tolerate standing water. It is not particular as to soil type or pH. It is highly tolerant of urban pollution and will even thrive in inner city environments. This is a selection of a native North American species.

As spring fast approaches, I find myself more obsessed with the trees than usual. I think it is because they are blooming so early that I can’t help but spot them from afar. One tree that is blooming everywhere is the ornamental purple leaf plum. This is one of my favorite trees, due to its purple/pink blooms and dark leaf color but this lovely tree does come with quite a few negatives.

Disease

Purple leaf plums, and indeed all plum trees in general, ornamental or fruit bearing, can suffer from a fungal disease called black knot. According to the Michigan State extension, once black knot is on your plum tree it is very difficult to stop. They recommend removal of the tree or major surgery to remove all limbs that are infected.

The best way to avoid getting black knot is to plant a resistant tree. The Michigan extension suggests planting the variety called ‘President’ for edibles. Unfortunately, purple leaf ornamental varieties are almost all susceptible to the fungus, so you may be taking a gamble if planting one.

Pests

Later in on the summer, the beautiful purple leaf plum suffers yet again. You see, they are a favorite food for Japanese beetles. When there is a bad infestation of the shiny green beetles, they can eat the whole canopy very quickly. This usually doesn’t kill the tree as it will push out more leaves after the attack is over, but it will look very strange for the rest of the season.

Some ways to control the Japanese beetles are to pick them off by hand and throw them into a bucket of hot, soapy water. I find that a little unrealistic for trees, so I suggest using a neem oil spray if you are an organic gardener or Sevin if it doesn’t bother you to spray your trees with a stronger chemical.

Ornamental plums are a favorite for the landscape. Their purple leaves pop in a sea of green, making it a fantastic feature tree. It is always important to investigate the problems a tree may develop before deciding which one is right for your yard. It may save you from a headache down the line.

Plum Tree Diseases, Pests, and Other Problems

Most Common Diseases in Plum Trees

Below are some of the most common disease problems in plum trees:

  • Leaf curl causes puckering and discoloration of leaves, with reddish lesions developing. The tree can become defoliated in severe cases. Remove fallen leaves to control.
  • Brown rot causes fruit to rot, turn brown, and develop spots. Affected fruits become mummified, often remaining on the tree. Mummified fruits contain spoors which renew the lifecycle of the pathogen. Citrus sprays can be effective along with good orchard hygiene.
  • Perennial canker is a fungus infecting damaged areas on the tree. Poorly drained soil can also lead to this problem. Gummy wounds and wood which looks water-soaked are other indicators. Plant trees in a well-drained location.
  • Crown gall reduces the growth rate of the tree and size of the leaves and fruit. Look for woody growths at the base of the tree.
  • Bacterial leaf spot often first appears on the underside of leaves. Spots frequently fall out, leaving a hole in the leaf, which may yellow as a result. Fruit is also affected with cracks and sunken spots.
  • Black knot appears in spring with velvety-green growths appearing on branches and twigs. These lesions later turn black and swell up. The damage can girdle the limbs or trunk, causing them to die. Prune-out infected branches and burn or dispose of off site.
  • Plum pox virus is a serious and often fatal disease of plum trees. The disease is transmitted by aphids and grafting. Control of aphids is important for management.
  • Scale is a pathogen with minute, circular, scales with yellow dots which can appear on branches, twigs, and fruit. Dormant oil sprays can be effective for controlling scale.

Plum Tree Pests

Some of the most common pests infesting plum trees include:

  • Plum circulio is a small, slow moving beetle with larvae and adults doing significant damage to the fruit. Insecticides and physical controls are effective against this pest.
  • Aphids are small, often green insects which can appear in large clusters on the underside of leaves, leaving a sticky substance called honeydew. Aphids are vectors for other fruit tree diseases. Citrus sprays can be effective for control, as well as washing the aphids off of the tree with a strong jet of water.

To minimize damage to the tree and fruit, treat disease and pest symptoms on plum trees as soon as they appear. Plant resistant cultivars, if available, and do not plant new trees in the same location as old trees.

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