Learn how to spot tree diseases, which trees are susceptible to tree diseases, the damage these diseases cause, and how to cure tree diseases.

Anthracnose

An anthracnose infestation first shows as spots or blotches on leaves, or as discolorations on evergreen needles. Spores of the fungus spread in spring through the air or by rainwater. Anthracnose stunts leaf growth, and may also kill buds, twigs and shoots before they mature. Cankers or irregular growths sometimes appear on    twigs, branches and bark. While most trees can weather an attack of anthracnose fungus, the damage it causes is an open door for other diseases and insect pests.

Damage and Treatment

Damage and Treatment

  • A fungus that attacks both deciduous and evergreen trees
  • Causes unsightly leaf spots, blotches, defoliation, shoot blight, twig cankers and dieback
  • While not commonly fatal, anthracnose can weaken resistance to insects, diseases

Anthracnose Damage

An anthracnose infestation first shows as spots or blotches on leaves, or as discolorations on evergreen needles. Spores of the fungus spread in spring through the air or by rainwater. Anthracnose stunts leaf growth, and may also kill buds, twigs and shoots before they mature. Cankers or irregular growths sometimes appear on twigs, branches and bark. While most trees can weather an attack of anthracnose fungus, the damage it causes is an open door for other diseases and insect pests.

Trees affected by Anthracnose canker

There are many individual types of anthracnose fungi, each of which attack a specific tree species. Trees native to most North American climates can fall victim, including:

  • Apple
  • Ash
  • Butternut
  • Dogwood
  • Citrus fruit trees
  • Oak
  • Pine
  • Poplar
  • Mulberry
  • Willow

Anthracnose treatment options

For further information on ways to deal with anthracnose and other fungal infections, or for help on beginning an anthracnose treatment program, please contact us.

Bacterial Leaf Scorch

Not every brown edged leaf is a sign of a tree or leaf disease. Leaves often show a  small amount of stress from late summer heat. If the browning of leaves is greater than normal however, the cause could be a serious plant disease that calls for prompt treatment.

Bacterial Leaf Scorch Damage

Bacterial Leaf Scorch Damage

The first sign of leaf scorch is the reddening or yellowing of leaves, a sign that vessels are clogged with balloon-like growths from Xylella Fastidiosa, the bacterium that causes leaf scorch. Bacteria can soon spread through the entire tree, causing:

  • Upward leaf curl
  • Delayed budding
  • Decreased fruit production

Stunted growth In the worst cases, bacterial leaf scorch can kill a tree.

Trees Affected by Bacterial Leaf Scorch

Bacterial Leaf Scorch is a common disease affecting leaves and trees in the southern half of the US and in Northern California. Xylella Fastidiosa bacteria moves from tree to tree on leafhoppers, spittlebugs and other insects that feed on tree sap. Trees affected by bacterial leaf scorch include:

  • Almond
  • Beautyberry
  • Buckeye
  • Dogwood
  • Elderberry
  • Elms
  • Grapevine
  • Hackberry
  • Maples
  • Mulberry
  • Oaks
  • Oleander
  • Pecan
  • Peppervine
  • Plum
  • Sweetgum
  • Sycamores
  • Virginia Creeper

Bacterial Leaf Scorch Treatment

Antibacterial treatments are among the few known remedies for bacterial leaf scorch. Arborists suggest injectable treatments containing Oxytetracycline Hydrochloride, the active ingredient in Mauget Mycoject Ultra. University studies have shown that Mycoject Ultra suppresses the symptoms of Xylella Fastidiosa within one month of application.*

For further information on ways to deal with bacterial leaf scorch, or for help on beginning a leaf scorch treatment program, contact us at Greenwood.

Fusarium Wilt

These destructive fungi can devastate trees and plants, and several species in particular, such asFusarium oxysporum (Fusarium Wilt), have become a serious concern for arborists and horticulturists caring for palm trees throughout Southern California. Fusarium wilt is almost always fatal, especially in young trees and plants, and is responsible for the increased die-off in Southern California’s ornamental palms.

More Information

The genus Fusarium represents a large and highly diverse group of mycotoxic fungal pathogens that cause a wide range of diseases and sickness in humans, livestock and nearly every species of ornamental and economical plants. These destructive fungi can devastate trees and plants, and several species in particular, such as Fusarium oxysporum, have become a serious concern for arborists and horticulturists caring for palm trees throughout Southern California.

Fusarium oxysporum, also known as Fusarium wilt, affects a small number of woody ornamental species, including:

  • Albizia
  • Pyracantha
  • Date trees
  • Palm trees

 

Symptoms of Fusarium Wilt

This destructive disease causes:

  • Yellowing and browning of leaves
  • Extreme wilting
  • Devastating root and corm rot
  • Complete vascular tissue browning or purpling in trees and plants

Fusarium oxysporum is almost always fatal, especially in young trees and plants, and is responsible for the increased die-off in Southern California’s ornamental palms.

Stopping the spread of a Fusarium oxysporum infestation is an extremely difficult task, as the fungus can jump from plant to plant through soil, irrigation and in spores carried by the wind. Like many fungus species, Fusarium oxysporum is most active during warm months, and can quickly destroy palm trees during excessively hot conditions, drought or when these trees are under stress. In addition, Fusarium species can be spread by insects, such as Euwallacea sp., a recently discovered invasive boring beetle species found in Southern California.

Fusarium Wilt Treatment

Identifying a Fusarium oxysporum outbreak is not an easy task, even for seasoned arborists and horticulturists. Fusarium oxysporum symptoms can look very similar to diseases caused by Cylindrocladium, Rhizoctonia, Pythium and Botrytis, so it is important to have your plants tested to ensure that you are dealing with Fusarium oxysporum. Testing must be performed on live root samples to ensure correct identification.

Fusarium oxysporum infestations are notoriously difficult to control, and once the fungus has entered the tree’s vascular system, the tree will almost always die, even with repeated fungicide applications. Trees that are well maintained with adequate water, drainage and nutrients have a better chance at resisting Fusarium oxysporum infestations, while under-watered or stressed trees become much more susceptible to Fusarium oxysporum, and can die as quickly as a few months after the first symptoms begin to appear.

When you discover a tree that has been affected by Fusarium oxysporum, it is extremely important to either have the tree professionally pruned or to outright remove the tree, the entire root ball and the soil around it as fast as possible. Any tools used to prune or remove the tree and the dirt must be sterilized with bleach or Lysol® to prevent further contamination, and the root ball must be bagged to prevent the spread of Fusarium spores. Be sure to never replace the palm with the same species, and instead use diamond scale species, such as the Australian fountain palm, the Mexican blue palm or the Chinese windmill palm.

While tree removal is effective for combating Fusarium oxysporum, prevention is always the best method. Arborists can use fungicide spray treatments to help prevent Fusarium damage, or injection-based tree care products.

Rhizosphaera Needle Cast

Rhizosphaera needle cast has been causing problems in Spruce trees throughout the Midwest and the Northeast the past several years. Although Rhizosphaera Needle Cast can affect a number of conifer trees it is primarily a problem on Colorado Blue Spruce. This disease causes the trees to defoliate which affects the overall appearance and eventually the health of the affected tree.

More Information

Rhizosphaera needle cast has been causing problems in Spruce trees throughout the Midwest and the Northeast the past several years. Although Rhizosphaera Needle Cast can affect a number of conifer trees it is primarily a problem on Colorado Blue Spruce. It is caused by the fungus Rhizosphaera kalkhoffii.

Rhizosphaera Needle Cast Symptoms

This disease causes the trees to defoliate which affects the overall appearance and eventually the health of the affected tree. The fungus thrives in the spring during cool, wet, weather conditions. In late summer or early fall the infected needles begin to show a yellow discoloration. The diseased needles remain attached to the tree throughout the winter.

The following spring, needles turn purple/brown and drop from the branch. Most defoliation occurs late in the summer the year after infection. Defoliation begins on the branches at the bottom of the tree and works its way up into the middle and top of the tree. Affected branches will die after several years of defoliation. The dead branches affect both the overall appearance of the tree as well as the tree’s health.

Rhizosphaera Needle Cast may be diagnosed by examining needles with a magnifying glass. Healthy spruce needles have rows of white dots, which are the stomata. The stomata on infected needles are darkened by growth of the Rhizosphaera fungus. The dark growths are the spore-producing structures of the fungus.

Rhizosphaera Treatment

  • Remove tall weeds that surround the tree to increase air movement to promote drying of the needles
  • Thin out or remove shrubs and trees that are blocking sunlight and air movement
  • Reduce disease pressure by removing and disposing of fallen (infected) needles
  • Avoid pruning trees when branches are wet
  • Reduce spread of disease by sterilizing tools after pruning affected trees

Rhizosphaera Needle Cast Fungicides:

In addition to cultural practices fungicides will prevent the spread of RNC. Infections are most effectively managed if they are detected and treated early, before several years of defoliation have occurred. Small trees may be sprayed with a product containing the active ingredient chlorothalonil. Apply when the fungus is most active during the springtime when needles are halfway elongated. Apply a second foliar application when needles are fully elongated, 2 – 4 weeks later. Two years of applications are recommended.

Trees that have a diameter 2 inched or greater may be treated with a microinjection of Fungisol. For best results the Fungisol should be injected in the early spring when there is evidence of new growth, indicating that the tree has emerged from winter dormancy. Two years of applications are recommended.

Fire Blight

As spring arrives, many plants come out of dormancy. With this, many diseases come out of dormancy as well. One common example is Fire Blight.

Fire Blight Symptoms

Fire Blight Symptoms

Fire blight often starts in the spring. The disease can grow in temperatures ranging from 60°F to 90°F, though outbreaks typically occur in 80°F -85°F temperature. Because the disease can spread when the tree is damaged, outbreaks can often occur after storms that cause damage or from bugs that damage plants, like cicadas.

Typical symptoms of fire blight include:

  • Blight of blossoms. The blossoms will look wet and dark, then shrivel and turn brown or black.
  • Leaves, twigs and branch tips turn brown or black
  • Cankers can grow and become discolored (often a reddish brown), and if severe, may kill the tree
  • Infections may ooze a cream, yellow or orange ooze

Trees Affected by Fire Blight Fire blight is common in Rosaceae trees, including:

  • Hawthorn
  • Pear
  • Brambles
  • Quince
  • Apple
  • Firethorn
  • Mountain ash

Fire Blight Treatment

Fire blight is best managed by prevention. Prevention can include planting fire blight resistant trees, pruning, and avoiding fertilizer. Sprays can be used as well as a preventative measure.