Tag Archives: Ash

Ash Yellows

What is ash yellows?  Ash yellows is a chronic, systemic disease that affects ash trees of all ages.  White ash is particularly susceptible to ash yellows.  Ash yellows likely occurs wherever ash is grown and has been reported widely in the United States and southern Canada.  The organism that causes ash yellows also causes a disease called lilac witches’-broom.

Brooming symptoms in an ash tree caused by ash yellows.
Brooming symptoms in an ash tree caused by ash yellows.

What does ash yellows look like?  Symptoms of ash yellows usually occur within three years of infection.  Infected trees typically grow at a much slower rate than non-infected trees, although this may be difficult to detect in an isolated, single tree.  The rate of growth of an infected tree may be as little as one half that of a healthy tree.  Leaves on infected trees are frequently smaller, thinner and lighter green than normal.  Often, but not always, affected trees will produce branches in tufts, a symptom that is called “brooming”.  Eventually, branches in the crown will die and this dieback can continue until the entire crown is dead.

Where does ash yellows come from?  Ash yellows is caused by the phytoplasma, Candidatus Phytoplasma fraxini.  Phytoplasmas are bacteria-like organisms that live and survive in the phloem (the food-conducting tissue) of infected plants.  Leafhoppers are thought to be the primary means by which this pathogen is moved from tree to tree.

How do I save a tree with ash yellows?  There is no known cure for ash yellows, but some infected trees may live and grow slowly with the disease for many years.  Ash trees suspected of having ash yellows should be tested for the disease, and those trees that test positive should be removed immediately to prevent spread of the ash yellows phytoplasma to other trees in the area.  Wood harvested from infected trees does not serve as a source of the phytoplasma and can be used for woodworking or firewood, or chipped for mulch.

How do I avoid problems with ash yellows in the future?  Avoid growing ash trees in areas where ash yellows is prevalent.  When choosing a lilac, select a variety of common lilac as these varieties appear to have tolerance to the ash yellows phytoplasma.  Avoid using S. josikaea, S. reticulata and S. sweginzowii (or hybrids of these species with either S. komarowii or S. villosa), as these lilacs appear to be highly susceptible.  It is unclear if the use of insecticides (or other means) to control leafhoppers can help control the spread of this pathogen.

For more information on ash yellows and ash yellows testing:  Contact your county Extension agent.

Anthracnose

Anthracnose is very common on many types of trees and shrubs. It often occurs on the leaves of ash (left) and maple (right) trees, causing blotchy-brown, dead areas.
Anthracnose is very common on many types of trees and shrubs. It often occurs on the leaves of ash (left) and maple (right) trees, causing blotchy-brown, dead areas.

What is anthracnose?  Anthracnose is the name of several common fungal diseases that affect the foliage of woody ornamentals in Wisconsin.  Trees that are most commonly and severely affected by anthracnose include ash, maple, white oak, sycamore, and walnut.  Anthracnose typically affects young leaf tissue.

What does anthracnose look like?  Symptoms of anthracnose vary from host to host, but in general include irregular spots, and dead areas on leaves that often follow the veins of the leaves.  Affected tissue can vary in color but is often tan or brown.  Severely affected leaves often curl and may fall off.  In some tree species, such as sycamore, twigs can also become infected leading to twig dieback.

Where does anthracnose come from?  Anthracnose is caused by several fungi (many historically classified in the genus Gloeosporium) that survive in leaf litter.  These fungi are host specific.  The anthracnose fungus that infects one type of tree (e.g., ash) is not the same one that infects another type of tree (e.g., maple).  However, when anthracnose occurs on one tree, then weather conditions (typically cool and moist conditions) are favorable for development of the disease on many types of trees.

Anthracnose can be severe on some hosts. On white oak (left), it can cause extensive leaf browning and curling. On sycamore (right), anthracnose can cause twig dieback.
Anthracnose can be severe on some hosts. On white oak (left), it can cause extensive leaf browning and curling. On sycamore (right), anthracnose can cause twig dieback.

Anthracnose can be severe on some hosts. On white oak (left), it can cause extensive leaf browning and curling. On sycamore (right), anthracnose can cause twig dieback.

How do I save a tree with anthracnose?  DO NOT panic.  For many trees, anthracnose is a cosmetic disease.  It may make a tree look a little ragged but will not kill the tree.  However, if a tree has been defoliated by anthracnose for several years, or it is a tree, such as a sycamore, where twig infections can occur, then you may want to use a fungicide for disease control.  Three treatments are typically needed for adequate control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded.  Fungicides containing copper, chlorothalonil, or mancozeb are registered for anthracnose control in Wisconsin.  DO NOT use the same active ingredient for all treatments.  Instead, alternate the use of at least two active ingredients to help minimize problems with fungicide-resistant strains of anthracnose fungi.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the fungicide(s) in the safest and most effective manner possible.

How do I avoid problems with anthracnose in the future?  You can reduce the number of spores that cause anthracnose infections by removing and disposing of fallen, infected leaves in the autumn.  Leaves can be burned (where allowed), buried or composted.  When composting, make sure that your compost pile reaches high temperature (approximately 140°F).  Also, make sure that your compost pile is routinely turned so that leaves on the outside of the pile eventually end up in the center of the pile.  The combination of high temperature and decay of leaf tissue in a compost pile helps eliminate anthracnose fungi.  Also, maintain good tree vigor by watering and fertilizing trees appropriately.  Check with your local county Extension agent for details on how to properly care for trees.

For more information on anthracnose:  Contact your county Extension agent.