Ash yellows phytoplasma

• Infected plants grow very slowly, and have a sparse thin canopy of leaves
• Leaves are small, yellow, often folded or cupped and grow in clumps along the branch
• Branches die throughout the canopy
• Many weak young sprouts with small yellow leaves arise from the base of the tree

Ash yellows is a chronic, systemic disease that affects ash trees of all ages. White ash is particularly susceptible to ash yellows. Ash yellows occur in the United States from New York and Pennsylvania west to Minnesota, Iowa, and Arkansas. The organism that causes ash yellows also causes a disease called lilac witches’-broom.

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 a 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 a frequently smaller, thinner and lighter green than usual. 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 die-back can continue until the entire crown is dead.

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

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 the 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 as firewood or chipped for mulch. Avoid growing ash trees in areas where ash yellows is prevalent.

Information source: hort.extension.wisc.edu

Branch cankers or Botryosphaeria sp. (and other fungi)

• Dead branches and twigs, often first observed in early spring
• Sunken, discolored canker on branches, oval-shaped to completely encircling the branch
• Dark stained sapwood visible if the bark is cut off of the discolored area of the branch
• Leaves on affected branches may wilt and die
• Small raised black pimple like bumps along the edge of the discolored area
• Common on trees stressed by drought, a recent transplant or other factors

Cankers are infections of shoots and branches that start as round to oval discolored areas where the bark has been killed.  As the infection progresses cankers girdle the stem resulting in wilt and death of any leaves above the canker.

Branches infected with canker-causing fungi often have discolored bark that may be cracked or oozing gums or dark-colored sap.  Spore-producing structures often emerge along the margins or on the face of the cankered area.  Examples of diseases that result in both leaf spots and cankers in Minnesota include Septoria leaf spot and canker of poplar and Septoria leaf spot and canker of dogwood.

Information source: https://extension.umn.edu

Clearwing borers (Ash borer and banded ash clearwing)

• Exit holes first appear in June and July
• Exit holes are round and 1/4 inch wide; frass (sawdust and excrement) can be conspicuous underneath
• Galleries occur deep in sapwood
• Pupae stick out of exit hole, empty pupal cases are commonly observed after moths have emerged
• Adults are wasp-like, lacking scales on most of their wings
• Larvae are caterpillars; have a brown head and cream-colored body; up to 1 1/3 inch long

Early signs of clearwing borer infestation are wilting of terminal shoots, and branch and crown dieback. Infestation sites often are marked by cankers, calluses, or cracked bark. Large limbs may die or become so weakened that they are easily broken in the wind. Established trees may persist in poor condition and be re-infested year after year.

Clearwing borers expel coarse, brown frass (sawdust-like fecal material) from cracks in the bark. In some hosts, especially Prunus species, the frass may be mixed with oozing sap or gum. When the adult moth emerges, it leaves an empty, tan shell (pupal skin) that protrudes from the bark. Feeding holes left by woodpeckers or other birds may indicate that a tree is infested.

Adult clearwing borers are delicate, day-flying moths that resemble small wasps. The moths feed only on nectar or not at all so they do not cause damage. The larvae are whitish, hairless caterpillars with brown heads. The most damaging clearwing borers are associated with dogwood, lilac, ash, oak, rhododendron, and ornamental Prunus species, including flowering peach, plums, and cherries.

Information source: University of Kentucky, College of Agriculture, Food and Environment, Department of Entomology

Coral spot canker or Nectria cinnabarina

• Dead branches and twigs, often first observed in early spring
• Sunken dark brown area on branch that is often cracked or has a ridge at the edge
• Raised cushion like bumps on affected branches, may be cream to orange or red, turn back with age
• Common on trees stressed by drought, recent transplant or other factors

Cankers are infections of shoots and branches that start as round to oval discolored areas where the bark has been killed.  As the infection progresses cankers girdle the stem resulting in wilt and death of any leaves above the canker.

Branches infected with canker-causing fungi often have discolored bark that may be cracked or oozing gums or dark-colored sap.  Spore-producing structures often emerge along the margins or on the face of the cankered area.  Examples of diseases that result in both leaf spots and cankers in Minnesota include Septoria leaf spot and canker of poplar and Septoria leaf spot and canker of dogwood.

Information source: https://extension.umn.edu

Emerald ash borers

• Chewing damage caused by adults occurs late May to early August
• Chews along the edges of leaves; defoliation is typically minor
• Slender bodied, 1/3 – 1/2 inch long; iridescent green with coppery colored head

Environmental stress including Drought, compact soils, flood damage, winter injury, other

• Leaves wilt and turn brown at the tips and the margins first, then completely brown
• Many weak young shoots/sprouts at the base of the tree
• Leaves appear drooped or wilted within the canopy

Information source: https://extension.umn.edu

Flatheaded borers or Primarily Chrysobothris sexsignata

• Exit holes first appear in May and June
• Found nearly always in black ash
• Exit holes are oval shaped and 3/16 inch wide
• Galleries start in phloem and eventually enter into sapwood; generally not very serpentine
• Adults are 1/2 inch long, bullet-shaped, and bronzed colored
• Larvae are whitish, flattened, up to 1 inch long; area behind enlarged and flattened; head generally inconspicuous; legless

Information source: University of Minnesota

Perennial Nectria canker or Neonectria ditissima

• Sunken round to oval cankers with target-shaped ridges of barkless wood on large branches or the main trunk
• A small dark sunken area on twigs that can girdle and kill the branch
• Red to reddish orange raised cushion as bumps can occasionally be seen on the edge of the canker

Cankers are infections of shoots and branches that start as round to oval discolored areas where the bark has been killed. As the infection progresses cankers girdle the stem resulting in wilt and death of any leaves above the canker. Branches infected with canker-causing fungi often have discolored bark that may be cracked or oozing gums or dark-colored sap. Spore-producing structures often emerge along the margins or on the face of the cankered area. Examples of diseases that result in both leaf spots and cankers in Minnesota include Septoria leaf spot and canker of poplar and Septoria leaf spot and canker of dogwood.

Information source: https://extension.umn.edu

Redheaded Ash Borer

• Exit holes first appear in June
• Exit holes are round and 3/8 inch wide
• Galleries start in phloem and eventually enter into sapwood; generally not very serpentine
• Adults are 1/2 to 5/8 inch long; reddish brown with four yellow bands across their wing covers
• Larvae are up to 4/5 inch long, whitish, cylindrical; area behind head enlarged and round, head generally inconspicuous; legless

The redheaded ash borer, Neoclytus acuminatus, is a multicolored beetle in the family Cerambycidae. Adults have a reddish head and thorax, and have four bands of fine yellow hairs that cross the dark brown wing covers. Another striking feature of this insect is its legs: the middle and hind legs are long, with the second section (femur) swollen, appearing almost muscular. Overall, the redheaded ash borer is small, only 4-18 mm long.

Typical of native borers, the targets of the redheaded ash borer are stressed and dying trees. These trees can be mature or newly planted, or they can be recently cut and still green (unseasoned). The host list for this borer includes many hardwood tree species, but the favored hosts are ash, oak, hickory, persimmon, and hackberry. This insect will also feed in fruit trees, and the author has recovered redheaded ash borers from grapevines.

Adults emerge from infested host wood, chewing 2-5 mm diameter round holes. If the insect host has been made into firewood, the adults can emerge from wood stored in the home prior to burning. Redheaded ash borer adults are seen as a nuisance since they do not lay eggs on household wood or harm occupants.

Information source: Iowa State University

Stem girdling roots

• A root circling the trunk of the tree may be seen at the soil line
• The trunk may become sunken in or compressed where it contacts the root
• If the girdling root is below ground the trunk will lack the natural widening or flare at the soil line, but rather will go straight into the earth like a telephone pole
• Affected trees have slow growth, poor color, change color and lose their leaves early in the fall
• Affected trees commonly exhibit water-stress symptoms such as marginal leaf scorch, wilting, sudden leaf fall
• Affected trees commonly exhibit excessive and abnormal winter damage including true frost cracks and dieback

A tree is girdled when something is tightly wrapped around the trunk or stem. A stem girdling root circles or partially circles the base of a tree at or just below the soil surface.

Stem girdling roots choke off the flow of water and nutrients between the roots and branches and food produced in the leaves from reaching the roots. They can also compress and weaken the trunk of a tree at or above the root collar flare (the junction between the trunk and the main roots) causing it to lean and lose its stability. Girdling roots may girdle other roots, but there is no known harm in this. Trees having stem girdling roots suffer a slow decline in health and premature death.

The appearance of a tree trunk will be affected by a girdling root. Usually, tree trunks flare out where they enter the ground. The root will prevent the collar flare, sometimes the trunk may get narrower and appear flattened or sunken. The threat depends on the size of the root and the amount of the tree’s circumference affected. It is almost impossible to predict if a developing girdling root will cause problems for a tree. However, if a tree has girdling roots it is more likely to have problems than one without them.

The causal factors may be genetic or cultural. At the end of this article is a list of trees that may be more prone to stem girdling roots. Cultural practices that may cause girdling include poor growing practices or poor planting techniques.

Most tree roots are in the top 6 to 24 inches of soil and grow out from the trunk in a spreading manner. Cultural practices that can adversely affect this natural root pattern include:

1. Planting in a hole that is too small so the roots cannot easily spread out.
2. Planting container-grown trees that have roots growing in a circular pattern.
3. Planting a bare root tree by twisting roots to fit into a small hole.
4. Leaving wire baskets, burlap and any part of a container in the planting hole.
5. Piling mulch against the trunk of a tree (creating a mulch volcano).

The most common theory of the cause of stem girdling roots is that they develop as a result of trees being planted too deeply. When root systems are buried, less oxygen and water is available. The roots will grow up towards the surface of the soil and tend to encircle the trunk. The more deeply buried the roots are, the fewer the roots available for the tree to become established.

Symptoms of stem girdling roots include:

1. Scorch, early fall color, early leaf drop, damage on one or two branches.
2. Abnormally small leaf size.
3. Excessive twig dieback, the appearance of large, dead, leafless branches (stagheading).
4. Thin appearance to the crown, overall stunting.
5. Little or no trunk taper at the collar.
6. Leaning.
7. Susceptibility to environmental extremes and other biotic problems.

Many of these symptoms can also be characteristic of other causes, such as drought or nutrient imbalances. A plant disease diagnostic laboratory cannot identify this problem. The only sure way to determine if a stem girdling root is the cause of a problem is to examine the root system and its relationship to the tree trunk.

Information source: https://extension.umn.edu and http://www.missouribotanicalgarden.org