Hypoxylon fungus

Very often when we are called to look at dead or dying oaks we find fungi in the genus Hypoxylon. These fungi are very ubiquitous and form latent colonies on healthy oaks and other hardwoods. Once the trees are weakened by stresses, such as drought, herbicide damage, insects or other diseases, Hypoxylon mobilizes to take advantage of the resources provided by a sick tree. In some cases, it may even slow the spread of more devastating diseases; trees succumbing to oak wilt are often rapidly colonized by Hypoxylon, which can use up the sugars and starch in the sapwood, preventing the oak wilt fungus from spreading.

Stromatal mat and fruiting bodies of a decaying fungus on an oak killed by flooding.

Stromatal mat on an oak killed by fungus.

Close up of stromatal mat.

Stromatal mats on willow oak that was flooded by beavers.

Stromatal mat of Hypoxylon on willow oak that has been killed by oak wilt.

 

Because Hypoxylon is so commonly found on dead and dying trees it is understandable that decline is often attributed to it. It is unlikely that Hypoxylon is ever the primary cause of mortality, but it can certainly play an important part in the decline of stressed trees. If other diseases or insects can be ruled out, conditions in the year or years prior to the onset of symptoms may be key.

Hypoxylon atropunctatum was associated with dieback and mortality of numerous oaks in the southeastern U.S. in 1981 after conditions of extreme heat and drought in 1980.

Fungi in the genus Hypoxylon are relatively easy to recognize. It decays the inner bark and sapwood so that the outer bark sloughs off, revealing the distinctive tan or gray stromatal mats. As the stromata mature they become black. Under some conditions black dome-like perithecial stromata may be formed.

 

 

Fall webworm

Caterpillars of the red-headed race of the fall webworm.

 

 You may be noticing webbing in trees and shrubs this time of year. In many cases these are the nests of the native caterpillar Hyphantria cunea, or the fall webworm. There are two or three generations a year in South Carolina and so we see the web nests into early fall, though they can be found in spring and summer, too.

Webbing constructed by caterpillars of the fall webworm.

 

For many years it was thought that there were two species of fall webworm; a black-headed species and a red-headed species. They do interbreed and so they are considered two races of the same species. The races are different in their coloration and their behavior. For instance, adults of the black-headed race tend to emerge almost a month earlier than the red-headed race. Both races lay their eggs in masses on the undersides of leaves, but the black-headed race lays a single layer of eggs, whereas the red-headed race lays two layers of eggs.

Black-headed form of the fall webworm. outside of its web nest.

Red-headed form of the fall webworm outside of its web nest.

 

 

The caterpillars spin the silk to make their nests and their nests are always at the terminals of branches, unlike the eastern tent caterpillar whose aggregation of webbing is always in the crotch of the host tree. The fall webworm is a polyphagous insect, attacking many hosts. In South Carolina we commonly see nests in persimmon and sweetgum, but they attack many other trees, including elms, hickories, walnuts, pecans, and maple, among many others.

The damage is mostly cosmetic. I have known landowners to mechanically remove the nests, pruning the affected terminals, but most trees can handle a certain level of defoliation, especially at the end of summer when leaves are getting ready to senesce anyway.

Young fall webworm larvae eating tissue of a sweetgum.

 

If you have a curious mind you can try rearing out parasitoids, wasps and flies that have laid their eggs on or in the caterpillars. More than fifty species have been reported from the fall webworm!

Adopt an ash tree!!!

An old ash tree in the mountains of North Carolina.

Emerald ash borer has been detected in more than 20 states. It is impossible to tell if quarantines have been successful in slowing the range expansion of the emerald ash borer, but it is clear that detection in South Carolina is inevitable.

What does this mean? There are four species of ash in South Carolina (green, white, Carolina and pumpkin ash) and all are attacked by the emerald ash borer. Ash is found in every county in South Carolina, but is most concentrated in moist soils associated with floodplains and rivers. It is also commonly planted as an ornamental shade tree in neighborhoods. The wood is used to make tool handles, furniture and is used in the hardwood veneer industry. Based on the experience of other states where emerald ash borer has been found, these trees could become rare or disappear!

Early detection may be key in protecting our trees.

What can you do? Adopt an ash tree or several! Look for ash trees in your neighborhood, city park, or favorite hiking spot, anywhere that you can easily visit weekly or monthly. Keep an eye on those trees throughout the year. During the winter you can look for flaking bark or woodpecker damage indicating an infestation of borers. In spring and summer you can look for sick foliage (fewer leaves, yellow leaves), sprouts from the base of the tree, D-shaped holes in the bark. If you see something suspicious contact the Forest Health section of the South Carolina Forestry Commission (djenkins@scfc.gov, or (803) 667-1002). DO NOT MOVE POSSIBLY INFESTED MATERIALS!!!   

Recognizing ash trees

Many of us don’t know an ash from our elbow, but with a little help you, too can identify ash trees.

In September ash trees produce winged oar-shaped seeds. These seeds will be common on the ground below a female ash… male ash trees do not produce seeds.

Seeds from a female ash tree. Seeds will be visible late in the summer and through winter. Some ash trees are male and will not have seeds.

 

The bark has deep diamond-shaped furrows.

Bark of an ash showing the distinct diamond-shaped furrows.

 

Foliage is compound; a leaf is composed of multiple leaflets.

Terminal stem of an ash tree showing the opposite compound leaves. In this drawing there are seven leaflets on each compound leaf.

 

Ash is one of the very few trees in our landscape that has opposite leaves, that is, the leaves come off of the stem opposite one another. Other trees that have opposite foliage are not easily confused with ash trees and include dogwoods, maples, horse chestnuts or buckeyes, and catalpas. The only problem is that many of the ash trees that we want to monitor won’t have leaves within easy reach!

If you would like more information or to learn other ways you can protect our forests contact us at: djenkins@scfc.gov, or (803) 667-1002.

Oak Wilt

Caused by the fungus Ceratocystis fagacearum, this is probably the most serious disease of oaks in the eastern United States. Only found in the United States, oak wilt occurs from the Mississippi River east to the Atlantic, with an isolated pocket in Texas.

Oak infected with oak wilt fungus, Ceratocystis fagacearum. Photo was taken in September. Photo credit: David Jenkins, South Carolina Forestry Commission.

All oaks are susceptible, but oaks in the red oak group (typically those with pointy foliage, like red oaks and turkey oaks) are affected much more severely than oaks in the white oak group (typically those oaks with rounded lobes, like white oaks). In fact, this disease has been used as a selective “herbicide” to remove red oaks from land where they are not desired! Symptoms progress slower in oaks from the white oak group and these oaks often survive.

The fungus reproduces in the tree’s vascular system, shutting down water transport in the xylem. Like many diseases that affect the vascular system, this results in symptoms very similar to those caused by drought. Symptoms often show up in the crown first, with leaves wilting (they aren’t getting water) and turning brown. The browning usually starts at the leaf tips and progresses inward, leaving an abrupt border between brown dying tissue and green tissue.

Leaves from an oak infected with oak wilt. Photo credit: C.E. Seliskar, Bugwood.org.

The fungus can spread through root grafts and can be transmitted by oak bark beetles and sap beetles. Transmission by root grafts often results in a center of dead trees surrounded by a ring of dying trees.

Pattern of tree death when oak wilt spreads by root grafts. Note the dead trees in the center surrounded by a ring of dying trees. Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org.

Under certain conditions, the fungus produces grey mats on the surface of the wood and on the inner surface of the bark. These grey mats produce a fruit odor and exert pressure on the bark, often causing the bark to rupture. Sap beetles are especially attracted to the odor of the fungus.

Fissures in bark due to pressure from underlying fungal mat. Photo credit: David Jenkins, South Carolina Forestry Commission.

 

Fungal mat under bark of infected oak. These mats are not always present. Photo credit: Fred Baker, Utah State University, Bugwood.org.

Stained entrance holes typical of sap beetles. Sap beetles are attracted to the odor of the fungal mats and can transmit fungal spores to healthy hosts. Photo credit: David Jenkins, South Carolina Forestry Commission.

 

Wounds caused by wind damage or pruning can be entry points for spores and for beetles that are carrying the spores.

The oak wilt fungus does not tolerate high temperatures and often dies back in the smaller limbs when the weather is hot. However, the fungus will continue to grow in the trunk and the roots where the temperature is buffered my more tissue and soil.

The dead and dying trees are attractive to a variety of secondary pests besides the bark beetles and sap beetles already mentioned. These will include wood-boring beetles and woodwasps, such as Tremex.

Eriotremex formosanus woodwasp attacking dying oak tree. Photo credit: David Jenkins, South Carolina Forestry Commission.

If you see symptoms consistent with oak wilt, you can contact the South Carolina Forestry Commission Insect and Disease Staff (David Jenkins ((803) 896-8838) office; (803) 667-1002 cell; or at djenkins@scfc.gov) or your local Forestry Commission office.

Sudden Oak Death

 

 

Sudden oak death is a disease caused by the water mold Phytophthora ramorum. Currently it is limited to California and Oregon and parts of Europe. This pathogen can infect a wide variety of plants, but oaks are most severely affected. Non-oak hosts may serve as important reservoirs of the disease and transport of infected ornamentals, such as rhododendron, may be important in moving this disease out of its current range.

Oaks infected with Phytophthora ramorum. Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org.

 

Weeping canker on infected oak. Photo credit: Bruce Moltzan, USDA Forest Service, Bugwood.org.

Symptoms include the wilting of new shoots, chlorosis of older foliage, and dead brown foliage that remains on the tree. Bleeding cankers exuding dark sap may appear on the lower trunk and the bark may fissure. As the tree dies back, suckers will appear the following spring only to wilt and die.

Oak leaves with symptoms of infection with Phytophthora ramorum. Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org.

 

Canker on oak crown caused by Phytophthora ramorum. Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org.

 

The weakened trees attract insects and allow the growth of other pathogens/saprophytes. Ambrosia beetles may attack dying trees, producing fine white sawdust at their entrance holes.

Tube of sawdust excavated by an ambrosia beetle. Photo credit: David Jenkins, South Carolina Forestry Commission.

 

Later, bark beetles will attack, producing red sawdust. Severe infestations of bark beetles can girdle trees.

Small black domes may appear on the bark. These are the fruiting bodies of Hypoxylon fungus, an opportunistic invader of weakened trees.

Fruiting bodies of Hypoxylon fungus. This is an opportunistic pathogen that only invades stressed or diseased trees. Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org.

 

Phytophthora ramorum produces resistant spores that are able to survive winter. It also produces flagellated spores that move in water. The spores can spread through splashing rainwater and in streams, where it can be moved greater distances. Wounds facilitate infection but are not required for this pathogen to gain entrance to its hosts.

Like many diseases, early detection is key in controlling sudden oak death. There is no cure for infected trees. Isolating infected trees and practicing good sanitation (removing foliage and debris from shoes when leaving an infected area) help reduce the spread.

If you see symptoms consistent with sudden oak death, please contact the South Carolina Forestry Commission Insect and Disease Staff (David Jenkins ((803) 896-8838) office; (803) 667-1002 cell; or at djenkins@scfc.gov) or your local Forestry Commission office.

 

Emerald Ash Borer

 

 

Figure 1. Adult emerald ash borer; photo credit: David Cappaert, Michigan State University, Bugwood.org

The emerald ash borer (scientific name Agrilus planipennis) is an Asian metallic wood boring beetle that was first discovered in North America in Michigan in 2002, though it was probably established much earlier. Adult emerald ash borers are about 8.5 mm (0.33 inches) long and chew on the foliage of ash trees. Females lay their eggs (between 40 and 200, depending on her longevity) in crevices and cracks in the bark. The larvae hatch approximately two weeks later and chew through the bark to the inner phloem, cambium, and outer xylem where they feed. As they feed they form long galleries that damage the tree’s vascular system, disrupting the tree’s ability to transport water and nutrients. In cooler climates, like Michigan, it takes two years for a larva to become an adult, but in South Carolina they can complete their lifecycle in one year. Characteristic of most metallic wood-boring beetles, adults emerge from infested trees, leaving D-shaped holes.



Figure 2. Adult and larval emerald ash borer next to a quarter to illustrate their small size. Photo credit: David Jenkins, South Carolina Forestry Commission.

 

Figure 3. Larvae of emerald ash borer and damage to cambium; photo credits:  Pennsylvania Dept. of Conservation and Natural Resources, Forestry Archive, Bugwood.org and Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org

Figure 4. D-shaped emergence hole of emerald ash borer; photo credit: Pennsylvania Dept. of Conservation and Natural Resources, Forestry Archives, Bugwood.org

Early attacks by this beetle are focused in the higher portions of the tree and may be difficult to detect. As the population grows the beetles begin to lay eggs on lower portions of the tree. By the time infestations are detected in the lower trunk of the tree, the upper part may have been infested for two years.

The damage to the vascular system causes the tree to decline, losing foliage. Infested trees may produce shoots at the base, a common response to pests and diseases. Since the larvae are tasty treats for woodpeckers it is common to see woodpecker damage on heavily infested trees.

Figure 5. Epicormic growth, or shoots coming from the base of an infested ash tree; photo credit: Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org

So far, emerald ash borers have only been found to attack species of ash, preferring green ash. Although they can attack healthy trees, they are most attracted to stressed and unhealthy trees. Ash trees may be recognized by their oppositely arranged compound leaves. Female trees may have samaras, or winged seeds on them. The bark has distinctive diamond-shaped ridges.

Figure 6. An ash tree branch with winged samaras, or seeds; photo credit: David Jenkins, South Carolina Forestry Commission

Figure 7. Diamond-shaped ridges on ash bark; photo credit: David Jenkins, South Carolina Forestry Commission

Research is being conducted on the use of biological control agents, including wasps that attack the larval and egg stages, and fungi that infect the larvae; however, these are not widespread yet. The use of systemic insecticides may be useful for some trees, for instance trees of cultural significance. However, systemic insecticides depend on transportation in the vascular system; transportation may be reduced in larger trees or trees with reduced foliage. Currently the recommended management method is to destroy infested trees before adults emerge and spread.

As of this year, the Clemson University Division of Plant Industry, in concert with USDA-APHIS, have been surveying South Carolina for emerald ash borer infestations. Large purple panels coated with sticky glue are baited with chemicals odors from ash trees and hung in the crowns of ash trees. Traps are checked weekly during the summer when adult beetles are flying.

Figure 8. Baited sticky traps used to monitor emerald ash borer; photo credit: Kelly Oten, North Carolina Forest Service, Bugwood.org

So far, no infestations by emerald ash borer have been found in South Carolina, but both North Carolina and Georgia have detected infestations, so we need to be alert!

Detections of emerald ash borer as of August 2015 can be found at: http://www.savatree.com/eab/eab-2014.png.

The adult beetles do not fly very far, but larvae and adults can be transmitted from infested areas through movement of nursery stock, unprocessed ash products and firewood.

If you suspect an infestation of emerald ash borer, please contact the South Carolina Forestry Commission Insect and Disease Staff (David Jenkins (803) 896-8838 office; (803) 667-1002 cell; or at djenkins@scfc.gov), or your local Forestry Commission office.

For more information you can contact us or visit the following sites:

http://www.emeraldashborer.info/#sthash.9u0YZruI.dpbs

http://www.clemson.edu/public/regulatory/plant_industry/pest_nursery_programs/invasive_exotic_programs/survey_programs/eabsurvey.html