Tag: fungus

Does My Elm Have Dutch Elm Disease?

A fungus called Ophiostoma ulmi that was introduced to the U.S. in the early 1930’s causes Dutch Elm Disease (DED). The American elm (Ulmus americana) is highly vulnerable and the disease has killed hundreds of thousands of elms across North America. All native elms are susceptible, as are European elms. However, the Asiatic elms, (U. parvifoli) and Siberian elm (U. pumila) are highly resistant to the disease.

The DED fungus is spread by two insect vectors: the native elm bark beetle (Hylurgopinus rufipes) and the European elm bark beetle (Scolytus multistriatus). The fungus is transported on the beetles from infected trees to healthy trees as they feed on twigs and upper branches. The beetles lay their eggs in the bark and wood of stressed trees along with elm firewood with the bark left on. Developing larvae form channels just under the bark and the fungus grows through the galleries until it reaches the tree’s water conducting cells, or xylem. Chemicals manufactured by the tree during its effort to fight the disease plug up the xylem, causing the tree to wilt.  In the Midwest, beetles typically have two generations per year.

DED is also transmitted through root grafts. A root graft happens when the roots of two trees intermingle and touch. Root grafts between trees are especially widespread in cramped urban street trees. Driveways and sidewalks are usually not effective in blocking root grafts, however, the disease usually does not spread in this manner beneath roads because road foundations are much deeper.

DIAGNOSIS:

elm branch showing the effects of dutch elm disease

During the early summer is when effected trees are the easiest to identify. Leaves on the upper branches will curl and turn a gray-green or yellow and finally, crunchy brown. This symptom is called “flagging”, although a flag alone is not complete assurance that the tree has DED. Another symptom is brown streaks in the sapwood beneath the bark of affected branches, which is the blocked xylem. However, only laboratory isolation and identification can positively confirm that the tree has DED. Check with your local extension or State University, usually they will perform this test for a nominal fee. Most arborists find these two symptoms are enough evidence to treat or remove an elm.

There are two other diseases that may look like DED, Elm Yellows and Bacterial Leaf Scorch. Below is a symptom checker:

Dutch Elm Disease Bacterial Leaf Scorch Elm Yellows
Caused by fungus Caused by bacteria Caused by phytoplasma
Affects individual branches first. Affects lower crown nearest root graft. Damage initially observed on single branches, and spreads to entire crown; oldest leaves affected first. Affects the entire crown at the same time.
Leaves wilt and turn yellow, then brown. Leaves brown along margin, with a yellow halo. Leaves turn yellow and may drop prematurely.
Symptoms often observed in early summer, however, could be anytime during the season. Symptoms appear in summer and early fall. Symptoms visible from July to September.
Brown streaking in sapwood. No discoloration in sapwood. No discoloration in sapwood.
No discoloration in inner bark. No discoloration of inner bark. Tan discoloration of inner bark.
No wintergreen odor. No wintergreen odor. Wintergreen odor in inner bark.

 

MANAGEMENT:

Elm tree with dutch elm disease

  • Branches infected with DED should be removed the same year the infection started. All infected branches should be pruned at least 5 feet, preferably 10 feet, below the last sign of streaking in the sapwood. Dip pruners often (best after each cut) in a solution of 10% bleach to prevent spreading the disease. Be sure to remove infected branches before the disease has moved into the main stem of the tree.
  • Trees with many branches infected with DED should be removed. There is no cure. The best thing to do to stop the spread of the disease is to promptly remove the tree.
  • Wood from DED infected elm trees need to be buried, burned, debarked, or chipped. When chipping and composting, temperatures must attain at least 120F. Cut logs from diseased trees should not be stored for firewood unless it has been debarked and there is no evidence of beetles.
  • Neighboring elm roots need to be severed with a vibratory plow or trencher before the infected tree is removed in order to prevent the movement through root graphs.
  • Choose cultivars that are resistant to Dutch elm disease. ‘Frontier’, ‘Homestead’, and ‘Valley Forge’ are a few that are offered in my area, but there are many more.
  • Healthy elms can be treated with a preventative fungicide injection to protect trees from infection by beetle feeding. Although, fungicide injections are not effective in averting infection through root grafts. Injections can only be done by a trained arborist and depending on the chosen fungicide, must be repeated on a 1-3 year cycle.
  • The consensus on treating the beetles with insecticide is not to. Contact insecticides require repeated applications during the growing season that may kill beneficial or harmless insects. Sanitation is by far the best way to control beetle populations.

Sadly, this is a prime example of what happens when we plant a monoculture of trees. Diversity is where it’s at!!

© The Naturarian

Are My Plants on Crack? Powdery Mildew on Plants

mildew grape leaf.JPG
On grape leaf – Credit: David B. Langston

There are many species of fungus that cause powdery mildew on plants. Most only infect the leaf surface or stems and do not attack the leaf tissue of the host plant. Powdery mildew is not usually a serious problem, but to avoid severe damage to plants, quick control methods need to be taken.

Symptoms of powdery mildew:

Powdery mildews are observed in late spring and early summer as a white or gray powdery growth on leaves, stems, flowers, and fruit. As the fungus developments, buds fail to open, leaves can become distorted, turn yellow, brown or become chlorotic, or may drop prematurely. Fruits may develop blemishes or abort early.

white mildew on peony leaves
Powdery mildew on peony

Powdery mildew grows predominantly on leaf surfaces and does not require water to infect the plant. Powdery mildew fungi overwinter in tiny black bodies called fungal threads, which can be found in leaf litter, twigs, and dormant buds. In Spring, the fungal threads produce spores that start the cycle, especially during periods of high humidity when days are warm and nights are cool, ideal temperatures range between 60F to 80F. Vulnerable plants are most susceptible while new shoots and leaves are expanding. Fungus is host specific, meaning the powdery mildew on phlox does not infect crabapples.

 

How to manage the mildew!

Cultural

Many powdery mildews, especially those that attack woody plants, are more unsightly than destructive. Good sanitation is highly important to reduce infections the next season. Powdery mildews can hibernate through the winter on dead and living plant tissue.

  • Be proactive and purchase disease resistant plants.
  • Space the plants properly, in-well drained soils where plants receive good air circulation.
  • Dispose of diseased leaves as soon as they drop.
  • Do not compost or use as mulch.
  • Always avoid working among plants with wet foliage. Stay inside on rainy days!

Chemical

Since most powdery mildew symptoms occur late in the growing season, it is usually not considered serious enough to justify chemical control. However, some plants may warrant protection and successful chemical control requires applying a fungicide properly and at the right time. Fungicides are a prophylactic, meaning it has to be sprayed on the plant before the infection occurs. Depending on what species or part of the plant (leaves, flower or fruit) you are trying to protect, spray times may be different.

One of my favorite, efficient fungicides to use is the Bordeaux mixture. In the early 19th century, many of the European grape vines were infected with blight caused by the aphid Phylloxera vastatrix (argued to have come from American grapes), but also mildew and other diseases caused by fungi.

In 1885, botany professor Pierre-Marie-Alexis Millardet of the University of Bordeaux studied powdery mildew in the vineyards of the Bordeaux region. He noticed the vines sprayed with copper and lime to keep nibblers away along the roads showed no signs of the disease. To this day, his solution is widely used in vineyards.

© The Naturarian

Help With Volutella Blight on Pachysandra

pachysandra ground cover with blight diseasePachysandra terminalis is a beautiful, lush, evergreen ground cover for a semi-shady spot. One of the most common problems with pachysandra is a fungal infection called, Volutella Blight. Generally, pachysandra has very few issues when well cared for. However, when other situations stress the plant out, opportunistic pests can take over.

Volutella Blight has a fungal ring associated with the damaged lesions. Winter damage has an even-toned brown to the damage.

How to not stress out your pachysandra:

    • Plant it in a partial shade or shade area. Not in the sun.
    • Do not overwater, water in the morning and use drip irrigation, not overhead.
    • Be sure to do a fall cleanup to remove any fallen leaves or plant debris from the bed to improve air circulation and reduce moisture levels. Blow lightly with blower.
    • It is also helpful to periodically thin the planting to prevent dense growth and increase air circulation. Use leaf mulch, not woody chips.

blight on pachysandrapachysandra with winter injury

Blight on the left / Winter damage on the right

Fungicides such as mancozeb and maneb can be used to protect remaining plants and the new growth of any pachysandra that have been cut back. These treatments can help deter infection but will not cure infected plants. You would need to spray at 7 to 14 day intervals from spring until early summer. Generally this time would coincide with the blooming of serviceberries (Amelancheir) and Redbuds (Cercis canadensis).

© The Naturarian

Ring Around the Lawn – Fairy Rings

fairy ring fungus in lawn a ring of darker colored grassFairy Ring fungi are in the soil to break down old tree stumps, roots, logs and other larger pieces of organic material in the soil below the lawn. The uniform outward growth of the fungus results in the development of rings. Once the material is exhausted, the fairy ring will disappear. This may take many years. Several fairy rings may appear close together, especially in lawns that were previously wooded areas.

When these fungi digest the organic material, they expel nitrogen. This is why the grass looks seemingly happy in the fairy ring. However, sometimes the opposite effect can happen, which depletes soil nutrients and produces toxic levels of hydrogen cyanide.

Fairy ring with mushrooms bloomingApproximately 50 species of fungi in the Basidiomycetes family are known to cause fairy rings in turf; however, there are only three outcomes:

  • Variety A: The most inconspicuous type of fairy ring. The dark ring of grass is absent. Only parts of the ring will show fruiting bodies (mushrooms) at different times of the year, mostly during wet springs.
    • Remove the mushrooms to help retard the spread in the area. Don’t over-water.
  • Variety B: It’s the dark green rings, with or without mushrooms, which identify these varieties of fairy rings. At worst, this type of ring can appear unsightly with its lush growth, accompanied with mushrooms.
    • Remove any mushrooms and use a balanced fertilizer to green up the rest of the lawn so the ring is not as obvious.
  • Variety C: This variety of fairy ring is the most destructive and damaging as it produces a ring of dead grass. The dead area can contain fruiting bodies. If a soil profile is pulled from the dead area, white thread-like structures called mycelia will be visible in the soil. Mycelium is hydrophobic. Because of this property, it causes water to move away from the circle, thus drying out the grass.

There are really no fast cures for fairy rings that aren’t extreme. Digging up the area to remove the organic matter the fungi is feeding on, along with all of the adjacent soil is one method. It’s been said that fairy rings do not cross. Some have said that digging up soil from one fairy ring and exchanging it for another has worked. Spraying fungicides are ineffective and a waste of money.

It is best to just be proactive in how you maintain the lawn. Do not over-water or over-fertilize, and be sure to aerate in the spring.

dancing fairiesThere’s another theory about how fairy rings are created…

Fairies create the circles by dancing within them.

Some cultures believe these circles to be dangerous to humans. Those violating fairy perimeters become invisible to those outside and may be unable leave the circle. The fairies then force the intruder to dance till exhausted, dead or in the throes of madness.

The only safe way to investigate a fairy ring is to run around it nine times. Doing this permits the runner to hear the fairies dancing underground. This must be done under a full moon and in the direction the sun travels.

Other cultures still believe in fairy activity and that fairy rings are omens of good fortune. Some legends see fairy circles as places of fertility and fortune. The Welsh believe that mountain sheep eating the grass from a fairy ring flourish and crops sown around tend to grow better. European folklore believe fairy rings are gateways into elfin kingdoms.

© The Naturarian

Attack of the Poo Tree

Black knot disease in treeThe first time I witnessed Black Knot, I was conducting a tree survey for a family that was putting their house up for sale. I started in the front and made my way around to the rear yard where the family’s three children where playing. I rounded the corner to see a very large plum tree that had a sever case of black knot. When the children saw me looking at the tree, they asked me, “Are you here to clean the poo off of our poo tree?” Ah, out of the mouths of babes….Black Knot

Black Knot of plums and cherries is a common and serious disease throughout the United States. The disease becomes increasingly worse during each growing season and unless effective control measures are taken, it can stunt or kill the tree. The black knot fungus can infect American, European, and Japanese varieties of cultivated plums and prunus. Sweet and tart cherries are also affected by the fungus, but are generally less susceptible than plum or prune. Sometimes, it may also infect apricots, peaches, and other Prunus species.

The fungus overwinters in the galls. During wet periods in the spring and when the buds of the tree swell, spores are expelled and windblown to infect young green shoots or wounded branches.

Once spores germinate, the fungus grows between the plant cells with no outward signs visible on the plant for several months. During this time, the fungus starts growing within the tree and releases hormones that cause the plant to initiate excessive cell growth that results in swollen black galls. The galls contain both plant and fungal tissue.

It is not uncommon for the gall to completely encircle and girdle the branch of the tree. Usually when this occurs, the leaves beyond the gall wilt and die.

black knot

Sometimes, the branch and the gall die after spores are released in the early spring. If the branch lives, the knot becomes perennial and continues to enlarge, producing new spores every spring. Although the Black Knot fungus will not cause trunk decay itself, the cracks formed by a trunk infection can provide an entry point for other wood rotting fungi.

TREATMENT:

  • Prune out galls during the winter. Cut should be approximately 10” inches away from the gall.
  • Fungicides should be applied when the host plant starts to bud, or when Magnolia x soulangiana is in pink bud to early bloom. Continue to spray every 7 – 10 days until there has been about 1 1/2” inches of growth or when Magnolia x soulangiana is dropping its petals.
  • Chemical treatments effective against black knot include fungicides with one of the following active ingredients:
    • Captan
    • Chlorothalonil
    • Thiophanate- methyl
    • Lime sulfur

© The Naturarian

Identifying Diplodia Tip Blight in Pines

Diplodia tip blight is a disease of pines in the Midwest area and the treatment window will soon be upon us. This disease is caused by the fungus Sphaeropsis sapinea and highly effects two-needled pines such as Austrian, scotch, mugo and red, but can infect all evergreens. Here, our Austrian Pines are the most affected and are no longer planted here.

pine with blight on needles

The disease will eventually kill the tree, but can take a long time, without treatment (5 years-ish). Although treatments can slow the process, careful thought is needed in a budgetary sense. The tree will begin to have die-back (larger branch death) and will require regular pruning to be aesthetically pleasing… if that’s even possible. Treatments can be costly, worse-case ineffective, if not applied correctly. The cost of removal will go up as the tree gets larger or becomes more hazardous to fell. In the end, depending where the tree is located, along with the ‘value’ placed on the tree, it may be more cost-effective to remove the tree and replace it as soon as diagnosed.

blight on pine needle

The Diplodia fungus overwinters on infected needles, cones, and within the bark of twigs. Spores are released from spring through late fall. New shoots are infected during the spring from bud break to the end of the growing season. The cones are infected during the spring of the second season, as it takes two years for cones to mature.

Spread of the disease is by the splashing of water, be it rain or over-head irrigation. Because this disease tends to overwinter and spread from infected cones, symptoms are first noticeable on the lower branches, as old cones collect under the tree. Symptoms of infected trees become visible in summer through fall and resemble stunted needle growth and yellowing. Spores can be seen on the needles & old cones as black dots. Because cones are more susceptible to infection, younger, non-cone bearing trees are often symptom-free.

Managing Diplodia tip blight focuses on tree health and sanitation. Providing proper care such as no overhead (and proper) watering, mulching, pest management and fertilization, helps suppress the disease. Removal of diseased cones from the ground helps, but is not practical in large stands of pines. Pruning of infected tips will aesthetically improve the tree, but will do little in the stop of the disease.

Severely infected trees should be removed. A fungicide spray program needs to be implemented in the spring and includes at least three applications. Make the first application just prior to bud break* (which will be soon) and make two additional applications at 10-day intervals. It is important to get the first application on the trees before any bud sheaths have broken (the papery tan cover). If the tree you’re trying to save is of high value, consult a licensed ISA arborist, as the chemicals available to professionals are usually more effective.

* Indicator plants to watch for blooming that coincide with bud break:

  • Spiraea x vanhouttei – Vanhoutti Spirea
  • Cercis canadensis – Eastern Redbud
  • Chaenomeles speciosa – Quince
  • Syringa vulgaris – Common Lilac

© The Naturarian