Got Nature? Blog

Sudden oak death, as the name suggests, is a disease that is capable of rapidly killing certain species of oaks.  It was first identified in California, in 1995. Two years earlier it was identified in Germany and the Netherlands, killing rhododendron. Because the pathogen originally infected and killed tanoaks, an undesirable, understory scrub tree, it generated little interest until other, more desirable oaks species began dying.  However, by this point, the disease was well established and eradication no longer an option, with millions of oak trees killed by the disease.  Currently, over 120 hosts in addition to oaks have been identified, and more continue to be added to this list.  What is most unusual about sudden oak death is the severity of disease symptoms coupled with the broad host range of the pathogen. This leads to difficulty in diagnosing and managing this disease.

What causes this disease?
The pathogen that causes SOD is Phytophthora ramorum (pronounced Fī-toff-thor-ă  ră-mor-ǔm).  This pathogen belongs to a group of organisms in the Kingdom Chromista, and has characteristics similar to fungi, plants and animals.  It spreads throughout the plant by hyphal threads (like fungi), produces spores (like fungi) that have flagella and swim through water (like animals), but its cell wall is made up of cellulose (like plants). When conditions dry up, Phytophthora can produce thick walled sexual spores called oospores, or asexual chlamydospores. Because P. ramorum is not a ‘true’ fungus, many fungicides labeled for control of other fungal diseases are not effective against it.

With such a broad range of plant hosts, it is important to stress that P. ramorum affects different species in different ways. Identification must be confirmed in the laboratory and cannot be identified on field symptoms alone. Many common landscape shrubs are also infected by other endemic Phytophthora species, and symptoms look similar. Boring insects and other root rots may be mistaken for this disease. For this reason, all Phytophthora infections should be screened by the Purdue Plant and Pest Diagnostic Laboratory.

What are the symptoms of SOD?
To understand this disease, it is important to recognize that there are two categories of hosts: bark canker hosts and foliar hosts. Further complicating this is the fact that oaks are divided into three subgroups, and only the red oak group are susceptible to this pathogen. Of our 17 oak species in Indiana, half are potentially, or known to be susceptible, and include black, blackjack, cherrybark, Northern pin, pin, red, scarlet, and Shumard oaks. Diagnostic symptoms of infected red oaks include oozing sap and red-brown cankers that often leading to death.

Our concern right now is on ‘the other’ hosts. Despite its name, sudden oak death primarily spreads through foliar hosts that are sold throughout the United States. Foliar hosts include rhododendrons, azalea, viburnum, lilac, and periwinkle (Vinca minor).

These hosts (and many others) are infected via the leaves and small branches. These infections rarely cause death, and can be mistaken for sunscald, twig canker, and dieback caused by other pathogens, including native Phytophthora species. Although symptoms from these infections are not severe, and are rarely fatal, the infections produce enormous numbers of spores that can infect neighboring, susceptible oaks—and other plant species. For this reason, we are asking people to examine any rhododendrons (or other co-mingled hosts like azalea, viburnum and lilac) purchased this spring from Walmart and Rural King, while the disease may still be controlled and the pathogen contained. Although this disease doesn’t look like much on rhododendron or lilac, its ability to spread to oaks and kill them is what makes it so devastating. These shrubs play a key role in the spread of P. ramorum, acting as a breeding ground for spores (inoculum) that can spread through water, wind-driven rain, plant material, or human activity. Oaks are considered terminal hosts, since the pathogen does not readily spread from intact bark cankers; they become infected only when exposed to spores produced on the leaves and twigs of neighboring plants.

For full article and photos view: Purdue Landscape Report

Other resources:
Sudden Oak Death, California Oak Mortality Task Force
Sudden Oak Death, Indiana Department of Natural Resources
White Oak, The Education Store, Purdue Extension resource center
Planting Forest Trees and Shrubs in Indiana, The Education Store
Successful Oak and Hickory Regeneration, The Hardwood Ecosystem Experiment: 2006-2016, The Education Store
Find a Certified Arborist, International Society of Arboriculture

Janna Beckerman, Professor
Purdue Botany and Plant Pathology

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The Invasive Terrestrial Plant Rule was signed by Governor Holcomb and published on March 18, 2019. the rule goes into effect 30 days after publishing, so it will be effective in April.

The Rule States that a person must not:

• sell, offer or grow for sale, gift, barter, exchange, or distribute a species;
• transport or transfer a species;
• introduce a species

with respect to the 44 invasive plant species (see full list in the Landscape Report).

Note: Selling, offering, distributing and transporting doesn’t go into effect until April of 2020, so nurseries will have some time to sell down their stock. This is an important component of the rule to minimize economic loss to nurseries that grow and/or sell the few commercially available species that are on the list. Currently there is no mandate to eradicate existing plantings in nurseries, landscapes, or forested areas

To learn more about what an invasive species is, what damage they do, what Indiana is doing, and more please read the Landscape Report, Terrestrial Invasive Species Rule Signed by Indiana Governor.

Resources
Mile-a-Minute Invasive Vine Found Indiana, Got Nature? Blog
Invasive plants: impact on environment and people, Purdue Extension The Education Store
Invasive Plant Species in Hardwood Tree Plantations, The Education Store
Invasive Plant Species: Callery Pear, Purdue Extension The Education Store
Invasive Plant Species: Wintercreeper, Purdue Extension The Education Store
Invasive Plant Species Oriental Bittersweet, Purdue Extension The Education Store
Report Invasive Species, Purdue Invasive Species
The GLEDN Phone App – Great Lakes Early Detection Network
EDDMaps – Early Detection and Distribution Mapping System (Report Invasives)
Cooperative Invasive Species Management Area (CISMA)
Indiana Department of Natural Resources: Invasive Species
Indiana Invasive Species Council

Indiana Department of Natural Resources (IDNR)

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Kristol from Tippecanoe County, IN, sent in question to the Purdue Extension-Forestry and Natural Resources experts (Ask an Expert) asking what resources are available to help with landscaping for a front yard and sidewalk area that accumulates water after a hard rain. She also asked for resources to improve drainage.

Purdue Extension has several articles and resources to help with this type of situation.

The resources in our Rainscaping and Master Gardeners Program shares several neat options:
Rain Gardens Go with the Flow, Indiana Yard and Garden, Purdue Horticulture
Rainscaping Program
Master Gardeners Program

Don’t miss the publications located in the Purdue Extension resource center, The Education Store, relating to the topic:
Tree Installation: Process and Practices
Planting Forest Trees and Shrubs in Indiana
Climate Change: How will you manage stormwater runoff?

For Midwest Landscapes, have a look at the Purdue Landscape Report:
Purdue Landscape Report

Check out upcoming workshops available for land and woodland owners, to talk with an expert:
Purdue Extension-Forestry and Natural Resources Calendar

Check out our Got Nature? posts as well, as this is always a great resource for new information:
Got Nature?, Forestry and Natural Resources-Purdue Extension

These resources give you lots of options that match what your looking for along with experts in the field to contact if needed.

We always appreciate the questions coming in, so keep them coming. Our experts will respond quickly and give you the guidance you need for your next steps.

Diana Evans, Extension Information Coordinator
Purdue Forestry and Natural Resources

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How do I remedy poor branching? Is my tree at risk of splitting, and how can pruning prevent that? Corrective pruning has many implications for tree structure, health, and longevity. Developing a strong, central branch structure in a deciduous tree is critical for preventing structural failure caused by storms, wind, and ice. This 8-page publication explains the problems resulting from a co-dominant stem structure and addresses pruning strategies for correcting poor structure.

To view this full publication please go to Corrective Pruning for Deciduous Trees located in The Education Store, Purdue Extension’s resource center.

Resources
Preparations to Prevent Southwest Tree Injury, Got Nature? Blog
When do you stake a tree?, Got Nature? Blog
Top 5 List for Tree Selection and Planting, Got Nature? Blog
Tree Selection for the “Un-natural” Environment, The Education Store, Purdue Extension
Tree Support Systems, The Education Store, Purdue Extension
Tree Installation: Process and Practices, The Education Store, Purdue Extension
Planting Your Tree Part 1: Choosing Your Tree, video, The Education Store, Purdue Extension

Lindsey Purcell, Urban Forestry Specialist
Purdue Forestry and Natural Resources

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The time is now to start protecting your trees!  Now that your ears are perked up, let’s talk a bit about Southwest injury on trees.

Bark cracking (Fig.1) is a phenomenon that occurs in many species of trees and can have many causes. One of the most common types of bark cracking is termed Southwest injury. Southwest injury occurs during the winter months on the lower section of the trunk on the southwest side. This happens when there is a sudden temperature drop, for example, the sun going behind a cloud during the winter. The freeze-thaw cycle happens very quickly when there is a change from very warm to cold conditions, which results in a crack. If there is a snow pack, the reflection of sunlight on the bark will actually increase the temperature in the bark.

Usually Southwest injury occurs on thin-barked trees, such as Acer spp., Cercis spp., Malus spp., and many others (Fig. 3). A thin-barked tree lacks the amount of cork cells in thicker-barked trees, thus allowing the vascular tissue to be located very close to the bark.  Thick bark trees tend to be more resistant to cracking due to a greater lag in the freeze/thaw cycle. Trees that are under stress due to environmental factors, herbicide injury, and/or insect and disease are more susceptible to cracking.

No matter the initial cause of the crack, the common denominator of a crack in the bark is a pre-set wound. The freeze-thaw cycle during the cold months causes the point of injury to expand and contract. Like with your vehicle windshield, a small point of injury in bark will expand and contract due to sudden heating or cooling, thus causing a large crack.

Any type of cracking that occurs, originates from a point of injury, such as a pruning or other mechanical injury. These are horizontal cracks that can range from <1” to the entire length of the trunk, though are usually localized near the bottom of the trunk (Fig. 4).

Once trees are greater than about four inch caliper, the likelihood of Southwest injury is diminished.  On trees four inches or less, tree guards (also called tree wraps) should be installed over each trunk.

White tree guards may help prevent this from occurring due to the reflection of the sun, preventing overheating on the bottom of the trunk (Fig. 5) In order to prevent cracking, try to prevent any type of mechanical damage that could cause cracking in the winter. Bark cracks become visible most often during the late winter/early spring. Tree guards should be removed in the spring, because the guards become a problem with disease due to moisture within the guard.

In some circumstances a healthy plant may heal, partitioning off the damaged area, but the bark on a plant under stress, due to drought, herbicide damage, etc., may last the entire life of the tree.

For full article, check out the Landscape Report

Resources
Trees and Storms: Understanding Damage, Risk and Recovery – Got Nature? Blog, Purdue Extension – FNR
Pruning Ornamental Trees and Shrubs, The Education Store
Why Hire an Arborist, The Education Store
Why Is My Tree Dying? – Got Nature? Blog, Purdue Extension – Forestry and Natural Resources
Weeping Cherry Trees Appear to be Damaged or Dead. Was This Past Winter Hard on These Types of Trees?, Got Nature? Blog

Lindsey Purcell, Urban Forestry Specialist
Purdue Forestry and Natural Resources

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The DNR Division of Entomology & Plant Pathology has discovered that a shipment of boxwood plants infected with boxwood blight was shipped to Indiana in May.

This is important because boxwood blight (Calonectria pseudonaviculata) is a fungal disease that infests members of the popular Buxaceae family, and is often transported through the nursery trade. Hosts include Buxus (boxwood), Pachysandra (Japanese spurge) and Sarcococca (sweetbox).

In total, 23 stores in Indiana received infected material in early spring (particularly “Graham Blandy” cultivar), and it’s possible that members of the public inadvertently purchased some plants.

The fungus, which can lay dormant in drier conditions, can be found on all above-ground portions of the plant and presents itself as dark leaf spots. It causes rapid defoliation, which typically starts on the bottom of the plant and moves toward the top. This fungal pathogen can move through sporulation  in water and from dropped leaves. As a result, infection can spread to surrounding plants from a single infected plant.

If you suspect one of your plants shows signs and symptoms of boxwood blight, please call (866) NO EXOTIC (866-663-9684) use the information at dnr.IN.gov/entomolo.

For more information on this pathogen see the following link extension.purdue.edu/extmedia/BP/BP-203-W.pdf

A DNR inspector found the plants at a national chain home and garden store in early October. The shipment originated at a nursery in Oregon. It was also sent to stores in 11 other states.

Upon confirmation of boxwood blight on these plants by the Purdue Plant and Pest Diagnostic Lab, the DNR required that the chain remove all boxwood from their shelves for disposal and that the stores mitigate the area through disinfection to ensure that the pathogen is no longer present and able to infect further shipments of plants.

The DNR is currently surveying for boxwood blight in Indiana. To date, the DNR has not found the pathogen, except for a few interceptions like this one.

To view all DNR news releases, please see dnr.IN.gov.

Resources:
Boxwood Blight Found in Indiana, full Landscape Report
Boxwood Blight, The Education Store, Purdue Resources

Tom Creswell, Clinical Engagement Associate Professor
Purdue Botany and Plant Pathology

Lindsey Purcell, Urban Forestry Specialist
Purdue Forestry and Natural Resources

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Trees provide many benefits for our homes with shade, beauty and improved air quality as just a few, however, if a tree has defects which could lead to a failure, your shade tree could become a liability. It is important to understand that tree owners have a legal duty to inspect and maintain their trees. All property owners should take reasonable steps to protect themselves and others by taking a look at trees around the property on a regular basis.  Here are some suggestions to consider in making your trees safer for everyone.

Reduce Tree Liabilities: In general, the law obligates tree owners to periodically inspect their property and take reasonable care to maintain it and this includes trees. Routine inspections also exhibit that the tree owner is actively managing their property and trees and thereby reduces their liability if a failure does occur.

When it comes to trees, it’s best to have a professional conduct risk and tree health assessments if there is any uncertainty.  However, Homeowners can look for tree defects, including dead branches, broken limbs, decay pockets or other conditions that reduce a tree’s strength. Review the tree from the top, down. Look at the tree’s crown, main branches, trunk and root area to see if there is anything abnormal. If you find easily recognizable defects like dead and falling branches, cavities, fungal fruiting bodies or newly-formed leans on a tree, consider having the tree examined by a certified arborist. This is especially important after a severe storm. Trees can easily survive normal weather conditions for many years, however, excessive winds can have a real impact.  Make certain trees aren’t removed prematurely out of fear without making an informed decision along with the arborist.

 

Schedule Tree Work: If risk or health issues are found during the inspection, schedule the tree work with a qualified arborist. Be sure to find a tree care company in the area that is reputable and can provide references. Also, being fully insured is another important item to be aware when choosing an arborist.  To find an arborist in your area, go to the website, www.treesaregood.org.

Inspection on a regular basis: Trees should be inspected regularly. These inspections should occur during the growing season and dormancy. Further inspections should be conducted after major weather occurrences. At a minimum, trees should be inspected every five years by an arborist, especially if there is decline and dieback present in your trees.

Article shared by: The Landscape Report, Why Tree Inspections?.

Resources:
Trees and Storms: Understanding Damage, Risk and Recovery – Got Nature? Blog, Purdue Extension – FNR
Tree Risk Management – Got Nature? Blog, Purdue Extension – FNR
Planting Problems: Trees Planted Too Deep, Video, Purdue Extension – Forestry and Natural Resources YouTube Channel
Planting Your Tree Part 1: Choosing Your Tree, Video, Purdue Extension YouTube Channel
Tree Planting Part 2: Planting a Tree, Video, Purdue Extension YouTube Channel
Tree Appraisal and the Value of Trees, The Educational Store, Purdue Extension resource center
Surface Root Syndrome, The Education Store
Iron Chlorosis of Trees and Shrubs, The Education Store
Tree Pruning Essentials, Publication & Video, The Education Store
Cold Injury to Trees, Got Nature? Post, Purdue FNR Extension

Urban Forestry
Purdue Extension – Forestry and Natural Resources (FNR)

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Stake or not to stake, that is the question!?

“No,” is the likely answer to these common questions about post-planting tree care. Trees establish themselves quite well in normal situations. Support systems such as staking and guying are, in most cases, unnecessary and can even be detrimental. Movement caused by the wind is crucial to help saplings develop into strong, structurally balanced trees.

However, in unusual conditions, staking, guying, or a similar system may be needed to hold tress upright until adequate root growth anchors them firmly in the soil. When necessary, the support system must be installed properly and removed at the appropriate time to prevent damage.

When to Stake Trees

When stakes are needed, timing depends on the environment and the type of tree.

• Bare-root trees and container-grown trees
• Large evergreen trees with high wind exposure
• Open sites exposed to strong winds
• Taller trees with undersized root balls
• Trees in areas with high rates of vandalism
• Threat of mechanical damage

Improperly staked trees suffer from poor development such as decreased truck diameters and smaller root systems – and may be unable to stay upright after you take the supports away. Often trunk tissue suffers from rubbing and may even be girdled by support materials. Also, due to poor development and taper, previously supported trunks are more likely to break off in high winds or blow over after stakes are removed.

Proper Methods and Materials of Guying and Staking

Staking and guying a tree trunk to keep it upright can be a necessary, temporary support system, but does not compensate for poor root development and establishment long-term.

• Guying is temporary and typically used on larger trees that are transplanted balled-and-burlapped. Three points of attachment provide the best support for these large-trees.
• Staking connects the trunk to a nearby steel or wooden post. This is a common approach on smaller trees or containerized tree stock.
• Underground stabilizing systems are also effective and economical for stabilizing the root balls on larger balled-and-burlapped trees. There are several commercial anchor systems available.

The cardinal sins of support include: staking trees too high, too tightly, and for too long which all cause tree damage. Improper staking can cause stem abrasions and trunk girdling. Review the anchor, attachment point, and tension on a regular basis, adjusting as needed to make certain the supports are effective and not damaging the tree. If a tree is supported, the ties and guys should be removed as soon as feasible, usually no later than after one growing season or one year. For more information see Purdue extension publication, Tree Support Systems.

Related Sources:
Stake or not to stake, that is the question?!, The Landscape Report
Tree Support Systems, The Education Store
Latest Issue of the Purdue Landscape Report, Got Nature Post
Plant for the Sun!, Got Nature Post

Lindsey Purcell, Urban Forestry Specialist
Purdue Forestry and Natural Resources

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The latest issue (18-11) of The Purdue Landscape Report has been released July 17th.  This issue contains four articles about common tree care accidents, problems of tree transplant shock, leaf loss, and poison ivy.

Will my Trees Recover After Losing their Leaves?
Damage caused by defoliating insects can be quite shocking. An effective response to this sort of defoliation should be based on your understanding of how losing leaves affects plant health.

Poison Ivy
Most landscape professionals and gardeners have heard of the wise advice “leaves of three, let it be” referring to the pest plant poison ivy. While not quite as catchy, the saying really should be “leaflets of three, let it be.”

Homeowner Tree Care Accidents
The Tree Care Industry Association (TCIA) conducted an analysis of 62 civilian tree care-related accidents reported by the media from January 2017 to June 2018. TCIA is a trade association that promotes professional tree care and discourages homeowners from taking unnecessary risks caring for their trees themselves.

Common Abiotic Problems of Ornamentals: Transplant Shock
Transplant shock occurs when plants become stressed due to poor root establishment, often mimicking drought stress.  The severity of transplant shock is dependent on many factors, which include plant species, soil type/quality, moisture, temperature, growth stage of the plant, root loss from the nursery, as well as many other factors.

Please check out the full articles at The Purdue Landscape Report 

Resources:
Poison Ivy, The Education Store, Purdue Extension resource center
Tree Support System, The Education Store
Construction & Trees: Guidelines for Protection, The Education Store

Cliff Sadof, Entomology Extension Coordinator
Purdue Department of Entomology

Rosie Lerner, Extension Consumer Horticulturist
Purdue Department of Horticulture and Landscape Architecture

Lindsey Purcell, Urban Forestry Specialist
Purdue Department of Forestry and Natural Resources

Kyle Daniel, Nursery & Landscape Outreach Specialist
Purdue Department of Horticulture and Landscape Architecture

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Most terrestrial plants are sessile. This inability to move forces has brought alternative methods to defend themselves. Typically, plants use three basic mechanisms of defense: avoidance, escape or tolerance. A recent work notes that plants may have evolved a fourth method; where healthy tissue is sacrificed in an effort to confine harmful bacteria to a small portion of the leaf.

Brown spots, if observed on previously unmarred leaves, may result from the plant employing this technique to slow or prevent bacterial spread. Scientists at the Salk Institute have identified a plant enzyme denoted SOBER1 that plants use to seemingly lower their resistance to infection. Future study on the gene may lead to ways to boost natural immunity or contain infections that would otherwise decimate entire agricultural crops and biofuel resources.

Additional experiments involved several model plant species (Arabidopsis, oilseed rape, and tobacco) and evaluated the structure and function of SOBER1 and an immune protein known as AvrBst. The ultimate goal of this work is to understand how bacterial resistance works in plants. The information gained may help identify new methods of improving agricultural and biofuel crop resistance to harmful bacterial infections.

References
A hydrophobic anchor mechanism defines a deacetylase family that suppresses host response against YopJ effectors, Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-02347-w, Marco Bürger, Björn C. Willige, Joanne Chory.
Unusual plant immune response to bacterial infection characterized, ScienceDaily, 8 January 2018, Salk Institute.

Resources
Consumer Horticulture: Fertilizing Woody Plants, The Education Store, Purdue Extension
Shrubs and Woody Vines of Indiana and the Midwest: Identification, Wildlife Values, and Landscaping Use, Purdue University Press

Shaneka Lawson, USDA Forest Service/HTIRC Research Plant Physiologist/Adjunct Assistant Professor
Purdue University Department of Forestry and Natural Resources

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