Natural Notes: Diagnosis and Plant Disorders
This post consists of my notes from a lecture on plant disorders as part of a training to become a certified arborist by the International Society of Arborculture. The speaker was Rob Klamcynski, a natural resources specialist with the Forest Preserves of Cook County and his lecture took place on February 6, 2015 at the Salt Creek Resource Management facility in Willow Springs, Illinois.
Introduction
There are challenges to diagnosing tree health problems. First of all, trees cannot talk and cannot tell us what is wrong. It is up to the arborist to ask all of the necessary questions. The history of the tree's health is hard (or impossible) to come by and the answers might not be accurate. Most of the time, it is too late.
Plant Problems
When analyzing a tree's health, the arborist must determine if the problem is a living agent or a non-living agent. Living agents include biotic disorders such as viruses, bacteria, fungi, and others. Non-living agents include environmental factors, mechanical damage, chemical injuries, soil compaction, and others.
Signs and symptoms
A symptom is how a tree responds to a disorder. Examples include chlorosis, wilting, leaf scorch, and others. Symptoms are often not specific to the disorder.
Signs are direct indications of primary or secondary agents or something that was left behind by one (e.g. emerald ash borer holes).
Systematic Steps to Diagnosis
1. It is important to accurately identify the tree. Many insects and diseases are specific to certain host trees.
2. Look for patterns of abnormality. What is normal? Compare the tree being analyzed to other plants on the site. Look for clues and differences such as non-uniform damage, which is often linked to biotic factors, as well as uniform damage, which is often connected with non-living (abiotic) factors.
3. Examine the site. Consider light levels, water availability, prevailing winds, slope, soil conditions, and whether or not the site is a newly built up area or an older community.
4. Note the size, color, and thickness of the leaves. Dieback in the crown is often a result of mechanical damage (usually to the roots). Twisted or curled leaves may indicate a viral infection, insects, or exposure to herbicides. Early fall color may be a symptom from girdled roots.
5. Check the trunk and branches, roots, and root collar. Look for wounds on the trunk. Small holes indicate the presence of borers or beetles. Assess the growth over time. Examine the soil (aerobic versus anaerobic).
Be sure to rule out any other possibilities. The time of year can help. For example, fall webworm occurs most frequently in the fall. Oak wilt can happen most often in the late summer. Also, certain species are vulnerable to a specific problem. For example, oaks (Quecus spp.) are vulnerable to oak wilt, maples often have girdled roots, and redbuds (Cercis spp.) are sensitive to herbicides.
Stress
Tree stress can be cumulative and can lead to the "spiral of decline". Trees need basic factors such as sufficient water, air movement, good drainage, proper temperature, and a proper balance of nutrients in order to live.
So how does stress exhibit itself? Indications of stress most often include reduced growth, abnormal foliage color or size, vigorous watersprouts, and premature leaf drop.
There are two types of stress: acute and chronic. Acute stress often arises from lightning damage, herbicide damage, or frost damage. Chronic stress is often from poor drainage, soil compaction, and poor species selection.
Abiotic Disoders
Abiotic disorders are often the primary stress factor(s) that cause the spiral of decline. It can be difficult to recognize, and it often mimics biotic disorders and are part of a complex interaction of problems. Knowing the tree and its site history are often the best clues.
Typical abiotic disorders include soil and site problems, physical and mechanical injuries, temperature extremes, competition, and chemical injury.
Weather extremes (which of course are abiotic) include frost cracks, lightning, wind damage, heat stress, ice, hail, frost, sun scald, and de-icing salts.
Soil and site problems are similar to root disorders. Soil and site problems are often overlooked. Crown symptoms are often a result of poor root health from stresses such as transplant shock, urban soils, and physical/mechanical injuries.
Plants compete for each other (e.g. allelopathy) and in this context they can be considered "viscous killers." Sunlight is usually the primary factor resulting in defect, reduced growth, or dieback. Available growing space is also a common limiting factor in in heavily urban areas. With allelopathy, a tree species releases toxins (e.g. Black Walnuts [Juglans nigra]). Other trees that exhibit allelopathy include sugar maple (Acer saccharum), Black Locust (Robinia pseodoacacia) and Buckthorn (Rhamnus spp.)!
Pollution damage is difficult to diagnose as it often mimics nutrient deficiencies. Pollution damage can cause acute and chronic injuries. Other abiotic factors include wind, humidity, soil grade, precipitation levels, and the site condition. Abiotic factors like pollution might also mimic insect injury.
Herbicides applied improperly are the most frequent culprits for chemical injuries.
Biotic Disoders
Biotic disorders include insects and other pests and disease from fungi, bacteria, phytoplasms, and others.
Insects may or may not be host specific. Some may be predators and some may be parasitic. Insects have complex life cycles that may be harmful in different developmental stages. Most insect species in general have little or no effect on tree health.
Insect species may or may not be host specific. For example, the Japanese Beetle (Popilla japonica) can eat many kinds of trees whereas the Emerald Ash Borer (Agrilis planipellis) just eats ash trees (Fraxinus spp.). Some insects will even prey on harmful insects.
Chewing insects may feed on the entire leaf or just the leaf margins. Some insects sheletonize the leaf where they just leave the leaf veins behind. Insects can also be vectors for pathogens.
Piercing-sucking insects will pierce plant cells and feed on the contents. This does not usually kill the tree right away.
Nematodes are microscopic roundworms and most of are not parasitic on plants. Some, however, may enter the root system or through wounds.
Other animals that can harm trees include sapsuckers, deer (bud-feeding), squirrels (bark-stripping), rabbits (in winter), and others.
For diseases, there are four requirements for a pathogen to infect (see figure 1).
Most plant diseases are caused by fungi. Not all fungi are bad, though. Example: Mycorhizae fungi. Look for fruiting bodies when assessing tree health problems that might be caused by a fungi.
For bacteria, there are only two bacterial pathogens that are of major importance. Signs for bacterial infections in trees include a water-soaked appearance and a foul odor.
For phytoplasms and viruses (PLOs), not much is known. There are none that are important viral diseases on trees.
Introduction
There are challenges to diagnosing tree health problems. First of all, trees cannot talk and cannot tell us what is wrong. It is up to the arborist to ask all of the necessary questions. The history of the tree's health is hard (or impossible) to come by and the answers might not be accurate. Most of the time, it is too late.
Plant Problems
When analyzing a tree's health, the arborist must determine if the problem is a living agent or a non-living agent. Living agents include biotic disorders such as viruses, bacteria, fungi, and others. Non-living agents include environmental factors, mechanical damage, chemical injuries, soil compaction, and others.
Signs and symptoms
A symptom is how a tree responds to a disorder. Examples include chlorosis, wilting, leaf scorch, and others. Symptoms are often not specific to the disorder.
Signs are direct indications of primary or secondary agents or something that was left behind by one (e.g. emerald ash borer holes).
Systematic Steps to Diagnosis
1. It is important to accurately identify the tree. Many insects and diseases are specific to certain host trees.
2. Look for patterns of abnormality. What is normal? Compare the tree being analyzed to other plants on the site. Look for clues and differences such as non-uniform damage, which is often linked to biotic factors, as well as uniform damage, which is often connected with non-living (abiotic) factors.
3. Examine the site. Consider light levels, water availability, prevailing winds, slope, soil conditions, and whether or not the site is a newly built up area or an older community.
4. Note the size, color, and thickness of the leaves. Dieback in the crown is often a result of mechanical damage (usually to the roots). Twisted or curled leaves may indicate a viral infection, insects, or exposure to herbicides. Early fall color may be a symptom from girdled roots.
5. Check the trunk and branches, roots, and root collar. Look for wounds on the trunk. Small holes indicate the presence of borers or beetles. Assess the growth over time. Examine the soil (aerobic versus anaerobic).
Be sure to rule out any other possibilities. The time of year can help. For example, fall webworm occurs most frequently in the fall. Oak wilt can happen most often in the late summer. Also, certain species are vulnerable to a specific problem. For example, oaks (Quecus spp.) are vulnerable to oak wilt, maples often have girdled roots, and redbuds (Cercis spp.) are sensitive to herbicides.
Stress
Tree stress can be cumulative and can lead to the "spiral of decline". Trees need basic factors such as sufficient water, air movement, good drainage, proper temperature, and a proper balance of nutrients in order to live.
So how does stress exhibit itself? Indications of stress most often include reduced growth, abnormal foliage color or size, vigorous watersprouts, and premature leaf drop.
There are two types of stress: acute and chronic. Acute stress often arises from lightning damage, herbicide damage, or frost damage. Chronic stress is often from poor drainage, soil compaction, and poor species selection.
Abiotic Disoders
Abiotic disorders are often the primary stress factor(s) that cause the spiral of decline. It can be difficult to recognize, and it often mimics biotic disorders and are part of a complex interaction of problems. Knowing the tree and its site history are often the best clues.
Typical abiotic disorders include soil and site problems, physical and mechanical injuries, temperature extremes, competition, and chemical injury.
Weather extremes (which of course are abiotic) include frost cracks, lightning, wind damage, heat stress, ice, hail, frost, sun scald, and de-icing salts.
Soil and site problems are similar to root disorders. Soil and site problems are often overlooked. Crown symptoms are often a result of poor root health from stresses such as transplant shock, urban soils, and physical/mechanical injuries.
Plants compete for each other (e.g. allelopathy) and in this context they can be considered "viscous killers." Sunlight is usually the primary factor resulting in defect, reduced growth, or dieback. Available growing space is also a common limiting factor in in heavily urban areas. With allelopathy, a tree species releases toxins (e.g. Black Walnuts [Juglans nigra]). Other trees that exhibit allelopathy include sugar maple (Acer saccharum), Black Locust (Robinia pseodoacacia) and Buckthorn (Rhamnus spp.)!
Pollution damage is difficult to diagnose as it often mimics nutrient deficiencies. Pollution damage can cause acute and chronic injuries. Other abiotic factors include wind, humidity, soil grade, precipitation levels, and the site condition. Abiotic factors like pollution might also mimic insect injury.
Herbicides applied improperly are the most frequent culprits for chemical injuries.
Biotic Disoders
Biotic disorders include insects and other pests and disease from fungi, bacteria, phytoplasms, and others.
Insects may or may not be host specific. Some may be predators and some may be parasitic. Insects have complex life cycles that may be harmful in different developmental stages. Most insect species in general have little or no effect on tree health.
Insect species may or may not be host specific. For example, the Japanese Beetle (Popilla japonica) can eat many kinds of trees whereas the Emerald Ash Borer (Agrilis planipellis) just eats ash trees (Fraxinus spp.). Some insects will even prey on harmful insects.
Chewing insects may feed on the entire leaf or just the leaf margins. Some insects sheletonize the leaf where they just leave the leaf veins behind. Insects can also be vectors for pathogens.
Piercing-sucking insects will pierce plant cells and feed on the contents. This does not usually kill the tree right away.
Nematodes are microscopic roundworms and most of are not parasitic on plants. Some, however, may enter the root system or through wounds.
Other animals that can harm trees include sapsuckers, deer (bud-feeding), squirrels (bark-stripping), rabbits (in winter), and others.
For diseases, there are four requirements for a pathogen to infect (see figure 1).
 |
| Figure 1: Disease pyramid |
Most plant diseases are caused by fungi. Not all fungi are bad, though. Example: Mycorhizae fungi. Look for fruiting bodies when assessing tree health problems that might be caused by a fungi.
For bacteria, there are only two bacterial pathogens that are of major importance. Signs for bacterial infections in trees include a water-soaked appearance and a foul odor.
For phytoplasms and viruses (PLOs), not much is known. There are none that are important viral diseases on trees.
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