Chapter 10: Diagnosis and Plant Disorders Flashcards
Two major groups of plant health problems?
living and nonliving
biotic disorders
disorder caused by an infectious living agent
types of living agents?
plant pathogens such as fungi, bacteria, viruses, phytoplasmas, parasitic plants, nematodes; insect pests, mites, and other animals
pathogen
causal agent of disease; usually refers to microorganisms; infectious
infectious
capable of being spread to plants from other plants or organisms
abiotic disorders
plant malady caused by nonliving, environmental, or man-made agents
noninfectious
disorders that are not caused by a pathogen and cannot be passed from one host to another
types of non-living agents?
environmental problems such as temperature and moisture extremes, mechanical injuries, soil compaction, mineral dificiencies
symptoms
plant reaction to a disease or disorder (e.g., wilting, dieback); how the plant responds to a disorder
Examples of symptoms?
chlorosis, wilting, leaf scorch
signs
physical evidence of a causal agent (e.g., insect eggs, borer hole, frass); direct indications of primary or secondary causal agents; something “left behind” by the causal agent
Examples of signs?
conks or fruiting bodies of fungi, insect frass, emergence holes, or discarded skins
frass
fecal material and/or wood shavings produced by insects; semi-digested wood
blight
any disease or disorder, regardless of the causal agent, that kills young plants tissues; dieback of leaves and twigs on major portions of the tree, especially young, growing tissues
canker
localized diseased area on stems, roots, and branches; often shrunken and discolored; localized dead stem tissue
chlorosis
whitish or yellowish leaf discoloration caused by lack of chlorophyll; often caused by nutrient deficiency; yellowing of normally green tissues
decay
an area of wood that is undergoing decomposition; decomposition of organic tissues by fungi or bacteria; rotting of wood tissue
dieback
condition in which the branches in the tree crown die from the tips toward the center; progressive death of twigs and leaves from the tip back
gall
abnormal swelling of plant tissues caused by gall wasps, mites, nematodes, and various insects and less commonly by fungi or bacteria; swollen plant tissue or irregular plant growth that may be induced by insects, mites, fungi, bacteria, or nematodes.
gummosis
exudation of sap or gum from the bark, often in response to disease or insect damage; from wounds or other openings in the bark
leaf blotch
irregularly shaped areas of disease on plant foliage; dead areas of tissue on the foliage, irregular in shape and larger than leaf spots
leaf spot
patches of disease or other damage on plant foliage; spots of dead tissue on the foliage; size, shape, and color varies with causal agent but are usually limited to small portions of the leaf
necrosis
localized death of tissue in a living organism; death of tissue
powdery mildew
any various fungi of the genus Erysiphe that produce powdery conidia that appear as a white, fuzzy coating on the upper leaf surfaces, often causing distortion of the leaf; white or grayish fungal growth on the surface of plant tissues, usually leaves
rust
disease caused by a certain group of fungi and characterized by reddish brown spots on the foliage and/or the formation of stem galls; orange or reddish brown pustules on leaves or fruit, or galls and cankers on stems caused by certain fungi
scorch
browning and shriveling of foliage, especially at the leaf margin; browning and death of indefinite areas along leaf margins and/or between veins
stunting
growth reduction of organisms, specifically plants or plant parts; abnormally small plant growth
vascular discoloration
darkening of the vascular tissues of woody plants in response to disease; darkening of the wood’s vascular elements, often along growth rings
wilt
infectious disease caused by a particular agent on a particular host or range of hosts; dropping of leaves or shoots, often due to lack of water in the tree
witch’s broom
plant disorder characterized by a shortening of the internodes and a proliferation of terminal shoots forming a dense, brushlike mass of twigs; abnormal development of multiple secondary shoots, forming a broom like effect
conk
fruiting body or nonfruiting body (sterile conk) of a fungus; often associated with decay
Steps in diagnosing a tree
- ) accurately identify the plant (certain species of plant are prone to specific abiotic disorders and some insects/diseases are specific to certain hosts)
- ) look for a pattern of abnormality (knowledge and recognition of what is normal; compare affected tree with other plants on site, look for differences in shape, color, and patterns within the canopy)
- ) carefully examine the site (light levels, soil characteristics, water availability, prevailing winds, contour of the land/structures, walkway, road, fence, compaction, construction, age, overcrowding, etc.)
- ) note the color, size, and thickness of the foliage (many disorders are first apparent in the foliage begin elsewhere, many disorders have similar effects on leaves)
- ) check the trunk and branches (examine buds and bark for any discoloration and drying, look for wounds on the trunk that could provide entrances for insects and diseases that rot wood, produce cankers, and disrupt the transport of materials between roots and leaves)
- ) examine the roots and root collar (poor site conditions, human caused site changes, poor selection of plants, or poor planting and management practices; note any soil odor, check for signs of decay in the major roots and collar)
Is it bad for pines to drop needles?
Not necessarily; it is normal for pines to shed their inside needles; check to see whether it is the inner, older needles or the new-growth needles that are dropping
What do nonuniform damage patterns among different species of plants, individuals of the same species, or tissues within a plant often indicate?
biotic factors, such as insects or pathogens; living agents rarely show uniform patterns
What do uniform pattern damage throughout the plant or over a large area with several plant species indicate?
nonliving factors, such as physical injury, water availability, or weather
What negative issues might trees near walkways, roads, and fences face?
disorders that result from wood preservatives, de-icing salts, or other harsh products
What negative issues might new community trees face?
stress associated compacted soil, construction damage, and newly transplanted trees
What negative issues might older community trees face?
age and overcrowding limit
What might cause dieback?
mechanical damage to the vascular system or environmental root stress
What might cause twisted or curled leaves
viral infection, insect feeding, or exposure to herbicides
What might cause early fall color?
stress from girdling roots or other root-related problems
What do small holes indicate in a tree?
presence of borers or bark beetles
Why would you assess tree growth as an indicator of potential sources of stress?
by measuring the distance between terminal bud scars from year to year, it may be possible to determine when the tree began to decline and whether growth is decreasing or improving; measure incremental growth by looking at growth rings if it won’t injure the tree
describe healthy roots
generally white inside, fleshy, flexible, and firm; indicates presence of sufficient oxygen levels in the soil and aerobic soil conditions
aerobic
with oxygen; process that occurs in the presence of oxygen
What do brown roots indicate?
dry soil conditions or the presence of toxic chemicals
What do black roots indicate?
overly wet soil or the presence of root-rotting organisms
anaerobic
without oxygen; process that occurs in the absence of oxygen; low oxygen
What is the cause of 70-90% of all plant problems?
adverse cultural and environmental conditions, such as soil compaction, drought, moisture fluctuations, temperature extremes, mechanical injuries, or poor species selection
complex
combination of factors contributing to the stress or decline of a tree; combination of living and nonliving stressors
primary agents
first stress the plant and start the decline process, which predisposes the plant to secondary agents
secondary agents
cause the plant more problems which may or may not be deadly; many insects and fungi are secondary only and only become a problem on already-stressed trees
basic factors that promote plant health?
sufficient water, air movement, drainage, optimal temperature and light, and nutrient availability
tree stress
factor that negatively affects the health of a plant; a factor that stimulates a response; any condition that causes a decline in tree health
two categories of stress
acute and chronic
acute
disorder or disease that occurs suddenly or over a short period of time; causes almost immediate damage
Examples of acute stress causes
lightning, improper pesticide applications, untimely frosts or freezing
chronic
disorder or disease occurring over a long period of time; takes a longer time to affect plant health
Examples of chronic stress causes
mineral nutrient deficiency, improper soil pH, poor drainage, soil compaction, long-term weather changes, suboptimal light exposure, pollution
Examples of early symptoms of stress
reduced growth, abnormal foliage color, vigorous water sprouting, premature leaf drop
What are the most common causes of tree stress?
site and/or environmental conditions; if a tree is not well suited for the site in which is has been planted, it is more likely to become stressed; trees subjected to site stress often change their metabolic processes to compensate for deficiencies
trunk flare
transition zone from trunk to roots where the trunk expands into the buttress roots or structural roots; root flare
physiological disorders
in plants, a disorder not directly caused by an insect, pathogen, or injury; develop over a long period of time
When does freezing injury occur?
when temperatures drop below freezing point; ice crystals form inside plant tissues which may potentially rupture cell membranes which leads to dehydration and death of tissue
chilling injury
injury that occurs from low temperatures that are above the freezing point; often affects the integrity of cell membranes causing leakiness
frost cracks
vertical split in the wood of a tree, generally near the base of the bole, caused by internal stresses and low temperatures; radial shake; crack in trunk or stem when temperature drops rapidly; outer wood and bark of the tree cools rapidly which causes shrinking and cracking or when moisture in inner wood freezes and expands splitting the bark
Where do frost cracks normally occur?
on the south or southwest side of trunks or branches
What causes sunscald?
rapid change in temperature resulting from solar heating or thin-barked trees and trees with bark that has been suddenly exposed to sunlight (due to removal of shade)
Types of storm damage
blow-over (when trees are physically pushed over by high winds), stem failure (when stem fails, often at wounds or cavities), crown twist, stem twisting (magnifies weakness around old injuries and during a storm, stem may split or branches may collapse), root failure (roots pulled or snapped causing trees to fall or lean), branch failure (branches tear downward along the stem or snap off)
sign of lightning strike
spiral scar running down the grain of the wood where the bark or sapwood has exploded off the trunk; if the cambium is killed the tree may not leaf out the following spring
defoliation
loss of leaves from a tree or other plant by biological or mechanical means
What is the most common form of competition between trees?
competing for sunlight; shade-intolerant trees growing under the canopy of larger trees may exhibit death of lower branches, stem curvature, and reduced growth
forms of competition
sunlight, available soil nutrients, water, growing space
allelopathy
chemical effect or inhibition of growth or development of plants that is induced by allelochemicals
How are allelopathic chemicals exuded?
directly - from the plant (to another plant)
indirectly - through decomposition
What do allelopathic chemicals do?
inhibit growth, seed germination, flowering, or fruiting of nearby plants
Examples of highly allelopathic trees
Walnuts (Juglans spp.) Sugar Maple (Acer saccharum) Black Locust (Robinia pseudoacacia)
Types of pollution
air, water, and soil
Categories of pollution
acute and chronic
systemic
substance that moves throughout an organism after it is absorbed; any condition, disease, disorder, or pest that affects the entire organism
phytotoxicity
quality of being phytotoxic (compound that is poisonous to plants); ability to kill plants
xerophytes
plants adapted to dry areas; plants with special adaptations (such as photosynthetic adaptations and thicker, leathery leaves, often with a waxy cuticle or hairy coating, and more extensive root systems) to dry ecosystems to allow for better water retention and/or water uptake
What is the best way to deal with girdling roots?
prevent them from occurring by carefully inspecting nursery stock for girdling/circling roots and not planting the tree to deeply and not allowing soil/mulch to collect around the base
How to remove girdling roots?
remove the portion in contact with the stem; often removing girdling roots requires severely damaging the structural support and uptake capabilities of the root system; do not remove roots that have become grafted to the trunk or are larger than 1/3 of the trunk diameter
What kinds of signs do biotic agents leave behind?
eggs, excrement, silk, wax, or fruiting bodies
Examples of insects that feed on a variety of host plants
Japanese beetle, aphids, scales, gypsy moth
Examples of insects that are specific to certain hosts
emerald ash borer, bronze birch borer, holly leafminer
What causes most insect damage to trees?
feeding or egg-laying activity
ovipositing
laying eggs
Examples of insects that chew on plant parts
catepillars, webworms, sawfly larvae, beetles, and weevils
What part of plant tissue do chewing insects eat?
leaves, flowers, buds, and twigs
Examples of insects that eat the entire leaf
gypsy moth, eastern tent caterpillar, and cankerworm
Example of insects that eat the leaf margin
black vine weevil (uneven or broken margins or notches on leaves)
Example of insects that eat the interveinal tissue of the leaf
Japanese beetle and elm leaf beetle
skeletonized
leaf-feeding damage caused by insects (skeletonizers) characterized by the loss of tissue between the leaf veins
borers
chewing insect larvae that tunnel under the bark and often into the wood of trees; eat the inner bark, phloem and cambium, and/or xylem; destroy the tree’s ability to transport water and nutrients between the roots and crown of the tree
Examples of insects that feed by piercing plant tissues and sucking out the liquid contents?
aphids, adelgids, scales, leafhoppers, psyllids, and true bugs
honeydew
sugary substance secreted by insects, including aphids and some scale insects when feeding on plants; liquid excrement that serves as the substrate for the growth of sooty mold
sooty mold
fungus that appears as a black coating on the surface of leaves, fruits, branches, and other surfaces; often found growing on sugary honeydew excreted by aphids; unsightly but nonpathogenic fungus
vectors
in pathology, biotic or abiotic agent that transmits a pathogen; carriers; transmit or spread the pathogen or disease-causing organisms from tree to tree
Examples of insects that are vectors
bark beetles spread the fungal pathogen dutch elm disease, bees spread fire blight bacteria when they collect nectar from flowers, aphids and leaf hoppers can transmit viruses
mites
arachnids (close relatives of spiders and ticks) that cause significant damage to woody plants; very small
nematode
microscopic roundworm; many are beneficial organisms (promote organic decay) but some feed on plant tissues and may cause disease or damage (attack the root system of the plant)
Examples of birds that damage trees
woodpecker (large and random holes) and sapsucker (smaller holes, usually in horizontal rows)
Examples of animals that damage trees
mammals: deer (browse on buds, twigs, and leaves; jagged/torn)
rabbits, rodents, squirrels, voles, beavers
What are the three requirements for a tree to become diseased? (disease triangle)
- ) tree must be susceptible to the pathogen
- ) the pathogen must be present
- ) the environment must be suitable for disease development
foliar diseases
affect foliage (and sometimes fruit) and can be a significant aesthetic problem
vascular wilt diseases
occur when pathogens enter the plant, often through wounds in the roots or other tissue, and colonize the xylem or phloem; disrupts the flow of water and nutrients between the roots and canopy leading to death
Examples of vascular diseases that result in rapid death of large trees
dutch elm disease and oak wilt
Three common diseases that bacteria cause
- ) fire blight (insect vector)
- ) bacterial leaf scorch (insect vector)
- ) crown gall
How are fungicides best used?
to prevent the establishment of disease; not eliminate existing problems
