Diagnosing Plant Problems - Kentucky Master Gardener Manual
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COOPERATIVE EXTENSION SERVICE • UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546
ID-194
Diagnosing Plant Problems
Kentucky Master Gardener Manual Chapter 7
By James L. Green, former extension horticulture specialist, Oregon State University; Otis Maloy, retired extension plant
pathologist, Washington State University; and Joseph Capizzi, extension entomologist emeritus, Oregon State University. Edited
for Kentucky by John Hartman, extension plant pathologist (retired), and Lee Townsend, extension entomologist, University of Kentucky.
T
o determine what factors have damaged a plant, you’ll need
In this chapter: to systematically and carefully observe the plant, its environ-
ment, and other plants in the area, then put all the pieces
Diagnostic Terms.................................................. 96 together to reconstruct the event(s) that produced the damage. You
Plant Identification and Appearance............ 97
must make an accurate diagnosis before taking corrective action.
Even if no corrective measures are available, it is good to know what
Damage Patterns.................................................. 98 the problem is and what its future development might be.
Development of Damage over Time............. 99 Factors causing plant damage can be grouped into two major
categories:
Distinguishing among Living
Causes of Damage.............................................100
• Living organisms such as pathogens (fungi, bacteria, viruses, and
nematodes) and pests (insects, mites, mollusks, mammals, and
A Step-by-Step Method of Diagnosis .........102 birds)
Distinguishing among Nonliving • Nonliving factors such as mechanical damage (for example,
Causes of Damage.............................................105 breakage or abrasions), environmental conditions (such as
For More Information........................................108 extremes of temperature, light, moisture, or oxygen), and chemi-
cals (such as herbicides or nutritional disorders)
Some pathogens, insects, and nonliving factors cause damage
only if a plant is weakened by other primary factors. For example,
borers generally attack only trees that already are suffering moisture
or other physical stress.
It’s frequently not enough to use symptoms alone for diagnosis,
because completely different factors may cause similar symptoms
on the same plant. In diagnosing plant damage, you can follow a
series of deductive steps, gathering clues from the general situation
down to an individual plant or plant part to determine the most
probable cause of the damage.
The first step is to identify the plant and the problem. Then,
attempt to distinguish between living and nonliving damaging fac-
tors based on observed damage patterns, development of patterns
over time, and other diagnostic clues. Once you have limited the
probable causes of the damage, you can obtain further information
to confirm your diagnosis from reference books, plant pathologists,
entomologists, horticulturists, and/or laboratory analyses.
These diagnostic steps are described in detail on the following
pages.
Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Economic Development
EXTENSION96 • Diagnosing Plant Problems Chapter 7
Diagnostic Terms Symptoms
Abscission—The dropping of leaves, flow-
Necrosis—Death of plant tissue.
Phyllody—A change from normal flower
ers, or fruit by a plant. structures to leafy structures.
General Blight—Rapid, extensive discoloration, Rot—Decomposition and destruction of
Bacterium—A single-celled, microscopic wilting, and death of plant tissue.
organism having a cell wall but no chlo- tissue.
rophyll. Reproduces by cell division. Blotch—A blot or spot (usually superfi- Rugose—Wrinkled.
cial and irregular in shape and size) on
Fungus—A plant organism that lacks chlo- leaves, shoots, or fruit. Russet—Yellowish-brown or reddish-
rophyll, reproduces via spores, and usu- brown scar tissue on a fruit’s surface.
ally has filamentous growth. Examples Canker—A dead place on the bark and
are molds, yeasts, and mushrooms. cortex of twigs, stems, or trunks; often Scab—A crustlike disease lesion.
discolored and either raised or sunken. Stippling—Small, light green or chlorotic
Larva—Immature stage of an insect with
complete metamorphosis that is special- Catfacing—Disfigurement or malformation specks.
ized for feeding. A larva looks very differ- of a fruit. Fruits typically affected include Water-soaked—Lesions that appear wet
ent than the adult stage (for example, a tomatoes and strawberries. and dark and usually are sunken and/or
caterpillar and a moth). translucent.
Chlorosis—An abnormal yellowish-white
Host—A plant afflicted with a disease or or gray color of plant parts resulting from Wilt—Lack of turgor and drooping of
insect pest. incomplete destruction of chlorophyll. leaves from lack of water.
Nematode—A microscopic roundworm, Defoliation—The unnatural loss of a plant’s Witches’ broom—Abnormal brushlike devel-
usually living in the soil. Many feed leaves, generally to the detriment of the opment of many weak shoots.
on plant roots and can be disease plant’s health. Can be caused by high
pathogens. wind, excess heat, drought, frost, chemi-
Nymph—Immature stage of an insect with
cals, insects, or disease. Signs
gradual metamorphosis. It looks very Desiccation—Drying out of plant tissue. Bacterial slime—A gooey or dried mass of
much like the adult but is smaller. For bacterial cells that oozes out of plant
instance, a grasshopper nymph looks like Dieback—Progressive death of shoots, tissues.
the adult but does not have wings. branches, or roots, generally starting at
the tips. Conk—A fungal fruiting structure (such as
Pathogen—Any organism that causes shelf or bracket fungi) formed on rotting
disease. Generally applied to bacteria, Dwarfing—The underdevelopment of any woody plants.
viruses, fungi, and nematodes. plant organ.
Cyst—The swollen, egg-containing female
Phytotoxic—Toxic to a plant (phyto = Enation—Epidermal outgrowths on leaves body of certain nematodes; can be seen
plant). or stems. on the outside of infected roots.
Sign—Direct evidence of a damaging Epinasty—An abnormal downward-curv- Frass—Sawdust-like material associated
factor (for example, a pest or pathogen ing growth or movement of a leaf, leaf with insects chewing into plant tissues.
itself, secretions, insect webbing, chemi- part, or stem.
Fruiting body—A fungal structure that
cal residues, records of weather extremes Etiolation—Yellow, long, spindly growth contains or bears spores.
or chemical applications). resulting from insufficient light.
Girdling—The cutting, removing, or
Symptom—A change in a plant’s growth Fasciation—A distortion of a plant that clamping of bark all the way around a
or appearance in response to living or results in thin, flattened, and sometimes trunk or branch, sometimes caused by
nonliving damaging factors. curved shoots. insect feeding.
Vector—A transmitter or carrier of disease. Flagging—Wilting and/or death of plant Honeydew—A sticky substance excreted
Virus—An infectious agent too small parts, usually starting from the tip(s) of by aphids and some other insects.
to see with a compound microscope. one or a few branches or stems.
Mine—Tunnel or cavity created by insects
Multiplies only in living cells. Gall—An abnormal, localized swelling on that feed within leaves or needles.
leaf, stem, or root tissue. Depending on the insect, it can appear
as a winding serpentine mine or as an
Mosaic—Nonuniform foliage coloration
irregularly rounded blotch mine.
with a more or less distinct intermingling
of normal green and light green or yel- Mycelia—Masses of fungal threads
lowish patches. (hyphae), which compose the vegetative
body of a fungus.
Mottle—An irregular pattern of light and
dark areas.Chapter 7 Diagnosing Plant Problems • 97
Plant Identification rhododendron cultivars, are covered
by conspicuous, fuzzy, epidermal hairs.
and Appearance They sometimes are thought to be evi-
First, determine whether a problem truly dence of disease, but they are a normal
exists. It is essential to identify the plant part of the leaf.
(genus, species, and cultivar or variety) to • Some plants have variegated foliage
know what it should look like. Use personal that may resemble symptoms of viral
knowledge or plant reference books or diseases.
consult experts. • Premature leaf or needle drop by ever-
If possible, compare the damaged plant green plants (for example, Ficus ben-
with a healthy or normal plant of the same jamina) frequently causes alarm. These
species and variety. Normal plant parts or plants normally retain their leaves or
seasonal changes sometimes are mistakenly needles for three to six years and gradu-
assumed to be evidence of disease. For ally lose the oldest ones during each
example: growing season (Figure 1a). This normal
• The ‘Sunburst’ honeylocust might seem leaf drop is obscured by the production
to be suffering from a nutrient deficiency of new leaves.
because of its chlorotic, yellowgreen leaf
color. However, it was selected for this However, prolonged drought or other
genetic characteristic, and the color is stress may cause the whole tree to tempo-
normal. rarily turn yellow and may accelerate leaf
• The brown, sporeproducing bodies on loss, but that is not a reason for concern.
the lower surface of fern leaves are a The leaves that drop or turn yellow are the
fern’s normal propagative organs, not oldest ones, and their dropping protects the
disease spores or insects. tree by reducing water loss.
• The small, brown, clublike tips that If new leaves drop, however, there prob-
develop on arborvitae foliage in early ably is a problem (Figure 1b). The cause may
spring are male flowers, not deformed be a pathogen, insect, chemical deficiency,
shoots. toxicity, or root problem.
• Small galls on the roots of legumes such In describing a plant abnormality,
as beans and peas most likely are nitro- distinguish between symptoms and signs.
gen-fixing nodules essential to normal Symptoms are changes in a plant’s growth
development, not symptoms of root- or appearance (for example, galls, blotches,
knot nematode infection. or wilting) in response to living or nonliving
• The leaves of some plants, such as some damaging factors. Many factors produce
the same symptoms, so symptoms do not
produce a definitive diagnosis.
Figure 1. Normal ver-
sus abnormal needle
or leaf drop from
evergreens: (a) If drop
is confined to older
leaves, it is normal.
(b) If newly produced
leaves are lost, there is
a problem.98 • Diagnosing Plant Problems Chapter 7
Figure 2. If all or a major portion of Figure 3. Nonuniform damage patterns Figure 4. Random, scattered damage on
a tree or shrub dies, suspect a root on a tree canopy. conifer needles.
problem.
Signs are direct evidence of the damag-
ing factor (for example, the pest or patho-
Damage Patterns
gen itself, secretions, chemical residues, or Patterns are excellent diagnostic clues
records of weather extremes). A combina- and are where you start making the distinc-
tion of signs and symptoms is more likely tion between living and nonliving causes of
to produce a definitive diagnosis than are plant damage.
symptoms alone.
Examine the entire plant. In defining a Nonuniform or Random
plant problem, it is essential to determine Damage (Living Factors)
the true primary problem, because the plant
part exhibiting obvious symptoms may With problems caused by living organ-
not be the part experiencing damage. For isms such as pathogens or insects, there
example, some root problems cause foliage usually is no uniform pattern of damage. It
symptoms. In this case, the primary prob- may appear randomly on parts of a plant or
lem is damage to roots, not foliage. on some plants in a group.
In general, if the entire top of a plant or If scattered damage occurs in the plant
entire branches look abnormal, examine the canopy, suspect a problem in the foliage or
plant downward to find the primary dam- aerial environment, not the roots (Figure 3).
age (Figure 2). Look for the factor causing If scattered branches gradually decline and
the damage at the edge of the symptomatic eventually die, suspect a canker pathogen,
area, and always examine the roots. shoot blight, or borers. Verticillium wilt, on
the other hand, is characteristically one-
sided on a tree or shrub and can develop
relatively quickly—in a month or so on
some species (for example, some maples).
Cracked
bark
Figure 5. Shoot dieback caused by a Figure 6. Uniform death of needle tips. Figure 7. Shoot dieback caused by
fungal infection. winter injury.Chapter 7 Diagnosing Plant Problems • 99
Similarly, living organisms usually dam- Damage caused by nonliving factors
age leaves or needles in a random pattern usually results in a sharp margin or edge
(Figure 4). For example, conifer needles between affected and healthy tissue.
usually are affected over varying lengths However, if bark and wood are cracked,
and often appear straw yellow or light tan. suspect winter injury (Figure 7), in which
Black fruiting fungal bodies may be present dieback often is gradual rather than sudden.
on diseased needles. Often, damage appears
first on lower and inner parts of the canopy,
where humidity is higher, and then pro- Development of
gresses upward and outward. Damage over Time
With living damaging factors, there may
Another clue for distinguishing between
not be a sharp line between affected and
living and nonliving factors is what you see
healthy tissues. Bacterial shoot blight is an
when you observe the pattern over time.
exception, however. With this disease, the
margin between affected and healthy tis-
sue often is irregular and sunken. Bacterial Sudden Decline
shoot blight usually causes the shoot tip to (Nonliving Factors)
wilt and bend over. Sudden decline generally is caused by a
With fungal shoot dieback, there may nonliving factor such as a toxic chemical or
be small, pinlike projections or bumps over extreme weather. All affected leaves might
the surface of dead bark (Figure 5). These die immediately after a chemical application
structures are the spore-producing parts of that is poisonous to plants. If branches die
the fungi. Note, however, that small, woody suddenly, especially if affected branches are
bumps normally radiate from all sides of concentrated on one side of the plant, suspect
spruce twigs where old needles were attached. weather, animal damage, or chemical drift.
If a nonliving damaging factor is not
Uniform Damage removed, damage will intensify. For exam-
(Nonliving Factors) ple, if a toxic chemical remains in the soil or
air, plant damage within the contaminated
Damage patterns produced by nonliving
area will continue to develop, but it won’t
factors, such as frost or toxic chemicals, gener-
spread to uncontaminated areas.
ally are more regular. For example, they:
Sudden decline can be associated with
• May appear on all leaves of a certain age
living factors, such as when a plant is weak-
(for example, those forming the plant
ened by disease or insects and then sub-
canopy when a toxic spray is applied)
• May affect all leaves with a certain expo- jected to an otherwise survivable stress (for
example, Phytophthora root rot followed by
sure (such as those on the southwest side
a normal summer drought period).
of a plant that are not shaded by other
leaves)
• Likely will appear on more than one Gradual Decline (Living Factors)
type or species of plant. Look for similar Gradual decline of an entire plant or a
damage patterns on weeds, neighboring major portion of it usually is caused by a liv-
plants, etc. ing factor (for example, Armillaria root rot,
Verticillium wilt, or root weevils. However,
Air pollutants frequently cause tip burn it can also be the result of marginally surviv-
on conifers, as do certain soil-applied able conditions such as nutrient-deficient
herbicides and excess fertilizer (Figure 6). soil.
Freezing may have a similar effect. All nee- Living organisms multiply and grow
dles at a specific growth stage usually are with time; therefore, they rarely afflict all
affected, and usually each needle is affected of the host plant or plants at once. Damage
to the same length. Affected tissue usually is generally appears first on one part of a plant
reddish brown. and spreads. Likewise, it progresses from100 • Diagnosing Plant Problems Chapter 7
Table 1. Symptoms and signs of fungal and bacterial leaf spots.
Abnormality Fungal Bacterial
Watersoaking Not common Common with rots of thick and succulent leaves and with
initial appearance of angular leaf spots
Texture Usually dry; may be papery Some dry, some slimy to sticky; may be papery when dry
Odor Usually none Foul (putrid to earthy, acrid) odor usually associated with
rots of fleshy plant parts
Pattern Irregular to circular; may Irregular to angular; often restricted by large veins
have concentric rings
Disintegration Uncommon Common with rots
Color changes Common: red, yellow, Less common, but may have irregular, yellow halos
purple halos
Pathogen Common: mycelia, spores, Wet or dried slime at edge of canker or leaf spot
structures spore structures
plant to plant. For example, gradual shoot Fungal diseases
decline with retention of dead leaves usually The presence of fungal mycelia and
indicates damage by a living factor. fruiting bodies are the best clue to a fungal
Bacterial shoot blight and Phytophthora disease. Fruiting bodies range in size from
canker are exceptions to the gradual decline
microscopic to those easily detectable with
rule. They can cause rapid dieback. the naked eye. They are found within the
leaf spot or stem rot area on an infected
Distinguishing among plant. Each type of fungus has its own
characteristic structures, which are used by
Living Causes of Damage plant pathologists for identification.
To identify the type of living factor that Fungal leaf spots and stem rots are char-
has damaged a plant, closely examine symp- acterized by various symptoms: dry texture,
toms and signs. Symptoms are the modified concentric rings, and discoloration. Spots
appearance of the affected plant, such as generally have distinct margins. They vary
necrotic tissues, chlorosis, cankers, galls, or in size and usually are round and occasion-
leaf distortion. Signs are direct evidence of ally elongated (Figure 8).
the actual organism. Examples are insects,
fungal mycelia, spores, egg masses, insect
Figure 8. Fungal leaf spots.
frass, and mite webbing. Signs can be clues
for identifying the specific organism that
produced the damage. A combination of
both symptoms and signs may be necessary
for the initial distinction between disease
and insect/mite damage.
Symptoms and Signs of Disease
Differentiating between bacterial and
fungal pathogens, especially those that
cause leaf spots, is not always clear-cut, but
certain symptoms are distinctive. Table 1
lists key distinguishing characteristics of
fungal and bacterial leaf spots.Chapter 7 Diagnosing Plant Problems • 101
Concentric rings result as the mycelium Erwinia blight is an example of a bacte-
grows outward from the point of initial rial disease that causes water-soaking. The
infection (much like the crocheting of a water-soaked appearance occurs when
doily). Leaf color ranges from tan (died bacteria dissolve the material holding plant
first) in the center to darker brown (recently cells together, thus destroying leaf or stem
died) to very dark. The outer ring may have integrity. Some fungi also produce water-
a light yellow, chlorotic edge where the soaking, but usually not as extensively as
infection is advancing. Margins of fungal Erwinia blight.
leaf spots and stem rots can be brightly Initially, bacterial leaf spot symptoms are
discolored. confined between leaf veins, resulting in
discrete, angular spots with straight sides
Bacterial diseases (Figure 9). Many bacterial leaf spots, such
Bacteria enter plant tissues through as Xanthomonas leaf spot on philodendron
wounds or natural openings in leaves, (also called red edge disease), expand until
stems, roots, or fruit. Once they enter a they reach a large leaf vein. The vein fre-
plant, they reproduce rapidly and release quently inhibits the bacteria from spreading
enzymes and toxins that kill plant cells. farther.
Bacterial leaf spot’s color usually is
Bacterial galls
uniform, though a chlorotic halo often
Crown gall bacteria genetically engineer
surrounds a spot. Spots may enlarge and
their host plant to make galls and amino
coalesce. In final stages, cracks may form
acids, thus giving the bacteria a place to
in the plant tissue; disintegration follows.
live and the chemicals they need to grow
Some lesions may exude bacteria-filled
and reproduce. The galls are characterized
fluid.
by hard, unspecialized plant cells. When
A few bacterial leaf blights, particularly
young, galls resemble a head of cauliflower,
on thick or spongy-textured leaves, are
but they harden with age.
slimy and may have a rotten odor.
Bacterial leaf spot
Vascular wilt
These bacteria usually enter through
In some cases, bacteria plug a plant’s
leaf stomata. A common symptom is a
water-conducting vascular tissue. The result
watersoaked appearance, which is usually
is yellowing, wilting, browning, and death of
revealed by holding an infected leaf to light.
leaves, stems, and roots.
The tissue may become translucent, papery,
and tan when dry.
Figure 9. Bacterial leaf spots. Figure 10. Typical signs of viral infection: (a) Vein
banding (b) mosaic.
(a)
(b)102 • Diagnosing Plant Problems Chapter 7
Viral diseases
A Step-by-Step Method of Diagnosis Viruses are submicroscopic entities
that infect individual plant cells. They are
1. Determine that a real problem exists, then define it. obligate parasites, meaning that they can
a. Identify the plant. Establish what a “normal” plant would replicate only within a host’s cell. As a virus
look like at this time of year. Describe the abnormality proliferates, it moves on to infect other cells.
(symptoms and signs). Because a virus commandeers its host
b. Examine the entire plant and its community. Locate the cell to manufacture viruses identical to
primary problem and the plant part where initial damage itself, the cell cannot function and grow
occurred. normally. Chlorophyll production may stop,
causing necrosis or the yellowing or blanch-
2. Look for patterns. Is the damage on more than one plant? On ing of chlorosis. In some cases, cells may
more than one plant species? grow and divide rapidly; in others, they may
a. A non-uniform damage pattern (irregular or random pat- grow very slowly or stop dividing, causing
tern of damage) is indicative of living factors (pathogens, distortion or stunting. The symptoms of
insects, mites, or other animals). most viral diseases fall into four categories:
b. A uniform damage pattern (such as damage on all leaves of Lack of chlorophyll in normally green organs—
a certain age or all plants in an area) indicates nonliving fac- A common first symptom is vein clearing,
tors (mechanical, physical, or chemical). in which veins look somewhat translu-
cent or transparent but interveinal tissue
3. Outline development of damage over time. remains green. In vein banding, a dark
a. Progressive spread of the damage on a plant or onto other green, light green, or yellow band of tissue
plants indicates damage caused by living organisms. appears along the veins (Figure 10a). (When
b. Damage that does not spread to other parts of the affected leaf veins remain green but tissue between
plant or to other plants, and a clear line between damaged veins becomes chlorotic, the cause may
and undamaged tissues, indicate damage caused by nonliv- be deficiency of a nutrient such as iron.)
ing factors. Virus-infected foliage also may be mottled
green and yellow, mosaic, ringed, or a rather
4. Gather information to identify possible causes of damage. uniform yellow (Figure 10b).
a. Distinguish among living factors. Stunting or other growth inhibition—As
1. Symptoms and signs of pathogens chlorophyll is lost, reduced photosynthesis
2. Symptoms and signs of insects, mites, and other animals leads to shorter internodes (spaces between
b. Distinguish among nonliving factors. nodes), smaller leaves and blossoms, and
1. Mechanical factors lower yield.
2. Physical factors Distortions—Strangely formed leaves and
a. Temperature extremes flowers, witches’ brooms, or rosettes result
b. Light extremes from non-uniform or uncontrolled growth.
c. Oxygen and moisture extremes Necrotic areas or lesions—Viruses require
3. Chemical factors their host’s survival for their own procre-
a. Pesticide or pollutant phytotoxicities ation, so they rarely cause death. Necrosis
b. Nutritional disorders usually is confined to discrete areas of the
c. Use references. You may need laboratory analyses to narrow plant.
the range of probable causes. These symptoms can be valuable clues
for virus identification but are easily con-
5. Synthesize information to determine probable causes. fused with symptoms of nutritional disor-
ders, chemical injury, or damage caused
by mites or insects. In addition, because
of their extremely small size, viruses
are not visible to the unaided eye. Virus
particles are detectable only through an
electron microscope or with special stains
and a compound (high-magnification)
microscope.Chapter 7 Diagnosing Plant Problems • 103
Viruses are transmitted from plant to insect pest. Knowing an insect’s life cycle
plant by insects, mites, fungi, nematodes, (complete or simple metamorphosis) also is
rubbing, abrasion, grafting, or other important when attempting to identify an
mechanical means. They occasionally are insect or design a control program.
transmitted in seed.
Feeding habits
Nematodes General groups may be distinguished
Nematodes are microscopic round- by their method of feeding. Beetles and
worms that damage plant tissues as they caterpillars use chewing mouthparts to eat
feed. Many feed on or in root tissues, but a portions of leaves, while aphids and plant-
few feed on foliage or other aboveground hoppers remove plant sap with tubelike
organs. sucking mouthparts. Thrips rasp leaf and
flower tissue; plant feeding mites remove
Root nematodes the contents of cells, leaving a stippling pat-
Root-infesting nematodes damage root tern or tiny white spots on leaves. Use the
systems, causing aboveground symptoms— following clues to find the cause of chew-
commonly moisture and nutrient stress and ing/rasping damage:
general stunting. Root-lesion nematodes • Caterpillars and some beetles consume
(Pratylenchus spp.) and burrowing nema- entire leaves, leaving only the toughest
todes (Radopholus similis) destroy root veins.
tissues as they feed. Rootknot nematodes • If distinct portions of the leaf are miss-
(Meloidogyne spp.) inject growth-regulating ing, the cause could be black vine weevil
substances into root tissues, stimulating (the adults cut distinct notches from leaf
growth of large, tender cells that become margins); leaf cutter bees (circular holes
permanent feeding sites. As root tissues cut from margins); or beetles, chafers,
grow around these sites, they form visible weevils, or grasshoppers (small, ran-
swollen galls or knots. Other root nema- domly scattered holes).
todes stunt growth, apparently by killing • Damaged (especially skeletonized) leaf
root meristems. surfaces may indicate slugs, leaf beetle
Shoot nematodes (Aphelenchoides spp.) larvae, pear slugs (pear sawfly larvae),
Shoot (foliar) nematodes feed inside elm leaf beetles, or thrips.
leaves between major veins, causing chlo- • Leaves tied with silken threads or rolled
rosis and necrosis. The tissue first collapses into tubes often harbor leafrollers or leaf-
in wedge-shaped areas between the larger tiers (for example, omnivorous leaftiers).
veins and then changes color. Injury most • If there is a discolored or swollen area on
often is seen at the base of older foliage. a leaf, hold it up to the light to look for
insects or frass in the damaged area. The
culprit may be leafminers, which feed
Symptoms and Signs between upper and lower leaf surfaces
of Insect Pests (for example, boxwood, holly, birch, and
Finding the insects feeding on a plant elm leafminers).
is the surest way to identify a problem. • If petioles are weakened and leaves fall
However, you may have to rely on other in early summer, suspect petiole and leaf
clues if the pest is no longer present. These stalk borers (for example, maple petiole
clues include feeding location on the plant, borers), which burrow into petioles near
type of feeding damage, time of year, and leaf blades or bases. Cut open a petiole to
types of plants being damaged. The loca- look for a small moth or sawfly larva.
tion and type of feeding damage are the • If a twig’s bark is girdled (cut, removed,
most important clues in identifying an or clamped all the way around), the cul-
prit may be vine weevil or twig-girdling
beetle.104 • Diagnosing Plant Problems Chapter 7
• If a plant or specific branch is in general • Leaf and stem distortion plus off-color
decline, examine it closely for frass, pitch, foliage is the result of aphids (for exam-
or holes in the bark. These signs are ple, rose aphids, black cherry aphids, or
caused by borers, which feed under the leaf curl plum aphids). It is often is con-
bark in cambium tissue, solid wood, or fused with injury from growth-regulating
xylem tissue. Examples are bark beetles, chemicals.
round and flatheaded borers, and clear- • Galls (swellings on leaf or stem tissue)
wing borers. may be caused by various species of
• General decline of a plant along with aphids, wasps, midges, and mites.
chewed roots may indicate damage by • Twigs that look like they’ve been split by
root weevil larvae or white grubs. a sharp instrument are the result of egg
laying (oviposition) by sucking insects
Sap removal by sucking insects can cause such as treehoppers and cicadas. Cicadas
wilting and occasionally damage to leaf in particular often split a branch enough
veins. A few inject saliva or toxic sub- to kill its tip.
stances that cause discoloration or distorted • General decline of an entire plant or
growth. Insects that secrete phytotoxic plant part, as indicated by poor color,
substances are called toxicgenic (toxin reduced growth, or dieback, may be the
producing). The resulting plant damage is result of root, stem, or branch feeders
called phytotoxemia or toxemia. such as scale insects or mealybugs.
Spotting or stippling occurs when chlo- • Accumulations of shiny honeydew
rophyll is destroyed at the feeding site but and sooty mold indicate infestations of
toxins do not diffuse throughout the leaf. aphids or soft scales.
Aphids, leafhoppers, planthoppers, and • Stunted tip growth of trees and shrubs
spider mites bugs commonly cause this type may be due to armored scales.
of injury.
Severe toxemias develop when toxic
saliva causes leaves to curl and pucker Insect life cycles
around an insect. Severe aphid infestations Most insects develop from egg to adult
may cause this type of damage. through gradual (also called simple or
In some cases, toxic effects spread incomplete) metamorphosis or complete
throughout the plant, resulting in reduced metamorphosis. Gradual metamorpho-
growth and chlorosis. This condition is sis has three stages—egg, nymph, adult.
known as systemic toxemia. Psyllid yellows Nymphs resemble adults and feed and
of potatoes and tomatoes and infestations behave much like them. Examples include
of scale insects or mealybugs may cause grasshoppers and aphids.
systemic toxemia. Complete metamorphosis has four
Look for these clues when determining stages—egg, larva (specialized feeding
the cause of sucking damage: stage), pupa, and adult. Examples include
• General (uniform) stippling, flecking, moths and beetles. Larvae look very differ-
or chlorotic patterns on spruce needles ent from the adult stage.
usually are caused by spider mite dam- In both types of metamorphosis, the
age. Lace bugs may be the cause on other nymphs or larvae increase in size in distinct
plants. steps when they molt (shed their external
• Random stipple patterns on leaves are skeleton). Discarded exoskeletons found
caused by leafhoppers and mites. near feeding sites on plants may be helpful
in identifying the pest. All growth is com-
pleted before the adult stage.Chapter 7 Diagnosing Plant Problems • 105
Symptoms and Signs of Distinguishing among
Other Animal Damage Nonliving Causes of Damage
A variety of other living organisms can
Uniform patterns of damage indicate
damage plants. For example:
that a nonliving factor is the probable cause.
Arachnids—Arachnids have eight legs
The three broad categories of nonliving fac-
(insects have six) and sucking mouthparts.
tors include the following:
Spider mites are an example. They have a
Mechanical factors—abrasion and bruising
simple life cycle and often cause leaf stip-
from construction or maintenance equip-
pling, with damaged leaves then turning
ment, handling during transplanting, or
pale on the underside. Severe infestation
lawn mowers.
causes leaf bronzing and death. Foliage may
Physical factors—environmental or
appear dirty, due to the presence of small,
weather changes such as temperature
fine webbing mixed with eggs and frass on
extremes, light, moisture, or wind.
the underside of leaves. Eriophyid mites,
Chemical factors—pesticide applications,
on the other hand, cause distorted new
aerial and soil pollutants, and nutritional
growth, rolled leaf margins, and swollen
disorders.
veins. Symptoms of arachnid damage often
Additional clues, as discussed below, will
are confused with damage from growth
help you determine which of these factors
regulators.
caused the damage.
Crustacea—Sowbugs and pillbugs usually
feed on decaying vegetation. Unless popula-
tions are high, they are not considered Mechanical Factors
damaging to live plants. First, consider whether there has been
Mollusca—Slugs and snails feed on low- recent excavation, construction, or paving
growing foliage and fruit growing in shaded, on the site. Then examine the damaged
humid areas. They use rasping mouthparts plant. Close examination often reveals
to scratch and loosen soft tissue. Look for whether stems or roots were broken or
slime trails on foliage and the surrounding girdled and whether leaves were bruised,
soil. punctured, or broken. For example, if stems
Miscellaneous animals—Millipedes (arthro- break because a plant is dropped during
pods) feed on decaying plants. They have transplanting, rapid wilting will occur above
many small legs, are brownish or white in the break.
color, and vary in size from 1⁄2 to 2 inches
long. They are not considered injurious to Physical (Environmental) Factors
live plants.
Small mammals—Chewed bark and Primary sources of diagnostic informa-
cambium tissue on small trees and shrubs tion for damage caused by physical factors
most frequently is caused by mice, rabbits, are damage patterns and weather records.
squirrels, or possibly beavers. Look for teeth Temperature extremes
marks.
Extremely hot or cold temperatures can
Large mammals—Cattle, goats, deer, and
damage plants. In both cases, recognizable
horses tear or cut branches.
damage patterns are likely to occur. Heat
Birds—Missing flower petals or punc-
damage is most likely to occur in the early
tured bark may be caused by yellowbellied
afternoon when the sun is in the southwest
sapsuckers. They make even rows of holes
quadrant of the sky. Therefore, damage
in tree trunks.
occurs primarily on outer, unshaded leaves
on a plant’s southwest side. Leaves shaded
by other leaves or those on the northeast
side may be undamaged. The most severe
damage occurs on plant parts farthest from
water-carrying roots, stems, and leaf veins.106 • Diagnosing Plant Problems Chapter 7
Thus, leaves on the outer perimeter of the Aboveground symptoms of cold damage
plant, leaf tips, and interveinal areas are to roots generally do not become evident
most commonly damaged. This damage until shoots begin to grow in the spring. At
pattern is likely to occur uniformly over all that time, leaf expansion may be incomplete
plants in an area. Cold damage occurs on because of restricted water and nutrient
the least hardy plants and is most severe on uptake by the damaged root system. The
the least hardy tissues of those plants. Plants result is smaller-than-normal leaves. As
vary in their hardiness (cold tolerance). By air temperature increases, water loss from
checking how low the temperature dropped shoots and leaves may exceed the roots’
and knowing the indicator plants for vari- ability to take up water. As a result, the plant
ous USDA cold hardiness zones, you can loses leaves or wilts, and it may die.
begin to determine whether plant damage
was caused by cold. Light extremes
A plant gains cold hardiness gradually Plants can acclimate to various light
beginning at its terminal (tip) buds, and conditions but need time to do so. They
regains it gradually (also beginning at the tip respond adversely to rapid light change. A
buds), so the location of cold damage on a sudden shift from low to high light destroys
plant will tell you approximately when the a plant’s chlorophyll and leads to yellow-
damage occurred. Damage to buds occurs ing and necrosis. Rapid change from high
most often in late winter or early spring, to low light, on the other hand, results in
while damage to lower plant parts may reduced growth and leaf drop. Under low
occur in the fall or early winter. light, new leaves are larger, thinner, and
On a given structure (such as a leaf or darker green than normal, while flowering
bud), exposed, nonhardy tissues are dam- is reduced, delayed, or absent.
aged in a recognizable pattern. For example:
• Spring frost damage uniformly kills new, Oxygen and moisture extremes
succulent growth. New growth emerging Oxygen and moisture extremes primar-
after the frost will be healthy. ily affect the root environment, where
• Frost cracks are lengthwise separations the quantities of oxygen and moisture are
of bark and wood that generally occur on inversely related. That means a waterlogged
the southwest side of a trunk. They are (saturated) root environment lacks suf-
the result of wide day/night temperature ficient oxygen for root metabolism and
fluctuations in winter. growth. Consequently, less water and nutri-
• The dividing cells on outer portions of ents are taken up by plants.
leaves may freeze while still inside the Drought and waterlogging produce
bud. As a result, distorted or lacelike leaf many of the same aboveground symptoms.
blades develop. The first symptoms to appear are wilt-
ing, chlorosis, and abscission (dropping)
Generally, root systems cannot survive of older leaves. Under severe, continuing
at as low a temperature as can aboveground moisture stress, wilting and necrosis occurs
plant parts. Fortunately, soil temperatures in on tips and interveinal regions of recently
winter usually are warmer and more stable expanded leaves and new growth.
than air temperatures. Thus, cold damage to
roots primarily is a concern with container- Chemical Toxicities
grown plants, where soil temperatures Patterns of chemical injury on indi-
fluctuate more than in ground soil. Examine vidual plants differ, depending primarily on
the root system to detect damage in whether a chemical causes damage directly
container-grown plants. It generally occurs on contact or is absorbed and moves
on the periphery of the root ball (near the throughout the plant.
container edge). Evidence includes black or
spongy roots that lack new growth or new
root hairs.Chapter 7 Diagnosing Plant Problems • 107
Direct-contact damage Figure 11. Foliar chemical spray injury.
Direct-contact damage can occur on
both foliage and roots.
Shoot/foliage contact
Symptoms from shoot-contact chemicals
occur over the general plant canopy. The
injury does not spread with time or move to
previously undamaged plants.
Injury is typified by chlorotic or necrotic
spotting. Spots usually are uniformly and
evenly distributed over the leaf surface and
generally are the same size. Color usually
is uniform across the spot, and the margin
between affected and healthy tissue usually
is sharp (Figure 11).
If a chemical is applied directly to
aboveground parts, you may be able to see
the application pattern. For example, the same result.
pattern of spray droplets may be visible or Keep in mind that many other factors
areas where spray accumulated along leaf also injure roots or inhibit their growth,
edges may show the most damage. In the including nematodes and other pathogens,
case of a toxic gas (volatile chemical), areas soil compaction, cold weather, salinity, and
between leaf veins and along leaf margins— nutritional deficiencies or excesses.
where water concentration is lowest—show Translocated chemical damage
damage first.
Some chemicals can move throughout
Examples of shoot/foliage contact
a plant after being absorbed. The effects of
chemicals are foliar-applied fertilizers; the
these mobile chemicals depend on whether
agricultural herbicides paraquat, acifluor-
they are transported in the xylem or the
fen, and dinoseb; and herbicidal oils. (Very
phloem.
few, if any, contact herbicides are available
If transported solely in the xylem, the
to home gardeners.)
chemical moves upward through the
Root contact plant, primarily causing symptoms in older
Toxic contact chemicals in the root zone, foliage. Examples of xylem-transported
including excess fertilizer, result in poor chemicals include urea fertilizer and the
root development. Roots are injured and agricultural herbicides triazine, alachlor,
root tips may be killed. and metolachlor.
Aboveground shoots may show water If transported in the phloem, a chemi-
and nutrient stress symptoms—for example, cal may move in many directions from
reduced growth, wilting, or chlorosis— the point of absorption; for example, it
because the roots are unable to obtain may move from the shoots to the roots or
water. In severe cases, wilting can occur vice versa. Symptoms caused by phloem-
even when the soil is wet. Lower leaves transported toxic chemicals occur primarily
generally wilt first, followed by drying of in the plant’s new growth and meristematic
leaf margins. regions. Affected young tissue is discol-
Herbicides that inhibit root growth ored or deformed, and injury may persist
include the agricultural herbicides dini- for several sets of new leaves. Examples
troanilines, DCPA (Dacthal), and diphena- of phloem-transported toxic chemicals
mid. Excess nitrogen fertilizer can have the include the common garden herbicides
2,4D, dicamba, and glyphosate.108 • Diagnosing Plant Problems Chapter 7
Nutrient Deficiencies Calendar for Common Kentucky Shade
Tree and Woody Ornamental Pests.
Like the effects of toxic chemicals, the http://www.ca.uky.edu/entomology/ent-
effects of nutrient deficiencies depend on facts/ef447.asp
whether the chemical is transported only in Woody Plant Disease Control Guide for
the xylem or also in the phloem. Kentucky (ID-88). http://www.ca.uky.
Nutrients that are transported solely in edu/agc/pubs/id/id88/id88.pdf
the xylem are immobile in a plant once they Guide for Control of Annual and Perennial
have been moved upward from the roots. Flower and Ground Cover Diseases in
They cannot be moved through the phloem the Landscape (ID-87). http://www.
to new growth if a soil deficiency develops, ca.uky.edu/agc/pubs/id/id87/id87.pdf
so symptoms of these chemicals typically
develop on new growth. Phloem-immobile
chemicals include boron, calcium, iron, Other publications
manganese, zinc, copper, molybdenum, Bennett, W.F., ed. Nutrient Deficiencies and
and, in some plant species, sulfur. Toxicities in Crop Plants (APS Press, St.
In contrast, a phloem-mobile nutrient Paul, MN, 1993). 202 pp.
can be withdrawn from older leaves and Borror, D.J., and R.E. White. A Field Guide
moved to growing root and shoot tips if a to the Insects of America North of
soil deficiency develops, so that deficien- Mexico (Houghton Mifflin Company,
cies of these nutrients will first be visible on Boston, 1970).
older leaves. Nitrogen, phosphorus, potas- Flint, M.L. Pests of the Garden and Small
sium, magnesium, chlorine, and, in some Farm: A Grower’s Guide to Using Less
plant species, sulfur, are phloem-mobile. Pesticide, Publication 3332 (University of
California, Los Angeles, 1999).
For More Information Johnson, W.T., and H.H. Lyon. Insects That
Feed on Trees and Shrubs, 2nd ed.,
Many other publications on specific rev. (Comstock Publishing Associates,
insect and disease problems are listed in Cornell University Press, Ithaca, NY,
other chapters. 1991).
The Ortho Problem Solver, 7th ed.
University of Kentucky Cooperative Extension
(Chevron Chemical Co., San Francisco,
publications
2008).
Timing Control Actions for Landscape Pirone, P.P. Diseases and Pests of
Insect Pests Using Flowering Plants as Ornamental Plants, 5th ed. (John Wiley
Indicators. http://www.ca.uky.edu/ento- & Sons, New York, 1978).
mology/entfacts/ent66.asp Pirone, P.P. Tree Maintenance, 7th ed.
(Oxford University Press, New York,
2000).
Sherf, A.F., and A.A. Macnab. Vegetable
Diseases and Their Control, 2nd ed.
(John Wiley & Sons, New York, 1986).
Sinclair, W.A., H.H. Lyon, and W.T Johnson.
Diseases of Trees and Shrubs, 2nd ed.
(Cornell University Press, Ithaca, NY,
2005).Chapter 7 Diagnosing Plant Problems • 109
Table 2. A diagnostic key to vegetables.
Symptoms Possible Causes Controls
General
Poor fruit yield; fruit may be Uneven moisture Water during dry periods.
small and have poor taste Poor soil fertility Soil test; supply nutrients based on results.
Plants grow slowly; leaves light Insufficient light Thin plants; do not plant in shade.
green. Cool weather Growth will improve when weather warms.
Poor soil fertility Soil test; supply nutrients based on results.
Improper pH Soil test; adjust pH as needed.
Excess water Do not overwater; improve drainage.
Seedlings don’t emerge Dry soil Water.
Damping-off (fungal disease) Use sterile pots and planting media; do not overwater;
allow soil to dry slightly between waterings; treat seed
with registered fungicide before planting.
Incorrect planting depth Plant at correct depth.
Slow germination due to weather Wait for appropriate weather conditions before planting.
Root maggots Use floating row cover; apply registered soil insecticide.
Wilted seedlings; seedlings Damping-off (fungal disease) Use sterile pots and planting media; do not overwater;
fall over allow soil to dry slightly between waterings; treat seed
with registered fungicide before planting.
Cutworms Use cutworm collars, biological control agent; apply regis-
tered soil insecticide.
Root maggots, wireworms Use floating row cover for seed maggots only; apply regis-
tered soil insecticide.
Chewed seedlings Rodents, rabbits, or birds Place fence around garden.
Slugs Use slug barrier or bait.
Various insects Identify insect; use appropriate nonchemical or chemical
control.
Wilted plants; bottom leaves Dry soil Water.
may turn yellow Root rot (fungal disease) Use sterile pots and planting media; do not overwater;
allow soil to dry slightly between waterings; treat seed
with registered fungicide before planting.
Vascular wilt (fungal disease, mainly Plant resistant varieties; rotate.
affecting tomatoes, potatoes, egg-
plants, and peppers)
Root-knot nematodes, white grubs Plant resistant varieties; rotate with nematodes that attack
insects; remove diseased plants; fumigate soil.
Various root-feeding nematodes Submit soil sample for nematode analysis; plant resistant
varieties; rotate; remove diseased plants; fumigate soil.
Waterlogged soil Improve drainage; do not overwater.
General leaf yellowing; no Nutrient deficiency Soil test; supply nutrients based on results.
wilting Insufficient light Thin plants; do not plant in shade.
Leaves stippled with tiny, Spider mites Use predatory mites; apply insecticidal soap or registered
white spots miticide.
Leaf margins turn brown and Dry soil Water.
shrivel Fertilizer burn Test soil for soluble salts; do not overfertilize; flush soil
with water.
Potassium deficiency Soil test; supply nutrients based on results.
Cold injury Do not plant too early.
Discrete, brown spots on Fungal or bacterial leaf spot disease See specific plant listings below.
leaves; some spots may Chemical injury Do not apply chemicals that are not registered for use on
coalesce the plant; apply chemicals at recommended rates and in
the right environmental conditions.
White, powdery growth on Powdery mildew (fungal disease) Use resistant varieties; space plants adequately for better
upper leaf surfaces air circulation; control weeds; apply registered fungicide.110 • Diagnosing Plant Problems Chapter 7
Table 2. A diagnostic key to vegetables.
Symptoms Possible Causes Controls
Leaves shredded or stripped Hail damage —
from plant Rodents Place fence around garden; use traps.
Slugs Use slug barrier or bait.
Dead tissue drops out after fungal Avoid wetting foliage; space plants adequately for better
infection air circulation; apply registered fungicide before problem
reaches this stage.
Various insects Identify insect; use appropriate nonchemical or chemical
control.
Leaves with yellow and green Viral disease Plant resistant varieties if available; plant certified,
mosaic or mottle pattern disease-free seeds or seedlings; control weeds; remove
and destroy affected plants.
Leaves curled, puckered, or Herbicide injury (common on toma- Be careful when using herbicides.
distorted toes and cucumbers)
Viral disease Plant resistant varieties if available; plant certified,
disease-free seeds or seedlings; control weeds; remove
and destroy affected plants.
Aphids Pick off, mash, or wash away insects; use biological control
agent; treat plant (especially underside of leaves) with
insecticidal soap or registered insecticide.
Tops turn yellow, brown, and Rust (fungal disease) Plant resistant varieties; cut tops close to ground in fall
die back; reddish-brown, and destroy; remove and destroy affected leaves; improve
orange, or black pustules air circulation; avoid wetting foliage; apply registered
appear on stems and leaves fungicide.
Shoots wilt, turn yellow, then Fusarium wilt (fungal disease) Plant resistant varieties; destroy affected plants; rotate for
brown; vascular tissue in Verticillium wilt (fungal disease) 2 to 4 years; fumigate soil.
crown area is reddish-brown
Asparagus
Small spears; immature plants Asparagus produces small spears for 2 or 3 years after planting.
Plants overharvested during previous Do not harvest late into the season: plants can’t store
year enough food for following season.
Poor fertility Soil test; supply nutrients based on results.
Poor drainage Do not overwater; plant in well-drained area.
Spears crooked Mechanical injury from windblown Be careful not to damage emerging spears when
sand or mishandling harvesting.
Asparagus beetles, Japanese beetles Beat foliage over a tray and discard the insects; apply
registered insecticide.
Spears turn brown and soft Frost injury Protect spears with mulch.
Root rot (fungal disease) Rotate; plant in well-drained area; do not overwater;
remove plant debris.
Leaves chewed; slime may be Slugs (emerge at night and hide dur- Use slug barrier or bait.
present on leaves; no evidence ing the day)
of insects.
Spears and leaves chewed or Asparagus, Japanese beetles Beat foliage over a tray and discard the insects; apply
scarred registered insecticide.
Beans
Skeletonized leaves Mexican bean beetle larvae and adults Apply registered insecticide.
Plants wilt/are stunted; leaves, Dry soil Water.
may turn yellow Root rot (fungal disease) Rotate; plant in well-drained area; do not overwater;
remove plant debris.
Root-knot nematodes Rotate; remove diseased plants; fumigate soil.
Poor fertility Soil test; supply nutrients based on results.Chapter 7 Diagnosing Plant Problems • 111
Table 2. A diagnostic key to vegetables.
Symptoms Possible Causes Controls
Failure to set pods High temperature causes blossoms to Wait for cooler weather.
drop
Dry soil Water.
Wet soil causes lack of oxygen to roots Do not overwater; plant in well-drained area.
Mature pods left on vines cause seed Pick pods regularly.
production rather than pod set
Rust-colored powdery spots Rust (fungal disease) Plant resistant varieties; remove plant debris and pods;
surrounded by yellow halos on remove and destroy affected leaves; apply registered
leaves and stems fungicide.
Soft, watery spots or white, White mold (fungal disease) Rotate; remove plant debris; improve air circulation; use
moldy growth on leaves, registered fungicide.
stems, and pods; plants wilt
and die
Water-soaked spots followed Halo blight (bacterial disease) Delay planting until warm weather; plant disease-free
by irregular brown spots on seed; rotate; remove plant debris.
underside of leaves
Mottled patterns on leaves; Mosaic (viral disease) Use resistant varieties; avoid planting beans near sweet,
leaves often curl downward, red, or crimson clover or gladioli, which may harbor the
may become chlorotic, soon disease.
die
Leaves lose color; underside Spider mites Use predatory mites, insecticidal soap, or registered
appears dusty and webbed miticide.
Young leaves curled, distorted, Aphids Pick off, mash, or wash away insects; use biological control
and yellow; clusters of tiny agent; apply insecticidal soap or registered insecticide.
insects on leaves and stems
Beets
Small, circular spots with light Cercospora leaf spot (fungal disease) Rotate; pick off and destroy affected leaves; thin planting;
centers and dark borders on avoid wetting foliage.
leaves
Roots cracked; black areas on Boron deficiency Maintain soil pH between 6 and 7; soil test; supply boron
surface and inside of roots; based on results.
plants stunted
Deformed roots Overcrowding Thin beets early.
Cloddy soil Prepare soil properly.
Leaves with many small holes Flea beetles Use floating row cover or biological control agent; apply
registered insecticide.
Irregular, tan blotches in leaves Leafminers Use floating row cover; remove and destroy infested
leaves.
Carrots
Inner leaves yellow; outer Aster yellows (phytoplasma disease) Remove and destroy affected plants; control weeds; con-
leaves reddish-purple; roots trol leafhoppers with registered insecticide.
stunted and bitter
Root tops green Roots exposed to sunlight Cover exposed roots with soil or mulch.
Roots deformed Overcrowding Thin carrots early.
Cloddy soil Prepare soil properly.
Root-knot nematodes Submit soil sample for nematode analysis; rotate; remove
diseased plants; fumigate soil.
Excess nitrogen Do not overfertilize.
Small maggots in roots Carrot rust fly larvae Rotate; plant resistant varieties; use floating row cover;
apply registered insecticide.112 • Diagnosing Plant Problems Chapter 7
Table 2. A diagnostic key to vegetables.
Symptoms Possible Causes Controls
Cole Crops (cabbage, broccoli, turnips, cauliflower, Brussels sprouts)
Cabbage heads crack Plant takes up excess water, causing Harvest heads as soon as mature.
head to burst
Poor heading Overcrowding Thin plants early.
Dry soil Water.
High temperature Wait for cooler weather.
Poor soil fertility Soil test; supply nutrients based on results.
Club root (fungal disease) Check roots for large swellings; rotate out of affected area
for 7 years; lime soil to raise pH above 7.0.
Root rot (fungal disease) Rotate; plant in well-drained area; do not overwater;
remove plant debris.
Discolored cauliflower heads Exposure to sun Tie leaves over heads early.
Plants wilt and turn yellow; Club root (fungal disease) Check roots for large swellings; rotate out of affected area
roots have large swellings for 7 years; lime soil to raise pH above 7.0.
(not to be confused with
smaller root knots caused by
nematodes)
Plants stunted and yellow Dry soil Water.
(especially cabbage); roots not Poor soil fertility Soil test; supply nutrients based on results.
discolored Cabbage maggots Use collars, floating row cover, or biological control agent;
work in a soil insecticide at planting time.
Heads soft and rotted Soft rot of broccoli (bacterial disease) Grow broccoli varieties that shed water (conical head);
provide good air circulation; avoid wetting heads.
Rough, brown, raised areas on Oedema (physiological problem due Water during dry periods; avoid overwatering in cool
underside of leaves to uneven water supply) conditions.
Leaves riddled with shot holes Flea beetles Use floating row cover or biological control agent; apply
registered insecticide.
Leaves chewed Imported cabbage worm, cabbage Identify insect; use floating row cover or biological control
looper, diamondback moth agent; apply registered insecticide.
Some leaves curled, yellow; Aphids Use floating row cover or biological control agent; apply
clusters of tiny gray or green insecticidal soap or registered insecticide.
insects
Corn
Stalks broken, pith tunnelled European corn borer Apply registered insecticide.
Ears not completely filled with Poor pollination Plant in blocks of three or four short rows rather than
kernels single long one.
White (smooth) or black (pow- Smut (fungal disease) Rotate; plant only 1 inch deep to encourage rapid germi-
dery) galls on stalks, leaves, nation; keep soil moist for first 4 weeks after germination;
ears, or tassels cut off galls before they turn black; remove plant debris.
Plants stunted; yellow and Maize dwarf mosaic (viral disease) Control weeds, especially wild grasses; control aphids;
green striped mosaic pattern destroy affected plants.
on leaves; older leaves pale
yellow
Leaves reddish on margins Phosphorus deficiency Soil test; supply nutrients based on results; avoid planting
in very cool soil.
Distorted leaves or stalks; Herbicide injury Be careful when applying herbicides.
leaves may fail to unfurl or
stalk may be bent
Caterpillars feeding on tips of Corn earworms Apply mineral oil or registered insecticide during silking
ears to prevent infestation.
Young plants disappear Cutworms Use cutworm collars or biological control agent; apply
registered insecticide.
Birds Use floating row cover or screen.You can also read
