Simple words are key to unlock pest and disease problems
This article really needs a Sponsor!
Disease names and pest symptoms/appearance are often very
simple, descriptive terms. To identify plant problems and control
information more quickly:
1) Focus on the part of the plant expressing symptoms:
• foliage and fruit or
• branches, canes, or
• water-conducting system,
or
• roots.
2) Choose two or three words to describe what you see. You might
scan/search the appropriate list below (use chart, or Search) to
find words that fit what you see, such as curl, sooty, wilt.
3) Combine the troubled plant's name with the descriptive term
you find here; e.g. maple blotch, aster spot
4) Use that combination of plant name and description to search
a book's index, this site or the Internet. Try your Internet with
the "Images" option selected, as well.
Some of the descriptions below are linked to images and articles
on that topic elsewhere on this site. Others are linked to
illustrated Extension bulletins or botanical garden
references.
Terms in the top half of the chart relate to diseases and other
non-insect issues. Bottom half of the chart refers primarily to
insect trouble.
Symptoms seen on foliage (leaf/needle), fruit
Descriptive term (Causal agent/s)
Definition.
Examples
Anthracnose. (Fungus.) Blistering,
ulcer-like marks, reddish to yellowish regions near leaf margin
which expand inward between veins. Can involve twigs,
branches.
dogwood-, honeylocust-, sycamore-, poplar-, maple
anthracnose
More, at Anthracnose Diseases of Eastern
Hardwoods, a U.S. Forestry Service bulletin.
Blight. (Fungus, Bacteria, Virus.)
Sudden cessation of growth, withering and death of plant parts
without rotting. Often as current year's new growth is reaching its
limit but before it hardens/becomes woody.
fireblight of rose family, late blight / early blight of
nightshade family
More, at Saving Harry Lauder and at Mysteries Solved
Blister.
(Fungus.) Leaves have bulges (or depressions, as seen from reverse
side of leaf).
oak leaf blister, white pine blister rust
More, at Plant Management Network, a non-profit
science-based horticulture site.
Blotch.
(Fungus.) Irregularly shaped areas darken and die on foliage, often
with distinctive marginal area, leaving dead tissue of predictable
color or texture. May destroy whole leaf or destroy tissue between
veins in particular pattern.
chestnut blotch
Borer
(Insects) Insect hatches within or chews into a growing shoot,
stem, leafstalk (petiole) or twig. Hollows out the petiole or eats
the growing point within the shoot. Leaf may drop off. Shoot
usually becomes distorted and may die above the borer's
location.
maple petiole borer, corn/aster shoot borer, squash vine
borer
More, in What's
Coming Up 140 and in Borers list...
Bud
blast. (Often cultural) Buds die and dry out before normal
budbreak.
daffodil bud blast, iris bud blast
Bud worm.
(Insects, may be maggot, caterpillar, etc.) Feeds within/chews or
tunnels into unopened buds.
rose bud worm, spruce bud worm, pine shoot moth
Cast, cast-off
(Various causes) Unnatural shedding of foliage, usually of
needles.
pine needle cast
Chewing.
(Moth, caterpillar, cankerworm, looper, sawfly.) Insect may move in
distinctive way or create a particular pattern as it eats. For
instance: Chews leaf margin, chews between veins creating lacy
pattern.
linden looper, azalea lacebug
Chlorosis. (Nutrient deficiency.)
Veins and/or portions of leaf close to petiole normally colored or
at darker green than tissue between the veins and along the margin
(edge) of leaf blade. Not to be confused with overall,
evenly-distributed paleness. What pattern or progression the
chlorosis takes may be significant: whether new- or old growth is
involved; whether a particular section of a plant becomes chlorotic
first or is the only part of the whole that shows the symptoms;
whether tissue becomes chlorotic and remains so or is first
chlorotic and then necrotic/dead.
More about this symptom in tree foliage, at Chlorosis, a Morton
Arboretum bulletin
Curl, leaf
curl.
(Caused by fungus.) Thickened tissue causes leaf to curve, pucker
or be otherwise malformed.
peach leaf curl
(Caused by sucking insect.) Causes malformed leaf/twig
above/beyond the insect's feeding location.
spittlebug damage, boxwood psyllid, honeysuckle witch's
broom
Galls.
(Insect. Bacteria. Mite.) Pest's feeding or infection causes
abnormal, tumor-like growth of plant's soft tissue.
maple
spindle gall, oak apple gall, oak spangle gall, goldenrod stem
gall, spruce tip
gall
Leaf
rollers. (Insect.) "Sheltered feeders" roll or double the
leaf then feed in the shelter thus created.
apple leaf roller
Leaf
tiers, tie -er. (Insect.) Pest uses web or glue to tie two
or more leaves together and then feeds within the shelter thus
created.
More, in a bulletin from Missouri Botanical Garden, Caterpillars: Leaf tiers, Rollers, Bagworms
and Web Formers
Lice, plant lice.
Tiny insects in large numbers on leaves/soft stems or shoots,
usually refers to aphids.
More, in bulletin EPP 7313 from the Oklahoma
Cooperative Extension, Home Vegetable Garden Insect Pest
Control
Mildew
Powdery mildew. (Fungus.) Leaf tissue yellows,
dies; While leaf tissue still alive, powdery fruiting bodies may
form on leaf/twig/flower surfaces. The "powder" can be rubbed off
as it is on the surface of the leaf.
powdery mildew of lilac, rose, lawn grass, mountain ash, apple, peony
More, in What's
Coming Up 101
More, in
What's Coming Up 40
Downy mildew. (Fungus.) Pale spots which then
become dead spots. They usually appear first on upper surfaces of
lower leaves. Spots turn color as they age, before becoming brown
and dead.. While infected leaf tissue still alive, dry-downy patch
of fruiting bodies is produced on leaf underside. Does not easily
rub off because it is growing from within the leaf.
downy mildew of rose
downy
mildew of impatiens
Mines, miner,
mining. (Insects.) An insect larva is laid as egg within a
leaf, then chews between upper and lower leaf surface creating
feeding trail or "mine" of more or less distinctive
pattern.
holly leaf
miner, birch leaf miner
More, with miner pictures in What's
Coming Up 140
Mites. (Spider
relatives.) Sucking pests, near microscopic. Dry, dusty appearance
to foliage, leaf said to be "stippled". If damage is to petioles or
emerging foliage leaves may appear puckered, irregular,
small.
red spider mite, spruce spider mite, cyclamen mite of African
violet
Mosaic.
(Virus.) Distinctive pattern in leaf color. Unlike leaf spots and
blotch, affected tissue may remain alive.
cucumber mosaic virus, ring spot virus
For more, with photos, see
What's Coming Up 137.
Rot.
(Fungus. Bacteria.) Infected tissue softens and darkens and then
shrivels. Fruit may rot before ripening. Growing point within a
shoot may rot as bud rot, or heart rot. Base of herbaceous stalk,
stem rot.
peach brown rot, celery heart rot, iris soft
rot
Right: The stem of this monkshood became infected by a
bacteria that caused a spot on the leaves. The infection spread
down the stem into the root/tuber. The same bacteria is at work in
a leaf spot, stem rot and root rot.
Rust. (Fungus.)
Fruiting stage of the fungus is rusty in color and appearance,
often on the underside of blemishes.
pine blister rust, wheat rust, cedar-apple rust,
cedar-hawthorn rust
More, in What's Coming
Up 119
More, with other problems illustrated, in a Powerpoint
presentation of common plant diseases, from North Dakota
Extension
Scab. (Fungus.)
Dead spot on leaf or fruit may become covered with dry, scabby
tissue.
apple scab, scabby potates
Scale.
(Sucking insects.) Young stages are mobile crawlers, often
concentrated on leaves, while adults most often immobile, fastened
in place like adhesive dots, may be soft bodied or armored, often
on twigs and stems.
pine tortoise shell scale, oyster shell scale, cottony maple
scale, magnolia scale
More, in What's
Coming Up 50
More, in Other scales same tales
and Holly
Trouble
Scorch.
(Fungus.) Margins or other portion of leaf scorched as if
sunburned. Often, these are opportunistic infecti0ns following some
environmental damage to the plant.
For more, see
What's Coming Up 137.
Shothole.
(Various.) Centers of blemishes created by insect, disease or
environmental damage eventually dry and fall out, so leaf appears
as if peppered by shotgun.
Skeletonizing, rasping (Insects
that feed by scraping: chafer, beetle, whitefly). Leaf surface not
chewed completely through. Membrane on one side often left.
oak leaf skeletonizer, elm leaf beetle
More, with pictures in What's
Coming Up 140
Smut (Fungus.) An
infection that causes the plant part to look smudged, gray. Most
often on members of the grass family
corn smut, violet smut
Sooty mold.
(Fungus.) Fungus causes darkening but underlying cause is sucking
insect infestation, which creates accumulation of liquid insect
excrement called honeydew. Darkens foliage.
Photo of sooty mold on leaf, in Other
scales same tales
Spot. (Fungus.)
Blemishes, often with modifier, such as black-, purple-, ink-,
greasy-, leaf-, flower-spot. Dead spots of specific size, shape,
often in particular area on leaf or on plant. Margins of a spot may
be more or less distinctly colored, and with more or less sharp
division between living/dead tissue. Margin's existence or color,
or presence of fruiting bodies are often telltales to spot type.
Multiple spots may coalesce to patches that have lost the
diagnostic telltales so observation in early stages
important.
black spot of rose, septoria leaf spot, viburnum leaf
spot
For more, see
What's Coming Up 137.
Above: A bacterial leaf spot has infected these monkshood
(Aconitum) leaves and is consuming each leaf. The infected
spots show as dark spots on the upper leaf surface, but appear
pinched and blistered on the leaf underside.
See also Stem Rot, further up in this
list, for an additional consequence of this infection.
Stings.
(Insects.) Damage made by piercing/sucking insect such as
aphid, bug, or leafhopper. Stings may be pale or brown, often
sunken pock marks. Heavy damage can coalesce, obscuring initial,
telltale marks.
Photo of plant bug stings/pock marks, in Mysteries
solved
Stippling. (Sucking insect
damage) Leaf surface has many tiny damaged areas that make it look
dry and pale. Where there are many tiny damaged spots they may
coalesce so a whole section of the leaf turns brown or colorless
and crumbly. Caused by mites, lace bugs, and other insects that
suck rather than chew.
Right: This leaf from Harry Lauder's walking stick
(Coryllus avellana 'Contorta') has suffered a summer of
sucking damage by alder lace bugs. From a few feet it
may appear to be coated with powdery mildew but this closer look
shows the leaf tissue itself has gone white.
Stunt. (Virus)
Growth is small and feeble.
Dahlia stunt
Yellows.
(Virus, with sucking insect as vector.) Foliage pales, leaves,
stem, flowers may be distorted.
aster yellows
Webworm,
tentworm. (Insects.) Web-making caterpillars, many
colonizers.
tent caterpillar, fall webworm, uglynest caterpillar
Weevils.
(Insects, beetle relatives.) Feeding may be distinctive leaf
notching or stings to leaf, bud or seedpod.
black vine weevil, strawberry root weevil, hollyhock
weevil
Right: The white spot in the coral bells root ball is a
black vine weevil grub. It's grazed on the roots all fall and early
spring so the plant is dry and popping up from the ground,
anchorless.
Below: Black vine weevil
adult.
Below, right: Black vine weevil adult and coral bell leaf
it has eaten in its characteristic pattern, notching the edge. (One
evening's damage.)
More about black vine weevils in What's
Coming Up #67.
Photo of hollyhock weevils, in Mysteries solved
Wilt. (Fungus, environmental problems.) Foliage and
soft twigs droop, shrivel, usually without any preliminary
darkening. The symptom may come and go as plant need overwhelms
root- or vascular system compromised by damage or fungus.
verticillium wilt, fusarium wilt
For example of environmental cause see photos at rot/root rot.
Symptoms seen on wood (twig, branch, trunk)
Blight. (Fungus. Bacteria.) Sudden
cessation of growth, darkening of foliage while still moist, and
death of new branch(es), usually with foliage intact.
fireblight of rose family (apples, pyracantha, mt. ash)
Eastern
filbert blight of Harry Lauder's walking stick
Borer, shoot
borer. (Insects.) Larvae of beetle or moth species that
tunnel into cambium and feed there where they may girdle stems, or
bore down into growing shoots, usually killing the shoot.
lilac borer, bronze birch borer, dogwood borer, flat-headed
apple borer, peach borer, pine tip borer
More, in What's
Coming Up 140
Canker
(Fungus, bacteria) Dead spot in woody tissue. Cambium below bark
destroyed. Surface more or less sunken, bark eventually sluffs off
and dead spot may enlarge and split as disease spreads in cambium
from original point of infection. May enlarge over years to girdle
the stem. Infection usually begins in a spot on a young shoot that
was not yet woody, caused by the same fungi or bacteria that also
cause flower- or leaf spot on that plant's foliage or flowers. A
canker's longer life, existing as it does on a part of the plant
which will become woody, distinguishes it from "spot."
stem canker, nectria canker of honeylocust, phomopsis canker
of juniper twigs, distinctive rows of canker in Eastern
filbert blight
Above: All of the older lavender twigs here are struggling to grow
because their stems have canker wounds.
Right: Arrow points to the scrap of bark and live cambium that
remains on one stem. It will soon be girdled completely as the
fungus increases its spread.
Conch, also
conk. (Fungus.) Hard-bodied mushroom, may resemble
seashell or shelf, can be very large. Fruiting body of fungus
inhabiting wood or roots, evidence of interior rot.
Decline
(Various environmental and cumulative problems.) General reduction
in vigor, foliage color, leaf size, growth rate. Often accompanied
by secondary problems which take the opportunity to infect or
infest a weakened plant.
More, in What's
Coming Up 50
Dieback
(Various.) Woody plant loses branches, where the loss is not caused
by direct damage to the limb by disease, insect or physical trauma.
Plant's overall mass diminshes. Usually associated with overall
loss of plant vigor, environmental change, root loss, etc.
tip dieback, crown dieback
More, in
What's
Coming Up 139
More, in What's
Coming Up 50
Frost
crack. (Environmental.) Crack in otherwise healthy layers
of wood, usually caused when wood overlays internal damage and
there are rapid changes in temperature that cause cells to swell
with water, and then suddenly freeze.
Gall.
(Bacteria. Insect. Mite.) Abnormal growth causes malformation of
cambium tissue and bark.
willow- and maple gall, eastern spruce twig gall, crown gall
(of Euonymus, Forsythia, etc.)
Knot. (Fungus.
Bacteria. Nematode.) Infection of cambium causes thickening and
discoloration of branch. Infestation of roots by microscopic
ringworm relatives (nematodes)
black knot of peach, cherry, root knot
Rot.
(Fungus.) Infected tissue softens, darkens and then shrivels.
Dormant or basal buds of a herbaceous plant may succumb to crown
rot. Might involve base of woody cane with infection and symptoms
occurring unseen under bark. May occur in center of old wood. May
affect root tips or damaged roots.
crown rot, collar rot, butt rot, heart rot, root rot
Right: The wilted stems on this Silver King artemisia are
the result of root rot. Below, right: Janet holds three stems from
that plant, one without wilt, one very wilted and one intermediate.
Notice the uppermost stem, which is the most wilted. It has lost
all its roots to rot. However, in this case the primary cause of
trouble is not the rot fungus but a drainage problem that
predisposed the roots to infection.
Scale.
(Insect.) Sucking insect of young wood, may congregate as adults on
trunk.
beech bark scale, pine bark scale
Below: Lecanium scale on (left) honey locust and (right)
purpleleaf sand cherry. Notice the fuzz on the sand cherry. It's
cottonwood seed fluff and other windblown debris trapped by the
sticky honeydew excreted by the scales.
Shakes.
(Various) Bark separates from wood beneath in unhealthy fashion.
Usually associated with decline, infection or destruction of
cambium below that bark.
Sooty
mold. (Fungus.) Fungus causes darkening but underlying
cause is sucking insect infestation, which creates accumulation of
liquid insect excrement called honeydew. Darkens wood surface,
foliage.
Photo of sooty mold on leaf, in Other
scales same tales
Twig pruner,
twig girdler. (Insect.) Destroys cambium or wood of twig
in fashion which causes twig death, twig may fall.
oak twig pruner, oak twig girdler
Witch's
broom. (Fungus. Bacteria. Insect. Environmental effect.)
Distorted, much-branched growth sometimes initiated by death of tip
buds, proliferation of replacement buds behind the first infection
and subsequent death of the replacement buds or twigs.
witch's broom of sycamore
Symptoms seen in the water-conducting portions (vascular
system)
Blight. (Fungus. Bacteria.
Virus.) Proliferation of pathogen within vascular system causes
sudden cessation of growth, wilting, death, usually without
rot.
elm blight, chestnut blight
Sapstreak. (Fungus) Water conducting
vessels become filled with fungal growth. A cut through wood (as in
a shaving) shows distinctive off-color streaks.
Wetwood.
(Bacteria. Fungus.) Excessive moisture builds up in wood, often
escapes through bark.
elm wetwood
Wilt. (Fungus. Bacteria.) Healthy
foliage and stems wilt. (Look for damage to roots, or infection and
clogging of water conducting system.)
Symptoms seen in roots
Borers in the
roots:
Iris borers are many
gardeners' first introduction to root dwelling insects.
Girdling
root. (Environmental, cultural and/or genetic.) Presence
of growing root across or around other roots or trunk causes
obstruction to growth.
some species seem prone to girdling root: Norway maple, silver
maple
Numerous articles on this site illustrate girdling roots,
symptoms, and treatment. Use "girdling root" as your search
terms.
Knot-
or club-root, malformed roots. (Fungus. Bacteria.
Mycoplasma.) Infection/infestation causes weakening, thickening and
distortion of roots, which may look like severely arthritic
joints.
clubroot, root knot
Mushroom.
(Fungus.) Its presence is evidence of advanced wood rot. Each type
of mushroom is distinctive in shape and color according to the
fungus species, as flowers are distinctive in plant species. Causal
fungus can be identified by its mushroom; e.g. dead man's fingers
is a fungus that infects injured live roots.
Nematodes,
eelworms. (Ringworm relatives). Near-microscopic organisms
which infest roots or other plant parts, causing general
debilitation and sometimes stunts, discolors or deforms
roots.
Phlox root-knot nematodes
Root rot.
(Fungus) Roots die, usually beginning at tips. Presence of brown-,
red-, or black stain may be telltale of particular fungus.
phytophthora root rot of rhodo/azalea
Weevil.
(Insect.) Larvae of a beetle relative; some eat roots and soft root
new tissue or cambium near ground level.
black vine weevil, pine collar weevil
See photos at weevil in Leaf
section.
Sponsor
needed!
We have many more links and photos that could be added here, but
we also have many more articles to post, and limited time. So we're
leaving this page for now. If you would like to see this topic
given more detail, and/or if what we have already placed here
helped you, please consider sponsoring this page!
Your Sponsorship of specific items on our website helps us set
priorities and gives us the resources to do more.