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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
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.
|blister, ulcer, anthracnose
cast, cast-off parts
leaf tied to leaf
leaf stuck to leaf
shot hole, shothole
malformation in roots
Descriptive term (Causal agent/s) Definition.
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.
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...
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 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
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
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.
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
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.
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.
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.
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.
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.
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
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
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
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.
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