Key To Plant Abnormalities

Plant AbnormalitiesThe following key, while not all-inclusive, can help to determine the probable cause or causes of many plant abnormalities. Once the general type of problem is identified, its exact nature or the specific causative organism can be determined from local literature or a plant disease laboratory. Your nearest garden center can also be very helpful. The following key should be used only as a guide to identification.

To use this key, first select statement 1a, 1b, 1c, or 1d, depending on which is most true of the problem being diagnosed.? Then proceed to the numbered pairs of statements as indicated.

1a. Symptoms mostly on or in foliage – see #2

1b. Symptoms mostly on or in young twigs – see #13

1c. Symptoms mostly on or in main branches or trunk – see #17

1d. Symptoms mostly on or in roots – see #20

2a. Leaves of normal size but off-color or with spots, holes, or off-color margins – see #5

2b. Leaves smaller than normal or wilted; not discolored or spotted – see #3

3a. Leaves wilted or drooping – see #4

3b. Leaves not wilted or drooping, but smaller than normal: cold injury; drought; viruses; mildews

4a. Stems not showing stain (cut stem with clean knife, as stain can result from residue on knife blade): soil too wet or too dry

4b. Stems with distinct stain in sapwood (cut diagonally with clean, sharp knife): wilt disease (Dutch Elm disease, vericillium wilt, etc.)

5a. Leaves with white or grey cast: powdery mildew fungus

5b. Leaves with spots or blotches – see #6

6a. Scattered spots or blotches on one or both leaf surfaces or circular holes in leaves – see #11

6b. Leaves not spotted but with yellow or brown margins, sometimes extending between veins – see #7

7a. Margin of leaves brown – see #8

7b. Margin of leaves yellowish, usually between veins: check soil for iron, zinc, or manganese deficiency or soil sterilants

8a. Weather conditions have been hot and dry: drought scorch or high salts

8b. Weather conditions have not been hot and dry – see #9

9a. Soils in area very acidic or sandy: test soil for potassium deficiency

9b. Soils not particularly acidic or sandy – see #10

10a. Weather conditions have been moist, humid: anthracnose and similar leafspot diseases

10b. Weather conditions have not been moist, humid: check for soil sterilants; air pollution also possible

11a. Leaves with relatively uniform holes; margins of holes brown or reddish (caution: some insects can cause similar damage): shothole fungus or xanthomonas caterium

11b. Leaves without holes, but with spots or blotches – see #12

12a. Leaves irregularly blotched with no particular pattern; sometimes several colors: spray damage; if blotches are red or white and ‘velvety’, probably eriophid mites

12b. Leaves with relatively uniform spots (brown bordered by yellow, red, or light green); usually most evident on upper surface: leafspot fungi

13a. Young twigs with raised pimplelike structures – see #16

13b. Young twigs dying back – see #14

14a. Dieback of twigs with buds that failed to open in spring: winter injury

14b. Young twigs dying back after buds open in spring – see #15

15a. New growth black or brown, curled backward: tipblight fungus; fireblight bacterium; frost injury

15b. New growth still greenish but shriveled; or if brown, still attached: drought injury; transplant shock; spray injury

16a. Raised structures orange or black; orange ooze or black powder may be present: fungus cankers such as Cytospora and Nectria

16b. Raised structures tan or usually lighter than surrounding bark; oval, round or lens shaped; regular in shape: normal lenticels in bark

17a. Main branches or trunk with localized sunken areas – see #19

17b. Main branches or trunk with raised or swollen structures – see #18

18a. Structures raised are like orange, reddish, or black pimples: fungus cankers such as Cytospora, Nectria, and Thronectria

18b. Structures are swollen stem or trunk parts; fissures in bark may have orange powder: stem rusts

19a. Sunken area discolored, cracked, and usually in a streak on the southwest side of trunk: sunscald

19b. Sunken area irregular, on any exposure, and often near base of trees:? mechanical impact bruises, or cankers

20a. Symptoms at base of tree trunks in flare of roots – see #21

20b. Symptoms in smaller roots – see #22

21a. Bark loose; wood beneath soft and punky when probed: root rot (often follows overwatering in compacted soils)

21b. Tumorlike growth from bark: crown gall bacterium

22a. Roots with small pealike swellings: root knot nematode or normal nodules of nitrifying bacteria (legumes)

22b. Fine roots (feeder roots) slimy, dark-colored; sometimes with sewerlike odor: many causes; oxygen starvation most common in landscape plantings


See also Identifying Insect Pests

See also Key For Identifying Pests Based On Feeding Damage

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Key For Identifying Pests Based On Feeding Damage

Feeding DamageThe following key is helpful in arriving at the general pest type based upon feeding damage. Start by select 1a, 1b, or 1c, as appropriate. Then proceed to numbered pairs as instructed.

1a. Leaves with damage – see #2

1b. Twigs or bark with damage – see #10

1c. Roots with damage – see #15

2a. Leaves appearing chewed or skeletonized (veins remaining) with tissue between veins on lower side missing – see #3

2b. Leaves not chewed; either off-colored and appearing “stippled” or silvery, or having galls or swollen tissues – see #5

3a. Leaves chewed mostly along margins – see #4

3b. Leaves chewed mostly underneath, appearing skeletonized: leaf beetles, pear ‘slug'(a wasp larva)

4a. Chewed leaf margins semicircular and smooth; not jagged: cutter bee (common on roses), blackvine weevil (common on euonymous)

4b. Chewed leaf margins jagged and irregular; not smooth and semicircular: grasshoppers; caterpillars; Japanese beetle

5a. Leaves with swellings or galls – see #9

5b. Leaves without swelling or galls, but stippled and silvery – see #6

6a. Leaves silvery in irregular pattern when view from above: thrips (common in privet)

6b. Leaves stippled, sometimes appearing grainy or mealy beneath – see #7

7a. Fine webbing present; leaves mealy beneath: spider mites

7b. No webbing present; leaves not mealy beneath; stippled yellow or brown – see #8

8a. Stippled leaves also curled or distorted; use caution here-some herbicides cause similar symptoms: eriopyid mites; leafhoppers; plant bugs; some aphids

8b. Stippled leaves not curled or distorted: many aphid species

9a. Swelling or galls nipplelike on leaf surface: psyllids; eriopyid mites (gall mites)

9b. Swellings variously shaped, but not nipplelike; sometimes on leaf petiole: gall wasps; spindle midges; gall midges

10a. Damage on twigs or buds only, not on main branches or tree trunks – see #12

10b. Damage on main branches or trunks – see #11

11a. Bark partially or completely chewed down to wood:? rodents (squirrels, mice), grasshoppers (in heavy infestations where food supply is short)

11b. Bark with circular or D-shaped holes; may be oozing sap, pitch or frass (‘sawdust’) may be present: borers (larvae of beetles, wasps, and flies); bark engravers (larvae of beetles)

12a. Twigs or buds forming galls or swollen areas – see #13

12b. Twigs or buds without galls; twigs with or central pith with channels – see #14

13a. Galls in buds: gall-forming eriophyid mites

13b. Galls in twigs: gall midges

14a. Twigs with holes, pith not channeled: borers; bark engravers; weevils

14b. Twigs with channeled pith: shoot-tip borers (larvae of moths); pith borers; cane borers

15a. Young roots with gall-like swellings (caution: some plants such as those n the pea family have nitrogen-fixing nodules on their roots, which look similar; these are beneficial): nematodes

15b. Roots chewed or with holes – see #16

16a. Roots chewed: rodents, insect grubs (beetle and moth larvae)

16b. Roots with holes: root borers; weevils (often these insects are secondary to roots undergoing decay from fungi)


See also Identifying Insect Pests

See also Key To Plant Abnormalities

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