The 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