|
|
|
Disease or
Pathogen |
| I. |
Leaves Affected |
| A. |
Leaves with definite
brown areas |
| | 1. | Localized brown or
red-brown spots | | Leaf spots |
| | 2. | Browning of leaves at
edges and near tips | | Winter injury |
| | 3. | Brown areas turning
white with small black dots | | Pestalotia leaf
spot |
| B. |
Leaves
off-color |
| | 1. | Leaves off-color with
white, powdery coating | | Powdery mildew |
| | 2. | New growth chlorotic
or yellow | | Nutrient deficiencies
Leaf and flower
gall
(Exobasidium) |
| | 3. | Yellowish mottling on
upper side of leaves; rolling of margins; flat, oval, transparent insects
evident on bottom side of
leaves | | Whitefly |
| | 4. | Whitish specks on
upper surface of leaves; sticky spots on lower surface of
leaves | | Lace bugs |
| | 5. | Leaves off-color; loss
of vigor; no insects evident on foliage | | Root problems |
| | 6. | Leaves off-color;
small "insects" evident on
foliage | | Mites |
| C. | Leaves eaten or chewed
at margins in half-circle pattern | |
Black vine
weevil |
| D. |
Leaves
distorted |
| | 1. | Leaves thickened or
fleshy, turn pale green or whitish | | Leaf and flower
gall
(Exobasidium) |
| | 2. | Leaves roll and droop;
no insects evident | | Water stress
Canker
Root problems |
| II. |
Branches and Twigs
Affected |
| A. |
Terminal buds and
leaves turn brown |
| | 1. | Stem shrivels and
definite canker forms; leaves roll and
droop | | Phytophthora dieback
Phytophthora
syringae blight |
| | 2. | Cankered area is rough
from protruding bodies of fungus; edges of leaves may be affected first, and
then entire leaves turn brown | | Botyrosphaeria
dieback
Phomopsis dieback |
| B. | Ends of branches die;
borer in stem tissue; yellow-white larvae about 1.3 cm long; small, black
adults with three yellow transverse stripes on
abdomen |
|
Rhododendron borer |
| C. | Buds and twigs
affected; primarily on azaleas, buds and twigs
killed |
|
Bud and twig
blight
(Briosia) |
| III. |
Flowers affected |
| A. | Flowers thickened or fleshy with gall-like appearance | | Leaf and flower
gall
(Exobasidium) |
| B. | Flowers water-soaked, collapsed |
|
Ovulinia petal blight |
| IV. |
Entire plants affected |
| A. | Plants become thin,
wilt, and eventually die; major portion of root may be
dead |
|
Crown rot or
wilt
(Phytophthora)
Crown
gall
(Agrobacterium)
Cylindrocladium blight |
| B. | Plants wilt and die
suddenly; bark chewed from roots and basal
stems |
|
Black vine weevil grubs |
| c. | Plants with poor
color; definite, easily removed growths on stems and
petioles | | Scale insects |
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