| AFFECTING LEAVES AND STEM: |
|
CONDITION
|
CAUSE
|
 |
Large
gray-brown spots with concentric rings; spots merge and cover entire
leaf |
Early blight (Alternaria
spp.)
|
|
Water-soaked
brown lesions on lower leaves first |
Late blight (Phytophthora
infestans)
|
|
Light-green
to yellow leaves with lower leaflets rolled upwards |
Leaf roll virus
|
|
Yellow,
mottled leaves accompanied by crinkling |
Mosaic virus
|
|
Yellow
leaves, stem black below soil line |
Blackleg (Erwinia
caratova)
|
|
Yellow,
puckered, curled leaves |
Potato aphids
|
|
Yellow,
stippled, stunted leaves |
Leafhoppers
|
|
Holes in
leaves are large; whole leaflets consumed |
Colorado potato
beetle (Leptinotarsa decemlineata)
|
|
Small
holes in leaves |
Flea beetles (Phyllotreta
spp.)
|
|
| AFFECTING WHOLE PLANT: |
|
CONDITION
|
CAUSE
|
|
Sprouts
die before emergence |
Rhizoctonia (Rhizoctonia
spp.)
|
|
Yellow,
stunted plants |
Root-knot nematodes
(Meloidogyne spp.)
|
|
Yellow
leaves, gradual wilting usually at flowering |
Verticillium wilt (Verticillium
spp.)
|
|
Plants
wilt suddenly |
Wireworms
|
|
| AFFECTING TUBERS: |
|
CONDITION
|
CAUSE
|
|
Brown to
black raised spots on potato |
Rhizoctonia (Rhizoctonia
spp.)
|
|
Rough,
raised lesions on potato |
Potato scab
|
|
Enlarging
brown to black blotches on potato; internal tissue is brown and dry
just below the surface |
Early blight (Alternaria
spp.)
|
|
Tiny
surface trails (or tunnels) just beneath potato skin |
Tuber flea beetle larvae (Phyllotreta
spp.)
|
|
Dark,
internal lesions on potatoes |
Phosphorus or
potassium deficiency
|
|
Dwarfed
potatoes |
Calcium deficiency
|
|
Green
coloration of tubers |
Exposure to light. Keep developing tubers covered with soil.
|
