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Latest revision as of 21:07, 7 November 2016
KEY TO ALFALFA AND HAY PESTS AND NUTRITIONAL DISORDERS
Contents
- 1 Seed
- 2 Seedling
- 3 Root
- 3.1 BLACK
- 3.2 BROWN
- 3.2.1 Aphanomyces root rot
- 3.2.2 Corky root rot
- 3.2.3 Crown and root rot complexes
- 3.2.4 Cylindrocarpon root rot
- 3.2.5 Dwarf
- 3.2.6 Fusarium wilt
- 3.2.7 Nitrogen deficiency; ineffective nodulation
- 3.2.8 Phosphorus deficiency
- 3.2.9 Phymatotrichum root rot
- 3.2.10 Root-knot nematode
- 3.2.11 Verticillium wilt
- 3.3 DARK GREEN
- 3.4 ORANGE
- 3.5 PURPLE
- 3.6 RED
- 3.7 TAN
- 3.8 VIOLET
- 3.9 YELLOW
- 3.10 YELLOW/BLACK
- 3.11 No Distinct Discoloration
- 4 Crown
- 5 Stem
- 6 Leaf
- 6.1 BLUE/GREEN
- 6.2 BROWN
- 6.2.1 Common leaf spot
- 6.2.2 Hydrogen fluoride
- 6.2.3 Leptosphaerulina leaf spot
- 6.2.4 Manganese deficiency
- 6.2.5 Manganese toxicity
- 6.2.6 Metribuzin; hexazinone; terbacil
- 6.2.7 Sclerotium blight
- 6.2.8 Spring black stem and leaf spot
- 6.2.9 Stemphylium leaf spot
- 6.2.10 Sulfur dioxide
- 6.2.11 Zinc deficiency
- 6.3 GRAY
- 6.4 GREEN
- 6.5 GREEN (PALE)
- 6.6 PURPLE
- 6.7 RED
- 6.8 SILVER
- 6.9 WHITE
- 6.10 WHITE/BLACK
- 6.11 WHITE/PURPLE
- 6.12 YELLOW
- 6.12.1 Alfalfa mosaic
- 6.12.2 Aluminum toxicity
- 6.12.3 Aphanomyces root rot
- 6.12.4 Atrazine
- 6.12.5 Bacterial leaf spot
- 6.12.6 Bacterial wilt; other bacterial diseases
- 6.12.7 Bromoxynil
- 6.12.8 Common leaf spot
- 6.12.9 Fusarium wilt
- 6.12.10 Iron deficiency
- 6.12.11 Lucerne transient streak
- 6.12.12 Magnesium deficiency
- 6.12.13 Manganese deficiency
- 6.12.14 Manganese toxicity
- 6.12.15 Metribuzin; hexazinone; terbacil
- 6.12.16 Nitrogen deficiency; ineffective nodulation
- 6.12.17 Red clover vein mosaic
- 6.12.18 Spring black stem and leaf spot
- 6.12.19 Sulfur dioxide
- 6.12.20 Verticillium wilt
- 6.12.21 Witches'-broom
- 6.13 YELLOW/ORANGE
- 6.14 No Distinct Discoloration
- 7 Flower
Seed
Seed disorders are limited to disorders caused while the seed is in the ground not to potential disorders inherent in the seed.
Seedling
DARK GREEN
Aluminum toxicity
Plants are stunted and dark green; chlorotic spots may occur on lower leaves; root growth restricted and stubby
GRAY
Aphanomyces root rot
Infected seedlings become chlorotic, roots are gray and water-soaked, but plants remain upright; on older plants nodules decay and lateral roots are destroyed, leaving restricted brown lesions on tap root surface; foliage becomes chlorotic
WHITE
Crown wart
Galls (white when young and gray to brown with age) form at or slightly below the soil surface on young crown buds; when exposed to sunlight, galls may become green; globose resting spores produced in internal tissue
YELLOW
Atrazine
Yellowing and necrosis of seedlings beginning at margins of oldest leaves
Bacterial leaf spot
Favored by high temperatures; seedlings may be severely stunted; leaf lesions are irregular, with yellowish to tan, papery, translucent centers and narrow, water-soaked borders that are most pronounced on lower leaf surface
Bacterial wilt; other bacterial diseases
Plants are stunted with small cupped leaves, yellow margins, many crown shoots; diseased plants scattered throughout stand; xylem tissue in taproot is tan to brown ; discoloration sometimes extends laterally to inside surface of dark
Bromoxynil
Burning of seedling leaves at margins first; small seedlings may die
Downy mildew
Favored by cool, moist conditions; most severe on seedling stands; yellow blotches on upper side of leaves; white to purplish downy growth on the lower surface; systemically infected shoots shortened and chlorotic; terminal leaves twisted
EPTC
Seedlings are stunted due to poor root development; leaves may be malformed
Root
BLACK
Brown root rot
Root rot associated with very cold winters and characterized by brown sunken lesions; brown to black pycnidia occur on surface of lesions or are embedded in the necrotic tissue
Mycoleptodiscus crown and root rot
Black discoloration of lateral and taproots; black sclerotia form in decayed tissue
Root-lesion nematode
Dark brown or black lesions on roots that may fuse to cause overall browning and reduced root growth
BROWN
Aphanomyces root rot
Infected seedlings become chlorotic, roots are gray and water-soaked, but plants remain upright; on older plants nodules decay and lateral roots are destroyed, leaving restricted brown lesions on tap root surface; foliage becomes chlorotic
Corky root rot
Dry, sunken cankers form on tap root and spread until entire root is girdled; the rotted root retains its shape but, due to corky consistency, is lighter in weight than healthy roots
Crown and root rot complexes
Dark brown necrotic tissue in crowns and roots; affected area may range from irregular rotted areas in cortex and xylem to complete disintegration of the root and crown; often difficult to determine causal organism(s)
Cylindrocarpon root rot
Light brown general root or crown rot extending either a short distance below crown or rotting entire root; stromata of causal organism may develop in cracks in the affected cortex of the taproot
Dwarf
Plants are stunted with small, dark green leaves resembling those caused by drought stress; xylem tissue in taproot is dark brown
Fusarium wilt
Favored by warm weather; plants usually have lower leaf yellowing and often a one-sided wilt; longitudinal streaks in xylem tissue of taproots are brick red to dark brown; mycelium may be seen in xylem vessel elements
Nitrogen deficiency; ineffective nodulation
Yellow older leaves; roots poorly nodulated
Phosphorus deficiency
Top growth is stunted, stiff, and erect, with small bluish green leaves; roots light brown with restricted growth
Phymatotrichum root rot
Necrotic lesions on taproots are brown, sunken, and irregular in shape; roots may be entirely rotted; rhizomorphs with cruciate hyphae on surface are highly diagnostic
Root-knot nematode
Stunted plants with excessively branched roots having small galls
Verticillium wilt
Symptoms are more evident at moderate temperatures; leaves become yellow, often in a V-shaped or one-sided pattern, plants wilt, and xylem tissue of taproot becomes brown; stem remains green for a while after all leaves on a shoot are killed
DARK GREEN
Aluminum toxicity
Plants are stunted and dark green; chlorotic spots may occur on lower leaves; root growth restricted and stubby
ORANGE
Stagonospora root and crown rot
Cortex and xylem tissue have distinctive orange to brick red flecks; bark of infected region may be rough or fissured longitudinally
PURPLE
Cylindrocladium root and crown rot
Shoots are killed following dark brown decay at crown; roots become purplish black; orange-red perithecia may form at base of plant
RED
Acrocalymma root and crown rot
Cortical and woody tissues of crown and upper taproot are flecked with reddish colored tissue; bark of affected plants is often fissured longitudinally; similar to Stagonospora root rot but with different morphology and no leaf spots
TAN
Bacterial wilt; other bacterial diseases
Plants are stunted with small cupped leaves, yellow margins, many crown shoots; diseased plants scattered throughout stand; xylem tissue in taproot is tan to brown ; discoloration sometimes extends laterally to inside surface of dark
VIOLET
Violet root rot
Plants in low spots in field die; patches are circular to irregular and enlarge as disease progresses; violet mycelium eventually forms a violet felt on taproots; bark loosens and slips from the central cylinder
YELLOW
Phytophthora root rot
Occurs in saturated soils; affected area on taproot is brown to yellow, eventually turns black, and has diffuse and irregular margins; rotted tissue is usually firm; taproot may rot off completely; oospores form in rotted tissue; new roots may emerge
YELLOW/BLACK
Rhizoctonia root canker
Brown to yellow elliptical cankers with entire margins form on the taproot at point of emergence of the lateral roots; cankers become black and inactive during winter; disease is important only in irrigated high-temperature desert areas
No Distinct Discoloration
Calcium deficiency
Root growth is severely impaired, and rotting may occur; petioles collapse and undersides of leaflets become reddish purple
EPTC
Seedlings are stunted due to poor root development; leaves may be malformed
Crown
BLACK
Anthracnose
Dark, bluish black necrotic area, sometimes V-shaped, extending into the crown from diseased stems
Mycoleptodiscus crown and root rot
Black discoloration of lateral and taproots; black sclerotia form in decayed tissue
BROWN
Crown and root rot complexes
Dark brown necrotic tissue in crowns and roots; affected area may range from irregular rotted areas in cortex and xylem to complete disintegration of the root and crown; often difficult to determine causal organism(s)
Cylindrocarpon root rot
Light brown general root or crown rot extending either a short distance below crown or rotting entire root; stromata of causal organism may develop in cracks in the affected cortex of the taproot
Winter crown rot
Patches of dead plants with dark brown rotted tissue on crown or on crown buds; white mycelium of the causal fungus may be seen on soil surface
GRAY/GREEN
Crown wart
Galls (white when young and gray to brown with age) form at or slightly below the soil surface on young crown buds; when exposed to sunlight, galls may become green; globose resting spores produced in internal tissue
GREEN
Witches'-broom
Short, spindly shoots are produced profusely on crowns; leaves are puckered, small, and marginally to generally chlorotic
ORANGE
Stagonospora root and crown rot
Cortex and xylem tissue have distinctive orange to brick red flecks; bark of infected region may be rough or fissured longitudinally
RED
Acrocalymma root and crown rot
Cortical and woody tissues of crown and upper taproot are flecked with reddish colored tissue; bark of affected plants is often fissured longitudinally; similar to Stagonospora root rot but with different morphology and no leaf spots
Cylindrocladium root and crown rot
Shoots are killed following dark brown decay at crown; roots become purplish black; orange-red perithecia may form at base of plant
WHITE
Winter crown rot
Patches of dead plants with dark brown rotted tissue on crown or on crown buds; white mycelium of the causal fungus may be seen on soil surface
WHITE/BLACK
Sclerotinia crown and stem rot
Favored by cool, humid conditions; leaves and stems become flaccid and collapse; white fluffy mycelium grown over dead parts and produces hard black sclerotia on and in infected tissue
YELLOW
Bacterial wilt; other bacterial diseases
Plants are stunted with small cupped leaves, yellow margins, many crown shoots; diseased plants scattered throughout stand; xylem tissue in taproot is tan to brown ; discoloration sometimes extends laterally to inside surface of dark
No Distinct Discoloration
Crown gall
Galls on crown branches are convoluted and irregular in shape; absence of globose resting spores in galled tissue differentiates the disease from crown ward; disease is rare
Stem
BLACK
Bacterial stem blight
Usually restricted to frost-damaged spring growth; rare in occurrence; stem lesions begin at point of leaf attachment and extend downward; water-soaked lesions become amber-colored and shiny, then blacken with age; bacteria in ooze from water-soaked areas
Spring black stem and leaf spot
Favored by low temperatures; small, irregular, black to brown spots enlarge and coalesce on leaves; infected leaves turn yellow, wither, and fall; stems blacken; pycnidia with conidia on overwintered stems
BROWN
Anthracnose
Favored by warm, humid conditions; stem lesions are sunken, whitish to tan, oval to diamond-shaped with brown borders mostly near base of plant and may girdle stems; black specks (acervuli) develop in lesions
Rhizoctonia stem blight
Favored by hot, humid conditions; bleached, elongated lesions with brown bands that girdle stems at base of plant; coarse brown mycelium usually on lesion
Sclerotium blight
Favored by hot, moist conditions; plants killed are devoid of green color; small, brown, spherical sclerotia resembling mustard seeds form on decayed tissue
GREEN
Sulfur deficiency
Plants are pale green, including veins on younger leaves; plants are stunted
Verticillium wilt
Symptoms are more evident at moderate temperatures; leaves become yellow, often in a V-shaped or one-sided pattern, plants wilt, and xylem tissue of taproot becomes brown; stem remains green for a while after all leaves on a shoot are killed
RED
Rust
Most prevalent late in the growing season or earlier in fields harvested for seed or if forage harvest is delayed; circular reddish brown pustules protruding from leaves and stems; the rusty spots (spores) rub off easily
Summer black stem and leaf spot
Favored by hot, humid conditions; leaf lesions are roughly circular, reddish brown, and up to 6 mm in diameter; conidia give lesions a silver appearance; brown stem lesions enlarge and coalesce
WHITE
Anthracnose
Favored by warm, humid conditions; stem lesions are sunken, whitish to tan, oval to diamond-shaped with brown borders mostly near base of plant and may girdle stems; black specks (acervuli) develop in lesions
Copper deficiency
Young leaves wilt and may bend back against lower side of petiole and develop necrotic gray to white spots on margins or on the basal half of leaflets; growing point dies
WHITE/BLACK
Sclerotinia crown and stem rot
Favored by cool, humid conditions; leaves and stems become flaccid and collapse; white fluffy mycelium grown over dead parts and produces hard black sclerotia on and in infected tissue
YELLOW
Bacterial leaf spot
Stem lesions are greasy and water-soaked, become grown, and usually coalesce; bacteria in ooze from water-soaked areas
Boron deficiency
Plants are dwarfed due to shortening of internodes; margins of youngest fully developed leaves become yellow, then purplish
No Distinct Discoloration
Downy mildew
Favored by cool, moist conditions; most severe on seedling stands; yellow blotches on upper side of leaves; white to purplish downy growth on the lower surface; systemically infected shoots shortened and chlorotic; terminal leaves twisted
Stem nematode
In cool, humid weather, leaves curled and distorted or white; stem internodes are greatly shortened, swollen, and engorged with nematodes
BLACK
Stagonospora leaf spot
Favored by cool to moderate temperatures of early spring and late fall; bleached, roughly circular leaf spots with dark specks (pycnidia)
Leaf
BLUE/GREEN
Phosphorus deficiency
Top growth is stunted, stiff, and erect, with small bluish green leaves; roots light brown with restricted growth
BROWN
Common leaf spot
Lesions are brown, 1-3 mm in diameter, and rarely coalesce; a raised disc (apothecium) to 1 mm in diameter develops in center of mature lesions on upper leaf surface; leaves turn yellow and drop
Hydrogen fluoride
Marginal necrosis of leaves
Leptosphaerulina leaf spot
Young regrowth burned (large bleached areas) during or shortly after cool, rainy periods; on older leaves, 1-3 mm diameter brown eyespots with lighter centers surrounded by chlorotic halos; ascocarps mostly on decayed leaves
Manganese deficiency
Reduced growth and severe interveinal chlorosis of the youngest leaves, followed by light brown necrotic areas on upper leaf surface
Manganese toxicity
Older leaves become chlorotic at leaf margins, which cup downward and develop small necrotic spots
Metribuzin; hexazinone; terbacil
Plants in established stands are stunted; leaves chlorotic and/or necrotic
Sclerotium blight
Favored by hot, moist conditions; plants killed are devoid of green color; small, brown, spherical sclerotia resembling mustard seeds form on decayed tissue
Spring black stem and leaf spot
Favored by low temperatures; small, irregular, black to brown spots enlarge and coalesce on leaves; infected leaves turn yellow, wither, and fall; stems blacken; pycnidia with conidia on overwintered stems
Stemphylium leaf spot
Favored by wet periods during summer and fall; lesions are oval, slightly sunken, and dark brown, with lighter centers and chlorotic halos; dark conidia develop profusely in older lesions
Sulfur dioxide
Necrotic margins and interveinal leaf areas on older leaves first; chlorosis also common
Zinc deficiency
Youngest leaves remain small and curl upward, then brown spots develop on upper surface around margins of the top (but not youngest) leaves
GRAY
Copper deficiency
Young leaves wilt and may bend back against lower side of petiole and develop necrotic gray to white spots on margins or on the basal half of leaflets; growing point dies
GREEN
Dwarf
Plants are stunted with small, dark green leaves resembling those caused by drought stress; xylem tissue in taproot is dark brown
GREEN (PALE)
Molybdenum deficiency
Plants are poorly nodulated, pale green, and stunted; lower leaflets show interveinal white notching and then whitening of tips and centers; they fall prematurely
PURPLE
Boron deficiency
Plants are dwarfed due to shortening of internodes; margins of youngest fully developed leaves become yellow, then purplish
RED
Calcium deficiency
Root growth is severely impaired, and rotting may occur; petioles collapse and undersides of leaflets become reddish purple
Magnesium deficiency
Interveinal chlorosis of lower leaves first; leaf margins initially remain green but later become chlorotic or red and finally die
Rust
Most prevalent late in the growing season or earlier in fields harvested for seed or if forage harvest is delayed; circular reddish brown pustules protruding from leaves and stems; the rusty spots (spores) rub off easily
SILVER
Summer black stem and leaf spot
Favored by hot, humid conditions; leaf lesions are roughly circular, reddish brown, and up to 6 mm in diameter; conidia give lesions a silver appearance; brown stem lesions enlarge and coalesce
WHITE
Molybdenum deficiency
Plants are poorly nodulated, pale green, and stunted; lower leaflets show interveinal white notching and then whitening of tips and centers; they fall prematurely
Potassium deficiency
Small white spots appear at margins on lower leaves first
Stem nematode
In cool, humid weather, leaves curled and distorted or white; stem internodes are greatly shortened, swollen, and engorged with nematodes
WHITE/BLACK
Sclerotinia crown and stem rot
Favored by cool, humid conditions; leaves and stems become flaccid and collapse; white fluffy mycelium grown over dead parts and produces hard black sclerotia on and in infected tissue
WHITE/PURPLE
Downy mildew
Favored by cool, moist conditions; most severe on seedling stands; yellow blotches on upper side of leaves; white to purplish downy growth on the lower surface; systemically infected shoots shortened and chlorotic; terminal leaves twisted
YELLOW
Alfalfa mosaic
During cool spring and autumn conditions, light green or yellow leaf mottle and leaf distortion
Aluminum toxicity
Plants are stunted and dark green; chlorotic spots may occur on lower leaves; root growth restricted and stubby
Aphanomyces root rot
Infected seedlings become chlorotic, roots are gray and water-soaked, but plants remain upright; on older plants nodules decay and lateral roots are destroyed, leaving restricted brown lesions on tap root surface; foliage becomes chlorotic
Atrazine
Yellowing and necrosis of seedlings beginning at margins of oldest leaves
Bacterial leaf spot
Favored by high temperatures; seedlings may be severely stunted; leaf lesions are irregular, with yellowish to tan, papery, translucent centers and narrow, water-soaked borders that are most pronounced on lower leaf surface
Bacterial wilt; other bacterial diseases
Plants are stunted with small cupped leaves, yellow margins, many crown shoots; diseased plants scattered throughout stand; xylem tissue in taproot is tan to brown ; discoloration sometimes extends laterally to inside surface of dark
Bromoxynil
Burning of seedling leaves at margins first; small seedlings may die
Common leaf spot
Lesions are brown, 1-3 mm in diameter, and rarely coalesce; a raised disc (apothecium) to 1 mm in diameter develops in center of mature lesions on upper leaf surface; leaves turn yellow and drop
Fusarium wilt
Favored by warm weather; plants usually have lower leaf yellowing and often a one-sided wilt; longitudinal streaks in xylem tissue of taproots are brick red to dark brown; mycelium may be seen in xylem vessel elements
Iron deficiency
Yellowish green interveinal chlorosis, first in youngest leaves; leaves turn yellow, then white; youngest leaves may die
Lucerne transient streak
Leaf vein chlorosis, chlorotic vein banding, and leaf distortion in spring growth
Magnesium deficiency
Interveinal chlorosis of lower leaves first; leaf margins initially remain green but later become chlorotic or red and finally die
Manganese deficiency
Reduced growth and severe interveinal chlorosis of the youngest leaves, followed by light brown necrotic areas on upper leaf surface
Manganese toxicity
Older leaves become chlorotic at leaf margins, which cup downward and develop small necrotic spots
Metribuzin; hexazinone; terbacil
Plants in established stands are stunted; leaves chlorotic and/or necrotic
Nitrogen deficiency; ineffective nodulation
Yellow older leaves; roots poorly nodulated
Red clover vein mosaic
Chlorosis at leaf edges and yellow vein mosaic that becomes necrotic
Spring black stem and leaf spot
Favored by low temperatures; small, irregular, black to brown spots enlarge and coalesce on leaves; infected leaves turn yellow, wither, and fall; stems blacken; pycnidia with conidia on overwintered stems
Sulfur dioxide
Necrotic margins and interveinal leaf areas on older leaves first; chlorosis also common
Verticillium wilt
Symptoms are more evident at moderate temperatures; leaves become yellow, often in a V-shaped or one-sided pattern, plants wilt, and xylem tissue of taproot becomes brown; stem remains green for a while after all leaves on a shoot are killed
Witches'-broom
Short, spindly shoots are produced profusely on crowns; leaves are puckered, small, and marginally to generally chlorotic
YELLOW/ORANGE
Yellow leaf blotch
Most prevalent in late spring and early summer; lesions elongate; chlorotic to yellowish-orange blotches parallel to leaf veins; numerous dark pinpoint dots (pycnidia) develop in the blotched areas
No Distinct Discoloration
2,4-D; MCPA
Twisted shoot terminals
Alfalfa enation
Erect, bushy plants with crinkled leaves and enations on underside of leaflet veins; flowers are deformed
EPTC
Seedlings are stunted due to poor root development; leaves may be malformed
Ozone
Chlorosis with small necrotic areas between veins of older leaves
Flower
No Distinct Discoloration
Alfalfa enation
Erect, bushy plants with crinkled leaves and enations on underside of leaflet veins; flowers are deformed
Calcium deficiency
Root growth is severely impaired, and rotting may occur; petioles collapse and undersides of leaflets become reddish purple