Symptoms and Controls of Crop Diseases
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PP-533 (Revised)
Symptoms
and Controls
of
Crop
Diseases
Marcia P. McMullen and H. Arthur Lamey
Extension Plant Pathologists
MARCH 1997
1▼ Wheat and Durum POWDERY MILDEW, Erysiphe graminis tritici
Symptoms. A white to grey, powdery superficial growth
occurs on leaves, stems and sometimes heads. Black
Stem and Leaf Diseases______ pin-head size dots may develop (fungus fruiting bodies).
Eventually, yellowing, browning and drying out of leaf tissue
occurs. If severe, yields are reduced.
Fungal
Survival and Spread. Spores are windblown from residue.
STEM RUST, Puccinia graminis tritici The disease is favored by cool, humid conditions.
Symptoms. Typical symptoms are elongated, brick red
Control. Crop rotation and destruction of host residues
pustules (eruptions) on the leaf blade, sheath, and stem.
through tillage reduce disease risk. Chemical control: spray
Pustules turn black late in the season. Pustules may also
sulfur or triadimefon fungicide at early boot to protect the
appear on glumes. Seed has low test weight and poor
flag leaf or spray propiconazole when flag leaf is emerging
emergence. Severe yield loss may occur.
(Feeke’s growth stage 8).
Survival and Spread. Red spores can be carried great
distances by the wind. Spores are carried by wind into
North Dakota from wheat growing areas to the south; SEPTORIA LEAF BLOTCH, Stagonospora
infection may repeat every eight to 14 days. nodorum, (= Septoria nodorum) Stagonospora
Other Crops Affected. Barley and wild grasses. (Septoria) avenae f. sp. triticea, and Septoria
tritici
Control. Most recommended hard red spring wheats and
durums grown in North Dakota are resistant to existing Symptoms. Leaves develop straw-colored spots that later
races. Winter wheats vary in resistance. Check the current form grayish-white centers. Very tiny black fruiting bodies
variety recommendations for variety susceptibility. Eradicate (specks) may develop in the spots. Severely diseased plants
common barberry, the alternate host of stem rust. Since the have “fired” leaves, yield loss, and shriveled seed. Stagono-
federal eradication program was abandoned, barberry is spora nodorum also infects the glumes (see Glume Blotch).
gradually moving back into the upper Midwest.
Survival and Spread. Survives on infected straw and
Remarks. New races may form on common barberry stubble and on seed. Spread by airborne spores and
(not Japanese barberry), and mutations may occur. splashing rain.
Other Crops Affected. Barley
LEAF RUST, Puccinia recondita Control. Differences in variety response exist: Check current
variety information for susceptibilities to leaf spot fungi. Use
Symptoms. Circular to oblong orange-colored pustules
fungicidal seed treatment to control seed-borne infection.
occur primarily on leaves. Later in the season the pustules
Fungicide sprays are available. Benomyl, copper hydroxide,
are black and usually do not break through the epidermis.
mancozeb, triadimefon, and propiconazole are registered
Seed test weight and yield are reduced.
for Septoria control, with some fungicides requiring tank
Survival and Spread. Orange spores are spread from mix partners for adequate control. Use crop rotation or bury
plant to plant by the wind; usually they blow in from major crop refuse with tillage. Clean seed severely and discard
winter wheat states in the southern plains. Temperatures shriveled kernels.
of 60-80°F and dew periods of six to eight hours favor
Remarks. Infection by all three fungi is favored by wet
infection.
weather and relatively warm temperatures (60-70°F for
Control. Use resistant varieties. Check the current variety S. avenae f. sp.triticea and S. tritici and 70-80°F for S.
information for susceptibility of available varieties. Fungicide nodorum).
control: spray mancozeb at early boot and 10 days later
to protect the flag leaf, or spray a single application of
triadimefon at early boot, or propiconazole when flag SPOT BLOTCH, Cochliobolus sativus
leaf is emerging (Feeke’s growth stage 8). (= Helminthosporium sativum)
Remarks. New races may occur by mutations. See description under barley.
PBTAN SPOT, Pyrenophora tritici-repentis by wind-driven rain and enters plants through wounds or
natural openings.
Symptoms. Elliptic or diamond shaped tan spots form on
leaves, often with a yellow border and a small chocolate Other Crops Affected. Barley and rye.
brown center. Severe disease causes “firing” of leaves,
Control. None recommended.
yield loss, and low test weight seed.
Survival and Spread. Survives on infected straw and
stubble, on wild grasses, and rarely on seed. Spores are Virus
airborne and also spread by splashing rain. Long periods
(24-48 hours) of moisture on the wheat leaves favor infection BARLEY YELLOW DWARF,
of modern cultivars. Barley Yellow Dwarf Virus
Other Crops Affected. Bromegrass, rye and wheat grass. See description under barley
Control. Varieties vary in susceptibility. Check variety
information publications for susceptibility to leaf spot fungi.
Crop rotations or burying crop refuse by tillage reduces early
WHEAT STREAK MOSAIC,
infection but may not prevent late infection. Later applica- Wheat Streak Mosaic Virus
tions may be directed to the flag leaf; propiconazole must be Symptoms. Leaves develop intermittent yellow and green
sprayed at early flag leaf emergence ( Feeke’s growth stage stripes or streaks. Severely diseased leaves turn brown and
8.) Early applications of mancozeb or propiconazole die. Plants are stunted. Yield is poor and seed has a low test
fungicides may protect the tillers from early infections. Both weight.
fungicides have good activity against leaf spots on wheat.
Survival and Spread. Survives in infected winter wheat,
Remarks. Late in season large numbers of spores may volunteer wheat, and several native grasses. Spread by
be blown considerable distances. the wheat curl mite (Aceria tulipae), which is wind-borne.
Other Crops Affected. Barley, corn, oats, rye, and some
Bacterial grasses and volunteer wheat.
Control. Plant winter wheat around mid-September and
BACTERIAL BLIGHT, Xanthomonas plant spring wheat early. Destroy volunteer wheat and
translucens pv. translucens grasses two weeks before planting winter wheat. Avoid
(= X. campestris pv. translucens) planting winter wheat next to corn and spring wheat next
to volunteer winter wheat. Do not overseed damaged winter
Symptoms. Water-soaked dark green stripes develop
wheat stands with spring wheat. Check winter wheat variety
on leaves, turning yellow and finally dark brown; a yellow
trial information for differences in susceptibility to wheat
exudate forms in wet weather. Also infects heads (see
streak mosaic.
Black Chaff). Early infection causes dwarfed heads and
shriveled seed. Remarks. A problem in the winter wheat areas of North
Dakota.
Survival and Spread. Survives on infected seed, straw
and winter grass hosts. Spread by splashing rain, aerosols,
and insects.
Non-Infectious
Other Crops Affected. Barley and rye.
Control. No satisfactory control; crop rotation and burying
HEAT CANKER, Non-Infectious
infected stubble is of limited value. Avoid seed from infected Symptoms. Seedling stems may be constricted at the soil
fields. Not controlled by foliar fungicides. line; the seedling may fall over. In less severe cases several
white bands may appear on one or more leaves; these
bands go across the leaf. May be common in a hot, dry
BACTERIAL LEAF BLIGHT, Pseudomonas spring.
syringae pv. syringae Survival and Spread. Non-infectious. Favored by dark soils
Symptoms. Develops on uppermost leaves after plant and hot sunny days before plants are large enough to shade
reaches boot stage. Initial tiny, water-soaked spots expand the soil - plant tissues at the soil line are injured by hot soil.
and become necrotic and turn from gray-green to tan-white. Mild injury causes white bands; each one corresponds to
Entire leaves may become necrotic. During very wet periods, high soil temperatures when that portion of the leaf was
white droplets of bacteria may be visible. in the whorl at soil line. Severe injury causes a stem
constriction.
Survival and Spread. Survives in soil and water. Spreads
3Control. Early planting, drilling rows north and south for LOOSE SMUT, Ustilago tritici
maximum shading and using higher seeding rates may
Symptoms. The fungus grows internally, along with the
reduce the damage.
growing point, following germination of the infected seed.
No symptoms appear until heading. Affected heads may
emerge earlier than healthy ones and are a powdery mass
Head and Seed Diseases _____ of black smut spores that replace grain and chaff. No smut
balls form.
Fungal Survival and Spread. Flowers are infected at blossom time
BLACK POINT, Cochliobolus sativus by wind-borne spores from smutted heads. Seed (embryo)
is invaded and cannot be distinguished from healthy seed.
(= Helminthosporium sativum) and related fungi
Other Crops Affected. Some grasses, but not barley or
Symptoms. In wet weather, developing seeds in the head
oats. Loose smuts on barley and oats are caused by similar
are infected by Helminthosporium or Alternaria, resulting
fungi, but not by the same fungus that causes wheat loose
in shriveled blackened kernels. The blackened area is often
smut.
near the embryo or germ end, hence the name black point.
The crease also may be blackened. Planting of black- Control. Several seed treatment fungicides, those contain-
pointed kernels may result in seedling blight. Seedlings turn ing carboxin, difenoconazole, or triadimenol, will control
yellow, roots are blackened and plants die or are stunted. loose smut.
Survival and Spread. Survives in soil, crop refuse, and on
and in black-pointed seed. Spread by wind and splashing
rain. SCAB (HEAD BLIGHT), Fusarium sp.
(Gibberella zeae)
Other Crops Affected. Barley and grasses.
Symptoms. All or any part of the head may blight any time
Control. Use fungicidal seed treatment to reduce seedling from flowering to maturity; affected parts turn white, or may
blight. Use crop rotation. Clean and condition black-pointed be salmon colored from the spores, in wet weather. Seeds
seed and discard shriveled seed. Bury crop refuse by tillage are light and shriveled, frequently grayish or pinkish “tomb-
to reduce chance of fungal spores splashing to the head. stones.” Yields and test weights are reduced. Seedlings
grown from infected seeds turn yellow and die or re-root
at soil line.
ERGOT, Claviceps purpurea
Survival and Spread. Spores airborne for considerable
See description under rye. distance. Fungus also soil-borne. Carried on and in infected
seed. Survives in infected seed and crop refuse; survives
very well in corn crop refuse.
GLUME BLOTCH, Stagonospora nodorum
Other Crops Affected. Barley, corn, grasses, oats and rye.
(= Septoria nodorum)
Control. Differences in susceptibility to scab exist among
Symptoms. Tips of glumes have either a bleached to
varieties. Check variety information for a variety’s response
greyish appearance or a brownish discoloration. Infected
to scab. Severely clean to remove badly infected seed.
awns exhibit brown spotting. Small fruiting bodies may
Use fungicidal seed treatment to prevent seedling blight.
be evident in glume tips. Grain is very shriveled.
Use tillage to bury crop refuse and use crop rotations.
Survival and Spread. Survives on infected straw and Avoid planting small grains on corn land. Benomyl fungicide
stubble and on seed. Spread by airborne spores and is registered (1996) for wheat for suppression of the head
splashing rain. infection of scab; other fungicides may also have some
ability to suppress scab.
Other Crops Affected. Barley.
Remarks. Scabby grain may contain a mycotoxin and can
Control. Check variety recommendations for susceptibility
to fungal leaf spots. Use fungicidal seed treatment to control cause vomiting and feed refusal in nonruminant livestock.
seed-borne infection. Clean seed severely and discard
shriveled kernels. Tillage to bury stubble and rotations away
from wheat minimizes carryover of the disease organism.
Foliar fungicides may reduce Septoria leaf blotch, but their
activity may not last sufficiently long to protect against glume
blotch.
PBSTINKING SMUT (BUNT), Tilletia foetida, BACTERIAL PINK SEED, Erwinia rhapontici
Tilletia caries Symptoms. Kernels appear pink but maintain plumpness
Symptoms. Infection occurs during seedling development and vitreousness. More easily seen in durum.
but no symptoms show until heading. Heads on infected Survival and Spread. Survives on crop residue. Generally
plants may be partly or entirely affected. Smut balls replace invades kernels harvested prematurely or grain in the swath.
seeds. Smut balls are enclosed with gray membranes that
break at harvest releasing black spores. Control. Occurs infrequently. No control measures
prescribed.
Survival and Spread. Survives as bunt balls and spores.
Balls break at harvest and black spores cover healthy seeds.
Spores can live eight years or more. May also survive in the
soil. Spread by wind. Root Diseases______________
Other Crops Affected. Rye and wild grasses.
Fungal
Control. Use protectant fungicide seed treatment.
COMMON ROOT ROT, Cochliobolus sativus
Remarks. Smutted wheat has a fishy odor, not suited for (= Helminthosporium sativum)
milling unless scoured — price discounted at elevator. Not
currently (1996) found in North Dakota but present in many Symptoms. Subcrown internode (portion connecting
other plains states. Could be introduced from out-of-state seed to crown), roots and crown tissue are dark brown
seed or from contaminated equipment. or with dark brown lesions. Spikelets on affected plants
are frequently empty and heads and whole plants are
prematurely ripened or bleached.
Bacterial Survival and Spread. Survives as spores and vegetative
strands in soil and on crop refuse.
BASAL GLUME ROT, Pseudomonas syringae
pv. atrofaciens Other Crops Affected. Barley and grasses.
Symptoms. Dark brownish-black streaks on the glumes, Control. Crop rotation. Use more tolerant varieties. Differ-
mostly on the lower half. Germ end of the seed varies from ences among varieties are listed in the North Dakota variety
faint brown to charcoal black and seed may be severely description circulars. Seed treatment fungicides, imazalil,
shrunken. difenoconazole, and triadimenol are available for suppres-
sion of common root rot.
Survival and Spread. Survives in infected seed and in soil.
Spread by wind and insects.
Control. Use clean seed. SNOW ROT AND SNOW MOLD,
Pythium and Fusarium spp.
Remarks. Fairly common in North Dakota, but usually not
highly significant. Symptoms. Irregular patches to scattered plants turn brown
to bleached in appearance. Roots and crown are decayed.
Survival and Spread. Survives in soil as spores, sclerotia
BLACK CHAFF, Xanthomonas translucens and vegetative growth. Most severe in winter wheat following
pv. translucens heavy snow cover, or following frequent snows or rains early
Symptoms. Stem at base of head develops thin black in spring.
stripes. Black stripes form on glumes and alternating dark Other Crops Affected. Winter cereals, lawn grasses.
and light spots develop on awns (“barber pole” effect).
Blighted seedlings develop when infected seed is planted. Control. Avoid planting in areas of frequent, dense snow
cover. Rotation helps reduce inoculum levels.
Survival and Spread. Survives on infected seed and straw.
Spread by splashing rain, aerosols, and insects.
Other Crops Affected. Barley and rye. Rarely attacks oats.
Control. No satisfactory control; crop rotation and burying
infected stubble is of limited value. Avoid seed from infected
fields. Not controlled by foliar fungicides.
5TAKE-ALL, Gaeumannomyces graminis tritici NET BLOTCH, Pyrenophora teres
Symptoms. Roots, crown and lower stem are distinctly Symptoms. Brown blotches on leaves are elongate and
blackened, often shiny black. Roots may be brittle. Prema- soon develop a “netting” pattern. Straw at harvest is dull
turely whitened heads and stunted plants also are typical. brown and weak. Small linear brown lesions develop on
kernels, with light brown discoloration of the seed.
Survival and Spread. Survives in soil and host debris.
Infection favored by high soil moisture and high soil Survival and Spread. Seed-borne and survives on crop
alkalinity. Most frequently found on irrigated ground refuse. Spread during the growing season is from airborne
but also in dryland crops in excessively wet years. spores.
Other Crops Affected. Barley, rye, wheat, grasses. Control. Use crop rotation and sanitation: bury crop residue
by tillage before planting. Use seed treatment to control
Control. Crop rotation to non-susceptible host. Avoid
seedling blight. Foliar applications of fungicides registered
excessive irrigation. Use of ammonium nitrogen, not nitrate
for barley (see tan spot of wheat) will prevent severe spotting
nitrogen forms, may reduce the risk of take-all. Seed
of flag leaf.
treatment products difenoconazole and triadimenol
are available for suppression of take-all. Remarks. Associated with cool temperatures; generally
more serious in northern North Dakota and on six-row
barleys more so than two-row barleys. Often abundant
on volunteer barley in a wet, late fall.
▼ Barley
POWDERY MILDEW, Erysiphe graminis hordei
Stem and Leaf Diseases______ See description under wheat.
Fungal Other Crops Affected. Wild barley.
STEM RUST, Puccinia graminis tritici and
Puccinia graminis secalis SCALD, Rhynchosporium secalis
Symptoms. See description under wheat. Symptoms. Water-soaked blue-green blotches appear on
the leaves. Later, these turn tan to steel gray, are diamond
Survival and Spread. See description under wheat. shaped, and have dark brown borders.
Other Crops Affected. Rye, wheat. Survival and Spread. Survives on crop refuse. Occasionally
Control. All currently (1996) available barley varieties are seed transmitted. Favored by cool wet weather. Spread by
susceptible to race QCC of stem rust. This race was first splashing rain.
discovered in North Dakota in 1989. Prior to discovery of this Control. Use crop rotations. Bury barley stubble and straw
new race, all commonly grown barley varieties were resis- before planting barley on barley. The foliar fungicide
tant to the prevalent races of stem rust. propiconazole is registered for barley scald control.
Remarks. Most common in northeastern North Dakota
LEAF RUST, Puccinia hordei near the Canadian border.
Symptoms. Small circular orange-brown pustules occur
on leaves. Seed test weight and yield may be reduced. SEPTORIA LEAF BLOTCH, Stagonospora
Survival and Spread. Orange spores blow in from the avenae f. sp. triticea and Septoria passerinii
south and spread from plant to plant. Usually, only late
Symptoms. Straw-colored, linear blotches develop on
planted barley is seriously damaged.
leaves; at maturity these blotches contain tiny black fungus
Control. All currently (1996) available varieties are fruiting bodies, and leaf sheaths show brownish-gray streaks
susceptible. and blotches. Weakened straw results in lodging. Kernels
may be shriveled.
Chemical control. Mancozeb and propiconazole fungicides
are registered for barley for leaf rust control. Survival and Spread. Seed-borne and survives on crop
residue. Spread during crop season by spores that are
rain-splash dispersed.
PBOther Crops Affected. Wheat and some grasses. Virus
Control. Use crop rotation and seed treatment. Foliar
application of fungicides (see leaf rust) can prevent severe
BARLEY YELLOW DWARF,
infection of the flag leaf. Barley Yellow Dwarf Virus
Symptoms. Leaf tips turn bright gold or yellow. Later, plants
are stunted and whole leaves are bright yellow, occasionally
SPOT BLOTCH, Cochliobolus sativus with some purpling discoloration. Affected fields may show
(= Helminthosporium sativum) uneven and patchy growth.
Symptoms. Round to oblong dark brown spots with definite Survival and Spread. Virus survives in winter grains,
margins develop on leaves; spots merge to form blotches; primarily in the southern plains. Transmitted by various aphid
nodes may turn black as crop matures. species — often introduced with aphid flights from the south.
Survival and Spread. Survives as spores and mycelium Other Crops Affected. Oats, wheat, various grasses.
in soil, on crop refuse, and is seed-borne. Leaf spots come
Control. No particular control available. Disease is sporadic
form airborne spores.
in nature, being most severe when virus-carrying aphid
Other Crops Affected. Wheat and grasses. populations are high.
Control. Use crop rotation. Current (1996) two-row barleys
are more susceptible than six-row varieties. Foliar fungicides
registered for barley may be used to protect the crop against Non-infectious
infection.
HEAT CANKER, Non-Infectious
Remarks. Leaf infections are severe under warm moist
See description under wheat.
conditions.
PHYSIOLOGICAL LEAF SPOTS,
Bacterial Non-Infectious
BACTERIAL BLIGHT, Symptoms. Irregular blotches or dark spots of varying size.
Xanthomonas translucens pv. translucens Survival and Spread. Non-infectious. Most common when
Synonym X. campestris pv. translucens temperatures and humidity are high.
Symptoms. Initial infection occurs on seedlings. On larger Other Crops Affected. Oats
leaves, dark green water-soaked stripes become yellowish
translucent blotches or stripes, then turn brown. In wet Control. Nutrient deficiencies may aggravate spotting.
weather, a yellowish exudate develops on lesions. This
exudate dries to produce a glistening surface on the leaf.
Similar lesions may also develop on kernels. Head and Seed Diseases _____
Survival and Spread. Seed-borne and survives on crop
residue. Favored by rainy, damp weather. Spread by Fungal
splashing rain and insects.
BLACK OR SEMI-LOOSE SMUT, Ustilago nigra
Other Crops Affected. Wild barley species, grasses
and wheat Symptoms. Infection occurs during seedling development,
but no symptoms show until heading. A black spore mass
Control. Use crop rotation and bury crop residue by tillage replaces kernels. Symptoms range from those of loose smut
before planting. Not controlled by foliar fungicides. to those of covered smut.
Survival and Spread. Spores spread to healthy seed in the
field or during threshing. Spores survive on seed and in soil.
Control. Use seed treatment with a protectant fungicide or
carboxin. Semi-loose smut is not detected by the embryo
test.
7COVERED SMUT, Ustilago hordei Bacterial
Symptoms. Infection occurs during seedling development,
BACTERIAL KERNEL BLIGHTS,
but no symptoms show until heading. In the head, a gray
membrane encloses black spore masses that replace the Pseudomonas syringae pathovars
kernels. Symptoms. Dark brown discoloration of the embryo end of
the kernel, or well-defined tan to dark brown discolorations
Survival and Spread. The spores survive in the smutted
heads; membrane breaks at harvest, covering healthy seed on kernel.
with spores. Spores survive on and under hulls cracked Other Crops Affected. Wheat, rye
during threshing.
Control. Plant disease-free seed. Some cultivars may have
Control. Seed treatments with a protectant fungicide or more resistance.
systemic fungicides provide effective control.
BLACK CHAFF, Xanthomonas translucens
BLACK POINT, Cochliobolus sativus pv. translucens
(= Helminthosporium sativum) and related fungi
See description under wheat.
See description under wheat.
ERGOT, Claviceps purpurea
Root Diseases______________
See description under rye. Fungal
COMMON ROOT ROT, Cochliobolus sativus
GLUME BLOTCH, Stagonospora nodorum (= Helminthosporium sativum)
(synonym Septoria nodorum) See description under wheat.
See description under wheat. Control. Crop rotation to non-host crop. Use tolerant
varieties. A seed treatment product, imazalil, is registered
for suppression of common root rot.
LOOSE SMUT, Ustilago nuda
Symptoms. See description under wheat.
TAKE-ALL, Gaeumannomyces graminis tritici
Survival and Spread. See description under wheat.
See description under wheat.
Other Crops Affected. Some grasses but not oats or wheat.
Control. Currently available (1996) varieties are susceptible.
Use embryo test and select non-infected seed or treat seed
with carboxin-containing fungicide if infection level is greater
than 1%.
▼ Oat
Stem and Leaf Diseases______
SCAB (HEAD BLIGHT),
Fusarium spp. (Gibberella zeae) Fungal
See description under wheat (head blight). STEM RUST, Puccinia graminis avenae
Symptoms. See description under wheat
Survival and Spread. See description under wheat.
Other Crops Affected. Confined to oats and wild oats.
Control. Varieties differ significantly in stem rust resistance
but those recently released (1996) by North Dakota (Jerry,
Paul, NewDak and Valley) are among those with resistance.
PBIf possible, plant early. Eradicate common barberry, as Virus
the sexual stage occurs on this alternate host, giving rise
to new races. OAT RED LEAF, Barley Yellow Dwarf Virus
Symptoms. Affected plants have bronze to reddish
discoloration of leaves. Plants are stunted. Yield losses
CROWN RUST OR LEAF RUST, can be severe if infection occurs early in season.
Puccinia coronata
See description under barley. Variety differences in
Symptoms. Early in the season elongated orange-yellow susceptibility to oat red leaf exist. See current variety
pustules develop on leaves; later black winter spores form description circulars for variety susceptibility.
in long raised streaks but do not break through the surface.
Survival and Spread. Black winter spores cause infections
of buckthorn in early spring. Later spread is back to oats.
Orange summer spores blow in from the south and also form
Head and Seed Diseases _____
the repeating stage of infections on oats.
Fungal
Other Crops Affected. Wild oats and grasses
BLACK LOOSE SMUT, Ustilago avenae
Control. Oat crown rust races have been shifting or chang-
ing rapidly and resistance to the prevalent races has been Symptoms. Infection occurs in early stages of germination
difficult to maintain. In 1996, only Paul and Milton were and seedling development, growing systemically but without
designated as resistant to the prevalent races of oat crown symptoms until heading. The grain is replaced by a black
rust. Check current variety circulars for descriptions of powdery mass which breaks apart readily; usually all
variety tolerance to crown rust. If possible, plant early. spikelets on a plant are affected.
Control wild oats; they serve as a susceptible host in early Survival and Spread. Spores are on and under the seed
spring for spores from buckthorn. Eradicate wild buckthorn hulls.
within a mile of oat fields; the fungus completes the sexual
stage on this plant and new races can develop from the Other Crops Affected. Grasses and wild oats, but not
sexual process. Mancozeb fungicides (various trade names) barley or wheat.
and Tilt foliar fungicides are registered for oat and could be Control. Use carboxin-containing seed treatment products.
used to control crown rust.
Remarks. Not presently common in North Dakota.
Bacterial COVERED SMUT, Ustilago kolleri
BACTERIAL STRIPE BLIGHT, Symptoms. Infection occurs in early stages of germination,
Pseudomonas striafaciens growing systemically but without symptoms until heading.
Less destruction of the hulls occurs than with loose smut,
Symptoms. First appears as sunken, water soaked dots
and the spore mass is blacker and does not break apart
which later enlarge to water-soaked blotches or stripes
as readily as in loose smut.
that become a rusty brown to black.
Survival and Spread. Survives and spreads as spores
Survival and Spread. Survives in crop residue and in seed.
adhering to surface of seed. Membrane enclosing smut
Disease develops in seedlings and spreads to other plants
spores breaks during combining.
by wind and splashing rain. Bacteria enter through stomata
(natural pores in leaves), insect punctures, and wounds. Other Crops Affected. Grasses and wild oats, but not
Most commonly observed during wet springs in western barley or wheat.
North Dakota.
Control. Use fungicidal seed treatment.
Other Crops Affected. Rye.
Remarks. Not presently common in North Dakota.
Control. Crop rotation. Bury crop refuse in spring with
tillage. Seed treatment is of doubtful value.
SCAB (HEAD BLIGHT),
Remarks. Another bacterial disease of oats, halo blight,
is rare in North Dakota. Fusarium spp. (Gibberella zeae)
See description under wheat. Not common in oats.
9Non-Infectious Head and Seed Diseases _____
BLAST, Physiologic disorder
Fungal
Symptoms. White empty spikelets (kernels), especially near
base of head; reduced yield. ERGOT, Claviceps purpurea
Control. None known. Symptoms. Large black ergot bodies replace the seed;
usually two to five occur per head. In addition, some empty
Remarks. Caused by environmental factors such as
florets (kernels) may occur.
drought, soil fertility, heat, etc. Occurs from tillering to
pollinating stage. Survival and Spread. Ergot bodies survive on soil from
one season to the next. Ergot bodies germinate, producing
air-borne spores that infect heads at blossom time. Early
infected heads produce spore-laden “honey dew” that is
▼ Rye carried to other heads by insects and wind-blown rain.
Other Crops Affected. Durum, grasses, triticale, wheats
Stem and Leaf Diseases______ and barley. Oat is less commonly affected.
Control. Clean seed thoroughly to remove ergot bodies.
Fungal Use crop rotation with non-cereals; ergot bodies usually
survive only one year. Mow or kill grass along fence rows
STEM RUST, Puccinia graminis secalis and rock piles before it goes to seed. If a cereal is planted
next year, plow under ergot bodies.
Symptoms. See description under wheat.
Remarks. Ergoty grain is poisonous to livestock and
Survival and Spread. See description under wheat
humans. Ergoty hay or pasture grass is poisonous to
Other Crops Affected. Barley and wild grasses. livestock. Wheat grain with 0.05% ergot is graded
“ergoty.” Barley is considered ergoty with 0.1% ergot.
Remarks. Rarely serious on rye in North Dakota.
Small quantities consumed by livestock may result in
unstable gait, poor circulation in extremities leading to
gangrene and even abortion in pregnant animals.
LEAF RUST OR BROWN RUST,
Puccinia recondita secalis
Symptoms. See description under wheat. SCAB (HEAD BLIGHT),
Survival and Spread. See description under wheat. Fursarium spp. (Gibberella zeae)
Symptoms. See description under wheat.
Other Crops Affected. Does not attack wheat.
Survival and Spread. See description under wheat.
Control. No satisfactory control available.
Control. See description under wheat.
Remarks. Summer spores must blow in from the south.
TAN SPOT, Pyrenophora tritici-repentis Root Diseases______________
Symptoms. See description under wheat.
Fungal
Survival and Spread. See description under wheat.
COMMON ROOT ROT AND OTHER FUNGI,
Control. Crop rotation reduces early-season infection.
Helminthosporium sativum and other fungi
Remarks. Usually less severe than on wheat.
Symptoms. See description of root rot and seedling blight
under wheat.
Survival and Spread. See description under wheat.
Control. See description under wheat.
Remarks. May occur with Fusarium root rot.
PB▼ Corn Control. Hybrids vary in resistance. Bury corn crop refuse by
tillage; use crop rotation.
Leaf Diseases______________ RUST, Puccinia sorghi
Symptoms. Pustules form on leaves and sometimes
Fungal on husks. Elongated red pustules bear summer spores; later,
black winter spores form in the pustules.
CRAZY TOP, Sclerophthora macrospora
Survival and Spread. Survives on its alternate host,
Symptoms. Tassels develop a mass of leafy structures; no
Oxalis sp. (wood sorrel), and as summer spores in the
pollen is formed. Ears may be replaced by leafy structures.
south. Summer spores blow up from the south. Favored
Severely infected plants may have narrow straplike leaves, by cool temperatures and dew.
produce no tassel or ears, be stunted, and develop exces-
sive suckering. Crazy top is rare but may be found in low Control. Rarely serious enough to require control. Hybrids
areas of a field where the soil may be flooded for brief vary in resistance.
periods shortly after planting.
Survival and Spread. The fungus survives in the soil and Bacterial
in infected crop residue. It is spread in water by swimming
spores which are produced when the soil is saturated for HOLCUS SPOT, Pseudomonas syringae
at least 48 hours. Infection may occur any time from seed
Symptoms. Elliptic to irregular shaped spots, usually
germination until the seedlings are in the four- to five-leaf
1/8-3/16 inches in diameter, with a water-soaked or dark
stage.
green greasy appearance. Later, the spots turn creamy
Other Crops Affected. Small grains, wild grasses, and white to tan, resembling parchment paper. On some hybrids
sorghum. a purple border forms around the spots. The spots are
Control. No seed treatment is effective and no information usually more numerous on the lower leaves.
is available about hybrid resistance. Provide adequate soil Survival and Spread. Survives on crop refuse and various
drainage. Control grassy weeds. Avoid planting in low, grasses. Favored by warm (77-86°F) weather with wet,
wet spots. windy conditions.
Control. Generally none needed, as this disease has not
been shown to be economic. Crop rotation and sanitation
EYESPOT, Kabatiella zeae (destruction of crop refuse) would reduce overwintering
Symptoms. Very small (1/16 to 1/8 inch), translucent bacteria.
circular to oval spots with yellow halos. Initial spots are Remarks. Common in North Dakota, especially on
water-soaked; the spots later develop a brown or purple sprinkler-irrigated corn.
border, hence called eyespot. Easily seen when leaf held
up to light and light transmitted through spots.
Survival and Spread. Overwinters in corn stubble. Spores Virus
carried to crop by wind or splashing rain.
MAIZE DWARF MOSAIC,
Control. Crop rotation and tillage reduce disease levels. Maize Dwarf Mosaic Virus
Symptoms. A light green mottle or mosaic forms on the
NORTHERN LEAF BLIGHT, upper leaves. Later, fine yellow-green stripes develop and
streaks of red may form when nights are cool (below 60°F).
Helminthosporium turcicum
The upper portion of the plant may be stunted.
Symptoms. Large elliptic water soaked lesions develop
on the leaves; these soon turn straw colored to dark brown Survival and Spread. Transmitted by aphids and also
mechanically by plant contact.
with a faint target pattern. Lesions form on the husk, but the
kernels are not attacked. Control. Hybrids may vary in susceptibility.
Survival and Spread. Fungus survives on crop residue, Remarks. Uncommon in North Dakota. More severe
producing wind-borne spores that infect the new crop. on sweet corn than on field corn. Sporadic appearance
depends on virus-carrying aphids migrating from over-
Other Crops Affected. Sorghums, sudangrass, and
Johnsongrass. wintering areas farther south.
11Other Crops Affected. Causes scab (head blight) in wheat,
Stalk and Ear Diseases ______ barley, and other small grains.
Fungal Control. Crop rotation: do not rotate with barley, corn
or wheat. Use balanced soil fertility. Control stalk-boring
COMMON SMUT, Ustilago maydis insects. Hybrids vary in resistance to stalk rot. Harvest
early, as soon as crop is mature.
Symptoms. Leaves, stalk, ear, and tassel may be affected
and replaced by black spore masses. Spore masses, Remarks. Feeding diseased grain or silage may cause feed
covered by a persistent grayish membrane, are of varying refusal problems in non-ruminant animals.
sizes, but frequently form large “boils.”
Survival and Spread. Survives on old crop residue. Spores
DIPLODIA STALK AND EAR ROT,
are airborne. Infections are common in plant injuries caused
by cultivation, hail, etc., or during periods unfavorable for Diplodia maydis
good plant growth, such as dry weather and a temperature Symptoms. Plants suddenly turn gray-green. Lower stalks
of 75-93°F or wet and cool weather. are rotted, with disorganized tan or brown pith. A grayish dry
rot develops on ears and kernels, progressing upward from
Control. Use crop rotation. Avoid excess nitrogen, especially
animal manure. Some hybrids are more resistant than the base.
others. Field corn is generally less susceptible than sweet Survival and Spread. Fungus survives on corn crop
corn. Smut is generally less when plant populations are residue, producing wind-borne spores that affect the new
12,000-20,000/A. Avoid mechanical damage during crop. Disease is favored by dry weather followed by 2-3
cultivation. Seed treatment does not control common smut. inches of rainfall several weeks after silking.
Control. Hybrids vary in resistance. Use balanced soil
fertility; avoid high nitrogen or low potassium. Avoid high
EAR ROT, Fusarium moniliforme,
plant populations. Harvest when mature.
Fusarium graminearum
Symptoms. Individual kernels or groups of kernels are
affected, turning pale salmon color to pink and with a HEAD SMUT, Sphacelotheca reiliana
tendency to be reddish in later stages. F. moniliforme also
Symptoms. Plants are systemically infected in the seedling
produces a stalk rot, similar to Gibberella (see below).
stage, may be severely stunted, and may have chlorotic
Often associated with insect injuries and bird damage. flecks on the leaves. Only the tassels and ears are smutted.
Survival and Spread. Survives on corn crop residue. All or part of these structures may be filled with black spores
Spreads by wind-borne spores and ear-feeding insects. covered with a thin membrane. The membrane breaks up
Favored by wet, rainy conditions as crop matures. easily and quickly exposes the black spores (in contrast
to common smut). Thread-like strands occur in the spore
Control. Use crop rotation and balanced soil fertility.
masses. Often either the ear or tassel may be partially
Hybrids vary in resistance to kernel rot; those with tight
sterile. Many leaf-like structures may form in the tassel —
husks, which reduce insect damage, show less damage.
this is called phyllody. Yields can be reduced considerably.
Remarks. Ear molds may produce fungal toxins which in
Survival and Spread. Spores are soil-borne and survive
turn can be harmful to livestock. Harvested grain with large
up to 10 years in the soil. The fungus may be introduced
amounts of ear molds should be tested for mycotoxins prior
into new areas by wind-borne spores or by spores borne
to feeding.
on the surface of the seed. Infection occurs in the seedling
stage and is most efficient from soil-borne spores. Buildup
is favored by continuous cropping of corn. Spores retain
GIBBERELLA STALK ROT, Gibberella zeae viability after passing through the digestive tracts of cattle
Symptoms. Stalks are weak; the pith is shredded and or sheep.
pinkish. Lodging frequently occurs. Yield losses occur due
Other Crops Affected. Different races attack corn and
to poor filling of ears, early ear drop, early dying of plant
sorghum (a few sorghum races attack both crops).
or stalk breakage.
Control. Use crop rotation. Plant resistant hybrids. To avoid
Survival and Spread. Fungus overwinters in stalks and
introducing into new areas, purchase seed treated with
stubble; wind-borne spores produce new infections. Stalk
carboxin + captan — this gives almost complete protection
rot is promoted by excess soil nitrogen, excessively high
against seed-borne infection and partial protection against
plant populations, high rainfall shortly after silking, insect
soil-borne infection.
injury, and mechanical damage.
PBRemarks. First observed in scattered fields in Minnesota weather or a bleached and shredded appearance in dry
and one in North Dakota in 1980 but has not become a weather. Hard black fungus bodies, sclerotia, form on the
serious problem. surface of diseased tissues and inside diseased stems.
Foliage of infected plants wilts, turns yellow and drops
prematurely. Late season infections produce chalky-colored,
lightweight bean seeds.
Non-Cereals Survival and Spread. Sclerotia survive many years in the
soil. Sclerotia near the soil surface germinate in wet weather
to form tiny (1/8-3/16 inch) trumpet-shaped mushroom
▼ Dry Edible Beans bodies called apothecia. The apothecia produce millions
of airborne spores that usually infect dry bean plants
through the dead blossoms but occasionally may infect
Stem and Leaf Diseases______ through dead leaf tissue or wounds. Infection may occur over
a wide range of temperatures (40-85°F), but moist weather
and moderate temperatures (68-77°F) are most favorable for
Fungal disease development. Fields may be infested through
RUST, Uromyces appendiculatus var. airborne spores infecting susceptible crops or weeds or
through sclerotia mixed with seed.
appendiculatus
Symptoms. Rusty-colored pustules erupt through the Other Crops Affected. Sunflower, mustard, and canola
surface of the leaf. Rusty-colored summer spores can be (rapeseed) are very susceptible. Other susceptible crops
brushed off the surface of the pustules. Pustules may also include field peas, garbanzo beans (chickpeas), lentils,
form on the pods. When rust is severe, leaves turn yellow, safflower and soybeans. Potatoes are infected occasionally.
dry out, and drop prematurely. Late in the season the Flax and buckwheat are only rarely infected. Many broad-
summer spores are replaced with dark-colored winter leaved weeds are also susceptible.
spores. Control. Plow down infected crop refuse in the spring.
Survival and Spread. Survives on infected crop residue. Benomyl or thiophanate methyl fungicide may be used
Favored by cool (60-75°F) moist weather with long periods at early to 100% bloom. To be effective, plant coverage is
of dew or rain. It is most serious in late-planted beans or important. The fungicide should be applied with adequate
on beans delayed in maturity by weather damage (hail), water and pressure (at least 40 psi); use drop nozzles to
high nitrogen fertility, etc. get spray on blossoms. Use crop rotation; avoid planting
dry beans, mustard, canola (rapeseed), or sunflower more
Control. Bury infected bean residue by deep plowing. than once in four years. Avoid planting next to a field that
Avoid planting next to fields that had severe rust last year. had severe white mold in the past four or five years. Use
Use a three- or four-year crop rotation. Monitor fields for upright varieties and wide (30 inch) row spacing. Control
rust. Use maneb or chlorothalonil fungicide when rust first broad-leaved weeds.
appears. Early detection of rust and early application of
fungicide is essential to rust management.
Remarks. Some varieties have shown resistance to the ALTERNARIA BLIGHT, Alternaria sp.
common races of rust, but races have changed recently Symptoms. Irregular brown lesions develop on the leaves.
(1996). Many rust races are present in North Dakota, and The spots often have light tan to whitish centers and dark
the dominant races may change from time to time, adversely purplish to black margins. After moist periods, the under-
affecting the resistance of certain varieties. Continued sides of lesions are covered with a black fuzzy growth
monitoring for rust is essential. (the spores). The lesions tend to tear, giving severely
affected leaves a tattered appearance.
Survival and Spread. Little is known, but the disease
WHITE MOLD (SCLEROTINIA ROT),
appears to be most severe after hailstorms or other
Sclerotinia sclerotiorum
wounding. Observations suggest that Alternaria may
Symptoms. A watery soft rot develops on pods, stems also infect the plant through bacterial brown spot lesions.
and foliage. First symptoms usually appear after flowering.
Control. Unknown.
The rotting areas develop a cottony white growth in wet
13Bacterial Survival and Spread. See common blight. Favored by
cool rainy weather.
COMMON BLIGHT, Xanthomonas campestris Control. See common blight. Copper fungicides will
pv. phaseoli suppress spread of halo blight, but are of little value
Symptoms. Large irregular patches of necrotic, brown against common blight. Pinto and navy beans have
tissue form, frequently at the edges of the leaves. Common some resistance to halo blight.
blight lesions on young foliage often have a narrow lemon
yellow border surrounding the dead tissue. Heavily infected
plants appear scorched. Dark greasy-green water soaked BROWN SPOT, Pseudomonas syringae pv.
spots form on the pods. In wet weather a yellow bacterial syringae
ooze forms on the spots; later this ooze dries to form a
Symptoms. Small (1/16-1/8 inch) chocolate-brown spots
yellow flaky surface which glistens in the sunlight. As the
form on leaves. The lesions are often surrounded by a
pod lesions age, they become sunken and develop a brick
narrow greenish yellow band and resemble warm-weather
red border. White bean seeds infected with common blight
halo blight symptoms when no large halos form. Symptoms
turn a butter-yellow color. Stem lesions are dark red; lesions
on stems and pods resemble those of common blight,
may girdle the stems and cause the plant to break.
except that any bacterial exudate which forms on the pods
Survival and Spread. The common blight bacteria are is cream-colored.
seed-borne and survive in infected bean crop residue.
Survival and Spread. See common blight. Brown spot is
Severely infected seeds are shriveled and often do not
more serious in protected areas where plants dry slowly.
germinate. Lightly-infected seeds germinate to produce
stunted, internally infected plants that can lead to rapid Control. See common blight.
disease spread in wet weather. Spread occurs in splashing
water and wind-blown aerosols. Spread is favored by warm,
wet weather, driving rains, and windblown sand or hail Non-Infectious
followed by rain. Blight may also be spread by field
cultivation when the plants are wet. ZINC DEFICIENCY
Control. Purchase certified seed. Certified seed is not Symptoms. Older leaves turn yellow, especially between the
blight-free but must meet certain standards. If possible, veins, and dead areas may develop between the veins
purchase seed that has been tested for blight using the beginning at the margins and proceeding inward. New
dome test: a dome score of 4 is usually satisfactory (has leaves may be small and mottled. Plants may be stunted.
a moderate blight risk); a 3 is preferable (lower risk), if Zinc deficiency may occur on alkaline soils, especially on
available; a 5 has a moderately high risk and should be certain varieties of navy beans. High phosphate levels favor
avoided, if possible. Seed with a test of 6 or 7 should not zinc deficiency.
be used under any circumstance. Use a three- or four-year Control. Apply 0.4 to 0.8 lbs actual zinc per acre in a
crop rotation. Treat seed with streptomycin to eliminate chelated form, or 3 to 6 lbs in inorganic form, where soil
surface bacteria. tests are low in zinc. If zinc deficiency symptoms develop
after emergence, the problem can be corrected by applica-
tion of 0.2 lbs. actual zinc per acre as a foliar spray. Prompt
HALO BLIGHT, Pseudomonas syringae pv. detection and treatment are essential for satisfactory results.
phaseolicola
Symptoms. Small (1/16-1/8 inch) chocolate-brown spots
form on leaves. In warm weather, these spots resemble BRONZING
bacterial brown spot. In cool weather, when temperatures Symptoms. Upper leaf surfaces are covered with small
are less than 70°F, the halo blight bacteria produce a toxin golden-brown spots which make the leaf appear bronze
that causes a light green halo to form around each spot. in color. Bronzing is caused by ozone from industrial or
These halos vary from 3/8 to 3/4 inch in diameter. Some- urban pollution or meteorological phenomena.
times the toxin is transported to the upper parts of the plant,
which turn greenish-yellow. Symptoms on stems and pods Control. None available.
resemble those of common blight, except that any bacterial
exudate which forms on the pods is cream-colored.
PBPod and Seed Diseases ______ ▼ Soybeans
Bacterial
COMMON BLIGHT, Xanthomonas campestris
Stem and Leaf Diseases______
pv. phaseoli Fungal
See description under Dry Edible Beans — Stem and Leaf
Diseases. SCLEROTINIA STEM ROT (WHITE MOLD),
Sclerotinia sclerotiorum
Symptoms. Often occurs as patches of plants that appear
HALO BLIGHT, Pseudomonas syringae pv. dead or slightly shorter due to lodging. Base of stem on
phaseolicola affected plants may be rotted or the upper stem can be
See description under Dry Edible Beans — Stem and Leaf infected. Tufts of white mold are common on stems and later
turn into hard black fungus bodies (sclerotia). Sclerotia form
Diseases.
inside and outside the stem. Leaves wilt or else are covered
with white mold. This is an increasingly common disease.
BROWN SPOT, Pseudomonas syringae pv. Survival and Spread. Sclerotia survive many years in soil
syringae and also can be spread with seed. In wet weather, over-
wintered sclerotia produce wind-borne spores that infect
See description under Dry Edible Beans — Stem and Leaf
dead blossoms.
Disease.
Other Crops Affected. Dry edible beans, field peas,
garbanzo beans (chickpeas), lentils, mustard, potatoes,
Root Diseases______________ rapeseed (Canola), safflower, and sunflower. Flax and
buckwheat are only rarely attacked. Cabbage, cucumbers,
melons and tomatoes also are susceptible.
Fungal
Control. Crop rotation — avoid highly susceptible crops
ROOT ROT, Fusarium spp., in the rotation. Some cultivars are less susceptible than
Rhizoctonia solani, and other fungi others. Use clean seed free of sclerotia. Solid seeding
favors disease. Reduce overhead irrigation during flowering.
Symptoms. Severely infected plants are stunted, wilted, and
have yellow leaves. Seedlings may damp off. Rhizoctonia
usually makes reddish-colored lesions on the roots. Heavily
STEM CANKER,
infected roots (hypocotyls) appear dry and rough and a
chocolate-colored rot may progress up the pith. Fusarium Diaporthe phaseolorum var. caulivora
causes elongated lesions without definite margins. Often Symptoms. Seldom found in North Dakota. Brown canker
the roots (hypocotyls) turn entirely brown in color. Fusarium forms above the soil line. Plants may be girdled before
seldom extends beyond the soil line. leaves mature. Leaves dry up and remain attached. Symp-
toms appear late in season as the crop approaches maturity.
Survival and Spread. Soil-borne. More common in soils
that have been planted to dry edible beans for many years. Survival and Spread. Seed-borne. Survives in soybean
Conditions such as drought or saline soils that prevent crop residue, producing wind-borne spores that infect
lateral root development intensify the symptom expression. new crop.
Control. Use long rotations. Hilling moist soil around the Control. Use disease-free seed and crop rotation.
base of the plant can stimulate lateral root development. Plow residue after harvest.
Avoid soil compaction. Plant tolerant varieties in fields with
a history of root rot. Avoid short rotations of sugarbeets and
dry beans, especially in fields with a history of Rhizoctonia POD AND STEM BLIGHT,
root rot in dry beans or Rhizoctonia disease in sugarbeets. Diaporthe phaseolorum var. sojae
Symptoms. Rows of dark fruiting bodies occur on stems
and are scattered on pods. Develops late in season on
senescent or dead tissue. Infected seed is cracked, often
with a white fungal growth.
15Survival and Spread. Seed-borne. Survives on soybean Bacterial
crop refuse. Spores can infect through wounds. Favored
by warm wet weather in late summer. BACTERIAL BLIGHT,
Control. Use fungicidal seed treatment, disease-free seed Pseudomonas syringae pv. glycinea
and crop rotation. Bury infected soybean stubble by tillage. Symptoms. The most common leaf disease in North
Dakota, but of minor importance. Leaves develop small,
angular water-soaked spots that become brown with a
BROWN STEM ROT, Phialophora gregata yellow border. Portions of the leaf tissue drop out. Black
( = Cephalosporium gregatum) lesions develop on the stem. Small water-soaked spots
develop on pods; the spots enlarge and become black;
Symptoms. A rare disease in North Dakota. Red-brown
seeds are shriveled.
discoloration develops in the stem pith, at first near the
soil line and at the nodes. Infected plants turn brown just Survival and Spread. Seed-borne. Overwinters in crop
before maturing (normally maturing plants turn yellow- residue. Spread by driving, splashing rain. Favored by cool
green). Infected plants may lodge. On leaves, brown areas temperatures and windy rain storms. Attacks only soybean.
occasionally develop between the veins.
Control. Plant high quality seed. Use crop rotation. Use
Survival and Spread. Survives in soil and soybean crop tillage to bury crop refuse when feasible. Do not cultivate
refuse. Occasionally seed-borne. Fungus invades through plants when wet.
roots. Favored by cool weather.
Control. Crop rotation: avoid alfalfa, red clover or soybeans
for three years. Virus
SOYBEAN MOSAIC, Soybean Mosaic virus
BROWN SPOT, Septoria glycines Symptoms. Not common in North Dakota. Leaves are
mottled green and yellow; small veins turn yellow. Leaves
Symptoms. Angular reddish-brown spots develop, starting
become crinkled in cool weather. Entire plant becomes
on lower leaves; affected leaves turn yellow and drop off.
stunted and yellow. Seed hilums may “bleed” and entire
A common disease in North Dakota but losses are seldom
seeds may be mottled brown or black. Some leaf symptoms
significant.
may be mistaken for 2,4-D injury.
Survival and Spread. Overwinters in soybean crop residue.
Survival and Spread. Seed-borne. May overwinter in
Seed-borne. Spread by wind and splashing rain. Develops
perennial weeds. Transmitted by aphids and by mechanical
during warm wet weather.
contact.
Control. Plant disease-free seed. Use crop rotation.
Other Crops Affected. Some other legumes, weeds.
Use tillage to bury crop refuse.
Control. Plant disease-free seed. Control weeds and aphids.
Rogue out infected plants from seed fields.
DOWNY MILDEW, Peronospora manshurica
Symptoms. This disease is fairly common in North Dakota
when summers are humid but is rarely serious. First symp-
Non-Infectious
toms are indefinite yellowish-green areas on the upper leaf
IRON CHLOROSIS, Iron deficiency
surface. Later, the spots turn gray-brown with yellow-green
margins; a downy gray growth forms on the under surface Symptoms. This extremely common problem is most
of lesions. A whitish crust develops on seed. prevalent in early to midseason. Plants are stunted with
yellow leaves and green veins. A few scattered plants may
Survival and Spread. Seed-borne. Overwinters in soybean be affected or large circular patches may develop. Appears
crop refuse. Spread by wind-borne spores. Favored by cool, on highly alkaline soils; it is more common when cool, wet
humid weather. Early infection from seed produces systemic weather follows seedling emergence.
invasion.
Control. Plants generally recover naturally. Sprays with
Control. Plant disease-free seed. Use fungicidal seed an iron chelate can overcome the deficiency. Varieties
treatment. Use crop rotation — one or more years out of differ in sensitivity to iron chlorosis. Check current variety
soybeans. Use tillage to bury crop refuse. Varieties differ recommendations for variety sensitivity.
in resistance.
PBwater-logged soils in warm weather. Symptoms appear in
Pod and Seed Diseases ______ seedlings and adult plants.
Fungal Survival and Spread. Soil-borne, mostly associated with
heavy soils and low spots in the field. Attacks throughout
POD AND STEM BLIGHT, the season. Survives many years in soil.
Diaporthe phaseolorum var. sojae Control. Resistant varieties. Determine the Phytophthora
See description under Soybeans — Stem and Leaf Disease. race present before selecting a resistant variety. Use seed
treatment with metalaxyl when planting resistant varieties
in high risk situations; metalaxy protects the seedling until
PURPLE STAIN, Cercospora kikuchii mature-plant resistance is expressed. Plant in warm
well-drained soil.
Symptoms. A rare disease in North Dakota. Seed is
discolored pink to purple, in small spots or on the entire
seed. Infected leaves have angular, crusty, dark spots. PYTHIUM ROOT ROT, Pythium spp.
Survival and Spread. Survives in crop refuse and in seed. Symptoms. Seedling decays before or after emergence
Spores are wind blown and splashed from infected seed- (called “damping off”). Seed may decay in soil. Roots
lings. Favored by warm, humid weather. develop a brown wet rot, causing the plant to wilt. This
Control. Crop rotation. Plant high quality seed. Fungicidal is a common disease problem.
seed treatment helps prevent seedling loss. Survival and Spread. Soil-borne. Usually occurs in low
areas of the field. Favored by cold, wet soil.
Other Crops Affected. Many.
Virus
Control. Fungicidal seed treatments, especially those
SOYBEAN MOSAIC, Soybean Mosaic Virus with metalaxyl, aid against seed decay and damping off.
See description under Soybeans — Stem and Leaf Use high quality seed and plant in warm, well drained soil.
Diseases.
RHIZOCTONIA ROOT ROT, Rhizoctonia solani
Root Diseases______________ Symptoms. A common and sometimes severe fungus
disease, especially on seedlings. Causes a reddish-brown
Fungal decay of the root and stem tissues. Plants are often attacked
early and can be girdled or killed. Usually occurs on a few
FUSARIUM ROOT ROT, Fusarium spp. scattered plants or groups of plants.
Symptoms. A common disease. Seedlings are stunted Survival and Spread. Soil-borne. Pathogen attacks a large
or damp off; adult plants show root rot. Dark brown to black number of broadleaved plants including soybeans, dry
lesions form on root and lower stem; plants may wilt in dry beans, flax, lentils, sugarbeet, and canola.
weather.
Control. Ridge soil up around base of plant to promote
Survival and Spread. Soil-borne. feeder roots from stem base. Fungicidal seed treatments
reduce seedling losses.
Control. Plant in warm, well drained soil. Do not cultivate
affected seedlings until adequate moisture is available.
Ridge soil up around base of plant to promote feeder roots
from stem base. Nematodal
Reduce soil compaction to promote root growth. SOYBEAN CYST NEMATODE,
Heterodera glycines
Symptoms. Not observed in North Dakota as of 1996, but
PHYTOPHTHORA ROOT ROT,
spreading in Minnesota and could develop in North Dakota
Phytophthora sojae within a few years. A potentially serious disease, plants are
Symptoms. Leaves turn yellow and wilt. Few lateral roots stunted and may have small pin-head sized cysts on roots.
form and a dark discoloration extends several inches up The cysts are white, later turning brown. Stunted plants
the stem from the root. Disease develops most rapidly on develop in elliptic or lens-shaped areas in the field with
the long axis parallel to the direction of major tillage.
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