Diseases of Wheat - Fungal

 
 
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 Black Point/Kernel Smudge | Common Bunt | Common Root Rot | Ergot | Fusarium Head Blight (Scab) | Leaf Rust | Loose Smut | Powdery Mildew | Speckled Leaf Blotch | Glume Blotch | Spot Blotch | Stem Rust | Stripe Rust | Take-All | Tan Spot | Red Smudge
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Black Point/Kernel Smudge
Alternaria alternata, Cochliobolus sativus

What to look for?
This is discoloration of the germ end of the wheat grain. In the commercial grading system, black point involves the germ end only and not extended into the grain crease. If more than half the grain is damaged and well into the crease, it is classified as smudge. Warm humid or wet weather during grain maturation usually late in August is generally the cause.

In addition to the above fungal pathogens, the tan spot fungus which causes red smudge in durum wheat, other fungi and even a bacterial infection such as Pseudomonas spp. may be involved in this disease.

Black point and smudge damaged wheat.
Photo: Duczek
Picture description
Black point and smudge damaged wheat.
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Management strategy
Fungicides may decrease the incidence of disease.

Common Bunt
Tilletia caries, Tilletia foetida

What to look for?
Bunt balls are roundish and break open to reveal masses of black telliospores that have a strong fishy odor that also blackens the grain.

Bunt spores can be blown to adjacent fields where they remain viable for a year or so. They can as soil-borne spores infect winter and spring wheat. As little as a 1 - 2% bunt infection will degrade bread wheat to feed status--both the odor and blackening of the white flour is unacceptable.

Infected heads such as on the left only stand out at maturity.
Photo: Duczek
Picture description
Infected heads such as on the left only stand out at maturity.
Healthy wheat, left and bunt balls, right.
Photo: Duczek
Picture description
Healthy wheat, left and bunt balls, right.
. Bunt balls, infested wheat grains and bunt-free wheat.
Photo: Evans
Picture description
Bunt balls, infested wheat grains and bunt-free wheat.
. Dirty Thirties - a heavily bunted crop of wheat taken 70 years ago. Both bunt species are very similar and will attack rye, triticale and several grass species as well as wheat.
Photo: Unknown
Picture description
Dirty Thirties - a heavily bunted crop of wheat taken 70 years ago. Both bunt species are very similar and will attack rye, triticale and several grass species as well as wheat.

Management strategy
Clean seed, fungicidal seed treatment and crop rotation are highly effective controls.

A more complete description of common bunt.

Common Root Rot
Cochliobolus sativus, Fusarium spp.

What to look for?

Sometimes called seedling blight, crown rot and foot rot. The fungus, primarily Cochliobolus sativus, can also attack the lower leaves and in wet season the upper leaves where it is called spot blotch. These are both barley and wheat infecting strains of Cochliobolus. Look for brown lesions on the crown and sub crown internodes.

Severe root rot causing plant death.
Photo: Duczek
Picture description
Severe root rot causing plant death.
Note browning of the crown and subcrown internode.
Photo: Tinline
Picture description
Note browning of the crown and subcrown internode.

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Management strategy
This disease is most prevalent under poor fertility or unbalanced fertility when wheat follows wheat. Seed treatments followed by adequate balanced fertility of nitrogen, phosphate, potash and sulphur along with the addition of copper fertilizer might greatly reduce the import of this disease.

A more complete description of common root rot.

Ergot
Claviceps purpurea

What to look for?
In almost all instances the appearance of ergot in wheat indicates copper deficiency, Copper deficiency is also the most common cause of frosted bran and greatly reduced yields up to 70% of the Canadian prairie cropland.

The original source of ergot that infests the wheat crop is usually from the open-pollenated wild grains that grow along the headlands. Nectar feeding insects primarily flies, play a major role in ergot infection in grain fields. Ergots are toxic and poisonous.

Low to deficient copper levels result in pollen sterility leading to the normally closed self-pollinated wheat flowers, which have receptive stigmas, to open and expose them to ergot infection. Male sterile wheats, barley, and oats for use in plant breeding are abject failures due to huge ergot infection levels in the male sterile plants. Several wheat herbicides may greatly enhance copper deficiency in wheat is a mechanism well recorded but not understood. Severe drought, July frosts may in some instances cause pollen failure also leading to ergot infection in wheat and other grains to levels of ergot infestation.

Ergots on wheat head.
Photo: Tekauz
Picture description
Ergots on wheat head.
Ergot and wheat grain.
Photo: Tekauz
Picture description
Ergot and wheat grain.

Management strategy
See under copper deficiency in both wheat and barley.

A more complete description of ergot.

.Fusarium Head Blight (Scab)
Fusarium graminearum, other Fusarium spp.

What to look for?
There are five or more species of Fusarium that can cause head blight in wheat and other cereals. Crown and root tissues may also be affected but only grain infection by F. graminearum is of real consequence. F. culmorum may also induce toxins in some instances such as on soft white wheat crops in southern Alberta. Only laboratory diagnoses can effectively distinguish between these various species of Fusarium.

Early seedling infection kills off the plants. Grain corn producing areas have huge levels of Fusarium spores since the huge quantities of leftover corn stover, in wet seasons, is a major food host for this fungus. The disease is most destructive when wheat and other small grains are grown in grain corn areas. In silage corn production the "stover" is removed from the field and therefore not a major source of Fusarium spore production.

Severe head blight.
Photo: Martin
Picture description
Severe head blight.
Fusarium infected wheat head.
Photo: Tekauz
Picture description
Fusarium infected wheat head.
The orange coloured sporodochia (left) produce abundant spores which spread to other wheat heads during the growing season.
Photo: Tekauz
Picture description
The orange colored sporodochia (left) produce abundant spores which spread to other wheat heads during the growing season.
Fusarium damaged kernels at levels greater than 2% are unfit as food or feed for monogastrics. Higher infection levels may be used as cattle feed.
Photo: Martin
Picture description
Fusarium damaged kernels at levels greater than 2% are unfit as food or feed for monogastrics. Higher infection levels may be used as cattle feed.
Infected wheat heads may produce shrivelled grain referred to as Fusarium Damaged Kernel (FDK).
Photo: Cooke
Picture description
Infected wheat heads may produce shrivelled grain referred to as Fusarium Damaged Kernel (FDK). Many of these kernels may be so shrivelled as to be blown out the back of the combine during harvesting. While reducing yield this may reduce the infection level in wheat. In infected barley or oat kernels this "blown-out" effect does not happen. In the US, this disease is referred to as tombstone or scab.
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Management strategy

Fusarium Head Blight of Barley and Wheat (Agdex 110/632-1) has a comprehensive management strategy.

A more complete description of fusarium head blight.

Alberta Fusarium graminearum Management Plan

Fusarium FAQ

Leaf Rust
Puccinia recondita (P. triticina)

What to look for?
A common disease of wheat that occurs very late in the season in Alberta. Initially, leaves are covered with orange pustules with urediniospores that eventually darken due to the formation of black telliospores. This disease does not overwinter in Alberta and has to move in every year from the United States.

Masses of orange urediniospores on the leaf surface.
Photo: Duczek
Picture description
Masses of orange urediniospores on the leaf surface.

Management strategy
It is a disease of little consequence due to its late arrival every year in this province.

A more complete description of leaf rust..

Loose Smut
Ustilago tritici

What to look for?
Loose smut of wheat is of common occurrence though usually at very low infection levels, but some wheat cultivars are very susceptible. Infection occurs at flowering when spores germinate and grow into the wheat grain and establishes itself in the developing embryo. Smut infected heads of wheat emerge before the healthy wheat heads. This allows the smutted head to break open and scatter black smut spores over healthy heads of wheat. Within a week or so, all that remains is a bare rachis (head) that is almost invisible in the wheat crop.

Loose smutted wheat head.
Photo: Duczek
Picture description
Loose smutted wheat head.

Management strategy
Systemic seed treatment and resistant varieties give very good control of this disease. The world's first ever plant systemic fungicide, specifically Carbathiin (marketed as Vitavax) was developed by an Albertan (Dr. Marshall Kulka from Smoky Lake for the Uniroyal Chemical Company to control loose smut in cereals) some 40 years ago at Elmira, Ontario.

A more complete description of loose smut..

Powdery Mildew
Erysiphe graminis

What to look for?
Powdery mildew affects wheat, barley and grasses in cool dry seasons. Western wheats are for the most part resistant to this fungus and it's various races.

Powdery mildew of wheat is specific to wheat and does not affect other cereals or grasses. Powdery mildew is most obvious on the lower leaves. In Eastern Canada, this disease can cause serious losses where systemic seed treatments and foliar fungicides have been used for disease control.

Light mildew infection.
Photo: Davidson
Picture description
Light mildew infection.
Heavy mildew infection.
Photo: Evans
Picture description
Heavy mildew infection.

Management strategy
No control procedures are generally needed in western Canada..

A more complete description of powdery mildew.

Speckled Leaf Blotch
Septoria avenae f.sp. tritici, S. nodorum

What to look for?
Septorias and Stagonospora species commonly occur on wheat and other small grains. Leaf lesions typically develop on the lower leaves as yellow, whitish or brown patches.

Disease severity is normally low but under wet or humid conditions, upper leaves and the heads of wheat may be affected.

Speckling of lower and upper wheat leaves.
Photo: Davidson
Picture description
Speckling of lower and upper wheat leaves.

Management strategy
Crop rotation and foliar fungicides will give control.

A more complete description of speckled leaf blotch.

Glume Blotch
Septoria nodorum or Stagonospora nodurum

What to look for?
Abundant conidia may be produced on the glumes and leaves in wet Augusts. No cultivars are resistant but disease prevalence is greater under conventional tillage than reduced tillage.

Septoria infection of the glumes.
Photo: McFadden
Picture description
Septoria infection of the glumes.

Management strategy
Rotations and foliar fungicides are effective controls.
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A more complete description of glume blotch.

Spot Blotch
Cochliobolus sativus

What to look for?
Spot blotch occasionally occurs on wheat under wet growing conditions, particularly when wheat is grown after wheat. This disease is much more severe in barley.

Diffuse brown blotches on middle and upper leaves. In some instances the glumes may be infected.
Photo: Tekauz
Picture description
Diffuse brown blotches on middle and upper leaves. In some instances the glumes may be infected.
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Management strategy
Crop rotations and foliar fungicides give good disease control in high yielding crops.
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A more complete description of spot blotch.

Stem Rust
Puccinia graminis f.sp. tritici

What to look for?
Stem rust or black stem rust is a major disease problem in Eastern Canada and the Eastern prairies. The disease either originates in the US or occasionally locally from wild susceptible barberry (Berberis sp) plants, the essential alternate host of this destructive fungus. In the Western prairies, we have no alternate hosts (barberry) and the inoculum from the US and Manitoba arrives too late in the season to be of any consequence in most years.

Heavy infection of the leaves by the red uredinial spore stage of the fungus.
Photo: Duczek
Picture description
Heavy infection of the leaves by the red uredinial spore stage of the fungus.
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Management strategy
Only once in 35 years has stem rust arrived in Alberta and caused some damage to the wheat crop. Consequently, in this province we can grow all stem rust susceptible small grain cereals with relative impunity.

A more complete description of stem rust.

Stripe Rust.
Puccinia striiformis

What to look for?
This is a sporadic disease of winter wheat in Alberta from whence it moves to spring wheat where it may be much more destructive. The fungus does not seem to have an alternate host typical of rusts. It overwinters in the US on winter wheat and some grasses. In mild Alberta winters it can overwinter on winter wheat. It can spread rapidly in May and June in the winter wheat and directly onto spring wheat. Losses in these occasional years can be significant.

Stripe rust in winter wheat.
Photo: Degenhardt
Picture description
Stripe rust in winter wheat.
Very distinct rust stripes on wheat. Disease can also occur on barley.
Photo: Evans
Picture description
Very distinct rust stripes on wheat. Disease can also occur on barley.

Management strategy
Fungicides provide good control.
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A more complete description of stripe rust.

Take-All
Gaeumannomyces graminis var. tritici

What to look for?
Take-all can be very destructive on spring and winter wheats, and occasionally on barley, oat and rye. Severely diseased plants produce whiteheads that may resemble Fusarium infection or wheat stem maggot infestations. Whole plants are infected often in small to large patches whereas these other look alikes infect only single stems.

Black shiny lower stems and subcrown internodes gives this disease it's other name--charcoal root rot. In the growing season, mycelia or runners move from plant to plant. The fungus overwinters as mycelium in or on crop residue and quackgrass rhizomes.

Take-all infected crowns.
Photo: McFadden
Picture description
Take-all infected crowns.
Common root rot on right, take-all on left.
Photo: Evans
Picture description
Common root rot on right, take-all on left.

Management strategy
Unbalanced fertility, wet growing conditions in alkaline soils greatly contribute to disease build-up. Soils around pH5.5 are much less conducive to this disease. In the case of neutral or alkaline soils when wheat is grown continuously, there is a build-up of microbial antagonists in the soil that suppresses the take-all fungus. Soils deficient in copper may result in severe lodging of the wheat crop giving a condition that resembles take-all but the wheat roots remain healthy. Copper is essential in wheat for lignin formation that gives the plant straw strength. The availability of manganese in the soil appears to play a significant role in the build-up and severity of this take-all disease. Where take-all is a significant problem grow wheat only every third or fourth year.

A more complete description of take all.

Tan Spot
Pyrenophora tritici-repentis

What to look for?
Tan spot is prevalent in cold wet springs when typical distinct tan spots appear on seedling leaves. The fungus overwinters on crop residue from whence ascospores are produced. Conidia may then be produced on older leaves leading to infection build-up. Under hot dry conditions, this disease may disappear from the crop.

Distinct tan spots on seedling leaves.
Photo: Duczek
Picture description
Distinct tan spots on seedling leaves.

Management strategy
If disease continues to build-up a foliar fungicide may be needed.

A more complete description of tan spot.

.Red Smudge
Pyrenophora tritici-repentis

What to look for?
When heads are infected by this tan spot fungus in bread wheats, black point may develop in the grain. In durum wheat, this head infection from the tan spot fungus can result in red smudge on the grain. Red smudge greatly downgrades the value of the harvested grain due to the distinct red smudge on the kernels. Late season rainfall, irrigation and warm moist weather favor smudge development.


Photo: Cooke
Picture description

Management strategy
Crop rotation and foliar fungicides can give effective disease control.

See Controlling Wheat Diseases in Direct Seeding Systems for more information on controlling diseases of wheat.

Photographs and information assembled and prepared for ARD by Dr. Ieaun R. Evans Agri-Trend Agrology Ltd.
 
 
 
 

Other Documents in the Series

 
  Diseases of Wheat - Fungal - Current Document
Diseases of Wheat - Non-Infectious
Diseases of Wheat - Viral
 
 
 
 
This document is maintained by Shelley Barkley.
This information published to the web on December 8, 2003.
Last Reviewed/Revised on March 14, 2008.