Managing Cereal Leaf Diseases

The 1990s have been good years for cereal leaf diseases. Higher moisture levels and progressive farming practices have created ideal conditions for leaf diseases to overwinter, infect crops, then thrive within thick, lush cereal crop canopies, and ultimately reduce yields and grades. Intensive crop production to meet the demands of the expanding hog industry is also contributing to the risk of leaf disease infections by enhancing soil fertility and water holding capacity.

Cereal leaf diseases continue to hurt growers on two fronts: yield and quality. This factsheet outlines best management practices to help farmers manage cereal leaf diseases and minimize the threat they pose to yields and quality.

Did You Know...?
Cereal Leaf Disease Risk Factors
Fusarium Head Blight
Best Management Practices
The Significance of the Flag Leaf
Fungicides Registered for In-Crop Control of Cereal Leaf Diseases
What are Cereal Leaf Diseases Costing Growers?

Did You Know...? that if kernels in a sample of durum wheat have red smudge (the kernel discoloration caused by the tan spot fungus*), grade can be reduced to No. 4 or 5? This could cost you as much as $2/bu.
that on average scald lowers barley yields 10 percent and in severe infestations can cut yields by up to 40 percent?
that malt barley rejected for malting due to poor quality and reduced kernel size could take $0.75 to $1.00/bu. out of your pocket?
that if more than 5 percent of the kernels in a sample of red spring wheat have a stain caused by Septoria (the result of glume blotch, caused by the same fungus producing blotches on leaves), the grade is reduced to feed?

Note: Although the same pathogen causes tan spot and red smudge in wheat, a crop may have severe tan spot without any red smudge or a crop may have severe red smudge without significant tan spot on the leaves.

Cereal Leaf Disease Risk Factors

Weather: When growing conditions - particularly moisture in the form of rain - are "good" for crops, these same conditions are generally good for cereal leaf disease development. Cereal leaf diseases thrive under moist conditions, particularly within the crop canopy. Thick, lush crop canopies provide the ideal environment for cereal leaf disease build up and for that infection to spread throughout the crop.

High Humidity: Humid weather, without rain, also creates the moist conditions that can result in severe cereal leaf disease development.

Infected Seed: Some cereal leaf diseases pathogens survive on infested and infected seed. Always use seed from a reliable source. Planting certified seed, grown under required crop rotation, reduces the risk of introducing diseases into a field and lessens the potential of disease developing early in the growing season.

Continuous Cereals: Crop residue is a main source of infection because fungi (inoculum) overwinter on stubble chaff and straw. Disease inoculum can build up if wheat follows wheat or barley follows barley for several years in a row. Inoculum build-up can be reduced if crop residue is buried by tillage. However, on farms where minimum or zero tillage is practiced, such operations can be counterproductive.

Harrington, the premier malting barley variety, is very susceptible to scald and net blotch and is sometimes grown year after year - greatly increasing the risk and levels of leaf disease infection.

Cropping Practices: Minimum and zero tillage involving direct seeding are now preferred "sustainable" farming practices that help better preserve and replenish organic matter, prevent or reduce wind and water erosion, and conserve soil moisture. It is important to understand, however, that these practices result in higher levels of surface crop residue in which cereal leaf disease inoculum overwinters. Burying crop residue through cultivation physically prevents inoculum from reaching leaves and hastens decomposition. However, the benefits of these tillage practices generally out-weigh the risk of early disease development.

Similarly, increasing seeding rates and matching balanced fertility levels to high target yields produces lush crop canopies, an ideal environment for cereal leaf disease fungi to thrive.

Hog Production: The rapid growth of the hog production industry on the Prairies and in Ontario will require increased demand for hog feed. Intensive cereal production and higher yields to meet feed requirements for this growing industry will require sound disease management. Effective manure disposal will also become a challenge. Although hog manure can be spread onto fields prior to growing cereals, excessive manure applications coupled with high soil fertility may result in dense, lush crop canopies, ideal environments for leaf disease development.

Fusarium Head Blight

Although not a leaf disease, Fusarium Head Blight (FHB) is a serious disease in wheat and barley that is gaining in prevalence. Like cereal leaf diseases, the fungi causing Fusarium head blight survive in the straw and stubble left in farm fields, including corn stover and on cereal seed.

Fusarium damages the kernels, causing scab or tombstone can contaminate grain with DON (vomitoxin) leading to feed refusal in hogs. Rain, particularly during flowering (anthesis) followed by wet or humid conditions are ideal for severe disease development. Conservation tillage practices and continuous cropping of cereals, or growing cereals in rotation with corn, contribute to the risk of FHB.

At this time, the problem is centered in the Red River Valley of Manitoba and in Ontario. Like cereal leaf diseases, Fusarium Head Blight is costing wheat producers millions of dollars annually.

Best Management Practices

The following Best Management Practices are recommended by the Cereal Leaf Diseases Directorate (LeaDD) for effective control of leaf diseases in all cereal crops, especially high value barleys and both spring and winter wheats.

Scouting

Scout fields at and following flag leaf emergence to check for disease levels. Healthy flag and upper leaves are critical since more than 50 percent of grain filling is contributed by upper leaves (see Significance of the Flag Leaf ).

Crop Rotations: Rotate crops (wheat/oilseed/barley/pulse, for example) to reduce the build-up of disease inoculum in crop residue. If at all possible, do not follow wheat with with wheat or barley with barley. When a short rotation is absolutely necessary, seed in the second year a variety that is more resistant to an anticipated problem disease.

If you are a malt barley grower who plans to grow Harrington year after year on the same field, fungicides are critical as a preventative measure for cereal leaf diseases.

Clean Seed: Use certified seed and/or seed that has been treated with an appropriate fungicide to reduce the possibility of introducing seed-borne inoculum into a field.

Seed Treatments: Seed treatments together with quality seed help emerging crops by controlling most seed-borne disease and allowing the crop to get a good start (quicker, more uniform plant emergence and better seedling vigor). Seed treatments protect young plants against seedling diseases but do not prevent later infection by cereal leaf diseases. Another benefit of protecting crops with seed treatments is that this may prevent or reduce the introduction of new virulent strains of foliar fungi in more resistant varieties.

Vigilance: Be aware of what your neighbours are growing and what diseases might be problems in their crops. Be vigilant about what diseases are prevalent in your area because inoculum spores of leaf diseases are spread by wind and rain.

Resistant Varieties: Provincial crop/seed guides provide a comprehensive listing of the performance of adapted cultivars, including their resistance status to specific diseases. Consult the guides for information that is current, and applicable to your region. In general: 2-row barleys are more susceptible to cereal leaf diseases than 6-row barleys; malting barleys are more susceptible than feed varieties; and durum wheats are more susceptible to tan spot but generally less susceptible to Septoria than either hard red spring or Canada prairie spring wheats.

Below are a few examples of varieties that are resistant (note that resistance can vary from fair to very good). Consult your provincial crop/seed guides for more detailed listings.

Crop	Variety	Resistance Status / Disease
Barley	AC Lacombe, AC Oxbow, B1215, CDC Earl, Manley	fair/net blotch
	AC Sterling, Viking	very good/powdery mildew fair/leaf rust
	AC Stacey, CDC Dawn, CDC Guardian, Falcon, Kasota	good/scald
Oat	AC Assiniboia, AC Medallion, Triple Crown	very good/crown rust
Wheat	AC Cora, AC Domain, Invader, Kyle, Sceptre	very good/ leaf rust

Cropping Practices: Begin to scout fields prior to flag leaf emergence and continue to monitor crops for symptoms of leaf diseases appearing on the lower leaves. Keep in mind that conservation tillage, direct seeding and continuous cereals can lead to higher levels of crop residue on fields, providing a natural home for cereal leaf disease inoculum to reside, overwinter and infect next year's crops. Cultivation may bury 30 percent to 90 percent of this disease inoculum. Evaluate residue-management practices and if practicing reduced tillage, consider the use of a broad spectrum fungicide to control the spread of leaf diseases.

Foliar Fungicides: Foliar fungicides applied at the proper time in accordance with manufacturer's recommendations can control cereal leaf diseases and help to attain target yields.

Spraying Practices: For maximum effectiveness, foliar fungicides should be applied preventatively (when infection levels are low). Good spray coverage with minimal drift is essential. Ideally, the best time to spray is when the wind is calm; humidity is above 60 percent; and air temperature is between 10 and 25 degrees C.

Rusts: Leaf, crown, stripe and stem rust can only be properly managed with resistant varieties or the application of fungicides. Early seeding is one method to avoid and minimize damage from rust infections on susceptible varieties.

Rust inoculum arrives annually on southerly winds from the U.S. Airborne spores that infect more mature crops have less impact on yield than when infection occurs at earlier crop development.

A NOTE TO WINTER WHEAT GROWERS: The yield and harvesting advantages of winter wheat have made winter wheat production increasingly popular. Because winter wheat is currently more susceptible to diseases than spring wheat crops, these Best Management Practices to control leaf diseases are essential for winter wheat growers.

The Significance of the Flag Leaf

A cereal crop goes through several growth stages before it's ready to be harvested as grain. Among the more important stages are germination, emergence, tillering, heading, filling and ripening. Another important growth stage occurs when the flag leaf emerges.

Yield depends on the number of spikes (heads) per square meter and the number and size (plumpness) of kernels within the heads. Although all of the plant contributes nutrients required to fill the kernels, the flag leaf is particularly important. Up to 50 percent of the final yield of a what crop depends on the health of the upper leaf, particularly the flag leaf (the flag leaf and the penultimate leaf - or the top 2 leaves - in barley).

Because the flag leaf sits at the top of the crop canopy, it receives more sunlight than other leaves; it is also younger and more efficient in producing photosynthetic nutrients (carbohydrates) that are needed to fill the kernels.

If cereal leaf diseases infect or damage the flag leaf, its ability to manufacture carbohydrates is compromised. If the flow of these essential nutrients to the head is reduced, kernels do not fill properly - they are smaller and thinner, which lowers yield, quality and likely grade.

Cereal leaf diseases usually affect lower leaves first, then move up the plant to the flag leaf. Ensuring the flag leaf is not infected, or has a minimal level of infection, is essential to maximizing returns to cereal crop production.

Fungicides Registered for In-Crop Control of Cereal Leaf Diseases

Three fungicides are registered for control of fungal cereal leaf diseases: propiconazole (Tilt), a broad spectrum systemic fungicide, is registered for use on wheat, barley and oats; and mancozeb (Dithane DG-NT), a contact fungicide, is registered for use on wheat; chlorothalonil (Bravo) is another contact fungicide registered for use on wheat. The table below lists the diseases controlled by these fungicides and describes use.

Crop	Product Name	Diseases Controlled	Use
Barley	Tilt^®	Leaf rust, net blotch, powdery mildew, scald, spot blotch, stem rust and Septoria leaf blotch	Apply at a very early stage of disease development, anytime from beginning of stem elongation to before the head is half emerged. Best results have been achieved when Tilt^® is applied just when the flag leaf emerges. Conditions which favor a good crop are often the same conditions which favor leaf disease.
Oat	Tilt^®	Crown rust and Septoria leaf blotch	See barley above.
Wheat	Tilt^®	Leaf rust, powdery mildew, Septoria glume blotch, Septoria leaf blotch, stem rust, stripe rust and tan spot	See barley above.
Wheat	Folicur^®	Fusarium Head Blight	Apply when 25 - 50% of main stem heads are in early anthesis
Wheat	Dithane DG-NT^{® Rainshield}	Leaf rust, Septoria and tan spot	Apply Dithane between the 3-leaf and tillering stages, and/or after the head is fully emerged but before flowering.
Wheat	Bravo^®	Tan spot, Septoria glume blotch and Septoria leaf spot	Begin application at flag leaf emergence and repeat 10 - 14 days later when ears are visible. Apply again when ears are fully emerged and if necessary, should conditions favour disease spread.
Source: provincial crop protection guides ^®Tilt is a registered trademark of Novartis Crop Protection Canada Inc. ^®Dithane DG-NT is a trademark of Rohm and Haas Company, Philadelphia, PA. Registered in Canada under Rohm and Haas Canada Inc. Bravo^®is a registered trademark of Zeneca Agro, Winnipeg, MB Folicur^® is a registered trademark of Bayer Agro

What are Cereal Leaf Diseases Costing Growers?

Yields
Plant pathologists and disease experts with the Cereal Leaf Disease Directorate (LeaDD) provided broad estimates of the annual economic impact of yield losses due to cereal leaf diseases in the prairie provinces and Ontario.

Note: these conservative estimates take only yield losses into account. Any reduction in grain quality caused by cereal leaf diseases will make the loss even greater.

Alberta:
Based on a 10 year average, Dr. Ieuan Evans, Plant Disease Specialist with Alberta Agriculture, Food and Rural Development, stated that research data has measured the impact of cereal leaf diseases:

average yield losses of 10 - 15 percent in western and northern Alberta cereal crops (in dry years, losses can be less than 10 percent, while in cool, wet seasons losses can be 30 percent or higher in individual crops)
an average of $17.5 million in wheat income is lost annually due to reduced yields
an average of $97.5 million in barley income is lost annually die to reduced yields

Saskatchewan:
Based on the 1997 growing season, Mike Celetti, Plant Disease Specialist with Saskatchewan Agriculture, Food and Rural Revitalization, estimated:

cereal leaf disease affected approximately one third of the cereal crops grown in 1997
estimated average yield losses of 10 percent in affected wheat and 15 percent in affected barley crops
$49 million in wheat income and $24 million in barley income was lost due to reduced yields caused by cereal leaf diseases in affected acres.

Manitoba:
1997 surveys estimated:

average yields losses of 10 percent in wheat crops and 3 percent in barley
$56 million in wheat income and $5 million in barley income was lost die to reduced yields from cereal leaf diseases
this works out to an average of $8,500 in income lost in 1997 by each Manitoba farm family due to cereal leaf diseases (includes leaf spots and fusarium head blight)

Source: Dr. Andy Tekauz, Plant Pathologist, Cereal Research Centre, Agriculture and Agri-Food Canada
Dr. Gary Platford, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives

Ontario:
Based on a five year average, Dr. Arend Smid, Research Agronomist with Ridgetown College of Agricultural Technology, University of Guelph, estimated:

average yield loss of 15 percent annually in winter wheat crops
an average of $22.1 million in winter wheat income is lost annually due to reduced yields from cereal leaf diseases

Kernel Quality: Losses and Paybacks

Barley
The downgrading of malt barley from malting quality to feed poses significant economic consequences for barley growers.

Kernel plumpness is a key attribute of malt barley quality. Uniformity of sample and low protein levels are also characteristics that maltsters monitor with great care. Shriveled kernels are often the most striking example of reduced quality. That's why leaf diseases in barley, which diminish kernel plumpness, raise protein levels and detract from the uniformity of sample, are so costly.

Wheat
Similarly, reductions in the quality of wheat lowers grade and hurts producers' bottom line. In wheat, leaf diseases prevalent throughout the prairie provinces and Ontario, reduce wheat quality, bushel weight and number of kernels per head, as well as affecting kernel appearance. This cuts the return on the crop.

Payback
The payback from effective management of cereal leaf diseases in wheat and barley is an increased likelihood of malt barley quality, better bushel weights in feed barley and better grades in wheat. Ultimately, a better bottom line from cereal growers.

Disease	Prevalence	Symptoms	Cycle	Conditions Favorable
Net Blotch	Infections widespread on barley everywhere, attacks leaves, sheaths and glumes.	Net form appears first as light green blotches on leaves, later symptoms show longitudinal streaks in typical net-like pattern and streaks usually are surrounded by chlorotic area. Spot form appears as brownish oval spots similar to spot blotch.	Overwinters on barley straw and stubble and on infected seed, seedling infection from wind-borne spores or infected seed, spores can be ejected more than 20 feet.	High humidity and rainfall. Optimal temps for infection are 15 - 25 degrees C but infection is possible within range of 8 - 33 degrees C. Continuous barley cropping, conservation tillage practices, hardest on susceptible varieties.
Scald	Infections widespread on barley although rare in Manitoba.	Can infect leaves, stem, florets and awns, initially oval shaped, water soaked, grey-green colour, centre dries out and becomes bleached, straw coloured, outer margins remain distinct dark brown.	Overwinters on barley straw and stubble, spreads by splashing rain, infected seed may cause seedling infection, bromegrass is an alternate host.	High humidity and rainfall, temperatures ranging from 12 - 20 degrees C. Continuous barley cropping, conservation tillage practices, hardest on susceptible varieties.
Septoria Leaf and Glume Blotch	Widespread in wheat across prairies, can also infect some barley and oats.	Infection up to flowering stage, often mistaken for maturing, begins with chlorotic flecks on lower leaves, progresses to irregularly shaped lesions, black pepper-like dots sometimes in the infected area. May cause infection and discoloration on heads as well.	Overwinters on infected stubble and straw, volunteer cereal and seed, spores will thrive up to three years on undisturbed stubble, wheat principle host, barley, rye and some grasses also affected, spores spread mainly by rain and wind.	Humid, wet, windy weather, 15 - 25 degrees C, more than 6 hours of continuous moist conditions, continuous wheat cropping, conservation tillage practices.
Tan Spot	Infects wheat, common throughout prairies.	Begins as tan-brown flecks/spots on leaves, expands to tan coloured lens shaped lesions, usually lesions have dark brown spot in centre with yellow margin.	Overwinters on infected wheat straw or stubble, spores move primarily by wind, wheat is primary host, forage grasses and rye are alternate hosts, barley and oats are highly resistant to tan spot.	Humid, wet, windy, cool to warm weather, more than 6 hours of continuous moist conditions, continuous wheat cropping, conservation tillage practices.
Rusts (Leaf, Crown, Stripe, & Stem)	Rusts infect mainly wheat and oats - leaf rust of wheat and crown rust of oats in the eastern prairies and stripe rust of wheat in southern Alberta, stem rust in barley is a potential problem in the eastern prairies, wind patterns make some regions more prone to rust, leaf and stem rust rarely a problem in western Saskatchewan or Alberta.	Infections can spread rapidly, appear as pustules which break through plant surfaces, yellow or red pustules darken as the growing season progresses.	Requires living plant matter on which to overwinter, moves with trade winds. Leaf and stem rust spores almost never reach Alberta or Western Saskatchewan to be of any consequence. Stripe rust can occur in some years in both Alberta and Saskatchewan on winter and irrigated wheats.	Humid, windy weather, temperatures ranging from 10 - 20 degrees C, hardest on susceptible varieties.
Powdery Mildew	Infects spring and winter wheats and barley, especially significant problem in soft white spring wheat under irrigation.	Cottony white mildew pustules on leaves with undersides pale green or yellow, pustules turn brown with age, can move rapidly to infect entire plant, including head.	Overwinters on stubble, straw, volunteer cereals and winter wheat, spores move primarily by wind, very susceptible to humidity and weather changes.	Humid conditions, moderate temperatures from 15 - 22 degrees C, higher seeding rates and fertility practices which lead to lush canopies, more problem with high humidity and irrigation.
Spot Blotch	Infects barley and wheat but most severe on barley, increasingly common in south and central Saskatchewan. This is the same fungus that is responsible for common root rot in both wheat and barley.	Causes oval, solid brown spots closely resembling the spotted form of net blotch, surrounding tissue may turn yellow, when severe it kills entire leaves.	Overwinters on wheat and barley straw and stubble and on infected seed. Spores spread by wind in spring. Seedling infection especially common in cool temps.	High humidity and rainfall, temperature range from 15 - 25 degrees C. Continuous cereal cropping, conservation tillage practices.
N.B. Because control procedures differ considerably, infectious diseases such as seed-borne fungal leaf stripe and bacterial leaf stripe are not included above. Bacterial leaf stripe can occur in unusually wet springs, particularly in barley, and in fact, resembles fungal leaf stripe. Non infectious leaf diseases that may occur frequently on the prairies are grey speck or manganese deficiency in oats and barley, usually in high pH soils and genetic stippling or blotching, physiological disorders that are not uncommon on specific wheat and barley cultivars.

This factsheet deals with cereal leaf diseases caused by fungi, which have been especially prevalent on the prairies during the 1990s. There are other types of disease-causing organisms (bacteria and viruses, for example) and other foliar fungi of lesser importance which also infect cereal crops. Growers should be aware that symptoms on cereal leaves might be physiological or be caused by non-fungal organisms; growers should also consult local extension representatives for further advice on how to manage these diseases.

The production of this publication was made possible through the help and support of the members of the Cereal Leaf Disease Directorate and Novartis Crop Protection Canada Inc.

For further information, contact your GO representative.