| Biology | Damage description | Diagnosis | Management strategy
Barley
stem rust - Puccinia graminis f. sp. secalis, P. graminisf. sp. tritici
leaf rust - P. hordei
stripe rust - P. striiformis
Oats
stem rust - P. grammis f. sp. avenae
crown rust - P. coronata
Rye
stem rust - P. graminis f. sp. avenae
crown rust - P. coronata
Triticale
stem rust - P. graminis f. sp. tritici
leaf rust - P. recondita
Wheat
stem rust - P. graminis f. sp.. tritici
leaf rust - P. recondita
stripe rust - P. striiformis
Biology
Many species of rust affect barley, oats, rye, triticale, wheat and grasses. Each rust species includes a number of strains that differ only in their ability to infect certain host crop varieties. Both stem and leaf rust require two different unrelated host species to complete their life cycle. Stripe rust has no known alternate host.
Because the alternate hosts for stem and leaf rust are not found in Alberta, infectious spores must be blown in from rust-infected crops in the United States. These rust spores directly infect susceptible cereal crops. A single spore pustule on a cereal leaf or stem may produce millions of infectious spores, which can infect other susceptible cereals.
The stripe rust fungus occasionally overwinter in Alberta as the infectious brown spore stage on susceptible winter wheats such as Norstar. Infectious brown spores from infected winter wheat are able to infect susceptible varieties of soft white wheat earlier in the season, causing considerable damage.
Stem and leaf rusts may cause some infection late in the season, but they are of no consequence in the next year. This is because the brown summer infectious spores die on the crop residue and the black overwinter spores can only infect the alternate hosts, which do not exist in Alberta. The same situation holds true for the destructive QCC race of barley stem rust in Manitoba.
Damage Description
- Stem rust
Stem rust produces reddish-brown, elongated pustules on the stems, leaves, glumes, awns and kernels. These contain masses of brown spores. As the plant matures later in the season, the pustules produce black overwinter spores.
- Leaf rust
Leaf rust appears as small, round, orange pustules on leaves and leaf sheaths. As the plant matures, the pustules turn dark gray.
- Stripe rust
Stripe rust develops as elongated, yellow-orange pustules in rows of varying lengths. This gives the appearance of narrow yellow stripes mainly on the leaves and on the grain heads. These later become dark brown pustules, which produce the overwinter spores.
- Crown rust
Crown rust of oats is similar to leaf rust of wheat and barley except the pustules may be present on both sides of the leaves and on the glumes. These are later replaced by black pustules. On the Prairies this disease causes significant losses only in Manitoba.
Rusts, except for stripe rust which may overwinter on winter wheat, do not usually cause significant yield losses. This is because the rust spores arrive from the eastern prairies too late in the growing season to do much damage, except on susceptible late-seeded and late-tillering crops. Yield losses depend on the crops' growth stage at the time of infection and the amount of leaf tissue destroyed. Early infection of upper leaves, stems, and heads can cause high yield losses in the form of shrivelled grain, reduced baking quality and impaired germination. Serious damage from stem and leaf rust in most years occurs only in Manitoba and sometimes eastern Saskatchewan. Western Saskatchewan and Alberta usually escape losses from these rust diseases in both wheat and barley.
Diagnosis
Examine the crops at the milky ripe stage (see Feekes scale). Assess no less than 25 main tillers selected at random along two diagonals from one corner to the opposite corner of the field. Assess the percentage of first and second leaves affected. Take the average of the first leaf and the second leaf and apply it to the following formula. This will give you a reasonable estimate of expected crop loss from scald.
% yield loss = 2/3 x % area of flag leaf infected + 1/2 x % area of second leaf infected / 2
Management Strategy
Stripe rust
- Use resistant cultivars. There are two types of resistance to stripe rust: seedling resistance and adult plant resistance. Seedling resistance lasts for the life of the plant whereas adult plant resistance only develops between booting and heading. Disease progresses rapidly until adult plant resistance starts, then the advancement of the disease slows dramatically. No licensed varieties have this latter form of resistance.
- Seed early and use early maturing varieties that complete most of their development before being infected.
- Destroy alternate hosts for stem and leaf rusts to reduce inoculum levels.
- Do not plant susceptible spring cultivars near winter wheat fields that may be infected with stripe rust.
- Apply a foliar fungicide.
Stem nest on barley - new races? that have arisen in the U.S.A. oput the Manitoba barley crop at risk. Such rust moves annually into Canada but the fungus rarely makes it to Alberta in time to affect crop yields.
Crown rust of oats, rust-like particles on oat leaves. Disease occurs only in Manitoba and eastern Canada.
Black stem rust on oats. Rust is red at first becoming black at the end of the season (Manitoba and eastern Saskatchewan.)
Black stem rust aecia on barberry (Berberis spp) leaf. The aecia on this alternate host shrub release produces the spores that produce black stem rust specific to wheat, oats or barley.
Leaf rust on wheat - masses of brown spore producing pustules.
Wheat stem rust - red rust spores from pustules on stems and leaves that later produce the overwintering black spore (black rust). This black overwintering spre can only produce condia that will infect barberry (Berberis spp.) the following spring.
Stripe rust (Puccinia striiformis) on soft white wheat - overwinters on leaves of winter wheat in Alberta in some seasons.
Stripe rust - uredia (spore producing structures) arranged in distinct stripes.
Text and captions courtesy of Dr. Ieuan R. Evans
Images courtesy of I. R. Evans and WCPD |