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WHEAT STRIPE RUST

Robert L. Bowden
Extension Specialist, Plant Pathology

Stripe rust is caused by the fungus Puccinia striiformis. It is a serious problem on wheat in regions where cool temperatures prevail through the wheat growing season. It is especially prevalent in Europe and the Pacific Northwest of the USA. It is an occasional problem elsewhere, such as the Central Plains, during the early to mid- spring. It has been more common than usual in 1999, 2000, and 2001 crop years in Kansas

Symptoms

Fig. 1. Comparison of the three rusts of wheat.


leaf rust	stem rust	stripe rust (yellow rust)

Fig. 2. Different types of genetic reactions to stripe rust infection in different varieties or experimental lines.


Moderately Resistant (long brown lesions but few active pustules)	Moderately Susceptible (typical striped appearance with no browning)	Very Susceptible (stripes coalesced)
KS92-P0630 Exp	2137	KS89180B Exp

Symptoms of stripe rust are long stripes of small yellowish orange pustules on the leaves. These pustules consist of masses of rust spores. It can sometimes be confused with leaf rust or stem rust (Fig. 1). (Note that stem rust can occur on both the stems and the leaves of susceptible varieties.) Stripe rust also goes by the name of yellow rust because it is a slightly lighter color than leaf rust or stem rust.

Sometimes stripe rust symptoms are confusing on moderately resistant varieties because pustules may be hard to see or absent (Fig. 2). In that case, symptoms can resemble bacterial leaf streak (black chaff) or Septoria leaf blotch.

Disease Cycle

Wheat is the only significant host of the stripe rust fungus. There is a related form on barley but it appears to be unadapted to wheat.

Stripe rust over-summers on volunteer wheat. In the fall and winter it may develop in the southern U.S. near the Gulf coast on newly seeded wheat. In the spring, rust spores may blow north to the Central Plains. It is favored by cool, humid weather. Disease development is most rapid between 50 and 60 F. The disease is inhibited when night time temperatures get above 65 F or we have several days in a row in the mid 80's.

In Kansas, we seldom have a significant problem with stripe rust for several reasons. First, stripe rust apparently does not over-winter in Kansas so it must blow up from the south. In most years, there is not much stripe rust in Texas or Oklahoma. However, we have seen above average stripe rust in Texas in the springs of 2000 and 2001. Second, most of our varieties have good resistance to stripe rust. Third, hot weather in May usually puts a halt to the epidemic before significant economic damage occurs.

Losses

Resistant vs. Susceptible for Stripe Rust on wheat

Fig. 3. Susceptible line (right) with severe stripe rust infection compared to resistant variety (left).

Stripe has the potential to cause losses of 40% or more if the variety if very susceptible and the stripe rust moves in early (Fig. 3). However, losses due to stripe rust in Kansas are normally too low to estimate. The largest historical loss estimate was in 2000 when the losses were estimated at 0.05% of the crop, which translates to about $500,000 statewide.

Control

Control of stripe rust is through use of resistant varieties. Fortunately, most varieties in the Central Plains have good resistance. There are some exceptions. 2137, 2163, Custer, Hondo, Lakin, Oro Blanco, Triumph64, and TAM302 are moderately susceptible. Trego, Venango, and 7853 are intermediate. Jagger is resistant. Breeding lines that are extremely susceptible, such as KS89180B Exp (Fig. 3), are usually discarded. Foliar fungicides are essentially never used for stripe rust in Kansas. However, Tilt, Quadris, and Stratego fungicides are all labeled for control of rusts, including stripe rust. Stratego has an early cut-off (flag leaf emergence), but Quadris and Tilt can be applied through fully headed in Kansas. Quadris should be applied prior to disease infection, but Tilt has some kick-back activity.

In the 2001 crop year, fungicides were applied in parts of Texas as a rescue treatment for stripe rust. On May 7, 2001, severe stripe rust was reported in some fields in southern Kansas. Although, warm weather will eventually stop the stripe rust epidemic, it may be cost-effective to spray seed production fields of susceptible varieties in order to protect the flag leaf if it can be done promptly.

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4/06/01 RLB