ITEMS FROM THE UNITED STATES

MINNESOTA

CEREAL DISEASE LABORATORY
(formerly CEREAL RUST LABORATORY)

USDA-ARS, University of Minnesota, 1551 Lindig, St. Paul, MN 55108, USA.

www.cdl.umn.edu

D.L. Long, J.A. Kolmer, Y. Jin, M.E. Hughes, and L.A. Wanschura.

Wheat Rusts in the United States in 2003. [p.238-248]

Wheat stem rust. The first reports of wheat stem rust in 2003 were in mid-April, when trace amounts were found in a plot of the susceptible cultivar McNair 701 in southern Texas at Uvalde. By late April, wheat stem rust was severe in plots of McNair 701 and Chinese Spring at Uvalde. In mid-May, late developing tillers provided good niches for the stem rust to develop in southern Texas. During late May, traces of stem rust were found in a plot of the susceptible cultivar McNair 701 in north central Oklahoma. In late May, stem rust was found in late maturing lines in the nursery at Baton Rouge, LA. Wheat stem rust was very light throughout the southern U.S. in 2003.

By mid-July, traces of wheat stem rust were observed on the susceptible spring wheat cultivar Baart in south central Minnesota plots. In late July, trace-20 % stem rust severities were observed on Baart and Max in southeastern North Dakota. Trace-30 % severities were observed on Baart in northwestern and north central Minnesota. Up to 30 % severities were observed on the winter wheat cultivar Norstar in northeastern North Dakota. The incidence of wheat stem rust infections was lighter than normal in the northern Great Plains this year, because little wheat stem rust developed in the southern and central U.S. All of the current spring wheat cultivars and most of the winter wheat cultivars are resistant to the current stem rust race population.

Wheat stem rust race virulence. Race QFCS was the most common stem rust race identified from collections made in the U.S. in 2003 (Table 1). Although this race was frequently found in surveys in previous years, it has become the predominant race on susceptible wheat, barley, and wild barley (Hordeum jubatum) in 2003. Race QFCS has virulence on Sr5, 8a, 9a, 9d, 9g, 10, 17, and 21. Several HRWW and soft wheats were found to be susceptible to QFCS based on seedling tests, including Thunderbolt, Onaga, Ankor, Nufrontier, Lakin, Truman, Roane, and Additions. However, the majority of wheat cultivars grown in the United States are resistant to race QFCS.

Wheat leaf rust. Southern Plains. In mid-February, light amounts of leaf rust were found on wheat in the central and Rolling Plains areas of Texas. The most severe rust was on the cultivar Jagger. In early March, wheat leaf rust development was slowed in central Texas plots, because of the cool temperatures in late February. The most severe rust was in border rows of TAM 110 where 10-20 % severities were observed on the lower leaves. In early-April, leaf rust infections were light in wheat fields and were at high levels on susceptible cultivars in nursery plots in southern and central Texas. In the last week of March in southern and central Texas, leaf rust severities up to 60 % were on the lower leaves of cultivars in breeding nurseries and trace-10 % severity levels were on the lower leaves in fields. The dry and cool weather in late March and early April contributed to the slow leaf rust development in the southern U.S.

In mid-April, even with the dry conditions, leaf rust was increasing throughout Texas, but overall rust severities were lighter than normal for this time of the year (Fig. 1). In a central Texas nursery on the susceptible cultivar Jagger, the leaves were completely dead because of the rust. In mid-April, leaf rust was increasing in southern Oklahoma on susceptible cultivars. In early May, susceptible cultivars in central Texas had moderate to light infections, whereas in northern Texas wheat at the late flower to early dough growth stages did not have any leaf rust infection. In early May, traces of leaf rust were found in plots of susceptible cultivars in southwestern Oklahoma. Leaf rust in Oklahoma developed when the crop was at the dough growth stage, which resulted in little loss due to leaf rust. Infection sites in the southern winter wheat provided inoculum for the northern wheat area.

Central Plains. In early May, wheat leaf rust was found in light amounts in south central Kansas fields. By the third week in May, severity levels as high as 10 % were observed on flag leaves in a few fields of Jagger. During the last week in May, leaf rust was severe in plots and fields of susceptible cultivars from central Kansas to west central Missouri (Fig. 1). In fields of Jagger at the late berry stage in south central Kansas, 60 % severities were found on flag leaves. In fields of Jagger in northeast Kansas, 10 % severities were observed on flag leaves. In central Kansas varietal plots, rust severities ranged from trace to 60 %. Throughout Kansas and Missouri wheat leaf rust and stripe rust were competing on many cultivars for the same leaf tissue. Usually stripe rust increases faster because it can develop earlier and increase faster at cooler temperatures than leaf rust. In southern Kansas, losses due to leaf rust were severe in cultivars like agger but in other leaf rust susceptible cultivars losses were light (Table 4). During late May, 20 % leaf rust severities were observed on Ae. cylindrica (goatgrass) growing in the roadside in south central Kansas.

In the second week in June in eastern Nebraska, low to moderate leaf rust severities were found in fields and plots. Drought-like conditions in areas like western Nebraska slowed leaf rust development.

Northern Plains. In late May, traces of wheat leaf rust were found in winter wheat plots in east central Minnesota. On 28 May, traces of wheat leaf rust were observed in spring wheat fields in south central and eastern North Dakota. In mid-June, low levels of leaf rust infections were observed on the flag leaves of HRWW at anthesis in an east central South Dakota nursery. In early June, leaf rust also was found in spring wheat cultivars in the South Dakota nursery.

During the second week in June, leaf rust infections were found in winter and spring wheat fields in the southeast and south central part of North Dakota. Leaf rust severities in the fields ranged from 1 to 25 %, with most fields at low severity levels. Warm temperatures and high humidity favored leaf rust development. In the third week in June, trace-10 % leaf rust severities were observed at anthesis in susceptible winter wheat plots in east central Minnesota. Infections were mostly on flag-1 and flag-2 leaves. In the final week in June, susceptible winter wheat cultivars from east central Minnesota to west central South Dakota had 60 % rust severities. Susceptible cultivars like Jagger and Expedition, had severities of 60 %, but most cultivars had only trace levels of infection on the flag leaves. The rust infections in South Dakota and Minnesota probably originated from inoculum sources in Texas, Oklahoma, and Kansas.

In the last week of June, susceptible spring wheat cultivars in southern Minnesota plots had 20 % rust severities, with most infections on the lower leaves. Traces of leaf rust were observed in many of the spring wheat fields in southern Minnesota. In mid-July, 20-40 % wheat leaf rust severities were observed on flag leaves of spring wheat cultivars in fields from southeastern North Dakota, northwestern South Dakota, to southwestern Minnesota. Many wheat fields were sprayed with fungicide which prevented losses due to rust.

In late July, trace-60 % leaf rust severities were observed in spring wheat varietal plots in central and eastern North Dakota plots. In farm fields in central and southeastern North Dakota severity levels of up to 40 % were observed on the commonly grown wheat cultivars. In the northern tier of counties in North Dakota leaf rust was at reduced levels because the crop maturity was later than normal. Many wheat fields in the Red River Valley of the north were sprayed with fungicide to reduce loss due to foliar diseases.

This year leaf rust was severe and concentrated in the upper Midwest. Rust inoculum arrived from the south in late May and early June with rain showers and temperature and moisture conditions were good for infection and spread of leaf rust. The spring wheat cultivars currently grown have less effective resistance to leaf rust than those that were popular 10-15 years ago. Losses to wheat leaf rust occurred in the most susceptible cultivars (Table 5).

Southeast. In late March, wheat leaf rust was light in plots in the southern SRWW area from Georgia to Louisiana. In mid-April, from central Louisiana to Georgia, light amounts of leaf rust were observed in research plots and fields. In early May, the highest leaf rust severities (60 %) were in plots of susceptible cultivars in central Louisiana and southwestern Georgia. Only trace levels of leaf rust were found in southeastern Arkansas wheat plots. In early May, leaf rust severities of 30 % were reported in susceptible wheat plots in Louisiana and severities of 60-70 % were reported in plots in south central Georgia. Wheat leaf rust was lighter and developed later than normal throughout the southern SRWW area and did not cause much yield loss. In late May in eastern Arkansas, leaf rust had developed late on several cultivars including CK9663 that had been previously highly resistant. Stripe rust developed first in this area reducing the development of leaf rust.

Mideast. During the second week in June, trace-10 % leaf rust severities were reported in plots, and traces in fields of soft red winter wheat cultivars from northeastern Missouri to northwestern Ohio. Leaf rust infections were reduced due to cooler than normal temperatures in the region and the presence of wheat stripe rust.

East. In early June, leaf rust severities ranged from trace to 15 % on susceptible cultivars in a nursery on the eastern shore of Virginia. In mid-June, a plot of the cultivar Massey in northwestern Virginia had leaf rust severity of 80 %. Wheat leaf rust was lighter than normal in the eastern U.S. this year.

California. In many areas of California in early May, wheat leaf rust was difficult to find because of the cool weather and abundance of stripe rust. However, leaf rust was severe in commercial fields in the Imperial Valley. Fields of the durum wheat cultivar Orita, at the soft dough stage, had 70-80 % leaf rust severities in early May. By mid-late May, wheat leaf rust was severe (50-80 % severity) on susceptible cultivars in yield trials and fields in the Central Valley of California. High levels were detected on the few susceptible cultivars that were not affected by stripe rust. No leaf rust Wheat Leaf Rust Virulence. The 2003 leaf rust race identifications from the most common races identified are presented in Table 2 and Table 3. A total of 46 leaf rust races were found in the U.S. in 2003. From the central and southern Plains the most common races were M-B- (virulent to Lr1, Lr3, Lr10, Lr17, +) (Table 3). Many of the MBDS and MCDS races were identified from collections made from Jagger, which is widely grown in the southern and central Plains states. There has been an increase in T-races (TBBJ, TBDS, and THBJ) in the northern wheat-growing area. Many of the T-races with virulence to Lr2a and Lrl6 were identified from rust collections made from northern hard spring wheats. There also has been an increase in the number of T-races (TNRJ and TNBJ) with virulence to Lr9, Lr10, and Lr24 in Texas. Many of the T-races with virulence to Lr9 and Lr24 were identified from collections made from the cultivars Lockett (Lr9 resistance) and Thunderbolt (Lr41 resistance).

Yield loss estimates due to leaf rust are in Table 4, Fig. 3 (winter wheat), and Table 5 (spring and durum wheat).

Wheat stripe rust. Southern Plains. In mid-February, many hot spots of stripe rust infection (1-3 feet in circumference) were found in central Texas wheat plots, suggesting stripe rust might have over wintered in this region. In a field 70 miles east of San Antonio, stripe rust was present in a commercial field of Ogallala and in the nursery plots severities were high on Ogallala and Coronado. In late February, cold temperatures in central Texas slowed stripe rust in plots, but conditions were still good for stripe rust to increase since there was regular precipitation in late February and early March. By early March, stripe rust had spread throughout the central Texas nurseries. In early April, wheat stripe rust severities were high in wheat fields in southern and central Texas (Fig 4). Stripe rust infections were high in several thousand acres of Coronado in central Texas. In mid-March, plants in a few fields of Coronado died because of stripe rust. Many of the fields in central Texas were sprayed for rust control. Stripe rust development slowed during the later part of March and early April because of dry field conditions. In early April, low levels of stripe rust infection were found in fields west of Dallas. The wheat cultivars Jagger, Cutter, and Jagelene had the best stripe rust resistance in the Texas nurseries. In mid-April, stripe rust development was slowing in south Texas, but it was still possible to find some fresh pustules at all locations. In central and north central Texas, stripe rust was severe even though much of the area had been under drought conditions. During the last week in April, wheat stripe rust infections were increasing on susceptible cultivars from central to northern Texas. This was the worst stripe rust epidemic in the last forty years in central Texas.

In 2003, stripe rust overwintering sites occurred in more locations than in previous years throughout the southern U.S. wheat-growing area. Where stripe rust spores are deposited and infect wheat in late autumn and early winter, overwintering sites develop that are very critical to where stripe rust will occur the next year.

In early May, hot spots of stripe rust foci were found in central to north central Oklahoma plots. A wheat field in north central Oklahoma was heavily infected with stripe rust. In early May in southwestern Oklahoma, plots of the susceptible cultivars 2137, Above, AP502CL, Custer, Trego, and Intrada had lost their flag leaves because of a combination of stripe rust and moisture stress. Resistant cultivars Jagger, Cutter, Thunderbolt and several advanced lines from Oklahoma, still had green leaves. Cultivars with an intermediate resistance to stripe rust (Ok101, 2174, and 2145) also had green flag leaves. In northern Oklahoma, susceptible cultivars had lost their flag leaves due to the stripe rust and drought. Other cultivars such as Jagger which were resistant to stripe rust did much better in this area. Losses due to stripe rust in Oklahoma will be less than in 2001 because of the drought-like conditions in some areas of the state in May (Table 4 and Fig. 4.).

Central Plains. In mid-May, wheat stripe rust was prevalent throughout the entire state of Kansas at varying degrees of severity. The disease was most severe in the southern areas of the state. Cultivars Jagger, Big Dawg, and Betty were resistant. In some areas of Kansas, the more susceptible cultivars such as 2137, AGSECO 7853, Kalvesta, OK101, Stanton, Venango, Oro Blanco, Lakin, Trego, TAM 107, and TAM 110 had high stripe rust severities. A 30-40 % yield loss was estimated for the highly susceptible cultivars.

In late May, stripe rust was severe (60 % infection level) in central and southern Kansas plots and fields (Fig. 2). There was much more stripe rust in Kansas in 2003 than in 2002. In both 2003 and 2002, a cool spring with nighttime temperatures in the 40s and 50s F plus humid weather were conducive for stripe rust development throughout the Great Plains. However, the rust inoculum load from Texas in 2003 was greater, which caused more rust development. Stripe rust losses were estimated at 10 % in Kansas in 2003 (Table 4). Wheat stripe rust development in 2003 in the southern and central Great Plains was comparable to 2001.

In late May, traces of stripe rust were found in plots of susceptible wheat in south central Nebraska. In mid-June, stripe rust was light in most fields in central and eastern Nebraska. During the last week of June, winter wheat fields and plots in western Nebraska had stripe rust severities from trace to 60 %.

Northern Plains. During late May, trace amounts of stripe rust were found at the late jointing growth stage in east central South Dakota winter wheat plots. In the second week of June in east central Minnesota, winter wheat plots had trace levels of stripe rust. A focal point of severe infection was found in a winter wheat plot in St. Paul, indicating that stripe rust may have over wintered in Minnesota or arrived in late April or early May. During the third week of June, 60% severities were observed in susceptible winter wheat plots (e.g., Coker 9835) at the Rosemount Experiment Station in east central Minnesota. In other winter wheat plots severities ranged from 0-40 %.

In early June, wheat stripe rust was found in winter wheat and spring wheat nurseries in eastern South Dakota. In some susceptible winter wheat lines (e.g., Trego) stripe rust severity was 100 %. During the last week in June, winter wheat fields and plots in south central South Dakota had stripe rust severities from trace to 60 %.

On 20 June, winter wheat plots in east central Minnesota had wheat stripe rust severity levels between trace to 60 %. Coker 9835 had severities between 40-60 %. Cultivars with Lr26/Yr9/Sr31 genes on the wheat-rye T1B·1R translocation also tended to have higher stripe rust severities. Many cultivars had a resistant response characterized by necrotic strips; moderately resistant cultivars had necrotic strips with stripe rust pustules, moderately susceptible cultivars had chlorotic strips with pustules, and susceptible cultivars had strips of pustules without necrosis or chlorosis. Cultivars known to have Lr34/Yr18 had a moderately resistant response.

In late June, stripe rust infections were found in spring wheat plots in east central Minnesota. Some of the cultivars (e.g. Briggs and Walworth) had stripe rust severities of 10 %. The cooler temperatures with sufficient moisture levels were conducive for stripe rust development in the north central region.

In late June, severe stripe rust was found in spring wheat fields in east central North Dakota. Fields sprayed with fungicides in the eastern North Dakota area were rust free. In mid-July, 40 % stripe rust severities were found on flag leaves in some wheat fields at the early berry stage in southeastern North Dakota. The rust pustules on the leaves were still sporulating, since the nighttime temperatures were less than 60 F in that area. In late July, active stripe rust pustules were observed in wheat varietal plots throughout the state of North Dakota.

Southeast. In early March, stripe rust was increasing on a few cultivars in south central Louisiana. Stripe rust was light but increasing in spots. Weather conditions were ideal for rust infection in early March. In early April, stripe rust infections were increasing throughout plots in southern Louisiana. Many wheat fields in Louisiana were sprayed for stripe rust.

By mid-April, stripe rust was severe in southern Louisiana nurseries, with 80 % severities in susceptible cultivars. Throughout Louisiana, stripe rust was common and many fields were sprayed with fungicides to reduce yield losses. Wheat cultivars Terral LA422 and AGS 2000, which are widely grown in Louisiana, were susceptible to stripe rust. Heavy infections of stripe rust have occurred in four of the last 6 years in Louisiana.

In early April, a focal point of stripe rust infection that had over wintered was found in wheat plots in northwestern Arkansas. In mid-April, stripe rust was increasing in southern and eastern Arkansas fields and many of the fields were sprayed with fungicides. Rust was found on most of the commonly grown cultivars. Numerous hot spots (foci) of rust infection were found throughout the area. In southeastern Arkansas, wheat plots of susceptible cultivars had 20-30 % stripe rust infection. There was a wide range in the amount of stripe rust on the cultivars in the breeding plots; some soft red winter wheat cultivars were highly resistant to stripe rust, whereas others were relatively susceptible. Stripe rust infections in Arkansas were scattered and light during the last week of April. In late May in west-central Missouri, 20 % wheat stripe rust severities were observed on flag leaves of soft red cultivars at the early berry stage. In mid-June fields of soft red winter wheat cultivars from northeastern Missouri to southern Indiana had 40-80 % stripe rust severities.

In both 2003 and 2002, stripe rust was severe in the soft wheat area growing areas of Arkansas and Missouri. Favorable weather conditions in 2003 and stripe rust inoculum from infection sites in Louisiana and Texas led to increased stripe rust in Arkansas and Missouri.

In mid-April, 20 % stripe rust severities were common in fields from northeastern Louisiana to central Georgia. However, the dry weather during the last 2 weeks of April slowed stripe rust development in many parts of the southern U.S. In late April in central Mississippi and central Alabama, wheat plots had stripe rust severities of 20 %. Infections were light in the commercial fields in this area. In mid-April, severe stripe rust was found in southern Georgia varietal plots at Plains with the most susceptible lines at 80-100 % severity. Entire plots were rusted indicating a uniform spore shower, not just isolated disease foci. Stripe rust (less than 5 % severity) also was found at Griffin, GA, 14 April on a few susceptible lines. By the end of the first week in May, stripe rust severities of 100 % were observed on susceptible cultivars in the south central Georgia wheat plots. This was the most severe wheat stripe rust ever seen in Georgia.

Mideast. In late May, stripe rust severities of 80 % were in a few fields in southern Illinois. In many of these wheat fields, stripe rust destroyed the flag leaves. In mid-June, from northwestern Ohio to north central Illinois, traces of stripe rust were observed in wheat fields. Stripe rust development in the northern soft red winter wheat growing area was greater than in 2002. Favorable weather conditions (cool temperatures and moisture) in 2003 and inoculum from many infection sites in the southern SRWW areas, allowed stripe rust to develop in the northern soft wheat area. The SRWW cultivars ranged from very resistant to fully susceptible to stripe rust.

East. In late May, wheat stripe rust foci were observed in plots at the Blacksburg Virginia experiment station. The incidence of stripe rust in the plots were trace to 5 %, whereas the severity in the major foci was 15-50 %. The Virginia cultivar Sisson that has the T1B·1R translocation had high stripe rust severity suggesting that stripe rust races with virulence to Yr9 were common.

In early June, several major stripe rust foci and frequent secondary foci were found in the eastern shore nursery plots at Painter, Virginia. In mid-June, one small infection focus was found in plots in Warsaw, Virginia. Stripe rust was found throughout Virginia in 2003 but developed too late to cause significant damage to the wheat crop.

California. Stripe rust on wheat was first detected on 20 February in nurseries in Davis, CA, which was the earliest onset of stripe rust in a number of years. Infection foci were at 50 % severity. By late February, wheat stripe rust had increased on susceptible cultivars in nurseries and fields in the Sacramento Valley and was severe on early planted forage wheat (Dirkwin) in the northern San Joaquin Valley. Low levels of infection also were detected in wheat nurseries and commercial fields throughout the San Joaquin Valley on 4-5 March. Fields ranged from early joint to boot stage. In early April, wheat stripe rust infections had increased throughout much of the Central Valley of California and surrounding areas. Most of the current wheat cultivars in California, including many durum cultivars, are susceptible to stripe rust. A mild winter with moisture and early infection of very susceptible cultivars produced an abundant inoculum load. Susceptible cultivars, such as Dirkwin, Cavalier, Yecora Rojo, Eldon, Yolo, and Klasic had 100 % stripe rust severities. A larger proportion of wheat fields in California were sprayed with fungicides than in previous years. The fungicide Tilt was used early in the growing season but Quadris was applied after the emergence of the flag leaves.

In mid-April, in the Central Valley (Sacramento and San Joaquin valleys) of California, stripe rust was severe in plots of susceptible wheat cultivars. In the first week of May stripe rust was severe in fields in the Central Valley due to favorable conditions. By the fourth week in May, wheat stripe rust continued to increase on common and durum wheat in nurseries throughout the Central Valley of California. Stripe rust was more severe in California in 2003 than 2002, because the moist conditions and cool temperatures were very favorable for rust development throughout the growing season. Losses to stripe rust were significant this year in California (Table 4).

Pacific Northwest. In late April, stripe rust was severe in susceptible winter wheat fields in southeastern Washington and northeastern Oregon. Infection foci with 60 % rust severities that were up to several hundred feet in diameter were found in wheat fields. The ground under the plants was covered with rust spores. Some fields in the area were sprayed with fungicides. By late April, stripe rust was also occurring on early-planted spring wheat cultivars in the Pendleton area of Oregon.

In 2003, in much of the Pacific Northwest, there were favorable conditions for over wintering of wheat stripe rust and the cool, moist conditions in late April and early May were favorable for rust development. In early May, severities of 90 % were observed on susceptible entries in the winter wheat nursery near Mt. Vernon in northeastern Washington. By mid-May, wheat stripe rust was severe in southeastern Washington winter wheat plots and fields. Many fields in eastern Washington were sprayed with fungicides. In irrigated spring wheat fields in southeastern Washington, rust severities of trace to 1 % were observed. Since abundant rust inoculum was in the region with favorable weather for rust development, stripe rust continued to spread and develop in eastern Washington and northern Idaho. By late May, 5-20 % wheat stripe rust severities were observed on susceptible winter wheat cultivars growing in fields and plots in the Palouse region of eastern Washington. In fields of SWWW, stripe rust infections were common, but most cultivars had resistant to moderately resistant reactions.

In mid-June, wheat stripe rust was developing rapidly in fields of susceptible spring wheat in eastern Washington. Some fields had incidence levels of 60 % stripe rust with severity levels up to 20 %. In mid-June, growers applied fungicides on susceptible spring wheat fields. In mid-June, 50 % severity levels were in irrigated plots of susceptible winter wheat cultivars in the dry land area of central Washington. Susceptible lines had 60 % severities in plots in a winter wheat nursery near Pullman, Washington, and fields in the area had only traces of rust. In July, dry conditions in Washington slowed stripe rust development.

Yield loss estimates due to leaf rust are in Table 4 (winter wheats) and Table 5 (spring and durum wheats).