Wheat Stripe Rust
This year, wheat stripe rust reported in a southern Georgia nursery for the first time since 1974. On May 9, a wheat stripe rust focus 1m in diameter, was found in northwest Georgia. This is one of the first records of stripe rust ever being found in north Georgia. In late April, stripe rust was light in northern Alabama plots. In west central Mississippi plots where it was dry, wheat stripe rust was more scattered and easier to evaluate than wheat leaf rust. Trace losses were reported throughout the southeastern U. S. In early March, light amounts of stripe rust were found in a wheat field in southern Louisiana. In late March, light stripe rust was found in plots in northeastern Louisiana. By the third week in April, wheat stripe rust was severe in commercial fields throughout northwestern Louisiana. The wheat stripe rust loss in Louisiana was estimated to be 0.5% (Table 5). In mid–March, stripe rust was widespread on the lower leaves and upper leaves of several cultivars in northwestern Arkansas where the rust had overwintered. During mid–April, stripe rust was increasing throughout the state of Arkansas. Foci several hundred feet in diameter were found where stripe rust had overwintered. More of the fungicide Tilt was sprayed this year in Arkansas than in any of the last 5 years. As of early May, stripe rust was still increasing in northern Arkansas because there still had not been any prolonged periods of hot weather, which usually stops stripe rust development. During the third week in May in northeastern Arkansas, active stripe rust sporulation was observed in wheat plots and fields. The crop matured fast and with the arrival of hot temperatures stripe rust development stopped. By the third week in May, 50%of the entries in northwestern Arkansas plots were either destroyed by stripe rust or severely damaged. Estimated losses to stripe rust in Arkansas reached 7.0%(Table 5), which was the largest loss reported in recent history. Southern Plains –During late March, infections of stripe rust that had overwintered were found on the lower leaves of soft red winter wheat cultivars at the Uvalde,Texas experiment station. By the third week in April, wheat stripe rust was severe in commercial fields throughout northeastern Texas. Entire fields were yellow from top to bottom and many fields were abandoned because of stripe rust. Many fields were sprayed with the fungicide Tilt which reduced yield loss. Late maturing soft red winter wheat fields had high stripe rust severities. The high level of stripe rust in March–April was due to the mild winter which allowed wheat to start growing early and more rust to overwinter. In the early spring there was good moisture with cool nighttime temperatures which provided perfect conditions for stripe rust development. There was an estimated 10% loss to wheat stripe rust in northeastern Texas and overall a 0.5% estimated loss in the state. By late April, wheat stripe rust was severe in southern Oklahoma. This year estimated losses to stripe rust totaled 1.0% (Table 5) of the yield in the state. Central Plains In mid–May, stripe rust was found throughout Kansas. The mild winter and cool spring were conducive for stripe rust development. In south central Kansas plots, stripe rust was severe on a few of the hard red winter cultivars, especially those with the 1B–1R gene translocation, which indicated a possible virulence to Yr9. In late May, stripe rust was observed throughout eastern Kansas, northwestern Missouri and southeastern Nebraska fields. In south central Kansas plots, severities ranged from traces to 60% while in Nebraska fields, 1% severities were observed. This year in the Great Plains the cool spring and nighttime temperatures, which were in the low 50s, were favorable for stripe rust development. However, the hot windy conditions the later part of May probably disrupted much of the stripe rust development. Losses to wheat stripe rust in Kansas were estimated to be 0.05% (Table 5). Northern Plains – Trace amounts of stripe rust were found in wheat breeding plots at Brookings, South Dakota in mid–May. The wheat plots ranged from late boot to heading stage. On June 8, light amounts of wheat stripe rust were found in soft red winter wheat plots at Rosemount, Minnesota. Hot temperatures that followed the initial rust sighting in the Minnesota plots may have delayed the rust development, but cooler weather in mid–June allowed further increase. In mid–June, traces of wheat stripe rust were found on the cultivar 2137 in southeastern North Dakota. In late June, wheat stripe rust was widespread in central and eastern South Dakota on winter wheat. In plots at Brookings, some winter wheat entries had a high level of infection, e.g., 80% on Siouxland, which has the 1B–1R gene translocation, which indicates a possible virulence to Yr9. Traces of stripe rust were found easily in spring wheat fields and nursery plots. In rust foci, 30% severities were observed in some spring varieties and lines. By the later part of the first week in July, stripe rust development had slowed in South Dakota because of the hot temperatures during the day and temperatures at night that were greater than 60 degrees. By late July, traces of stripe rust were found in spring wheat fields and 50% severities were reported in irrigated plots in northeastern Montana. Traces of stripe rust were scattered throughout northern North Dakota spring wheat fields and in plots severities ranged from trace to 20% (e.g. McNeal and NorPro). There was little yield loss to stripe rust in the northern Great Plains. During the second week in June, wheat stripe rust was found in a northeastern Colorado field. Normally, stripe rust is found at higher elevations in Colorado, i.e., San Luis Valley (7,500 ft) or in the front range of the Rockies. Midwest – In central Indiana, light stripe rust was found in late May in fields and in breeding nurseries where it was more severe. By mid–June, wheat stripe rust development was extensive from central Illinois to southwestern Michigan and severities ranged from traces to 20%. This was the most widely dispersed stripe rust development observed throughout the northern soft red winter wheat area in at least 20 years. In the northern most locations rust severities ranged from trace to 10% with large sporulating pustules. At many of these locations stripe rust was found together with leaf rust on the same leaf which could mean that they developed from the same spore shower. Much of this stripe rust development originated from spores produced farther south in Texas, Arkansas, or adjacent states.
In mid–May, traces of stripe rust were found in plots in Blacksburg, Virginia. This is one of the first reports of wheat stripe rust east of the Appalachian mountains. Wheat stripe rust this year was the most widespread throughout the southern U.S. than has ever been reported (Fig. 2). Last year, no stripe rust was reported in south central U.S., but two years ago light amounts of wheat stripe rust were scattered from the lower Mississippi Valley north to east central Minnesota. This year stripe rust was found early because it overwintered in many areas in the southern U.S., where the winter was milder than normal. Furthermore, the spring weather has been cooler than normal, favoring stripe rust development. It appears that there was a large source of inoculum that arrived early in the crop growing year in the southern U.S. from some location like Mexico. Preliminary data from the wheat stripe rust collections indicate a shift in the stripe rust virulences from 1998 to 2000 in the southern U.S.
In mid–May, temperatures were cool and several storm systems provided moisture that allowed stripe rust to continue to increase in the Central Valley of California. There were reports of wheat stripe rust at 100% severity in commercial fields of the widely grown variety RSI 5 throughout the Sacramento Valley and the northern part of the San Joaquin Valley. Cool spring weather also allowed wheat stripe rust to increase in commercial fields of several varieties in the central and southern portion of the San Joaquin Valley. Severities of 100% were observed on breeding lines and varieties in nurseries in this area. Estimated losses to stripe rust were 3.0% in California this year (Table 5).
By mid–March, wheat stripe rust was increasing in plots and fields in western Washington. In mid–April, wheat stripe rust severities of 60% were reported on susceptible winter wheat lines in the Skagit valley nursery in western Washington. By the first week in May, wheat stripe rust was prevalent throughout the state of Washington. Stripe rust exceeded 70% severity on susceptible winter wheat cultivars in northwestern Washington. By late May, in eastern Washington, stripe rust was starting to increase in winter wheats and development was slower than normal because of the dry conditions in early and mid–May which were not conducive for rust development. By late June, wheat stripe rust was starting to increase on spring wheats in the Pacific Northwest, and the susceptible cultivars were sprayed with fungicides. Rust losses were 1.0% or less, since most of the cultivars have high temperature, adult plant resistance (Table 5).
In late July, trace to l5% stripe rust severities were reported in spring wheat fields in southeastern and south central areas of Manitoba. Due to the early planting of most cereal fields this year and cooler than average June temperatures, susceptible wheat varieties that were not sprayed with fungicides experienced low levels of stripe rust infection and associated yield losses. However, later planted fields avoided infection due to higher July temperatures that impeded further development of stripe rust.