Posted: Friday, June 11, 2010 12:00 AM
Expert advises fungicide use on susceptible varieties
The next few weeks are critical for Northwest wheat growers to combat stripe rust, said a top expert in the field.
Xianming Chen, plant pathologist for the USDA Agricultural Research Service in Pullman, Wash., said unusually frequent rain has created ideal conditions for stripe rust infection.
The next two weeks will be critical for stripe rust control, Chen said. He recommended farmers check their fields and apply fungicides as necessary.
In a recent field survey in eastern Washington and Idaho, stripe rust was found to be widespread, Chen said in a stripe rust alert.
Most fields were below 10 percent severity and 20 percent incidents, Chen said. Two winter wheat fields, one west of Colfax, Wash., and one north of St. John, Wash., had large hot spots with 100 percent of plants infected and 40 to 80 percent severity. Plants in these fields had necrotic stripes with limited rust pustules, which Chen said could be due to moderate resistance or fungicide application. The fields could have been sprayed earlier to reduce yield loss, he said.
The rust has impacted Oregon, Eastern Washington and Northern Idaho.
Because Southern Idaho has a later season, Chen said there haven't yet been reports of the disease. Farmers there should check their fields, he said, although that region will probably not see as much rust as the rest of the Northwest.
In his e-mail alert, Chen said rust severity would increase rapidly in the most susceptible varieties. With temperatures lower than normal, adult plant resistance might not fully kick in, and varieties with resistance may also need to be sprayed with fungicides.
That may prove to be somewhat difficult due to weather conditions, Chen said. Rain hinders fungicide application.
Stripe rust continues to infect the crops, germinating in water drops or dew that stands for more than three hours on the plant's surface.
Chen said warmer weather next week will help reduce the frequency of the stripe rust, and help some varieties where resistance works better in higher temperatures.
"If not sprayed, we will see a very big increase in susceptible varieties," he said.
Most labeled fungicides can only be used before the flowering stage and the winter wheat crop is near the flowering stage in the Northwest.
Fields of uniformly susceptible varieties should have 5 to 10 percent stripe rust before fungicide is used, Chen said. Because their crops are farther along, farmers in Washington's Walla Walla and Columbia counties should use a 10 to 20 percent threshold.
Chen said the good news is that many winter wheat fields have already been sprayed.
In some locations, infected winter varieties are beginning to affect planted spring varieties. He advised spring wheat growers with fields that are further along, such as in Walla Walla County, to check their fields, while others who started later, such as on the Palouse, can afford to wait a week or so, until after the current stripe rust outbreak is dealt with.
Growers also have another chemical option, Folicur, Chen said, that can be used in addition to Tilt, Quilt, Quadris, Stratego and Headline.
In his alert, Chen advised that the following varieties should not be sprayed: Eltan, Madsen, Eltan/Madsen, Chukar, Finch, Skiles, ORCF-102, Coda, Madsen/Rod, Legion, Bitteroot, Breuhl, Stephens, Brundage, Eltan/Tubbs06, KCF9002, Goetze/Skiles, Cara and George.
The varieties AP Legacy, Salute, KCF9003, CDC Ptarmigan, Paladin, Eddy, Finley, Goetze, Finway and Buchanan should be sprayed.
Tubbs 06, Simon, Xerpha, Rod/Tubbs 06, Lambert, Masami, WB-528, AP700CL, RJames, ORCL 103, Farnum and Bauermeister can be sprayed, depending on their location and yield potential.
If grown in Walla Walla, Columbia and Garfield counties and southwestern Whitman County, where rust severity has reached significant levels, these varieties may be sprayed.
In most other areas, rust levels are still low and high-temperature adult plant resistance is supposed to kick in with higher temperatures next week.