Most Arkansas wheat farmers remember stripe rust from the spring of 2000. This yellow-orange rust, favored by cool, moist weather, affected 300,000 acres that year.
Most of that acreage was protected by timely fungicide applications (thanks to statewide monitoring by county agents, consultants, field men and growers during March and April), but yields in some unprotected fields were cut 50 percent.
That same spring several popular wheat varieties that previously had been resistant to stripe rust were suddenly susceptible. Stripe rust taught a lot of us about the speed and impact of a widespread plant disease epidemic.
While a stripe rust epidemic like that of 2000 is uncommon in Arkansas, some stripe rust occurs in the state each year, usually in localized wheat fields in the Arkansas River Valley.
Okay, enough history. During the last week of March 2002 we started receiving calls about wheat with rust. For the most part, the rust turned out to be stripe rust, and it was active. Most pustules were on lower leaves, but there were some fresh ones on upper leaves. Wheat fields were in Feeke's growth stage 6-7.
As of April 1, stripe rust was reported in Arkansas in commercial fields in Prairie, Lonoke, Arkansas, Jefferson, Lincoln, Monroe, Cross, and St. Francis counties, and in test plots in Lafayette County. Either leaf or stripe rust was reported also in Chicot and Lawrence counties. (Note: This is a big area and it is early in the year for this much rust.)
Most early reports involved Pioneer 26R38, but other varieties were also affected, including NK Coker 9663, FFR 510, Armor 4045 and AgriPro Shelby. More varieties are expected to have the disease as well.
So, will the Arkansas wheat crop suffer a stripe rust epidemic akin to that of 2000? That would add insult to injury, given the water damage to our crop.
Current evidence suggests that stripe rust damage in Arkansas is now likely, but disease epidemics are about as predictable as the weather.
What to do? Don't panic and watch your good wheat fields. Most experts want fields to have a yield potential of 40 bushels per acre or more before they consider using a fungicide.
Several highly effective fungicides are registered on wheat, including Tilt, Propimax, Stratego and Quadris. In Arkansas, all of them can be used through heading — but before flowering. But check labels and regulations in your state.
If stripe rust is active, the fungicides should be applied during the boot stage or earlier. Fields with active hot spots of stripe rust should be treated as soon as practical.
Inspect other fields and make fungicide decisions on a case-by-case basis. Timing depends on field conditions and careful scouting. In 2000 we sprayed some fields as early as growth stage 9 (flag leaves fully emerged) to early heading, all during April.
Stripe rust will keep going two to four days after a fungicide treatment, but then it will stop and the wheat should be fine.
If you have questions, contact your local county Extension agent or an experienced consultant for advice.
We publish a weekly wheat pest management newsletter, available on the Arkansas Extension Website at http://www.aragriculture.org/News/wheatdisease/default.asp. It has good information about what's happening on wheat in Arkansas during the spring.
Rick Cartwright is an Extension plant pathologist with the University of Arkansas Division of Agriculture.