Major stripe rust epidemics have not occurred in Nebraska since 2005, says a University of Nebraska plant pathologist. However, given the unusually high levels of stripe rust reported in Southern states and cool, wet weather in parts of the Plains, the risk of stripe rust development in Nebraska is high, says Stephen Wegulo.
"Growers should routinely scout their fields for leaf rust and stripe rust and to be prepared to apply an appropriate fungicide to prevent damaging levels of these and other foliar diseases," Wegulo says. "Fungicide applications should be timed to protect the flag leaf."
As of April 28, wheat diseases in Nebraska were at very low levels. However, Wegulo says wet weather and overcast skies were favorable to the development of several diseases, including leaf spots, powdery mildew and leaf and stripe rusts.
"Leaf rust and stripe rust have been reported in the southern states and most recently in Kansas," Wegulo says. "Stripe rust has been found in central and northeastern Kansas."
On April 29, stripe rust was confirmed on a sample from Johnson County in southeast Nebraska. On April 26, leaf rust was found in Nuckolls County, Nebraska.
"This is one of the earliest dates leaf rust has been found in Nebraska in recent years," Wegulo says. "Leaf rust is usually first seen in the growing season after the first week of May, most often around mid-May.
"Stripe rust is more damaging than leaf rust. This year it has been reported on varieties that previously were resistant, indicating that there may be a new race of the stripe rust fungus.
As for Kansas wheat growers, all evidence to date suggests that stripe rust, leaf rust and other diseases are likely reach levels that can be damaging to wheat yields, says Erick DeWolf, Kansas State University plant pathologist.
"The biggest threat may come from stripe rust because variants of this fungus have emerged that can overcome the resistance of some widely grown cultivars in the state, including Fuller, Santa Fe, Overley, PostRock, Jagalene and Jagger," DeWolf says. "All of these varieties should now be considered susceptible to stripe rust."
Research suggests that the best time to apply a foliar fungicide to wheat is between flag leaf emergence and anthesis (flowering), DeWolf adds. Most product labels will prevent application to wheat that has reached the fully headed or flowering stages of growth. Wheat in many parts of the state will be at critical growth stages during the next few weeks.
The current weather forecast for this region includes temperatures near 70 F and scattered showers. DeWolf says growers should be on alert for potential development of stripe rust and other diseases in their fields, and be ready to apply a fungicide if warranted. Finding even low levels of stripe rust or leaf rust prior to flag leaf emergence is cause for concern.
"The average yield response to fungicides is approximately 10%, but can exceed 20% when disease becomes established early," DeWolf says. "The decision to apply may rest on the price of grain. With the price of wheat hovering around $4, the price of the fungicide will strongly influence the decision to spray for disease control. Seed production fields should be a top priority."
DeWolf says fungicide costs this spring ranged from $4 to $20 per acre depending on the product choice and rate. Nearly all fungicides currently marketed provide very good to excellent control of leaf rust and stripe rust.
"The choice of fungicide is more important when stripe rust is already present in a field because this fungus has the potential to spread systemically within a leaf," DeWolf says. "Products containing a triazole fungicide, or pre-mix of a triazole with a strobilurin, are the best option when stripe rust is present in a field because these products are known to have stronger curative activity.
Here are more details on fungicide products.