March 14, 2019

Foliar Disease Watchouts From WestBred® Wheat

By Mark Lubbers, WestBred® Technical Product Manager

With the wet conditions that have defined this winter in the southern and central U.S., wheat growers need to be especially vigilant with their disease scouting and protection. While many growers may remember the 2018 spring season favorably in terms of low disease pressure, this year will likely not be the same. Knowing which diseases have the potential to be problematic in your geographic area is key to identifying them early and mitigating them before they take hold.

Below are four diseases to keep an eye on in 2019:

1. Powdery Mildew

Plants affected by Powdery Mildew will display white powder-like spots (resembling cottony growth) on leaves and stems. Typically, the upper surfaces of the lower leaves are the most affected areas. Symptoms are visible early in the season and can be particularly prevalent during mild (between 59 and 70 degrees Fahrenheit), wet conditions. If these conditions persist, the entire leaf can turn yellow and die, reducing the plant’s yield potential. This is most often the case in Central and Eastern Kansas and in Nebraska fields with dense stands and high nitrogen fertility.

When it comes to foliar disease control, we mostly think about protecting the upper leaves, specifically the flag leaf; however, if early-season Powdery Mildew pressure is moderate to heavy on the lower leaves, a fungicide will be needed to protect the developing tillers. A second spray may be necessary again at flag leaf if the disease is visible three to four weeks after the first spray.

2. Stripe Rust (Yellow Rust)

Stripe Rust, a potentially major concern across most of Kansas, Nebraska and Colorado, is characterized by its yellow-orange pustules that appear primarily on the leaves; however, they can also appear on the glumes and base of the awns. These pustules differ from Leaf Rust and Stem Rust as they are generally arranged in a row or stripe. Stripe Rust typically appears earlier in the season since its development is favored by cool (between 50 and 65 degrees Fahrenheit), humid conditions. Like Powdery Mildew, when daytime temperatures rise above 80 degrees Fahrenheit, Stripe Rust development will generally cease or be severely restricted.

Genetic resistance and/or timely fungicide applications can help control the disease and decrease potential yield loss. When applying fungicides, it’s best to wait until after the flag leaf is at least 50 percent emerged to ensure adequate coverage since most fungicides have little mobility in the plant.

3. Leaf Rust (Brown Rust)

Leaf Rust is the most common of the three rust diseases that affect wheat in the Central Plains. It is typically found throughout the eastern half of Kansas and Nebraska, but it can also occur in western Kansas and Nebraska and eastern Colorado. Leaf Rust is characterized by its small reddish-brown pustules found on the upper surfaces of the leaves. Pustule colors of Leaf Rust and Stem Rust may look similar, but a key difference is that Leaf Rust pustules are small and will only appear on the leaves, while Stem Rust pustules are larger and can be found on the leaves, stems and heads. Mild temperatures (between 68 and 77 degrees Fahrenheit) and humid conditions are optimum for disease development.

Control of Leaf Rust is very similar to that of Stripe Rust and includes selecting a variety with genetic resistance and applying a timely fungicide. Due to warmer temperatures required for Leaf Rust development, make sure to follow all fungicide label requirements regarding growth stages and pre-harvest intervals.

4. Fusarium Head Blight (Head Scab)

Fusarium Head Blight (FHB) is a major disease for wheat growers in the eastern half of Kansas and Nebraska. In 2018, localized outbreaks did occur in western Kansas and eastern Colorado; therefore, growers need to be aware of the conditions favorable for disease infection. Wheat planted in corn residue is at primary risk, since the pathogen that causes FHB is also responsible for Gibberella Stalk Rot and Ear Rot in corn.  

As the wheat crop reaches flowering, it is most vulnerable to FHB infection. High humidity and temperatures between 75 and 85 degrees Fahrenheit are ideal for infection. Early symptoms include spikelets or entire heads appearing prematurely whitened or bleached.  

Fungicides provide partial suppression of FHB (particularly the triazole class of fungicides, including Prosaro® fungicide). To be effective, the fungicide must be applied at flowering with uniform coverage. In areas prone to FHB infection, it is advised to combine fungicide applications with resistant varieties such as WB4269 or WB4699.

These four fungal diseases are among the most prevalent and costly to wheat growers in the central U.S. — but they are definitely not the only threats to a profitable growing season. For additional agronomic tips or to learn which varieties are the best fit for your acres, visit WestBred.com or contact me at mark.lubbers@bayer.com.