Fungicide application timing critical for managing wheat diseases

BLOOMINGTON, Ill. — Winter wheat acreage is up in Illinois and Indiana and farmers are checking their fields for yield-robbing diseases.

Illinois’ projected harvested area of 790,000 acres is 230,000 above 2022, and Indiana will have an estimated harvested area of 380,000 acres, 140,000 more than last year, according to the U.S. Department of Agriculture May crop production report.

Cody Pettit, Pioneer field agronomist, provided recommendations for fungicide application timing for successful disease management, with a focus on fusarium head blight, or head scab.

“One of the ways to maximize yield potential is by spraying a fungicide and there are two different times you can spray a fungicide — flag leaf (at Feekes 9) and flowering (at Feekes 10.51),” Pettit said.

“If you were to spray one single fungicide, the best bang for your buck is probably spraying at early flowering when you’re spraying for fusarium head blight.”

Fusarium head blight can be the most devastating disease of wheat when conditions favor its development.

The disease reduces both grain yield and quality. Quality losses can be due to lower test weights and production of a toxin — deoxynivalenol, or DON — by the head scab fungus.

Both low test weight and contamination of the grain by DON can cause serious problems for producers and millers.

This disease overwinters in diseased seed and residues of wheat, corn and other grasses in surrounding fields.

Spores are produced and blown onto the wheat heads, which germinate in free water on the head and invade the flower.

Telltale Signs

Symptoms occur on the head after flowering. Individual spikelets or the entire head may be prematurely bleached.

The bleached spikelets usually contain shriveled, scabby seeds and brown or black lesions may be present where the head joins the stem.

The fungal pathogen that causes fusarium head blight in wheat also causes gibberella stalk and ear rot in corn.

Since corn is widely grown in rotation with wheat, the pathogen is already present in most fields and disease development depends on prevailing weather patterns.

Because wheat is susceptible to the disease during flowering, weather conditions from flowering through kernel development play a key role in the incidence and severity of scab.

Moderate temperatures, between 75 and 85 degrees, prolonged high humidity and prolonged wet periods favor disease development.

“As far as application timing for head scab, you’re going to have that head fully emerged from the plant. Once you start to see that, you should be out checking your fields. Beginning flowering is that stage. So, you’re going to start to see those anthers pop up from that head,” Pettit noted.

“Now, keep in mind pollination can happen within about a week. So, you’ve got to be out there every single day after you start to notice those heads to capture that perfect application timing.

“Also, you want to get 50% of that field to that early flowering stage before you spray. It’s just like with corn where we want to get 50% of the field to tassel before spraying fungicide. It’s the same scenario for wheat.”

He recommends applying a triazole fungicide.

Application of products containing strobilurin fungicides may result in elevated levels of the mycotoxin DON in grain damaged by head scab.