Missouri Ag Connection - Stripe Rust and Powdery Mildew in Wheat

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Stripe Rust and Powdery Mildew in Wheat
Missouri Ag Connection - 04/24/2017

Jill Scheidt, agronomy specialist with University of Missouri Extension, scouted fields south of Jasper, near Base Line Road for the crop scouting update.

Wheat was found to be in the boot to heading stages.

Temporary phosphorus and potassium deficiencies were seen in some fields, likely caused by the wet and cool weather according to Scheidt.

"Phosphorus deficiency usually causes purple leaf tips and potassium deficiency usually causes yellow scorching of the leaf tip edges. These symptoms will likely fade as temperatures warm," said Scheidt.

Powdery mildew and stripe rust were in the lower canopy of leaves.

"The diseases did not appear to be moving up the plant," said Scheidt.

If the forecast calls for overcast days or moisture, Scheidt recommends applying a fungicide to prevent diseases from affecting the flag leaf.

"Most foliar fungicides only prevent diseases and do not control them, if diseases appear to be moving up the plant, spray a fungicide as quickly as possible. Be aware that it is off-label to apply certain fungicides after heads are fully emerged," said Scheidt.

Stripe rust is usually on the leaves and runs parallel to leaf veins. This disease is commonly associated with cooler temperatures, especially cooler nights.

Stripe Rust does not survive in infested residue; it can be reintroduced each season when spores are carried up on air currents from the south.

Recommended fungicides for stripe rust are listed online at https://ipm.missouri.edu/IPCM/2012/3/Stripe-Rust-Damages-Some-Southeast-Missouri-Wheat/ .

Powdery mildew infections begin as light-green to yellow flecks on the leaf surface and develops into cottony white mold growth, then a grayish-white to grayish-brown color with small black fungal fruiting bodies. Powdery mildew development is favored by temperatures of 59-72 F and prolonged periods of cloudy weather. Powdery mildew likes high nitrogen levels, lush growth and dense canopies.

Scheidt observed a few greenbug aphids in one field. "The aphids were below threshold level and no other aphids were seen. Aphids should be scouted for all season long; they are usually on the underside of the leaf and on the kernels," said Scheidt.

The weekly field scouting report is sponsored by University of Missouri and Barton County Extension.

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