Early season disease management: It’s time to start scouting for wheat diseases

Scouting your fields early in the season will put you ahead of the game in the fight against wheat diseases.

Powdery mildew on wheat
Powdery mildew on wheat. Photo by Martin Nagelkirk.

Even though disease pressure is not at its peak at this time, scouting wheat is recommended for early disease detection, especially because of the increased moisture levels due to the amount of rain/snow in the past few weeks.

How to scout for diseases

When scouting, choose a representative area of the field, or if possible, scout the whole field. Walk through the field every seven to 10 days. Regularly stop to examine plants closely looking for symptoms in the upper and lower crop canopy. Pull out some plants to inspect for root or crown discoloration, which are symptoms that might be caused by soilborne fungal pathogens.

What to look for when scouting

In Michigan, early season diseases to pay special attention to are Septoria leaf spot and powdery mildew.

Symptoms of Septoria leaf spot first appear on lower parts of the plant as lesions showing irregular shapes with a tan center and yellowish margin. When favorable conditions occur, such as cold, humid weather, and frequent rainfalls, lesions acquire a rectangular shape with the presence of black dots in the center of the lesions and without the clear yellowish margin, spreading up to the upper leaves and stems and also to nearby plants.

Powdery mildew also starts on the lower parts of the plant where high moisture remains for more extended periods. Powdery mildew can be plentiful in the lower canopy, but not visible on the top of the wheat crop. The main characteristics of this disease are white, cottony patches on the plant surface. Later in the season, the white spots turn dull gray-brown.

Because both diseases start in the lower parts of the plant, it is imperative to look in the lower canopy when scouting.

Septoria on wheat
Septoria leaf spot on wheat. Photo by Dennis Pennington, MSU.

How to manage these diseases

Scout for the presence of Septoria leaf spot and powdery mildew in April and May, but hold off treatment until the wheat begins to joint. Both diseases will not start actively growing until the wheat plant reaches Feekes 6 stage (jointing). Fungicides have little activity on dormant fungi. Depending on the disease levels, treatment might not even be necessary, especially if weather conditions are dry and hot since Septoria leaf spot and powdery mildew requires moist, humid and mild temperature conditions to thrive.

Overall, choosing resistant varieties is the best approach for managing Septoria leaf spot and powdery mildew. Planting wheat following another small cereal grain can encourage fungal disease development because of the “green bridge.” Also, excessive rates of fertilizer nitrogen can lead to overly dense stands that tend to promote leaf diseases.

If your variety is susceptible to any of these diseases, a fungicide application between flag leaf and head emergence (Feekes 8 to 10.5) will provide very good control. Most of the available fungicides are equally effective against both infections. To see the list of available products, please refer to “Fungicide Efficacy for Control of Wheat Diseases” from the Crop Protection Network.

Did you find this article useful?