Northern corn leaf blight first became visible three weeks ago in Dodge and Washington counties. The disease severity has been increasing in some high risk environments (disease present last year, corn-after-corn, and a moderate to susceptible hybrid). In low risk environments, such as corn planted after alfalfa, lesions have not been observed. However, some NCLB lesions can be found in many no-till corn fields that followed soybeans and more prominently in corn following corn where a susceptible hybrid was planted (Figure 1).
In some of these higher risk growing conditions, the disease has spread within the corn canopy to upper leaves. Hybrids with both low to moderate ratings are being impacted in these environments. Septoria brown spot on the lower leaves in the soybean canopy can already be seen in the area, which is not a concern unless we see progression of symptoms upward in to the mid-canopy. In spite of the wet weather, some area producers have been concerned about the amount of grasshoppers in field borders this week.
Agronomic concerns for the week:
- Scout all corn fields for Northern corn leaf blight to determine which fields may warrant fungicide application at tasseling.
- Monitor grasshopper pressure in field borders.
- Scout soybeans for Septoria brown spot in the lower canopy and watch for upward movement in the coming weeks.