July really pushed corn and soybean development along. Corn fields across the state are mostly in the late R3 to R5 growth stages, and soybeans are mostly in the R4 to R5 growth stages as well. Even though it may feel like we are heading into the downhill stretch for these crops, continue to scout fields. Below, ISU Extension and Outreach field agronomists share what they have been finding and hearing about in fields around the state this past week.

A modern 110-day corn hybrid in central Iowa produces about 19 leaves but can only maintain 12-14 leaves on the plant. The first leaves begin senescing around the V5 stage, and by silking (R1) approximately 6-8 bottom leaves have already senesced (Figure 1). From R1 to R5, leaf senescence progresses slowly, with about 2-3 additional leaves senescing. Most leaves are rapidly senescing near physiological maturity (R6) or black layer.

The “cooler” temperatures were welcomed last week. Rainfall was spotty across the state, and unfortunately, the western part of the state, which has been drier, missed out on most of the rain. Corn pollination has wrapped up or is wrapping up, and soybeans are starting to fill pods. Overall, disease and insect pressure remain low across the state. Read on for more specifics on what ISU Extension field agronomists are hearing and seeing in fields around the state.