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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.

Rainfall this spring and into midsummer wasn't unusual in total amount, but it was unusual in how it arrived in central Iowa. Cumulative rainfall data from Boone, Iowa (April 1–July 20) was in the upper-middle range of the 30-year record at 19.5 inches (range: 6.5” in 2011 to 26.5” in 2008; Figure 1).

The Iowa Environmental Mesonet (IEM) celebrated its 25-year anniversary this summer! IEM helps farmers, researchers, meteorologists and everyone in between make informed decisions using weather and climate data. Daryl Herzmann is a systems analyst at Iowa State University and the person who creates the magic behind the scenes.  

If you’ve been checking the Crop Outlook Map you will have noticed that southern rust was confirmed in Benton, Mahaska, Muscatine and Louisa Counties on 21 July 2026. In all locations, the disease was found on a few plants at low severity (few pustules per leaf). Similarly, in 2025 and 2024, southern rust was also reported in Iowa in mid-July. In 2024, we estimated 4% yield loss in Iowa due to southern rust, while in 2025, yield losses were estimated at 7.5%.

The last week was a hot and dry one for most of the state. Storms did roll across the state Monday into Tuesday of this week that brought some rain but also strong winds and hail. While disease pressure remains low in both corn and soybeans, southern rust has been confirmed in four counties in Iowa. In the fields southern rust was found in, it was found at very low levels.

One of the largest and least visible sources of nitrogen (N) for Iowa corn is the soil itself. Through N mineralization, soil microbes convert organic N into plant-available forms every day. In many fields, this natural process supplies well over 100 lb N/acre during the growing season. 

Corn fields around the state, if not tasseling currently, will be soon. Soybeans are mostly in the R2 to R3 stages. Overall, disease pressure remains low with reports of gray leaf spot and bacterial leaf streak being found in corn and bacterial blight, septoria brown spot and phytophthora being found in soybeans. Insects reported include Japanese beetles, grasshoppers, and corn rootworm beetles.

The hot and humid conditions last week really pushed the crops along. The week also brought heavy rainfall to parts of the state – including areas in central Iowa getting 12+ inches over a 3-day period. Corn fields are starting to tassel, and soybeans are fully in the reproductive stages now. Bacterial leaf streak, Goss’s wilt, weed escapes, Japanese beetles, and adult corn rootworm beetles emerging are some of the issues observed by ISU extension field agronomists this past week.

In the next week or so, corn fields across Iowa will start to tassel and the buzz of crop dusters will no doubt join the buzz of insects. Research has consistently shown that the best time to apply a fungicide to manage foliar diseases, like tar spot, southern rust, northern corn leaf blight and gray leaf spot, is at tassel (VT) through milk (R3) stage. But do you really need to spray a fungicide? Fungicides protect yield potential by reducing foliar disease within the canopy.

Regional Update: 

Crop Lookout is a new interactive tool on the Crop Protection Network. This interactive map shows real-time what has been observed in fields this growing season, not only in Iowa but across the U.S. and in Canada. It can help farmers and agronomists see what’s being found in fields to help guide local scouting and management decisions. 

Another week with a similar pattern in rainfall with northwest and west-central Iowa getting lower amounts and heavier amounts in east-central and southeast Iowa. Both of these extremes are having an impact on crops. With corn getting into the mid-vegetative stages now and soybeans starting to reach the reproductive stages, ISU Extension and Outreach field agronomists share what they are hearing and seeing in their respective areas of the state.  

It is June 19, 2026, and another round of storms moved through the state earlier this week, bringing high winds and rain. This is yet another storm that has impacted the state in the past week.

 So far in June, Iowa has experienced

From industrial applications to hobbyist platforms, Unmanned Aerial Vehicles (UAVs), commonly referred to as drones, have rapidly integrated into the agricultural landscape. Equipped with high-resolution sensors, these aerial platforms have fundamentally altered how modern production agriculture monitors crop development.

The storms that rolled across the state last week also brought along with them heavy rain, wind, and even some hail. While most areas did receive some rainfall, parts of northwest Iowa missed out and the drier conditions are starting to show. Weeds continue to be the biggest challenge across the state as many are struggling to get their postemergence herbicide applications made with the wet field conditions. Read on for more specifics on what’s happening around the state.

Photo by: John Sawyer, ISU Extension Retired

It's a question that arrives in our inboxes every spring without fail: "It's been raining — have I lost nitrogen, and do I need to apply more?" This year is no exception. With a highly variable spring precipitation pattern across Iowa (see map below) and corn now approaching or past the critical V6 growth stage, many producers are seeing yellowing in their fields and wondering what to do next.

Reports of tar spot from Madison, Jaspar and Calhoun counties have been received over the weekend and today (June 13-15, 2026). The disease is present at very low incidence (one to a few plants in a field) and low severity (one spot on a leaf).  In addition, the disease is being observed on the lowest leaves of the canopy.