Southwest Michigan field crops update – September 4, 2025

Nicolle Ritchie<ritchi67@msu.edu> and Angie Gradiz<gradizme@msu.edu>, Michigan State University Extension - September 04, 2025

Seed corn harvest started and storage potato harvest will begin this week. Soybeans are progressing toward senescence, and corn is approaching black layer.

Hand holding a green soybean pod split open, showing three plump green seeds inside at late reproductive stage (R6.5). — Photo by Nicolle Ritchie, MSU Extension.

Weather

Conditions remained cool and mostly dry throughout the past week. Scattered showers resulted in small amounts of precipitation throughout southwest Michigan. The next week will be even cooler and drier but will heat up again in time for next weekend.

Four NOAA maps showing U.S. 6–10 day and 8–14 day outlooks for temperature and precipitation, valid mid-September 2025, with warmer-than-normal temperatures forecast in much of the country. — Weather Underground forecast chart from Sept. 3, 2025, showing daily icons, temperature trends, precipitation, humidity, cloud cover, wind speed, and pressure for the upcoming week.

Crops and pests

Soybeans are mostly at R6 (full seed). Some fields have hit R7, which is where one pod anywhere on the plant has reached mature pod color. White mold and sudden death syndrome are out in fields. Sudden death syndrome, brown stem rot and red crown rot all have similar symptoms, so don’t hesitate to send in samples for disease confirmation. Watch especially for red crown rot, which has not been confirmed in Michigan yet. Learn more about it from the Michigan State University Extension article, "Red crown rot: A new threat to soybean production.”

Side-by-side images of soybean plants. Left: leaf with brown lesions between green veins, symptoms of sudden death syndrome (SDS). Right: soybean stem with white mold growth and sclerotia. — Sudden death syndrome (left) and white mold (right) symptoms are becoming visible in fields. Photo by Nicolle Ritchie, MSU Extension.

Corn is mostly at R5 (dent) and approaching R6 (black layer). Corn enters R6 when a black layer forms on the tip of the kernel where it attaches to the cob. Scrape the tip and if a hard, black layer is visible, corn has reached physiological maturity.

Hand holding two cross-sections of sweet corn ears at R5 stage, showing yellow kernels with reddish discoloration at the base and white pith in the center. — During R5, liquidy white parts of kernels are converting to starchier, more yellow parts. The visible delineation between these two parts of the kernel is referred to as the milk line. Photo by Nicolle Ritchie, MSU Extension.

Seed corn harvest began, and defoliation sprays continued to go out on some acres.

Scout for ear rots as corn is in R5. The Crop Protection Network published a helpful overview of ear rots to guide identification and scouting. Foliar diseases such as tar spot and southern rust are in fields throughout southwest Michigan. However, at this point in the season, applying fungicides for any foliar disease is not likely to provide any benefit.

Side-by-side images of corn leaves showing disease symptoms. Left: tar spot with numerous small black specks. Right: southern rust with yellow-orange lesions scattered across the leaf. — Tar spot (left) and southern rust (right) can be found throughout southwest Michigan, but at this point in the season, a fungicide to manage them is unlikely to provide a return on investment. Photo by Nicolle Ritchie, MSU Extension.

In potatoes, fresh crop harvest continued. Storage harvest will begin this week. Upcoming cooler temperatures and dry weather spell out better conditions than usual for the beginning of storage harvest.

Potato harvest in progress. A harvester raises dust in the distance while a white pickup truck is parked nearby. Cloudy skies hang over the freshly worked field bordered by trees. — Potato harvesters running in St. Joseph County last week. Photo by Nicolle Ritchie, MSU Extension.

Many growers cut alfalfa and forages last week. As fall approaches, potassium is especially important to help perennial plants overwinter well. Watch Michigan State University (MSU) forage specialist Kim Cassida’s Virtual Breakfast presentation on potassium for forages for more information.

Weekly water use

Deciding when to stop irrigation is one of the toughest calls of the season. Stop too early, and crops may not get the water they need, risking yield loss. Keep going too long, and you waste water, energy and time.

The goal of the last irrigation is simple: to give crops enough water to finish strong while leaving the soil in good shape for harvest.

Here are three key things to check:

Crop maturity: Corn no longer benefits from irrigation once it reaches black layer. Soybeans need water until at least 50% of the pods on the main stem turn yellow.
Soil moisture: Try to keep at least half of your soil’s water capacity. You can use scheduling tools or do a check with the U.S. Department of Agriculture “feel and appearance” method.
Weather forecast: A timely rain may save you a pass, but remember that extra moisture can also worsen white mold in soybeans or tar spot in corn.

Right now, corn at dent stage uses about 0.14 inches of water per day and drops to 0.09 inches at black layer. Soybeans at R6 are still using about 0.15 inches per day, just over an inch per week.

Watching crop stage, soil moisture and weather together will help you make the best call for your last irrigation of the season. Irrigation Scheduling Tools can help estimate crop water needs and decide timing and application.

Estimated weekly crop water use for field crops in Michigan (inches/week) for the week of Sept. 1-7:

Crop	Growth stage	Constantine	Entrican	Hart
Corn	Reference ET	0.96	0.84	0.74
Corn	VT, Silk, Blister, Dough, Begin Dent	1.06	0.92	0.82
Corn	Full Dent	0.96	0.84	0.74
Corn	Black Layer	0.64	0.55	0.49
Soybeans	R5 Begin seed / R6 Full seed	1.06	0.92	0.82
Soybeans	R7 Begin Mature	0.96	0.84	0.74
Soybeans	R8 95% Pods Mature	0.19	0.17	0.15

The table above presents estimated crop water use for various field crops across three locations in Michigan. This data helps irrigation management decisions by showcasing potential crop evapotranspiration, calculated based on reference evapotranspiration and crop coefficients for each crop growth stage. It is crucial to note that crop water use values vary across regions due to differences in weather conditions, growth stages, agronomic practices and soil properties.         

When using these values for irrigation scheduling, be mindful that they assume all applied irrigation water will be utilized by the plants without any loss. Additionally, these values do not account for any precipitation that may occur during the week of calculation.      

Reference evapotranspiration data was obtained from Michigan State University Enviroweather, which also offers a model for determining potential crop evapotranspiration. To access this tool, visit Enviroweather, click on "Crops," select your crop and use the potential evapotranspiration tool by choosing your nearest weather station, the latest date of interest and other crop information.  

Field Crops Virtual Breakfast Series

Decorative image.

Using yield data effectively, presented by Rich Price, was the topic for the MSU Extension Field Crops Virtual Breakfast this week. Yield data can help guide future crop management decisions, but only if you know how to use it.

Recordings of this and all the Virtual Breakfast meetings are closed-captioned and available at the Field Crops Virtual Breakfast webpage and the MSU Extension Field Crops Team social media platforms: Facebook, Spotify, YouTube, Apple Podcasts and Twitter/X. 

This work is supported by the Crop Protection and Pest Management Program [grant no 2024-70006-43569] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.  

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