Southwest Michigan field crops update – July 24, 2025

Nicolle Ritchie<ritchi67@msu.edu> and Angie Gradiz<gradizme@msu.edu>, Michigan State University Extension - July 24, 2025

Hot and dry conditions hit crops hard in areas of southwest Michigan. Potato harvest began, and wheat harvest is wrapping up.

Close-up image of a cornfield under bright sun. The corn leaves are curled, indicating drought stress, with tassels emerging from the top. The sky is mostly clear with a few clouds, highlighting hot, dry weather conditions. — Crops in some parts of Michigan are experiencing significant drought stress, which is especially damaging during pollination and early kernel fill. Photo by Nicolle Ritchie, MSU Extension.

Weather

This past week saw occasional scattered showers, which has been the story of southwest Michigan since mid-May. Some areas are extremely dry, and others have received adequate moisture for dryland crop production. Late last week brought a couple days of cool weather before returning to the hot and humid conditions we’ve experienced nearly every week. Heat indexes yesterday, July 23, and today are especially high due to temperatures and high dew points. Significant precipitation is forecast for this weekend.

NOAA 4-panel outlook maps show U.S. temperature and precipitation forecasts issued July 23, 2025. For July 29–Aug 2, much of the central and eastern U.S. is warmer than normal; precipitation is above normal in the northern Plains and Southeast. For July 31–Aug 6, heat continues in the South and West, cooler in the Midwest; precipitation above normal in the West, Southeast, and Great Lakes, below normal in the Northeast. — The 6-10 day (July 29- Aug. 2, top) and 8-10 day (July 31-Aug. 6, bottom) outlooks for temperature (left) and precipitation (right).

Crops and pests

Soybeans are mostly in early pod stages. R3 starts when a pod at the fourth node down the main stem is 3/16 inches long. At R4, a pod at the fourth node is 0.75 inches long. Fungicides to prevent white mold should be applied between R1 and R3. Once soybeans hit R4, fungicides have very little if any efficacy on white mold prevention. Risk models based on weather show high white mold risk on irrigated fields and low white mold risk on unirrigated fields for the next several days. The moist environments of irrigated fields increase the risk of disease development. Frog-eye leaf spot risk is moderate.

A hand holds a soybean stem in front of a green soybean field. A white circle and arrow label the fourth node, indicating reproductive stage R4. The plant has broad leaves and small purple flowers are visible near the node. — This soybean plant is at R4, identifiable by counting down to the fourth node on the main stem and measuring the length of the pod(s) present there (circled in white). If the pod is 0.75 inches long, as in this picture, the plant is at R4. Photo by Nicolle Ritchie, MSU Extension.

Corn continues to progress in reproductive stages. Silks have emerged on corn ears (R1), and some ears are at R2, which is when the kernels are full of clear liquid (like a blister). Seed corn detasseling continued this past week.

Tar spot was confirmed in Calhoun County this past week. The best timing for a single fungicide application is still between VT and R3-4. Risk models show low tar spot risk for the next week for unirrigated fields, but moisture increases tar spot infection, so irrigated fields are at higher risk.

Western bean cutworm moth flights have been low. Prioritize scouting on corn that is close to tasseling or freshly tasseled. Watch for egg masses in the upper two thirds of the canopy by walking with the sun backlighting the plants. Egg masses will appear as dark shadows on the leaves.

Two-panel image showing signs of western bean cutworm (WBC) in corn. Left: WBC moth silhouette on the underside of a corn leaf. Right: Frass (insect waste) on a corn leaf, indicated by a circle, with a person’s finger for scale. — Scout for western bean cutworm by putting the sun behind the corn and watching for dark shadows (left). Flip the leaf over to see if it is an egg mass (right). In this case, the shadow was from soil on the leaf surface, not an egg mass. Photo by Nicolle Ritchie, MSU Extension.

Bucket traps in Berrien (near Niles), Branch (near Union City), St. Joseph (near Centreville and Sturgis) and Van Buren (near Paw Paw) counties have caught the following western bean cutworm moths:

Date	Branch 1	Branch 2	Centreville	Niles	Paw Paw	Sturgis
7/21	74	72	7	--	57	32

Winter wheat harvest continued and is close to wrapping up. Today’s Field Crops Virtual Breakfast Series touched on cover crop options for after wheat. The Michigan State University Extension article, “Considering double-crop soybeans after a winter cereal this year?,” the Midwest Cover Crops Council’s cover crop recipe for planting after wheat going into corn or soybean and the Michigan State University Extension fact sheet “Cover crop tolerance to winter wheat herbicides” can help guide decisions on what to plant after wheat.

A combine harvester moves through a golden wheat field under a blue sky, kicking up dust as it harvests. The machine is on the right side of the frame, moving toward the trees lining the background. — Wheat harvest is nearly wrapped up. Photo by Nicolle Ritchie, MSU Extension.

Fresh crop chip potato harvest started late last week. Vine kill also started on early-harvest tablestock potatoes. The heat and humidity are conducive to vine rot. While humidity contributes to late blight spread, temperatures have generally been higher than the disease prefers, so the forecasted late blight risk is low.

Colonizing aphid pressure will continue probably until vine kill. Make sure to rotate insecticide modes of action and not apply one mode of action more than twice consecutively.

Close-up of potato plants with visible vine damage. Stems are decaying and collapsed in some areas, exposing bare, cracked soil beneath. Signs of vine rot are apparent in the lower canopy. — Vine rot is an annual challenge for potato producers in Michigan. As vines rot, the canopy opens. As the canopy opens, soil moisture evaporates more readily, and the soil and tubers heat up. This reduces quality, requires more irrigation to keep the crop going and increases chances of plant death from potato early die. Irrigation in turn flares up vine rot. Photo by Nicolle Ritchie, MSU Extension.

Alfalfa and forages continue at variable stages of development; however, many fields were at the cutting and baling stage over this past week.

Weekly water use

Corn is currently at peak water use, with the most critical period occurring between VT (tasseling) and R3 (early grain fill). This window often aligns with the hottest part of the summer, when transpiration demand exceeds the plant's water uptake, increasing the risk of water deficiency. Ensuring adequate soil moisture during this time is essential to avoid delayed silk emergence, poor pollination and yield or quality loss. Weekly water use for corn is around 1.5-1.55 inches and often exceeds rainfall in dry areas.

Soybeans are most sensitive to water stress during the R3 to R6 stages (pod development through seed fill). Stress during these stages can lead to flower and pod abortion, leaf drop and reduced yield potential. Leaf flipping, exposing the silvery-green underside, is an early symptom of stress. Water use for soybeans is around 1.5-1.55 inches per week. For efficient irrigation, apply enough water to meet five to six days of crop water use, typically 1 to 1.25 inches per irrigation. Be sure to adjust for recent rainfall and leave room in the soil profile to capture future precipitation.

For more information, please refer to the peak water use article. Irrigation Scheduling Tools can help estimate crop water needs and decide timing and application.

Estimated weekly crop water use for field crops in Michigan (in/week) for the week of July 21-27.

Crop	Growth stage	Constantine	Entrican	Hart
	Reference ET	1.42	1.4	1.31
Corn	V10	1.08	1.06	1
Corn	V12	1.42	1.4	1.31
Corn	V16, VT, Silk, Blister, Dough, Begin Dent	1.56	1.54	1.44
Soybeans	R1 Beginning Bloom	1.42	1.4	1.31
Soybeans	R2 Full Bloom	1.56	1.54	1.44
Soybeans	R3 Begin Pod / R4 Full pod	1.56	1.54	1.44

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

2025 VB graphic (3).jpg

Cover crops after wheat, presented by Brook Wilke, associate director at the Kellogg Biological Station, was the topic for the MSU Extension Field Crops Virtual Breakfast this week. There are several cover crop species that do well when planted after wheat, but there are some considerations to be aware of.

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.   

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

MSU Extension Field Crops