Southwest Michigan field crops update – August 6, 2026
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EmailMost soybeans and corn are moving into seed fill stages.
Rain over the past weekend ranged throughout the region from negligible to over half an inch. Otherwise, the past week was mostly sunny, warm and clear. Temperatures are expected to remain about the same moving into the next week, but there is a much higher chance of precipitation forecast for today, Aug. 6, until Tuesday, Aug. 11. Currently, the forecast calls for nearly an inch of precipitation, which would be a welcome addition to the dry soil conditions.
Crops and pests
Most full-season soybeans have moved into R5 (seed 1/8 inch long within pod) or will soon. For fields that are still in flowering and early pod formation, R3 is the last effective stage to apply a white mold preventative fungicide. The Crop Protection Network’s Crop Risk Tool showed high risk of white mold development on irrigated soybeans and low on non-irrigated soybeans in southwest Michigan for the past week.
Corn has mostly started into kernel development stages. At R2 (blister), the kernels are filled with clear fluid. At R3 (milk), the fluid becomes milky as starches accumulate. R4 (dough) has a pasty consistency. Male row destruction in seed corn picked up over the past week.
Continue to scout for tar spot by looking for small dark lesions on leaves. Make sure to add water and try to rub the lesion off. If it can be rubbed off, it is not tar spot, but insect droppings. Tar spot fungicides are most profitable when applied between R1 (silking) and R3 (milky kernel) in corn. Tar spot has been confirmed in Calhoun and Jackson Counties this season, according to the Tar Spot Map. The Crop Risk Tool showed low to moderate risk for tar spot development over the past week. Cooler temperatures and irrigation increase tar spot risk.
Most fields are out of the highest risk window for western bean cutworm. Fields that are close to tasseling or freshly tasseled should continue to be scouted by putting the sun behind the leaves to watch for egg masses, which will appear as dark shadows on the backlit leaves of the upper canopy.
Western bean cutworm adult moth counts dropped last week and will probably remain low for the rest of the season. Bucket traps in Berrien (Eau Claire), Branch (Union City), St. Joseph (Centreville and Sturgis) and Van Buren (Lawrence) counties have caught the following:
|
Date |
Branch 1 |
Branch 2 |
Centreville |
Eau Claire |
Lawrence |
Sturgis |
|---|---|---|---|---|---|---|
|
7/20 |
109 |
9 |
14 |
41 |
93 |
21 |
|
7/27 |
13 |
1 |
5 |
46 |
38 |
30 |
|
8/3 |
2 |
5 |
0 |
3 |
7 |
5 |
Potatoes are in tuber bulking stages or awaiting harvest. Vine kill began a couple weeks ago on early crop Russets to allow them to set skins before harvest. In full-season and storage potatoes, continue to scout for aphids and late blight. Late blight risk over the past week was mainly moderate with some areas of low risk, according to the Vegetable Disease and Insect Forecasting Network.
Irrigation and water use
Corn and soybeans remain at peak water use, requiring approximately 1.35 inches of water per week (0.19 inches per day). Maintaining adequate soil moisture during these critical growth stages is essential to minimize water stress and protect yield potential.
Potatoes in the bulking stage are beginning to decrease water use, now requiring approximately 0.70 inches per week (0.10 inches per day). Water demand will continue to decline as the crop matures.
Rainfall is expected across most regions this week. Account for effective rainfall when scheduling irrigation to avoid over-irrigation, and monitor irrigated soybeans for increased white mold risk.
To improve irrigation management, consider using irrigation scheduling tools such as the free and updated MSU Irrigation Scheduling Mobile App, available for Apple and Android devices. The app provides field-specific irrigation recommendations based on crop growth, weather, and soil type.
This year, weekly crop water use updates will continue to be shared through the Southwest Michigan Crop Updates, and for added convenience, updates will also be sent through direct email and text messages. If you would like to see an additional location included in the report, please contact Angie Gradiz at gradizme@msu.edu or 531-249-4956.
The table below summarizes estimated crop water use (inches per week) for major irrigated field crops across Michigan's primary irrigated regions.
Estimated weekly crop water use for field crops in Michigan (in/week) week of Aug. 3–9, 2026:
|
Crop |
Growth stage |
Constantine |
Berrien Springs |
Entrican |
Hart |
|---|---|---|---|---|---|
|
Reference ET |
1.23 |
1.28 |
1.07 |
1.24 |
|
|
Corn |
V12 |
1.23 |
1.28 |
1.07 |
1.24 |
|
Corn |
VT, Silk, Blister, Dough, Begin Dent |
1.35 |
1.41 |
1.18 |
1.36 |
|
Corn |
Full Dent |
1.23 |
1.28 |
1.07 |
1.24 |
|
Soybeans |
R2 (Full bloom) |
1.35 |
1.41 |
1.18 |
1.36 |
|
Soybeans |
R3 (Begin pod) - R4 (Full pod) |
1.35 |
1.41 |
1.18 |
1.36 |
|
Soybeans |
R5 (Begin seed) |
1.35 |
1.41 |
1.18 |
1.36 |
|
Potato |
Tuber bulk |
1.05 |
1.09 |
0.91 |
1.05 |
|
Potato |
Bulk |
0.74 |
0.77 |
0.64 |
0.74 |
|
Potato |
Pre-Senescence |
0.37 |
0.38 |
0.32 |
0.37 |
Field Crops Virtual Breakfast Series
Hot topics, presented by various specialists, was the topic for the MSU Extension Field Crops Virtual Breakfast this week.
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, Mediaspace, 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.
