Southwest Michigan field crops update – July 18, 2024

Nicolle Ritchie<ritchi67@msu.edu> and Angie Gradiz<gradizme@msu.edu>, Michigan State University Extension - July 25, 2024

More rainfall this week left fields and crops saturated, which affected field work. Most soybeans and corn throughout the region are in or entering reproductive stages.

A flooded field. — Between the rainfall last week and this week, many fields have standing water. Photo by Nicolle Ritchie, MSU Extension.

Weather

More precipitation early this week (over 3 inches in some places) further impacted fieldwork and crop health. In the past month, southern Michigan has received between 200-300% more rainfall than normal. Several fields have standing water. As many crops enter peak water uptake, the soil profile will be able to provide that water. Cooler and drier weather is expected throughout the weekend, with the next opportunity for precipitation forecast to arrive Tuesday, July 23. As next week continues, temperatures are expected to increase.

10 day WU forecast as of 7-18.png — Ten-day Weather Underground forecast as of July 18, 2024.

6-10 and 8-14 as of 7-18.png — The 6-10 day (July 23-27, top) and 8-10 day (July 25-31, bottom) outlooks for temperature (left) and precipitation (right).

Crops and pests

Most soybeans range from R2 to R5. According to “Identifying soybean reproductive growth stages” from Michigan State University Extension R3 begins when any of the four uppermost nodes with a fully developed leaf has one pod of just under 0.25 inches (3/16-inch to be precise). At R4, one pod on any of the four uppermost nodes (with a fully developed leaf) is 0.75 inches long. A soybean enters R5, referred to as beginning seed, when a pod in one of the four uppermost nodes (with a fully developed leaf) has a seed 1/8 inches long.

Soybean beginning pods.jpg — Pods 3/4-inch long or longer (such as these) in the top four nodes means that the soybean has entered R4. Split the pods open to see if any seeds are at least 1/8 inches long, which would put the plant at R5. Photo by Nicolle Ritchie, MSU Extension.

The window for white mold application is slowly closing as more soybeans advance through the reproductive stages. For those still between R1 and R3, the Sporecaster app shows high white mold risk in nearly all counties in southwest Michigan for July 18, 2024. Other disease pressures include bacterial blight and septoria brown spot, although neither are reported to be present at concerning levels.

Soybean bacterial blight.jpg — Soybean bacterial leaf blight. Photo by Nicolle Ritchie, MSU Extension.

Sporecaster WM risk 7-18.png — Soybean white mold risk from the Sporecaster app, based on 15-inch rows, flowers present and over canopy threshold. A risk score of 40% or higher during flowering implies a white mold spray may be warranted.

Many acres of both seed and commercial corn had tassels out this week. Seed corn detasseling began a couple weeks ago and continued in earnest this week. Commercial corn is mostly between R1 and R2. R1 is defined as silk outside the husk, and R2, referred to as blister, has kernels filled with clear liquid.

Tar spot has been found in Branch, Calhoun and St. Joseph counties so far. This does not necessarily mean that sprays are needed in all those counties. However, it does mean that scouting should be occurring. Focus on areas that might hold moisture, such as western tree lines or standing water under a pivot. Watch for the small black raised lesions of tar spot and use moisture to rub at the spots on the leaf to make sure they are truly lesions and not just insect frass (insect poop). Flip the leaf over to see if the lesion continues to the underside. Check out the Michigan State University (MSU) Extension article "Managing tar spot in corn" and the Field Crops Virtual Breakfast – White Mold in Soybeans and Tar Spot in Corn with MSU pathologist and Extension specialist Marty Chilvers for more information. The Tarspotter app shows low tar spot risk for July 18, 2024.

Com corn R2 partial husk.jpg — Corn just entering R2, referred to as blister. The kernels fill with liquid that comes out clear when pressed. Photo by Nicolle Ritchie, MSU Extension.

Tarspotter tar spot risk 7-18.png — Corn tar spot risk from the Tarspotter app. The app sets a default risk score of 35% or higher between VT to R3 to imply a tar spot spray may be warranted.

Western bean cutworm moth counts were down this week in most areas. Scout at ear level and above for western bean cutworm. Timing and coverage are most important for controlling western bean cutworm. Although not causing significant yield loss, it opens the ear up to pathogens and quality issues, particularly Gibberella ear rot. The risk model for Fusarium head scab shows that risks for Gibberella ear rot are high right now. Bucket traps in Branch (near Union City), Berrien (near Eau Claire), Cass (near Cassopolis) and St. Joseph (Centreville and Sturgis) counties have caught the following:

Date	Berrien	Cassopolis	Centreville 1	Centreville 2	Sturgis	Union City 1	Union City 2
6/24	2	0	6	9	0	5	3
7/1	1	81	29	46	29	61	4
7/8	4	123	40	34	22	90	31
7/15	10	57	24	11	16	79	37

WBC moth better cropped (1).jpg — Western bean cutworm moth. Note the crescent shaped marking, tan dot and white outer stripe on the wing. Photo by Nicolle Ritchie, MSU Extension.

Vine rot and pathogen inoculation risks continue in potatoes. Vine kill began on some early Russet fields, which puts potential harvest around the first week of August—much earlier than normal.

Alfalfa and forage crops resumed cutting and baling activities over the weekend and in the past couple days where possible. The forecast shows several days without precipitation coming up, so this will provide a good window of opportunity for cutting crops that are still standing and baling what has been cut.

Weekly water use

Estimated weekly crop water use for field crops in Michigan (in/week) Week of July 15 – 21, 2024
Crop	Growth stage	Constantine	Entrican	Hart
Corn	V8	0.71	0.67	0.72
	V10	0.97	0.91	0.97
	V12	1.28	1.20	1.28
	VT	1.40	1.32	1.40
	Silk, Dough, Blister	1.40	1.32	1.40
	V3 3rd node	0.77	0.72	0.77
Soybeans	R1 Beginning bloom	1.28	1.2	1.28
	R2 Full bloom	1.40	1.32	1.40
	R3 Beginning pod/Pod filling	1.40	1.32	1.40

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. For more tools and information on irrigation scheduling tools, please refer to: Irrigation Scheduling Tools.

Reference evapotranspiration data was obtained from MSU 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

VB 2024 graphic.jpg

White mold in soybeans and corn tar spot, presented by MSU pathologist and Extension specialist Marty Chilvers, was the topic for the MSU Extension Field Crops Virtual Breakfast this week. Management factors for white mold and tar spot were the focus. 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 @MSUExtension.

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).