Southwest Michigan field crops update – July 14, 2022

Eric Anderson<eander32@msu.edu>, Michigan State University Extension - July 14, 2022

Both corn and soybean are entering key reproductive stages as warm temperatures continue.

Field corn. — Corn has reached the silking stage in earlier-planted fields, triggering several management decisions as the key stage of pollination commences.

Weather

Temperatures this past week were near-normal to slightly below-normal on average in the southwest. We picked up 200 growing degree days (GDD, base 40 for alfalfa) or 130 GDD₅₀ (for corn and soybean) this past week. The forecasted reference evapotranspiration (FRET) rate will be 1.3-1.4 inches this coming week. The forecast predicts the addition of another 220 GDD₄₀ or 150 GDD₅₀ in the coming week. Both the 6-10 day and 8-14 day outlooks point to above-normal temperatures for the last week of July.

Weekly forecasted reference evapotranspiration rate for the week ending July 20.

Precipitation was less than half an inch for most of the region outside of an E-W band in the second and third tier of counties that received as much as 2 inches this past week. We were dry in the last half of June but mostly wetter than normal so far in July, so the last 30 days have been near normal on average. The forecast is for only another 0.25-0.50 inch of rain in the coming week with essentially all of that predicted to fall on Sunday. The medium-range outlooks call for normal to slightly lower than normal chances of rainfall for the last week of July.

Precipitation totals from the past 7 days (left) and percent of normal for the past 14 days (right) as of July 13. Note: these do not include the pop-up showers that passed through the region on Wednesday.

The 6-10 day (July 19-23, top) and 8-14 day (July 21-27, bottom) outlooks for temperature (left) and precipitation (right).

Crops and pests

Corn and soybean continue to look healthy with 66 and 60 % of the crop rated good to excellent, respectively. Early-planted corn has reached the silking stage while most fields are still pre-tassel. Soybean in most fields is still at beginning flower (R1, open flower at any node) or full flower stage (R2, open flower at one of the two uppermost nodes) with pods forming at the base of many plants. A few plants in early-planted fields with short-season varieties had reached the beginning pod growth stage (R3, 3/16 inch or longer appear at one of the four uppermost nodes). Only minor bean leaf beetle and Japanese beetle feeding has been found in soybean, and no signs of tar spot have been found yet in the lower canopy in corn fields.

Early-planted corn at silking (R1) growth stage in St. Joseph County. Photo courtesy of Eric Anderson.

Soybean plant at full flower (R2, open flower at one of the two uppermost nodes). The canopy has not yet closed in this field planted on 30-inch row spacing. Photo courtesy of Eric Anderson.

Weeds. Recently a graduate student from the MSU weeds group visited southwest Michigan to collect samples of several weed species for a molecular study including waterhemp and Palmer amaranth. These amaranth species are related to both redroot and smooth pigweeds and can be difficult to tell apart for those who have not spent time looking closely at the plants. The following pictures will help in distinguishing these species. The MSU weeds group has two related resources available online to aid in identification and to manage these weeds—“Keys to distinguishing Palmer amaranth from other species” and “Management of multiple-resistant Palmer amaranth—and Purdue has a similar fact sheet available online, “Palmer Amaranth Biology, Identification, and Management.” If you find either waterhemp or Palmer amaranth in your fields, please contact the St. Joseph County Extension office (msue.stjoseph@county.msu.edu or 269-467-5511) and we will come and collect samples for this study.

Waterhemp (left side of each picture) can be distinguished from redroot and smooth pigweeds (right side of each picture) by the absence of find hairs on the stems of waterhemp. Photos courtesy of Eric Anderson.

Newest leaves of Palmer amaranth can have a distinctive light green color. Photo courtesy of Eric Anderson.

7-14 sw field 10 — The petiole is longer than the leaf blade, a characteristic easy to see on more mature leaves. Photo courtesy of Eric Anderson.

7-14 sw field 11 — The petiole (stem-like connection from the leaflet to the main stem) of Palmer amaranth is longer than the leaf itself (left) and spiny bracts are found at the base of the leaves. Photos courtesy of Eric Anderson.

Insects. There was a significant uptick in moth catches for western bean cutworm (WBC) this week. This is a little surprising since the trap catches in Indiana last week were meager, and they usually see increases in moth flights before we do. Unfortunately, the moths timed their arrival to coincide with many fields in the region being about a week away from tasseling, and the peak flight may arrive just when most fields will be pre-tassel, the stage when the females lay eggs. No fall armyworm (FAW) were caught again this week.

Pre-tassel corn is the stage targeted by female western bean cutworm moths for laying eggs. Increased moth captures this past week are not a welcome sight. Photo courtesy of Darin LaBar.

Moth captures for WBC in southwest Michigan.

	5-Jul	12-Jul
WBC1	1	12
WBC2	1	25
WBC3	0	6
WBC4	2	33
WBC5	10	109
WBC6	2	23

Irrigation

Corn at V16 all the way through beginning dent (R5) has a Kc of 1.2 and will require 1.5-1.7 inches this week. Soybeans at R1 (beginning bloom, Kc=1.0) will use 1.3-1.4 inches, those at R2 (full bloom, Kc=1.1) will use 1.4-1.5 inches, and early fields that have reached R3 (beginning pod, Kc=1.2) will use 1.5-1.7 inches.

Field Crops Virtual Breakfast

The topic of this week’s MSU Extension Field Crops Virtual Breakfast was focused on sugar beet management which is not pertinent for our region. However, next week on July 21 we will have another “hot topics” edition of the Virtual Breakfast, so plan to join with your pressing questions.

If you were not able to join the session, the recordings will be 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.

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).