As we near the end of the growing season, corn across the state is mostly in the R5 stage with some already reaching R6. Corn silage harvest is underway. Soybeans are mainly late R5 to R7. Observations from fields or topics of concern continue to center around southern rust, tar spot, sudden death syndrome (SDS), and weed escapes. ISU Extension and Outreach field agronomists share more specifics below about what is happening in fields in their regions around the state over this last week.
Leah Ten Napel (Region 1):
Cherokee, Ida, Lyon, Monona, O'Brien, Osceola, Plymouth, Sioux, Woodbury counties
“Both corn and soybeans are progressing very nicely in NW Iowa. Most corn is in the R5 stage, while soybeans are R5 to R6 stage. The main pests causing issues in soybeans are waterhemp escapes as well as soybean aphids. Southern rust and tar spot are the main diseases impacting corn. Insect pressure has remained relatively low for both crops. Pasture and hay fields are looking good this year because of adequate moisture, but that has made hay harvest more difficult as well. As the growing season wraps up it is important to continue scouting to avoid surprises in the combine. It is also helpful to scout stalk quality to begin planning harvest priorities.”
Angie Rieck-Hinz (Region 3):
Cerro Gordo, Franklin, Hamilton, Hardin, Humboldt, Webster, Worth, Wright counties
“Corn is mostly R5.5 and even R6 (physiological maturity). At R6 corn has reached maximum dry mater and moisture averages around 35%. If you are located in Wright County, Iowa, planted a 108-day maturity hybrid on April 11, your predicted black layer based on the average of the last 30 years, would be September 7. At this location, we a running about 147 GDDs ahead (about 7 days) of the 30-year average due to our warm summer. Other stressors such as too much water and disease pressure can also push maturity. You can calculate your own GDDs based on location, planting date, relative maturity and current date by using the by using the U2U Corn Growing Degree Calculator hosted by the Midwest Regional Climate Center. After field observations today, if you have southern rust pressure, I suggest you evaluate stalk integrity as many fields without a fungicide and some with are shutting down early and stalk integrity has degraded to the point when you push the corn stalks they are collapsing or breaking, as shown in the photo below. Soybeans are primarily R6 or full seed. Sudden death syndrome, frogeye leaf spot, bacterial blight, and white mold can all be found in soybeans. "
Josh Michel (Region 5):
Allamakee, Buchanan, Clayton, Delaware, Dubuque, Fayette, Jones, Linn, Winneshiek counties
“Showers early last week resulted in most of the region receiving 0.10 to 0.50 inch of rainfall, with some isolated areas in Winneshiek and Allamakee counties receiving around 1.5 inches. Thankfully, dry weather the rest of the week and over the weekend has allowed producers to start getting back into the fields. In general, most corn fields are at late R4 (dough stage) to R5 (dent stage). Some fields that are further along are quickly reaching 1/2 milk line. I continue to see and hear increasing reports of southern rust. Silage harvest is beginning in most areas as fields continue to dry out. Soybeans are generally around late R5 (beginning seed fill) to R6 (full seed fill). While soybean-related disease concerns remain low, reports of SDS continue to come in and show up in some isolated areas. Forages continue to look good, and I’ve been seeing some cover crops getting aerial seeded. The majority of field calls this past week centered around weed management, forage management and silage harvesting.”
Meaghan Anderson (Region 7):
Boone, Dallas, Jasper, Madison, Marshall, Polk, Story, Tama, Warren counties
“Most of central Iowa was spared from any significant rainfall for the first time in quite a while this week. The crops are noticeably changing as they continue maturing, with most corn in the mid or even late R5 growth stage and soybeans in the late R5 to R6 growth stage. The same issues that have been commonly coming up in conversation for the past several weeks continue to: southern rust, weeds, and sudden death syndrome. I received an image on Monday (8/25) of corn that was testing at 32% moisture and several images of fields that look much closer to harvest-ready than we’d like them to be. With southern rust and moisture taking fields/parts of fields down early, this fall will be an important one to scout for standability of the crop, choose harvest order carefully, and take care to keep yourselves and your equipment safe from all the dust we’re likely to see.”
Rebecca Vittetoe (Region 8):
Iowa, Jefferson, Keokuk, Poweshiek, Washington, Johnson counties
“As we are nearing the end this growing season, corn is mainly in the mid to late R5 stage. There may be some fields that have reached R6. Soybeans are mostly late R5 to R6. The cooler conditions here recently may be slowing southern rust down some, but tar spot is becoming more apparent in some corn fields. In addition to the foliar disease concerns in corn, I’ve received some reports of corns aphids showing up and hearing a little more on ear molds being found as well. Continue to monitor fields for stalk quality. Based on some of the fields I’ve been in, this could be a concern this fall. On the soybean side, SDS continues to expand in fields, and I’ve received additional reports of white mold showing up in fields as well. Forages look great for the end of August. While I’ve received fewer calls about fall armyworms this last week, continue to keep your eyes out for this pest.”
Virgil Schmitt (Region 9):
Cedar, Clinton, Des Moines, Henry, Jackson, Lee, Louisa, Muscatine, Scott counties
“In general, the counties I cover received 0.5 to 1.0 inch of rain last week, with a few areas receiving between 1.0 and 1.5 inch. Most corn is R5 and about 1/3 to 1/2 milk line and generally looks good. Southern rust of corn “exploded” last week. Other corn diseases continue to easily be found. Soybeans are generally late R5 to R6. More spots of soybean sudden death syndrome are appearing, and “older” spots are enlarging. Forages continue to look good. Third cutting of hay is underway and is making good progress with the drier weather. Calls last week mostly centered around southern rust of corn and weed management.”
Aaron Saeugling (Region 10):
Adair, Adams, Cass, Clarke, Decatur, East Pottawattamie, Fremont, Mills, Montgomery, Page, Ringgold, Taylor, Union, West Pottawattamie counties
“While July was the top 10 for rainfall, August has slowed the pace allowing fields to dry the top few inches of topsoil. Temperatures and humidity have still been typical for this time of year. Corn is mostly in the R4 to R5 stage with most conversations centered around the continued advancement of southern rust in fields. While true this will take some yield off the top end depending on infection severity and time of infection, no one knows for sure the full impact it will have on yield. Silage choppers are just getting a start and will be busy this next month, so we can get a glimpse into yields and corn dry down in September. Grain dry down will begin after R6 (physiological maturity). Corn can drop moisture at the rate of 0.5 to 0.75% per day based on the weather conditions until it reaches 20% moisture. Continue to watch corn fields for dry down and lodging for harvest. Soybeans will begin a rapid maturity phase now that most are in the R6 stage and disease is moving crop maturity along quickly. Once soybeans hit R7, they hold approximately 60% moisture, so moisture up until R7 is still critical to yield for soybeans. Monitor soybean moisture as fall progresses and try to take advantage of harvest moisture around 13%. Last year it was impossible to get soybeans harvested at the proper moisture, and we left some yield due to dry harvest conditions. Pastures and hay fields look great for this time of year. Be sure to try some rotational grazing and begin stockpiling fescue pastures for late season grazing where possible. Also, note the typical late season killing frost for SW Iowa is the last week of October. Keep this in mind when thinking about taking that last cutting of alfalfa this fall. It is recommended to either cut 5 weeks before a killing frost to allow for regrowth, harvest so we don't accumulate more than 200 GDD between the last cutting and a killing frost, or wait until after we have that killing frost."
Logan McCrea (Region 11):
Appanoose, Davis, Lucas, Mahaska, Marion, Monroe, Van Buren, Wapello, Wayne counties
“Over the last week, much of my area has been dry in comparison to the rest of the summer. Corn ranges from R5 to R6 and is very noticeably moving rapidly through the starch lines of the R5 stage. Silage season has begun, and some choppers have been running hard lately trying to keep pace with the rapidly developing corn. Soybeans are R5 to R7 with SDS continuing to pop up in growers’ fields. Forages look tremendous for this time of the year, and the weather is giving producers a great late window to finish getting hay put up. Fall armyworm has continued to cause some issues in forages, but most that I have talked with have been right on top of it and been able to manage it when needed.”
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- Field Agronomist in EC/SE Iowa