Regional Update: August 7 - 23, 2023

August 23, 2023 8:27 AM
Blog Post

The rains earlier in August across much of the state and more moderate temperatures have been replaced by hotter and drier conditions. While some fields across the state look pretty good, others are showing more signs of stress here this week. Other common observations made in fields across the state over the last couple of weeks have included insect pests like aphids, grasshoppers, soybean gall midge as well as diseases like sudden death syndrome, brown stem rot, white mold, and Phytopthora in soybeans and tar spot and gray leaf spot in corn. Read on for more specifics on what’s happening in fields across the state.  

North Central Iowa

Angie Rieck-Hinz (Region 3): “Much like most of Iowa, NC Iowa has good looking crops and some not so good looking crops. This is based on rainfall amounts and distribution. Most corn is R5 or dent, the most mature corn I have found is R5.5. At R5.5 the corn kernel is about 40% moisture and has accumulated 90% of its dry matter. The R5.5 stage average duration is about 10 days. (Corn Growth and Development, 2011). Disease pressure is still low across NC Iowa, but you can find tar spot and grey leaf spot. Soybeans are R5 or beginning seed, although some areas in fields are starting to turn a bit prematurely. During the time of halfway from R5 to R6, dry weight and nutrient accumulation start to redistribute from the leaves, stems and petioles to the developing soybean. Stress (heat and drought) during this time can impact yield by reducing the number of pods per plant and decreasing beans per pod. In the past week I have found sudden death syndrome (SDS), Phytophthora, brown stem rot and white mold in soybean fields.”


White mold in soybean as depicted by fuzzy, white growth and sclerotia.  Photo credit: Angie Rieck-Hinz, August 2023. 

Northeast Iowa

Josh Michel (Region 5): “Most of NE Iowa has received around one inch of rainfall over the past two weeks. The exception was an isolated severe storm that delivered up to three inches in parts of Dubuque County. That being said, the limited soil moisture combined with warmer than normal temperatures continue to cause significant heat stress for many crops. The current U.S. Drought Monitor displays D2, severe drought, for most of the region. Corn is generally around R5. Silage harvest has started in some areas, with growing concerns about high nitrate levels. Soybeans are also around R5 or beginning seed development inside the pods. Japanese beetles and grasshoppers continue to be the main defoliators. I’m also starting to see and hear of some disease issues popping up in isolated areas, primarily sudden death syndrome and brown stem rot. The third crop of alfalfa is getting finished up with reports of potato leafhoppers being found in many areas. Field calls over the past two weeks centered around insect thresholds, weed management, forage management, silage nitrate concerns, and fall fertilizer planning.”

Central Iowa

Meaghan Anderson (Region 7): “Most of central Iowa remains well below normal rainfall for the last 90 days, with most areas only 50-75% of normal for that timeframe. Parts of Polk, Marshall, and Tama counties are less than 50% of normal rainfall for the last 90 days. While some central Iowa farms received substantial rainfall in the last two weeks, much of my area got under an inch. With the recent heat, the crops are showing stress, particularly soybeans in lighter soils. Corn is in R5 (dent) stage, and it’s almost time to do those end-of-season sweeps to make yield estimates, do the “push” test for stalk rots, and evaluate corn disease on the ear leaf and above. Making those disease evaluations now is more effective than doing combine scouting. Numerous issues are popping up in soybean fields, including soybean gall midge, white mold, sudden death syndrome (SDS), and weeds. Scout fields to evaluate what is causing yellowing, wilting, or other noticeable issues! Finally, a new Palmer amaranth find was discovered in central Iowa in July; please look carefully at waterhemp to make sure they aren’t actually Palmer amaranth!”


Palmer amaranth, which tends to have a denser, leafy canopy than waterhemp, was identified in a new field in Central Iowa in July 2023. Photo credit: Meaghan Anderson, ISU. 

Southwest Iowa

Aaron Saeugling (Region 10): “My how times have changed. As we are all aware the weather in Iowa is average, and average means the middle of the extremes. We turn from adequate moisture and moderate temperatures the past two weeks to a literal furnace this week. The extreme temperatures forecasted for the next four days will show all the previous stressed areas in fields. Corn in SW Iowa is between R4 (dough) to R5 (dent). Corn silage harvest began this week and more is expected in the coming weeks as the milk line begins to progress. Typically, it takes 14 days to complete the R5 growth stage in an average year, but this is no average year. I expect this process to be faster based on the current forecast. Early indications are good for corn yield in areas not affected by poorer soils, isolated hail, and wind damage areas. For farmers using corn for livestock feed, be ready to go sooner than usual. We have seen a tremendous uptick in corn disease incidence in most fields. At this point in the growing season most corn is past the opportunity for fungicide applications. Soybeans in SW Iowa have had big challenges this season including early season cold stress, early season dry weather, and moisture stress during flowering. With heavy rainfall in most areas in late July and early August, soybean disease has also increased. Most notable diseases include white mold, sudden death syndrome, and brown stem rot. Click here for information on “Fungicide Efficacy for Control of Soybean Foliar Diseases”. Soybeans range from R4 (full pod) to R7 (beginning maturity). Stress in the R5 to R6 stage can cause fewer pods per plant and fewer beans per pod, so watch areas with high disease pressure and areas of the field with prior moisture stress to affect yield.


Take time to scout soybean fields and see what's going on as we've been seeing an uptick in soybean diseases from the rains we recieved in late July/early August. Photo credit: Aaron Saeugling, ISU. 

East Central, Southeast, and South-Central Iowa

Rebecca Vittetoe (Region 8): “Rainfall totals over the last two weeks ranged from just shy of a 0.25 inch to some isolated areas receiving two plus inches. Most of this rain came the week of August 7. The heat this week is causing crops to show more signs of stress, especially in the drier areas or areas with lighter soils. Most corn and soybean fields are at the R5 stage with some soybean fields being further along. Issues observed in fields over the last two weeks have included aphids in corn and soybeans, grasshoppers, and soybean diseases including sudden death syndrome, white mold, and brown stem rot. Questions coming in have mostly involved late season fungicide or insecticide applications, late summer seeding of forages with the drier conditions, early husk senescence in corn, and high nitrate concerns for corn silage or green chopped corn in drier areas.”


Aphids found on a corn plant in Keokuk County. Photo credit: Rebecca Vittetoe, ISU. 

Virgil Schmitt (Region 9): “Rainfall during the last two weeks in the counties I cover ranged from 0.5 to 2.0 inches. Most corn is from early R5 to about 1/3 milk line and generally good to excellent except in “tough” soils. Some fields have considerable tip back, though. Most soybeans are R5 and generally look good to excellent except in “tough” soils. Phone calls, emails, and field visits last two weeks mostly involved fungicides (mostly two weeks ago), weed management, two-spotter spider mites in soybean, and soil fertility planning.”


Source: mrcc.purdue.edu/CLIMATE/Maps/stnMap_btd2.jsp

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Rebecca Vittetoe Field Agronomist in EC Iowa

Rebecca Vittetoe is an extension field agronomist in east central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, soybeans, and...