Walking Rows: Row spacing, pests and more
July 2, 2025 | Kriss Nelson
Iowa Soybean Association (ISA) agronomists are reporting that the recent warmup in temperatures and rains has given crops a growth spurt. Although welcomed, the weather has hindered post-emergent herbicides in soybeans. Farmers are cautioned to be aware of soybean growth stages when trying to accomplish that task.
Scouting efforts should focus on corn diseases like tar spot, insect pests such as Japanese beetles and weed escapes.
Alex Schaffer - Central/South Central Iowa
A lot of farmers have finished up most of their fieldwork and now wait until fungicide season.
Soybean crops have progressed to the reproductive phase, with early plantings at R2 and later plantings at R1 with early planted corn rapidly approaching reproductive stages.
Speaking of fungicide, if the moisture keeps up, it will be a big season for fungicide applications. I have heard reports of tar spot surrounding states and five counties in Iowa.
Our last two years of fungicide trials on soybeans did not show a return on investment in fungicide application when disease was not present. We recommend considering the disease triangle when making a fungicide application decision and always scout your field before applying.
Another thing I have been paying attention to this week is canopy closure in soybeans. I have noticed many of the 7.5- and 10-inch row-spaced soybeans getting close to closing the canopy while 20- and 30-inch soybeans are still working toward closing. I have a trial this year comparing soybeans planted at approximately 140,000 seeds per acre with 20-inch drilled and 30-inch row-spaced soybeans planted at around 90,000 seeds per acre using a high-speed John Deere planter that included some nitrogen starter fertilizer at planting. We are hoping to see greater return on investment with the lower population planted more accurately in 30-inch rows with the added option of including some liquid fertilizer at planting or later in the season. We will also test the farmer's herbicide program as the rows are slower to close the canopy with the 30-inch spacing. I'm feeling pretty confident that we will maintain yield with the wider row spacing and lower population, given that we already have significantly more branches. The only question is whether we can keep the weeds under control.
Shane Beck – Northeast/Northern Iowa
Over the past week, a large part of the area enjoyed much-needed rain and warm temperatures, giving the corn and soybeans a boost in growth.
Most soybeans in my area are between V4 to R2 growth stages. I saw a field the other day that was close to canopying, so that is very encouraging that the soybeans are catching up from the slow-growing conditions in May.
The corn’s growth stage is between V8 to V12. We will probably see some early planted corn tassel in the next couple of weeks. Also, the oats around my area are ripening quickly. I am expecting to see some combines rolling here in the next few weeks as well.
Overall, the crops are looking good and we are seeing a lot of good growth.
With corn tasseling right around the corner, that means there will be a lot of planes in the air and high clearance sprayers ready to put on fungicide. So far, there have been five counties confirmed to have tar spot in Iowa. Four of the counties are in south central Iowa and the other is in eastern Iowa. Tar spot progression should slow down as the average temperatures get above 73 degrees and if we have higher humidity.
Some other diseases to be on the lookout for in corn, especially with all the rain we have received lately and the high humidity that we continue to have, are gray leaf spot, northern corn leaf blight and common rust.
Except for rust spores, which are carried on the wind from the southern U.S., all the rest survive on diseased residue from a previous year’s crop. These can be areas to look at this year, especially with all the corn-on-corn ground. If you know you had a disease in a field last year, those fields would be the ones to target first and monitor closely for disease progression. The ideal time to spray fungicides for corn is the VT to R1 growth stage.
Another pest that I have noticed in several fields over the last few days is the Japanese beetle. I have not seen them do any significant damage to the crops yet, but they are increasing their presence in the field. The economic injury level for Japanese beetles is 20% to 30% leaf damage from feeding.
As the season progresses, especially in corn, Japanese beetles can be a significant concern, particularly if they feed on the silks. Currently, I have not identified any fields that warrant a management practice, but it is something to monitor over the next couple of weeks.
Mikaela Connelly - Southwest/West Central Iowa
Some much-needed rain fell in districts 4 and 7 last week. I’ve observed more consistent flower development on early-planted soybeans. The growth stages range from V5/V6 to R1.
For corn, I would say early planted corn will be tasseling by the end of the week, given the moisture and temperatures we’ve had, and later-planted corn won’t be too far behind, with those fields having growth stages around V10 to V12. The warm weather we’ve had has really helped some of the later-planted crops develop quickly.
Now is the time to be scouting for Japanese beetles and grasshoppers, as I have noticed those pests making their appearance this season.
As July begins and crops reach reproductive stages, the fungicide season is quickly approaching. Considering the recent heat, humidity and moisture, disease could to be a problem this year. In areas that were submerged or flooded by the recent rains, diseases could also be present.
I would recommend scouting your fields regularly to assess if there is disease pressure. We often consider fungicide applications to be both preventative and curative; however, if disease is already present in your field, a fungicide application may not alleviate much pressure, depending on the product and FRAC modes of action selected.
ISA’s Research Center for Farming Innovation has conducted fungicide trials in the last couple of summers with various products. You can view the cross-site report here.
Craig Woods – Northwest Iowa
Growth stages in soybeans in northwest Iowa range from the V3 to R1 growth stages, and corn is closing up its canopy. Due to wet conditions, accessing the field to wrap up post-emergence has been somewhat challenging. There were also reports of isolated hail damage.
For fields with flowering soybeans that still need a post-emergence herbicide pass, it will be important to verify that the treatment won’t cause a yield impact as they continue into the reproductive stage.
Waterhemp is once again proving to be one of the more difficult weeds to manage in northwest Iowa this year. It's important to understand the factors affecting post-emergence herbicide efficacy. For more, refer to the recent article, "Waterhemp Escape Highlights Herbicide-Resistant Challenges."
With ample moisture and expected temperatures around mid-80s, the daytime conditions will be favorable for diseases to develop on newly flowered plants as the canopy begins to close. Scouting fields will be important, as pairing targeted applications for fields that have disease pressure and correct timing will lead to successful fungicide applications.
Evan Brehm - Southeast/Eastern Iowa
Soybeans have perked up after a slow start. Most of the soybean fields I’ve walked through are in the flowering (R1) stage.
Corn is mostly entering mid-vegetative stages. Some replanted corn is behind, but that’s to be expected. A Pioneer seed salesman in Clayton County said this was one of his record years for replants. However, warmer temperatures have been encouraging for those replanted acres. Side dressing is wrapping up in most areas in eastern Iowa.
I am beginning to see corn rootworm beetles from time to time. It’s actually been noted more in flowers and vegetable crops as the Western Corn Rootworm Beetle (aka cucumber beetle) is showing up. No reports on Japanese beetles, but as these soybeans push into the R2 growth stage, be on the lookout.
Nitrogen-deficient corn has been reported in pockets. Rains and high temperatures, with proper split applications, have assisted in overcoming this issue. I recommend working with your local co-op or agronomist to conduct tissue sampling in either corn or soybeans as we approach fungicide season.
The shading of rows is increasing as drilled and narrow-row soybeans begin to canopy. Minimal weed problems encountered to date. Thirty-inch row soybeans, using timely herbicide or cover crops, show excellent weed control now. It will be important from now on to continue to scout these fields for breakouts of weeds given the wider row spacing.
The window for the Enlist application at flowering is nearly closed. This has been a challenge with the recent rains and winds.
A soil amendment from Fish Head Farms product is being researched on corn planted into a living rye cover crop. The rye was terminated two days after the corn was planted. Root ball, tissue and soil health samples have been taken prior to planting, at the V3 and V10 growth stages. Results will be calculated and released in the future on the effect of the products on soil health and overall yield.
A comparison across fence rows of two fields of soybeans planted three weeks apart into standing rye and wheat cover crops. The early-planted soybeans (on the left) were planted April 15, struggled, but have now gained momentum. The later-planted soybeans caught up to the earlier-planted soybeans. Weed control in both fields is now perfect. This is encouraging, as it suggests that earlier-planted soybeans can be used as cover crops.
Gathered by Kriss Nelson.
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