Harvest Aid Considerations for Weedy Soybean Fields

Authored by: Sam Bibby, Regional Crops & Soils Educator- UW Madison Extension; Dr. Rodrigo Werle, Associate Professor and Extension Cropping Systems Weed Scientist- UW Madison; and Dr. Shawn P. Conley, Professor and Soybean & Small Grains Extension Funded Campus-Based Faculty- UW Madison

There are a lot of weedy soybean fields across Wisconsin this year and the dry conditions are the major culprit. A lack of precipitation reduced the effectiveness of many residual herbicides and drought- affected soybeans were slower to close the canopy. To make matters worse, the dry conditions seem to be accelerating soybean dry down while weeds remain green. In Wisconsin, we usually get a killing frost around early to mid-October. Fields with heavy weed pressure may not be physically harvestable until then. This leaves us with the very real possibility of harvesting too-dry soybeans from fields under heavy weed pressure.

Harvest loss from pod shatter increases significantly when soybeans get below 11% moisture or when they undergo several drying-rewetting cycles. As a rule of thumb, when measuring harvest loss, four seeds per square foot equate to a bushel per acre of yield loss. Shrink loss, caused by soybeans sold below 13% moisture is another large concern and often goes unnoticed. As an example, harvesting and selling soybeans at 9% moisture and $12 per bushel with an average yield of 40 bushels per acre will result in a loss of $21 per acre compared with the same harvest at 13% moisture. In 2023, a desiccant application may prove to be cost effective for growers with weed infested fields that are still expected to yield. Here are some points to consider:

  • Sharpen (suflufenacil) is currently the main herbicide that is labeled for, and somewhat effectively desiccates, hard-to-control, potentially herbicide-resistant weeds like waterhemp, giant ragweed, marestail and common lambsquarters in soybeans.
  • Glyphosate is an option for growers dealing with heavy grass weed pressure or may be tank mixed with Sharpen for burndown of some broadleaf weeds.
  • Spray Sharpen at physiological maturity, stage R7, indicated by one mature-colored pod anywhere on the main stem.
  • Sharpen may be applied at a rate of 1.5-2 fl oz per acre or 1-2 fl oz per acre when tank mixed with another desiccant. A minimum carrier volume of 10 gallons per acre for ground rigs and 5 gallons per acre for aerial application is recommended for desiccation. Higher carrier volume rates will increase burndown efficacy. MSO at 1% v/v and AMS at 8.5lbs/100 gal are recommended adjuvants.
  • Maintain a pre-harvest interval of 3 days when using Sharpen or 7 days if glyphosate is used alone or in tank mix.
  • Soybean fields sprayed with Sharpen for a harvest aid should not be harvested for seed or any form of feed/forage.
  • Winter wheat for grain and other cereal grain cover crops, such as winter rye, may be planted following harvest of soybean fields sprayed with Sharpen. However broadleaf cover crops should be avoided following an application of Sharpen.
  • Small grain forage and hay must not be fed or grazed sooner than 30 days after application.

Spot spraying weedy patches may also be a cost-effective method of ensuring the whole field may be harvested at once. Using a harvest aid such as Sharpen in Wisconsin may only be economical if it is likely harvest will be delayed significantly by weeds so it is important to get out and scout fields now to make that decision as soon as possible.






Application Timing of Harvest Aid Herbicides Affects Soybean Harvest and Yield. Joseph M. Boudreaux and James L. Griffin*https://www.mssoy.org/uploads/files/griffin-weed-tech-reprint.pdf


Wildfire smoke and potential impacts to crops

Written by: Christopher J. Kucharik

The presence of wildfire smoke in our skies has the potential to impact crops in three primary ways: 1) reduction in amount of solar radiation received by plants, 2) an increase in the ratio of diffuse to direct beam radiation, and 3) supporting the development of ozone in the lower atmosphere. Any significant reduction in the total amount of radiation intercepted by crops would lead to a reduction in photosynthesis and potentially yield if the presence of smoke was sustained for long periods (weeks to months) during the growing season. However, the increase in diffuse radiation created by smoke can actually be beneficial to crops by increasing light use efficiency. Diffuse radiation can increase the amount of light received by canopy leaves that are normally shaded (and darker) and don’t receive direct beam radiation from the sun. This effect of increased diffuse radiation would be most pronounced when canopies are tall and leaf area index is greatest, which typically is towards the end of the vegetative stage and persisting through the reproductive phase. Which one of these effects (reduced total light vs. increased diffuse light) wins out is a difficult question to answer given there is a lack of solid research on the topic.

Given the amount and duration of smoke during the 2023 growing season thus far, it is likely that the fluctuations in light have had a minimal impact on crop growth to this point. The reduction in total radiation from smoke on the worst days (June 27-28) was approximately 5-15% during mid-day hours (when peak photosynthesis occurs) at the Arlington Ag Research Station, but the increase in diffuse radiation and having more canopy leaf area exposed to increased diffuse light could have offset that reduction. Keep in mind that cloud cover associated with precipitation and more moisture in the atmosphere can also greatly diminish solar radiation received by plants, to an extent that may be on the same order of magnitude or greater than the effects of smoke on a given day. During June when smoke was most persistent and air quality was the worst, we were also in the middle of a drought whereby we likely had more radiation due to reduced cloud cover compared to other growing seasons. Thus, it is possible that crops actually intercepted greater solar radiation during June than typically occurs in seasons when we receive normal (around 4-5.5 inches) or above normal precipitation.

Therefore, while wildfire smoke can most definitely have impacts to our crops, there are both positive and negative effects and other confounding factors like cloud cover, temperature, and soil moisture that make it difficult to determine whether smoke is causing a reduction in photosynthesis. But for now it’s more likely that smoke has not had a significant impact to this point of the 2023 growing season and other environmental controls like rainfall and temperature – like any other year – will be the dominant drivers of spatial variability in crop growth and end-of-season yields.

Impact of Early Season Drought on Soybean Yield?

Authors: Shawn P. Conley and Dr. James Specht (UNL)….well mostly Dr. Specht, but I did have to double-check his Nowledge… tee hee!

It’s been a week since the article A Flash Drought, Cover Crops and Dry Dirt… Which Soybean Seeds Are Still Viable? was published. At this point we have likely figured out which soybean seeds have either germinated and emerged, are dry and viable upon the next rainfall event, or are dead. Given the continued drought conditions lets work through a few real world scenarios and questions that have popped up over the past week regarding soybean and drought.

Scenario #1. My soybean crop is at the early Vn stages, but it is dryer than a popcorn fart out there. What yield impact is this drought going to have on my soybean crop? Luckily very little! As long as that tap root continues to dig deep and find some water, early soybean vegetative node development, after stage V1, is not really impacted by early season lack of rainfall.  For early season MG’s (~1-3) after soybeans hit the V1 growth stage a new main stem node is produced about every 3.7 days within the range of normal temperatures where these MG cultivars are adapted.  Lack of rainfall will, however, diminish leaflet size (i.e., leaf area) for those nodal trifoliolate leaflets that happen to be expanding during the drought period.  Still, drought during vegetative development is seldom a factor in final yield determination.  Remember that unlike corn, soybean, the superior crop, will only accumulate <15% of its total biomass by R1 or first flower so very little water is utilized/demanded for vegetative growth (Figure 1.).

Figure 1. Soybean biomass accumulation throughout the season.

More problematic is lack of rainfall during August – (post – R3) which we (and others) have found to be the most critical period for drought to have an impact on soybean seed yield. Remember early soybean planting sets us up for maximizing yield, but rainfall during seed-fill realizes that yield!

Scenario #2. You are making a pass across your soybean field and you are tempted to toss in a fungicide to help with plant health and drought mitigation. Don’t fall victim to the plant health fungicide pitch. Even in Ohio they know that Drought Projections Do Not Go Well With Fungicide Applications.

Scenario #3. The soybean seeds you planted are sitting in dry soil and are still viable because they have not imbibed water. Or they may have imbibed water, then dried out and died. If the seeds are not viable (dead), I would check herbicide labels and replant new seed into dry soil, no deeper than ~2.0 inches deep. Remember dry in the dirt is the same as dry in the bag. One method of getting the seeds into moisture if you have row cleaners is to set them to move a couple inches of soil away from the tops of the furrow as you plant and place the seed into 1-2 inches of soil moisture if possible. I have no issues planting them 3 to 3.5 inches “deep” if you will. Check with your seed dealer, but most soybean varieties today can emerge from ~3 inches deep under current soil temperatures.

Scenario #4.  The soil is dry below the soybean seed placement layer and you get a rainfall event that wets the soil down to the seed placement layer but is not sufficient to connect to the deeper wetter soil zone. In this scenario the soybean seed will germinate, but the radicle will not penetrate into a dry soil layer below the seed placement zone.  This scenario happened to a NE farmer a few years ago in a dry spring when he killed his cover crop with glyphosate just before they planted soybean into the dry soil on the same day. They then got what they thought was a nice 0.80″ rainfall event that evening.  Trouble was that water amount was not sufficient to wet below the 1.75″ deep seed placement zone (there was still a dry layer below) and though the seed germinated, the seedlings withered and died because the radicle was not penetrating the dry soil layer. This field needed to be replanted. Such a scenario may be infrequent, but 2023 is certainly shaping up to be a year this could be widespread.  In this case, a pivot was used to mitigate the subsequent dry soil layer, but irrigation is not common to most soybean farmers.

Scenario #5. We don’t talk about scenario #5.

Literature cited:

Gaspar, A., C. Laboski, S. Naeve, and S.P. Conley. 2017. Dry Matter and Nitrogen Uptake, Partitioning, and Removal across a Wide Range of Soybean Seed Yield Levels. Crop Sci. doi: 10.2135/cropsci2016.05.0322

Juan Ignacio Rattalino Edreira, S. Mourtzinis, S.P. Conley, A.C. Roth; I.A. Ciampitti, M. A. Licht, H. Kandel, P.M. Kyveryga, L.E. Lindsey,  D.S. Mueller, S.L. Naeve, E. Nafziger, J.E. Specht, J. Stanley; M.J. Staton, P. Grassini. 2017. Assessing causes of yield gaps in agricultural areas with diversity in climate and soils. Agricultural and Forest Meteorology. dx.doi.org/10.1016/j.agrformet.2017.07.010

Mourtzinis, S., J. Specht, S.P. Conley. 2019. Defining Optimal Soybean Sowing Dates across the US. Scientific Reports. 9:2800 | https://doi.org/10.1038/s41598-019-38971-3

A Flash Drought, Cover Crops and Dry Dirt… Which Soybean Seeds Are Still Viable?

Many of us, including myself, have finished our 2023 soybean planting in less than ideal soil conditions. Often the ground was worked, a little on the wet side, leading to clods and variable seeding depths or we no-tilled into a standing cereal rye cover crop, with less than adequate soil moisture, during a flash drought. Beginning reports of variable and delayed soybean emergence in conventional (more common) and no-till cereal rye cover crop systems are raising replant and seed viability questions in several areas across the Midwest.

Image 1. Soybean seed planted into adequate soil moisture in a conventional tillage system on 5/29/2023 and germinating normally (image taken on 6/1/2023).

Image 2. Soybean seed planted into a no-till cereal rye cover crop system on 5/29/2023 and had enough soil moisture to swell but not brake the seed coat…yet… (image taken on 6/1/2023).

If soybean was planted into dry soil and had not imbibed water (seed did not swell) then there is little to no replant concern for growers.  Once a significant rainfall event occurs, the soybean will imbibe water, germinate, and should emerge normally.  For yield estimates, we would assign the day it rained as the new planting date.

The more difficult question to answer is “How viable is the soybean seed once imbibition and/or germination has begun?”  The critical seed moisture content for soybean germination is ~20%.  A soybean seed that has imbibed water, has a split seed coat, or has an emerged radicle will continue to germinate and grow as normal once the seed is re-hydrated if the seed (embryo) remains above 20% moisture (Senaratna and McKersie, 1983) (Image 3).

Image 3. Soybean germination

If the moisture content within a soybean seed falls to 10% due to dry conditions after germination has started, then a dramatic difference exists among the different seed germination stages.  If the seed has imbibed water for 6 hours (seed is swollen, but the seed coat has not broken), then the seed is dehydrated to 10% moisture, germination is not affected.  If the seed has imbibed water for 12 to 24 hours (seed coat broken, but prior to radicle emergence), then germination is reduced to 60 to 65%.  If the radicle has emerged and seed moisture levels drop to 10%, then no survivors can be expected (Image 4).

Image 4. Variation in soybean seed imbibition.

To test seed viability, growers can conduct a simple germination test.  First excavate 100 soybean seeds from your field and wrap them in a damp paper towel.  Place these seeds in a warm location, and after 24 to 36 hours, count the number of seeds that have germinated (Image 5).  Remember that a typical soybean germination is 90%.

Image 5. Soybean germination roll test

Literature Cited:

Senaratna, T. and B. D. McKersie.  1983.  Dehydration Injury in Germinating Soybean (Glycine max L. Merr.) Seeds.  Plant Physiology 72: 620-624.

Mirror, Mirror on the Wall, Will My Wheat and Soybean Crop Freeze and Fall?

Well folks its the end of May and frost was in the air. I figured we would be getting some questions about the impact of the predicted cold temperatures on the wheat and soybean crop. Here is my coolbean take!

First lets start with the wheat crop which in WI ranges from jointing to flag leaf emergence. Cold temperature would need to reach 30 degrees F or less for 2 plus hours before injury occurred. I just don’t see that happening in any major wheat growing region in WI last night.

Table 1. Wheat Resistance to Freeze Injury (From: Spring Freeze Injury to Kansas Wheat)

Now let’s talk about soybean. I am also optimistic that if the forecast temperatures hold, the soybean crop will in fact be #COOLBEANS, but also unaffected. My optimism lies in the Nowledge I received in an email from Dr. Jim Specht from UNL a few years ago (modified slightly by me for context). For the most-part, farmers and their soybeans in WI fall within the context of this email.

First of all  temps above 32F will not impact above-ground tissue.  Second, tissue freezing does not even take place at 32F because cell cytoplasm has solutes in it – like a modest anti-freeze, which depresses freezing point of the tissue a degree or two less than 32F – thus air temps surrounding the tissue have to get to below 31 or 30F before tissue freezing can occur.  Third, the soil surface is typically warmer than the air temperature (particularly when the soil is wet) and does not give up heat acquired during a sunny day as fast as the air does after sunset.  In actuality, the interface between soil surface temp and the air temp near that soil surface will be closer to the soil temp than to the air temp which most peopled measure on thermometers viewable at their height (not at ground level).  Biophysically, control of the soil temp over the air temp this is called the “boundary layer effect”).  So don’t trust air temperatures read on thermometers unless you know what the air temperature near the soil surface was (put a thermometer on the soil surface where the cotyledons are and check it just before dawn (when the soil surface temp reaches its nadir for a 24-hour temperature cycle).  Fourth, the cotyledons are a huge mass of tissue that are about 95% water.  That big amount of water-filled tissue is hard to freeze unless the exposure to temps of 30F at the soil-air interface is many, many hours.  Cotyledons will freeze faster (in fewer hours) but only if the soil surface temps get well below 30F (say 25F).  The only concern I would have is when cotyledons are no longer closed and protecting the young stem tip.  However, if that is in fact frozen off, the nodes to which the cotyledons are attached will regenerate TWO main stem tips.  Not an ideal way to start the growing season, but better than having to replant (0.5 bu/ac loss per each day that soybeans are NOT in the ground on May 1). Text courtesy of Dr. Jim Specht (UNL)!

For additional information please view my YouTube video that discusses common early season emergence issues (including frost injury) and just in case the forecast was way off and you got hammered with colder than noted temperatures here is our replant article entitled:

Soybean Replant Decisions: Just the Facts Jack!

Analyzing more than two decades of Wisconsin soybean planting progress (2000-2022)

Authors: Tatiane Severo Silva, Spyros Mourtzinis, James Specht (UNL), Shawn P. Conley

In a bean pod:        

  •  Twenty-two out of the past 23 years, the 50% WI soybean planting progress date was attained between May 13 to May 30.
  • A one-day delay in the 23-year Wisconsin soybean 50% progress date was related with 0.45 bu/ac yield decrease.
  • The 23-year historic average date for Wisconsin soybean 50% planting progress was May 24th.
  • Wisconsin soybean growers who reached the 50% progress date 11-days earlier than the 23-year average of May 24 would have potentially gained 3.6 bu/ac in yield.


USDA-NASS has reported Wisconsin soybean planting progress on a weekly basis since 2000. Full-text reports for the 23 past years (2000-2022) are available here. Here, we explore the Wisconsin historical soybean planting progress data and provide insights into trends in planting dates and their effects on yields. According to recent UW-Madison research, soybean yield is likely to increase when planted earlier in the season (see here and here). This article seeks to explore whether Wisconsin soybean growers have been shifting their planting dates forward over the course of more than two decades, and how this trend might affect potential yield. We provide an analytical overview of soybean planting progress in Wisconsin, along with the possible yield effects.

NASS Weekly Wisconsin Soybean Planting Progress (Example Remarkable Past Years)

Figure 1 shows weekly estimates of Wisconsin soybean planting progress (represented by solid dots) from NASS for four notable years in the past (2004 = red, 2012 = black, 2019 = green, and 2021 = blue). Planting progress was modeled by the Logistic Equation (illustrated in the figure text boxes) with Sigmoid (S-shaped) curve, which illustrates planting progress across WI from the start (0%) to the end (100%). The sigmoid curves illustrated in Figures 1 and 2 characterize the slow initial progress of planting that gradually picks up pace until it reaches a midway point of 50% progress (represented by a thick black horizontal line), and then slows down as it nears completion.

Using the equation, we computed the Logistic Xm value for each curve, which represents the specific spring date when the planting progress reached 50%. The vertical lines in different colors in the figure indicate the Day of Year (bottom axis) and Month-Day (top axis). In addition, we computed a Logistic k rate value for each curve, which is a numerical measure of the pace at which planting progress took place. The greater the Logistic k rate, the more rapid the ascent of the curve (e.g., 2012 curve [k = 0.20]), indicating rapid planting progress, while a slower k rate generates a flatter curve (e.g., 2004 curve [k = 0.09]). The shaded area characterizes the 95% confidence interval (CI) for the regression planting progress error estimation.

The four curves depicted in Figure 1 correspond to the most rapid (black line), slowest (red line), earliest (blue line), and latest (green line) soybean planting progress data observed over the 23-year period to date. For instance, the earliest 50% of soybean progress was attained in 2021 (May 13), whereas the latest 50% date was attained in 2019 (Jun 6). The 50% soybean progress in 2021 outpaced that of 2019 by 23 days.

 Figure 1. Notable example years (2004, 2012, 2019, and 2021) of soybean planting progress in Wisconsin.

NASS Weekly Wisconsin Soybean Planting Progress (2000-2022)

Figure 2 shows all 23-years sigmoid curves generated from the extracted NASS soybean weekly planting progress report data. The colored S-shaped curves in the figure represent different years interval (2000-2005 = red, 2006-2016 = black, and 2017-2022 = blue). Out of the 23 soybean progress curves, 13 had 50% dates falling within a 9-day interval between May 13 and May 22 and 22 had 50% dates falling within a 17-day interval between May 13-30. Apparently, over the last 23 years 50% of soybean progress date varied year by year depending on other factors, which could be mainly related to weather conditions and logistics management. However, if we take a closer look to the last 3-years (2020-2022) compared to the interval between 2017-2019, it seems that in the last three years growers have been planting as early as manageable possible (<May 22).

Figure 2. Historic record of 23 years of soybean planting progress in Wisconsin.

Trends in the 2000-2022 Wisconsin Soybean 50% Planting Progress Date

Figure 3 demonstrates the spring dates of 50% planting progress (circle dots) in relation to each year’s S-curve model generated by the logistic equation from 2000-2022. The minimum, maximum, and mean values for the spring 50% planting progress date are represented as black dashed horizontal lines in the figure. Over the last 23-years, there has been no clear indication that Wisconsin soybean 50% progress has been shifting for earlier planting. Since 2000, spring dates for 50% soybean planting progress have ranged from as early as May 13 (2021) to as late as Jun 6 (2019). If the late 2013 and 2019 spring dates are considered as outlier data points, the spring dates for 50% soybean planting progress ranged from May 13 (2021) to late May 30 (2004). As of the latest NASS May 7 estimate for 2023, Wisconsin soybean planting progress stands at 11%, which is 5% greater than at the same period last year in 2022.

Figure 3. Variation of 50% soybean planting progress date in Wisconsin over the last 23 years.

Can the 50% Planting Progress Date be used to predict Wisconsin soybean yield?

Figure 4 represents soybean yield (vertical axis) and 50% spring dates (horizontal axis displays Day of Year at the bottom and Month-Day at the top). The solid green line denotes the linear regression considering all data points from 2000 to 2022. The dashed blue line displays the linear regression excluding the conjectured outlier years (2013 and 2019). The green trend line reveals that a one-day delay in the 50% progress date may potentially reduce soybean yield by 0.45 bu/ac. When the two extreme 50% soybean plant date years (2013 and 2019) were excluded from the regression analyses (green dashed trend line), the yield benefit reached 0.75 bu/ac per day. Thus, reaching the 50% planting progress point early in the season would enhance soybean yield.

Picking 2021 as one example, Wisconsin growers moved up the 50% soybean progress date by 11 days (May 13) in 2021 from a 23-year mean of May 24 (black vertical line). That 11-day change to earlier soybean planting in Wisconsin would have resulted 0.45 x 8 = ~ 3.6 bu/ac greater yield. It’s important to note that it’s not only the first soybean field that matters, but also getting the final field planted early for maximum yield benefit. So, if the conditions are favorable, it’s best to start planting as early and fast as you can manage.

Figure 4. Correlation between soybean historical yield with 23-year 50% planting progress in Wisconsin.

Overall, these results are aligned with previously reports that support early planting to achieve high soybean yields (see here and here). Early planting is crucial for higher yields due to increase light interception, crop growth rate, node number, and consequent yield benefits. Planting soybean early can also be improved by planting longer maturity soybean varieties (see here). However, some risks come with this practice. For example, very early planting may be associated with higher early season frost risk or significantly reduced crop stands. Additionally, early planting should not be considered as a silver bullet that necessarily leads to high yield. Choosing best management practices, such as optimum maturity group, row spacing, seeding rates and applying proper herbicide programs are essential to lead to the expected higher yields and profit.

Soybean Replant Decisions Made Easy(ish)!

I think the message is out that farmers should consider planting soybean ahead of their corn crop as soybean planting progress is WAY ahead of schedule across much of the Midwest. Over the next week Twitter will erupt with widespread images of soybean beginning to crack and emerge. As farmers, agronomists and technical service providers begin to assess their 2023 soybean stands, below are a few factors our Science For Success team have compiled to help make any replant decision as easy as possible!

For more detailed information regarding the factors above please see our full resource guide entitled: Soybean Plant Stands: Is Replanting Necessary?

For specific WI recommendations please see below!

  1. Get an accurate stand assessment. We are often drawn to the worst areas of fields and over-blow how bad the overall stand really is. You can go old school and use the tape or hula-hoop method or try a digital approach such as Bean Cam the WSMB funded soybean replant app!
    1. Link to the app store for iPhone and iPad
    2. Link to the app store for Android

      Bean Cam app calculations/results.

  2. An effective stand is obviously important to maximize soybean seed yield. However the downside yield risk for a sub-par stand is minimal until stands fall below 50,000 plants per acre. The synergy of early planting coupled with breeders adding 3x yield to soybean branches at low populations have effectively reduced the yield penalty for thins stands by 1/2 (Suhre et al. 2014) . Therefore we recommend the following.
    • Early planted soybean yield is maximized with stands that range from 100,000 (high yield environment) to 135,000+ (low yield environment) plants per acre.
    • When soybean stands are less than 50,000k plants per acre, inter-plant new seed with a similar maturity into the existing stand. DO NOT TEAR UP THE STAND AND START OVER.
    • When stands fall between optimal and 50,000k plants per acre Think Twice Before Replanting Soybeans! Our data shows a nominal ~2 bu yield increase in this situation. Even if you have a “free replant” guarantee the numbers don’t make economic sense. As a grower you are better off investing $$$ in an effective in-season residual herbicide to control weeds such as Palmer and waterhemp.


Gaspar, A. and S.P. Conley. 2015. Responses of canopy reflectance, light interception and soybean seed yield to replanting sub-optimum stands. Crop Sci.55: 377-385. doi: 10.2135/cropsci2014.03.0200

Suhre, J.J., Weidenbenner, N., ‡Rowntree, S., Wilson, E., S., Naeve, S. Casteel, S.P. Conley, Diers, B., Esker, P., Specht, J., and Davis, V. 2014. Soybean Yield Partitioning Changes Revealed by Genetic Gain and Seeding Rate Interactions. Agron. J. 106:1631–1642.

Just the Facts Jack: Soybean Planting Date, Seeding Rate and Seed Treatment Recommendations

When I am asked a direct question from a farmer or a crop consultant my response is always as follows…Do you want the short answer or the long answer as I can say the same thing in 5 minutes or 5 hours. Their response to me is almost always the same…”Just the Facts Jack”. In this blog I will attempt to answer three very agronomically important and challenging questions in a very succinct manner.  However as we all know brevity can be a gift or a curse depending upon the context of the question. With that being said here we go!

Question #1. When should I start planting soybean? My general response is to start planting your soybean crop ~7 to 10 days before you start putting your corn in the ground with the caveat that the soil is fit and you are following your crop insurance replant dates (Please review updated RMA map). We have measured soybean yield loss due to delayed planting date as early as ~April 10th in parts of the Midwest however the rapid yield decline (up to 0.5+ bpa per day) occurs at ~May 10th. As you would expect the magnitude of this planting date yield response is soil and climate dependent and yield losses in some areas (TED’s) where as high as 2.8 bpa per week for delayed planting (Figures 1 and 2). For a deeper dig please review the below supplemental documents.


Figure 1. Map of the North Central US region showing nine technology extrapolation domains (TEDs) used in this analysis.

Figure 2. Producer soybean yield plotted against planting date in 9 technology extrapolation domains (TED) in the NC USA region.

Question #2. What is the optimal soybean seeding rate? The quest for the optimal agronomic soybean seeding rate for yield vs. the optimal economic seeding rate has been an ongoing debate. Fortunately a large group of academics and industry (thank you Corteva) were able to combine data sets and address this question (Figure 3). Our results suggest that for “on-time” soybean planting dates the optimal agronomic soybean seeding rate to achieve 99% yield potential ranged from 237,000 to 128,000 seeds per acre (assuming 90% germ) across environments; whereas the optimal economic soybean seeding rate ranged from 157,000 to 103,000 seeds per acre. Thankfully this roughly confirms my original recommendation that you buy a bag an acre (140K) and place ~20% more seed on the low yielding acres and ~20% less on the high yielding acres, especially in areas of high white mold concern. If planting is delayed however we do recommend that you increase your seeding rate accordingly (Adjust Your Seeding Rate (Higher) But Not Your Maturity Group For Late May Planted Soybean ). For a deeper dig please review the below supplemental document.

 Location of 211 trial site-years that are included in the database and their respective environmental cluster classifications.

Figure 3. Location of 211 trial site-years that are included in the database and their respective environmental cluster classifications.

Table 1. Agronomic and Economic Optimal Soybean Seeding Rates by Environmental Cluster.

Cluster 1

Cluster 2

Cluster 3

Yield level (bu a-1)

Agronomic/(Economic) Optimal Seeding Rate1,2

< 58




58 – 71




> 72




1Agronomic optimal seeding rate (x1000 seeds) based on 99% maximum yield level.

2Economic analysis based on $62 a unit (140k) for seed and $9 a bushel pricing; soybean price and seed cost fluctuations will change the EOSR.

Question #3. When do I use a soybean seed treatment? I purposely placed this questions last as I know it will draw significant ire; however the data are what they are. Soybean seed treatments should only be used in some early planted soybean situations and/or if you have a history of or have scouted for an insect (i.e. Bean leaf beetle) or a pathogen (i.e. SDS) that exceeds economic thresholds. For a deeper dig please review the below supplemental document.

Th-th-th-that’s all folks!

The WSMB Free Soybean Cyst Nematode Testing Program is Back in 2023!

Ann MacGuidwin, Damon Smith and Shawn P. Conley

The WI Soybean Marketing Board (WSMB) sponsors free nematode testing to help producers stay ahead of the most important nematode pest of soybean, the soybean cyst nematode (SCN). Eggs of SCN persist in the soil between soybean crops so a sample can be submitted any time that is convenient. The soil test report indicates the number of eggs in the sample and is useful for selecting the right variety for the next soybean crop. Retests of fields planted with SCN-resistant varieties over multiple years shows how the nematode population is responding to variety resistance and provides an early warning should the nematode population adapt to host genetics.

In the spring of 2012, the WSMB expanded the nematode testing program to include other pest nematodes in addition to SCN. These nematodes are less damaging to soybean than SCN but can cause enough yield loss to warrant treatment. As is the case for SCN, there are no rescue treatments for nematodes so the primary purpose of this year’s soil test is to plan for next year’s crop. Soil samples collected in corn for nematode analysis have predictive value for explaining yield if they are collected before the corn V6 growth stage. Sampling early in the season will provide information about the risk potential for the current corn crop AND the next soybean crop.

The assays used to recover nematode pests other than SCN in soil require that the nematodes are alive. So, it is important to keep the samples moist and at least room temperature cool. Collecting a sample that includes multiple cores ensures that there will be plenty of root pieces to assay. It is not necessary to include live plants in the sample. The soil test report will indicate which pest nematodes are present and at what quantities and their damage potential to soybean and corn based on the numbers recovered.

For more information on SCN testing and management practices or to request a free soil sample test kits please contact: Jillene Fisch at (freescntest@mailplus.wisc.edu).

Click to view more information on our WI SCN testing program or visit The SCN Coalition.

Remember the first step in fixing a nematode problem is to know if you have one! The WSMB sponsored nematode testing program provides you that opportunity. So Wisconsin farmers….”What’s you number?”

Winners of the 2022 WI Soybean Yield Contest are Announced

Division 4:

1st           Don and Doug Midthun, Arlington (96.57 bu/a with Asgrow AG20X9)

2nd          Ron Digman, Mount Hope (96.33 bu/a with Pioneer P28A42X)

Division 3:

1st           Kelley Farms, Arlington (88.33 bu/a with Asgrow AG24XF1)

2nd          Jim Salentine, Luxemburg (74.58 bu/a with Stine 19EC32)

  • *UW Bean Team (Mark Kendall, Andrew Malcomson, Haleigh Ortmeier-Clarke), Madison (84.08 bu/a with Pioneer P20A22X). The UW Bean Team is ineligible for official prizes as they are graduate students of Dr. Conley; however, their efforts are still unofficially recognized.

Division 2:

-No entries were submitted for Division 2-

Division 1: 

1st           Josey W. Wilson, St. Croix Falls (72.44 bu/a with Pioneer P16A84X)

2nd          Jim Wilson, St. Croix Falls (63.89 bu/a with Asgrow AG11X8)

New Contestant Award

  • Daniel Ballmer, Janesville (90.01 bu/a with Dyna-Gro S28XF92)

The contest is sponsored by the WI Soybean Program and organized to encourage the development of new and innovative management practices and to show the importance of using sound cultural practices in WI soybean production.

For more information please contact Shawn Conley, WI State Soybean Specialist at 608-800-7056 or spconley@wisc.edu