Soybean Planting Date by Maturity Group Considerations for 2015

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Article coauthored by Dr. Shawn P. Conley and Adam Gaspar
Early May planting in Wisconsin has been documented to increase soybean seed yield due to increased light interception (Gaspar and Conley, 2015).  In theory, earlier planting can potentially intercept greater amounts of solar radiation due to a longer growing season and therefore longer maturity group (MG) soybean varieties may be better suited to maximize yield if they can mature before a hard fall frost.  Unlike 2013 and 2014, 2015 may provide growers with an opportunity to plant their soybean crop earlier than ever before. Yet, in some instances (weather or logistical problems) planting will be delayed or replanting may be needed. Therefore, investigating the effect of different MG’s at multiple planting dates across the state would provide WI growers with BMP’s for soybean establishment regardless of planting timing.
To answer this question field trials were initiated at Arlington, Hancock, and Spooner, WI in spring of 2014.  The five planting dates at each location were planting roughly on: (1) May 7th, (2) May 20th, (3) June 1st, (4) June 10th, and (5) June 20th.  Planting after June 20th is not recommended in WI.  Two varieties within each MG from a 2.5 all the way down to a 00.5 were tested depending upon the location and planting date and are displayed in Table 1.

Table 1. Maturity Group’s tested within each location and planting date.
Planting Date
Arlington
Hancock
Spooner
1 (May 7th)
2.5, 2.0, 1.5
2.5, 2.0, 1.5
1.5, 1.0, 0.5
2 (May 20th)
2.5, 2.0, 1.5
2.5, 2.0, 1.5
1.5, 1.0, 0.5
3 (June 1st)
2.0, 1.5, 1.0
2.0, 1.5, 1.0
1.0, 0.5, 0.0
4 (June 10th)
2.0, 1.5, 1.0
2.0, 1.5, 1.0
1.0, 0.5, 0.0
5 (June 20th)
1.5, 1.0, 0.5
1.5, 1.0, 0.5
0.5, 0.0, 00.5

Let’s start with the easy and redundant part, get your soybeans in the ground ASAP to maximize yield.  This is evident again in this trial, where Figure 1 shows the effect of planting date across all MG’s (varieties) tested in 2014.  If the soil is fit, soil temps are near 50 ˚F, and the forecast is favorable….. get the planter rolling!
Figure 1. Dots represent the mean yield within each planting date for each location.  The average yield loss per day for delaying planting past May 7th is presented in the legend.
However, the question still remains for many producers, should I use a longer maturity variety in early planting situations (very possible in 2015) and should I switch to an earlier maturing variety when planting is delayed?  

Table 2. Effect of Maturity Group on Yield tested within each location and planting date.
Planting Date
Arlington
Hancock
Spooner
1 (May 7th)
NS
NS
NS
2 (May 20th)
NS
NS
NS
3 (May 30th)
NS
**
NS
4 (June 10th)
NS
NS
NS
5 (June 20th)
**
NS
NS
** MG had a significant effect on yield at the  P ≤ 0.05 level

Based upon the 2014 data, only 2 out of 15 location x planting date combinations displayed a significant effect of MG on yield (Table 2).  So the moral of the story is that within a realistic MG range for your region and planting date, variety selection should be based heavily upon the varieties past local and regional performance, disease package, and etc.  Variety selection heavily based upon the MG is not a silver bullet to frequently increasing yields.
However, there are always caveats…… Growers may consider trying a slightly longer maturing soybean on a portion of their acres because there is a “potential”, but not guarantee, for higher yields with no additional dollars spent.  Within planting date 1, there was no significant MG effect, but MG 2.5 did yield the highest numerically in Arlington and Hancock with no fall frost damage, while the same is true for MG 1.5 in Spooner.  The longest MG tested within each planting date in our study numerically yielded the highest through June 10th(planting date 4). 
On the back end of the planting season, the inverse was seen.  Within planting date 5 at Arlington and Hancock, MG 1.5 did not mature before the first fall frost and was the lowest yielding.  Therefore, growers may consider switching to an earlier maturing variety as planting is delayed into June.  If switching to an earlier maturing variety, don’t use a variety less than 0.5 MG earlier than a full season variety (2.5 in southern WI) in early June.  However, if planting is delayed into mid to late June then a variety that is greater than or equal to a full MG earlier should be considered.
Acknowledgements: The authors would like to thank the Wisconsin Soybean Marketing Board and DuPont Pioneer for supporting this research.
References:
Gaspar, A.P. and S.P. Conley. 2015. Responses of canopy reflectance, light interception, and soybean seed yield to replanting suboptimal stands. Crop Sci. 55:377-385.

Wisconsin Soybean Marketing Board Continues Free Nematode Testing Program for 2015

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Four out of every five animals on earth today is a nematode so it is not surprising that agricultural fields are home to many nematode species. Fortunately, most nematodes are beneficial to crop growth and soil health because their activities help decompose crop residues and cycle nitrogen and other nutrients. Pest nematodes do not threaten yield if their numbers remain low. The key to avoiding population explosions of nematode pests is to be proactive – know what the situation is and take appropriate measures when nematode numbers indicate a problem is brewing. 

The WSMB sponsors free nematode testing to help producers stay ahead of the most important nematode pest of soybean, the soybean cyst nematode (SCN) (Figure 1). 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.

Figure 1. WI Counties Confirmed to Have SCN as of 2013.

In 2015, the WSMB is again offering the expanded 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.

Free soil sample test kits are available now and can be requested at (freescntest@mailplus.wisc.edu).
 

For more information on SCN testing and management practices to help reduce the losses from this pest, please contact: Shawn Conley: spconley@wisc.edu; 608-262-7975 or visit www.coolbean.info. 
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.

Soybean Management Strategies to Facilitate Timely Winter Wheat Establishment

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Winter wheat acres across WI have declined over the past few years due to high corn and soybean prices and late grain harvests. As farmers get ready to kick off the 2015 growing season here are a few suggestions to help get your 2016 winter wheat crop established on time. 

  • Plant early. If weather and soil conditions allow for it plant the acreage you intend to go to winter wheat first. This is regardless of which crop you plan to follow (soybean, corn silage or field corn). Remember the optimal planting date window for most of our WI winter wheat acres is the last week of September through the first week in October. In Figure 1 below you will notice a 17 day delay in planting (May 5 to May 22) led to an average 7-10 day delay in when the soybean varieties hit R7. For a majority of the varieties examined (80%) this equates to roughly 21-28 days for that soybean crop to progress to the harvest ripe growth stage so we can establish our wheat crop on time.
Table 1. Calendar date for reaching R5 (beginning seed fill) and R7 (beginning maturity) growth stage (G.S.) by planting date and maturity group (M.G.) for the 2014 growing season at Hancock WI.
Timing of G.S. Initiation
Planting Date M.G. R5 R7
5-May 1.9 29-Jul 3-Sep
2.1 3-Aug 13-Sep
2.1 29-Jul 3-Sep
2.1 29-Jul 3-Sep
2.3 29-Jul 3-Sep
2.3 1-Aug 6-Sep
2.4 3-Aug 6-Sep
2.5 29-Jul 6-Sep
2.5 30-Jul 6-Sep
2.5 31-Jul 13-Sep
22-May 1.9 12-Aug 12-Sep
2.1 9-Aug 20-Sep
2.1 12-Aug 16-Sep
2.1 12-Aug 20-Sep
2.3 12-Aug 20-Sep
2.3 9-Aug 20-Sep
2.4 12-Aug 16-Sep
2.5 12-Aug 16-Sep
2.5 12-Aug 20-Sep
2.5 12-Aug 20-Sep
11-Jun 1.9 23-Aug 27-Sep
2.1 23-Aug 2-Oct
2.1 23-Aug 30-Sep
2.1 23-Aug 2-Oct
2.3 23-Aug 2-Oct
2.3 23-Aug 30-Sep
2.4 23-Aug 1-Oct
2.5 23-Aug 2-Oct
2.5 23-Aug 2-Oct
2.5 23-Aug 2-Oct

  • Crop rotation matters. Our long-term rotation data suggests winter wheat yields are greatest following soybean, followed by corn silage and lastly corn for grain.  Therefore plan your rotation accordingly to maximize yield and system efficiency.
  • Consider an earlier maturity group soybean. Plant a high yielding, earlier maturity group soybean to help get that soybean crop harvested on time. Though later maturing varieties “on-average” produce the greatest yields, data from our 2014 WI Soybean Variety Test Results show the maturity group range that included a starred variety (starred varieties do not differ from the highest yield variety in that test) was 1.9-2.8, 1.1-2.4, and 0.9-2.0 in our southern, central and north central regions respectively. This suggests that the “relative” maturity group rating is trumped by individual cultivar genetic yield potential. Therefore growers have options to plant an early maturity group soybean that will be harvested on time and not sacrifice yield.
  • Manage for the system not necessarily the crop. If you are serious about maximizing wheat grain and straw yield on your farm one of the biggest contributing factors for both of these in WI is timely wheat planting. Make management decisions to facilitate that. *We all know what inputs can extend maturity that don’t necessarily guarantee greater yields. So instead of listing them and fielding angry emails all weekend I am being strategically vague here*  As a producer is it better to sacrifice 0-2 bushels of soybean yield or 10-20 bushels of wheat grain yield and 0.5 tons of straw?  

As we all know mother nature holds the ultimate trump card on whether we will get our winter wheat crop established in that optimal window. These aforementioned strategies are relatively low risk to the farmer and regardless of what weather patterns we run into are agronomically sound.

Go Bucky!

Factors to Consider While Assessing Your 2015 Winter Wheat Crop Stand and Spring Nitrogen Timing

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As the snow begins to melt and we finally put the 2014/15 winter behind us, many growers and consultants alike are beginning to venture out to their winter wheat fields to assess winter injury and nitrogen timings. Though it is a premature to make any rash decisions here are a few considerations for assessing your spring 2015 winter wheat stands.

  1. As you look across your wheat landscape vibrant green patches will be interspersed with drab brown areas. The brown areas do not necessarily indicate those plants are dead.
    2015 Arlington Winter Wheat Variety Trial – Roadside Assessment
    2015 In Field Stand Assessment
    2015 Planting Depth and Tiller Assessment
    Growers and consultants can either reassess in a week or pull plants from the field and place in warm environments. Milk houses and kitchens work perfect. Root regrowth will appear from the crown and will appear as vibrant white roots as shown below.
    Spring Root Regrowth in Winter Wheat

    If plants do not recover our critical threshold for turning over a field is 12 to 15 live plants per square foot. Below this threshold is an automatic replant. For more detailed information on assessing winterkill please view Wheat Stand Assessment, Winterkill Yield loss, and Nitrogen Application. 

  2. Evaluate tiller number and make the N timing decisions. It is important to remember that the functional purpose of spring N is to 1. stimulate tillering and 2. provide crop nutrition. If ample tillering (> 70 tillers per square foot) has occurred growers can delay N applications up to pre-joint (Feekes 4-5; Zadoks 30). This practice will aid in minimizing early spring N loss. Applications of N made after this growth stage may lead to wheel track damage. If growers have < 70 tillers per square foot it is important to get across those fields as soon as possible to minimize yield loss due to low tiller/head counts. For more information on tiller counts and spring N timing please view my YouTube video entitled: Wheat Stand Assessment and Nitrogen Timing.  
  3. Lastly remember that wheat grain in itself is only part of the revenue you capture with winter wheat. The price of winter wheat straw remains strong so please consider that revenue stream before any replant decisions are made.

Winners of the 2014 WI Soybean Contest are Announced

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The 1st place winner in Division 4, Bahr Farms Inc. of Darlington, grew Channel 2402R2 Brand and harvested 84.99 bu/a.  In second place, McComish Family Farms of Shullsburg grew Channel 2402R2 Brand and harvested 79.62 bu/a.  In Division 3, Ellis Farms Inc. of Walworth won 1st place with Jung 1250RR2 at 73.80 bu/a, and in 2ndplace, Caliber Custom Services of Kaukauna harvested 63.32 bu/a with DuPont Pioneer P22T69R.  Also in Division 3, the Wisconsin Bean Team of UW Graduate students Adam Gaspar, David Marburger, and Ethan Smidt grew Pioneer P28T33R and harvested 89.58 bu/a. The WI Bean Team is ineligible for official prizes as they are grad students of Dr. Conley; however their efforts are still unofficially recognized.   In Division 2, Stetzer Brothers LLC of Melrose achieved 81.78 bu/a from NK Brand 17G8 for first place.  In 2nd place, Kloos Acres of Stratford harvested 60.60 bu/a from DuPont Pioneer 91Y90 soybeans.  In Division 1 at 54.72 bu/a was Jerry Koser from Almena who planted Pioneer 91M10.  2ndplace winner in Division 1 was Paul Graf Farms LLC from Sturgeon Bay.  They harvested 38.45 bu/a from Pioneer 90Y90.  

Reported production practices of yield contest winners.

 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.

2014 Geographic Division Map
For more information please contact Shawn Conley, WI State Soybean Specialist at 608-262-7975 or spconley@wisc.edu

Should We Be Using Soybean Maturity Group as a Tool for Variety Selection?

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Over the last decade I have noticed a subtle shift across much of the northern soybean growing region towards planting later maturity group soybeans. This shift, either conscious or unconscious, may be attributed to earlier planting dates, relatively favorable fall harvest windows, and the drive for maximum yield as influenced by high commodity prices. As with all trends sooner or later, we have a correction year: 2014 was that year for many farmers. As farmers, consultants, and the battered and bruised seed suppliers sort through the plethora of product offerings for 2015, a common question arises: “In 2015, how much weight should we really give to maturity group in these seed decisions?”. For those of you with short attention spans like me, the short answer for soybean is not much….for the rest of you please read on to understand my reasoning.

In 2011, the WI Soybean Research Program published an article in the journal Crop Management entitled: “Optimal Soybean Maturity Groups for Seed Yield and Quality in WI” (Furseth et al, 2011). In this data set we looked at 893 varieties across 6 growing seasons (2004-2009) and three production regions in WI . Within each region we identified the optimal maturity group range for maximum yield. Those were 2.6-2.9, 2.1-2.4, and 2.0-2.2 for our southern, central and north central regions respectively.  After I make this provocative statement this is usually where the audience either falls asleep, starts texting their neighbor about the lame and inept speaker (me), or uses the restroom and fails to hear as the great Paul Harvey would say ……the rest of the story.

Within each figure below you will also notice a maroon line directly below the black yield regression slope. This maroon line indicates the range of maturity groups that lie within 10% of maximum yield. These figures suggest that regardless of growing region in WI growers can select a variety that is almost one full maturity group earlier than the optimal maturity group range for maximum yield and still be within 10% of maximum yield.

These data further support Joe Lauer’s assertion that “Every hybrid (or in our case cultivar or variety) must stand on its own” (Happy Thanksgiving JGL, you were positively quoted in a soybean article). In our recently released 2014 WI Soybean Variety Test Results book the maturity group range that included a starred variety (starred varieties do not differ from the highest yield variety in that test) was 1.9-2.8, 1.1-2.4,and 0.9-2.0 in our southern, central and north central regions respectively. This amplifies my assertion that the “relative” maturity group rating is trumped by individual cultivar genetic yield potential.

Lastly, since I brought it up lets also discuss our “relative” soybean maturity group rating system. If anyone has ever observed a multi-company variety trial in the fall, they may have notice many differences in maturity amongst varieties that have the same MG rating. For example in our 2014 Southern Region Glyphosate Tolerant Soybean Test we noted a 7 day maturity date range among all the 2.4 maturity group varieties listed. This may not seem important at the end of September, but in years when we plant late (Table 1), have a cool growing season and apply a fungicide those few days may matter. 

As seed decisions are made for 2015, it is fine to keep the relative maturity rating on your check list, just don’t have it near the top!

Table 1. Calendar date for reaching R5 (beginning seed fill) and R7 (beginning maturity) growth stage (G.S.) by planting date and maturity group (M.G.) for the 2014 growing season at Hancock WI.

Timing of G.S. Initiation
Planting Date M.G. R5 R7
5-May 1.9 29-Jul 3-Sep
2.1 3-Aug 13-Sep
2.1 29-Jul 3-Sep
2.1 29-Jul 3-Sep
2.3 29-Jul 3-Sep
2.3 1-Aug 6-Sep
2.4 3-Aug 6-Sep
2.5 29-Jul 6-Sep
2.5 30-Jul 6-Sep
2.5 31-Jul 13-Sep
22-May 1.9 12-Aug 12-Sep
2.1 9-Aug 20-Sep
2.1 12-Aug 16-Sep
2.1 12-Aug 20-Sep
2.3 12-Aug 20-Sep
2.3 9-Aug 20-Sep
2.4 12-Aug 16-Sep
2.5 12-Aug 16-Sep
2.5 12-Aug 20-Sep
2.5 12-Aug 20-Sep
11-Jun 1.9 23-Aug 27-Sep
2.1 23-Aug 2-Oct
2.1 23-Aug 30-Sep
2.1 23-Aug 2-Oct
2.3 23-Aug 2-Oct
2.3 23-Aug 30-Sep
2.4 23-Aug 1-Oct
2.5 23-Aug 2-Oct
2.5 23-Aug 2-Oct
2.5 23-Aug 2-Oct
Literature cited: 
Furseth, B. J., Zhao, Y., Conley,S. P., Martinka, M., and Gaska, J. 2011. Optimum Soybean Maturity Groups for Seed Yield and Quality in Wisconsin. Crop Management. Online. Crop Management doi:10.1094/CM-2011-0622-01-RS.

Finalists for the 2014 WI Soybean Yield Contest are Announced

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The 2014 growing season proved to be yet another challenging year for many WI soybean growers.  Given these widespread challenges, we again experienced great interest in the 2014 WSA/WSMB Soybean Yield Contest.  The top two entries in each division (in no particular order) were:

Division 4: 
  • Tim McComish, Shullsburg (planted Channel 2402R2 Brand)
  • Kevin Bahr, Darlington (planted Channel 2402R2 Brand)
Division 3:
  • Travis Van De Hey, Kaukauna (planted DuPont Pioneer P22T69R)
  • Ron Ellis, Walworth (planted Jung 1250RR2)  
  • *WI Bean Team (Adam Gaspar, David Marbuger, Ethan Smidt), Madison (planted DuPont Pioneer P28T33R) 
*The WI Bean Team is ineligible for official prizes as they are grad students of Dr. Conley; however their efforts are still unofficially recognized.  

Division 2:

  • Steven Stetzer, Melrose (planted NK Brand 17G8) 
  • Steven Kloos, Stratford (planted  DuPont Pioneer 91Y90) 
Division 1: 
  • Paul Graf, Sturgeon Bay (planted DuPont Pioneer 90Y90) 
  • Jerry Koser, Almena (planted DuPont Pioneer 91M10)
The final ranking and awards will be presented at the 2015 Corn Soy Expo to be held at the Kalahari Convention Center, Wisconsin Dells on Thursday January 29th during the WSA/WSMB annual meeting.

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 608-262-7975 or spconley@wisc.edu

Fall is Still a Good Time to Sample for SCN and Other Plant Parasitic Nematodes

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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.  
Free soil sample test kits are available now and can be requested from Jillene Fisch at (freescntest@mailplus.wisc.edu) or at 608-262-1390.
For more information on SCN testing and management practices to help reduce the losses from this pest, please contact: Shawn Conley: spconley@wisc.edu; 608-262-7975 or visit www.coolbean.info.
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.

Harvest Considerations for Variable Soybean Maturity

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Variable soil types, knolls, flooding and drought have left many growers with extreme in-field variability of soybean maturity.   There are areas in fields where the soybean seed is 13% or less moisture adjacent to areas with green seed.  The prevailing question is “When should the grower harvest?” Obviously there is no simple answer, as each field is different. However here are a set of guidelines to consider:
1.    The easiest answer is harvest the field at two different times. Take what is dry today and come back in two weeks and harvest the rest. The challenge with this approach is that today’s equipment is large and not easily moved from field to field. Furthermore many growers rent or own land over large areas where this is impractical and the whole field must be taken at once. So……
2.     The next simple answer is wait until the whole field is ready to go. As noted in our article Drought Induced Shatter, we are seeing areas across the Midwest where shattering is occurring. The general rule of thumb is 4 seeds per square foot = one bushel yield loss. At local cash prices dipping below $10.00 per bushel this is hard to see happen and not harvest. Furthermore, waiting will also lead to moisture loss in the field. As we learned the past few years, you do not get compensated for harvesting below 13% moisture. So…..
3.     If growers are concerned with shatter and/or other harvest losses the next logical approach is harvest ASAP. This opens a whole new can of worms. Harvesting ASAP will lead to a mixture of dry, wet, and immature (green) soybean seed. Be aware that if you harvest this mixture regardless of the ratio, your combine moisture sensor may not detect the correct moisture, be prepared for that initial shock when the elevator tests the grain. Next be prepared for the dockage. Most combines will leave more beans in the pod when they are wet or immature.   These beans may end up on the ground or in the grain tank as unthreshed soybeans. Harvesting seed with this variability will be very similar to handling frosted soybean seed so discounts may occur due to moisture shrink, damage (green beans are considered damage), foreign material (this is usually higher when harvesting wet beans), test weight, and heating. If you choose on farm storage to address some of the dockage concerns please refer to Soybean Drying and Storage for questions.  

4.  The last consideration I would bring forward is that the mature areas are likely going to be the low yielding pockets due to drought whereas the yet to mature areas will likely be the higher yielding areas within the field. So, in short, which yield environment would you rather focus your time and efforts to protect?  

      The question ultimately comes down to the bottom line and where you make the most $$$. If shatter is not occurring and you have good equipment that does not incur significant harvest loss, will harvesting grain that is over-dry make you more money than harvesting seed that may incur significant dockage? My guess is yes but you tell me!
Image 1. Variable Maturity (M. Rankin)

Odds My Soybean Crop Will Mature Before A Killing Frost Hits

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The Wisconsin soybean crop is slowly starting to mature, however many growers and crop consultants are still concerned about the risk of frost damage to late planted fields.  In soybean an extended period (several hours) of temperatures 28 degrees F or lower is required to completely kill a soybean plant, though temperatures 32 degrees or less can still damage top growth. Those growers considering the state of their soybean crop and wondering the odds of making it to maturity before significant yield loss occurs must first correctly identify the soybean growth stage.

Once the crop growth stage has been determined we can estimate the number of days it will take for your field to reach R7 or physiological maturity.  Across our Arlington and Hancock field sites in 2014 it has taken 5-8 days to go from R3 to R4, 7-8 days to go from R4 to R5, 10-14 days from R5 to R6 and 15-20 days from R6 to R7. As a point of reference our June 20th planted soybean at both locations just hit R6 this week. Next using the three figures below that show the 10th percentile, median, and 90th percentile date when you can expect a freeze event you can estimate the risk of a frost based on your crop growth stage.

For example: If you lived in SW Marathon county there is a 10% chance that a freeze event would have occurred prior to September 11-20, a 50/50 chance that a freeze event would occur prior to September 21-30, and a 90% chance a freeze event would have occurred prior to October 1-10. So if your soybean crop just entered the R5 crop growth stage today 9/8/14 there is a greater than a 50/50 chance that crop won’t make grain based on historical weather data.

Lastly if you are concerned about a freeze event please refer to Table 1 below that provides yield loss estimates of freeze damage by crop crop stage. This may help you decide whether you should risk taking the late planted soybean field as a grain crop or would that field be more valuable as a forage or green manure?

Table 1. Soybean Response to Freeze Damage
Growth Stage
Yield Reduction
R4 – Full pod
70%-80%
R5 – Beginning seed
50%-70%
R6 – Full seed
15%-30%
R7 – Beginning maturity
0%-5%
R8 – Full maturity
0%

Source: Saliba et. at. Kansas State University, 1982