Category Archives: Yield

Management Recommendations for Frost-Damaged Soybean

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While most of our double-cropped soybean were planted in a timely manner, many acres were not.  And I use the word “timely” very loosely here.  This year, “timely” means that they were planted by early- to mid-July.  Usually I refer to July planting as “late”, even if the soybean are planted during the first week of July.  But, the wet June and July did not allow “timely” planting in many parts of the Commonwealth.  Much of Virginia’s double-crop soybean were planted in July and some acres were even planted in early-August.Frost-Damaged Soybean Suffolk 20131028

As a review (maybe a disclaimer?), I did suggest that we continue planting soybean though mid-July because I’ve seen some pretty good yields (in the 30’s) from July-planted soybean.  But, planting after mid-July is always risky.  With a relatively warm and sunny August and September, late-July and even August-planted beans can catch up and mature before the frost – if the frost waits until early-November.  Of course, this year was neither warm or sunny and our first frost came in late-October.  Maturity was slowed.  The end result is frost- and freeze-damaged soybean.

We are experiencing several scenarios:

  1. Freeze-Damaged Immature Soybean.  Soybean were in the R6 stage (green pods and seed) and a hard freeze killed the plant.  In this worst case scenario, the crop will not mature and you’ll be left with green seed that you cannot sell.  Hopefully very little of our crop experienced this.
  2. Frost-Damaged Immature Soybean. Soybean was in the R6 stage and a frost damaged many of the leaves on the plant (see photo above).  In this case, the plants were not killed; therefore, they should continue to mature.  But, maturity will be delayed and drying time will be extended.  I cannot guarantee that you won’t have some green seed when you harvest, but the number should be much less than for scenario 1.  This all depends on how close you were to physiological maturity (R7).  And, it’s very likely that the seed will be smaller (photosynthate from the leaves can’t move to the seed if the leaves aren’t there).
  3. Frost/Freeze-Damaged Mature Soybean.  Soybean were physiologically mature (R7 stage; at least one pod on 50% of the plants has reached its final brown color).  In this case, whether the crop experienced just a frost or a even a hard freeze, the crop will mature but the seed will take a little longer to dry.Frost-damaged Sobyean Suffolk 20131028

Regardless of the scenario you may be experiencing, there are some management tactics that you can use to minimize further damage.  Instead of spelling out all of these tactics myself, I’ll borrow an article from Mike Staton, Michigan State University Extension Educator.  He is probably more experienced with frost/freeze-damaged soybean than I and he has summarized the issue well.

Management Recommendations for Frost-Damaged Soybeans

Mike Staton, MSU Extension CURE Soybean Educator

 This article will help soybean producers reduce the adverse effects of an early frost.

The late planting season combined with some early frost events has increased the potential for frost damage to occur in soybeans this fall. The following recommendations from Michigan State University Extension will help you reduce the adverse impacts in the event that some of your soybean fields are damaged by frost.

 Frost-damaged soybeans are generally considered salvageable as long as the plants reached the R6 growth stage at the time the killing frost occurred. The R6 growth stage occurs when the beans completely fill one pod at one of the upper four nodes on the main stem on 50% of the plants in the field. In dense, green soybeans, frost/freeze damage kills the upper leaves but rarely penetrates deeply into the canopy when temperatures remain above 30o F. However, once the upper leaves have been damaged, subsequent freeze events will penetrate deeper into the canopy. Once the plants reach the R7 growth stage, yield reductions due to frost/freeze injury will be minor. The R7 growth stage occurs when one pod on the main stem has attained its mature color on 50% of the plants in the field.

 Combine Adjustment:

Frost-damaged beans will probably be wetter than normal and more difficult to thresh. Your first step in adjusting for this condition is to reduce the concave clearance. If acceptable threshing still does not occur, increase the speed of the cylinder. Make incremental adjustments and check your progress after each adjustment.

 Harvest at Higher Moisture Contents:

Soybeans that experienced severe frost/freeze damage extending well into the crop canopy will dry down slowly. In this case, producers should avoid significant harvest delays by harvesting frost-damaged fields at moisture levels between 16 and 18%. Data from the University of Wisconsin showed that shatter losses of 0.2 bushels per acre per day occur after the beans reach 16 to 18% moisture. The beans will need to be dried to a safe moisture level for storage (12% for 6 months). Electronic moisture meters tend to underestimate the moisture levels in green and immature soybeans so remember to add 1.5 percentage points to the moisture meter readings when testing mixtures of green, immature and mature beans and adjust drying times accordingly. In fields where only the upper leaves were damaged by frost, producers should wait and allow the beans to mature and dry to 14 to 15% in the field if possible.

 Drying Frost-Damaged Soybeans with Ambient Air:

If only 2 to 3 points of moisture need to be removed, the air temperature is above 60o F and below 75% relative humidity; no supplemental heat is required in drying bins equipped with full perforated floors and fans capable of producing one to two cfm/bu. However, drying will occur slowly. Drying times depend on initial moisture content, air flow, grain depth and weather conditions. Aeration fans should be run continuously as long as the beans are above 15% moisture and the average humidity of the air is below 70 to 75%.

 Drying Frost-Damaged Soybeans with Supplemental Heat:

If you plan to add supplemental heat, be careful as soybeans are more fragile than corn and can be damaged by drying temperatures above 130o F. These temperatures will cause excessive seed coat cracking and split beans. The relative humidity of the drying air should always be maintained above 40% to protect the integrity of the seed coats and prevent splits. Relative humidity is cut in half for each 20 degrees that the air is warmed. Growers can control the heat and humidity of the drying air by using short burner cycles or by changing the burner jets. 

 Store Frost-Damaged Beans

Green and immature soybeans are included in the total damage factor in the U.S. soybean grading standard. Elevators will discount loads containing green and immature soybeans and in some cases may reject entire loads if the damage levels are high. Discounts can be reduced by screening out the small beans, drying the rest to 12% moisture and storing them in aerated bins for at least six weeks. The green color may fade and marketing concerns should be reduced after this amount of time.

 This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.

Soybean Crop is Still at Risk to Drought & Pests

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Our soybean crop is moving right along.  Much of our May-planted crop has hit or it approaching the R6 stage.  Our double-cropped soybeans are in the R4-R5 stage depending on their maturity, planting date, and whether or not they experienced early-season drought.  There’s a tendency for us to believe that the crop is made after the seed have met in the pod.  However, as shown below, only 50% of our yield has been made at the R6 stage. 

Dry weight will continue to accumulate in the seed for the next 3 weeks until the crop reaches the R7 stage (physiological maturity), which is defined as one pod on the plant that has reached its final mature color.  Much of this seed weight is due to translocation from other plant parts, especially the leaves and petioles (remobilization).  Sometimes soybean is called a self-destructing plant.  This is largely true.  As photosynthate is moved from the leaves to the seed, the leaves will turn yellow and drop from the plant.  If the leaves are yellowing and dropping due to this natural process, then we shouldn’t be concerned.  However, if the leaves are dropping due to another reason such as dry weather or disease, we should take notice.  It is important to keep the leaves green as long as possible to maximize yield.

It takes about 2 weeks to move from the R5 to R6 stage and another 3 weeks for to move from R6 to R7.  This is a long time and much can happen during this period.  First, we must protect the developing seed from insects such as corn earworm and stink bugs.  After R6, these two pests are not as much of a concern, but defoliators such as soybean looper can still remove green leaf area, which I’ve already stressed, is vital for maximum yield.  We also need to be concerned about foliar disease, which can also rob us of green leaf area

The Good and Bad of a Wet September

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We gained much needed rain in late August with Hurricane Irene.  It also brought substantial lodging, which reduced our yield potential.  But, I have yet to see a poor soybean crop lodge.  That August rain by itself would have pretty much finished out our full-season crop; our full-season soybean may not benefit much from the continued rain that we are still experiencing.  However, the double-crop plantings still had lots of yield to make; therefore, the September rains helped fill out that crop.

Any yield increases with September rains will come mainly in the form of greater seed size.  So, how important are larger seed?  Although number of seeds (mainly through number of pods) affect soybean yield most, seed size is second in importance.  The photo below may help illustrate this point.

In the above example, the weight of the larger seed is more than 50% greater than the small seed.  Of course these differences resulted from two extremely different environments.  The seed to the left of the pencil formed under late-season drought conditions.  The seed to the right of the pencil was produced under excellent seed fill environment, similar to this year.  If we were to assume that there were an equal number of seed and pods in both cases, the crop with the larger seed would have resulted in about 10 bushels more yield in a 20 bushel environment, 15 bushels more in a 30 bushel environment, and so on.  Don’t misunderstand.  Plants with lots of seed and pods will not make very big seed.  We won’t get that much of a yield increase from this year’s late-August and September rains.  A large yield increase would have only resulted if we were to compare to a crop where little to no rain occurred during the seed-fill period.  Still, these late-season rains should definitely add 10-20% to our overall yields.

Now for the bad news – with these September rains comes an increase in disease affecting seed quality.  Furthermore, with heavy October rains, there is the possibility of pod splitting or seed sprouting in the pods before harvest.  This does not happen often, but years like this one will set the crop up for such a scenario.  In the remainder of this article, I’ll focus on the most common seed quality issues.

Phomopsis Seed Decay.  When soybeans mature during warm and wet conditions, we can expect seed quality to deteriorate.  Because this disease develops more rapidly on plants that are maturing under warm and wet conditions, we usually have more problems with early-maturing varieties.  We can however have seed decay on our later- maturing varieties if October is warm.

Infected seed are shriveled, elongated, and cracked.  Severely infected seed may appear white and chalky.  Test weight can be lower.  High occurrence of these seed can lead to discounts or rejection.

There are a few things that can be done to reduce the disease incidence.  It resides in the soil and on infected residue.  So, rotation is very important.  Later-maturing varieties and later planting dates that delay maturity into the cooler parts of the year will reduce the incidence.  Still, timely harvest is the best management strategy.  The longer you leave the soybeans in the field, the worse the disease.  So, only plant as many early varieties as you can harvest in a timely manner.  Foliar fungicides will decrease the incidence of seed decay if applied from mid pod development to early seed filling stages (R3-R5).

Purple Seed Stain.  Purple seed stain is caused by the organism Cercospora kikuchii, the same organism that causes Cercospora blight.  Although little of this disease was present early in the year, its incidence has increased dramatically since late-August.  Right now, fields with Cercospora blight can usually be recognized by reddish leaves and reddish purple blotches on the stem and leaf petioles.  When severe, defoliation of the upper leaves of the plant will take place.  In many cases, the blotching progressed up the stem and to the pods.  In the past, you may have noticed the dark, nearly black pods on some varieties.  Once it progresses to the pods, there is a higher likelihood that the seed will be stained.

Purple seed stain is very noticeable.  The seed will contain pink to pale purple to dark purple splotches, which can cover the entire seed coat.  The purple stain itself does not reduce yield, but seed with nearly 100% discoloration may be lower in oil and higher in protein.  A lot of staining can result in discounts.  Germination of seed with 50% or more staining will likely be delayed.  This year, our insect scout, Mr. Ed Seymore, is already noticing dark pods and some purple seed stain.

Usually, the disease first appears on the plant during early seed development.  If conditions are right (average temperatures over 80o for several days), then the disease will build up rapidly.  We had those conditions this year.  Other weather factors do not generally affect seed infection.  Severity of the infection is largely related to amount of infected leaf debris and residue.  Therefore, rotation with a non-legume crop is critical for control.

Other control measures include variety selection, planting high quality seed free of visual staining, and fungicides.  Varieties differ in their susceptibility of Cercospora kikuchii, but that information is rarely available in seed catalogs.  We routinely evaluate purple seed stain in our variety tests.  Strobilurin fungicides such as Quadris or Headline seem to give some control if applied during pod or seed formation.

Sprouting Seed.  One of the most disturbing late-season issues can be pod splitting or seed sprouting in the pod.  Back in 2005, we saw a lot of this.  That year was very dry up until September and October, when it began raining and didn’t seem to want to quit.  What causes pod splitting?  The verdict is still out on this, but here are my observations.  Generally this happens when the crop is under severe stress, usually drought conditions up until the full-seed stage (R6).  Pods are generally small due to the drought.  Then rains set in between R6, and R7 (Physiological maturity).  The seed grow and grow, and seem to outgrow the pods, causing them to split.  Obviously, this splitting can then lead to seed quality issues.

In 2005, not only were the some pods splitting, but October rains brought on sprouting seed.  The sprouting seed was not always directly related to the pod splitting; many of the pods in which we found sprouting seed were did not split until the seed sprouted.  We saw up to 30% of the pods with sprouted seed in some locations.  This is a very unusual occurrence, but can occur if soybean seed drop below 50% moisture, then increase to 50% or more moisture.  We immediately began looking in other fields and contacting county agents to do the same.  Soon after our discovery, I heard of reports from North Carolina of sprouting and reports from Pennsylvania of seed swelling in the pod.  However, after getting several reports back from county agents and farmers, and after we checked several other fields, we found that the problem was not nearly as severe as in our fungicide trial or as widespread as we may have thought.  Below is a summary of our findings:

  1. The sprouting problem was worse in southeastern Virginia.  Although we had reports as far north as Essex County, the incidence of sprouting seed declined as we moved north and west.
  2. More sprouting was occurring on the later-planted, later-maturing varieties.  This was verified in our variety test and by several county agents.
  3. More sprouting was occurring in pods showing Cercospora blight (very dark pods).  This was verified in a fungicide trial, our variety test, and by several agents.  We did not understand why this happened and could not definitely relate the sprouting to this disease.  But, there seemed to be a relationship.
  4. Sprouting occurred primarily at the top of the plant when dark pods (also occurring primarily at the top of the plant) were common.  Otherwise, most sprouting (especially that occurring on earlier-planted, earlier-maturing varieties) occurred at the bottom of the plant where the relative humidity was higher.
  5. After a week of drying conditions, the sprouted seed had dried up, and in some cases fallen out of the pods.

Why did the seed sprouting occur on the later-planted, later-maturing varieties in 2005?  There are two or three possible explanations.  One is that these varieties may have just dropped below 50% moisture; therefore the seed needed to absorb less total moisture to raise it back above 50%.  A second explanation is that these varieties still had significant amount of leaves, therefore held the moisture within the soybean canopy better.  Finally, in 2005, there was more Cercospora in the later-planted later-maturing varieties (note: Cercospora is not always worse in one maturity group or another,  but depends on the environment during early seed fill).

So, will we see pod splitting or seed sprouting in 2011?  I would expect some pod splitting from fields under drought stress during the summer followed by lots of September rain.  But, usually, the number of split pods is low and will not affect overall yield or quality substantially.  If seed sprouting occurs, the problem will not likely be widespread and should not affect our overall seed quality very much.  At the worst, there could be some lower test weight and seed could contain more foreign material (from the dried up sprouts).  However, the light seed will likely be blown out the back of the combine.  If you do observe the problem and it is severe, I suggest that the air on the combine be adjusted to remove those light, sprouted seed at harvest.  Too many sprouted seed in the bin could lead to rejection by the buyer.

Hurricane Irene May Be Beneficial to Virginia Soybeans …Still Lodging Will Lower Yield Potential

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Hurricane Irene roared along the Virginia coast with high winds and significant rainfall.  The rainfall was needed, desperately needed for some parts of the Commonwealth.  On the other hand, the high winds caused considerable lodging to the best looking of Virginia’s crop and this lodging will likely lower yield potential.  But, because the damage to soybean was not as severe as other crops such and corn, cotton, or tobacco, Virginia’s soybean crop may, in the end, benefit from the storm.

Below are the National Weather Service’s average estimates of rainfall received from Hurricane Irene (you can obtain these maps from http://water.weather.gov/precip/).   The greatest amounts occurred in eastern Virginia, but most of our soybean growing regions received rain.  Ironically, the hurricane might have saved the soybean crop on the Eastern Shore, which was very dry.  The rain comes at a very critical time for this year’s crop.  It will insure that pods and seed continue to fill and not abort due to moisture stress.  In most areas, the soil profile should be full; therefore, adequate soil moisture should be available to take us as least to the beginning of the R6 (full-seed, seed meeting each other in the pod) stage.  I am not however implying that the crop is made.  At the beginning of R6, only 50% of the yield is made.  But, cooler temperatures and a few more timely rains should insure good yields.

Now for the down side of the hurricane – lodging.  How much will the lodging from the hurricane cost us in yield?  This will depend on the degree of lodging and the stage that the soybeans were in.  In general, I’d say that our full-season crop is in the R5 (beginning seed) to R6 (full seed) and the double-crop soybeans are somewhere between R4 (late pod) and R5.  Yield is most severely affected when the lodging occurs at the R5 (beginning seed) development stage.  Although yield is still affected at R6, yield losses are only half as severe at this stage.  Many double-crop soybeans are only in the R4 stage throughout the state.  Yield losses due to lodging at this stage is probably not as great as if the crop was in R5, but could greater than if the crop was in R6 (assuming the same degree of lodging).  Still, double-cropped soybeans are usually much shorter and do not have the severe lodging that the more full-canopied full-season crop has.  In general, I’d expect less yield loss for the late-planted crop.

So, what’s my estimate on the amount of loss that we’ll incur?  First, we have to distinguish harvest or traffic loss from physiological yield loss.  Harvest losses can vary anywhere from 3-10% depending on many factors.  In some cases, we may have to run the combine of the most severely lodged soybeans in one direction.  But, with that said, I expect the soybeans to stand up quite a bit as soon as leaves begin falling.  I’ve even seen some recovery only after a few days.

Similar to harvest losses, if we have to drive over the lodged soybean for a late insecticide or another spray, we can see some loss due to running over soybean.  We have data from running over R4 stage soybean to make a fungicide application.  Depending on the size of the sprayer (larger boom widths cause less loss) and row spacing (7.5-inch soybean yield losses were less than 15-inch soybean), losses ranged from 1 to 4%.  Hopefully, we won’t need another insecticide spray.

There is little data on physiological yield loss, but what’s out there seems to be pretty consistent.  What do I mean by physiological yield loss?  That’s the loss in yield from lodging if all of the soybeans that are now on the plant can be harvested.  In controlled studies where researchers simulated lodging and compared it to a crop that was artificially supported, losses have ranged from 0% to over 30%.  Why such a range in yield loss?  It depends on the severity of lodging and the stage of development in which the lodging occurred.

Let’s first address the severity of lodging.  Soybean researchers have traditionally rated lodging on a scale of 1 to 5 as follows:

1.0          = almost all plants erect

2.0          = either all plants leaning slightly, or a few plants down

3.0          = either all plants leaning moderately (45O angle), or 25-50% down

4.0          = either all plants leaning considerably, or 50-80% down

5.0          = all plants down

As you may expect, a rating of 4.0 to 5.0 is very severe lodging.  I have seen this in a couple of locations, but at this time I’d rate most of the lodging between 2.0 and 4.0.  Yield loss will be minimal unless most plants are leaning at a 45O angle or more.  Otherwise, yield losses can range from 10-35%, depending on the stage in which the lodging occurred.

Why does lodging cause yield loss?  It’s not completely clear, but the generally accepted reason is a reduction in net photosynthesis.  With less photosynthesis, there is less energy going to the developing pods and seeds.  When plants are lodged, relatively less of the upper leaves and more of the lower leaves are exposed to sunlight.  The upper leaves are more photosynthetically active and the lower leaves are less active.  When lodging occurs, the entire energy-producing mechanism is disturbed.  In other words, we are now exposing less of the most productive leaves and more of the least productive leaves to the sun.  So, yield will decline.

Let’s assume that lodging rated above 3.0 will cause a 10-30% loss.  Now the severity of the yield loss will depend on the development stage that the soybean plant was in.  As I said earlier, there’s little hard data on this subject, but a few older experiments give us some information.  In a study conducted in 1972-73, S.J. Woods and M.L. Swearingin of Purdue University indicated that the R5 stage was the most critical time for lodging to occur.  At this stage, yield was reduced by 18-32%.  At stages R3 and R6, yield was reduced by 12-18% and 13-15%, respectively.  Details of that experiment are shown to the right.

In that study, the plots were manually lodged with a long aluminum bar at the indicated soybean stage.  Although lodging ratings were not given, I would consider it to be in the 3.5 to 4.0 range from the description given.  Two varieties were tested. ‘Corsoy’ was more susceptible to lodging, but was able to branch more; therefore, it yielded higher when lodged.  ‘Wells’ is more resistant to lodging, but did not branch as much; therefore, was unable to compensate as much for the lodging.  In the natural lodged plots, only slight (2.0 or less) lodging occurred.

From the above data and a few other studies, I’d estimate that where we had moderate to severe lodging and the soybean were in the R4 or R6 stage, we’ll probably lower our yield potential by 10-15%.  If the plants were in the R5 stage and lodging was severe, then losses could be 15-25%.  But, most of our lodging was not likely as severe as in the study.  In general double-cropped soybeans are not as lodged due to their smaller height, therefore will not suffer as much damage.

One more thing must be mentioned.  If soybeans were in even later stages (mid-R6), then yield loss will be less.  Our full-season maturity group 3 soybeans planted in mid-May are getting close to physiological maturity (R7, one pod reaching its final brown color) and some early-maturing group 4 soybeans are well into the R6 stage.  Once a plant reaches physiological maturity, 100% of the dry matter has accumulated; so there will be no yield loss.  Plus, the plants with fewer leaves lodged less.

In summary, there will be some loss in yield potential due to Hurricane Irene.  I must stress that this is loss in yield potential, which is the yield that soybeans would have made after receiving the rain from Irene, but not the wind that caused lodging.  In dry spots or in places that were becoming dry, the hurricane likely benefitted the soybean crop more than it hurt.  Overall, average yields may now be greater than before Irene.