Category Archives: Soybean

Late-Season Drought Hurting Soybean in Virginia

I had never seen fields as wet as they were back in the second week of July.  But, things change very rapidly.

In August, it appeared that full-season yield potential was 60 to 80 bushels per acre.  Growth was excellent and the crop was loaded with pods and seed.  Likewise, corn yield potential was excellent.  Double-crop soybean did not look nearly as good, struggling with general poor growth due late planting, wet feet early, and dry soils later.

Now the situation is just the opposite.  Well almost – corn yields are coming in very good.  But, pods and seed on our full-season soybean crop are rapidly aborting due to the dry weather.  Leaves are falling.  It appears that the crop is maturing more rapidly.  This is not a good thing as yield strongly depends on the length of seed filling.  I’ve even seen some soybean dying in the corners of center pivots on the Eastern Shore.  Irrigation will definitely pay off this year.  As shown in the precipitation deficit map, we are below our seasonal average rainfall over the past 60 days.

This photo was taken this past Tuesday 8:30 am in the Official Variety Test at our Eastern Shore AREC. ? It looks like maturity group 3 varieties will out-yield group 4s, which will yield better than group 5s.  However, a timely rain this week may salvage the late 5s.  I don’t expect yields to top 40 bushels and they could possibly be less than 20 bushels if the drought persists.

On the other hand, I feel much better about double-crop soybean.  Although there is little growth, these soybean are not showing signs of drought, at least not to the extent of the full-season crop.  This photo is from the field adjacent to the full-season soybean shown above.

?The main reason for this lack of visual stress is less vegetative growth (usually not an advantage) pulling less moisture from the soil.  We also started the season with a soil profile full of water, but not excessive moisture (probably because the wheat had more-or-less depleted the soil moisture by May).  Furthermore, these double-crop soybean are just now entering the pod and seed development stages.  The seed is not yet requiring great amounts of water.  These soybean can also “wait” for a rain as, at this time, there are still excess pods on the plant.

Below are a few more images that show flower, pod, and seed abortion.

The number of seed per acre controls yield most – the number of seed is mainly ?controlled by the the number of pods at harvest; seed per pod has less effect.  Seed size can also greatly affect yield, but not to the extent of seed number.  With late-season rains, we can still increase seed size substantially, especially where there has been lots of seed and pod abortion.

?

Is there anything to be done about this?  No, not really – short of irrigation.  There’s nothing that you can apply to relieve the stress.  But, we can learn from such devastating experience and apply these learnings to the future.

  • First and foremost, diversify.  Although early-maturing varieties don’t usually do as well in full-season systems as those best adapted to a given area, it may be worth it to devote some acreage to such varieties.  It may also help to plant a few varieties that mature a little later than the ones you normally plant.
  • Keep double-crop small grain-soybean systems in your cropping mix.  Not only will it increase total income and improve your soils without a cover crop, it will reduce risks by diversifying your crop mix.
  • Review university, on-farm, and company variety test results to help select drought-tolerant varieties.  Not since 2010 have we seen drought to this extent in our variety tests; therefore, we have little information on how current varieties perform under drought stress conditions.
  • Other stresses such as vascular disease and nematodes will greatly enhance the effects of drought.  Identify those poor-yielding fields or parts of fields and take corrective actions next year.
  • Improve your soils with no-till and cover crops.  Better soil structure, more organic matter, and better chemical and biological activity will minimize drought stress.

 

 

Soybean aphid being found at threshold levels in soybean fields

For reasons I cannot explain, our soybean field scouts have recently reported finding large numbers of soybean aphids in many soybean fields. Threshold levels have been found in soybean fields in 11 counties (Goochland, Buckingham, Cumberland, Culpeper, Fauquier, Rappahannock, Warren, Clark, Fredrick, Shenandoah and Rockingham). We typically see only a very limited number of fields infested with soybean aphids so this widespread infestation is very unusual. From past investigations we determined that soybean aphid likely does not overwinter in Virginia, as their required winter host plant, buckthorn, is very uncommon in our state. We believe it migrates in from the north central states and Canada when large infestations develop in those areas. The alates, or winged forms, take flight and can be transported long distances by prevailing winds and storm events. What is unusual is that soybean aphid seems to prefer a climate that is cooler than our normal summertime temperatures so have been the most troublesome only in summers that were cooler. I think we can all agree that our summer has NOT been a cool one. So why this widespread infestation? Not sure!

Soybean aphid is not hard to identify on soybean as there are no other aphid species that reach these high numbers—basically a light yellow/green aphid with black tips on the cornicles. There are good economic thresholds for determining if a field needs to be treated. A treatment is suggest when an average of 250 or more are found per plant, in two consecutive field visits 5-7 days apart, and beans are in the R2-R5 growth stage (see the attached threshold chart). Between R5 and R6 the number can be much higher and after R6, fields are safe. From our past experience, if a treatment is warranted most pyrethroids registered for use in soybeans will do a good job of controlling them.

soybean_aphid

SBA_threshold

 

BMSB and kudzu bug distribution maps for the week ending August 27, 2015

Brown marmorated stink bug and kudzu bug were found in soybean in several additional Virginia counties this week–please refer to the distribution maps below.  Fields at or above the BMSB threshold of 3 to 5 total adults + medium and large nymphs in a 2-minute visual count were found in the following counties:  Bedford (12 BMSB per sample), Shenandoah (8 BMSB), Nelson (4 BMSB) and Henry (3 BMSB).   Thanks to our scouts Ed Seymore and Jamie Hogue, and to ANR Agent Scott Reiter for their reports this week.  BMSB_map_27_Aug_2015KB_map_26_Aug_2015

Soybean disease update – frogeye leaf spot

I have received numerous reports of soybean fields with moderate to severe frogeye leaf spot (FLS) over the past several weeks. In most cases, the disease is showing up in fields planted to a FLS susceptible variety and/or in fields that have been in continuous soybean. FLS can cause significant yield loss in susceptible varieties, so fungicides may be needed to control the disease in high risk fields (see accompanying blog post “Foliar fungicide applications in soybean”). Unfortunately, FLS isolates resistant to strobilurin (QoI, Group 11) fungicides have been confirmed from some locations in Virginia, so fungicide control failures can occur if the proper fungicide chemistries are not selected as illustrated in the pictures below. A soybean fungicide efficacy table with ratings based on data from multiple field trials in multiple states can be downloaded below. We are currently surveying fields in Virginia for strobilurin-resistant FLS and will have data on the frequency and distribution of resistance later this year. In the meantime, it should be assumed that FLS will not be controlled by strobilurin fungicides, and other fungicide chemistries (e.g. triazoles) should be applied in fields with FLS either alone or in combination with a strobilurin. Keep in mind that strobilurin fungicides still provide good control of other diseases that can occur in soybean.

FLS - untreated

FLS – untreated

FLS - 2 fungicide applications

FLS – 2 fungicide applications

Soybean disease scouting & fungicide guide 2015

Foliar fungicide applications in soybean

If and when to make a foliar fungicide application is a decision soybean producers must make each growing season. Every year is slightly different, and it is difficult to predict whether or not a fungicide application will be profitable. However, the risk factors listed below can be used to make an educated decision of whether or not to spray. The greater the number of risk factors in your field, the more likely it is that a fungicide application will be profitable.

  1. Growth stage of the crop. Disease is most likely to impact yield during pod and seed development since this is when the yield of the crop is being formed. Fungicides are more likely to result in a yield response if disease occurs between the beginning pod (R3) and full seed (R6) growth stages, a period that lasts approximately 30 days. Results from research conducted in 2014 suggest that a fungicide application is most likely to result in a yield response if weather conditions (see #2 below) conducive for disease development occur within two weeks of the R3/R4 growth stage. Overall, the optimum timing for a fungicide is at the R3/R4 growth stage, though later applications can be beneficial if diseases develop later in the season. Fungicide applications after the R5 growth stage are not recommended.
  2. Weather conditions. Currently, research is being conducted to develop a weather-based fungicide decision aid for soybean. Infection, growth, and sporulation by foliar pathogens occurs when temperatures are moderately warm and during periods of rainfall or high humidity. To determine the relative disease risk based on weather conditions, find a source of hourly temperature, rainfall, and relative humidity data (e.g. Weather Underground or a personal weather station). If over the past week the following conditions occurred on two or more days, the risk of disease development in the crop is high:
    • Average daily temperatures from 65-80 °F AND
    • 10 or more hours of relative humidity at or above 95% OR a rainfall event
    These conditions have occurred in many areas throughout Virginia over the past week as storms have moved through. However, before making a fungicide application consider the other risk factors below.
  3. Susceptibility of soybean variety to disease. Soybean varieties vary in their susceptibility to diseases, and more susceptible varieties are more likely to need a fungicide to protect yield. Keep in mind that a variety may be relatively resistant/tolerant to one or a few diseases but susceptible to others, so be aware of which diseases are most likely to occur in your field (see #4 and #5 below).
  4. Field history. Soybean debris is a source of pathogen inoculum, so diseases will show up earlier and be more severe in fields planted to soybean year after year compared to those in rotation with corn or another crop. History of a particular disease in a field should also be considered since it is likely to occur year after year.
  5. Confirmation of disease in a field. If you see a foliar disease starting to develop in your soybean crop, it may be a sign that it is time to apply a fungicide. Scouting may be useful for some diseases such as frogeye leaf spot, but other diseases (e.g. Cercospora blight) do not show symptoms until long after infections have occurred. Fungicides are more effective when applied preventatively, but applications shortly after the onset of symptoms will slow the progress of the disease. Thresholds have not been established for frogeye leaf spot or other foliar diseases of soybean.
  6. Yield potential. This year some soybean fields got off to a poor start and never really recovered. If growth is poor and yield potential is low, you do not have much yield to protect and fungicide applications are less likely to be profitable. In contrast, if a crop has high yield potential, a fungicide application can help to maximize that yield, especially if the variety is susceptible to disease.

The Virginia Soybean Field Day is this Thursday

VIRGINIA SOYBEAN FIELD DAY
Thursday August 20, 2015

Eastern Virginia Agricultural Research & Extension Center
2229 Menokin Road
Warsaw, VA 22572
(804) 333-3485

Sponsored by
Virginia Soybean Association
Virginia Agricultural Experiment Station
Virginia Cooperative Extension

Join us to see the latest research on soybean varieties, disease and weed management, IPM and sorghum varieties. Experts will also demonstrate no-till drill maintenance and update you on the mid-Atlantic double crop initiative. Registration begins at 8:00 am and field tours begin at 8:50 am. The program will end at noon with a delicious meal by Nixon Catering.

Topics include:
– Soybean Disease Management – Dr. Hillary Mehl
– Soybean Weed Management – Dr. Mike Flessner
– Soybean Insect IPM – Mr. Mike Parish and Drs. Sean Malone and Ames Herbert
– No-Till Drill Maintenance – Mr. Keith Burgess
– Grain Sorghum Management – Dr. Joseph Oakes
– Roundup-Ready Public Soybean Varieties – Dr. Bo Zhang
– Mid-Atlantic Double-Crop Soybean Initiative – Dr. David Holshouser

We hope to see you there!