WI Soybean Crop Starting to Bloom

Across many areas of Wisconsin the soybean crop is just starting to bloom. As we enter the soybean reproductive growth phase there are a few things to keep in mind. The first is that soybean will produce flowers for ~3 to five weeks, depending upon planting date and environment. Soybean will abort anywhere from 20 to 80% of the flowers that they produce. Generally it is the first and last flush of flowers produced that are most likely to be aborted.

Second of all the timing window for our glyphosate applications in soybean are quickly closing. Chris Boerboom, Former UW Extension Weed Scientist stated that:

"Monsanto has clarified the definition of “throughout flowering” in regard to the latest stage that glyphosate can be applied to glyphosate-resistant soybean. Soybean flowering is defined as the R2 growth stage. The R3 growth stage begins when one of the four top nodes with a fully developed leaf has a 3/16 inch long pod. With this definition, glyphosate can be applied through the R2 growth stage, but not after the R3 stage begins. Applications made after the R3 stage are off-label applications."

On average it takes ~ 4 days to move from R1 (beginning flower) to R2 (full flower) and ~10 days from R2 to the start of R3 (beginning pod). That means we have ~2 weeks for glyphosate applications to occur.

Next, wheel track damage made from ground applications may start to reduce yield. Sprayer wheel traffic from first flower (R1) through harvest can damage soybean plants and reduce yield (Hanna et al. 2008). Our research suggests that an adequate soybean stand (more than 100,000 plants per acre) planted in late April though mid-May can compensate for wheel tracks made when a field is sprayed at R1. Yield loss can occur, however, when wheel tracks are made at R1 or later in thin soybean stands (less than 100,000 plants per acre) or late planted soybeans. Regardless of stand, plants could not compensate for wheel tracks made at R3 (early pod development) or R5 (early seed development). The average yield loss per acre is based on sprayer boom width (distance between wheel track passes). In our trials yield losses averaged 2.5, 1.9, and 1.3% when sprayer boom widths measured 60, 90, and 120 foot, respectively. Multiple trips along the same wheel tracks did not increase yield loss over the first trip.

Lastly, for white mold questions please refer to the following information: White Mold in Soybean in 2010: Factors to Consider

Image 1. Soybean crop beginning to bloom.

Risk Factors Associated with White Mold in Soybean

With the soybean crop moving closer (or in some cases at) flowering, now is an excellent time to review factors that may impact the risk of white mold in 2010 (caused by Sclerotinia sclerotiorum). The first two factors that should be considered have already occurred...knowledge of the field history of the disease and the level of resistance in the soybean variety that was planted. These can be used to provide a baseline assessment of risk. If you are unsure of the level of resistance in your soybean variety, I would recommend consulting with your seeds person to obtain that information. In addition, there are several abiotic and biotic factors that need to be considered to understand if there is an increased risk of white mold. If temperatures are in the moderate range (70's are optimal), rainfall is normal to above normal, soil moisture is at or above field capacity, and there are extended periods of prolonged fog and leaf wetness at or just after flowering, these can increase the risk of white mold in the field. Also, agronomic practices that are used to promote high yield potential in soybean (in particular those practices that encourage early canopy closure) like early planting date, higher plant populations, and narrow row spacing can also increase of the risk of this disease.

Active scouting should commence as we move into flowering for presence of apothecia, which are tan, cup-shaped mushrooms (0.5-2mm in diameter) that can be found on the soil surface (Figure 1). Apothecia produce the spores of S. sclerotiorum that infect soybean plants. Previous research has shown that apothecia production is related to soil moisture and temperature, and the timing and density of the crop canopy closure.


Figure 1. Apothecia of Sclerotinia sclerotiorum. These small (0.5-2 mm in diameter), tan fruiting structures produce spores that can infect senescing soybean flowers. Parting the soybean canopy and inspecting the soil for apothecia is an important way to determine your risk of white mold.

Management options include foliar fungicides (like Topsin M, Domark, and Endura) or herbicides (Cobra). Several questions have been raised about the efficacy of these products and in 2009 results variable when comparing Marshfield, WI and DeKalb, IL. Also, several questions have been raised regarding the use of other herbicides that cause similar changes to the soybean canopy like Cobra. Keep in mind that white mold suppression is listed on the Cobra label, while this is not indicated in other herbicides in the same chemical class. If the decision to spray a fungicide/herbicide is made, make sure that proper application timing occurs - applications should be made at flowering to protect senescing flowers from infection. Also, make sure that there is excellent spray coverage, which means that canopy penetration is essential to protect the developing soybean flowers.

For further information about white mold, please check Soyhealth and also UWEX YouTube.

White Mold Video Available on UWEX YouTube

As we move further into soybean development, we have started to receive an increase in questions about white mold (syn., Sclerotinia stem rot). During 2009, we made a video that is available on the UWEX YouTube webpage that discussed many of the factors we need to consider regarding the risk of white mold in soybean as well as scouting. We will provide further updates over the next few weeks regarding early risk and management for white mold.


Fig. 1. White mold in Iowa County in 2009.

Same Yellow Beans but different Culprit in 2010

2009 was known to many in WI as the "Year of the Yellow Bean". Growers are again experiencing yellow soybeans in 2010, but for a different reason (Image 1). We must first remember that in soybean, active N-fixtion does not begin until the V2-V3 (2 to 3 open trifoliates) growth stages. Even if you were to properly dig a soybean plant, identify and split a nodule, the red appearance does not necessarily mean that fixation has fully begun (Image 2).

Image 1. Field of yellow soybean.

Image 2. Soybean nodulation.

In 2009, dry soils were a contributing factor limiting nodulation and leading to early season low leaf N content. In 2010, our soils have been at or above field capacity for the last 10 days to 2 weeks (Figure 1). If soils are waterlogged depleted oxygen and increases carbon dioxide levels can lead to reduced root growth, shoot growth, nodulation, nitrogen fixation, photosynthesis, biomass accumulation, stomatal conductance, and plant death due to diseases and physiological stress (Oosterhuis et al., 1990; VanToai et al., 1994 and 2003). Given our growth stage and the fact that nodules are present I do not foresee any yield impact in the yellow soybeans. A few days of dry weather and warmer temperatures will quickly alleviate these symptoms.

Figure 1. Rainfall and soil water content at Arlington WI in 2010 (6/42010 to 6/16/2010)

Literature Cited:

Oosterhuis, D.M. H.D. Scott, R.E. Hampton and S.D. Wullschleger 1990. Physiological response of two soybean [Glycine max, (L.) Merr.] cultivars to short term flooding. Env. Exp. Bot. 30:85-92.

VanToai, T.T., J.E. Beuerlien, A.F. Schmithenner, and S.K. St. Martin, 1994. Genetic variability for flooding tolerance in soybeans. Crop Sci. 34:1112-1115.

VanToai, T.T., S. K. St. Martin, K. Chase, G. Boru, V. Schnipke, A. F. Schmitthenner,and K. G. Lark. (2001) Identification of a QTL associated with tolerance of soybean to soil water-logging. Crop Sci. 41,1247-1252.

VanToai, T. Y. Yang, P. Ling, G. Boru, M. Karica, V. Roberts, D. Hua, B. Bishop. (2003) Monitoring soybean tolerance to flooding stress by image processing technique. In T.T. VanToai, et al. (ed) Digital Imaging and Spectral Techniques: Applications to Precision Agriculture and Crop Physiology. ASA Special Publication No 66. The American Society of Agronomy. Madison, WI. Pp 43-51.

2010 WI Soybean Yield Contest Entry Deadline Approaching

Now that all of your soybeans have been planted and have emerged it is a great time to pick the field or fields you plan to enter into the 2010 WI Soybean Yield Contest.

Top prize for each contest class in $1,000.

For contest rules and entry forms please either visit www.coolbean.info or contact.

Shawn P. Conley
Soybean and Wheat Extension Specialist
Department of Agronomy
University of Wisconsin, Madison
1575 Linden Drive
Madison, WI 53706
Office: 608-262-7975
Cell: 608-279-6211

To enter the 2010 WI Soybean Yield Contest you must be a member of the Wisconsin Soybean Association. There is a $75 fee per entry.

The deadline to enter in July 15th, 2010.

Good luck and Coolbeans!!!!!

IPM Field Day - July 6

Please join us for the annual Pest Management Field Day on July 6 at the Arlington Agricultural Research Station. This will be an excellent opportunity to hear results from new and ongoing research projects and to network with researchers, extension staff as well as your own colleagues.

Speakers and topics are:

Joe Lauer, Agronomy, “A Wisconsin Transgene Walkabout”
Paul Esker, Plant Pathology, “Evaluations of Fungicide Treatments for White Mold in Soybean”
Dave Hogg, Entomology “Interactions Between Host Plant Resistance and Biological Control for Soybean aphid”
Camila Botero, Entomology, “Release of a Soybean Aphid Parasitoid”
Tim Trower, Agronomy, “Fall Dandelion Control”
Branden Furseth and Shawn Conley, Agronomy, “Evaluating 2010 Soybean Seed Treatment Decisions”
Marie Schmidt, Agronomy, “Germination Timing of Pasture Weeds”
Mark Renz, Agronomy, “Switchgrass Establishment: Year Two”

Field tours will depart from the Public Events Facility at 8:30 am and return by noon. In case of rain, “field tours” will be conducted inside. Lunch ($10) will be served after tours return.

The Public Events Facility is located on the Arlington Agricultural Research Station, N695 Hopkins Road. If traveling from the south, exit I 90/94 onto Hwy 51 North. Look for the Arlington Ag. Research Station sign north of Deforest. Turn left (west) onto Badger Lane. Travel 1 mile and turn left (south) onto Hopkins Rd. If traveling from the north, exit I 90/94 onto Hwy 60. Travel east through Arlington and turn south onto Hwy 51. For more detailed driving direction click on http://www.ars.wisc.edu/arlington/directions.html

Fusarium Head Blight Update - 9 June 2010

While most of the winter wheat crop is past flowering in many parts of the state, we are continuing to monitor the Fusarium head blight risk especially for later maturing wheat or spring wheat in the state. Today's risk map has shown a change in the risk of infection in pockets of state since we have seen heavier rainfall amounts the past week in many areas. There are several pockets that are in the medium to high risk of infection but it is important to pay close attention to the wheat growth stage regarding fungicide applications (see previous postings and also the Wisconsin Crop Manager for further information).

Summer 2010 Field Days Related to IPM and Fied Crop Diseases

During this summer, several field days have been proposed. At all of these field days, several topics will be covered across a range of topics, however, those related to diseases may include discussion of integrated strategies for managing corn, soybean, wheat, and alfalfa diseases. These field days are also subject to change and we will keep you up to date as the schedules develop for each field day.

July 6, Arlington, WI: Integrated Pest Management Field Day (Organizers: Bryan Jensen and Paul Esker)
July 7, Independence, WI: Western WI IPM Field Day (Local Host: Jon Zander)
July 8, Monroe County, WI (site TBD): Western WI IPM Field Day (Local Host: Bill Halfman)
July 27, Arlington, WI: DTC Troubleshooting Clinic (Organizer: Dan Heider)
August 17, Arlington, WI: DTC Crop and Pest Management Workshop (Organizer: Dan Heider)
August 25, Arlington, WI: UW Agronomy Field Day
August 31, Durand, WI: Late Season IPM Field Day (Local Host: Bob Cropp)
September 2, Mindoro, WI: Late Season IPM Field Day (Local Host; Steve Huntzicker)

For further information regarding these events, contact the local host listed or Paul: esker@wisc.edu.