Finalists for the 2012 WI Soybean Yield Contest are Announced

The 2012 growing season proved to be a challenge for many growers and a bin buster for others.  Given these widespread challenges we again experienced great interest in the 2012 WSA/WSMB Soybean Yield Contest.  The top two entries in each division (in no particular order) were:

Division 4: 

• Kevin and Dale Bahr, Belmont (planted Trelay 24RR19)
• Nick Viney, Edgerton (planted FS HS24A01)

Division 3:

• Josh Trautman, Edgerton (planted FS HS24A01)
• Rick Devoe, Monroe (planted Pioneer 93Y43)  
• *WI Bean Team (Adam Gaspar, David Marbuger, Scott Rowntree) Madison (planted Pioneer 92Y51) 

*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:

• Jerry Koser, Almena (planted Pioneer 91M10) 
• Jim Kroeplien, Sheboygan Falls (planted NK S21-N6) 

Division 1: 

• Steven Kloos, Stratford (planted Pioneer 91Y30) 
• Paul Graf, Sturgeon Bay (planted Asgrow AG1031) 

The final ranking and awards will be presented at the 2013 Corn Soy Expo to be held at the Kalahari Convention Center, Wisconsin Dells on Thursday January 31st 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

Drought Impact on Soil Rhizobia Populations

Severe drought conditions limited soybean production (6.2% per acre yield decline from 2011) across much of the United States in 2012. Though 2012 will soon be behind us, the implications of the 2012 drought may progress well into the 2013 growing season (Image 1). One area of concern among growers is the impact of the drought on soil microbial populations; most importantly Bradyrhizobium japonicum. Soybean live in a symbiotic (mutually beneficial) relationship with B. japonicum. The soybean plant provides nutrients and a protective growing environment for the rhizobia. In turn, the rhizobia “fix” atmospheric nitrogen into ammonia (NH3), which can then be used by the soybean plant. For this relationship to exist and benefit the soybean plant, effective nitrogen-fixing bacteria must be present in the soil in relatively high numbers at planting time (Conley and Christmas, 2005).

Image 1. U.S. Drought Monitor Map for December 11, 2012.

To date, little research has been published that quantifies the impact of soil desiccation (e.g. drought) on endemic B. japonicum populations. Pena-Cabriales and Alexander (1979) reported a biphasic decline in Rhizobium japonicum numbers in soils undergoing drying. The initial rapid phase of R. japonicum loss coincided with major water loss (simulated drought) whereas the secondary and subsequently slower decline in numbers was governed by the soil water content of specific soils. Pena-Cabriales and Alexander (1979) also noted that organic matter content provided little protection against R. japonicum desiccation and loss. In a parallel study Oso-Afiana and Alexander (1982) reported similar results when comparing strains of R. japonicum and cowpea rhizobia under desiccation. As one would expect, variation exists among Rhizobium spp. as well as individual isolates within species in their response to soil desiccation, though significant losses were evident regardless of species or isolate (Foulds, 1971; Trotman and Weaver, 1995).

To further complicate the situation, most soybean acres will be planted into corn ground that was subjected to severe drought stress. This suggests that excess nitrogen may be present for the 2013 soybean crop. In excess situations soybean will generally utilize the background nitrogen prior to initiating maximum N fixation. This may lead to luxurious early season growth, which in fields with a history of white mold, may cause problems if weather conditions are conducive. High soil N reserves may also lead to increased lodging. In either case, manage your soybean crop accordingly to minimize risk of white mold or lodging. This can be accomplished through variety selection (e.g. white mold tolerance, short statured soybean cultivars or good lodging tolerance), decreasing seeding rates, and proper scouting to time fungicide applications if needed.    

I am not advocating that every soybean acre automatically receive an inoculant treatment, however, the small amount of research that is available on the topic does suggest that growers may expect lowered B. japonicum populations going into the 2013 growing season.   

Literature Cited.

Conley, S. P. and Christmas, E. P. 2005. Utilizing Inoculants in a Corn-Soybean Rotation. Purdue Extension, SPS-100-W. 4 p.

Foulds, W. 1971. Effect of drought on three species of rhizobium. Plant and Soil 35:665-667.

Furseth, B. J., Conley, S. P., and Ané, J.. 2010. Enumeration of Soybean-Associated Rhizobia with Quantitative Real Time Polymerase Chain Reaction. Crop Sci. 50: 2591-2596.

Osa-Afiana, L. O. and M. Alexander. 1982. Clays anmd the survival of rhizobium in soils during dessication. Soil. Sci. Soc. Am J. 46: 285-288.

Pena-Cabriales, J.J. and M. Alexander. 1979. Soil. Sci. Soc. Am J. 43:962-966.

Trotman, A.P. and R. W. Weaver. 1995. Tolerance of clover rhizobia to heat and desiccation stresses in soil. Soil. Sci. Soc. Am J. 59:466-470.

2012 Area Soybean Conferences: December 11-13

First Announcement: The Wisconsin Soybean Association, Soybean Marketing Board, and Cooperative Extension are hosting the 2012 WI Area Soybean Conferences. They will be held on December 11-13 in Holmen, Ripon, and Janesville, WI. Topical areas include:

• The 2012 Drought Impact on the 2013 Soybean Crop
• Assessing Soybean ROI. Where Should I Spend my Money for 2013
• New Soil Fertility Recommendations for Soybean
• Do Soybean Leaf Tissue Tests Tell you the Real Story
• The National Soybean Sustainability Initiative and Why You Should Care
• Soybean Disease Considerations for 2013
• Marketing Tips for 2013
• New products
• Membership

 Registration information will be available November 1st.

A review of glyphosate use for preharvest weed control

From Vince M. Davis – Extension Weed Scientist

Late-season weed escapes are very prevalent in corn and soybean fields this year. Poor residual herbicide activation and poor postemergence herbicide efficacy is part of the reason. Additionally, and perhaps more importantly, poor crop canopy development and late-season rainfall encouraged large weed flushes much later this year. In some cases, weed densities are quite high and a preharvest herbicide application may help limit seed production of some annual weed species and improve the efficiency of harvest operations. This will be particularly true where thick grassy weeds or lots of large broadleaf weeds like giant ragweed, common lambsquarters, and velvetleaf are in soybean fields.

We’ve already received a couple questions regarding preharvest applications of glyphosate in soybean. First, there are a couple other herbicides besides glyphosate, like paraquat and carfentrazone, which could also be used in this manner. Paraquat (Gramoxone Inteon) and carfentrazone  (Aim) are both contact herbicides. The advantages of these products versus glyphosate will be faster desiccation of weeds. However, proper nozzle selection to deliver appropriate droplet sizes and higher carrier volumes will be very important. Additionally, carfentrazone has a much narrower weed spectrum than glyphosate or paraquat. For more details regarding the preharvest use of carfentrazone or gramoxone products, please read and follow the directions accordingly. However, we get many more questions about how to use glyphosate as a preharvest aid so I will try to elaborate a little further.

There are too many glyphosate formulations for me to know them all, so the most important message is to read and follow the herbicide label for the specific product you are using. But, I’ll give you some ‘cliff notes’ that are important to know. Unlike paraquat and carfentrazone mentioned above, glyphosate is a systemic herbicide. A systemic herbicide translocates to the growing point once it is inside the plant. This movement typically happens with the phloem of the plant (i.e. with the ‘food’ for the plant), and we call this movement ‘source to sink’. In many ways, this movement is an advantage over contact herbicides because it is the new growth of the plant you most want to terminate. I went through that very brief lesson on herbicide action to make a very important point when it comes to using glyphosate as a preharvest aid, and that is; appropriate timing is very important.

Preharvest applications can be made in corn, but I know it is more common in soybean so I will focus on that crop. It is illegal to spray glyphosate after full bloom (R2) until soybean pods have lost all their green color. Why, because between R2 and R8 the soybean plant is developing seed. As the seeds develop, they are a ‘sink’.  Technically, the R8 growth stage is the final growth stage call ‘full maturity’.  Full maturity is defined as 95% of the pods having lost green color and is usually 5 to 10 days before the field is ready to harvest. However, the glyphosate label reads (as I’ve already stated) that preharvest applications should be made after ALL pods have lost green color. Also note, you should not make preharvest applications to beans used for seed because a reduction in germination or vigor may occur.  Applications made too early in pod maturity run greater risk of glyphosate being translocated into the seed tissue resulting in illegal residues in the seed.

On the flip side, there is a required preharvest interval for grain of 14 days between a glyphosate application and harvest of glyphosate-resistant (Roundup Ready and Roundup Ready 2 Yield) soybean.  Moreover, because glyphosate often takes some time to ‘work’ it may take near those 14 days before complete activity will be achieved.  So, in order to have time for the weeds to desiccate to the maximize amount, and to avoid excessive shattering from delayed harvest, it is imperative to scout fields closely in the final days of maturity to time the application correctly. This will be an even greater challenge in fields that reach maturity very un-uniformly this year due to the variable field moisture conditions.

Now for some good news, because of the translocation effect of glyphosate is from source to sink, in annual weed species that are setting seed glyphosate may help to significantly reduce the number of viable seeds following the preharvest application, versus no application at all. At this point in the season the application can’t reduce biomass, or save the production of yield, but could limit the size of future weed problems. Moreover, a glyphosate application will have much greater efficacy on any biennial and perennial weed species like thistles, quackgrass and common dandelion because their active ‘sink’ in the fall is the root system. So, a preharvest application will also reduce populations of those weeds more than an application of a contact herbicide.

How much glyphosate and adjuvant to use at a preharvest application? Rates and surfactants should be added according to the label for each specific glyphosate product. In the case of Roundup PowerMax, no additional surfactant is needed. The rate for a preharvest application on Roundup Ready and Roundup Ready 2 Yield soybean is 22 fluid oz/a.

Maximum Application Rates of Roundup PowerMAX on glyphosate-resistant soybean
Combined total per year for all applications	5.3 quarts per acre
Total of all Preplant, At-Planting, Preemergence applications	3.3 quarts per acre
Total of all in-crop applications from cracking through flowering (R2 state soybeans)	64 fluid ounces per acre
Maximum preharvest application rate	22 fluid ounces per acre

Hopefully this helps with making properly timed and legal preharvest glyphosate applications where deemed beneficial.