2012 Area Soybean Conferences: December 11-13

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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

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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.

Drought Induced Shatter

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The drought of 2012 continues to introduce new issues even as we progress into R7 (beginning maturity) soybean.  Reports out of SW WI and verified at our Lancaster research site show drought induced shattering localized in the upper pods (Images 1 and 2 below). This issue is mainly occurring in the early maturity group soybeans and is being noted in other states. I have two running hypothesis for this phenomenon. The first hypothesis that Emerson Nafziger (University of IL), Seth Naeve (University of MN) and I agree on is (and I will quote Dr. Nafziger)…

“Preharvest shatter is an issue here with early-maturing beans – the ones that were already at R7 before it rained a lot the first days of September. Those would not have added any more weight to speak of, but they might have swelled with the rain. Dew has been heavy the last week or so as well, and rewetting and drying has occurred on a daily cycle. We’ve seen before that drought conditions during pod development simply result in weak pod sutures, and when pods (and beans, maybe) rewet after they’ve dried, they simply open more easily.”

My second hypothesis is that this is a drought induced mechanism of survival or seed dispersal. This is less plausible given “that soybeans have had their natural tendency to shatter beaten out of them as much as possible by breeders“. However given the severity of the drought coupled with shatter timing (pre-R7) it may be a possibility.

Regardless of cause shatter can significantly impact yield especially if  it begins weeks prior to harvest ripe (Image 3). As a general rule of thumb a loss of 4 seeds per square foot equals one bushel per acre yield loss. I have yet to reach an average of 4 seeds per square foot in my research plots however if you are concerned and are questioning harvest timing to minimize shatter in your early maturity group soybeans please see Check Combine Settings to Minimize Soybean Harvest Loss.

 Image 1. Open pod with exposed seed.
 Image 2. Curled pods post shatter. 
 

 Image 3. Shattered seed on the ground.
 

Spider Mites: My Lessons Learned and Varietal Differences Noted

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Like many growers and crop consultants if I don’t see spider mites for another 24 years it will be too soon. As we transition into physiological maturity and put this season behind us it is always a good idea to reflect back on what we have experienced and learned so a documented record is present for the next time these infrequent events occur. So here is what I learned battling spider mites in 2012.

  1. There are product efficacy differences. I sprayed our Janesville, East Troy, Fond du Lac, and Arlington (twice) sites in 2012 for spider mites. All of the locations were sprayed with Dimethoate except Fond du Lac which received bifenthrin. For the most part I was pleased with control at all locations. 
  2. I waited too long to spray. I am a strong proponent of IPM guidelines and follow them religiously with excellent success. My mistake was that I did not effectively scout the large border areas surrounding our Arlington research trials. This did not lead to any significant plot loss or impact my research but it did lead to a continuous re-supply of spider mites due to egg numbers that I had to manage.
  3. Rain did not help. Rain did knock down populations for a couple days but they quickly rebounded and required chemical control.
  4. Varietal differences are evident. Plot to plot variability was noted at our Janesville and Fond du Lac sites so we took plot notes to quantify (0-10, where 0 = no plot damage and 10 = 100 of plot injured. this variability. Analysis of the data indicated significant varietal differences (0 to 8 at Janesville and 0 to 3 at Fond du Lac). It is unclear whether these differences where due to initial selection, preferential feeding, or increased fecundity (more eggs) but they were real. Given the infrequency of spider mites for Midwest growers I would not select varieties based on this criteria, but it may help explain infestation or control variability for 2012.

Even in a Drought Late Season Soybean Diseases Can Still Show Up

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The 2012 growing season has been one of great variability in terms of the weather and its impact on soybean diseases. Early stand issues were mainly caused by crusted soils due to driving rains or shallow planting into dry soil. Very few soybean disease related questions have been expressed……until now. Last Friday (8/3/12) I walked a field near the Arlington Ag Research Station. It was expressing classic Phytophthora root and stem rot (PRR) symptomology. Yesterday I also received similar questions out of the LaCrosse area. As you examine the symptomatic plants it is important that you differentiate PRR from stem canker as they can easily be confused.

Yesterday I also saw the first report of sudden death syndrome (SDS) from @FS_Mark. Weather conditions will likely limit the severity of SDS statewide however this pathogen was confirmed north of Eau Claire in 2010 so vigilance in those areas that have  received rainfall is important.  As always  make sure that the disease identification is correct for SDS, since foliar symptoms are similar to brown stem rot (BSR). In particular, make sure to examine the whole plant, including stems (looking for internal browning due to BSR) and roots (looking for a root rot and also a bluish hue that is the fungus of SDS). Do not just rely on the foliar symptoms to verify your diagnosis of either disease.

Lastly, in spite of the heat during flowering across the state, we will still see white mold somewhere in the state. This is not necessarily a surprise as we do find the disease each growing season. Based on our current observations and reports though, it appears that the disease intensity will be low, although variation to the soybean variety is be evident.

WI Soybean Yield Contest Entry Deadline Extended to 8/31/12

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Drought conditions across Southern WI had dampened grower enthusiasm to enter the WI Soybean Yield Contest. Recent rainfalls, promising forecasts and rapid soybean recovery has again piqued grower interest. To facilitate this interest we are extending the entry due date to August 31st to enter the contest.  Below please find links for entry forms and rules. Good Luck!!!

Getting Additional Forage This Fall

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Dan Undersander and Shawn Conley
Some farmers need additional forage and want to plant a second crop following wheat or corn taken early for silage due to drought.  As of July 15, the best option is to wait until after August 1, and then consider planting oats with or without peas.
While corn may yield as well as any other crop, it is more expensive to plant and will need a frost to dry down the forage sufficiently for ensiling.  Sorghum-sudangrass, sudangrass and millet require 80 degree or higher temperatures for significant growth.  Hot as it may seem now, those temperatures are not likely to occur on a daily basis after Sept 1.  So little fall growth will occur and yield will be low.
Oats, planted the first week of August can be expected to produce 2.5 to 3 t/a dry matter in an average year.  Other small grains will generally produce about half as much since they do not put out a stem.  Adding 20 lb/a peas to the oats will increase palatability but will not affect yield. 
Coblentz, USDA Dairy Forage Research Center, found that a late-maturing forage cultivar (ForagePlus) produced maximum annual yields ranging from 2 to 3.5 t DM/a.  Because the forage cultivar matured slowly it was better able to respond to sometimes erratic late-summer precipitation. These types mature later and produce more tonnage of quality forage.  If seed of a forage type is not available, plant a late maturing oat variety.  After the first week of August use of a forage type oat will provide less advantage and grain-type cultivars often may be better management choices.
The fall planted oat is higher in forage quality than spring planted oats.  Research at the University of Wisconsin by Albrecht found that maturation of summer-sown (August) oats was delayed, resulting in 10 to 15% less neutral detergent fiber (NDF), 18% greater digestibility, and 250% more water soluble carbohydrate than spring-sown oat.
The recommendation would be to plant 1.5 to 2 bu oats/acre (with or without peas).  Soil test to determine if sufficient residual nitrogen remains for the oat crop following the drought-reduced corn crop.  If not, fertilize with 60 to 70 lb nitrogen per acre at planting.  It is also important to check for any herbicide plant back restrictions prior to planting the oat or oat/pea mixture.  Planting should occur during the first week of August as earlier planting will result in earlier maturation and reduced yield. Selection of a forage-type cultivar likely will result in superior yield and nutritive value for planting dates as late as the first week of August.
Figure 1. Concentrations of total digestible nutrients (TDN) from oat forages planted on August 1 and harvested on five dates throughout the fall at Marshfield, WI (Coblentz et al., 2012).

Deadline Approaching for Entering the 2012 Wisconsin Soybean Association Yield Contest

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Drought conditions in the Southern part of WI coupled with record high temperatures statewide has dampened the excitement of last year’s yield contest where Joe Zenz from Lancaster topped the 2011 Non-Irrigated WI Soybean Yield contest at 92.8 bu a-1planting Asgrow 2403. Jason Weigel from S+W Farms LLC, Platteville placed second at 89.7 bu a-1 with Dairyland DSR-2770/RR and last year’s winner Rick Devoe from RnK Devoe Farms, Monroe placed third at 87.4 bu per a-1with Pioneer 92Y51.  
If we do get into a rainfall pattern there is still significant yield to be gained so as a friendly reminder:
  • The deadline to enter the 2012 WI Soybean Yield Contest is 8/1/12. 
  • The objective of this contest is to encourage the development of new and innovative management practices and to show the importance of using sound cultural practices in WI soybean production. 
  • The two major changes to the 2012 contest are that irrigated and dry-land entries are combined and two winners will be selected from each of four geographical districts in the state. 
  • Districts are based on long term county soybean yield averages (Image 1 below). 
  • For more information please see the contest brochure or review contest rules. Entry forms will be posted shortly on www.coolbean.info.

For more information related to this contest please contact Shawn Conley at spconley@wisc.edu.

Preliminary Wheat Yield Results – Janesville, WI

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Preliminary winter wheat yields at our Janesville, WI variety trial site have been averaging 85 bu per acre. Test weights have all been above 60 pounds with moisture ranges of 12 to 13%. The highest plot yield noted so far has been 108 bu per acre.

Late-Season Weed Escapes in Wisconsin Corn and Soybean Fields

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The potential increase of glyphosate-resistant weeds is a major threat to corn and soybean production across the Nation.  Integrated Weed Management tactics, including diversified herbicide use, are important components of management to delay the onset of glyphosate resistance.  Identifying geographies that may be most vulnerable to resistance development could help direct attention and pro-active resistance management tactics before wide-scale control failures occur.  To help with this, the University of Wisconsin-Madison Field Crops Weed Science Extension program is asking for your participation in a research study investigating the weed species diversity in Wisconsin Corn and Soybean fields due to reduced atrazine use and subsequent increased use of glyphosate. The purpose of this research is to identify areas in the state where there may be a shift to weeds that are more difficult to control with glyphosate, or where weeds that are resistant to glyphosate may first appear. 
This survey asks questions about target weed species and limited management history information relating to crop production fields. There are two levels of participation in this survey.  The first level simply includes filling out an on-line survey with information from ONLY ONE CROP PRODUCTION FIELD per survey form.  If you are willing to provide information about more than one field, please repeat the survey.  The second level of participation, if you would please participate further, is to allow weed science research staff from the University of Wisconsin-Madison to survey your crop fields for weed escapes in late-summer months. 
We expect the survey to take only 5 to 10 minutes of your time, and we don’t anticipate any risks to you.  For fields we scout for weed escapes in the late summer, we will provide a detailed weed scouting report to participants.
You may ask questions about the research at any time by contacting Vince M. Davis at vmdavis@wisc.edu (608) 262-1392 or Ross Recker at rrecker@wisc.edu.  Your participation is completely voluntary.  By completing and electronically submitting this survey, you consent for participating in the first stage of the survey. If you would like to participate in the second stage, and allow UW weed science researcher to scout your production fields, please complete the last question of the survey by providing your contact information.
To complete the survey, please visit: http://www.zoomerang.com/Survey/WEB22FSESTMEKJ
We THANK YOU in advance!  
Vince M. Davis, Extension Weed Scientist and Ross Recker, Graduate Research Assistant