C.O.R.N. Newsletter 2011-40

Dates Covered: 
November 23, 2011 - December 5, 2011
Editor: 
David Dugan
Season Wrap Up on Soybean Diseases, Part I

Season Wrap Up on Soybean Diseases, Part I

I think this has been one of the most challenging years on record for getting this crop in the ground and getting it harvested and now we are trying to make sense of all the research data.  In the meantime, let’s recap some things that actually did not happen and some that did.

a. Soybean Rust.

Really have not had to say much about this pathogen this year.  Inoculum levels were very, very low in the spring thanks to a very hard winter last year in the southern US.  It was hot and dry early and it took a long time for this disease to get started.  My colleagues in the south who search for soybean rust, were talking about the Mississippi river spilling over its banks into fields that were totally suffering from drought. 

More evidence of a very strange year.  As it ended up, soybean rust was only found in three states, Florida, Louisiana, and Georgia, very late in the season.  The Georgia findings are quite interesting as rust skipped the whole middle of the state, and was found in a northern county – most likely due to the spore movement of an earlier hurricane.  Monitoring for this will begin again in the southern states in March and April to assess, how much will survive the winter. 

b. Those plants with strange looking pods. 

Several samples came in this year with plants that had crinkled leaves, and pods that were turned up.  All of these, to date, came back positive for bean pod mottle virus based on tissue assays with ELISA.  ELISA is a lab test that uses antibodies to match the specific virus.  We first identified this virus in Ohio in 1999.  Severe infections can have leaf malformations (figure 1), reduced plant height, reduced yield, but also some streaking of the hilum.  This streaking of the hilum impacts food grade beans more severely as they are docked or no longer suitable. 

This virus is spread most commonly by leaf feeding insects, specifically the Bean leaf beetle, which was quite common this year in some parts of the state.  If a beetle is carrying the virus, once it feeds on a plant, that plant becomes infected.  We have inoculated plants at 3 different growth stages and all became infected to some degree.  A very simple, yet effective, management strategy is to plant food grade soybean after those that will be used for grain.  The overwintering adults will feed on the soybean for grain, and will either be finished with their cycle by the time the food grade beans emerge.

There is some discussion in the north central region if BPMV is the sole cause of the “green stem syndrome”.  This is where totally green plants are scattered throughout the field and never mature.  There are physiological issues with soybean plants, if a plant never forms pods then it will also not mature and stay green.  There are most likely several other causes that can contribute to this phenomenon, and we would expect that they would be different in the different parts of the soybean belt

Moldy Corn and Upright Ears

As corn harvest nears completion across the state, moldy ear problems have been reported in NW Ohio especially in certain corn hybrids planted late after June 1. The moldy ears have been attributed to Diplodia and Gibberella fungal infection (Figure 1). Vomitoxins (associated with Gibberalla) have been found in some of the later planted, wetter corn (>25%). The few preliminary reports received to date suggest that vomitoxin levels are lower and vomitoxin problems far more limited in scope than in 2009. This is largely because, compared to 2009, conditions this year were relatively dry during the first few weeks after pollination, which restricted the development of Gibberella ear rot. Although some level of infection may have occurred at silking, conditions during early grain-fill were in general not favorable for widespread ear rot development and mycotoxin contamination, except in some of the later planted fields. As was the case in 2009, molds have often been associated with upright ears (Figure 2). Ears that remain erect after physiological maturity (black layer development) are more likely to have ear molds because they trap water, especially at the base of the ear. These ears may also be affected by opportunistic saprophytic organisms taking advantage of the moist, nutritious environment at the base of the ear. These saprophytes are usually not associated with vomitoxin production, so not all moldy ears will be contaminated. It is important to first identify the ear mold you are dealing with in order to determine whether you will have a problem with mycotoxins.   

There are several factors that determine whether a corn ear remains erect or “droops” (points downward) following physiological maturity. Ears of corn normally remain erect until sometime after physiological maturity has occurred (black layer development), after which the ear shanks eventually collapse and the ears droop (Nielsen, 2011). However ears may droop in drought-stressed fields that have not yet reached physiological maturity.  A loss of turgidity in the ear shank due to water stress, possibly combined with some cannibalization of carbohydrates in the ear shank may eventually cause the ear shank to collapses, resulting in ear drooping. In certain hybrids, ears remain upright following physiological maturity (or remain erect for a longer duration) which can be related to a shorter ear shank.  According to some seed company agronomists, prior to the development of Bt hybrids, corn breeders tried to reduce ear drop due to European corn borer damage by shortening ear shanks. Much of that germplasm has continued to be used in more recent hybrids. These agronomists acknowledge the concerns that upright ears are slower to dry or more prone to ear molds and indicate that companies are looking for more droopy shanks to help protect ears from water damage. However they contend that there are other genetic components to these traits and that the effects of upright ears on fungal infections may not be as pronounced as is widely thought.

In addition to genetic differences among hybrids, environmental conditions and cultural practices may affect ear orientation during the drydown period prior to harvest. In a 2010 OSU field study that compared 16 hybrids varying in maturity from 101 to 118 days relative maturity at two locations, differential responses to plant population for % ear erectness (at maturity) were observed. At S. Charleston, growing conditions were favorable and yields averaged 235 bu/A. At Hoytville, yields averaged 134 bu/A due to drought stress.  At S. Charleston, % erect ears decreased as plant population increased - 93%, 74% and 49% at 18,000, 30,000, and 43,000 plants/A, respectively.  At Hoytville, % erect ears remain basically unchanged with increase in plant populations (ranging from 88% to 86%). These results suggest that factors other than hybrid genetics can determine if an ear is in an erect or droopy position at harvest.

Reference:

Nielsen, R.L. 2011 Are Your Ears (of corn) Sagging? Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/Droopy.html

Moldy Corn

Figure 1. Moldy ears from a 2011 NW Ohio corn field that was associated which tested positive of vomitoxins (Source: Glen Arnold, OSU Extension)

 

Droopy Ears

Figure 2.  Droopy and erect ears in OSU Defiance County 2011 test plot. Only 15% of the ears were erect at harvest but nearly all were moldy whereas no mold was visible in the droopy ears (Source: Bruce Clevenger, OSU Extension)

Soil Test Phosphorus Variability in .33 Acre Grids

Soil sampling is an essential practice to maximizing yields and economic returns while protecting the environment in grain crop production systems. To that end, Grid Soil Sampling (GSS) has been widely utilized by many of Ohio farmers with the purpose of gathering soil test information on small areas of a field to facilitate better nutrient management.  Soil samples taken are geo-referenced thus permitting varying amounts of fertilizer or lime to be applied per soil test result in designated smaller areas as opposed to blanket applications across a field.  Further by overlaying soil test results, yield maps, soil type maps and topographic maps, better associations of the factors influencing yield (and profit) can be made along with the appropriate management actions.  

Traditional agricultural crop soil test results (2.5 acre grids or field samples of 10 acres in size or larger) are often quite variable.  To examine soil test variability over smaller field areas; 0.33 acre square grids were geo-referenced and soil tests taken from the same spot for 5 years in north central Ohio.  An analysis of 6 randomly selected 0.33 acre grids from a total of 15 grids was conducted to examine the stability of soil test P over time, fertilizer applications and crop removal.  The soil tests were taken in November of each year. There were not any crops grown in year one of initial soil testing.

Soil P Variability (ppm)

Randomly Selected Grids

Year

Grid 1

Grid 2

Grid 3

Grid 4

Grid 5

Grid 6

Average

5

34

24

21

33

34

23

28

4

48

38

40

31

57

32

41

3

40

36

39

37

36

44

39

2

39

33

33

24

26

24

30

1

10

16

26

19

15

13

17

Phosphorus removed per unit of yield  over the time period (180 bu/A corn 2 crop years; 48 bu/A soybean for one crop year, and  one crop year of 93 bu/A wheat ), was calculated at 230 lbs/acre P2O5.  The total amount of fertilizer applied in the four year period was 309 lbs P2O5.  Thus, P soil test levels would be expected to go up and that occurred in 5 out of the 6 randomly selected grids from year 1 soil test values to year 5 soil test result.  Average soil test level P over the 6 grids went from 17 to 28 ppm P.  

If the following relationship were to be used to measure soil test P buildup (soil test P increase by 1 ppm for every 20 pounds P2O5/ applied over crop removal); the expected soil test P increase would be 4 ppm (309-230/20). The increase in P (11 ppm) is not totally explained by the fertilizer applied, crop removal budget or relationship used to calculate the increase in soil test P.  However, research done in Kentucky by Thom and Dollarhide in 2002 found initial soil test P to be a major factor influencing how much P2O5 is needed to increase soil test P level.  Thus, many factors such as: soil type, initial soil test level, soil pH, soil test method, type of phosphorus applied, weather, time of year of the soil testing, soil test location, soil test P laboratory calibration, etc. may have impact on the final soil test P result.  In conclusion, even though variability in soil test P can be expected, soil testing is an essential practice to estimating plant available P needed to  protect and preserve crop yields, manage fertilizer applications, and  protect the environment.

Cost of Ruts in Your Fields

What impact does a fall harvest that requires tracking of your fields as you combine cost? You can look at costs of tillage to smooth out ruts and lost production due to compaction. We might assume an extra pass of disk/chiseling at $15/A (see http://www.extension.iastate.edu/agdm/crops/pdf/a3-10.pdf). So if 25% of a field were rutted and production in those areas reduced by 10%; that would mean a 2.5% yield loss. At 200 bu/A and corn at $6/bu that would be $30 lost/A.

So perhaps $50 cost per acre for rutting is not unrealistic.

CCA of the Year Nominations Due

Certified Crop Advisers are the folks who make seed, pest and fertilizer recommendations; they work at the co-op, the ag retailer, the seed supplier, the fertilizer dealer, as the independent crop advisor, or at the OSU Extension office. The Ohio CCA Board is looking for the best CCA in Ohio for 2011, if she or he works with you or for you, then please nominate them.

The Ohio Certified Crop Adviser (CCA) Program is sponsoring a state award titled “Ohio Certified Crop Adviser of the Year“. The award program is designed to recognize an individual who is highly motivated and delivers exceptional customer service to their farmer clients.

The Ohio Certified Crop Adviser of the Year Award will be presented at the 2012 Conservation Tillage Conference on March 6th in Ada, Ohio.  The state award includes a plaque, recognition in industry publications, and a cash award from the agronomic supply industry.

Nomination forms due December 1st  to Ohio CCA Board c/o Ohio AgriBusiness Association, 5151 Reed Rd. Suite 200-A, Columbus, Ohio 43220-2598, Email: Info@OABA.net.

The nomination form is available on the AgCrops website: http://go.osu.edu/CCAofYear. Nominate your CCA by December 1st.

OSU Performance Trials – Corn & Soybean

With the late harvest we are all having, performance trial harvest and data analysis is running late this year. But the 2011 Corn Performance Trials are posted and the Soybean Trials are posted as of Tuesday November 29th.

See the Ohio State Corn Performance Trials: http://www.oardc.ohio-state.edu/corntrials/

And the Soybean Trials are at the links on the Soybean page of the Agronomic Crops website: https://agcrops.osu.edu/specialists/soybean.

 

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.