C.O.R.N. Newsletter 2011-19

Dates Covered: 
June 20, 2011 - June 26, 2011
Editor: 
Jon Rausch

Wet Weather, Should You Be Concerned About Nitrogen Loss in Corn?

The wet weather continues and many may be concerned about the risk of nitrogen loss.  Some areas of the state have seen sizable rainfall amounts that can increase the risk of leaching or denitrification. There is no diagnostic tool that can give an absolute answer for N loss. However, a series of questions that were developed by the University of Minnesota does assist in determining whether N loss has occurred at levels that may affect yields. We have adapted this system to Ohio conditions with the following questions:

1) What N source was utilized?
1 point - Anhydrous ammonia with nitrification inhibitor
2 points - Anhydrous ammonia
3 points - Other fertilizer banded
4 points - Other fertilizer broadcast

2) When was the N applied?
2 points - After April 20
5 points - Before April 20

3) How much N has been applied?
1 point - >200 lbs/A
2 points - 150-200 lbs/A
3 points - 100-150 lbs/A
6 points - <100 lbs/A

4) What has been the predominant soil moisture status in the field this spring?
1 point - Normal
2 points - Wet
4 points - Excessively wet (saturated – standing water)

5) What is crop’s condition?
1 point - Green plants > 12” tall
2 points - Green plants < 12” tall
3 points - Chlorotic plants < 12” tall
5 points - Chlorotic plants > 12” tall

Total the score and use the following guidelines:
Less than 13 - Additional fertilizer not recommended
13-16 - Evaluate again in 4-7 days
17 or greater - Add an additional 40-70 lbs N/A

Some producers may consider the use of the presidedress soil nitrate test (PSNT) to determine if additional N fertilizer is warranted. To attain a representative soil sample, collect 15, 1-ft deep random cores from a field and mix them thoroughly. Submit a grab sample from the composite to a reputable lab (a list of labs is available at the following web address: https://agcrops.osu.edu/specialists/fertility/resources/of-interest/testlabs.pdf). You may want to contact the lab and find out the turn-around time (some may be able to complete analysis in a couple of days). If the nitrate level in the soil is between 25-30 ppm then additional N is probably not warranted. Nitrate levels lower than 25 ppm have an increased likelihood of response, but the rates should not be greater than 70 lbs N/A.

These tools are intended to serve as guides and not as definitive determination of N needs. The best tools available are your own experiences and tissue testing (although tissue testing will not give you any indication as to how much you should apply). Whether you use the PSNT or the Minnesota evaluation scale, research by the University of Illinois showed that application of only 50 lbs N/A often provided maximum yield over a wide variety of growing conditions after there was a concern of loss from earlier applications. Also remember, each field needs to be evaluated individually.

 

Look at those stands – seedling diseases may be an issue

Most of the stands look great across the state, but there are a few spots that appear to have some issues.  Poor stands can be caused by a number of different stresses including diseases, poor quality seed, insects, slugs, and Ohio’s famous hardened cement where the ground is sealed tight following a hard rain and hot days.  This piece will focus on the primary soybean seedling pathogens.  But first, for a correct diagnosis the samples should be examined under a microscope to look for signs of the pathogen.  If you have seedlings that are in the process of dying, we would be happy to look at them.  I have two new students that are quick learners and identifying these seedling pathogens will be a key helping me decide our next direction for management studies.  Pack the seedlings in a plastic bag, do not add paper towel and ship to my attention:  Dr. Anne Dorrance, Dept. of Plant Pathology, OARDC, 1680 Madison Ave., Wooster, OH  44691.  Label the bag with contact information, variety and seed treatment if known.  Samples should only come from Ohio, for other states, please send your samples to your state diagnostic lab.

Symptoms of many seedling diseases look the same.  But there are a few that can be distinguished.  Brick-red colored lesion on the base of the stem is indicative of Rhizoctonia.  This pathogen is controlled by resistance and primarily the fungicide Maxim.  Fuzzy, pink discoloration is indicative of Fusarium graminearum, the same fungus that causes head scab of wheat and Gibberella stalk rot of corn.  The watermolds, both Pythium and Phytophthora sojae, symptoms are the same.  The seedlings will appear light brown to dark brown, and soft.  For all of these diseases, the stand loss will occur in patches or a few seedlings here and there scattered across the field. 

The best management of seedling diseases is first to choose varieties that have resistance.  The second is to work on drainage.  For problem fields, improving soil drainage will go a long way to minimize stand losses in years like 2011 where it doesn’t seem to stop raining.  Seed treatments can also play a role in protecting seeds and seedlings, but they only protect under moderate saturation levels.  When soils are totally saturated for weeks, that is just too much to expect from the seed treatment.  Finally, long-term no-till fields may also see more seedling pathogens as the inoculum will build up in the top few inches of soil. 

Photos from left to right: Fusarium, Rhizoctonia and the last two are Pythium or Phytophthora (source: Anne Dorrance).

 Fusarium graminearumRhizoctoniaPythium or Phytophthora2Pythium or Phytophthora

June 20 Wheat Scab Update and Grain Harvesting TipsWheat Head Scab 2011

June 20 Wheat Scab Update and Grain Harvesting Tips

The first set of scab scores are in from 67 fields surveyed in southern, central, and parts of northern Ohio, with average incidence ranging from 1 to 45%. This means that the fields examined had between 1 and 45 heads out of every 100 heads with scab symptoms. Incidence was greater than 5% in 47 fields, greater than 10% in 33 fields, and greater than 25% in only four fields. Fungicide treated fields generally had lower levels of disease than untreated fields, and fields planted with moderately resistant varieties had lower levels of scab than those planted with susceptible varieties. However, there were a few treated fields with relatively high incidence and a few untreated fields with incidence below 5%. This is probably because some of the treated fields were sprayed too early, and some of the late, untreated fields flowered when conditions were less favorable for scab. Similarly, a few late-flowering, susceptible fields also had relatively low incidence. Fields in northern Ohio will be surveyed this week.

These numbers show that scab levels are generally lower this year than they were last year. However, for those fields with more than 10% incidence (more than 50% the fields surveyed so far), vomitoxin may still be a concern. Grain with vomitoxin levels above 2 ppm may be docked or may receive a price discount at elevators. To minimize these discounts or even prevent dockage, harvest grain from scabby fields separately from more healthy fields, and turn up the combine fan to blow out scabby, lightweight grain. Our research shows that when harvesting normal-sized grain from scabby fields, increasing fan speed reduces the amount of scabby grain and vomitoxin in the grain lot. However, this is not the most effective strategy when the overall size of the grain is small because of a short grain-fill period or poor grain-fill because of foliar diseases. When the grain is small, too high a fan speed may result in healthy grain being removed along with scabby grain, and as a result, less grain being harvested. 

Do Foliar Applications of Sugar Improve Soybean Yield?

Shawn Conley, Soybean and Wheat Extension Specialist, University of Wisconsin

 High commodity prices have led growers to consider many novel soybean inputs. One input that has garnered considerable attention is the foliar application of sugar products to increase soybean yield. The objective of this research was to evaluate soybean yield in response to various sources of foliar-applied sugar across four states in the Midwest. Field research studies were conducted at Arlington, Wisconsin; Urbana, Illinois; St. Paul, Minnesota; and West Lafayette, Indiana in 2010.The four sources of sugar evaluated in this study were:

1. granulated cane sugar

2. high fructose corn syrup

3. molasses

4. blackstrap molasses

All treatments were applied at the equivalent rate of 3 lb sugar acre and applied at 15 to 20 gal acre. The treatments consisted of an untreated check, all four sources of sugar applied at V4, granulated cane sugar and blackstrap molasses applied at R1, granulated cane sugar applied at V4 and R1, and blackstrap molasses applied at V4 and R1. No positive or negative (phytotoxic) effects were visually observed on the soybean foliage at any location within 10 days following foliar applications (data not shown). Furthermore, sugar did not increase soybean yield within location (data no shown) or across locations regardless of source. While this study cannot conclusively prove foliar applications of sugar will not increase soybean yield, the authors conclude that other management strategies to improve soybean yield should take precedence over applying sugar. A more complete version of this article can be found at:  http://ipcm.wisc.edu/LinkClick.aspx?fileticket=6T%2blZv%2fJSPc%3d&tabid=114&mid=669

 Source: University of Wisconsin Crop Manager, June 16, 2011, Volume 18 Number 14

Current postemergence herbicide situations

It may be a good year to see every possible weed control situation that can exist in corn and soybeans.   There is good news and bad news here.  First – the good news.  Due to the month or so delay in planting, POST applications will occur later in the window of weed emergence compared with a “normal” year.  As a result, weed populations should generally be lower, and there will be less likelihood of weeds emerging after POST applications.  The faster rate of crop growth will also result in more rapid canopy closure, at least where stands are good, which helps with weed control.  As a result, this is probably the year to err on the side of applying POST herbicides early, when weeds are small.  Early application can improve herbicide activity and possibly allow for lower herbicide rates or fewer herbicides in the mix.  This applies only to those fields that were weedfree at the time of planting of course.  Bottom line – there is a fairly low risk to applying POST herbicides early, and it could result in some cost savings. 

Applying early can also minimize the risk of crop injury from herbicides.  Corn has been advancing through growth stages rapidly, but does not necessarily have the typical amount of elongation between nodes, which means that it can be shorter than expected for a certain growth stage.  Height may therefore be a less effective indicator of growth stage than in some years.  Be sure to count corn collars where appropriate, including the small more spoon-shaped leaf collar that is often missing once corn exceeds 12 inches or so in height.  Shifting POST applications earlier is one strategy to help ensure that the crop has not exceeded a critical growth stage, such as the V5-V6 corn stage with regard to broadcast application of ALS-inhibiting herbicides. 

And now the bad news – there are some really weedy corn and soybean fields around the state.  In many of these, it is evident that burndown herbicides were not applied before the crop emerged, and the POST herbicides will have to control weeds that have been in the field for several months.  The size and age of the weeds in these fields can create some extremely challenging situations.  Broadleaf weeds are more of a concern than grasses in these fields, as long as a glyphosate-resistant crop has been planted, because glyphosate usually effectively controls even large grasses.  Marestail, giant ragweed, and lambsquarters are of primary concern, because the combination of possible herbicide resistance, size and age can preclude effective control with glyphosate.  The two primary recommendations for these fields are: 

1) increase glyphosate rates to the maximum allowed in the first POST application.  This is a more effective approach than using a low rate first and applying a second time at the higher rate. 

2) Do not apply glyphosate alone.  Mix it with another herbicide that is effective on the broadleaf weeds of concern.  Adding Status or another dicamba product is a generally effective strategy for control of many broadleaf weeds in corn, but other POST corn herbicides cn help control large broadleaf weeds in a mix with glyphosate.  Classic, FirstRate and Synchrony can help control many broadleaf weeds in soybeans, but will not  control ALS-resistant weeds.  Where the population is resistant to both glyphosate and ALS inhbitors, Flexstar or Cobra can be mixed with glyphosate, although at a higher cost and greater risk of soybean injury.  Be cautious about adding more herbicide than needed in this situation.  The combination of a higher glyphosate rate and one other herbicide can be adequate without causing too much injury to soybeans.  Soybeans usually recover well from herbicide injury so that yield is unaffected.  However, substantial injury can be more of a problem in late-planted soybeans due to the more limited time for the crop to recover and reach full yield potential.

We don't have a consistently effective recommendation for control of marestail in emerged soybeans.   Response of the marestail to the herbicides that can control it – glyphosate, FirstRate, or Classic – will be variable depending upon the type of herbicide resistance that the population exhibits and plant size.  Our primary recommendation is a combination of glyphosate and FirstRate or Classic.  We have not found any other POST soybean herbicides that have significant activity on marestail, except for Ignite, which can only be applied to LibertyLink soybeans.

 

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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.