C.O.R.N. Newsletter 2010-22

Dates Covered: 
July 19, 2010 - July 27, 2010
Editor: 
Harold Watters

Can warm nights reduce grain yield in corn?

High night temperatures (in the 70s or 80s) can result in wasteful respiration and a lower net amount of dry matter accumulation in plants. The rate of respiration of plants increases rapidly as the temperature increases, approximately doubling for each 13 degree F increase. With high night temperatures more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield. High night time temperatures result in faster heat unit (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields.

Past research at the University of Illinois indicates that corn grown at night temperatures in the mid-60s outyields corn grown at temperatures in the mid-80s. Corn yields are often higher with irrigation in western states, which have low humidity and limited rainfall. While these areas are characterized by hot sunny days, night temperatures are often cooler than in the Eastern Corn Belt.  Low night temperatures during grain fill have been associated with some of Ohio’s highest corn yields in past years. Last year, when the highest corn average yield to date were achieved, 174 bu/A, Ohio experienced one of its coolest Julys on record. The cool night temperatures may have reduced respiration losses during early grain fill and lengthened the rain fill period. 

Western Bean Cutworm Update: Eggs and Larvae FoundWestern bean cutworm larvae

Western Bean Cutworm Update: Eggs and Larvae Found

For the first time, we have found western bean cutworm egg masses in Ohio.  Last Tuesday, July 13, a field in Fulton county was inspected where egg masses were found.  Pictures from this field including the egg masses and newly hatched larvae can be found on our Agronomic Crops Insects website: http://entomology.osu.edu/ag/pageview3.asp?id=1150.   

Western bean cutworm eggs on corn

Remember, egg masses are first white, then tan, and then turn a deep purple color immediately before they hatch.  

Western bean cutworm eggs near hatch

(Be sure not to confuse western bean cutworm eggs with stink bug eggs.  Stink bug eggs are first white, then turn a dark brown before hatch—images of stink bug eggs are at the above website for comparison).  Western bean cutworm eggs of all stages were found in this Fulton county field.  In addition, some 1st instar larvae were found feeding on the unemerged tassel within in the whorl.  However, the good news is that this particular field was under economic threshold (threshold is 5% of corn inspected with egg masses or larvae).  These observations indicate that oviposition and egg hatch is underway.  Corn fields should continue to be inspected for both eggs and larvae, especially in pre-tassel corn.  Once tasselling is complete, these corn plants are less preferred hosts for western bean cutworm.  In pre-tassel corn, the top-most 1-3 leaves that are still mostly vertical in orientation should be searched for egg masses on the upper surface of the leaf. Often time you might see the shadow of the egg mass on the underside of the leaf when viewed facing the sun (a picture of this is also at the web site).  In corn that has tasseled, inspection should also include the possibility of larvae.  Larvae can be found feeding on the leaves or on the silk.  These next few weeks will be critical as, if chemical application is needed, it must be applied after egg hatch and before larvae enter the ear. 

 

It is difficult to determine if we have reached peak flight yet.  Counts are increasing in some areas (northwest and northeast Ohio), while more southern and central locations are seeing a decrease.  Previous years have seen peak flight during the 3rd or 4th week of July, and, because of the warm June and July, we may be in peak flight now.  Our total count as of July 19 is 1,659.  Please see our updated trap counts for Ohio at http://entomology.osu.edu/ag/pageview3.asp?id=1390. Again, if you find what you think are western bean cutworm egg masses or larvae, please contact entomology specialists at michel.70@osu.edu or hammond.5@osu.edu.

Foliar Diseases Showing up in Corn

Foliar diseases, especially gray leaf spot, are beginning to show up in some corn fields, and questions are being asked about the need for foliar fungicides. This is not surprising, since we have had several warm and humid days over the past two weeks, with dew and fog during the mornings. These are the conditions favorable for gray leaf spot. However, we have also received reports of leaf rust, eye spot, and northern corn leaf blight.

Foliar diseases of corn are generally a concern when they develop early and progress up the plant before grain fill is complete. This is especially true when the hybrid is susceptible. In most years, gray leaf spot usually develops late and has very little or no effect on the crop. This will certainly be the case in some fields again this year. However, we have already received reports of gray leaf spot at or above the ear leaf in some areas.

Because of the wide variation in our planting dates this year, with some fields planted in late April and others planted in late May, the corn crop is at growth stages ranging from about V10 (ten-leaf stage) to brown silk across the state. With such a wide variation in crop development, if the weather continues to be favorable for disease development, some fields and some hybrids could certainly be infected early and could suffer yield reduction if not treated.

Scout fields for foliar diseases, especially those planted with susceptible hybrids in an area with a history of gray leaf spot or northern corn leaf blight or in a continuous-corn, no-till field. These fields are the ones most likely to benefit from a fungicide application. Use hybrid susceptibility, weather conditions, field history, and current disease level as guide when making a decision to apply a fungicide. There are several very good fungicides to choose from.

Follow the labels and keep your eyes on the fungicide price and application cost when making a decision: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/Corn%20foliar%20fungicide%20chart%202008.pdf   

 

Evaluation of three commercial mycotoxin inhibitors added to Vomitoxin (DON) contaminated corn diets for weanling pigs

A regional study involving 12 experiment stations using a total of 904 weanling pigs in 27 replicates evaluated three commercial mycotoxin inhibitors added to two different vomitoxin (DON) contaminated corn sources. The first corn analyzed 2.0 ppm DON while the second analyzed 7.0 ppm DON. The complete diet, mixed and provided in meal form from one mixing facility, was calculated to contain 1.0 and 3.9 ppm DON, respectively.

The companies that produced these mycotoxin inhibitors were asked to recommend their level of product (Defusion®, Integral®, Biofix®) to be added to the diets. The study was blinded from participating companies and investigators to prevent bias. The test period was conducted after a 10 day adjustment period to a common diet. The test period that evaluated these mycotoxin inhibitors was conducted from 10 to 31 day post weaning.

The results showed that the high DON corn diet reduced performance responses more severely than diets with low DON contamination. Defusion®, added at 10 lb per ton was the most effective mycotoxin inhibitor in our study in both corn sources while the other mycotoxin inhibitors were ineffective. Lighter weight pigs were more severely affected by the DON contaminated diets than pigs of a heavier body weight, but both weight groups responded positively to Defusion®. It is questionable if the feeding of a low DON contaminated corn would justify the added expense of the product while it was beneficial when DON was at a high level.

The entire report may be found on the Ohio Pork Information Center website: http://porkinfo.osu.edu/documents/VomitoxnFinalReport07-16-20101.pdf

 

Inoculum for Sclerotinia apothecia is present in some fields

Sclerotinia white mold, also known as Sclerotinia stem rot has a very interesting disease cycle.  The inoculum comes from very small fruiting bodies called apothecia that form from the sclerotia. There are several papers that have looked at the formation of these, but they tend to be from lab conditions.  Last week, we found apothocia in fields in north east Ohio (Figure 1). Sclerotinia apothecium 2010

This was a bit of a surprise as the 2 weeks prior to this were dry, but rains did fall 3 to 4 days prior, the night time temperatures hit below 70 a couple of nights and more importantly – there was still heavy dew on the plants at noon.  My pants were soaked.  In addition to apothecia from Sclerotinia we also found birds’ nest fungus (Figure 2) 

Bird's nest and Yellow fungus

and another yellow fungus (Figure 3). 

Yellow fungus

Both the Bird’s nest fungus and the Yellow one, were on the decaying residue and not found with sclerotia.  Neither of these contribute to white mold but do help in degrading the soybean residue.  When it is wet, there are lots of different fungi found on the residue of soybean fields (and corn and wheat as well) but only those that germinate from sclerotia (the rat turds) are associated with development of Sclerotinia stem rot.

These fields are those that always have some white mold in them – this disease does not occur in every field across the state – for those historically positive fields – this is a year to watch.  Fungicides (Topsin M) needs to be applied at the R1-R2 growth stage for any management of this disease.  We have soybeans at just about every growth stage from V1 to R4 – so it will be interesting.  Monitor the growth and development of soybeans – fields that have been historically positive for Sclerotinia, form a dense canopy prior to flowering and have consistent moisture and a few cool nights are at the highest risk for this disease.

Note: whenever you apply a fungicide – always leave a control strip or 2 (not the edge of the field) to evaluate if the treatment worked.  If it didn’t then, a) reassess if you truly needed the treatments or b) double check the timing of the application.  All fungicide applications work best when applied prior to arrival of fungal spores, as protectants on the leaves or stems depending on the disease in question.

 

Foliar diseases are absent in soybeans

Soybean rust is not here in Ohio.  It is still “hugging” the gulf coast in Florida and Alabama.  It has been moist this year but temperatures have been warm.  It is going to take some cooler weather before this starts moving in these southern states.

There are no reports of frogeye leaf spot this year.  To date samples have been negative and appear to be herbicide or adjuvant related.  With the stress on the soybeans from root rots, late planting dates, caution should be exercised if you are going to apply a fungicide.  This is the year to leave 2 to 4 control strips and harvest each strip separately and make some comparisons.  Scout to look for differences in disease at that R5-R6 growth stage in the mid canopy.  This will be key to determine if there was control.

 

Scab Resistant Soft Red Winter Wheat Varieties are Available for Fall Planting

Producers who planted resistant wheat varieties and applied a fungicide at flowering had lower levels of scab and vomitoxin in their wheat in 2009 than those who planted susceptible varieties. So, as you prepare to plant wheat this fall, scab resistance should be a top priority on your list. In the past, there were very few Ohio grown winter wheat varieties with decent scab resistance, and some of those varieties yielded poorly or did not grew well under our conditions. Today we have far more varieties with very good scab resistance in combination with very good yield potential. No variety is completely resistant or immune to scab, so if conditions are wet and humid during flowering, even varieties considered resistant will develop scab and become contaminated with vomitoxin, however, disease and toxin levels will be lower in resistant varieties than in susceptible varieties. In addition, with a scab resistant variety growers will likely see greater benefit from the use of fungicides if scab develops. In general, relative to the most susceptible varieties, scab and vomitoxin reductions tend to be much higher when fungicides are applied to resistant varieties than to susceptible varieties.

2010 OHIO WHEAT PREFORMANCE TEST

Brand

Cultivar

Scab (%)

Scab Rating

AGI

205

28.9

MR

AGI

206B

19.4

MR

AgriPro

W1104

28.9

MR

AgriPro

W1377

27.2

MR

Beck

113

26.1

MR

Ebberts

590

23.9

MR

Ebberts

595

23.9

MR

Ebberts

634

16.1

MR

Ebberts

661

20.6

MR

Excel

180

28.9

MR

Excel

209

18.9

MR

Excel

442

20.0

MR

Pub. Certified

Freedom

25.6

MR

Pub. Certified

Roane

22.8

MR

Rupp

RS 934

23.9

MR

Rupp

RS 935

28.3

MR

Rupp

RS 978

25.0

MR

Seed Consultants

SC 1321

18.3

MR

Shur Grow

SG-1540

18.9

MR

Shur Grow

SG-1549

18.9

MR

Steyer

Quin-Lee

16.7

MR

Strike Genetics

936

21.7

MR

Va. Tech

Merl

26.7

MR

Wellman

W 132

19.4

MR

AGI

106

40.0

MS

AgriPro

Branson

36.7

MS

Buckeye

Abe

31.7

MS

Dyna-Gro

9922

34.4

MS

Pioneer Brand

25R56

35.0

MS

Pioneer Brand

25R62

33.9

MS

Pub. Certified

Hopewell

36.7

MS

Seed Consultants

SC 1298

17.8

MS

Wellman

Sunburst w/ Encase

17.8

MS

Wellman

W 123

18.9

MS

Excel

234

12.2

R

Excel

242

14.4

R

Pub. Certified

Malabar

10.6

R

Pub. Certified

Truman

15.6

R

Rupp

RS 967

15.0

R

Seed Consultants

SC 1301

15.0

R

Seed Consultants

SC 1311

14.4

R

Seed Consultants

SC 1341

15.6

R

Steyer

Ashlyn

9.2

R

Steyer

Kenton

13.3

R

Steyer

Marion

13.3

R

Strike Genetics

937

13.3

R

Strike Genetics

938

10.6

R

AGI

107

50.0

S

AGI

402B

37.2

S

AgriPro

W1566

55.6

S

Beck

122

35.6

S

Beck

134

48.3

S

Beck

135

42.2

S

Dyna-Gro

Shirley

60.0

S

Dyna-Gro

V9723

33.3

S

Excel

170

51.1

S

Pioneer Brand

25R39

51.1

S

Pioneer Brand

25R47

39.4

S

Pro. Certified

Bravo

35.6

S

Pro. Certified

Sunburst

30.0

S

Shur Grow

SG-1559

37.2

S

Wellman

W 122

33.9

S

This table shows the scab resistance ratings of the wheat varieties planted in this year’s wheat performance trials. R = resistance, indicating that a variety has resistance comparable to Truman, one of the most scab resistant soft red winter wheat varieties. MR = moderately resistant, indicating that a variety has resistance comparable to Freedom. MS = moderately susceptible, and S = susceptible.  More than 20% of the varieties evaluated in this year’s trial were considered resistant (R) and more that 38% moderately resistant (MR), for a total of approximately 58% of the varieties rated as at least moderately resistant. More information about the varieties shown in the table will be published in the 2010 Wheat Performance Trial. 

 

Wheat Seed Treatments 2010

Seed treatments can play an important role in achieving uniform seedling emergence under certain conditions. Seed treatments can protect seeds or seedlings from early-season diseases, and fungicides are available to provide such protection. However, seed treatments should not be considered a cure-all for the selection of poor quality seed lots. Seed treatments will not increase poor germination due to excessive mechanical damage, poor storage conditions, genetic differences in variety, or other damage.

Head scab and Stagonospora glume blotch were at high levels in many fields this year, therefore growers need to limit losses due to these and other seed-borne pathogens by treating seed. In addition, be sure to use crop rotation and plant resistant or less susceptible varieties. Be especially concerned that saved seed may be contaminated. If head scab or Stagonospora was present at high levels in your wheat field do not use that grain for seed. These seed infesting fungi will contribute to poor quality seed resulting in reduced yield and lower test weight.

However, if you absolutely have to use scabby wheat for seed, cleaning, germ test, and fungicide seed treatment are absolutely necessary. Use the level of scabby kernels and test weight as your guide. You can determine the percent scabby kernels of you lot by using the visual chart found on the Field Crops Disease website. Cleaning will get rid of light, scabby material, and this will naturally increase the test weight of the lot. If you can increase a test weight to about 56 lb/bu (after cleaning) and your germ is above 80%, then you have decent quality seed. Gravity table would be your best option for cleaning.  In addition to cleaning and treating, seeds should be stored under cool, dry conditions until planting to prevent mold development. Blending of scabby wheat with healthy wheat is another good option to increase the overall quality of the lot.

The systemic fungicide Dividend Extreme is effective in controlling seed-borne Stagonospora, but it is more effective against seed-borne scab at the higher rate than at the lower rate. Products containing Raxil used at the labeled rates are effective against seed-borne Stagonospora and have relatively good activity against seed-borne scab.

See the following websites and the pdf file for more on rating scabby wheat and fungicide seed treatment:

http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/WheatKernels2.htm           

Wheat seed treatment chart 2010.pdf

 

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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.