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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2007-23

Dates Covered: 
July 23, 2007 - July 30, 2007
Howard Siegrist

Kernel Development in Corn: Drought Impact

Authors: Peter Thomison

Many Ohio corn fields received 1 to 2 inches of rain last week, which has helped at least temporarily reduce the impact of the current drought. However, more rain is needed to recharge soil moisture and limit drought stress injury during the upcoming weeks until grain fill is complete. Kernel development has started in many corn fields that were planted in April and early May. Following pollination, kernel development (or grain fill) is the most critical period in the development of the corn plant for the determination of grain yield. Kernel development proceeds through a number of stages which have been characterized by such terms as blister, milk, roasting ear, soft dough, dent, etc. Since these descriptive terms can sometimes be difficult to interpret, alternative systems have been proposed. A staging system widely used by agronomists and crop consultants divides kernel development into six stages, designated numerically as R1, R2, through R6. The table below lists kernel developmental stages in sequence and provides a brief description of each phase.

Kernel Development Stages in Corn
    Avg. Approx.
    No. of Days
    Days/ from
Stage* Description Stage Silking
Silking(R1) Fresh green silks-no visible blisters 4 --
Pre-blister Silks brown-not necessarily 4 8
  dry visible kernel pimples    
  contain little clear fluid    
Blister(R2) Visible blisters w/abundant fluid 4 12
Early Milk Mostly white kernels 4 16
  w/milky-white fluid    
  some yellow kernels    
Milk(R3) Mostly yellow kernels w/milky-white fluid 4 20
  no solids yet(“Roasting Ear” stage)    
Late Milk- Solids beginning to form 4 24
Early Dough kernel pasty texture (barely edible)    
Soft Dough Pasty or semi-solid (not edible) 5 28
(R4) no visible denting    
Late Dough- Few kernels beginning to dent 5 33
Early Dent especially near butt of ear    
Dent(R5) Majority of kernels dented or 8 38
Late Dent Essentially all kernels dented 17 52
  milk line may just be visible    
Black Layer Maximum kernel dry weight-kernel 10 62
R6) moisture 27-32%    

*R-stages 1 through 6; specific number of days associated with each stage may vary from season to season, from location to location, and from hybrid to hybrid.

Keep in mind that the values for average number of days per stage and approximate days from silking in the table above are based on timely corn planting (e.g. early May). When corn is planted later, it generally requires fewer heat units to achieve R6, physiological maturity or “black layer”, and this may affect the number of days per stage and days from silking.

The water deficits we’re currently experiencing in many areas may cause varying degrees of kernel abortion toward the ear tip (“tip dieback”). Ear tip kernel abortion occurs when the youngest kernels resulting from the most recent pollination are cut off from nutrient flow (i.e. sugars produced by the leaf canopy) because the supply is insufficient to fill all the kernels that have been set. Such kernel abortion is most likely to occur during the first two weeks after pollination (during R2, the blister stage). Four days of severe drought at the blister stage has the potential of reducing yields 30 to 40%, and at dough stage, 20 to 30%. Drought stress may also reduce kernel size and weight. Premature plant death resulting from drought cuts off starch accumulation and results in small, light-weight (low test weight) kernels.


Drought-Stressed Corn for Silage

Authors: Bill Weiss

The dry conditions in many parts of the state have greatly reduced hay and hay silage yields which has reduced forage inventory on many dairy farms. In addition, corn plants are becoming stunted and grains yields are likely to be poor. Low forage inventory and the desire to salvage some value from corn fields means that much of the drought-stressed corn in the state will be chapped for silage. Drought-stressed corn silage can be a good feed for dairy cows and other ruminants if some guidelines are followed.

1. Chop at the correct dry matter: 30 to 38% dry matter. Corn plants, whether drought-stressed or not, must contain the proper amount of moisture for good fermentation in the silo. Corn plants that are chopped with less than about 30% dry matter (especially less than 27% dry matter) are at high risk of a poor fermentation (high acetic acid, low pH, etc). Corn plants chopped with much more than 38 to 40% dry matter usually under go a limited fermentation and can mold and spoil during storage and feed out. Drought-stressed corn often is much wetter than normal corn because normal corn has more kernels and kernels are drier than the vegetative part of the plant. Before chopping drought-stressed corn for silage, cut some stalks and run dry matter analysis. If the crop is too wet to make silage, do not chop. Forage supplies are likely to be very tight this fall and winter. Do not exacerbate the situation by chopping at the incorrect dry matter concentration and making poor quality silage. Even under severe drought, it is extremely likely that corn plants are too wet to make into silage in mid-July.

2. Nitrates might be a problem and greenchopping corn plants is not recommended. Silage fermentation can greatly reduce nitrate concentrations. Therefore, very often silage is safe to feed even though the plants would have been toxic if fed fresh. If greenchopping must be done because of limited forage supplies, set the chopper high because nitrates accumulate in the lower stalk.

3. Nutrient value of drought-stress corn silage can be fairly high. Compared with normal corn silage, drought-stressed corn silage usually has 1 to 2 percentage units more crude protein, 10 to 20 percentage units more neutral detergent fiber (the fewer the number of ears, the higher the fiber concentration), and 15 to 25 percentage units less starch. Even though fiber concentrations are high and starch concentrations are low, energy values (TDN, net energy, etc.) of drought-stressed corn are usually 90 to 90% as high as normal corn silage because the fiber is highly digestible. The bottom line is that if drought-stressed corn silage ferments properly (see point #1), it is quite acceptable as a forage for even high producing dairy cows. However, the nutrient composition of drought-stressed corn will be more variable than normal corn silage and it must be sampled and analyzed for nutrient composition and diets balanced accordingly.

Chopping Soybean for Silage

Authors: Bill Weiss

Because of dry conditions, soybeans may not mature adequately to justify harvesting the crop as beans. An alternative is to chop the entire plant and make silage out of it. If harvested at correct stage of maturity and good silage making practices are followed soybean silage can be a good feed for cattle.

1. The crop must contain adequate water for fermentation. The best fermentation usually occurs when soybeans contain 35 to 45% dry matter (wetter silages for bunkers and drier silages for upright silos).

2. Excessive fat (oil) in the seeds can inhibit fermentation. Soybeans at the R-6 stage usually do not contain enough oil (6 to 9% of the whole plant dry matter) to cause problems. Under normal growing R-7 stage beans contain about 10% fat (whole plant) which can cause some fermentation problems but under drought conditions, R-7 may still ferment adequately. If your soybeans contain much more than about 10% fat, they should be blended with other crops (corn plants) at the time of ensiling.

3. Silage must be chopped relatively finely to encourage consumption of stems. A theoretical length of chop of 3/8 inch should be adequate but chop length should be evaluated at the time of cutting. Chop several feet of material and look at the forage. If several long stems remain, reduce TLC, if you cannot find any stem pieces that are about an inch long, increase TLC (not all the pieces should be 1 inch but you should be able to find some.

4. Nutrient value of soybean silage chopped at R-6 stage is similar to early to midbloom alfalfa. Average concentrations (dry matter basis) of some nutrients are: Crude protein - 19%; Neutral detergent fiber (NDF) - 40%; Fat - 6%.

5. Certain herbicides that are used for soybeans may not be approved when harvesting the crop as silage. Check with your chemical supplier.

Mid-Season Soybean Diseases

Authors: Anne Dorrance

Quite a mix of symptoms appeared on soybeans this past month primarily due to root pathogens. Environmental conditions have been challenging this year with rains in cold weather in the spring followed by an extended drought. Some areas have been unlucky and have gotten 3 inches of rain and have flooding injury.

Charcoal rot – this one we would expect to find in areas that have extended dry conditions. Symptoms include wilted plants that turn yellow and wilt but the leaves remain attached to the plant. Check the lower part of the stem and pull back the epidermis (skin or outside layer on the stem). If charcoal rot is present numerous black bodies (sclerotia) give the tissue a “peppered look”. Black dots are embedded in the tissue and can appear as black streaks.

Phytophthora stem and root rot – surprisingly, Phytophthora is showing up this year. This is associated with wet conditions. The best time to look is about one week after a rain. Plants will appear yellow and wilt, but with a chocolate-brown lesion moving up the stem. Underneath the epidermis will be a brown discoloration of the tissue.

General root rots – red brick lesions at the soil margin on the stem, tan, brown or black secondary roots all indicate a number different root rot pathogens or a complex. This is especially common this year in areas of the field which are poorly drained and often are compacted. Some of the plants that we are getting have the lower portion in the shape of a ‘J’.

The best management practice for all of these diseases is the use of resistant varieties, but also good soil management practices that promote good drainage.

Sentinel Plot Update

Authors: Anne Dorrance

Fifty-four plots were surveyed last week in Ohio for soybean rust and other foliar diseases. Soybean rust at this point is limited to the Texas, Louisiana, Florida, and Mississippi. Today (July 23rd) Arkansas identified soybean rust in the far southwest corner of the state. I would expect from the rain patterns in the south that we will see more counties turn red over the next 3 weeks – provided that the same weather pattern continues. Ohio’s soybeans are moving into the R2 to R3 growth stage across the state and the risk of soybean rust is very, very low at this time.

Central Ohio Agronomy Crop Sprayer Field Day

Authors: Howard Siegrist

The Central Ohio Agronomy Crop Sprayer Field Day will be held on Tuesday, July 31st from 2:00 p.m. to 8:30 p.m. at the farm of Ed and Kathy Parrish near Millersport, OH.

Those attending will have the opportunity to test drive and operate sprayers from major manufacturers from 2:00 to 5:00 p.m. Both self-propelled & pull type sprayers will be featured. At 5:00 p.m. there will be a complimentary supper provided by equipment manufacturers and pest management supply companies. At 5:30 p.m. there will be updates on field crop pests and diseases from Ron Hammond an OSU field crop entomologist and Anne Dorrance an OSU soybean pathologist.

At 5:30 p.m. commercial and private pesticide applicator credits will be available for $15.00 for a private license and $30 for a commercial applicator in the following areas: core, grains, stored grains, non-cropland and forages. Certified crop advisors can receive three hours of continuing education credits.

The site is located on Lancaster Street immediately north of Millersport, OH (two miles south of I-70). From I-70 take S.R. 37 south ½ mile to S.R. 79 and proceed east ½ mile to Lancaster Street. Turn right on Lancaster Street and proceed south ½ mile to field day site. No advance registration is required for the free program which includes supper. The event is sponsored by: the OSU Extension offices in Fairfield, Licking, Perry, and Pickaway counties. For further information contact Howard Siegrist, Extension Educator of Licking County (740)670-5315.

Fungicide Use on Corn

Authors: Dennis Mills, Pierce Paul

Interest in fungicide applications on field corn is very high this summer. If you are confused over all the information and “coffee shop talk” below is a few links to recent Web articles from university Extension specialists that may shed a "third party" perspective on the subject. From Purdue’s “Chat 'n Chew Café”.

Robertson, Alison and Daren Mueller. 7/11/07. Iowa State Univ.

Mueller, Daren. 5/15/06. Fungicides: Terminology. Iowa State Univ.
The first of an 8-part series. A good primer on fungicides for non-plant pathologists.

Jackson, Tamra. 7/13/07. Results of Nebraska Foliar Fungicide Trials on Corn. Univ. of Nebraska.

Shaner, Greg. 7/13/07. Purdue Univ.

Sweets, Laura. 7/13/07. Foliar Fungicides Labeled for Use on Field Corn. Univ. of Missouri.

Malvick, Dean. 7/12/07. Corn Foliar Diseases and Fungicides in Minnesota – Delving into the Uncertain. Univ. of Minnesota.

Brown-Rytlewski, Diane. 7/12/07. Michigan State Univ.

Dorrance, Anne, Pierce Paul, & Dennis Mills. 7/9/07. Ohio State Univ.

Vincelli, Paul. 7/2/07. Univ. of Kentucky.

Shaner, Greg. 6/29/07. Will Fungicides Be of Value on Corn This Year? Purdue Univ.

Robertson, Alison, Daren Mueller, Carol Pilcher and Kristine Schaefer. 6/25/07. Fungicide applications in corn may be increasing. Iowa State Univ.

Nafziger, Emerson. 6/29/07. Univ. of Illinois.

Bradley, Carl and Matt Montgomery. 6/8/07. Prophylactic Fungicide Applications on Corn: A Good Practice? Univ. of Illinois.

Paul, Pierce. 5/28/07. 5/21/07. Foliar Fungicide Use in Corn. Ohio State Univ.

Larson, Erick. 5/14/07. Fungicides on Corn? Mississippi State Univ.

Vincelli, Paul. 4/30/07. Fungicide considerations for corn in 2007. Univ. of Kentucky.


Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pierce Paul, and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Mark Loux, (Horticulture and Crop Sciences), Peter Thomison (Horticulture and Crop Sciences), Bill Weiss (Animal Sciences). Extension Educators: Roger Bender (Shelby), Howard Siegrist (Licking), Steve Prochaska (Crawford), Todd Mangen (Mercer), Harold Watters (Champaign), Greg LaBarge (Fulton), Gary Wilson (Hancock), Alan Sundermeier (Wood), Steve Foster (Darke), Glen Arnold (Putnam), Wesley Haun (Logan), Bruce Clevenger (Defiance), Mark Koenig (Sandusky).

Crop Observation and Recommendation Network

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.