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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2009-17

Dates Covered: 
June 9, 2009 - June 15, 2009
Jonah T. Johnson

Assessing hail damaged corn

Authors: Peter Thomison

Last week I received reports of hail storms that caused severe injury to corn in southwestern Ohio. The impact of hail damage is largely dependent on the crop's stage of development. Hail affects yield primarily by reducing stands and defoliating plants with most of the damage resulting from defoliation. Corn becomes increasingly vulnerable to hail damage at later vegetative stages of development with the tassel stage/pollen shedding stage (VT) being the most critical period.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs (i.e. if damage occurs prior to tasseling). For this reason, estimates of hail damage should be delayed several days to allow for this period of re-growth.

The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V7 plant according to the leaf collar method would probably correspond to a 9-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Corn growth stages will vary considerably depending on location, planting date, etc.. Moreover, there is also variability in growth within fields because of uneven emergence and development. I suspect most corn in Ohio has not progressed much beyond the V7 stage (as of 6-8-09). Based on estimates of the National Crop Insurance Association, at the 9-leaf stage (or about V7), if 50% of the leaf tissue is destroyed by hail, a corn plant loses about 4% of its grain yield potential; if 100% defoliation occurs, a corn plant loses about 13% of its yield potential.

For more detailed information on evaluating hail injury in corn, consult "Assessing Hail Damage to Corn" National Corn Handbook Chapter 1 (NCH-1)." Available on-line at

(verified 6/8/09).

Percent yield loss in corn based on growth stage & defoliation (adapted from NCIA Corn Loss Instructions, rev. 1984)
Percent Leaf Defoliation
Growth Stage* 25% 50% 75% 100%
7-leaf (V5)** 0 2 5 9
8-leaf (V6) 0 3 6 11
9-leaf (V7) 1 4 7 13
*as determined using the hail adjustor’s leaf staging method
** approximate leaf collar stage within parentheses


Hail damage may result in tied leaf whorls in corn

Authors: Peter Thomison, Todd Mangen

With recent reports of severe hail damage to corn in localized areas of SW Ohio, growers should not be surprised if they observe “twisted” or “tied” leaf whorls. Hail damage prior to the 6 to 7-leaf stage (about V5-6 according to the leaf collar staging system) often results in tied leaf whorls as injured plants recover and new leaves try to unroll. Corn plants usually grow out of this problem and tied whorls seldom cause major yield loss. In 1999, we evaluated effects of tied whorls and stalk bruising caused by hail damage in early June on corn performance at four on-farm sites in south central Ohio by comparing plots within the fields with major and minor hail damage. During the three- to four-week period following the hail storm, the number of plants exhibiting tied whorls decreased sharply. Plots that received major damage from hail exhibited 36 to 61% tied whorls on June 12, which decreased to 0 to 9% by July 6. Silking was delayed approximately 1 to 1.5 weeks in the plots with major damage vs. plots with minor damage. Severe stalk bruising did not increase lodging; lodging was negligible across farm sites, averaging less than 2%. Kernel moisture at harvest was generally higher in plots with major damage (in three of the four fields), and yields were lower compared to the plots with minor damage. More information on this evaluation is in the 2000 Agronomic Crops Team On-Farm Research Projects Summary available on-line at

Corn and The Ugly Duckling

Authors: Bob Nielson

This article posted on the “Chat ‘n Chew Café” ( on June 7th, 2009.

• “Ugly ducklings can change into beautiful swans.”

What little corn that was planted back in late April and early May is beginning to reach an important milestone in its growth and development. Recognition of this event helps explain the annual transition from a slow-growing, often ugly, field of corn to one that grows like wildfire.

Every year, for the first five weeks or so after corn planting is finished, the guys down at the Chat 'n Chew Cafe complain royally about the looks of the crop. Gripes about uneven stands, poor color, and slow growth abound around the tables as everyone airs their concerns about the looks of their neighbors' fields.

Then suddenly one day, the tone of the conversation in between the coffee and sweet rolls perks up. Almost overnight, the crop has taken off like a rocket. The color of the leaves turns a dark, almost-blue green and they develop a distinct shine. From that point on, any connoisseur of corn feels better about life in general. What happens?

During the first five weeks or so after planting, the corn plant is going about the business of creating all of the leaves it will ever have. A few of these leaves are visible, but most are wrapped tightly deep inside the whorl, biding their time until its their turn to emerge.

Some root development ( is also occurring during these same first five weeks. In fact, the successful development of the first three or four sets of nodal roots during this time will go a long ways to ensuring successful stand establishment of the crop.

Even though new leaves and some roots are developing during this time, the rate of increase in total plant dry matter is relatively slow. The photosynthetic 'factory' is small, as is the size of the raw material accumulator devices (the roots).

Once the corn plant reaches the five or six leaf stage (determined by number of visible leaf collars), a miraculous turn of events occurs. The final leaf is created at the main growing point ( of the plant (near the top of the 'pyramid' of stalk tissue) and the plant turns its attention toward developing the reproductive structures known as the tassel and ears.

At the same time, the size of the photosynthetic 'factory' and its supporting staff of roots is reaching a critical mass that is finally capable of manufacturing greater and greater amounts of energy. With greater amounts of available energy, the 'factory' begins to convert more and more of the incoming nutrients and carbon dioxide into sugars, starches, and other plant dry matter.
Subsequently, the stalk begins to elongate rapidly, the roots begin to develop rapidly, the tassel develops rapidly, the tiny ears within the ear shoots develop rapidly, and suddenly the plant is growing like wildfire. From about knee-high corn to the onset of pollination, the corn crop progresses through its most rapid growth phase (above- and below-ground), including the uptake of the lion's share of soil nutrients for use during the grain fill period.

By now you may be wondering what's the moral of this story? Primarily, it's a reminder to take time once in a while to look at this King of Crops in awe and wonder. Secondarily, be reminded that an ugly duckling of a corn crop that reaches the five to six leaf stage in reasonably good condition will usually turn the corner and become a beautiful swan of a corn crop during the next few weeks.

Thirdly, be reminded that true yield potential is just beginning to be determined at the start of this rapid growth phase. Ugly corn up to this point in time has not necessarily lost its yield potential. Ear size is determined ( from about knee-high to shoulder-high corn. Weather during pollination and grain fill finish off the yield determination. While we often moan and complain about the looks of young corn, it often surprises us with acceptable yields in the fall.

Related References
Nielsen, RL (Bob). 2007. Ear Size Determination in Corn. Corny News Network, Purdue Univ. [online]. Available at [URL accessed June 2009].

Nielsen, RL (Bob). 2008. Growing Points of Interest. Corny News Network, Purdue Univ. [online]. Available at [URL accessed June 2009].

Nielsen, RL (Bob). 2009. Root Development in Young Corn. Corny News Network, Purdue Univ. [online]. Available at [URL accessed June 2009].

Lack of rain on preemergence herbicides

Authors: Mark Loux

There are widespread reports of inadequate weed control from preemergence (PRE) herbicides due to lack of timely rainfall. Many of these fields would have received a postemergence (POST) herbicide application at some point anyway, but the POST strategy may have to be altered when PRE herbicides fail to provide the expected control. Some things to consider:

1. When the PRE herbicides are initially effective and prevent weed-crop competition for the first several weeks after planting, the POST application can often be delayed to control late-emerging weeds. So, weed size is not necessarily the determining factor for POST timing (although small weeds are always most easily controlled), and in some cases the POST can be applied just prior to crop canopy closure. When the PRE herbicides fail to adequately control weeds from the start, weed size should be the determining factor for POST timing. To prevent weeds that emerge with the crop from being a yield-limiting factor, POST herbicides should be applied in corn when weeds are less than 2 to 3 inches tall and in soybeans before weeds exceed about 6 inches in height. This principle applies to non-GMO and herbicide-resistant crops.

2. When lack of control from PRE herbicides forces an earlier POST timing, later-emerging weeds are likely to be a problem. This can be solved by applying POST herbicides a second time, which is generally easier to accomplish in soybeans than in corn, due to the height of corn later in the season. It is also possible to add some residual herbicide to the first POST application, which may provide enough control so that a second POST application is not needed. In soybeans, the addition of Scepter, Pursuit (or apply a premix of glyphosate + Pursuit), or FirstRate can provide residual broadleaf weed control. Pursuit and Outlook provide residual grass control, but Outlook can be applied only up to 3rd trifoliate soybeans. Depending upon corn height, atrazine, atrazine premix products, Hornet, or SureStart can be used postemergence in corn for residual weed control. Resolve products can provide limited residual control of grass and small-seeded broadleaf weeds in corn.

3. Impact and Laudis may be among the more inexpensive options for controlling a variety of small broadleaf and grass weeds where PRE herbicides have failed in non-GMO corn, as long as the grasses are no more than 2 inches tall. These products are most effective when mixed with atrazine and MSO. Where the grass is larger, use of Option or a product containing nicosulfuron (Accent, Steadfast, NIC-IT) will usually be required, and these should be mixed with another herbicide to control broadleaf weeds.

4. The program outlined in our fact sheet on non-GMO weed control, available at, should be adequate even where PRE herbicides have not worked that well. Keys to making this work include: a) applying the first POST application where weeds are less than 4 to 6 inches tall; b) altering the POST herbicide program to take weeds such as lambsquarters into account (adding Harmony or Synchrony), since this weed is usually controlled by PRE herbicides; and c) if needed, making the second POST application about 3 weeks after the first POST application. Don’t guess on this last part – scout field thoroughly 3 weeks after the first application and apply whatever is needed when weeds are still small. Herbicides will make their way through the crop to small weeds. Waiting to spray until weeds are above the crop is a good way to ensure poor end-of-season control.

Wheat Scab Update June 8 2009: Southern States Got Hit Hard - The Value of Planting Resistant Varieties Highlighted in News Release

Authors: Pierce Paul, Dennis Mills, Clay Sneller

Some southern winter wheat states got hammered by head scab. Wheat in parts of Kentucky, Maryland, Arkansas, Georgia, Virginia and North Carolina flowered between late April and the first half of May, at a time when it rained consistently ( Reports from plant pathologist and wheat breeders suggest that the damage currently ranges from moderate to extremely severe in some areas and seems to be getting worst with every new update. Check out the news release on the US Wheat and Barley Scab Initiative website for more details: (

Following are quotes from university and USDA scientists highlighting the value of planting scab resistant varieties.

Christina Cowger, North Carolina State University-based USDA-ARS small grains pathologist, “Severe scab symptoms have been observed in a number of fields of susceptible varieties, while nearby fields of moderately resistant varieties have much less severe scab… most growers did not use scab resistance as a criterion in selecting varieties…”

Don Hershman, University of Kentucky Extension Plant pathologist, “…the situation looked “ugly” in numerous fields… In those cases where fungicides were applied properly in a timely manner, fields visually seemed to be holding up well … Resistant varieties, where used, have also made a difference…”

Jose Costa, University of Maryland wheat breeder, “… high infection levels had shown up at three Eastern Shore yield trial locations ... Differences between susceptible varieties and those with at least moderate resistance were very apparent…”

Reports coming out of Nebraska and Kansas suggest that hard red winter wheat was also affected by head scab in some parts of those states. It is still about a week or two too early to tell whether Ohio and other northern soft red winter states will have a severe scab problem this year, however, early reports coming in from southern Ohio suggest that southern counties may have escaped a scab epidemic.

Very little can be done for wheat after head scab damage has occurred. However, selecting the right variety at planting can be the difference between minor and heavy losses in a severe scab year. Wheat breeding programs across the country, such as OSU/OARDC's, have made great progress developing scab resistant varieties. We now have several moderately resistant varieties with decent yield to choose from. OSU/OARDC recently released two new public wheat varieties, Malabar and Bromfield, which are moderately resistant to scab and yield better than Hopewell. Other moderately resistant varieties include Truman, Bess, Roane and other listed in our wheat performance trial report (

Modified Relay Intercrop Field Day on June 23

Authors: Steve Prochaska, Mike Gastier

Modified Relay Intercropping (MRI) is the planting of soybeans into headed wheat. In north central Ohio, thousands of acres of wheat have been interseeded with soybeans over the last 10 days. There are many permutations of wheat row spacing used in MRI (see for images). An evening field day on MRI has been scheduled for June 23, 2009 at Stieber Brothers Farm, 1457 Schaffer Rd, Norwalk, OH 44857. Program will begin at 7:00 PM and will focus on production factors for wheat and soybeans, equipment options, and the economics of the system. The field day is free and open to anyone interested in this practice.

Directions to Stieber Brothers from the East: Take US Route 20 west of Norwalk to Halfway Road (at drive-in theater). Head North on Halfway Rd 1.5 miles until it dead ends into Settlement Road. Turn right (east) on Settlement Road for 0.5 miles until it turns to the North and becomes Huber Rd. Take Huber Road 2 miles to Schaffer Road which Tees to the right (east). Drive one mile on Schaffer to Stieber Bros. which is on the former site of Stieber Imp.

From the South using Route 4: Bring Route 4 North to US Route 20. Proceed on Route 20 east of Monroeville to Halfway Rd (at the drive-in theater). Then follow the directions above.

If you are familiar with the Milan area, an alternate route to Stieber Bros. is to take State Route 113 2 miles west of US Route 250 to Lovers Lane Rd. which tees to the south. Proceed 2 miles on Lovers Lane Rd. to Schaffer Rd. Turn Right on Schaffer and you will be at Stieber Bros. shop. For more information and a flyer on this event, see

Soybean Aphids Found in Michigan

Authors: Chris DiFonzo

This article posted on the Michigan State University Field Crop Team Alert webpage ( on June 4th, 2009) .

Soybean aphids were found on the MSU campus on Tuesday, June 2, in an early-planted research plot. Beans were nearly V1 (first trifoliate expanded). Aphids were actually fairly common along the edge of the field, with perhaps 5 percent of the plants with an aphid. Aphids tend to land on plants near clean-cultivated borders. We found mature non-winged mothers with new nymphs, so these mothers were deposited perhaps 7-10 days previous. Winged aphids were common too, indicating that there had been a flight of aphids, maybe deposited with a rain event last week. We did not find aphids in a nearby field that was closer to the VC stage, which shows the difference that even a few days emergence can make in early infestations of aphids.

Weather Update

Authors: Jim Noel

The forecast for the 2009 growing season remains on track.

Expect some scattered showers and storms in the north and southeast today and statewide tonight (6/8/09) and early Tuesday (6/9/09). More widespread activity will move through Wednesday (6/10/09) and Thursday (6/11/09) with more early next week.

For the next 2 weeks, expect near normal temperatures and precipitation with rainfall about every 2-4 days.

Maximum temperatures will be a bit below normal with overnight minimum temperatures a bit above normal which will yield near normal.

This trend should continue throughout summer as of now.
No “big heat” is sought to be seen in June right now. About 90 degrees F. should be the upper limit this month, give or take a few degrees from north to south. It does look warmer later next week into the week of June 22.


Archive Issue Contributors: 

Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Peter Thomison (Corn Specialist), Mark Loux (Weed Science Specialist), Jim Noel (NOAA), Chris DiFonzo (Michigan State University Extension Specialist-Entomology) and Bob Nielsen (Purdue University Corn Specialist). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Harold Watters (Champaign), Mark Koenig (Sandusky), Wes Haun (Logan), Jonah Johnson (Clark), Ed Lentz (Seneca), Les Ober (Geauga), Steve Prochaska (Crawford), Gary Wilson (Hancock), Suzanne Mills-Wasniak (Montgomery) and Tim Fine (Miami.)

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.