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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-19

Dates Covered: 
June 23, 2008 - July 1, 2008
Jonah T. Johnson

Hail damage in corn

Authors: Peter Thomison

Some of the recent thunderstorms have been accompanied by hail which has damaged corn in localized areas. 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 V9 plant according to the leaf collar method would probably correspond to a 11-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. This year it’s not unusual to see corn vary by three or more growth stages across fields because of the range in planting dates. 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 V9 stage (as of 6-23-08). Based on estimates of the National Crop Insurance Association, at the 11-leaf stage (or about V9) if 50% of the leaf tissue is destroyed by hail, a corn plant loses about 7% of its grain yield potential; if 100% defoliation occurs, a corn plant loses about 22% 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 6/23/08)

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%
9-leaf (V7)** 1 4 7 13
11-leaf (V9) 1 7 12 22
13-leaf (V11) 2 10 19 34

*as determined using the hail adjustor’s leaf staging method; ** approximate leaf collar stage within parentheses.


Hail damage in corn often results in tied leaf whorls

Authors: Peter Thomison, Todd Mangen

Severe hail damage prior to the 6 to 7-leaf stage (about V5-6 according to the leaf collar staging system) often results in “twisted” or “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

Evaluate early June hail damage to soybeans - By Seth Naeve, Jeff Coulter and David Nicolai, University of Minnesota Extension

*The article below is an excerpt from the University of Minnesota Extension website accessed on June 23, 2008 at 6:11 p.m. at:

ST. PAUL, Minn. (6/10/2008) - Recent severe weather events across the Midwest have left crops in many parts of Minnesota affected by hail damage.
Assessing hail damage to soybeans in early June can be a bit tricky, with many variables to consider on your way to making a final decision to replant or maintain the existing stand.
One helpful resource from the University of Minnesota is the “Soybean Growers Field Guide to Evaluating Crop Damage and Replant Options,” available online at:

Here are a few key steps from that publication:
1. First, estimate the surviving plant stand. Hail damage is highly variable within fields, therefore accurate plant stands must be measured in as many locations within a management unit as possible. Making a replant decision based on a few stand counts near the field entrance will likely lead to a poor ultimate decision.
Count several areas that are equal to 1/1000 of an acre. This is equal to a row length of 17 feet, 5 inches in 30-inch rows, and 23 feet, 9 inches in 22-inch rows. Soybean plants with significant amounts of green tissue remaining (more than one green cotyledon and/or remaining leaf tissue) are likely to survive early season hail damage.
Soybeans can tolerate low populations very well, with only small reductions in yield potential across wide ranges in plant loss. For instance, populations near 100,000 per acre are likely to produce maximum yields, and those around 80,000 will yield about 90 percent of the maximum. However, expected yields drop more rapidly in stands below 50,000, with 39,000 plants per acre likely to produce about 75 percent of the normal yield.

2. Next establish the expected replant date. With widespread rain in the forecast, many fields will not be in condition to plant until after mid-June. Yield potential for late-planted soybeans drops rapidly throughout June. When compared to the yield from an early May planting, yield potentials for June 9, 14, 19, and 24 plantings are expected to be 76, 70, 64, and 57 percent, respectively.

3. Determine replant costs. These will include time, fuel and seed costs. Additional costs may include penalties associated with variety selection when the very best genetics are no longer available. Mid-June replants should utilize soybean varieties that are approximately 0.5 maturity units shorter than full-season varieties adapted to your region. Planting in late June will require a shift of one full maturity unit.

In summary, only those fields with remaining stands below 30,000 to 40,000 plants per acre are likely to produce greater yields when replanted.
Due to increased fuel and seed costs, the economics of replanting will often be cost prohibitive with remaining stands above 30,000. So, take many stand counts throughout the field and carefully weigh the economics of the situation.

Be sure to speak with your insurer and leave appropriate check strips if needed.

Jeff Coulter is a corn specialist with University of Minnesota Extension, Seth Naeve is a soybean specialist with University of Minnesota Extension, and David Nicolai is an Extension educator in crops management.

Scout for European corn borer Damage

Authors: Andy Michel, Ron Hammond, Bruce Eisley

We have begun hearing isolated reports of economic damage from 1st generation European Corn Borer (ECB) larvae. Damage from ECB was spotted in an early planted field of sweet corn (~16 inches tall) in Wayne County and after scouting, was found to be close to the economic threshold. This correlates well from our previous report of seeing the presence of adult moths. Adult moths continue to be caught (67 adults were caught between June 5th and June 15th in Coshocton County) and larvae will continue to hatch, although survival on late-planted corn is reduced.

Transgenic corn containing the Bt corn borer gene is safe from damage by this insect. However, refuge areas, and fields without the gene, especially those few early planted fields, should be checked for first brood borers. Although difficult, egg masses may be found on the underside of corn foliage. If fields are nearing the whorl stage, then signs of early larval activity may be found if one inspects a significant number of plants. If whorl injury (shot holes, pin-holes and window-pane feeding) is apparent, then about 20 plants should be inspected at 5 locations to determine the percentage of stand exhibiting whorl injury. During scouting, a number of whorls should be pulled and opened to determine presence or absence of ECB larvae (2-3 for every 20 plants). When larvae are found, the average number of larvae per plant may be estimated based on the proportion of stand exhibiting whorl injury and the proportion of injured plants actually having larvae present.

Rescue treatment for first-generation control is warranted when 50 percent or more of the plants exhibit feeding damage in the whorl and early instar larvae can be readily found either on the foliage or in the whorl. Treatment must be done before larvae begin tunneling into stalks, where exposure to chemical control is greatly reduced. There are a variety of treatment options available and can be found at: Additional information about ECB can be found at:

Texas, Louisiana and Mississippi are dry; Florida soybean rust levels are very, very low

Authors: Anne Dorrance

Overall soybean rust levels in the southern US are still very, very low. Texas is still reporting only one kudzu patch that is positive for soybean rust and they are hitting a hot dry spell in much of the state. Soybean rust was found for the first time on soybeans in the panhandle of Florida last week. It was only one rust pustule out of 150 leaves. Not much to get excited about from a pathologist’s perspective, nor from an impact towards Ohio soybean production. In the short term forecast, dry weather is impacting soybean production in Mississippi and westward. So for the remainder of this year, it looks like it is going to be a slow build-up of disease in the southern US. Again, our risk in Ohio for soybean rust in 2008 is extremely low for soybeans planted in April through the beginning of June. We will keep monitoring soybean rust in the south through the summer to assess the risk for our late planted and double crop soybeans. For now, the sentinel plots in Ohio, growth stages range from V1 to V3 with NO disease present across the state; not even brown spot!

Seedling diseases are doing well this year

Authors: Anne Dorrance

Soybean stands across the state fall into two categories: beautiful or ratty. Both types of fields can be found across the state. For the most part, Pythium spp., Phytophthora sojae and flooding injury are all culprits contributing to the “ratty” stands. This is one case where seed treatments can minimize the number of replants in many of these situations.

Here in the lab, we routinely bait these seedling pathogens from soils collected across the state. First, we dry the soil down and grind it and place it in plastic pots. We have to grind it to break up all of the clay chunks so we can mix it and actually get the soil into pots. The next step is to flood the soil for 24 hours, then incubate it for at least 2 weeks. The soil remains moist and a bit sticky during this time period. The next step is to plant and then flood again about 3 days after planting. We get lots of diseases when we follow this scenario; we get more diseased plants if we take those pots, plant them again and re-flood them. Sound like some of our field situations this year? If the pots dry out between plantings, we need to start the flooding and incubation process all over again.

Seed treatments can protect seeds and seedlings in the situations where a field never truly dries out (you plant it and it rains again before those seedlings emerge). Very similar to what we have had in many locations this year. Some areas of the state are reporting 20 to 30% replant and they are looking at going in again into the same field areas. If the hole or spot in the field ends up submerged where a pond forms for several days, then the seed treatment is not going to help. In this situation, flooding is the culprit and focus needs to be given to drainage. Improving the drainage in that area of the field will be a better use of time and money.

Rainfall and Nitrogen Loss, Should I Be Concerned?

Authors: Edwin Lentz, Keith Diedrick, Robert Mullen

Some producers applied some nitrogen the past few weeks and are concerned about nitrogen loss; the question is was my nitrogen at risk for loss? This is a complicated issue that we will try to clarify and help you determine your risk of loss (because we cannot tell you exactly how much was lost). The following flowcharts were developed to help you determine your actual risk.

Notice the primary factors being considered are how long the nitrogen was out in the field prior to the rainfall events and how long the soil was saturated. The reason for concern regarding length of time between application and rainfall is how much of the total nitrogen was at actual risk for loss. The only form subject to loss is nitrate (ignoring volatilization losses), so that is the only fraction of concern. The speed of transformation to nitrate is dependent upon the form applied. Anhydrous ammonia converts relatively slowly to nitrate, so it remains in the ammonium form longer (less susceptible to loss). Urea-ammonium nitrate contains 25% nitrate that is capable of being lost immediately so the time factor is shorter. Urea or ammonium sulfate must be converted to nitrate and that takes some time even under warm soil conditions, but the conversion occurs faster than anhydrous ammonia nitrogen. The other factor of interest is the period of water saturation; the longer the soil is saturated, the greater the risk of nitrogen loss.

A minimal risk of nitrogen loss translates into very little risk of loss of a large amount of applied nitrogen. Some may have been lost, but the amount would be considered negligible. Moderate risk means some nitrogen was lost, and the crop should be monitored closely to determine if additional nitrogen supplementation is necessary (i.e. tissue analysis). A substantial risk means that supplemental nitrogen is likely needed to ensure adequate nutrition for the plant, and producers should monitor the crops closely. This does not mean that another large application rate is necessary. Based upon a study conducted in Illinois in the ‘90s, an application of 50 pounds of nitrogen per acre was usually adequate to achieve maximum corn yields in clay soils.

For Flow Charts 1-3, see Blog site: for full article. Click on thumbnails for a full screen view!

Western OARDC Agronomy Field Day and New Building Dedication

Authors: Jonah Johnson

Come one come all to Western OARDC in South Charleston, OH for their new building dedication followed by a very informative afternoon Agronomy Field Day! Western Branch’s new facility represents an investment of $850,000, which includes office space, a conference room, seed storage, and equipment maintenance shop as well as machinery storage. This grand facility will replace outdated buildings that were constructed in the mid-1960s. The dedication begins at 10:00 a.m.

Following the dedication will be this year’s “Agronomy Field Day” from 2:00 p.m. - 5:00 p.m.
See and talk about this year’s field conditions with OSU Extension specialists and scientists from OSU Extension and O.A.R.D.C. Topics that will be discussed are: Weed control Issues for 2008, Nitrogen Management in a Global Economy, Corn Disease Management, Current and Future Corn Insect Concerns plus specialty crop information on pumpkin and sweetcorn production!

There will be wagon transportation and free refreshments.

Please RSVP for the dedication ceremony so we can plan for lunch: e-mail, or call 330-263-3771.

Modified Relay Intercropping Program at Schlessman’s Seeds - June 26

Authors: Steve Prochaska

Soybeans are growing in wheat fields on north central Ohio farms. This planting of soybeans into standing wheat is called Modified Relay Intercropping (MRI). A program on MRI will be held on June 26, 2008 at Schlessman’s Seeds which is located on the corner of Hoover and Mason Roads north of Milan, Ohio. The MRI session will begin at 11:15 AM. For additional information on the field day contact either: Steve Prochaska, OSU Extension, at or call Larry Craft of Schlessman’s at 419.366.6917.

Harvest aids for wheat

Authors: Mark Loux

Several herbicides are approved for application to mature wheat to prevent weeds from interfering with harvest. Ragweeds, thistle, and lambsquarters are some of the weeds most likely to be a problem at the time of harvest, especially where wheat stands were not of uniform density. Take precautions to reduce spray drift when applying harvest aids, since sensitive crops and other desirable plants are likely to be growing in adjacent areas. Some specifics on the application of harvest aids follow (consult labels for more information).

- Various 2,4-D products are labeled as harvest aids at rates of 0.5 to 1.5 lbs ai/A, depending upon the product. 2,4-D can be applied with ground or aerial equipment after wheat has reached the hard dough stage. Some labels advise that crop injury can occur, and spot treatments should be used to minimize the extent of injury. Do not feed wheat straw to livestock where 2,4-D is applied as a harvest aid. Amine formulations have less potential than ester formulations to volatilize and move off-target, but spray particle drift is possible with either.

- Many glyphosate products can be applied as a preharvest treatment in wheat for control of annual and perennial weeds. Application rate is 0.75 lb ae/A, which corresponds to 22 oz of PowerMax, 24 oz of Durango and Touchdown products, and 32 oz of products that contain 3 lbs of glyphosate acid per gallon (Buccaneer, Credit Extra, Glyfos, etc). Apply at least 7 days prior to harvest, and after the hard dough stage when grain moisture is 30% or less. Glyphosate can be applied with ground or aerial equipment, and some glyphosate products can be mixed with 2,4-D. Wheat grown for seed should not be treated with glyphosate.

- Several premixes of dicamba and 2,4-D (WeedMaster, Brash, etc) can be applied at least 7 days before harvest when wheat is in the hard dough stage, and after all green color has disappeared from the nodes of the wheat stem. This product can be mixed with glyphosate. Do not use treated wheat for seed unless a germination test is performed on the seed prior to planting.

- Aim can be applied as a preharvest treatment at the rate of 1 to 2 oz/A, but is likely to have a more narrow spectrum of activity compared with other products mentioned here. Apply at least 3 days before harvest with nonionic surfactant or crop oil concentrate.

Mid-season management of glyphosate

Authors: Mark Loux

Most of the early-planted soybeans should have already been treated with post-emergence (POST) herbicides at this point in the growing season. The results of weed-crop interference studies show that weeds should be treated with herbicide before they exceed a size of 6 to 8 inches in order to ensure that weed interference is not a limiting factor in soybean yield. Weeds may not have reached this size in later-planted soybeans, or where pre-emergence herbicide activity reduced weed populations and growth. Some points to consider in the management of post soybean herbicides:

1. It is possible to apply POST herbicides too soon after planting in early-planted soybeans, and the end result can be the need for a second POST herbicide application to control later-emerging weeds. However, the risk of applying too early decreases when soybeans are planted in late May or in June, since weed emergence tends to peak about this same time. Soybeans treated POST for the first time in late June are subject to much less weed re-infestation. Bottom line – in later planted soybeans, POST herbicides can be applied sooner after planting when weeds are small, which maximizes POST herbicide activity and reduces the need for higher glyphosate rates.

2. Glyphosate rates should generally be based on weed size and age, environmental conditions, and the previous history of glyphosate effectiveness in the target weed population. If is possible to use the lowest labeled rate of glyphosate, 0.75 lba ae/A, and these are the factors that can make it possible to do so: weeds are less than 6 inches tall; weeds have not survived tillage or a previous herbicide application or other stresses that “age” them and reduce sensitivity to herbicides; glyphosate is applied following use of a pre-emergence herbicide that reduced the number and size of weeds; and environmental conditions are extremely favorable for herbicide activity (warm temperatures, moderate to high humidity, and adequate soil moisture). Increasing the glyphosate rate to 1.1 to 1.5 lbs ae/A can greatly increase effectiveness when weeds are more than 6 inches tall and/or other conditions are not optimum for herbicide activity. Our research with glyphosate resistance clearly shows that in any situation where glyphosate activity could be reduced (large weeds, drought stress, low level resistance), most effective control results from using a high glyphosate rate in the first post-emergence application, and following with a lower rate in a second application if needed. Using a low rate in the first application and then trying to “bail out” the resulting poor control with a second application at a higher rate will have a much lower rate of success.

3. Where a second post-emergence glyphosate application is needed to control plants that survived the first application, our research indicates that about three-week intervals between application may result in the best control. This provides time for plants to resume growth after the first application so that glyphosate can have activity in the plant, but does not allow time for plants to regrow to a large size. Waiting until enough regrowth occurs so that plants can be seen above the crop from a road survey is not the best approach. Applying the second glyphosate treatment too soon after the first is also not optimum, since plants that have not recovered from the first application cannot respond to the second.

4. Deciding how to manage glyphosate in soybean fields with a history of poor glyphosate performance can be more involved than just increasing rates. It is possible for glyphosate to provide adequate control of populations that have a low level of glyphosate resistance. This can be achieved by making the first application of 1.5 lbs when plants are small, and following with a second application at 0.75 lb about 3 weeks later. Weed populations with a higher level of glyphosate resistance (fields where glyphosate has largely failed on at least part of the weed population in a previous year) will require treatment with a full rate of an alternative to glyphosate. In this situation, adjuvants should be selected to optimize the activity of the alternative herbicide. For example, Flexstar can be added to glyphosate in a field where giant ragweed is resistant to glyphosate, and this mixture should be applied with MSO and AMS to optimize the activity of the Flexstar.

5. In situations where conditions are less than ideal for herbicide activity, full rates of true AMS (ammonium sulfate) may be more effective than AMS substitutes or products than contain reduced rates of AMS. The same holds true when mixing glyphosate and manganese in foliar applications.

6. Glyphosate activity can increase when applied in low spray volumes, but this has to be balanced against the need for penetration of spray into dense weed/crop canopies or to obtain better coverage of large weeds. For the latter situations, it’s possible that spray volumes of 15 to 20 gpa may be more effective than 10 gpa or less. Be cautious also of using too many drift-reduction measures, such as combinations of low drift nozzles and drift-reducing agents. This can result in too few droplets of too large a size, which can reduce control.

7. Increasing the rate of a glyphosate product applied will usually be more effective than adding nonionic surfactant. Most glyphosate products already contain a relatively high concentration of surfactant. Increasing the rate of product applied results in the application of higher rates of both glyphosate and the surfactants that are part of the formulation.

8. The time of day of application affects herbicide effectiveness. Previous research by OSU and other universities has shown that activity can be reduced when herbicides are applied in early morning or in the evening (or at night). We have observed this with glyphosate, Flexstar, and FirstRate, and we assume most other POST herbicides are similarly affected. A general rule of thumb that might avoid most problems due to time of day effects: avoid POST herbicide application before about 7:30 in the morning or after about 7:30 in the evening.

Weather Update

Authors: Jim Noel

Past Week:
During the past week we saw below normal temperatures and normal to below normal rainfall. Most places saw 0.25 to 1.0 inches of rain with a few isolated areas that received 2 inch or more in total rainfall.

This week:
A cool start to the week will turn warm and humid. Some scattered light activity today will turn to dry weather Tuesday and most of Wednesday. However, an active pattern of storm clusters will move across the area Thursday through Saturday. Some areas could receive 3-6 inch rains with most places receiving at least an inch. The greatest risks for the heavy rainfall later this week appears to be western and southern Ohio.

Next week:
It starts cool again with high in the 70’s and lows in the 50’s but turns warm and humid again with highs back to 85-90 degrees and lows around 65-70 degrees by late in the week. Rainfall looks to be near normal and mainly in the second half of next week.

Next month:
Overall, expect near normal temperatures and rainfall. However, there is still risk for above normal rainfall in areas. The risk for hot and dry weather looks to be rather low at this point through the month of July. Bottom line, there is a greater risk of wetter versus drier conditions for the next 30 days with the most likely outcome close to normal. The risks for above or below normal temperatures appear close to even with a slightly higher risk of below normal. Therefore, we expect close to normal temperatures and rainfall; but wanted to give you all which side we could error on.

Upcoming OSU Agronomic Field Day Events

Great Lakes Manure Handling Expo - July 9th, 2008
Start Time: 8:30 am - 5:00 pm
County of Meeting Location: Madison

Name of Meeting Place: Molly Caren Agricultural Center
Meeting Place Address: State Route 40
Meeting Place Town: London, OH
Cost: Free to the public
No Private or Commercial PAT credits offered.
Meeting Coordinator Name: Mary Wicks or Jon Rausch
Phone Number: 330-202-3533 or 614-292-4504
e-Mail: or
Agenda Web Link:

OSU Extension Weed Science Tour - July 9th, 2008
Start Time: 9:00 am - 3:00 pm
County of Meeting Location: Clark

Name of Meeting Place: Western OARDC
Meeting Place Address: 7721 South Charleston Pike
Meeting Place Town: South Charleston, OH
Cost: Free to the public

Meeting Coordinator Name: Mark Loux
Phone Number: 614 - 292-9081


Archive Issue Contributors: 

Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Jim Beuerlein (Soybean & Small Grain Production), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Mark Loux (Weed Science)and Jim Noel (NOAA). Extension Agents and Associates: Jonah T. Johnson (Clark), Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Greg LaBarge (Fulton), Steve Foster (Darke), Harold Watters (Champaign), Mike Gastier (Huron), Wes Haun (Logan), Les Ober (Geauga), Steve Bartels (Butler), Alan Sundermeier (Wood), Gary Wilson (Hancock), Todd Mangen (Mercer), Steve Prochaska (Crawford), Tim Fine (Miami) and Suzanne Mills-Wasniak (Montgomery).

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.