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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2010-13

Dates Covered: 
May 17, 2010 - May 25, 2010
Glen Arnold
Wheat Head Scab Risk for Ohio as of May 17, 2010 wheat heads in flower

Wheat Head Scab Risk for Ohio as of May 17, 2010

Reports from Southern Ohio indicate wheat has entered the flowering growth stage, making the crop vulnerable to Fusarium head blight (head scab). For wheat flowering between May 14 -17, the risk assessment tool ( indicates a low risk of scab for the majority of Ohio. The tool uses weather conditions seven days leading up to flowering to calculate risk. In general, prolonged periods of warm and wet conditions increase the risk of scab. Cool weather last week and dry conditions experienced over the weekend have minimized the scab risk. Since May 1, we have had fairly frequent, but variable amounts of rainfall, ranging from 0.05 to a little over 3 inches, depending on where you are in the state. During this same time, temperatures have been on the cool side, with an average high of 66 F and low of 47 F. So even though it may be raining today, the previous six to seven days have been cool, with several days without rain.

A moderate scab risk is predicted for portions of Lawrence and Gallia counties (just north of Huntington, West Virginia) for wheat flowering on May 17-18. Please check the risk assessment tool frequently over the next few days to monitor your scab risk level. If wet, humid conditions continue, the scab risk may increase and spread to other wheat-growing counties in Southern Ohio. A well timed fungicide application at flowering will reduce scab severity and vomitoxin contamination. Please contact your local extension educator and state specialist to discuss your concerns and management options.

If it warms up over the next few days, current rainfall patterns may increase the risk of scab in areas of Central and parts of Northern Ohio, where the wheat will likely begin to flower by the end of this week. For instance, in Wooeter, the forecast is for more rain today, 50% chance of rain over the next two days, followed by a dry day, and then more rain the following two days. Temperatures are forecasted to reach mid 70s later this week. So, if the forecast is true (worse case scenario) and your wheat flowers on Friday of this week, you would have had 6 out of 7 days with some rain by the time your crop flowers. As your wheat approaches flowering, check the risk tool frequently. You may use up to 72 hours of forecasted weather data to predict scab risk. We will continue to monitor the scab risk in Ohio and provide updated commentary and alerts.

An Ohio Factsheet for Head Scab is located on the Ohio Field Crop Disease web site. Go to the front page "Wheat Fusarium Head Blight Prediction Center" and click on (Fact Sheet)

Wheat Scab Risk: Commentary and Scab Alert in your Pocket

The wheat scab risk assessment tool ( uses weather conditions for seven days leading up to flowering to wheat head at flowercalculate the risk of scab. Once a flowering date is selected, the map will show color changes corresponding to the relative risk in your part of the state, with red indicating high risk, yellow moderate risk, and green low risk. To aid in the assessment of scab risk and interpretation of the risk tool, your state extension specialist will provide commentaries at the bottom of the risk maps. As the wheat growing season progresses, commentaries will be updated regularly to inform producers of the risk of scab occurring as weather conditions change and the crop begins to flower. These comments will help users assess risk both on the map and local observations made by the state specialist and extension educators. The commentary will also provide information regarding observations of crop growth, weather patterns and other diseases of importance in the State.

In addition to the commentaries on the scab website, the US Wheat and Barley Scab Initiative ( just launched SCAB ALERT. With scab alert producers, crop consultants, grain processors and others in the wheat industry can stay up-to-date on the scab situation, even when they are away from their fields and computers. According to Dave Van Sanford, co-chair of the USWBSI, SCAB ALERT was developed to provide advance notice of the risk of a scab outbreak by way of cell phone to those who sign up for the service. You can sign up by going to and you will receive real-time alerts via cell phone and/or email based on the commentaries provided on the scab risk tool by state specialists. You can customize SCAB ALERT to meet your needs by choosing what you want to receive (by regions) and how it should be sent to you (cell phone, email or both).

Another tool now available to help you manage scab is SCAB SMART. Hit the following link and you will find information on best management practices for scab using Fungicides (timing and application technology), variety resistance (based on data from our wheat performance trials), crop rotation, residue management, planting date, and harvest practices.

No Soybean Rust in Southern US

As of Friday, May 14th, no soybean rust had been identified in the southern Gulf States. Soybean sentinel plots are planted and they are at early vegetative stages and the kudzu has recovered from the cold winter and is growing strong. As Dr. Ed Sikora states, most of the first finds in Alabama, Florida, and Louisiana have been in late May to early June.  The weather has been favorable. But for Ohio this indicates a very low risk that soybean rust will be an issue during our production season in 2010.

Soybean Seedling Diseases – Rain Favors the Water Molds

Cool soil temperatures, and saturated soil conditions are very favorable for many of our soil borne pathogens. These are the conditions which favor the germination of many of the survival structures. Seed rot and damping-off are the key symptoms. If the hypocotyl has a brick-red lesion it is likely that it was caused by Rhizoctonia seedling blight. If the plant is brown, this is most likely caused by Pythium spp. and/or Phytophthora sojae. For Phytophthora sojae, on heavy ground with a history of Phytophthora the high rate of metalaxyl (1.5 fl oz/cwt) or mefenoxam (0.64 fl oz/cwt) is needed. The graph is a bar chart of a new metalaxyl product which shows the benefit of the higher rate.

Fungicide rate table

When replanting occurs, remember the pathogens are ready to go. Conditions have been favorable for the pathogen, so it is even more critical to use a seed treatment for replanting. Areas of the field where flooding or plants were submerged in water are another issue. Where flooding has occurred, the epidermis is killed and you can easily pull this off the roots and expose the root stele (center) which is white. If it is was infected with a pathogen, all of the root will be brown and totally missing.

Late Spring Plantings and Insects

As was the situation last year, we have seen an increase in the frequency of rainfall in Ohio the past couple of weeks, and many fields still need to be planted. We published an article at this time in 2009, and realized it was relevant again this year.  Because of the continued rainfall and what will be late plantings for many fields, a portion of the corn and soybean crop will be relatively short in height and growth going into late May and early June. However, the insect populations are somewhat on schedule. Growers should be aware that the presence of smaller plants can intensify the injury that can occur. Many of our thresholds relate to the size of the plants, and thus, later planted crops will be at a higher risk of economic damage. On corn for example, the black cutworm threshold, 3% or more plants cut or tunneled and larvae still 1 inch or less, is for plants in the second to sixth leaf stage. Some of the corn will not even be reaching the second stage for a few weeks considering some of it is not yet emerged or even planted. On soybean, slugs, as well as bean leaf beetles, are more damaging to plants that are recently emerged with unifoliate leaves just opening. We would suggest that growers check their late planted fields as they begin to emerge to prevent unexpected injury from insect pests that would not be of much concern if crops had been planted earlier. See our Agronomic Crops Insects website,, for information on many of our common pests, including fact sheets, thresholds, and insecticide recommendations.

Slugs in mid-May slug on soybean plant

Slugs in mid-May

Although we are just at the beginning of slug season in field crops, we are already getting more reports this year of heavier slug populations that. These reports include not only more fields being affected, but also what appear to be heavier slug populations. Some crop consultants fear more slug problems than they have seen in the past few years. No-till growers, especially those who have experienced slug issues in the past, should be checking their fields for building slug densities and injury. Read the other insect-related article in this issue that discusses late plantings; those fields will be much more susceptible to slug damage. See our Agronomic Crops Insects website,, for more information on slugs in corn and soybean. If applications of molluscicide baits are made, remember the need for good, even coverage to obtain acceptable control.

corn with slug feeding

Higher Seeding Rates - Higher Nitrogen Rates?

A common question of late from growers and consultants is whether or not nitrogen rates should to be adjusted higher for corn when seeding at higher rates. Though it seems that additional nitrogen would be necessary to feed more plants per acre to an equivalent level of fewer plants, yield data from a number of experiments does not clearly indicate that this is the case.

Ohio State University has conducted field research the last four years at the Northwest Research Station near Custar, OH on the impact of seeding rate on nitrogen rate response. Two different cropping rotations were evaluated – corn after soybeans and corn after corn. The two seeding rates used were 30,000 and 40,000 seeds/acre. In 5 out of 8 site-years, seeding rate had no impact on fertilizer N response (the optimum N rate was similar regardless of seeding rate). When there were differences in optimum N rates, it was not because the higher seeding rate required more N. Only 1 out of the 8 site-years (2006 for corn after corn) revealed that the higher seeding rate required more N.  In only 2 out of 8 site-years was there a yield increase associated with the higher seeding rate (that being 2007 for both rotations).

From a study conducted at Purdue (2005, 2006, and 2007 seasons), three seeding rates and three nitrogen rates were studied: 21,900, 32,000, 42,000 seeds/acre, and 0, 147, 295 lb/acre N. In two of the three years, the 42,000 seeding rate yielded significantly better with 295 lbs N/ac than 42,000 seeds at 147 lb N/ac. However, grain yields were consistently higher or similar at 32,000 seeds/acre at either nitrogen rate compared to yields from the 42,000 seeds/acre rate. Higher seeding rates were more responsive to N, but there was no yield advantage when compared to the lower seeding rate at lower N rates.

The take-home message is that higher seeding rates do not necessarily require higher nitrogen rates. Based upon the current scientific evidence, higher seeding rates also do not necessarily translate into higher yields. Thus, the lack of increased demand for fertilizer N from the crop is not that surprising. Even in environments where higher yields were achievable with higher seeding rates (2007 at the Northwest Research Station) higher fertilizer N rates were not necessary.

Source: Boomsma, et al. 2009. Maize Morphophysiological Responses to Intense Crowding and Low Nitrogen Availability: An Analysis and Review. Agronomy Journal 101: p.1426–1452. Available for public access at:

Corn Replanting Considerations

There’s littleevidence that most corn plantings in Ohio have been jeopardized by the cool temperatures and wet soils we’ve experienced during the past 1-2 weeks. However, there are fields that may have been adversely affected by localized ponding and protracted saturated soil conditions. Freeze injury followed by heavy rains or brief flooding may have also predisposed some corn to bacterial soft rots. Farmers confronted with poor stands due to these conditions, as well as other problems that affect corn stands, may be considering replanting  their fields.

Replant decisions in corn should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. Don’t make a final assessment on the extent of damage and stand loss too quickly. For more on assessing low temperature and ponding effects on corn survival, consult recent newsletter articles (;

The following are some guidelines to consider when making a replant decision. If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:

  • Original target plant population/Intended plant stand
  • Plant stand after damage
  • Uniformity of plant stand after damage
  • Original planting date
  • Possible replanting date
  • Likely replanting pest control and seed costs

To estimate after‑damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient. Table 4-12 in the OSU Agronomy Guide (on-line at shows row lengths required to equal 1/1000 acre when corn is planted at various row widths.

A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Table 4-15 in the OSU Agronomy Guide is a chart developed by Dr. Emerson Nafziger at the University of Illinois (on-line at that show effects of planting date and plant population on final grain yield for the central Corn Belt. Dr. Bob Nielsen has modified this table to provide estimates of potential yield losses for planting dates in early June (on-line at

Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.

Here's how the table from the OSU Agronomy Guide ( can be used to arrive at a replant decision. Let's assume that a farmer planted on April 30 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 4-15, the expected yield for the existing stand would be 82% of the optimum. If the corn crop was planted the next day on May 29, and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting would be negative (81 minus 82, or minus 1 percentage point) and indicate no advantage to replanting.

However, it’s also important to note plant distribution within the row. Remember that values in replant charts like Table 4-15 from the OSU Agronomy Guide are based on a uniform distribution of plants within the row. Add a 5% yield loss penalty if the field assessment reveals several gaps of 4‑6 feet within rows and a 2% penalty for gaps of 1‑3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction. It’s also important to consider the condition of the existing corn.

When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio.

You also need to review herbicide and insecticide programs under late‑planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control. Concerning insect control, if soil insecticides were applied in the row at initial planting, check insecticide label restrictions before re‑application. Also remember that later May and June planting dates generally increase the possibility of damage from European corn borer (ECB) so planting ECB Bt hybrids is often beneficial.

The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is.

Ugly Duckling Corn & Frost Damaged Soybeans

Issue 7 of the Purdue University Crop & Pest Newsletter had an excellent article on how ugly-duckling corn (due to frosty weather and saturated soils we are dealing with) can still produce swan-like yields. Bob Neilson reminds us the true yield potential of corn is still yet to be determined. 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. Favorable weather during pollination and grain fill finish off the final yield of the crop.

Shawn Casteel also wrote an article in the same newsletter concerning soybeans surviving the recent cold snap. There have been scattered reports across Ohio of soybeans being damaged or killed by the frost last week. His article shows pictures of soybean plants that will recover from the frost and soybean plants that will not recover. Essentially the soybean plant will die or is already dead if the hypocotyl (the stem of the plant) is discolored or water-soaked. These articles can be found on the Purdue website:


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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.