CFAES Give Today
Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2012-11

Dates Covered: 
May 1, 2012 - May 7, 2012
Steve Prochaska
Ohio Wheat Crop is Ahead of Schedule. Is that Good or Bad?

Ohio Wheat Crop is Ahead of Schedule. Is that Good or Bad?

On Friday April 27, wheat heads were observed in some fields in southern Ohio (Figure 1). This is about two weeks earlier than expected. With the warm temperatures forecasted for the next few days, these fields will likely reach flowering within the next week or so. Producers are asking whether such early development will likely have a negative effect on their crop. There is no easy answer to such a question; it all depends on the weather conditions over the next several weeks.

If cool weather occurs during most of the month of May, this will extend the grain fill period. Cool conditions will also reduce the development of foliar and head diseases such as Stagonospora and head scab, especially if it remains dry. Extended grain fill coupled with low disease severity will likely lead to higher grain yield and quality. However, wheat heading or flowering at the end of April or in early May is at greater risk for freezing injury. The forecast was for temperatures in the low 30s during the weekend of April 28-29. Two hours or more of exposure to 30o F could cause severe damage to wheat at the heading growth stage. Less injury could be expected if plants are exposed to less than two hours of freezing temperatures. In addition, since the development of the crop is never uniform across a wheat field (secondary tillers are usually delayed in development), it is highly unlikely that entire fields would have been affected if temperatures did indeed reach the lower 30s. Wheat at earlier growth stages (Feekes 8-10) would have only suffered freezing injuries if temperatures had dropped below 30o F.

High temperatures (> 85 F) over the next few weeks could also have a negative effect on the crop, especially if conditions are wet and humid. Warm temperatures will reduce the grain fill period, reducing grain yield and quality. But most importantly, warm, humid conditions favor disease development, and if not managed with a well-timed fungicide application, further grain yield and quality losses will likely occur. Scout fields for foliar diseases and visit the head scab forecasting website ( to determine the risk of head scab. If the risk of scab is moderate to high, apply Prosaro or Caramba at flowering (Feekes 10.5.1). These fungicides, applied at this growth stage, will give you the best results in terms of scab and vomitoxin reduction. An application made at Feekes 10.5.1 also usually provides adequate control of Stagonospora glume blotch and leaf rust.       

Wheat Head Scab Forecasting and Alert Systems 2012

Wheat is already at the heading growth stage in southern Ohio and will likely reach flowering within the next week or so. In the Northern half of the state, wheat is between Feekes 8 (flag emergence) and Feekes 10 (boot). This is the time to start monitoring the risk of Head Scab and vomitoxin in order to make a fungicide application decision. Wheat is most susceptible to scab during the flowering growth stage, especially if conditions are wet and humid. The scab fungus infects the heads when wet, humid conditions occur during flowering (when anthers and seen sticking out of the heads), leading to yield loss and vomitoxin contamination of the grain. The best and only way to protect your crop against head scab once it is already in the field is to apply a TRIAZOLE FUNGICIDE (Prosaro or Caramba) AT FLOWERING. Earlier applications will not control scab or vomoitoxin. No fungicide will provide 100% control of scab, but will certainly reduce disease and vomitoxin levels. However, the decision to apply a fungicide for head scab control is not always that straightforward. It has to be made at flowering, well before the disease develops and before the producer knows if it will actually develop.

The Wheat Scab forecasting system ( is up and running and is now available for use in Ohio. This is an excellent tool to help guide fungicide application decisions. Based on the flowering date of his/her crop and the weather conditions leading up to flowering, a producer can estimate the risk of scab occurring and make a timely fungicide application to control scab and vomitoxin. The commentary section at the bottom of the forecasting website provides up-to-date information to help producers assess the risk of scab and decide if a fungicide should be applied. You can also gain access to these commentaries directly on your cell phone or via email. Commentaries will be updated regularly and sent directly to the emails or cell phones of those who sign up to receive the alerts. Once there is cell phone coverage and email access, you will receive the alerts anywhere in the country. You can then visit the website to see whether your crop is at risk and contact your state specialist for more information.

To sign up, click on this link: and complete the form with your name, email address, cell phone number and other requested information. You can choose whether you want to receive the scab alert via email, test message (on your cell phone), or both. You can also choose whether you want to receive alerts from all over the country or only from the Mid-West / Mid-South Soft Winter Wheat region.    

New Wheat Disease found in Kentucky - Could it be in Ohio?

A news release from University of Kentucky ( reports the occurrence of wheat blast (caused by the fungus Magnaporthe oryzae/Pyricularia grisea), a disease that has caused up to 40 to 100% crop loss in South America. Could it be that wheat blast is already present in Ohio? We do not know. It is important for us to know if the disease is already present in Ohio in order to determine whether our wheat crop is at risk and to develop appropriate management strategies.

As is often the case with most new diseases, we do not know how susceptible our varieties are to wheat blast, how well it will develop under conditions in Ohio, or whether it will survive our harsh winters. We encourage Ohio wheat producers, extension educators, and crop consultants to scout fields for bleached, discolored heads and send samples to the cereal pathology lab for analysis. In particular, begin scouting fields shortly after heading, since wheat blast is believed to develop earlier than head scab, which typically develops about three weeks after flowering. In addition, scout ryegrass fields for gray leaf spot, which usually shows up as elliptical or roughly diamond-shaped, grayish to tan lesions on the leaf, with a thin, brown border. Send wheat head and ryegrass leaf samples to:
Pierce A. Paul
Department of Plant Pathology
115 Selby Hall
1680 Madison Ave.
Wooster, Ohio 44691 

According to Dr. Don Hershman and colleagues from UK, “wheat blast was found on a single wheat head on May 18, 2011 at a UK Research and Education Center research plot in Princeton. No additional instances of the disease were found even after extensive scouting of the involved research plots and neighboring fields by UK researchers. It is likely, however, that additional infected heads existed but at levels too low to make detection possible.”

Although the Kentucky find was the first documented occurrence of wheat blast in the US, related fungi have been causing gray leaf spot on annual and perennial ryegrass and blast on rice in the US for years. According to a UK Plant Pathologist, Mark Farman, the wheat blast fungus discovered in Kentucky is genetically very similar to the fungus causing gray leaf spot on annual ryegrass. Farman believes that over the years, the ryegrass fungus has gained the ability to infect wheat, and suggests that the fungus did not likely come from South America, but has existed in the US for more than a decade.

Researchers in the Department of Plant Pathology at Ohio State have been studying a related disease, rice blast, for several years, and more recently, have been collaborating with scientists at UK, Kansas State, and in Brazil to study wheat blast. These researchers hope to use the knowledge gained studying rice blast to better understand wheat blast, including 1) how the fungus evolved from a ryegrass pathogen to become a wheat pathogen; 2) how and when it infects wheat, important for developing fungicide application programs; 3) what conditions are necessary for it to develop, important for predicting when and where it will occur; and 4) how wheat defends itself against the fungus, important for developing resistant varieties. For this, it is important for us know whether wheat blast occurs in Ohio, and if so, whether the Ohio population of the fungus is similar in terms of genetics, temperature and moisture requirements, and ability to cause disease to populations in regions where wheat blast is already problem.

Spring Field Crop Insects Update

With planting occurring at full speed, all crops might be planted within the next few weeks.  This is the time of year that numerous insect pests should be taken into consideration when monitoring crop emergence and early plant growth.  We brought this concern up on April 10 in CORN #8, and thought it appropriate to bring it up again because it is now the time to consider and be scouting these potential pests.  See for information on all the pests, thresholds, and treatment choices. 

Black Cutworm on Corn – this past warm spring allowed for an early migration of adult moths into the Midwest, with some states observing more than usual.  Growers should plan on scouting for early signs of plant cutting as corn begins to grow, and use established thresholds to determine need for treatment.  Based on experience, we would recommend scouting all corn at risk:  especially corn planted no-till into weedy fields,  and do not exclude scouting any seed treated corn and/or transgenic hybrids. 

Corn Flea Beetle on Corn – because of the warm winter, corn flea beetle might be heavier than normal, and should be monitored. 

Cereal Leaf Beetle on Wheat and Oats – although we have had no reports yet of problems, we have heard of eggs and young larvae on wheat.  Growers should plan on scouting their wheat and oats over the next week as temperatures begin to warm for signs of larger larvae and feeding injury.  The threshold for this insect in Ohio is set at 1 larva per stem. 

Slugs on Corn and Soybean– because of the warm winter and March, we would expect slugs to hatch out earlier this spring and begin their feeding sooner.  We would recommend to growers who have experienced slug problems to keep a closer watch on their fields. 

Bean Leaf Beetles on Soybean – with the warm winter, we also expect these pests to arrive earlier in soybean fields, perhaps in slightly higher numbers.  However, it appears that most areas have a large amount of their soybeans already planted and ready for emergence.  Experience shows us that the more fields of soybeans in an area, the more the overwintered beetles spread out over all those fields, with few fields getting large numbers.  Remember that the threshold is are over 50% defoliation or obvious stunting of the young plants, which hopefully will be uncommon this year with the amount of soybeans already planted.  

Insects on Alfalfa – although most first cuttings are soon to occur, we have received some reports of alfalfa weevil reaching treatable levels.  Prior to treating, decide if the alfalfa is tall enough to cut, and if so, consider early cutting.  If early cutting is done, scout the regrowth for possible continued feeding by weevil larvae.  Also, following the cutting, remember that potato leafhopper will be occurring shortly, which will be discussed in future C.O.R.N. newsletter.


Corn Emergence and Heat Unit Accumulation

The cold weather of the past week slowed corn germination and emergence. According to NASS ( estimates as of April 29, 57 percent of the corn crop in Ohio has been planted, but only 6 percent has emerged. Much warmer temperature forecast this week should accelerate emergence.

Corn typically requires 100-120 growing degrees days (GDDs) to emerge (but emergence requirements can vary from 90 to150 GDDs). To determine daily GDD accumulation, calculate the average daily air temperature (high + low)/2 and subtract the base temperature which is 50 degrees F for corn. If the daily low temperature is above 50 degrees, and the high is 86 or less, then this calculation is performed using actual temperatures, but if the low temperature is less than 50 degrees, use 50 degrees as the low in the formula. Similarly, if the high is above 86 degrees, use 86 degrees in the formula.

If it takes a corn hybrid 110 GDDs to emerge, and daily high and low temperatures average 70 and 50 degrees following planting, 10 GDDs accumulate per day, and corn should emerge in about 11 days (110 GDDs to emerge/10 GDDs per day = 11 days). However, if daily high and low temperatures are cooler, averaging 60 and 45 degrees after planting, 5 GDDs accumulate per day, and it may take more than 3 weeks (110 GDDs to emerge/5 GDDs per day = 22 days) for corn to emerge. In past years, corn planted in mid- April has taken as much as 3 to 4 weeks to emerge in many fields.

Given the relationship between GDD accumulation and emergence, we should not be too surprised that it takes early planted corn up to 3 or more weeks to emerge. Seedling emergence is dependent on soil temperature and air temperature. Also, keep in mind that estimates of emergence based on GDDs are approximate and can be influenced by various factors including residue cover, tillage, planting depth, hybrid differences, and soil organic matter (soil "color") and moisture content.

Corn emergence can be slowed by inadequate soil moisture. Moreover, dry soil conditions can cause uneven emergence in some fields that may impact yield if emergence delays exceed 1.5 - 2 weeks. Crops vary widely with regard to the minimum moisture content required for emergence. For corn, the minimum moisture content at which the radicle emerges is 30% of the seed dry weight. In contrast, for soybean, the reported minimum moisture content required for germination is 50%. However since a soybean seed generally weighs only 2/3 or less the weight of a corn seed, a soybean seed requires less water to germinate.

For more on the germination and emergence process, including great pictures showing key stages, check the following article -

Nielsen, R. 2010. Visual Indicators of Germination in Corn. Corny News Network, Purdue Univ. online at

Corn Replanting Considerations

So far, there is little evidence that most corn plantings in Ohio have been jeopardized by the cool temperatures we experienced during the past week. However, in some localized areas there may be fields where cold soil temperatures resulted in loss of stand. Farmers confronted with poor stands due to freezing temperatures, 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. 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 these tables might be used to arrive at a replant decision (Table 4-15 will be used in this example). Let’s assume that a farmer planted on May 9 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 79% 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 is 81 minus 79, or 2 percentage points. At a yield level of 175 bushels per acre, this increase would amount to about 3.5 bu per acre.

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.  


Some Weed Management Odds and Ends

1.  We are hearing rumors that some early-planted corn might have to be replanted.  It is of course necessary to kill the existing poor corn stand in these situations, and there are not a lot of options here for control of herbicide-tolerant corn.  Newsletters from other states have already provided some articles that cover this, including this one: U of Illinois - Options to Control Corn Plants from the Initial Planting (

2.  In those situations where soybeans are planted but have not emerged, it won’t be possible to use 2,4-D in burndown treatments.  Best alternatives include the following:
Glyphosate (1.5 lbs ae/A) + Sharpen + Canopy/Cloak DF
Liberty (32 to 36 oz/A) + Canopy/Cloak DF

It’s possible to use metribuzin instead of Canopy/Cloak DF in these treatments, but the chlorimuron in the latter will improve control of many broadleaf weeds.  Where the RR soybeans have actually emerged without burndown, we suggest a mixture of glyphosate (1.5 lbs ae/A) plus high rates of Classic or FirstRate.  Effectiveness of these mixtures will be variable and not adequate in some fields, especially on marestail.

3.  Several companies issued special labels this spring allowing mixtures of Sharpen with products containing flumioxazin (Valor) or sulfentrazone (Authority/Spartan).  BASF never officially approved of this use apparently, and some of the special labels are no longer valid.  At least one company (Valent) has now revoked their earlier labels, so that mixtures of Sharpen and Valor/Valor XLT are no longer legal.  FMC has informed us that the labels for mixtures of Sharpen and Authority products are still valid (FMC assumes liability for this use).  We have not heard from Dupont (Envive/Enlite) or Dow (Sonic) about this yet.   

4.  We are getting calls asking about the possibility of applying more residual herbicide to fields that will be planted to soybeans, which were treated with residual back in March or early April.   We discussed this situation in an article about a month ago.  Our suggestion would be to go ahead and apply additional residual herbicide, since soybeans planted now or within a few weeks will not canopy until mid-June or later.  The residual herbicide applied earlier in spring won’t necessarily hold weeds that long.  Some precautions here:

- It’s possible to make a second application of the same herbicide that was applied earlier in spring, but do not exceed the maximum total rate allowed for the soil type.  For example:  Envive applied at 2.5 oz/A in March can be followed with another 2 oz/A of Envive as long as the maximum rate for that soil type and pH is at least 4.5 oz/A.  If you are using two different chlorimuron-containing herbicides, be sure that the total amount of chlorimuron applied is within the range that labels specify.

- Scout the field prior to the second residual herbicide application and add burndown herbicide as necessary where weeds have emerged.  Do not rely on glyphosate for this where marestail are evident.  Alternatives include Liberty and Gramoxone, and lower labeled rates should be adequate assuming that the field was treated with burndown herbicides earlier in spring.  Sharpen and/or metribuzin can be added to improve control of larger weeds.  

Certified Livestock Manager Training

Certified Livestock Manager (CLM) Training will be held June 19-20 at the Ohio Department of Agriculture headquarters in Reynoldsburg, Ohio. Those required to attend are anyone who buys, sells or land applies more than 4,500 dry tons of solid manure or 25 million gallons of liquid manure per year or anyone who manages and/or handles manure at a major concentrated animal facility. Those who buy, sell, or land apply less manure are welcome to attend but do not need to be certified. Continuing education credits will be offered for current CLMs. Registration information can be found here:

Archive Issue Contributors: 
Archive Issue Authors: 

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.