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Ohio State University Extension


C.O.R.N. Newsletter 2012-05

Dates Covered: 
March 5, 2012 - March 20, 2012
Harold Watters

Late March weather expectations

Nothing has changed since our last update. 

The outlook for the rest of March is for an active pattern with above normal temperatures, above normal rainfall and some risk of severe weather. 

What will be quite different in 2012 versus 2011 is that the spring will not be as cool. It also will be wet but not as wet as 2011 and the wetness will likely end earlier than 2011. The threat for severe storms, however, is elevated due to the warm temperatures and active pattern.

Corn Flea Beetle and Stewart's Leaf Blight

The adult corn flea beetle is not only a pest itself, but it is the vector and means for spread of the bacterium that causes Stewart's bacterial wilt and leaf blight on both field and sweet corn. Beetle adults that overwinter become active in the spring when the soil temperatures reach 65 F, and are most active on sunny, warm, windless days. Those adults that fed on corn plants with Stewart’s disease in the previous late summer or fall may acquire and carry the bacterium from one growing season to another. By feeding on young plants in the spring, they may spread the bacterium which in turn causes seedling wilt and leaf blight. The occurrence of Stewart's bacterial disease is totally dependent on the level of bacteria-carrying flea beetle survival over the winter.

For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. An index is developed that helps to predict the likelihood of the disease threat. This 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February.  We checked the indices for the past 8-10 years, and the last time the numbers were high suggesting an elevated concern was in 2006.  Having checked average temperatures for various locations in Ohio the past three month, we find that all areas of the state have indexes over 100 suggesting that risk is severe in 2012. The locations and the corresponding indexes are: Wooster (OARDC) 102.5, Ashtabula 103.1, Hoytville (Northwest Research Station) 100.2, South Charleston (Western Research Station) 105.7, and Piketon 103.1.

The flea beetle index is:
- Index values less than 90 indicate negligible disease threat,
- 90-95 indicate low to moderate levels,
- 95-100 indicate moderate to severe and
- values over 100 predict severe disease threat.

We would recommend that growers scout for flea beetles, especially if they have planted a hybrid that is susceptible to Stewart's disease.  Normally we would recommend that growers wanting to take preventive action against flea beetles apply a commercially applied insecticide seed treatment labeled for flea beetles. However, the realization is that most field corn planted these days, especially all transgenic hybrids, already comes with an insecticide seed treatment applied.   Thus, it is mostly non-transgenic corn that might need to be treated specifically for this concern.  Also, most field corn hybrids are more resistant to wilt than sweet corn. Dent corn hybrids vary greatly in their resistance to the leaf blight stage phase of the disease. All sweet corn varieties are susceptible to wilt in the first leaf stage. A few are resistant by the second leaf stage and many are resistant in the third and fourth leaf stage. Consult your seed supplier for information on resistant varieties and hybrids.

 The question becomes, "how prevalent is Stewart’s bacterial blight in our state?" While the warmer temperatures this winter might allow for an increase in corn flea beetle numbers, in doesn’t automatically result in higher incidence of Stewart’s.  The surviving flea beetles need to be carrying the bacterium in order to infect plant in the spring, and in order for them to acquire the bacterium, they needed to feed on diseased plants last season. So, with the level of Stewart’s disease being low during 2011, it is quite possible that beetles, even if they survived due to the mild winter, may not be carrying the bacterium.

You can see pictures of flea beetle injury and Stewart’s bacterial blight, and get additional information on Stewart's disease of corn, on the Ohio Field Crop Diseases web site at   Additional information on the flea beetle can be obtained from OSU Extension Fact Sheet AC-37-2001 .  


2011 Ohio Corn Performance Test sampled for nematodes

Several seed companies submitted hybrid entries in the 2011 Ohio Corn Performance Test that included nematicide seed treatments ( Nematodes are receiving more attention as a potential yield limiting factor in corn (Paul et al., 2012). To assess whether nematodes may be affecting hybrid performance, we sampled the ten Ohio Corn Performance Test sites to evaluate corn nematodes following sampling procedures recommended by university extension nematologists (Niblack, 2010). Two bulk samples (of 20 cores each) were taken at each site. All of the test sites have a history of some form of conservation tillage.  Nine of the sites followed soybeans; one followed corn.  Samples were submitted to the Michigan State University (MSU) Diagnostic Services laboratory ( for analysis. Pioneer Hi-Bred, A DuPont Company, funded the nematode testing.

No visible evidence of nematode injury (e.g. uneven growth, stunted plants) was evident in sampled plots. The MSU lab results provided populations and a risk index for root-lesion, dagger, lance, stunt, pin, and spiral nematodes. Nematode populations were generally low to non-existent, with spiral nematodes being the most common nematode present in any quantities.  With the exception of one sample from the Beloit location (in Mahoning County), the risk index for the different nematode populations was “none detected” to “low”.  At Beloit, one sample contained 56 dagger nematodes, indicating the potential for a “moderate” risk of damage. The other Beloit sample indicated that nematodes were low to non-existent.  


Minyo, R., A. Geyer, P. Thomison, B. Bishop, and D.G. Lohnes , Ohio State University, Ohio Corn Performance Trials. 2011 Department of Horticulture and Crop Science Series 215. Avaialble at

Niblack, T. 2010. Time to Plan for Corn Nematode Sampling. The Bulletin. University of Illinois Extension, Issue No. 4, Article 6/April 29, 2010 (available at

Paul, P., T. Niblack, and A. Dorrance. 2012. Nematodes in Corn. C.O.R.N. Newsletter 2012-04 February 20, 2012 - March 6, 2012le at (available at


The Warm Winter and Field Crop Insects

This past winter has been the warmest Ohio has experienced in recent memory.  A question that is being asked is what impact the warm winter will have on field crop insects.  The point we can make is that it depends on the insect and crop in question.  Although warmer temperatures will affect the various insects differently, other factors might impact the crops greater because it will still depend on when crops get planted.  Although the warmer temperatures will allow for soil to warm up earlier, higher than expected spring rains might not allow for earlier crop planting if soils remain wet.   

Our feeling is that while “warmer” temperatures have been the norm and could result in greater survival, our “normal” winters in the state are not that cold compared to the temperatures probably required to cause significant mortality.  And remember that snow acts as a great insulator.  Thus, while survival might be greater, it remains to be seen if we see hugely greater densities of many of our crop pests.

The area where warmer temperatures can, and probably will, impact field crop insects concerns when the pests might show up and require scouting.  The first good example is with alfalfa weevil on alfalfa.  The time to begin sampling for weevils and larval feeding is dependent on weather, with heat unit accumulations beginning on Jan 1.  At 300 heat units, we recommend sampling.  Thus, the time for scouting will probably come earlier in the season.  However, because alfalfa is already planted and in the field, we would expect alfalfa growth to also begin its green-up earlier, probably at the same relative rate as we see with weevil growth.  Thus, we might expect that relationship between feeding and alfalfa growth to remain the same, albeit earlier than normal.  As usual, we would recommend sampling to determine the actual need for treatment.  Then, there are the many insects that migrate from southern areas, so their development is affected by weather conditions further south, e.g., black cutworm, true armyworm, potato leafhopper.  Whether they migrate earlier or not into Ohio will depend on the weather conditions later this spring. 

For those insects who do overwinter in Ohio, we would expect to see them emerging from their overwintering sites earlier than normal because temperatures often drive this event.  What will determine whether they become economic issues on crops will depend greatly on the stage of crop development and growth.  If insects arrive in fields early but no crop is even planted, this could lead to greater mortality if they cannot find alternative hosts.   However, if the insect arrives or begins feeding earlier when crops are smaller in size, a greater potential for injury exists.  This latter scenario is especially true for slugs on corn and soybeans.  A few years ago we saw soybean aphids hatch earlier on buckthorn, their overwintering host, because of warmer temperatures, but suffer significant mortality because of a late spring freeze.  There is one crop pest that we specifically tie into winter temperatures, corn flea beetles and their ability to vector Stewart’s bacterial wilt.   Because of the warmer temperatures during Dec, Jan, and Feb, more corn flea beetles are expected, and thus, the potential for greater Stewart’s bacterial wilt.  There is another article on this relationship and winter temperatures in this issue of the C.O.R.N. newsletter. 

To summarize, the warmer temperatures that Ohio experienced the past three months will impact insect pests to some degree.  However, whether economic problems will increase, or perhaps decrease, depends on the specific pest/crop relationship, and then the weather conditions over the next two to three months.  But remember a significant player on whether we will have earlier economic problems depends on the crop, and when they get planted.  Will the spring continue to be warm or will it turn cold?  How will rainfall impact crop planting?  Stayed tuned to the C.O.R.N. newsletter, and as always, plan on scouting your fields to watch how the situation unfolds.


2011 Ohio Yield and Production Estimates for Corn, Soybeans and Wheat

Ohio has 13.7 million acres in farmland with about 62.8 percent of that land in corn, soybean and wheat crops in 2011. There were about 74,700 farmers in Ohio with an average size farm being about 183 acres. (National Agricultural Statistics Service; However, according to the 2007 Census of Agriculture; 3.6% of the farm operations in Ohio have 34% of land in farms while 42.3% of the farms have 4.8% of the land in farms. 

In regard to Ohio corn, soybean and wheat production in in 2011; total acreage and production were decreased.  This may have been partially due to the very wet season and concomitantly late planting which resulted in ‘Prevented Planting’ being taken on some Ohio farm ground. Ohio crop yields in 2011 were good with corn averaging 158 bushels per acre and soybeans 47.5 bushels per acre. Wheat averaged 61 bushels per acre in 2011. 

·       The top three Ohio counties by yield (bushels per acre) for corn were:  Crawford @ 187.7, Wood @ 177.4 and Greene @ 176.0.  Darke, Wood and Madison led Ohio counties over corn production with 16.5, 15.8, and 15.4 million bushels respectively produced in 2011.

·       For soybeans, top Ohio counties over yields (bushels per acre) were:  Crawford @ 54.3, Fairfield @ 53.6 and Wood @ 52.1.   Wood, Putnam and Hancock led Ohio counties over soybean production with 7.1, 6.6, and 6.4 million bushels respectively produced in 2011.

·       In regard to wheat, top yielding counties were Fulton @ 72, Tuscarawas @69.7 and Wyandot tied with Crawford @68.5 bushels per acre.  Wood, Henry and Putnam led Ohio in production at 3.2, 2.5 and 2.4 million bushels respectively.

2011 Ohio Corn, Soybean and Wheat Yields, Acres & Production (bushels/ace)


























State Average







Total Acres







Total Produced







Source: National Agricultural Statistics Service;


Label changes allow use of Sharpen with Authority and Valor products

FMC and Valent have made label changes that allow use of Authority and Valor products in mixtures with Sharpen.  Mixtures of this type were were previously prohibited by the Sharpen label.  BASF does not plan to change the Sharpen label, so the liability for this use rests with FMC and Valent.  The Sharpen rate is limited to 1 oz/A in these mixtures, and they should include glyphosate or Liberty.  They also cannot be used on coarse soils with less than 2% organic matter.  Related information on herbicide rates and timing for Sharpen mixtures:

Valor – rates up to 3 oz/A can be applied anytime prior to planting.

Valor XLT – rates up to 3 oz/A can be applied anytime prior to planting; rates of 3 to 5 oz/A must be applied at least 10 days before planting.

Authority First, Authority XL – rates up to 4 oz/A can be applied anytime prior to planting; rates greater then 4 oz/A must be applied at least 10 days before planting.

One of the principles of effective marestail management is starting free of weeds at the time of planting.  This has been accomplished most often through use of mixtures of glyphosate and 2,4-D, which require a wait of at least 7 days between application and planting.  Mixtures of glyphosate and Sharpen can be effective for marestail burndown, and there is no required delay between application and planting for the 1 oz rate of Sharpen (14 days before planting for the 1.5 oz rate). 

Prior to these label changes, we suggested that metribuzin or Canopy plus metribuzin were the most effective herbicides that could be mixed with Sharpen for residual marestail control.  The label changes outlined here provide additional options for residual marestail control when using Sharpen, and also facilitate the addition of Sharpen to other burndown treatments to improve marestail control.  We have been suggesting that growers generally consider using higher rates of Valor and Authority products to improve residual control of marestail, especially ALS-resistant populations, but be aware that use of the higher rates of these residual herbicides in combination with Sharpen can require a 10-day wait between application and planting.

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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.