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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-12

Dates Covered: 
May 3, 2004 - May 11, 2004
Greg La Barge

Slug Update

Authors: Ron Hammond, Bruce Eisley

We have observed slug eggs beginning to hatch in parts of the state. Thus, growers should be aware of problems beginning within the next 3-4 weeks and continuing into June. As slugs continue to hatch out and grow, and fields are planting later in May and early June, the concern with slugs will become greater. Growers should monitor the slug situation in their fields closely.
When treating, the most commonly used molluscicide is Deadline MPs, which should be broadcast evenly across the field at 10 lbs per acre. If past history suggests that only certain areas of a field have had a problem, only those areas need to be treated. Check areas, approximately 100 by 100 ft, should be left to determine the treatment's efficacy. We will continue to update the slug situation.

Early Season Bean Leaf Beetle

Authors: Bruce Eisley, Ron Hammond

Growers should plan on monitoring emerging soybean fields for the presence of populations of bean leaf beetle. Although populations were not especially high during the fall of 2003, we did see many fields with significant numbers in mid-summer. If early defoliation reaches 50%, plants appear stunted, and stand loss appears imminent and insects are still active, insecticide treatment would be recommended. Remember that bean leaf beetles tend to be most numerous in early-planted fields. Thus, growers who have already planted their soybean fields should watch their fields closely as they begin to emerge. Bean leaf beetles will be especially attracted to them.

Additionally, there is still the concern among some growers with the beetle's ability to vector bean pod mottle virus. The bean leaf beetle transmits this virus, especially in early season during feeding by the over-wintering beetle. If growers choose to treat the bean leaf beetle for virus control, they should consider spraying for the bean leaf beetle at the VE-VC stage after the soybeans emerge from the soil and when beetles are first seen in the field.

The recommendation also suggests that for optimal control of the virus, a second spray against the beetle is necessary in July at the occurrence of the first beetle generation. This recommendation is from work done at Iowa State University. Ohio is currently researching this management approach, as are other states.

Increase in Black Cutworm Moth Catch

Authors: Bruce Eisley, Ron Hammond

Research has shown that pheromone trap catches of black cutworm (BCW) moths can be used to predict when cutting should occur. The research found that when 9 or more moths are caught over a 2 day period it is considered an intense capture and if degree days (base 50° F) are accumulated starting from this day, cutting should begin at approximately 300 degree days. An intense capture of BCW moths was made last Wednesday and Thursday, April 28 and 29, at Columbus (12 moths/trap) and Western Agriculture Research Station (10 moths/trap). We will begin accumulating degree-days from these dates and use that to determine when cutting might occur. It still does not indicate if BCW will be a problem or in which fields they might be a problem but it can help determine when to start scouting for cutworm in the field.

Powdery Mildew Increasing In Fields Of Susceptible Varieties

Authors: Patrick Lipps, Dennis Mills

We have received several reports of powdery mildew becoming prevalent in fields in northern Ohio during the past week. The affected wheat is in stem elongation growth stages (first or second node visible or Feekes stages 6 and 7). The white powdery mildew pustules are confined to the lower leaves but it is causes leaves to turn yellow giving fields an overall yellow appearance. We do not recommend spraying for mildew this early, but as soon as the flag leaves emerge, which will likely be the end of this week or early next week a fungicide application can be made. Our research indicates the best yield response occurs when a fungicide application is made as the flag leaf emerges if mildew is rapidly moving up the plant.

Although it may look bad now, it is likely to get worse if the variety is susceptible and the night and day temperatures stay in the 50 to 75 degree F range. Remember the most important thing is to keep the flag leaf (leaf F) and the second leaf (leaf F-1) disease free; we generally do not worry about the lower leaves. At Feekes growth stage 6 and 7 there are three leaves above that first node. Find the first node at the base of the stem and count the number of leaves above it. Since we usually count the leaves from the top down, leaves F-3, F-2 and F-1 are exposed and only leaf F-3 and F-2 are fully expanded at growth stage 6. Flag leaf emergence (Feekes growth stage 8) occurs when you can count 4 leaves above the lowest node. The flag leaf (F) is the last leaf out and can be detected as a spike above fully expanded leaf F-1.

Scout fields of susceptible varieties at flag leaf emergence and if mildew is moving up the plant such that the leaf below the flag leaf (the F-1 leaf) is in danger of becoming infected, then a spray is warranted. The products with the best efficacy against powdery mildew have propiconazole as the active ingredient. Tilt, PropiMax and Quilt contain propiconazole. To get maximum effect in controlling powdery mildew apply 4.0 fl oz/A of Tilt or PropiMax or 14 fl oz/A of Quilt. Applications at these rates will provide about 3 weeks of disease control and should also protect against Stagonospora leaf blotch and tan spot that generally show up in mid to late May.

You can avoid the issue of powdery mildew altogether by planting resistant or moderately resistant varieties. Variety selection is the most important management decision. Planting high numbers of seed (more than 1.6 million/A) and applying high levels of nitrogen (more than 100 lb N/A per year), will increase the problem of powdery mildew in the field, especially on susceptible varieties. In other words, discuss your powdery mildew problem with your seed salesman.

Estimating N Losses from Burning of Corn Residue

Authors: Peter Thomison, Robert Mullen

With dry weather and corn stubble sitting in the field, residue can be quickly turned to ashes due to accidental fires. The question most frequently asked afterward is how much nitrogen (N) just went up in smoke? Fire damage in a field is usually variable in scale. Not all material is completely turned to ash, and rarely is the entire field burned (from one end to another). Understanding what was burned and how much area was affected has an impact on the total amount of N lost. The amount of N contained in corn residue has been well documented from the late 60’s and clearly delineated more recently (Iowa State webpage,

To estimate how much N was lost, the grain yield level for the previous year must be considered. The harvest index is another piece of information that must be known (if unknown – assume 0.5). Providing a relatively accurate measure of the area affected is obviously important. Additionally, recognizing the residue remaining and adjusting the material burned can provide a more quantitative measure of the actual damage (if this is unknown - assume 100%).

The table below provides a simple estimate of N lost based on the previous year’s corn yield (assuming a harvest index of 0.5 and yield adjusted to 15.5% moisture). (Remember: the N contained within the corn residue would not have been released and made plant available for next season’s crop.)

Yield (bu/A)
N lost (lb/A)

Along with the loss of N, carbon contained in the plant material is lost as well. It would have been incorporated into the soil organic fraction. This too has value. While there is no specific dollar amount tied directly to a loss of organic matter, an Iowa State University article recommends that one dollar per acre should be claimed. Unfortunately, the economic impact associated with the loss of residue can not be fully realized until later, especially in fields with high erosion potential.

Early Corn Plantings and Heat Unit Requirements for Emergence

Authors: Peter Thomison

Favorable weather and soil conditions have allowed earlier than normal planting of many corn fields. As much as 80% of the corn acreage has been planted in some northwestern Ohio counties where rainfall was limited during April. There are also reports that corn emergence is nearly complete in many of these fields, which were planted in mid to late April.

Corn requires about 100 growing degrees days (GDDs) to emerge (note that emergence requirements can vary from 90 to150 GDDs). To determine daily GDD accumulation, calculate the average daily 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 100 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 10 days (100 GDDs to emerge/10 GDDs per day = 10 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 nearly 3 weeks (100 GDDs to emerge/5 GDDs per day = 20 days) for corn to emerge.

Given the relationship between GDD accumulation and emergence, we should not be too surprised that some of the mid -early April planted corn has already emerged. In April, we has periods with warmer than average air temperatures and fields with soil temperatures above normal for the time of year. 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, and soil organic matter (soil "color") and moisture content.

Although corn planting and early growth is furthest along in NW Ohio, there have been reports that corn emergence has been slowed by inadequate soil moisture. Dry soil conditions have caused 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.

Burndown Situations Get Tougher

Authors: Mark Loux

This is just a reminder that weeds are getting larger in no-till fields, and herbicide rates/programs should be adjusted accordingly. Some points to keep in mind:

- Where there is enough time before planting, we still suggest the use of 2,4-D ester in burndown treatments.

- Glyphosate rates should be increased as weeds get larger, especially since glyphosate prices keep decreasing. The standard 0.75 lb acid equivalent rate (22 oz of WeatherMax or 32 oz of most other glyphosate products) may not be adequate in many fields. It is much better to get effective control of emerged weeds at this point, rather then relying on later glyphosate applications to “finish off” weeds that burndown treatments don’t completely kill.

- The cold conditions early this week can reduce activity of glyphosate and 2,4-D on some weeds, especially dandelions. We suggest delaying applications until a day or so after warmer conditions return. Avoid applications the day after extremely cold nights.

- The addition of CanopyXL to glyphosate can improve control of dandelions, marestail, ragweeds, and some other weeds, especially where it is not possible to use 2,4-D ester. FirstRate/Amplify will improve control of marestail and ragweeds. Note: neither herbicide will improve control of ALS-resistant weeds.

- Some producers have expressed reluctance to use CanopyXL based on its potential to reduce the rate of soybean growth early in the season (and comments we make in the OSU/Indiana Weed Control Guide to this effect). We rarely observe this type of injury, and usually only at high rates in combination with excess rainfall and slow soybean emergence. In OSU research, the use of CanopyXL has not reduced soybean yield compared to other residual herbicides or glyphosate-only programs. In fact, we have occasionally observed a yield increase compared to glyphosate-only programs due to the early-season weed control provided by CanopyXL and other residual herbicides, which reduces weed interference and creates more flexibility in postemergence application timing.

Management That Increases Soybean Yield

Authors: Jim Beuerlein

Higher soybean prices have prompted many producers to ask what they can do to increase yield. Although the answers to this question are more important when prices are low, they can generate even more profits when prices are high. The two biggest profit makers are planting date and row spacing. Yield potential starts to decrease in early May most years and by late May is just over a half bushel per acre per day. A five day delay in planting the last week of May will reduce income by $30.00 per acre if soybean is worth $10.00 per bushel. Switching to narrow rows will also increase yield and profit. On light colored soil, the row spacing should be as narrow as possible regardless of planting date. On dark colored soil, row spacings should no wider than 15 inches in May and as narrow as possible for June plantings. Yield increases about one-third bushel per acre as the row spacing is decreased from 30 inches to 7 inches.

If you are already planting early in narrow rows there are two other very profitable practices, fungicide seed treatments and inoculation, that can greatly increase profits. Fungicide seed treatments will ward off infection of the root rot diseases for two to three weeks allowing plants to get a head start on diseases and be better able to ward off the yield loss caused by disease. In 2003 we got yield increases of up to 7.0 bushels per acre due to fungicide seed treatments. The average yield increase for eight different seed treatments averaged over five test sites was 1.6 bushels per acre. Those test sites were selected because they had a very low potential for disease. Over time, the use of fungicide seed treatments in Ohio will increase yield three to eight bushels per acre depending on soil drainage, crop rotation, variety selection, etc. This year, seed treatment could increase profit from $30 to $80 per acre if the price of soybeans stays at $10.00 per bushel.

We have conducted sixty inoculation trials in producer fields that were selected because they had a very low potential for a yield increase due to inoculation. The average yield increase from those 60 trials was 1.9 bushels per acre. Most producers can expect yield increases of three to eight bushels per acre depending on soil characteristics and yield potential. In about a fourth of our trials there was no yield increase due either dry soil or waterlogged soil for several days after planting. Over time however, our $3.00 investment in inoculation material has produced yield worth about $11.00 per acre. With beans worth $10 per bushel, that $3.00 investment would return us about $20.00 worth of yield. Because most producers will get higher yields due to inoculation than we have experienced and because grain prices are high, $3.00 worth of inoculation has the potential to increase profits by $20 - $40 per acre for most producers and up to $80 per acre in some fields if the price of beans is around $10.00 per bushel.

Will Low Temperatures Injure Early Planted Corn Fields?

Authors: Peter Thomison

Temperatures dropped into the low 30's Monday morning in parts of Ohio, especially the Northwest. How will these low temperatures impact early planted fields in which corn has or is emerging? Since the corn plant's growing point is at or below the soil surface until the 6-leaf collar stage (V6), corn can usually withstand low air temperatures much better than soybean. However, if the soil freezes or if soil temperatures near the growing point are at or below freezing for extended periods, injury can occur. The corn plant can survive brief periods of low temperature, but when when temperatures remain below 32 degrees F for 4 to 5 hours, or when temperatures decline to 28 degrees or lower for even a few minutes, substantial damage or death may result. Since the weather forecast calls for warmer temperatures by the weekend, growers should be able to determine if growth and plant stands have been affected in several days. For more on the impact of low temperatures check out the following article by Dr. Bob Nielsen at Purdue University, Freeze Injury Potential for Early-Planted Corn, available online at

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Soybeans & Small Grain), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); District Specialists: Ed Lentz (Agronomy); Extension Agents: Roger Bender (Shelby), Ray Wells (Ross), Barry Ward (Champaign), Steve Foster (Darke),Todd Mangen (Mercer), Gary Wilson (Hancock), Greg La Barge (Fulton), Howard Siegrist (Licking), Alan Sundermeier (Wood), Glen Arnold (Putnam) Mark Keonig (Sandusky), Harold Watters (Miami), and Dusty Sonneberg (Henry).

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.