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Ohio State University Extension


C.O.R.N. Newsletter 2004-10

Dates Covered: 
April 20, 2004 - April 27, 2004
Steve Prochaska

Application Rules for Nitrification and Urease Inhibitors

Authors: Robert Mullen

In order to maximize nitrogen (N) availability during the growing season and minimize N losses prior to plant uptake, nitrification and urease inhibitors products are utilized. The general theory is that application of these additives or land applied materials will inhibit (slow down) N turnover by slowing down a specific process in the soil. Nitrification inhibitors slow oxidation of N to nitrate, causing N to stay in the more immobile form of ammonium. It does not inhibit nitrification indefinitely. The length of inhibition is usually between 4 to 10 weeks depending upon soil temperature and pH. If N fertilizers are applied in the fall (not optimum for summer crops), addition of nitrification inhibitors is encouraged (primarily with anhydrous ammonia – OSU does not recommend other sources of N for fall application). When it comes to spring application of N fertilizers, soil texture, soil drainage, and tillage regimen should be considered. Follow these general rules for applying nitrification inhibitors:

1. loamy soils without improved drainage and clay soils with improved drainage have a good probability of seeing yield increases (>60%)

2. clay soils without improved drainage have a moderate chance of seeing yield increases (35-60%) (N should be applied as close to planting as possible)

3. loamy soils with improved drainage have a better chance of seeing yield increases if N is applied earlier in the spring (early spring – 35-60%, later spring - <35%)

4. no-till systems increase the probability of seeing yield increases.

The most common nitrification inhibitor is N-serve (nitrapyrin). Ammonium thiosulfate (ATS) is a newer nitrification inhibitor that can inhibit nitrification (currently considered less capable than N-serve), but ATS is not compatible with anhydrous ammonia application.

Urease inhibitors block the activity of the urease enzyme which breaks down urea to form ammonium. This allows urea to remain in its un-hydrolyzed form longer increasing its staying power. Hydrolyzed urea can be subject to volatilization losses if incorporation does not follow surface application (either with rain or tillage). This is an attractive material for surface applied urea-based compounds (especially in no-till production). The most common urease inhibitor is Agrotain. Ammonium thiosulfate (ATS) also has exhibited some ability to inhibit the urease enzyme, but much less information is available for ATS.

Wheat Growth And Early Disease Development

Authors: Patrick Lipps, Dennis Mills

The warmer weather this past week has promoted continued rapid development of the wheat crop in Ohio. In southern Ohio the wheat has advanced to the early jointing growth stages ( Feekes growth stage 6 and 7), but in northern Ohio the wheat has not yet advanced to jointing (Feekes growth stage 4 and 5). Here at Wooster our most advanced fields, planted on the Hessian Fly Free date, are in the leaf sheath erect stage or Feekes growth stage 5). Therefore the wheat is developing at about the normal rate this year. Most fields have adequate tiller numbers to attain excellent yields assuming the weather conditions remain favorable throughout May and early June.

There has been considerable variability in the amount of precipitation that has fallen this spring across the state. Eastern, southern and central Ohio have had wet fields for most of the month whereas northwest and west central Ohio is dry. In the wetter areas you may be able to detect powdery mildew beginning to develop in fields planted to susceptible varieties. We detected it on the lowermost leaves of plants in our plots at Wooster. Spread will likely remain slow for the next week or so but it will likely be wise to keep an eye on fields for disease development. We recommend that fields be scouted for the first time as plants reach the flag leaf emergence growth stage (Feekes growth stage 8). This will likely occur in southern Ohio later this week or early next week, but in northern Ohio the flag leaves will likely begin to emerge during the first week of May assuming continued mild weather.

If powdery mildew becomes a problem you will not have trouble scouting for it. The white powdery growth on the leaves becomes quite apparent on susceptible varieties if they need to be sprayed with a fungicide. It is best to visit fields as they reach flag leaf emergence, pick about 50 tillers (stems) randomly in the field and examine the top leaves of the tillers. If powdery mildew is beginning to grow on the second leaf (the leaf below the flag leaf) then a fungicide application may be needed. Yield responses to fungicide application are generally dependent on the amount of disease on each plant, how early disease attacks the upper leaves and the level of susceptibility of the variety to the disease. Contact your seed dealer to determine if the variety is susceptible to powdery mildew or any other leaf diseases. To review the symptoms of the common leaf diseases of wheat and to learn more about fungicide application for disease management in wheat visit the Ohio Field Crop Disease web site at

Warmer Weather and Alfalfa Weevil

Authors: Bruce Eisley, Ron Hammond

The warmer temperatures the past few days and those that will occur in the coming weeks means that we will need to begin scouting alfalfa for alfalfa weevil (AW). We have not yet had any reports of weevils or damage from alfalfa this spring, but we recommend that scouting begin in southern and central Ohio and within the next week in northern OH. Fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier.
Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. See the OSU Alfalfa Weevil FactSheet for more on alfalfa weevil scouting and thresholds.

Chemicals currently labeled for use on alfalfa for alfalfa weevil include:
Ambush rate 6.4 to 12.8 fl oz/A
Baythroid 2 rate 1.6 to 2.8 fl oz/A
Furadan 4F rate ½ to 1 pint/A
Guthion Solupak rate 50WP @ ¾ to 1 lb/A
Imidan 70-W rate 1 to 1.33 lb/A
Lannate LV rate 3 pint/A
Lannate SP rate 1 lb/A
Lorsban 4E rate 1 to 2 pint/A
Malathion (check label for rate)
Mustang Max rate 2.24 to 4.0 fl oz/A
Pounce 3.2EC rate 4 to 8 fl oz/A
Sevin 80S rate 1-7/8 lb/A
Warrior 1CS rate 2.56 to 3.84 fl oz/A

Note: All but Sevin, Imidan and Malathion are RESTRICTED USE PESTICIDES and may only be used by certified pesticide applicators

Plant Full-Season Corn Hybrids First

Authors: Peter Thomison

Plant full-season hybrids first, then alternately plant early-season and mid-season hybrids, to take full advantage of maturity ranges and to give the later-maturing hybrids the benefit of maximum heat-unit accumulation. Full-season hybrids generally show greater yield reduction when planting is delayed compared with short- to mid-season hybrids. In areas with longer growing seasons, consider planting some acreage to early hybrids to have new corn for the early market (which usually commands a premium price and thus partially offsets the income effect of the lower yield associated with early hybrids). Planting early hybrids first, followed by mid-season, and lastly the full-season hybrids spreads the pollination interval for all the corn acres over a longer time period and may be a good strategy for some drought-prone areas.

Reminders on Preplant Burndown Herbicide Applications

Authors: Mark Loux

As a result of weed shifts and herbicide resistance issues that have developed over the past several years, use of the appropriate timing and selection of herbicides in no-till burndown treatments is more important than ever. Our assessment of these shifts in weed populations is that many have been caused by changes in herbicide programs, and more specifically, by the delay of burndown treatments from April into May (or elimination of burndown treatments in Roundup Ready soybeans), and the failure to include 2,4-D or other herbicides that are more effective than glyphosate alone on certain weeds. We have observed glyphosate-resistant marestail primarily in Roundup Ready soybean fields where glyphosate was the only herbicide used in the year of soybean production, and we assume that the inclusion of 2,4-D ester has helped delay resistance in many other fields. At this time, winter annual weeds are somewhat ahead of previous years in their development, and will require earlier treatment to prevent seed production and future increases in population density. Marestail in southern Ohio has started to bolt (stem elongation), and this weed is generally most easily controlled before stems exceed several inches in height. Some other reminders on herbicide treatments for burndown in no-till fields:

1. We strongly suggest including 2,4-D ester with glyphosate in all burndown treatments applied at least 7 days before planting, and including 2,4-D ester should be considered essentially mandatory in fields with marestail and dandelion. 2,4-D ester can be applied at a rate of 0.5 lb ae/A up to 7 days before soybean planting. When applied at least 15 days before soybean planting, several 2,4-D products (E-99 and Weedone 650) are labeled at the rate of 1.0 lb ae/A. The higher rate can be helpful on dandelion, larger marestail and giant ragweed, and dock species, among other weeds.

2. In soybeans, the addition of CanopyXL to glyphosate or glyphosate/2,4-D can improve control of a number of weeds, including dandelion, marestail, giant ragweed, prickly lettuce, and a number of winter annuals. The combination of CanopyXL plus glyphosate plus 2,4-D ester has been the most effective spring treatment for dandelion control, and the combination of glyphosate plus CanopyXL has been the most effective treatment on this weed where lack of time until planting precludes the use of 2,4-D ester. Including FirstRate/Amplify with glyphosate or glyphosate/2,4-D will improve control of marestail and giant ragweed. However, CanopyXL and FirstRate/Amplify will not improve control of emerged ALS-resistant marestail or ragweeds.

3. Most preplant soybean herbicides other than CanopyXL and FirstRate/Amplify do not contribute much to burndown activity. One exception is Sencor, which has effective activity on small, emerged weeds in combination with 2,4-D ester or 2,4-D ester plus Gramoxone. The combination of Sencor plus Gramoxone plus 2,4-D ester is effective for control of glyphosate- or ALS-resistant marestail up to a height of about 4 inches. Python also helps control small annual broadleaf weeds in mixtures with 2,4-D and/or glyphosate, but is generally less effective than CanopyXL. Several other herbicides, including Valor and Aim, may result in more rapid development of symptoms, but rarely improve control in combinations with glyphosate and 2,4-D ester.

4. Glyphosate containing treatments should be applied with ammonium sulfate or a similar product, and with nonionic surfactant where required by the label. Glyphosate activity can be reduced when applied in 28% or similar fertilizer solutions, especially on perennial or larger annual weeds. Treatments that do not contain glyphosate should generally be applied with crop oil concentrate, and the addition of low rates of 28% can improve control.

5. In corn, effective burndown options include Lumax, FieldMaster, Expert, or other combinations of glyphosate with preemergence residual herbicides. 2,4-D ester can be added to improve control of certain weeds, but treatments containing 2,4-D ester should be applied a week or so before corn planting where possible to reduce risk of corn injury. In OSU research in 2003, Lumax and Lumax plus 2,4-D were the most effective dandelion treatments, followed by mixtures of 2,4-D plus glyphosate plus residual herbicides.

What Should Be Planted First - Soybeans or Corn?

Authors: Steve Prochaska

Farmers today are planting corn and soybeans much earlier than farmers of 20 years ago. And this opportunity, when occurs, to pant early into dry soils may be beneficial because the growing season is extended and soils are not compacted. However, there are risks to planting very early and these risks will vary by crop. What follows below is risk/benefit analysis to early corn and /or soybean planting.

Soybeans - Benefits To Early Planting Soybeans (only when soils are dry!)

1. Extended growing seasons with high quality sunlight (more photosynthesis possible). The maximum amount of sunlight occurs in the months of May, June and July in Ohio.
2. Adequate moisture for crop development.
3. Perhaps the best seedbed of year and thus no soil compaction.
4. Spreading of work load (both fall and spring)
5. Newer seed treatments such as Apron, Maxim and Rival can help protect soybeans from certain plant pathogens during time periods unfavorable for growth.
6. Weed control costs may be reduced due to earlier canopy.
7. Opportunity to plant wheat in a timely fashion in September.
8. Time to evaluate and make a mitigating response in the event of a poor soybean stand.
9. Soybeans have the ability to flex over different environmental conditions, weather extremes and planting dates, and still yield well.
10. No loss of primary nutrients (P2O5 and K2O) applied in event of crop failures.
11. Most favorable temperatures for crop growth and development may occur from April 15 to July 15, as opposed to July 15 to September 1 (more carbohydrate deposition).
12. Opportunity to grow and harvest high yield soybeans (yields greater than 60 bushels/acre). Later planting may not allow such an opportunity due to loss of growing season.

Corn - Benefits to Early Planting (only when soils are dry!)

1. Extended growing season with high quality sunlight (more photosynthesis possible). The maximum amount of sunlight occurs in the months of May, June and July in Ohio.
2. Adequate moisture for early crop development.
3. Favorable temperatures for crop growth and development and thus carbohydrate deposition. Pollination may also occur during a period of cooler temperatures.
4. Perhaps the best seedbed of year and thus no soil compaction.
5. Spreading out of the work load (both spring and fall).
6. Newer seed treatments such as Apron and Maxim can help to protect (for relatively short periods of time) corn from certain diseases favored by adverse weather and soil environments.
7. Reduced weed control costs possible due to earlier canopy.
8. Can withstand a frost as long as growing points below ground.
9.Opportunity to grow and harvest very high yielding corn.
10. Longer growing season and thus the opportunity to have dryer corn at harvest.

Risks to Early Planted Soybeans

1. Hard freeze after soybeans are up (soybeans may withstand temperatures to about 26 degrees F for a short time) may kill plants.
2. Poor emergence due to extended periods or wet, cold weather (>25 days). More exposure to plant injuring insects and diseases.
3. Cost of replanting in the event of stand failure.
4. Lack of time to replant on a timely basis.
5. Additional weed control costs due to lack of early crop canopy.
6. Loss of yield due to loss of growing season in the event the initial planting fails.

Risks to Early Planted Corn

1. One chance to get good stand!
2. Poor emergence due to extended periods or wet, cold weather. More exposure to plant injuring insects and diseases.
3. Cost of replanting in the event of failure.
4. Lack of time to replant on a timely basis.
5. Additional weed control costs due to lack of early crop canopy.
6. Loss of yield due to loss of growing season in the event the initial planting fails.
7. Potential loss of applied preplant nitrogen via leaching or denitrification.
8. Corn herbicides may preclude planting soybeans in the event of corn stand failure.


One of the major attributes of successful farmers is timeliness. As farm knowledge and technology increase, corn and soybeans have been planted earlier. With our present knowledge and experience of planting corn and soybeans, there are reasons to consider planting soybeans before corn.

First, with farm size increasing, and many working off the farm, it is imperative to effectively utilize all available planting days. Stating it in another way, one of the major impediments to large or small farm operation success is the lack of planting time on dry soils. Planting on wet soils is a disaster that not only robs crop yields but forces additional tillage to rectify damage. And, more tillage creates the potential for greater soil erosion and concomitantly reduced farm profit. Thus, realizing there are additional windows to replant soybeans or repair poor stands (you realistically have one chance to get a good stand with corn) soybeans might be a better option for very early planting. Further, the benefits (in the years it is available) to very early soybean planting opportunities into dry soils may outweigh the risk to possible later cold weather and/or wet soils suitable to compaction.

Archive Issue Contributors: 

State Specialists: Robert Mullen (Fertility Specialist), Pat Lipps, Ann Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); Extension Agents and Distict Staff: Ed Lentz (West District), Roger Bender (Shelby), Ray Wells (Ross), Todd Mangen (Mercer), Mark Koening (Sandusky), Allan Sundermeier (Wood), Glen Arnold (Putnam), Barry Ward (Champaign), Gary Wilson (Hancock), Glen Arnold (Putnam), Harold Watters (Miami), Dusty Sonneberg (Henry), Tammy Dobbels (Logan) and Steve Prochaska (Crawford).

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.