C.O.R.N. Newsletter 2006-34

Dates Covered: 
October 10, 2006 - October 16, 2006
Editor: 
Curtis E. Young

Nutrient Management: A Common Sense Approach with Today's Economics

Authors: Robert Mullen

For those who have had the opportunity to see me give a presentation, I often say that the University Extension system has a mantra and that is "It Depends!" This may seem like a cop out statement, but the reality is the biological system we are working in is dependent upon so many factors that a single observation is actually the result of interactions between several different phenomena. The biological system is confusing enough, but when we consider economics to make an agronomic decision, the waters are muddied even further. Fertilizer management is one issue that is not as simplistic as it appears upon first glance. Efficiently and economically managing nutrient inputs is no simple exercise, but it should not be so daunting a task to scare individuals away. Fertilizer bills have grown considerably over the last few years forcing many growers to reevaluate their nutrient management program to ensure that they maintain profitability.

Potassium deficiencies were noted across the state for both corn and soybean, so remember those areas that were exhibiting the symptom. Potassium deficiencies show up as yellowing leaf edges on lower leaves. Do not confuse this with nitrogen deficiency which shows up as a yellowing progressing from the leaf tip to the base of the leaf, but it affects the entire leaf not just the leaf edges. If you had areas that you suspect were potassium deficient collect soil samples from those areas this fall to determine a corrective course of action. If those fields show similar problems next year, collect tissue samples to help diagnose the problem.

Potassium deficiencies may be the result of high potash prices the past couple of years and the unwillingness to apply potash. While no one likes paying a high fertility bill, supplying enough nutrients to insure good crop production is necessary. Unlike nitrogen, potassium and phosphorus soil levels can be determined by soil testing allowing us to identify an optimum rate. If soil test levels are below the established critical levels, bushels can be left in the field. Established critical levels for potassium and phosphorus can be found at: http://ohioline.osu.edu/e2567/index.html.

A question that has been raised with more frequency recently is "I have fixed amount of money that I am willing (or able) to spend on fertility, which nutrient can I cut back on?" There is no easy answer for this question because it depends (see first line of document) upon the soil and its fertility level. If adequate levels of phosphorus and potassium are present in the soil then less money can be spent on them without seeing a short-term economic penalty and more money can be spent on nitrogen fertilizer. Remember though, eventually you will have to supply phosphorus and potassium to the soil to replace what has been utilized. If phosphorus and/or potassium are deficient some money will have to be spent on those nutrients and less spent on nitrogen.

Agronomically sound fertility practices like soil testing and applying nutrients to the soil at the optimum rate are still most the economic and effective methods of making nutrient applications. Non-traditional methods of fertilization should not be used to supplement soil testing and soil-based fertilization. If they are to be used they should complement or fill in gaps in the fertility program. Like CORN Newsletter articles this past summer have discussed foliar feeding of macronutrients (potassium and phosphorus specifically) may not deliver optimum results and rarely match soil-based applications. One more thing to remember, there are no miracle products out there that can replace sound agronomic practices (at least nothing that has been proven scientifically).

New Transgenic Corn

Authors: Bruce Eisley, Ron Hammond

Syngenta just announced the release of a new transgenic line to their family of corn traits. The new line is Agrisure RW, containing the mCry3Aa gene, with built-in control of corn rootworm. In terms of insect management, this line joins their corn borer resistant line, Agrisure CB/LL (with Liberty herbicide tolerance). Both these lines are currently available in combination with Agrisure GT (glysophate-tolerant). Approval for the stacked hybrid with both the RW and CB traits is expected over the coming months. A triple stack with CB, RW, and GT is not expected until 2008. When considering using a transgenic corn hybrid for corn rootworm control, growers can now choose from three lines, YieldGard RW, Herculex RW, or Agrisure RW, or one of the available stacked hybrids.

Fall Applications of Lime and Lime Rate Calculator

Authors: Robert Mullen

Post-soybean harvest is the best time to take care of a lot of fertility operations including liming. As soybean harvest progresses and soil sampling begins evaluate your current soil pH levels and determine whether or not you need to apply some lime. This is the best time to apply lime since you have the opportunity to incorporate it with tillage, and it will give the lime time to begin neutralizing soil acidity well before next spring. The decision to apply lime is based solely on your soil pH level, and if the pH level is well below the optimum for your next crop (or one of the crops in your rotation - more specifically soybeans which perform better at higher pHs (around 6.5)) you should consider lime application. Any soil samples submitted to any of the labs in this area will measure soil pH as well as buffer pH. Buffer pH is used to determine the actual amount of lime needed to lime the soil to the desired level.

To help you make your lime decisions, an Excel spreadsheet has recently been posted on the Soil Fertility portion of the Agronomic Crops Team Web Page (https://agcrops.osu.edu/fertility/). The spreadsheet allows you enter your soil pH and buffer pH values from your soil test report to give you a lime recommendation. Additionally, you can enter the effective neutralizing power (ENP) and cost of the lime source from your local retailer to determine how much of their liming material you will have to supply to achieve the desired change in pH and how much it will cost.

Soybeans and Insecticide Seed Treatments

Authors: Bruce Eisley, Ron Hammond

In a recent CORN article, we discussed decisions about insect management when purchasing corn seed. Corn rootworm was the topic, whether to use granular insecticides, seed treatment, or transgenic hybrids. This week we will address decisions concerning seed treatments on soybeans, including soil pests, overwintering beetles, and most importantly, soybean aphids.

There are two seed treatments now labeled on soybeans, Cruiser (thiamethoxam), available in combination with fungicides as CruiserMaxx, and Gaucho (imidacloprid). Both are effective at managing seedcorn maggot, overwintered bean leaf beetle and Mexican bean beetle (Cruiser only), and early season soybean aphid.

Should growers use them for these insect pests? Our general recommendation for these pests is to use the seed treatments only if you have a situation or a history where you might expect problems. For seedcorn maggot, research over 15 years indicates that they are economic problems only when planting into fields that have had a green, living cover crop incorporated into the soil in the spring. This might be an old alfalfa field, a rye cover crop, or even heavy weed growth. There is also some evidence this might occur if a heavy application of manure is incorporated. In years of research, we have never seed a significant seedcorn maggot infestation under no-till situations.

With overwintered beetles, we know that these seed treatments, being systemic, will reduce their numbers. If a grower has experienced heavy spring feeding from either the bean leaf beetle or Mexican bean beetle, this is one option to help reduce it. However, instances of such heavy feeding is very rare, and growers are better off scouting their emerging soybeans for the presence of the two insects and making a foliar application when needed. The use of seed treatments for this purpose is very preventive in nature, without any knowledge of the likelihood of these pests being a problem.

A situation where controlling overwintered beetles is perhaps warranted is with bean leaf beetle because of its ability to vector bean pod mottle virus. While this virus is not that common in Ohio, seed producers and food grade soybean growers are often concerned with the impact that the virus can have on seed quality. For those growers who wish to reduce virus transmission by controlling the insect, a seed treatment is an option. Although there are still more questions than answers on this approach, we do suggest using seed treatments as a possible starting point. However, foliar insecticide applications following crop emergence are still an alternative for those growers.

The final use suggested for seed treatments is for soybean aphid management. While research has shown that they will control early season aphids, up through at least the V4-V5 growth stage of soybeans, the ability to have an impact on later season aphid numbers is limited. While we expect soybean aphids to cause economic concerns in 2007, the vast majority of the problems will come in mid-to-late July and early August, after the seed treatments lose their effectiveness. And remember, we do have good thresholds to determine the need for treatment, and excellent insecticides with which to control them. The only situation where seed treatments might have a use is in the extreme northwest section of the state which has experienced early season soybean aphid problems in late June during the V4-V6 growth stages. However, the few fields that have had problems are considered exceptions to what we normally see in Ohio. These outbreaks begin from soybean aphids that have recently moved off buckthorn, their overwintering host. Because most of the overwintering occurs in extreme northwest OH or most likely lower Michigan, northwest OH is the only area we have seen these early outbreaks. Although seed treatments would help to manage these aphids, we still recommend using a scouting program, and treating with a foliar insecticide when the population reaches the 250 aphids per plant threshold. Reasons for this include: 1) seed treatments are preventive treatments, without knowing whether or not a field will even have a problem; the vast majority of fields will NOT have an early problem; 2) you still have the ability to control the aphid with foliar insecticides on a NEEDED basis; you only spend the money for aphid control when truly warranted; and 3) control of this early population will NOT impact later aphid populations; the likelihood of a second spray in mid to late summer will remain high. This latter point is critical. Many fields needing treatment early in the summer will often require a second application following the large flight of winged aphids in July. Thus, the use of a seed treatment will NOT reduce the need to scout the entire summer and most likely, need a foliar application in mid to late summer.

Estimating Nutrient Losses from Burning of Corn Residue

Authors: Peter Thomison, Robert Mullen

A typical fall phenomena is the accidental burning of corn residue, and the first question most frequently asked afterward is how much nutrient did I lose in the process? Burning (oxidation) of corn residue will only really result in the loss of one major plant nutrient that being nitrogen (N). All the other macronutrients (phosphorus, potassium, etc.) will remain in the field relatively unaffected (at least in availability; their forms will be different). Thus we will primarily focus on N losses. First recognize 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, http://www.ipm.iastate.edu/ipm/icm/2000/10-23-2000/dryfallfires.html). 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.)

   
120 40
130 44
140 47
150 50
160 54
170 57
180 60
190 64
200 67

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.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Jeff Stachler (Weed Science), Peter Thomison (Corn Production) and Robert Mullen (Soil Fertility). Extension Educators: Howard Seigrist (Licking), Roger Bender (Shelby), Harold Watters (Champaign), Curtis Young (Allen), Greg La Barge (Fulton), Glen Arnold (Putnam), Mike Gastier (Huron), Mark Koenig (Sandusky), Steve Prochaska (Crawford), and Wesley Haun (Logan).

About the C.O.R.N. Newsletter

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.