CORN
Crop Observation and Recommendation Network

September 15-21, 2003
C.O.R.N. 2003-31

In This Issue:

A) Planting Wheat for Improved Yields
B) Weed Management in No-tillage Winter Wheat
C) Soybeans Dying Early? Plant Wheat in Those Fields!
D) Corn Harvest Losses and Grain Drying Rates
E) Phosphorus and Potash Recommendations for Corn and Soybeans
F) Weed Control in Wheat Stubble and Fallow Fields

A) Planting Wheat for Improved Yields - Jim Beuerlein, Pat Lipps, and Ed Lentz CORN Questions

Shooting for ultra high yields by using extra inputs is not profitable for most Ohio wheat producers. That is because the weather and climate of Ohio is usually not ideal for high yield wheat production. Most years, our weather is too wet in the spring resulting in serious disease and loss of yield. June is usually too hot and kills our crop well before it has time to reach its maximum yield potential. When we have one of those rare dry springs and little disease followed by a cool June, the yields of some fields have hit 120 bu/ac or more. Because those good growing seasons are very rare, we should manage for the more normal weather which usually prevents us from taking advantage of high management inputs such as high seeding rates, and extra nitrogen.

The more prudent production system is one of defensive management: planting after the fly-safe date to eliminate some diseases as a threat; holding seeding and nitrogen rates down to reduce disease and lower production costs; using resistant varieties instead of applying fungicides, etc. This management system will not produce the maximum possible yield in those really good years, but it will be the most profitable system for all those other years (the norm) when the weather is not ideal for yields greater than 100 bu/ac. An important point to keep in mind is that the most profitable amount of any input is always less than the amount needed to produce the highest yield.

Select wheat varieties with high yield potential, high test weight, good winter hardiness and good standability. Always select varieties with resistance to wheat spindle streak mosaic, powdery mildew and leaf rust, and any other diseases prevalent in your area. Varieties with moderate resistance to Stagonospora glume blotch and Fusarium head scab are also available. Plant more then one variety each year to reduce the risk of disease losses and to spread out harvest.

Information on wheat variety performance can be obtained in the annual "Ohio Wheat Performance Trial" OSU Horticulture and Crop Science Department Series 228 available at the County Extension office or on the Internet at "www.ag.ohio-state.edu/~perf".

Plant wheat within the first 10 days after the Hessian Fly Safe date to avoid serious insect and disease problems including Hessian Fly, Barley yellow dwarf virus and several foliar diseases. Early planting (before the Fly safe date) has reduced yield by up to 20% in research trials due to increase disease levels as compared to those planted after the Hessian Fly Safe Date.

The optimum seeding rates for Ohio are between 1.2 and 1.6 million seeds per acre or 16 to 21 seed per foot of 7.5-inch row which is 90 to 120 pounds per acre when there are 13,000 seeds per pound). High seeding rates (above 30 seeds per foot of row) increased lodging potential, costs more money, but does not increase yield. Plant seeds 1 to 1.5 inches deep uniformly across the field . This planting depth is critical to winter survival and tiller development. Before planting, apply 20 to 30 pounds of nitrogen to increase fall growth, improve winter hardiness and increase yield. Wheat also requires at least 45 parts per million of available phosphorus per acre in the soil to produce really good grain yields. If a soil test indicates less than 40 parts per million, then apply 80 to 100 pounds of P2O5 at planting. Soil potassium should be maintained at levels of 135, 165, and 185 parts per million for soils with cation exchange capacities of 10, 20 or 30, respectively. If potassium levels are low, apply 60 to 100 pounds of K2O at planting. In Ohio, limed soils usually have adequate calcium, magnesium and sulfur for wheat. Soil pH should be between 6.5 and 7.0.

B) Weed Management in No-tillage Winter Wheat - Jeff Stachler and Mark Loux CORN Questions

As mentioned in a previous newsletter article, a preplant or preemergence application of glyphosate in no-tillage winter wheat is becoming a necessity. Fields that are infested with winter annual grasses such as annual bluegrass, downy brome, and cheat and/or winter annual broadleaf weeds such as field pennycress, marestail (horseweed), and common chickweed should be treated with glyphosate prior to wheat emergence. This will greatly reduce the populations of these weeds throughout the remainder of the fall and into next spring. In addition, dandelion is most effectively controlled in wheat with a preplant application of glyphosate.

The rate of glyphosate will depend upon the weed species present. For winter annual weeds, a glyphosate rate of 0.375 pound acid equivalent (ae)/A (11 oz/A of Roundup WeatherMax or 16 oz/A of 3.0 lb ae/gallon glyphosate formulations) should be adequate. An exception would be glyphosate-resistant marestail, which can be a problem south of I-70, and especially in southwestern Ohio. Where dandelions are present and/or the presence of glyphosate-resistant marestail has been confirmed or is suspected, the glyphosate rate should be at least 0.75 lb ae/A (22 oz/A of Roundup WeatherMax or 32 oz/A of 3.0 lb ae/gallon glyphosate formulations). This rate of glyphosate will provide more effective (although not necessarily complete) control of small glyphosate-resistant marestail plants. If dandelions are present and glyphosate is applied before mid-October, higher glyphosate rates should provide more effective control, but may not be cost effective.

C) Soybeans Dying Early? Plant Wheat in Those Fields! - Anne Dorrance CORN Questions

From the number of diseased plant samples, conversations with ag consultants, phone calls and field visits, I think we have tripled our acres affected by sudden death syndrome (SDS) this past year. In addition to SDS, soybean cyst nematode, Phytophthora root rot, brown stem rot and flooding injury are all causing premature senescence in many fields across Ohio. All these problems can cause leaf symptoms known as interveinal necrosis where the leaf veins remain green and the space between the veins dies and turns brown.

Crop rotation has many benefits of which the primary is reducing pathogen numbers (SCN) or preventing a rapid increase in the pathogen population (SDS and Phytophthora). I am also very concerned at the numbers of cysts we are finding in these SDS areas on SCN resistant beans. We do expect to find the female cysts or "white pearls" on the roots of resistant beans, but there should be fewer of them.

Resistance to SCN works by reducing the reproduction of the nematode -- not a total prevention of feeding. Once a SCN population begins to adapt to a source of resistance, such as PI88788, and soybeans with this source of resistance are planted again in the field, there is slow increase in SCN numbers the first two years. By year 3 the rate of increase in nematode numbers is the same as a susceptible soybean. So if you put a SCN resistant variety in a field with high cyst numbers, you are going to skip the lag phase and break the resistance that much sooner. We will see what companies have to offer for new SCN resistant varieties, but most seed companies are still depending on the resistance that is from the soybean plant introduction PI88788.

There was a very nice study from Arkansas that looked at crop rotation and the pathogen population of SDS. They documented that when wheat was used in the rotation the pathogen numbers dropped significantly. For fields in Ohio, with SCN, SDS, brown stem rot and Phytophthora - it's time to get wheat back in the rotation. Crop rotation is essential to reduce these pathogen numbers or prevent them from getting out of hand and causing losses in 50 to 100 acre areas of fields instead of just along the edge of a field. These fields would also benefit from reduced tillage practices to prevent dragging and mixing soil with these pathogens over a whole field.

D) Corn Harvest Losses and Grain Drying Rates - Peter Thomison CORN Questions

Corn growers may encounter slower than normal drydown this fall due to relatively cool weather conditions and late crop development in parts of the state, especially the northeast. The ideal kernel moisture level at which to harvest corn for dry grain storage is about 24 to 25%. This year the yield potential of many corn fields could drop considerably if harvesting is delayed much beyond maturity because of stalk lodging associated with poor stalk quality. Root lodging caused by wind storms earlier this year may also slow harvest and contribute to yield losses.

The loss of one "normal" sized ear per 100 feet of row translates into a loss of more than one bushel/acre. In fact, an average harvest loss of 2 kernels per square foot is about 1 bu/acre! According to an OSU ag engineering study, most harvest losses occur at the gathering unit with 80% of the machine loss caused by corn never getting into the combine.

Corn will normally dry approximately 3/4 to 1% per day during favorable drying weather (sunny and breezy) during the early warmer part of the harvest season from mid-September through late September. By early to mid-October, drydown rates will usually drop to 1/2 to 3/4% per day. By late October to early November, field dry-down rates will usually drop to 1/4 to 1/2% per day and by mid November, probably 0 to 1/4% per day. By late November, drying rates will be negligible.

Estimating dry-down rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25 to 20 percent requires about 45 GDDs per point of moisture. In September we average about 10 to 15 GDDs per day. In October (as things cool down) the rate drops to 5-10 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids vary from this pattern of drydown.

Past evaluations of corn drydown at the OSU-OARDC Western Branch Research Farm, near S. Charleston, OH provide some insight on effects of weather conditions on grain drying. In 1991, under warm, dry fall conditions, grain moisture loss per day ranged from 0.76 to 0.92%. Under cool, wet fall conditions in 1992, grain moisture loss per day ranged from 0.32 to 0.35%. Grain moisture losses based on GDDs ranged from 24 to 29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24 to 29 GDD) in 1991, whereas moisture loss ranged from 20 to 22 GDD in 1992. The number of GDDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.

E) Phosphorus and Potash Recommendations for Corn and Soybeans - Ed Lentz CORN Questions

The Ohio State University phosphorus and potassium recommendations follow a buildup and maintenance approach for nutrient management. In this approach, recommendations are given to meet the needs of the crop, and to build or maintain nutrients at soil levels where additional fertilizer may not be required for one or more years. A soil test will be needed to determine whether a specific field should require a buildup, maintenance (crop removal), or a reduction for a phosphorus or potassium program for next year's corn or soybean crop.

Generally corn or soybeans have more than adequate phosphorus when soil levels are above 40 ppm (80 lb). Additional applications at or above this level will accumulate in the soil but not benefit the crop, and may even cause environmental concerns. At adequate levels (15 - 30 ppm/30 - 60 lb), additional phosphorus should be applied to equal the amount removed by the crop. For corn, crop removal equals the yield goal multiplied by 0.35; for soybeans, crop removal equals the yield goal multiplied by 0.83. Between 30 - 40 ppm, application amounts less than crop removal would be recommended. If soil levels were below 15 ppm, then applications would include crop removal and a program that raises the overall soil P level. For example, if soil P levels were 10 ppm (20 lb), then a 160 bu/A corn crop would require 85 lb/A P and a 50 bu/A soybean crop would require 65 lb/A.

Potash recommendations follow the same philosophy as phosphorus except consideration is given for soil cation exchange capacity (CEC). Since applied potash may be held more tightly by soils with high CEC, potash rates increase as the soil CEC increases. Regardless of CEC and yield goals, corn and soybean yields would not respond to additional potash at soil potash levels above 200 ppm (400 lb). Corn and soybeans grown on soils that have a CEC less than 10 would not respond to additional potash when the soil test level is greater than 150 ppm (300 lb). Tables on page 14 in the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa guide provide potash rates for corn and soybeans at various yield goals and soil CEC. Many private soil testing laboratories have the capability to make recommendations from this guide upon request.

In summary, by understanding your soil tests, phosphorus and potash recommendations may be adjusted to reduce input costs without lowering corn and soybean yields. More details on soil fertility may be obtained in Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa, Bulletin E-2567, available through you county Extension Office (or online at http://ohioline.osu.edu/e2567/). Recommendations from this publication incorporate over 40 years of data from field calibration and correlation studies.

F) Weed Control in Wheat Stubble and Fallow Fields - Stachler and Loux CORN Questions

Now is the time to scout for weeds in wheat stubble and CRP fields that may go into production next season. Determine what the most prevalent or most troublesome weed species are in the field in order to determine when to apply herbicides. If warm-season perennials such as johnsongrass, wirestem muhly, milkweeds, hemp dogbane, groundcherries, horsenettle, bindweeds, or bigroot morningglory (wild sweet potato) are the major targets, then NOW is the time for an herbicide application.

A tank-mixture of glyphosate and 2,4-D ester will provide the most effective control of most species. However, 2,4-D can reduce the effectiveness of glyphosate on perennial grasses and Canada thistle. Increasing the glyphosate rate will decrease the antagonism caused by 2,4-D. The minimum rates of glyphosate plus 2,4-D ester should be 1.125 lb ae/A glyphosate (33 oz/A of Roundup WeatherMax or 48 oz/A of 3.0 lb ae/gallon glyphosate formulations) and 1.0 pt/A (for 4.0 lb ai/gallon formulations) 2,4-D ester, respectively. Further increases in glyphosate and 2,4-D rates will provide more effective control of nightshade, perennial morningglory species, and other glyphosate-tolerant species.

If cool-season perennials such as quackgrass, tall fescue, Canada thistle, dandelion, and curly dock are present, the preferred herbicide application timing is mid-October or later. If these species are presently taller than 10 inches or are in the flowering stage, the above treatment can be fairly effective in controlling these cool-season species. If these cool-season species are less than 10 inches or are not flowering, waiting until mid-October is essential for the most effective long-term control. Consider high spray volumes (20 to 30 gallons/A) for non-mowed CRP fields going into production next season or wheat stubble fields because of the dense plant and residue canopy. Low growing weeds such as dandelion, curly dock, wild carrot, or poison hemlock may not be completely controlled in fields with dense canopy of weeds.

If a CRP field will be plowed this fall, a herbicide application before a frost or October will be extremely beneficial for long-term control of all perennial weed species, compared to plowing alone. The combination of herbicides and tillage should be the most effective method for control of all perennial weed species compared to no-tillage crop production. Allow at least 3, but preferably 5 to 7 days between the glyphosate application and tillage. This is necessary to allow maximum translocation of glyphosate to the vegetative propagules (rhizomes, stolons, tubers, etc.).

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

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.

Editor: Andy Kleinschmidt        Web Editor: Nathan Watermeier

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