CORN
Crop Observation and Recommendation Network

Mid February, 2001
C.O.R.N. 2001-3

In This Issue:

A) Weed Control Product Formulation Changes
B) Glyphosate, Glyphosate, And More Glyphosate
C) Nitrogen Topdress For Wheat
D) Gray Leaf Spot On Corn And Labeled Fungicides
E) Dr. Harold R. Willson

A) Weed Control Product Formulation Changes - Mark Loux CORN Questions

Balance Pro 4L is a liquid formulation of isoxaflutole (Balance), which may reduce tank-mixing problems that occasionally occurred with the 75WDG formulation.

Canopy SP 58.3DF replaces Canopy 75DF. The ratio of chlorimuron to metribuzin is unchanged, but product use rates increase due to the lower percentage of active ingredient in the formulation. Dupont may be phasing out all Canopy formulations, with Canopy XL as the replacement.

Harmony GT 75DF replaces Pinnacle 25DF, and is labeled for soybeans (1/12 oz/A) and wheat (0.5 to 0.6 oz/A). This will reduce the cost of lambsquarters control in soybeans, and provide another option for control of wild garlic and winter annual weeds in wheat.

Hornet WDG is a 78.5% active ingredient formulation that replaces Hornet 86DF. Common use rates are now 3,4, and 5 oz/A, instead of 2.4, 3.2, and 4 oz/A.

Gramoxone Max replaces Gramoxone Extra, and the new formulation contains 3 lbs paraquat per gallon. Product use rates are thus reduced slightly compared to the previous 2.5 lb per gallon formulation.

Roundup Ultra Max replaces Roundup Ultra. The amount of glyphosate acid equivalent per gallon increases from 3 to 3.75 lbs/gallon, with a reduction in the amount of product per acre.

B) Glyphosate, Glyphosate, And More Glyphosate - Mark Loux CORN Questions

A number of glyphosate products are currently available, including Roundup Ultra Max, Roundup Original, Roundup Ultra Dry, Glyphomax, Glyphomax Plus, Touchdown 5, and others. Most are labeled for preplant burndown in any crop and postemergence use in Roundup Ready soybeans, but not all are labeled for postemergence use in Roundup Ready corn.

In OSU research, few differences in weed control have been observed when comparing the various glyphosate products. However, differences among formulations may result in differences in rainfastness, surfactant recommendations, or control under adverse conditions. For example, the rainfast interval indicated on the Roundup Ultra Max label is one hour, while other glyphosate product labels specify longer rainfast intervals. Some products have optimized surfactant packages in the formulation. This may not improve control compared to other glyphosate products applied with high-quality surfactants. However, choice of surfactant may influence control under certain conditions when the applicator has to decide which surfactant to use.

Comparing the amount of active ingredient in glyphosate products can be difficult. The true indicator of the activity of a glyphosate formulation is often not the total pounds of glyphosate shown on the label, but rather the pounds of glyphosate acid (or acid equivalent). This is the figure that should be considered when comparing the rates and costs of glyphosate formulations. The form of glyphosate found in Touchdown is a slight variation on the original glyphosate molecule, but has essentially the same specific activity or effectiveness per pound of glyphosate acid. The following table shows the amount of product required to provide the equivalent of 0.75 lbs glyphosate acid, or one quart of Roundup Ultra.

Product/formulation Rate for 0.75 lb glyphosate acid

Other premix products that contain glyphosate include:

Backdraft (BASF), a premix of imazaquin (Scepter) plus glyphosate for control of emerged weeds and residual control of broadleaf weeds. This product is targeted primarily for preplant or preemergence application to any type of soybean, but can be applied postemergence on Roundup Ready soybeans. The rate of glyphosate in this product may be too low for many burndown situations - the 1.5 quart/A rate provides an amount of glyphosate equivalent to 13 oz of Roundup Ultra Max (or 1 pint of Roundup Ultra).

Extreme (BASF), a premix of imazethapyr (Pursuit) plus glyphosate for postemergence plus residual weed control in Roundup Ready soybeans. This product may improve velvetleaf control, compared to glyphosate alone. The residual control from the imazethapyr may also help control annual grasses, black nightshade, and a few other weeds that can emerge after postemergence applications. The use rate provides the equivalent of a labeled rate of Pursuit plus 20 oz/A of Roundup Ultra Max.

Ready Master ATZ (Monsanto), a premix of glyphosate (Roundup Ultra Max) plus atrazine. This product can be applied preemergence on any corn hybrid, and postemergence on Roundup Ready hybrids only. The 2-quart rate provides the equivalent of 1 lb/A of atrazine plus 26 ounces of Roundup Ultra Max.

C) Nitrogen Topdress For Wheat - Ed Lentz CORN Questions

Soon it will be time to apply nitrogen as wheat fields begin to green-up. With the high cost of nitrogen and low grain prices, producers are looking for ways to get the most out their fertilizer program. It is tempting to arbitrarily decrease nitrogen rates without considering the impact. Wheat yields will be greatly affected without adequate nitrogen, but what is adequate?

Nitrogen recommendations for Ohio wheat are based on the following rate equation: 40 + [1.75 x (yield potential - 50)]

This equation shows that a realistic yield goal is the first place to consider rate adjustments. For example, if the yield goal has been 100 bushels per acre, but yields have actually been 90, then the crop has received 20 pounds that were not needed for yield. If the goal had been 100 bushels and average yields have been 80, 35 pounds of extra nitrogen had been applied each year.

Another area for potential savings is to credit fall nitrogen applications. For example, 130 pounds of nitrogen would be required for a yield potential of 100 bushels. If 30 pounds of N had been applied in the fall, only 100 additional pounds should be applied in the spring. If the yield potential would have been 90 or 80 in the same scenario, the spring nitrogen rate should be 80 and 60 pounds, respectively. Credits are not given for previous crops. A legume, such as soybeans, will eventually provide available nitrogen to the soil but often too late for the wheat crop. The above rates are based on mineral soils, which have both 1-5% organic matter and adequate drainage. Nitrogen rates would need to be reduced on soils with high organic matter to decrease the risk of lodging.

Besides the rate of nitrogen, application time is also important. In most years, nitrogen may be applied between early March and early April. A split spring application program may be a benefit in poorly drained fields that are prone to nitrogen loss. For these programs, it is important that the first application occurs soon after initial green-up and the second application at initial jointing (Feekes Growth Stage 6). The time of application is not as critical in a single topdress (providing some nitrogen was applied in the fall), but applications should be made after initial green-up and before the second visible node on the stem.

Most sources of nitrogen are satisfactory for wheat, but price and availability may limit some products this year. Urea and 28% solution (urea-ammonium nitrate) are often the most common. Urea has the least potential to cause damage to the crop. Damage is generally insignificant from broadcast applications of 28% solution applied early, but the potential for damage increases as the crop matures. Dribble band applications will minimize damage from 28% solutions. Urea-ammonium nitrate solutions will have some nitrogen available immediately at application time; urea will have a short lag as it converts to ammonium and nitrate forms of nitrogen. Generally, 28% solutions have the greatest potential for nitrogen losses since part of it is immediately in the nitrate form. Urea may have volatilization losses if temperatures are exceedingly warm.

In summary, except where water has been standing, the wheat crop looks well at this time and should have the potential for optimal yields. Carefully, consider reducing nitrogen rates. Leaving out sulfur and unproven amendments would be a better management decision than making large reductions in nitrogen rates (note, low CEC sands may need sulfur).

For more detailed information, please refer to the Extension bulletin E-2567, Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa.

D) Gray Leaf Spot On Corn And Labeled Fungicides - Pat Lipps CORN Questions

Gray leaf spot (GLS) is a potential threat to corn production each year in Ohio. Some areas of the state are more prone to yield losses from this leaf disease than others due to the predominating production practices and environmental conditions. Generally, the severity of the disease is related to reduced tillage, especially in fields planted continuously to corn. During years with exceptionally warm and humid weather, gray leaf spot can become important throughout the state as in 1995.

Control of the disease has been achieved through the use of resistant hybrids, tillage to destroy corn residues and adequate crop rotation with soybeans, wheat or forage crops. Where conservation tillage is used, a two year rotation away from corn is necessary because the fungus survives in corn residues left on the soil surface for up to two years.

Fungicides are available for use on corn to control GLS, but the economics of corn production have not permitted common use of these materials except on sweet corn, pop corn or seed corn. Fungicide applications have been evaluated in Ohio for control of GLS on field corn. During the growing seasons of 1996 through 2000, the yield response due to fungicide application on susceptible hybrids ranged from 2 to 32 bu/A. Obviously, the greatest yield responses occurred during years with highest disease pressure (1996 = 27 bu/A, 1997 = 2 bu/A, 1998 = 32 bu/A, 1999 = 19 bu/A, 2000 = 2 bu/A).

There are two fungicides labeled for control of GLS on corn, Tilt 3.6 EC and Quadris 2.08 SC. Tilt (2.0 - 4.0 oz/A) is labeled for control of several foliar diseases through end of silking (R2 stage of growth). Quadris Flowable Fungicide recently received a federal label for control of several foliar diseases on corn at 6.2-9.2 fl oz/A applied at disease onset, and can be used until 7 days of harvest. Other directions and restrictions are described on the labels.

Both of these fungicides are labeled for more than one application during the growing season, but due to the relatively low price of corn, multiple applications during the growing season is cost prohibitive. In Ohio and other states, two applications of Tilt or Quadris has provided better disease control than one, but in most tests there was no significant additional yield benefit from the second application. It appears that the most economical use of these products on susceptible hybrids is a single application. Tilt has provided the best results when applied at the V14 to R2 growth stage using the 4.0 fl. oz./A rate. Quadris appears to benefit from a slightly earlier application. Apply Quadris from V10- V14 growth stage using 9.2 fl. oz. /A. The label suggests that an adjuvant be added to improve coverage. When using ground equipment add drop nozzles to improve coverage of the leaves at and above the ear. We recommend treating susceptible hybrids; not hybrids with some degree of resistance to GLS.

In several (though not all) tests, Quadris provided superior disease control to that provided by Tilt. Thus, in terms of efficacy against gray leaf spot, Quadris may prove to be the better choice. However, because Quadris is used at an application rate over twice that of Tilt, the per-acre cost of Quadris is about twice as high as that of Tilt.

E) Dr. Harold R. Willson CORN Questions

Dr. Harold (Hal) Willson was involved in Integrated Pest Management for field crops as State Entomologist for The Ohio State University since 1983. Dr Willson died January 23 at St. Luke's Hospital in Maumee from complications of a stroke at age 59.

Hal had an active research and extension program to benefit Ohio's farmers in corn, soybean, wheat and alfalfa insect control techniques as well as stored grain pest management. Hal was a regular contributor to this newsletter where he shared updates on insect problems occurring across the state and best management practices to control those pest problems. He loved to get into the fields and get his hands dirty.

Dr. Willson was born in California and had degrees from University California in Riverside, University of California at Davis and Humboldt State University. His interest in international work began by serving in the Peace Corps in India during the 1960's. He met his wife Sally during his Peace Corps service. They had two children. His international work extended into his career at OSU and took him to places as diverse as South Africa, Switzerland, Columbia, Germany, Eritrea, Uganda and the Ukraine.

Prior to coming to OSU he was at Cornell University in Ithaca and the New York State Agricultural Experiment Station.

Hal got a great deal of pleasure working with farmers whether they were from Ohio or Uganda. He had a great love of international work and thus a memorial has been established to send his collection of entomology journals to Kampala, Uganda. Contribution can be made "H.R. Willson-Uganda Fund" c/o Steinhaus Financial Group 7650 Rivers Edge Drive, Columbus, OH 43235.

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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: Greg LaBarge        Web Editor: Tom Rosati

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