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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2005-06

Dates Covered: 
March 22, 2005 - April 4, 2005
Steve Prochaska

Guidelines for Wheat Herbicides

Authors: Mark Loux

Winter annual weeds should be controlled in winter wheat as soon as the weeds have at least 1 inch of new growth. This is especially true for winter annual grasses such as downy brome, cheat, annual bluegrass, and annual ryegrass. There are only two wheat herbicides that can be applied in the spring in Ohio to effectively control grasses. The larger the winter annual weeds, the more difficult they become to control.

If herbicides are applied now, later-emerging summer annuals, such as ragweeds and the creeping perennial, Canada thistle will not be controlled because these weeds have not emerged yet. Fields should be scouted within a few weeks to determine if the populations of ragweeds and Canada thistle merit additional herbicide treatments. In fields without winter annuals, delay herbicide application until that time, and select products based on scouting. Be sure to follow label guidelines to minimize risk of crop injury and yield loss. When wheat has not yet reached the jointing stage, any herbicide labeled for wheat can be safely applied. Dicamba has the greatest potential to reduce wheat yield when applied after the jointing stage. As wheat growth stage advances past jointing, and later past boot stage, herbicide choices become much more limited. Guidelines are as follows – see the OSU/Indiana Weed Control Guide and labels for more information.

2,4-D: all 2,4-D products are labeled for application before jointing. A few are labeled up to early boot stage. 2,4-D is generally safe up to early boot, but the risk of injury increases after jointing. 2,4-D will not control chickweed or henbit, and can be weak on smartweed and deadnettle. MCPA products have characteristics and labeling similar to 2,4-D products.

Dicamba (Banvel, Sterling, Clarity, etc): Apply before jointing. Rate labeled for wheat is low, and will be most effective in a tank-mix or premix with another herbicide (e.g WeedMaster is a premix of 2,4-D amine plus dicamba). Not as effective as 2,4-D on mustard species, but more effective on smartweed. Weak on chickweed, deadnettle, henbit, and wild garlic.

Bromoxynil (Buctril, Moxy, etc): Apply before the boot stage. Applying in fertilizer solution increases leaf burn. Weak on most winter annuals, dandelion, and wild garlic, but effective on most summer annuals. For best results apply before weeds reach the 4-leaf stage or a height of 2 inches.

Curtail: premix of 2,4-D plus Stinger. Apply up to 2 pints before jointing, and up to 1.5 pints before boot stage. Excellent control of ragweeds and Canada thistle, and among the most effective wheat herbicides on dandelion. Weak on chickweed, henbit, and wild garlic. Do not plant double crop soybeans in fields treated with Curtail.

Harmony Extra: Apply before flag leaf is visible and when weeds are less than 4 inches tall or across (rosette). Apply with nonionic surfactant. Effective for wild garlic (at high rates) and most winter annuals. Weak on ragweeds and ALS-resistant marestail. DuPont strongly discourages the use of liquid nitrogen as a carrier.

Harmony GT: Similar to Harmony Extra, but less effective on Canada thistle, chickweed, and a few other winter annuals. Apply with nonionic surfactant. DuPont strongly discourages the use of liquid nitrogen as a carrier.

Express: Apply before the flag leaf is visible when weeds are less than 4 inches tall or across (rosette). Not as broad spectrum as Harmony Extra, but more effective on Canada thistle and dandelion. Apply with 2,4-D for most effective dandelion control. Apply with nonionic surfactant. DuPont strongly discourages the use of liquid nitrogen as a carrier.

Peak: Apply before 2nd node is detectable in wheat stem elongation, and when weeds are 1 to 3 inches tall. Do not plant double crop soybeans in fields treated with Peak. Apply with crop oil concentrate or nonionic surfactant.

Olympus: Apply before jointing. Effective on cheat, foxtail barley, and many mustard species and should suppress downy brome, quackgrass, and henbit. May be tank-mixed with all of the above herbicides, except Express. Apply with nonionic surfactant. Olympus may be applied in a liquid carrier of up to 50% liquid nitrogen. This product has a long residual period, therefore, corn and soybeans should not be planted without a successful bioassay and clearly later than 4 months after application and potentially 18 months for corn.

Osprey: Apply before jointing. Effective on annual bluegrass, annual ryegrass, and wild mustard and may suppress common chickweed, henbit, and downy brome. May be tank-mixed with all of the above broadleaf herbicides, except Express, 2,4-D, and dicamba. Apply with methylated seed oil (MSO), unless restricted by the tank-mix partner. May be applied in a liquid carrier of up to 15% liquid nitrogen. Soybeans may be planted 90 days after application, but corm may not be planted until 12 months after application.

Planter Maintenance and Stand Establishment in Corn

Authors: Peter Thomison

Uneven plant spacing and emergence may reduce yield potential in corn. Seed should be spaced as uniformly as possible within the row to ensure maximum yields and optimal crop performance. Corn plants next to a gap in the row may produce a larger ear or additional ears (if the hybrid has a prolific tendency), compensating to some extent for missing plants. Skips can reduce yield in fields where the intended population is at or below the optimum, while doubles increase yield when populations are less than optimum. Reduced plant stands will yield better if plants are spaced uniformly than if there are large gaps in the row. As a "rule of thumb", yields are reduced an additional 5 percent if there are gaps of 4 to 6 feet in the row and an additional 2 percent for gaps of 1 to 3 feet.

Uneven corn emergence will generally have a greater impact on grain yield than uneven plant spacing. Uneven emergence affects corn performance because competition from larger, early-emerging plants decreases the yield from smaller, later-emerging plants. If the delay in emergence is less than two weeks, replanting increases yields less than 5 percent, regardless of the pattern of unevenness. However, if one-half or more of the plants in the stand emerge three weeks late or later, then replanting may increase yields up to 10 percent. Emergence delays of 10 days or more usually translate to growth stage differences of two leaves or more. When two plants differ by two leaves or more, the younger, smaller plant is more likely to be barren or produce nubbin ears. Weeds also tend to be a greater problem in those areas of a field characterized by skips and gaps in the corn rows, and slow, erratic corn emergence.

Corn sometimes emerges unevenly because of environmental conditions beyond the control of growers. However, timely planter servicing and adjustment, as well as appropriate management practices, can help prevent many stand uniformity problems.
The following are some tips for improving the uniformity of seed placement during planting:

Keep the planting speed within the range specified in the planter's manual.

Match the seed grade with the planter plate.

Check planters with finger pickups for wear on the back plate and brush (use a feeler gauge to check tension on the fingers, then tighten them correctly).

Check for wear on double-disc openers and seed tubes.

Make sure the sprocket settings on the planter transmission are correct.

Check for worn chains, stiff chain links, and improper tire pressure.

Make sure seed drop tubes are clean and clear of any obstructions.

Clean seed tube sensors if a planter monitor is being used.
Make sure coulters and disc openers are aligned.

Match the air pressure to the weight of the seed being planted.

Make planter adjustments and follow lubricant recommendations when using seed-applied insecticides (e.g. Poncho and Cruiser)

I’ve been told by some seed company agronomists that as much as 40% of the corn seed they’re selling in Ohio in 2005 is treated with seed-applied insecticides (e.g.. Poncho and Cruiser). While these seed insecticides can help reduce stand losses from soil insects, it is critical that corn growers make planter adjustments and follow lubricant recommendations when using these seed-applied insecticides. Unless these precautions are followed, the extra chemical loading on the seed may adversely affect the “plantability” of seed – vacuum planters may underseed and finger pickup planters may overseed. To improve planter accuracy, talc or graphite should be used according to the planter manufacturer’s recommendations. With vacuum planters, it will probably be necessary to raise the vacuum to achieve more accurate seed drop.

For more information on planter adjustments to improve stand establishment in corn, consult: "Tips to Reduce Planter Performance Effects on Corn Yield" OSU Extension Fact Sheet AGF-150-01

Dr. Bob Nielsen at Purdue University has prepared a good article entitled “Planter Maintenance: Less Down Time, More Yield ” (Chat 'n Chew Café, 21 Feb 2005). It includes links to the service support Web pages at Case-IH, Deere, and Kinze and is accessible online at

Early Burndown Herbicides

Authors: Mark Loux

The goal of winter annual weed management should be to prevent or drastically reduce seed production. In order to accomplish this, burndown herbicides must be applied before mid-April. Any application after this point in time will allow greater seed production and continued winter annual pressure for next season.

Weeds such as marestail/horseweed, dandelion, curly dock, cressleaf groundsel, wild carrot, and poison hemlock are best controlled by a combination of 2,4-D and glyphosate. The rate of 2,4-D should be at least 0.5 lb ai/A (0.67 pt/A of a 6.0 pound/gallon product or 1.0 pt/A of a 4.0 pound/gallon product) and the rate of glyphosate should be at least 0.75 pound acid equivalent/A (20-32 ounce/A, depending upon product). Higher rates of glyphosate will provide more consistent results, especially under stressful conditions.

When applying burndown herbicides before planting, the addition of a residual herbicide such as Gangster, Valor, Sencor, Python, etc., will keep the field free of weeds. This will allow for faster soil dry-down, reduced early-season weed competition, allow for a wider window of the POST application, and should provide residual control of some species that are difficult for glyphosate to control.

Gangster, Valor, and Sencor can antagonize glyphosate on many weed species. To overcome the antagonism, add 2,4-D ester and/or increase the rate of glyphosate.

To effectively control marestail/horseweed, apply the appropriate herbicides before the marestail begin to produce a stem (bolt). After plants have bolted they become more difficult to control for all herbicides. For the most effective burndown control of any type of resistant marestail, apply three-way mixtures. The most effective mixtures will be 2,4-D (0.5 pound active ingredient/A) plus glyphosate (at least 1.1 pounds acid equivalent/A) plus cloransulam (at least 0.25 ounce active ingredient/A) and 2,4-D (0.5 pound active ingredient/A) plus Gramoxone Max (at least 1.3 pint/A before bolting and at least 1.7 pint/A after bolting) plus Sencor (8.0 oz/A). Burndown applications before mid-May will require the addition of a residual herbicide that effectively controls marestail. Those herbicides providing good residual control include Gangster, Sencor, Valor, Canopy XL, FirstRate, Python, Synchrony XP, Canopy EX and possibly high rates of Sencor plus metolachlor. For those populations that are ALS-resistant, the FirstRate, Python, Synchrony XP, and Canopy EX will not effectively control marestail. For more information about marestail biology and control look at the publication, “Biology and Management of Horseweed”, which can be found at the following web address:

Most residual herbicides in soybeans can effectively control common lambsquarters. Those herbicides that are least effective include s-metolachlor, metolachlor, and alachlor. The application of a residual herbicide in soybeans may completely control all lambsquarters or at least allow the POST herbicide to more effectively control what few lambsquarters that will be present at the time of application.

What Makes a Spray Fine , Very Fine or Not Fine?

Authors: Erdal Ozkan

More and more we started seeing some specific recommendations/requirements on pesticide labels such as: apply this product with nozzles producing a medium spray quality". If you don't know the difference between "fine", "medium" or "very fine" spray qualities, you are not ready to fight against Soybean Rust disease. Perhaps you have already seen in writing or heard from some one that the nozzles producing fine to medium quality spray are more likely to provide better coverage on leaves, and for that reason, should provide better protection against Soybean Rust.

What is a “fine” quality or a “medium” quality spray, and how do we achieve that quality of spray? Why did we have to categorize spray quality in this fashion? Here are the answers to these and other related questions.

Perhaps Soybean Rust made spray quality a household name, but the work for classification of sprays based on the size of droplets was started because we wanted to rate nozzles based on their drift potentials. After wind speed and direction, spray droplet size is the second most important factor affecting drift. Each class of nozzles, even the same type of nozzle with different orifice sizes (flow rates) , or the same nozzle operating under different conditions all will have different droplet size distributions, consisting of droplets ranging from very small to very large at different proportions. To avoid drift, one should choose the best nozzle and operate it under most optimum pressure settings.

Almost all major agricultural nozzle manufacturers have recently introduced their version of “Low Drift” nozzles. These nozzles are designed to create larger droplets at the same flow rate and operating pressure than comparable conventional flat fan nozzles. However, if operated at low pressures, some conventional nozzles can be as effective in reducing drift as the low drift nozzles operating at higher pressures. Mostly for this reason, pesticide manufacturers were not able to recommend one particular type of a nozzle for drift control. On the other hand, US EPA has been requesting some type of information on labels which applicators can use to determine nozzle size, type and operating parameters to reduce drift. To help manufacturers of pesticides and regulatory agencies such as EPA, American Society of Agricultural Engineers has developed a standard called Spray Nozzle Classification by Droplet Spectra (ASAE S-572). This Standard defines droplet spectrum categories for the classification of spray nozzles, relative to specified reference nozzles discharging spray into static air. It defines a means for relative nozzle comparisons based on droplet size only.

This Standard identified 6 spray quality categories: very fine, fine, medium, coarse, very coarse, and extremely coarse. Also, a unique color is assigned to each class. (This color should not be confused with the color coding for flow rates). Following table gives the classification categories, their symbols and corresponding color codes. Also shown are approximate VMD (Volume Median Diameter) droplet sizes associated with each class. The droplet sizes given are for comparison purposes only and should not be used for all nozzles, and operating conditions. Nozzle flow rate, spray pressure, and physical changes to nozzle geometry and operation can affect nozzle classification. In other words, a given nozzle can be classified into one or more droplet size categories, depending on the selection of flow rate, operating pressure, and other operational conditions. To determine the exact drop size classification of a nozzle under a given set of operating condition, one should always check the data given in nozzle manufacturer catalogs.

Classification categories, symbols, and corresponding color codes are as follows:

Size (VMD
Symbol Color Code
Droplet Size
Very fine VF
<150 micron
Coarse C
Very Coarse
>500 micron

** VMD, Volume Median Diameter droplet size, is the size of the droplet which divides the spray in two equal parts by volume. Half of the spray volume is contained in droplets smaller than the VMD, the other half of the spray volume is contained in droplets larger than the VMD. (For reference: There are 125,000 microns in one inch. Thickness of human hair is about 75 to 100 micron)..

Soybean Rust Update for March 21

Authors: Anne Dorrance

Much activity the past few weeks – so I will break it down by bullet point.

1. Soybean Rust has been removed from the list of select agents. This is a key move to help manage this disease. For those that were not aware, 9 plant pathogens were placed on list of select agents, mainly those pathogens which could potentially be used a bioterrorism threats against US Agriculture. Since soybean rust has arrived here NATURALLY, as it was predicted – then there is no reason to have this still in place. How does this affect you as producers? It means that the FBI will not show up on your doorstep once it is found in Ohio. We still, however, must follow protocols for the first finds in a state to be submitted to Ohio’s C.Wayne Ellett Plant and Pest Diagnostic Clinic and there have always been restrictions in place regarding movement of plant pathogens across state lines. Anyone can send samples to the clinic for diagnosis – because the clinics have the permits to accept these samples and a protocol to handle and diagnose. How does this affect me as an OSU researcher? Once it is found in Ohio, and not until then, I can begin studying this plant pathogen and develop studies to determine the best means to manage this pathogen under Ohio’s environmental conditions.

2. More requests for Section 18s were submitted to EPA. The one that maybe the most pertinent to this coming season is for Headline SBR and Headline STAR. The active ingredients are tebuconazole (Folicur) and Pyraclostrobin (Headline). If approved by EPA, they will be sold as a co-pack mixture or premix. Headline alone already has Section 3 labeling and Folicur recently received Section 18 approval. We will keep you posted on when EPA approves this for Ohio.

3. Lot’s of confusion over 2 or 3 applications for the materials that have been given Section 18 approval. To date, EPA has only approved 2 total applications per season of section 18 products for the growing season, with the exception of Domark, which can only be used once. We have applied for 3, but as of today (March 21) this has not been approved. Also, just to correct some rumors out there. This means 2 applications, it does not matter whether you apply at the low rate or high rate; it is for 2 applications total. For rust diseases, outstanding coverage and the high rates are required for best management of these diseases.

4. USDA has launched their soybean rust website This site will have more links and information on soybean rust throughout the growing season. Under the section labeled on the first page – follow the link to SBR in the United States. This is where you will be able to find information on the distribution and severity of soybean rust in the different states. Click on the state of Ohio; you will get specific information on Ohio’s sentinel plot system and fungicide guidelines for the state after soybeans have been planted and are up and growing!

Archive Issue Contributors: 

Mark Loux and Jeff Stachler (Weed Science), Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Erdal Ozkan (Engineering)(Peter Thomison (Corn Production), Robert Mullen (Soil Fertility) Extension Agents and Associates: Roger Bender(Shelby), Steve Bartels (Butler), Dusty Sonnenberg (Henry), Bruce Clevenger (Defiance) Harold Watters (Miami), Todd Mangen (Mercer), Glenn Arnold (Putnam) 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.