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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-07

Dates Covered: 
March 30, 2004 - April 6, 2004
Greg La Barge

Planter Adjustments – A Key Step in Achieving Uniform Stands 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.

1. Keep the planting speed within the range specified in the planter's manual.
2. Match the seed grade with the planter plate.
3. 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).
4. Check for wear on double-disc openers and seed tubes.
5. Make sure the sprocket settings on the planter transmission are correct.
6. Check for worn chains, stiff chain links, and improper tire pressure.
7. Make sure seed drop tubes are clean and clear of any obstructions.
8. Clean seed tube sensors if a planter monitor is being used.
9. Make sure coulters and disc openers are aligned.
10. Match the air pressure to the weight of the seed being planted.
11. Make planter adjustments and follow lubricant recommendations when using seed-applied insecticides (e.g. Poncho and Cruiser)

In 2004, as much as 20% or more of the corn acreage in Ohio may be planted with seed-applied insecticides (e.g.. Poncho and Cruiser). While these seed insecticides may 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

Winter annual weeds - it’s the seed production !!

Authors: Mark Loux

Sometimes we get so wrapped up in the use of herbicides, and how to maximize their effectiveness, that we forget to think about weeds’’s biology. Spring burndown programs are a good example, especially with regard to winter annual weeds. Many producers would like to delay burndown herbicide applications as late in the spring as possible, especially in Roundup Ready soybeans, with the goal of minimizing the number of trips across the field and the amount of glyphosate that is required for the entire season. This strategy may be the cause of more severe winter annual weed problems the following year, however.

A primary goal of spring weed management programs should be prevention of seed production by winter annual weeds. The seed of common chickweed, purple deadnettle, and other winter annual weeds generally lacks dormancy, and the seed produced this spring is the source of a new winter annual infestation this coming fall. The relative lack of dormancy also results in a fairly short seed life in soil for many winter annuals, so weed management programs that prevent seed production in spring can result in greatly reduced populations in coming years.

There are a number of reasons to control winter annuals early in spring in addition to preventing seed production. Winter annuals prevent the soil from drying out and warming up, they can interfere with tillage, they can attract black cutworms and other insects, and it can just be difficult to effectively establish no-till crops in a dense mat of weeds. So, rather than waiting to control winter annuals until the time of soybean planting, consider application of burndown herbicides combined with residual herbicides as soon as soil conditions allow traffic.

Early spring application of 2,4-D ester plus residual herbicides such as CanopyXL or Sencor will generally reduce the amount of glyphosate that is required. As applications are delayed later into April and May, the need for glyphosate will increase. Early-spring treatments of 2,4-D plus residual herbicides are effective on many winter annuals, but can be weak on common chickweed. The addition of Sencor, glyphosate, or Gramoxone will often be required for chickweed control. In a dense winter annual weed situation, where rapid death and dessication of weeds is desirable to enable crop establishment, a combination of 2,4-D ester plus Sencor plus Gramoxone can be a more effective choice that systemic herbicides such as Canopy and glyphosate.

In corn, most combinations that include atrazine and 2,4-D will effectively control winter annuals, but the addition of glyphosate or paraquat will aid in control of dense infestations, especially later in spring. Gramoxone and atrazine work especially well together where rapid death and dessication are desirable. We generally suggest that residual herbicides for corn (especially grass herbicides) be applied no more than about a week before planting to maximize later-season grass control, unless you are in a planned preemergence followed by postemergence herbicide program.

Guidelines for Wheat Herbicides

Authors: Mark Loux

Winter annual weeds should be controlled as soon as possible in fields where herbicides have not been applied. However, herbicides applied now will not adequately control later-emerging summer annuals, such as ragweeds and Canada thistle. Fields should be scouted within a few weeks to determine if the populations of summer annuals 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. As wheat growth stage advances past jointing, and then 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, 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.

Harmony GT: Similar to Harmony Extra, but less effective on Canada thistle, chickweed, and a few other winter annuals. Apply with nonionic surfactant.

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.

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.

Fine Tune your Sprayer

Authors: Erdal Ozkan

Keeping any farm equipment fine-tuned is critical to cutting production costs and reducing the risk of harming the crop or the environment. This is particularly true with equipment that handles any pesticides. Higher pesticide costs and new chemicals designed to be used in lower doses make accurate application more important than ever. There is no better time than early spring to take a closer look at your sprayer.

Six tips for success
Here are some things I would check to achieve efficient and effective application of pesticides:

•Double-check your sprayer for mechanical problems before you start using it. You won’t have time to do this when planting is in full swing.

•Clean the sprayer tank thoroughly and make sure nozzle filters are clean.

•Clean spray nozzles, check their flow rates, and replace any that are spraying more than 10 percent of the intended output.

•Check the agitator in the tank to make sure it’s working properly.

•Run water through the spray system to make sure everything is working properly

•Find out if the sprayer is delivering the proper application rate (gallons per acre).

Calibrate, calibrate, calibrate
One can determine if the chemicals are applied at the proper rate only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production. Applying too little pesticide may result in ineffective pest control. Too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating ground water and environment.

Results of many "Sprayer Calibration Clinics" I participated in in Ohio shows that only one out of three applicators are applying chemicals at a rate that is within 5 % (plus or minus) of their intended rate. Of the two-thirds missing the mark, about half are under spraying. In one case, the sprayer was over applying by 75%.

Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration. Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate. More frequent calibration leads to more accurate application.

There are several ways to calibrate a sprayer and it takes about half an hour. You need only three things: a watch with a second hand, a measuring tape, and a jar graduated in ounces. One particular method that I like is simple, straightforward, and does not require the memorization of equations. This method is explained in OSU Extension Fact Sheet AEX-520. This publication can be obtained by contacting your County Extension Office, or from the web site:

Get within 5 percent
If the difference between your intended application rate and the actual rate determined after calibration is greater than ± 5 percent, you should make some adjustments. For small changes try adjusting the pressure. For larger changes either adjust the travel speed or replace nozzles with the appropriate size. Then repeat the calibration process until your application error is within 5 percent.

Archive Issue Contributors: 

State Specialists: Anne Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux (Weed Science), Jeff Stachler (Weed Science),Erdal Ozkan (Agricultural Engineer), Bruce Eisley (IPM) and Ron Hammond (Entomology); Extension Agents: Roger Bender (Shelby), Barry Ward (Champaign), Todd Mangen (Mercer), Greg La Barge (Fulton), Howard Siegrist (Licking), and Harold Watters (Miami)

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.