C.O.R.N. Newsletter 2007-32

Dates Covered: 
September 24, 2007 - October 1, 2007
Andy Kleinschmidt

The ABC’s of Fall Herbicide Treatments

Authors: Mark Loux

Fall herbicide treatments have become a fairly common practice for some no-till producers, who recognize their value for managing certain tough winter weeds and providing a weedfree seedbed in the spring. Fall herbicide treatments should accomplish two major goals. First, the fall treatment has to control winter annual, biennial, and perennial weeds that emerge in late summer or fall or are already present at the end of the previous crop’s harvest. Weeds in this category include chickweed, annual bluegrass, purple deadnettle, marestail, wild carrot, and dandelion, among others. These weeds overwinter and regrow in the spring, interfering with crop establishment and early-season growth, and they need to be controlled by a fall or early-spring herbicide application. A secondary goal is to prevent seed production by these weeds, which reduces future weed infestations. While they may not provide complete control, fall herbicide treatments are by far the most effective method for controlling dandelion, poison hemlock, and wild carrot.

The primary value of fall herbicide treatments is control of weeds that have emerged by the time of application, which typically results in a weed-free field next spring, at least until sometime later in April. This can be accomplished with about $6 to $12 worth if herbicide. Some considerations for fall treatments:

1. Effectiveness of the treatment is important – speed of control is not. The most effective fall treatments will result in weed-free fields the following spring, even if they do not appear to be controlling much later in the fall.

2. There is a core group of herbicides that will control emerged weeds when applied in the fall. Combinations of two herbicides are usually more effective than any single herbicide, since every herbicide is weak on at least one or two weeds that are found in fields in the fall. Effective fall herbicide treatments include the following:

Any crop next spring
Glyphosate + 2,4-D

Soybeans next spring
Canopy EX or DF + 2,4-D
Glyphosate + 2,4-D
Sencor + 2,4-D (excluding dandelions)
Autumn + glyphosate or 2,4-D

Corn next spring
Basis + 2,4-D
Glyphosate + 2,4-D
Simazine + 2,4-D
Autumn + glyphosate or 2,4-D

3. Some additional comments on these treatments, based on the results of OSU research:

- Glyphosate + 2,4-D is the most effective for control of perennials (other than dandelion) and most biennial weeds (glyphosate can be added to the other treatments to accomplish this). Control with glyphosate applied alone is often similar to the combination of glyphosate + 2,4-D, but the 2,4-D is needed for glyphosate-resistant marestail. Application of 2,4-D alone controls many winter annual weeds, but 2,4-D will not control chickweed and is less effective on dandelion applied alone versus mixtures with other herbicides.

- Combinations of 2,4-D plus Canopy or Basis have been the most consistently effective on dandelion. The combination of Express plus 2,4-D is also effective, but does not have residual activity on later-emerging weeds.

- Autumn has been more effective when mixed with glyphosate, rather than 2,4-D.

- In OSU research, Canopy + 2,4-D treatments have been the most effective for fields planted to soybeans the following spring. Control of emerged weeds in the fall can be similar between Canopy EX/DF and the other treatments, but Canopy provides the most effective residual control of spring-emerging winter and summer annuals. Within the labeled rate range, any Canopy rate is usually effective for control of emerged weeds, but the increasing the rate can improve the control of summer annual weeds that emerge the following May/June.

- Basis and simazine treatments provide limited residual control of spring-emerging weeds, and primarily early-emerging winter annuals. The choice of herbicide programs for in-season weed control in the following year’s corn should largely not be based on what was applied in the fall. In other words, a comprehensive herbicide program is needed in corn regardless of whether herbicides were applied the previous fall, with the exception that the preemergence herbicides may not need to have much burndown activity in fall-treated fields.

4. For control of winter annual weeds, apply herbicides anytime after early October. The amount of crop residue on the soil surface has not appeared to affect herbicide activity in our research. However, there may be some benefit to waiting a week or more after harvest, where possible, to allow crop residue to settle. For the most effective dandelion control, delay application until after a frost. We have applied as late as early December for control of winter annual weeds, but we generally recommend application when dandelions are still mostly green, or by mid-November if possible.

5.Apply glyphosate-containing treatments with ammonium sulfate, and additional nonionic surfactant if specified by the product label. We have generally used crop oil concentrate (plus 28% in some instances) in treatments that do not include glyphosate, but manufacturers may have specific adjuvant recommendations that optimize their product’s activity.

6. We question the value of treatments that cost more than about $12, because the additional money does not result in more effective control of emerged weeds. Treatments that cost more can be the result of adding; 1) herbicides that speed up activity, but do not improve the end result (Aim, for example); or 2) herbicides with residual activity (Valor, Scepter, etc), to control spring-emerging weeds. Whether fall is a good time to apply residual herbicides is debatable, as discussed in the article that follows.

Should Residual Soybean Herbicides be Applied in the Fall?

Authors: Mark Loux

Our experience has been that the primary benefit of fall treatments is control of weeds that are present at the time of treatment, not residual control of weeds the following year. Any effective fall treatment usually results in a field that is mostly free of weeds until about late April, and this goes for treatments without residual as well as those with residual. In other words, in late April we cannot usually discern much difference between a fall treatment of glyphosate plus 2,4-D versus Canopy EX/DF plus 2,4-D, even though the Canopy provides residual activity into the spring. However, the effect of the residual herbicide becomes much more apparent by the end of May, when its activity on summer annual weeds comes into play.

The issue here is not really control at the time of soybean planting, since any effective fall treatment results in a relatively weed-free field at the end of April. The issue is how well the residual herbicide controls weeds after planting, in order to build more flexibility into the postemergence application window. This flexibility can result in less risk of early-season yield loss from weed interference and result in a better chance of getting the postemergence herbicides applied to the right size weeds. We also look to the residual herbicide to help control several weeds that glyphosate can be somewhat variable on, such as giant ragweed and lambsquarters, and also to aid in control of glyphosate-resistant weeds, such as marestail. If glyphosate is being managed properly, it is typically going to be extremely difficult to get by with one postemergence glyphosate application unless the residual herbicide applied in the fall provides substantial weed control into late May. Even when this occurs, a second postemergence application is often needed to obtain season-long control.

Herbicides other than Canopy EX/DF can provide residual control of certain weeds when applied in the fall, but they tend to control fewer weed species and/or be generally less effective than Canopy, or more expensive. For example, Valor provides residual control of lambsquarters into early June, but is less effective than Canopy EX and provides very little control of giant ragweed. Scepter provides very little control of lambsquarters or giant ragweed when applied in the fall, whereas it can provide substantial residual control of these weeds when applied in the spring. Fall application of Valor XLT has foliar and residual activity similar to Canopy, but at a substantially higher price.

The bottom line on fall herbicide treatments – choose an effective treatment from the list in the previous article, and be cautious about adding residual herbicides that claim to improve control of weeds that emerge in the spring. The utility of most residual herbicides is maximized when applied in the spring prior to planting, not in the fall. A better alternative may be to use a non-residual herbicide program in the fall, such as glyphosate plus 2,4-D, followed by spring application of residual herbicides. This approach provides for the greatest flexibility in the postemergence application window and the most effective control of weeds such as lambsquarters, marestail, and giant ragweed.

Minimizing Harvest Losses in Drought Damaged Corn Fields

Authors: Peter Thomison

Drought stress, combined with uneven emergence and development problems, has resulted in smaller than normal ears, and a greater percentage of "nubbin" ears in many Ohio corn fields. In some fields, plants are shorter than normal with reduced ear heights. Debris deposited by late season flooding in parts of NW and NC Ohio will make harvesting more difficult, as will dust associated with soiled plants. As a result of these conditions, some combine and harvesting adjustments may be necessary.

The following are management suggestions from ag engineers and equipment specialists on harvesting drought damaged crops.

1. Review the operator's manual for suggestions on harvesting a "light crop".

2. With short or lodged corn, run the gathering snouts and chains low. Watch for stones, logs and other debris, and be sure stone protective devises are working.

3. Drive carefully and at normal speeds to avoid excessive harvest loss and machine damage from stones.

4. For small ears, set stalk rolls and snapping plates closer than normal to snap off a higher percentage of ears. Do not attempt to snap off barren cobs.

5. If clean shelling is a problem, increase cylinder speed slightly, and if necessary, decrease concave clearance. With a rotary machine, check rotary concave clearance. Avoid excessive damage to kernels from good ears.

6. If cleaning losses are high, open the chaffer and chaffer extension slightly.

7. Initially decrease the amount of air from the cleaning fan. If cleaning becomes a problem, increase the fan blast, and close the lower sieve slightly.

8. Be alert to changes in weather and crop conditions, and make adjustments as necessary.

Wheat Seed Size and Seeding Rate

Authors: Pierce Paul, Jim Beuerlein

Because of the warm, dry weather experienced in some parts of the state this past season, some of the wheat seed fields harvested this spring had short grain fill periods which resulted in smaller seeds for planting this fall. Normally, there are thirteen to seventeen thousand wheat seeds per pound, but some of the seed lots we will plant this fall may have more seeds per pound. Although the number of seeds per foot of row is the same as in previous years, the pounds of seed per acre may be less this fall.

Calibrate the drill for each variety and each seed lot planted. The optimum seeding rate is 1.2 to 1.6 million seeds per acre for 7.5-inch rows when planting during the two weeks following the fly-safe date. During the third and fourth week after the fly-safe date, plant 1.6 to 2.0 million seeds per acre. Do not plant faster than the speed at which the drill was calibrated. The number of seeds per pound and germination rates are critical factors that need to be known before the proper seeding rate can be determined and the drill calibrated. That information should be listed on the bag of seed. The following table shows the pounds of seed needed per acre to accomplish various seeding rates using different sizes of seed.

The following table provides information on pounds of seed needed to plant from 1.2 Million to 2.0 Million seeds per acre with different size wheat seed:

---Millions of Seed Per Acre----

Seeds per Pound





























































Managing Black Cutworms with Fall Herbicide Applications

Authors: Ron Hammond, Bruce Eisley

In this week’s CORN newsletter, Mark Loux writes an article on the benefits on fall herbicide treatments and providing a weed free seedbed in the spring. Another outcome that is possible from providing a weed free seedbed in the spring relates to an insect pest that can cause significant damage to field crops, black cutworms. Having seen increased cutworm problems the past few years, growers should be reminded how various cultural practices, fall herbicide applications in this case, that can help reduce the level of this insect pest.

The adult black cutworm moth migrates from more southern locations each spring, laying their eggs on numerous perennial weeds in the spring followed by movement to corn. Much of this insect movement occurs when the weeds are killed in the spring with a spring herbicide application.

A management practice known for years is providing a weed free situation in the spring; without the weeds, the likelihood of cutworm problems are greatly diminished. An easy way to accomplishment this is with a fall herbicide application that not only rids the field of the weeds, but removes the oviposition sites for this insect. Thus, when considering the benefits to a fall herbicide application, do not forget the added benefit of black cutworm management. With the various seed treatments not providing acceptable management of black cutworms, eliminating weeds is an excellent preventive tactic to begin your corn insect management for 2008!

Lime Considerations

Authors: Edwin Lentz, Robert Mullen

Fall is an excellent time to test soil pH and determine whether any lime needs to be applied for future crops. Proper soil pH is important for nutrient availability, herbicide activity, and crop development. For most soils, additional lime is not needed every year. Consider these points before liming your fields:

1. Do I need lime? Each year we hear stories of people adding lime to their fields without a soil test. The grower has a source of free waste-product lime that they pick up and apply to their fields. In many cases their soil pH was fine, but they did not want to pass up a "good deal". Without knowing the soil pH, a grower may inadvertently raise their soil pH to the high 7's. At this elevated pH, certain nutrients may become limited and the productivity of their crop may be reduced and require special management practices. Northwest Ohio has the greatest risk of elevating soil pH from careless applications of lime. A soil analysis is the best step to determine if a field needs lime.

2. What is the pH of my subsoil? Generally a laboratory recommends lime when the soil pH drops two to three units below the desired value. The desired value depends upon the crop and the pH of the subsoil. In parts of Ohio where the subsoil pH is less than 6.0 for mineral soils (eastern Ohio), additional lime is recommended after the soil pH drops to 6.2 for corn and soybean, and 6.5 for alfalfa. In other parts of the state (generally western Ohio), the subsoil pH for mineral soils is greater than 6.0 and lime is not needed until the soil pH drops below 6.0 for corn and soybeans, and 6.2 for alfalfa. Private laboratories may not take in account the subsoil pH and use recommendations based on a subsoil pH less than 6.0 for all parts of the state, possibly recommending lime applications several years earlier than needed for some areas.

3. Do I need magnesium (Mg)? Several parts of the state are historically low in soil magnesium (eastern and extreme southern Ohio). Adequate soil magnesium is important to reduce the risk of such problems as grass tetany for grazing animals. Soil test magnesium levels need to be greater than 50 ppm (100 lb) for optimal corn, soybean, wheat, and alfalfa production. Often areas low in magnesium also need lime, which has made the application of dolomitic lime an economic solution for both concerns. Unfortunately, some producers have been led to believe that magnesium levels in dolomitic lime may be undesirable. The Ohio State University has shown that crops yield the same over a wide range of calcium to magnesium ratios and is not critical as long as a lime source contains more calcium than magnesium. Thus the level of magnesium is unimportant as long as the calcium level is above magnesium. The focus should be selecting lime on its Effective Neutralizing Power (ENP) rather than its calcium level.

4. What is the Effective Neutralizing Power of my lime? An important item from a lime analysis report is the Effective Neutralizing Power (ENP) value, which is required for material sold as lime for agricultural purposes in Ohio. This value allows a producer to compare the quality among lime sources because ENP considers the purity, neutralizing power (including fineness) and moisture content. In other words, the ENP tells you how much of that ton of lime actually neutralizes soil acidity. The unit for ENP is pounds/ton (be careful not to use %ENP, which may also be on a lime analysis report). The ENP allows a producer to compare different lime sources because they can now determine price per pound or ton of actual neutralizing material.

In summary, make sure you take a soil test, determine if lime is needed, determine if magnesium is needed, know the historic pH of your subsoil, and then use the ENP to select the most cost effective lime material. A soil test every three to four years will determine the lime requirements for your fields. Additional information on ENP and lime sources may be found at


and a lime application rate calculator may be found at


Soybean Disease Update for September 2007

Authors: Anne Dorrance

Ohio’s crop is mostly ready for harvest with few late season problems. Albeit there are pockets of Sclerotinia and Frogeye – but on the whole things look great. There are a few comments about green soybeans. It is worth the time to go and check to be sure that those green soybeans do have pods on them. Soybeans with malformed pods due to virus diseases will not die until a frost, and it is much better to harvest a field when it reaches the right moisture instead of letting it sit in the rain. Fields that are allowed to sit run the risk of secondary diseases caused by a number of fungi including: Phomposis, Diaporthe, Fusarium, and Cercospora. All of these can have a negative impact on seed quality. There is no point in waiting if the green plants do not have harvestable seed in them.

Soybean rust. Many of Ohio’s sentinel plots are finished and some have been harvested. At this point we are still negative. Numerous new finds of soybean rust in the southern and south central part of the US; Kansas, western Kentucky, and South Carolina reported finds. The Kansas and Kentucky finds relate back to rains that occurred during the week of September 5th. What is interesting in both of these is that the rain was a slow gentle rain, not a driving hard rain. Kentucky also reports that the incidence is 13% (13 out of 100 leaves were positive for rust) and the severity is very, very low (1%). At this point there is no reason to spray any of Ohio’s double crop soybeans.

Fall Herbicide Treatments in Pastures and Hayfields

Authors: Mark Loux

Fall herbicide treatments are an effective tool for control of certain weeds in pastures and hayfields. The biennial weeds that are common in pastures, such as bull thistle, burdock, and poison hemlock, can be effectively controlled at this time of the year. This is also the best time of the year to apply herbicides for control of Canada thistle and many other perennials. Warm-season perennials, such as horsenettle, should be treated before the first frost. Cool-season perennials, such as Canada thistle and dandelion, can be treated into late fall. See the “Pasture” section of the “Weed Control Guide for Ohio and Indiana” for more information on herbicide effectiveness on specific weeds.

Late-summer seedings of alfalfa often become infested with winter annual weeds, such as chickweed, mustards, field pennycress, wild turnip, and wild radish. These weeds can compete with the alfalfa in the fall and early spring, reducing the health of the stand and the quality of the first cutting next spring. Wild radish and wild turnip can be extremely difficult to control in the spring, because overwintering plants already have a well-developed, large root by the time herbicides can be applied. Fall herbicide treatments provide the most effective control of these two weeds. We have somewhat limited research on the control of wild radish and wild turnip, but results so far show that Butyrac (2 qts/A) or Pursuit plus Butyrac (1.44 oz + 1 qt/A) is among the most effective treatments. Pursuit will injure any grasses in the field, especially in new seedings. In Roundup Ready alfalfa, fall application of glyphosate (0.75 lb ae/A) should also control most winter annual weeds and dandelions.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Robert Mullen (Soil Fertility), Ron Hammond and Bruce Eisley (Entomology), Jim Beuerlein (Small Grains), Mark Loux (Weed Science), and Peter Thomison (Corn Production) Extension Educators: Harold Watters (Champaign), Howard Siegrist (Licking), Steve Bartels (Butler), Jonah Johnson (Clark), Roger Bender (Shelby), Mike Gastier (Huron), Glen Arnold (Putnam), Ed Lentz (Seneca), Keith Diedrick (Wayne), Wes Haun (Logan), Mark Koenig (Ottawa/Sandusky), Gary Wilson (Hancock), and Todd Mangen (Mercer).

About the C.O.R.N. Newsletter

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.