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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-33

Dates Covered: 
September 27, 2004 - October 4, 2004
Andy Kleinschmidt

The Basics of Fall Herbicide Treatments

Authors: Mark Loux

Fall herbicide treatments have become a fairly common practice in some no-till fields, and they can be an effective tool for management of dense populations of winter annual and biennial weeds, and cool-season perennials such as dandelion. It is important to recognize that not all fields require fall herbicide treatments, though, and they are an added expense in weed management programs. The increase in winter weeds in some fields has been due to the failure to apply burndown treatments early enough in spring, which allows winter weeds to go to seed, thus increasing the problem in future years. Fields best suited for fall treatments are those where winter weed populations are already high, or where it is not likely that burndown herbicides will be applied by the end of April. However, in fields where winter weed populations have not increased due to consistent use of early-spring burndown treatments, there should be little need to use fall treatments. The rest of this article provides some guidelines for fall treatments, based on OSU research.

When to apply fall herbicide treatments:
For control of winter annual weeds, apply herbicide anytime after early October. 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. Canada thistle and quackgrass can also be controlled into November, as long as plants have not been greatly damaged by cold weather.

The most effective fall herbicide treatments:
The following treatments are among the most effective of those labeled for use in the fall. Other herbicides (Valor, Scepter, Python, Aim, etc) can be applied in the fall, but most of these will not effectively control winter weeds unless they are combined with one or more of the following herbicide treatments. Effective control in the fall can be attained with treatments costing $5 to $10 (excluding application cost), and we question the value of treatments that cost more than $10.

CanopyXL + Express + 2,4-D: Effective for control of most winter annual weeds and dandelion, but not effective on most other perennials. This treatment will provide weed control later in the spring than other soybean herbicides (Valor, Scepter, Sencor, etc), and is therefore usually the best choice where the intent is to use only one application of glyphosate in the following year’s Roundup Ready soybeans. Rates of CanopyXL range from 2.5 to 4.5 oz/A, although some companies recommend lower rates in combination with glyphosate for residual seedling dandelion control. The 2.5 oz rate is adequate for control of emerged weeds in the fall, but higher rates can extend the length of weed control the following spring. Do not use more than 2.5 oz where soil pH is greater than 6.8. Use only where soybeans will be planted the following spring.

Glyphosate + 2,4-D: Effective for control of most winter annual and biennial weeds, and also dandelion, Canada thistle, and quackgrass. A glyphosate rate of 0.38 lb of glyphosate acid should be adequate for many winter annuals, but rate should be increased to 0.75 lbs acid where dandelion and other perennials and biennials are present. Apply with ammonium sulfate. Can be applied the fall prior to any spring-seeded crop.

Sencor + 2,4-D: Controls most winter annual weeds, but not biennial or perennial weeds. We suggest a Sencor rate of at least 8 oz/A, which is slightly less effective than the previous two treatments on some winter annuals (80 to 90% control for Sencor/2,4-D vs 90 to 100% for the Canopy and glyphosate treatments). Labeled for use in the fall prior to soybeans, but should not injure corn planted the following spring where planting intentions need to be altered.

2,4-D (1 to 2 lbs ai/A): Will control many winter annual weeds, but not chickweed (can be mixed with Express to control chickweed). Not as effective on dandelion as the Canopy or glyphosate treatments (70 to 80% control for 2,4-D vs 85 to 80 to 95% for the others). We view a glyphosate/2,4-D combination as more effective then 2,4-D alone for about the same cost, since glyphosate is priced about the same as 2,4-D. (who would have guessed this 10 years ago!)

Simazine (1 lb ai/A) + 2,4-D: Controls most winter annual weeds, but less effective on dandelion than Basis + 2,4-D or glyphosate + 2,4-D. Can be used the fall prior to corn only. Simazine does not provide much residual control of problem summer annual weeds the following spring, so expect to use a typical herbicide program in next year’s corn.

Basis + 2,4-D: Controls most winter annual weeds and dandelion (control of dandelion can sometimes be improved by the addition of simazine). Basis does not provide much residual control of problem summer annual weeds the following spring, so expect to use a typical herbicide program in next year’s corn.

We recommend adding 2,4-D to all fall herbicide treatments, including glyphosate, because a mixture of herbicides with several different sites of action should delay the development of herbicide-resistant weed populations. 2,4-D will also help control a number of winter annual and perennial broadleaf weeds. A 2,4-D rate of 0.5 lb ai/A should be adequate in most treatments. Mixing 2,4-D with glyphosate can reduce control of Canada thistle and some perennial grasses, compared to glyphosate alone, but this type of antagonism should not be a problem with other weeds. Apply glyphosate-containing treatments with ammonium sulfate, and additional nonionic surfactant if specified by the product label. Treatments that do not contain glyphosate should generally be applied with crop oil concentrate for best results.

The Importance of a Preemergence Glyphosate Application in No-Till Wheat

Authors: Mark Loux

Many winter weed problems in no-tillage wheat can be managed with a preplant or preemergence application of glyphosate. Dandelion and winter annual weeds such as chickweed and purple deadnettle have been serious problems in wheat in recent years. Producers are often not aware that these weeds are a problem until late fall or early spring. However, many winter annual weeds have emerged by early October and are easily controlled with relatively low rates of glyphosate prior to wheat planting. This can be a more effective treatment for dandelion and winter annuals, compared to the herbicides that can be applied broadcast to wheat in late fall or early spring. A dense population of winter annuals or dandelion may have already suppressed wheat growth by the time a spring treatment can be applied.

Dandelion is especially problematic because most postemergence wheat herbicides have limited effectiveness on this weed. Dandelion should be controlled with tillage or glyphosate prior to wheat emergence, since options after emergence are less effective. Tillage must be thorough enough to completely disrupt dandelion plants, and this may not be accomplished with one pass of an implement designed primarily for seedbed preparation. Therefore, consider a glyphosate application prior to tillage for most effective dandelion control. We suggest a glyphosate rate of at least 0.75 lb of glyphosate acid per acre in any field that contains dandelion. Include ammonium sulfate in glyphosate treatments, and the appropriate amount of surfactant if specified by the product label. The activity of herbicides on dandelions may be reduced if applied under our current dry conditions when dandelions have relatively little foliar growth. However, we believe the control attained by a glyphosate application makes it worth the effort even if dandelions are not in the optimum condition. Where possible, apply the glyphosate several days before tillage or planting. Otherwise, be sure to apply before the wheat emerges!

Late Season Flood Damage to Corn: Management Considerations

Authors: Peter Thomison

Recent flooding in parts of southern and southeastern Ohio caused major damage to many cornfields. In some river bottom fields, corn was immersed up to the tassels. Most of the corn was in the dent stage at about 1/3 to 2/3 milk line when flooded. Some of the affected corn has been flooded twice in recent weeks. The impact of this flood damage on corn will be highly dependent on kernel stage of development, length of the flooding period, how much of the corn plant was immersed during flooding, and subsequent weather conditions.

Since late season flooding is an uncommon event, little information is available on its effects on corn at this stage of kernel development, and how to best salvage damaged corn. A major concern is the impact of flooding on grain and silage quality. In past reports, when corn in the dent stage was covered by flood water for six hours or more and nearly completely caked with mud for up to two weeks, damage from ear rots and premature kernel sprouting was extensive in those areas of fields where water had covered the ears the longest. Although such damage may be negligible in fields where water never covered the ears, prolonged flooding may cause significant injury to the roots, if not premature root death. Such plants will be more vulnerable to stalk rots thereby increasing the likelihood of stalk lodging, especially if harvesting is delayed. Therefore, as soon as plants have dried, stalks should be inspected to determine the degree of rot. If rot is extensive, these affected fields should be harvested first to minimize further yield loss.

Another issue that may impact injury from immersion is whether ears were in an upright or downward position when flooded. If most plants had not yet reached black layer when flooding occurred, most ears were probably in an upright position which would probably result in ears catching and retaining more soil, etc. Corn growers in the South have observed that once the ears are soaked from flooding, they quickly rot at high temperatures so prompt harvesting is necessary.

When dealing with flood damaged corn, a common suggestion is to allow rains to wash off as much soil as possible before harvesting. Another observation is that flooding often deposits considerable debris on fields making harvesting difficult, as will dust associated with soiled plants.

For more information on salvaging flood damaged corn consult the University of Kentucky publication “Harvesting Flood Damaged Corn for Silage or Grain” available online at:

Use of Corn Plants from Flooded Fields for Silage

Authors: Bill Weiss

We have received several questions regarding flooded corn fields. Below is some information that might be helpful.

Some corn fields in areas of the state were flooded to varying degrees. Much of this corn could be salvaged by making corn silage. If this is done, the following guidelines might be useful.

1. Make sure the corn plants are at the correct moisture concentration before chopping. For upright silos and silo bags, moisture contents between 62 and 68% are ideal. For bunker silos, recommended moisture concentrations are between 65 and 70%. If the flooding did not kill the plants, delay harvest until the correct moisture concentrations are obtained. If the flooding killed the plants, delaying harvest until the right moisture concentrations are obtained will likely result in development of molds. Because of the risk for mycotoxins, areas of fields that are visibly moldy should probably not be chopped for silage.

2. Because of contamination by soil bacteria, a proven silage inoculant (lactic acid producing bacteria) should be applied at the time of chopping or silo filling. Follow label direction regarding application rates but generally 1 million viable colony forming units per gram of wet silage is required to observe a fermentation response.

3. Soil contamination of plants will increase the ash content of the silage. Ash provides no energy and will dilute organic nutrients. In addition to routine nutrient analysis, silage made from fields that were flooded should also be analyzed for ash concentration (most commercial feed labs can conduct this analysis). When formulating diets, the energy concentration of the corn silage should be adjusted to account for ash dilution. Normal corn silage has 4 to 5% ash.

Price Outlook for Fertilizers

Authors: Robert Mullen

Ammonia production costs will continue to be high as natural gas prices approach $6.00/MMBtu and beyond at the wellhead. Forecasts predict that domestic natural gas prices will remain high over the next few years. This is due to the fact that natural gas is a more attractive alternative to oil and coal for energy production. Unfortunately, this means that high nitrogen prices will be with us for at least a couple of years (and may be as many as four – when we get a large infussion of natural gas imports).

Higher ammonia costs also translate into higher costs of phosphorus fertilizers that contain nitrogen (specifically – DAP, MAP, and APP). As China and Brazil continue to import large quantities of potash, the cost of potassium will likely rise this coming year (in fact, it is already on the rise).

So what does this mean for this coming year? Producers that have historically maintained adequate soil P and K levels may want to consider holding off on application this coming spring or this fall. Soil test levels well above the critical value do not respond to additional inputs, so skipping a maintenance application for next year’s crop is an option that will not be detrimental. If fields are known to have different soil test levels of P and K, invest in areas that are below the critical level and hold off application on areas with adequate levels. Nitrogen will be required, so manage N as efficiently as possible. If applying N this fall as anhydrous because of the potential high prices next spring, recognize the risk and apply a nitrification inhibitor and make sure soil temps are well below 50 F prior to application. Sidedressing is an attractive alternative, primarily because of the potential for loss early next spring depending upon environmental conditions. Remember fall N prices are lower but the potential for N loss is greater, so the cost benefit of fall application may be offset by the yield loss due to a lack of N next summer.

European Corn Borer Populations in Ohio

Authors: Bruce Eisley, Ron Hammond

We have been splitting corn stalks to check for European Corn Borer (ECB) damage at the Western and Northwest Ag Research Stations during the past week. Corn in these plots was planted either in late April or late May. This is the eighth year that corn plots at both Stations have been checked for ECB damage at this time of year. Populations remain low in all the plots ranging from 0.25 to 0.55 cavities/stalk. While these numbers are not very high there are probably fields in Ohio with higher ECB damage.

This is a good time to inspect fields for ECB damage because most of the larval damage has already occurred. Damage from ECB larvae can appear either as frass on the outside of the plant or as stalk breakage above or below the ear zone. If plants are breaking below the ear zone, plants should be split to determine if ECB is causing the trouble and the field should be noted. Fields with heavy ECB damage should be harvested as soon as possible before additional plants go down from larval damage.

Fall Sampling for Slugs

Authors: Bruce Eisley, Ron Hammond

The coming month is the time period when growers should scout their fields for slug populations. Sampling can be done both prior to and following harvest. While we do not have thresholds, sampling will indicate whether a field has a small or large slug population. A large population of slugs will help indicate which fields need extra monitoring next spring.

There are a number of ways to sample for slugs. The main technique is placing wood boards or roofing shingles on the ground across the field and checking them weekly throughout the fall and counting the number of adult slugs underneath the traps. It is best to count the slugs in the morning. Ten traps in a field would be a good number to begin with. Other ways of determining if fields have a lot of slugs is by visiting the fields in late evening before dusk or early in the morning during periods of heavy dew or fog. Slugs will often be crawling on the plants, especially corn, if not yet harvested.

Growers are also advised to look underneath the leaves of larger weeds that are covering the ground. Numerous slugs are often found in those situations. To repeat, although no thresholds are available, fields with large numbers of slugs should be monitored more closely next spring.

Archive Issue Contributors: 

State Specialists: Anne Dorrance and Dennis Mills (Plant Pathology), Robert Mullen (Fertility), Peter Thomison (Corn Production), Ron Hammond (Entomology), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM), and Ed Lentz (Agronomy); Extension Educators: Steve Foster (Darke), Bruce Clevenger (Defiance), Todd Mangen (Mercer), Glen Arnold (Putnam), Roger Bender (Shelby), Mark Koenig (Sandusky), Ray Wells (Ross), Barry Ward (Champaign), Dusty Sonnenberg (Henry), 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.