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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-10

Dates Covered: 
April 22, 2008 - April 29, 2008
Steve Prochaska

Burndown Herbicide Treatments – Can You Afford Not To Use 2,4-D Ester?

Authors: Mark Loux

The weather has been up to now less than ideal for field activities, and many no-till fields that would have typically received a preplant burndown herbicide treatment by now remain untreated. The delay in treatment is in itself not necessarily an issue for control. Although weeds get larger and vegetation becomes denser with delays in treatment, a well thought out mixture of herbicides will still provide the needed control. In our experience, a combination of glyphosate and 2,4-D ester will typically be effective into early May or later in no-till fields. The bigger issue here is that when soil conditions prevent traffic until late April, planting and burndown applications tend to occur at about the same time in some fields. This often leads to omission of 2,4-D ester from burndown programs, especially in soybeans, because it’s not always possible to wait the required 7 days between 2,4-D application and soybean planting.

We cannot emphasize enough the importance of a “clean” start in no-till fields. The most effective weed control and highest yield potential results from using fall or spring burndown herbicides, and establishing the crop under weed free conditions. Failure to use an effective burndown treatment that includes several different herbicide sites of action also increases the risk of herbicide resistance. The advantages of 2,4-D must be weighed against the delay in planting as a result of its use. Keep in mind that the inclusion of 2,4-D ester in burndown programs can help control a number of large or tough winter weeds, including marestail, dandelion, wild carrot, poison hemlock, mustards, etc. Adding 2,4-D to glyphosate-based burndown programs also greatly reduces the selection for glyphosate resistance in early-emerging summer annuals, including marestail, lambsquarters, and giant and common ragweed. Populations of these weeds have already developed resistance to glyphosate in Ohio fields, and some of the glyphosate-resistant ragweed populations have resistance to ALS-inhibiting herbicides also. Our research shows that control of resistant populations in soybeans can be almost impossible unless the field is weed-free at the time of planting, and use of 2,4-D ester is required to achieve this where glyphosate resistance has developed.

A quick review of the guidelines for 2,4-D ester use in no-till corn and soybeans follows:

1. 2,4-D ester can be applied preplant or preemergence to corn, but labels vary with regard to specific recommendations on timing of application. Labels for some products recommend application either 7 to 14 days before planting or 3 to 5 days after planting but before the corn has emerged, while others specify application any time after planting.
2. Applications of 2,4-D around the time of planting can injure corn. This is more likely to occur in coarse-textured soils with low organic matter content, and when above-average rainfall and prolonged soil moisture occur within a week after planting. Injury may be more severe when 2,4-D is applied with chloracetamide herbicides.
3. Many 2,4-D products are labeled for use in the spring prior to no-till soybean planting. OSU recommends the use of only 2,4-D low-volatile ester (LVE) or similar products for this application. 2,4-D amine products are more water-soluble and may leach into the seed zone. For 2,4-D ester, rates up to 0.5 lb active ingredient per acre must be applied at least 7 days before soybean planting. Application rates of more than 0.5 lb up to 1.0 lb active ingredient per acre generally must be applied at least 30 days before planting. Several 2,4-D ester products, including E-99, Salvo, and Weedone 650, can be applied at a rate of 1.0 lb ai/A up to 15 days before planting.
4. Aside from waiting the required amount of time between application and planting, other keys to avoiding 2,4-D injury include making sure that seeds are well covered with soil and that the planting furrow seals. In addition, fields that have been treated with 2,4-D ester should not be tilled prior to planting. The exception to this rule would be where 2,4-D ester was applied very early in spring, and there has been adequate time for degradation. When 2,4-D is applied before planting, avoidance of crop injury is based on the fairly rapid degradation in soil and the relative immobility of the ester formulation on the soil surface (e.g. its tendency not to readily move below the soil surface unless a lot of rain occurs). Tilling the soil after 2,4-D application can move it down into the seed germination zone, which increases the risk of uptake by seed, leading to germination and emergence problems.

It is possible to effectively control emerged weeds in a no-till field without the use of 2,4-D. However, this statement really holds true only in fields where herbicide resistance has not occurred. Failure to use 2,4-D in burndown programs has been a major cause of glyphosate resistance in our opinion. Some prioritizing of fields would be in order here, with regard to whether it makes more sense to use 2,4-D ester and wait 7 days to plant, or forgo the use of 2,4-D in order to get the field planted as soon as possible. We consider use of 2,4-D mandatory in non-GMO soybeans, so planting of these fields should defintitely be delayed to allow 2,4-D use. Another suggestion would be to start planting corn first, while at the same time treating soybean fields with 2,4-D containing burndown programs. This suggestion is based on the availability of several preplant herbicides for corn that can effectively control no-till weeds even where 2,4-D is not used. Options for burndown in corn include: atrazine plus Gramoxone (especially when applied in 28%); Lexar or Lumax (most effective dandelion control in OSU/Purdue research); Basis or Resolve plus atrazine; glyphosate plus an atrazine premix product.

In soybeans, we would strongly suggest that where it’s not possible to use 2,4-D ester, consider applying a combination of glyphosate plus a chlorimuron-containing product, such as Canopy DF, Valor XLT, or Envive. While even this mixture benefits from the inclusion of 2,4-D, it will provide generally broad-spectrum control of no-till weeds in the absence of 2,4-D. In addition, it has been one of the more effective treatments for control of dandelion. Mixtures of glyphosate with a cloransulam-containing product, FirstRate, Gangester, or Sonic/Authority First, are also more broad-spectrum than glyphosate alone. Cloransulam can be more effective than chlorimuron for control of emerged ragweeds and marestail (as long as they are not ALS-resistant), but is less effective than chlorimuron on a number of winter annual weeds and dandelion.

Increasing the glyphosate rate from 0.75 lbs ae/A (22 oz of PowerMax, 24 oz of Durango, Touchdown, 32 oz of generic glyphosate products) to 1.1 or 1.5 lbs ae/A can improve control in these mixtures. Mixtures of glyphosate and chlorimuron or cloransulam will not control populations of marestail or ragweeds that have developed resistance to both glyphosate and ALS inhibitors. For growers determined not to use 2,4-D ester or one of the mixtures mentioned here, our suggestion would be to apply glyphosate at a rate of at least 1.5 lb (or at the rate you know will work based on the field history), and hope for the best.

And finally – a few comments on Gramoxone use in soybeans. It would be in the best interest of continued glyphosate utility if more preplant burndown programs were based on the use of Gramoxone instead of glyphosate. Gramoxone can have a good fit in many no-till soybean fields, but it needs to be used in the appropriate mixture of herbicides to ensure that it provides effective control. Gramoxone should generally be applied in combination with 2,4-D ester and a metribuzin-containing herbicide for control of a broad spectrum of winter annual and summer annual weeds. The best possible treatment along these lines – Gramoxone + 2,4-D ester + Canopy DF + metribuzin. Our research indicates control with Gramoxone-based treatments in soybeans may be less than adequate when 2,4-D ester is omitted, especially where marestail and dandelions are present. Fields with a moderate to high dandelion infestation would be better treated with a mixture of glyphosate plus chlorimuron (plus 2,4-D ester where possible).

The Wheat Crop May be Further Along Than It Seems

Authors: Dennis Mills, Rich Minyo, Jim Beuerlein, Pierce Paul

Throughout most of the state, the wheat crop is either at growth stage 6 (Feeke’s GS 6) or will be at that growth stage by the end of the week. However, for some varieties, simply looking at the plants from a distance without actually walking field and examining tillers, the crop may appear to be at a much earlier growth stage. Relatively low air and soil temperatures have prevented some varieties from reaching the height that is expected when the crop is at growth stage 6. Remember, short-looking wheat does not mean that the crop is not developing and advancing through the different growth stages. Growers who rely on the height of the crop as an indicator of crop development may be missing Feeke’s GS 6, a critical growth stage for herbicide application After a relatively slow start, the wheat crop now seems to be about a week or two ahead, but for some varieties, the height of the plants tells a different story.

Walk fields and pull main tillers from multiple places. Remove the lower leaves from the tillers and look for the first node which is indicative of Feeke’s GS 6. Do not rely on the height of the plant or the calendar date alone to make management decisions in regard to herbicide and/or fertilizer applications.

Remember, failure to correctly identify crop growth stages may lead to improper timing of applications, which may result in violation of pesticide label restrictions (products being applied off label), inferior control efficacy, and injury to the crop.

Winter Injury in Alfalfa

Authors: Mark Sulc

Reports are coming in from around the state about winter injury in alfalfa. Reports range from heaving to outright winter kill of plants without heaving. Considering the stressful conditions last year and through the winter and cutting management decisions that were made late last fall, the reports are not surprising.

The 2007 Easter freeze followed by very dry conditions the remainder of the growing season left alfalfa stands in a weakened state going into the winter. Where a late fall harvest was made, no plant cover was left to insulate the crowns and the soil from alternative freezing-thaw cycles. Research in Wayne county demonstrated that early November harvests dramatically increased heaving in alfalfa stands compared with where a late harvest was not made. Furthermore, very wet soils throughout the winter probably contributed to lack of oxygen for alfalfa roots, and wet soils are also known to decrease cold tolerance of alfalfa.

A careful inspection of all alfalfa stands at this point in time is very important. A “windshield inspection” is inadequate to accurately assess the health of alfalfa stands this year. Walk your fields and get a broad view to determine whether spring growth appears uniform. If growth is spotty or nonexistent, it is very likely that plants have suffered severe winter injury or heaving.

Heaving in alfalfa stands has been reported from north to south in Ohio and in older as well as newly seeded fields. Severity ranges from mild to severe, both within fields and between fields. Heaving is usually more severe in areas with less than ideal internal and surface soil drainage.

Plants with crowns heaved up 2 or more inches are already dead, or are in the process of desiccating and will soon die. Plants that are heaved 1 to 1.5 inches above the soil surface or less may on casual inspection appear normal and healthy with decent spring growth. But closer inspection may reveal some moderate heaving, which will likely limit the productive life of the plant. Such plants will desiccate more quickly, be injured by wheel traffic, and crowns may break or be cut off at the first harvest. Some of those plants may survive through the first harvest, but their yield potential is compromised and they will likely disappear from the stand at some point during the growing season.

Plants can also be killed by cold temperatures. Forage agronomists (Cosgrove and Undersander) at the University of Wisconsin describe freezing injury in alfalfa as follows: “Winter killed roots will have a gray, water-soaked appearance early, just after soils thaw. Once water leaves the root, the tissue will become brown, dehydrated and stringy (see Figure 2). If the root is soft and water can be easily squeezed from it, or is brown, dry and stringy, it is most likely winter killed.” For a picture of freeze injury, refer to their fact sheet at .

To evaluate an alfalfa stand, estimate the number of live plants per square foot. The best way to do this is to dig up and count the plants in a 1 to 2-square foot area in several parts of the field. Second year stands (seeded last year) should have 10 to 12 plants per square foot, and third year or older stands should have 5 to 6 plants per square foot for optimal yield potential. When making plant counts, consider only those plants that appear healthy with vigorous shoot growth.

Carefully evaluate the condition of new buds and new shoots for evidence of injury. Healthy plants with no winter injury will show vigorous, symmetrical growth all the way around the crown. Injured legume plants will often show asymmetrical growth caused by injury to part of the crown.

Take a random sample of the plants that were dug up for making stand counts. Split the taproots lengthwise to look for internal discoloration of the taproot tissue. Healthy taproots will be firm and creamy white. Root and crown rot will appear as various darker shades. The degree of root and crown rot affects plant productivity, vigor, and long-term survival. If taproots are watery, tan or yellow, or already desiccating, it is an indication that freeze injury has occurred and the plants will likely die.

Visually estimate the ground cover of desirable forage plants as the stand develops 4 to 6 inches of new growth. Stands with more than 80% ground cover and good vigor will produce excellent yields, stands with 60-80% ground cover should produce fair yields, stands with 40 to 60% ground cover will probably produce yields in the 60% range of normal, and stands of 20-40% ground cover will yield less than half their normal potential. Weeds will become a real problem in the thinner stands, and over seeding with grass or destroying the stand and rotating out to another crop should be considered.

Starter Fertilizers for Corn, Where Are They Needed And What Concerns Should One Have?

Authors: Robert Mullen, Edwin Lentz

Starter fertilizers can be an effective way to supply early nutrients to your corn crop and may be used to supplement broadcast applications, but is there use warranted and what concerns should you have.

Before we get into the actual discussion of starter placement, we will first discuss starter response and the need for starter fertilizer. Early-season response to starter fertilizer in the form of more vigorous growth is common, but the early-season response does not necessarily translate into a yield gain at the end of the season. For starter applications, we would recommend a 2x2 placement simply because we can supply more nitrogen (N), which is normally our most limiting nutrient. Application of starter N will allow us to delay side dress applications (if soybean planting or inclement weather get in the way). Inclusion of phosphorus (P2O5) and potassium (K2O) in a starter package may be warranted if soil test levels for those two nutrients are below the established critical values (Tri-State Fertilizer Recommendations). Soils that have a history of adequate or perhaps even a little excessive P and K fertilization resulting in a high soil test levels are unlikely to benefit (yield-wise) from the inclusion of P and K in the starter. Notice we focused on a yield benefit, often times we can see visual differences due to application of P specifically in cool, wet springs, but it does not necessarily translate into a yield increase. Soils that are low in P and K (below the established critical value) can benefit, especially if broadcast applications were not made the previous fall or in the spring. Starter response is also affected by the tillage regime utilized. No-till systems result in cooler, wetter soils and are more likely to benefit from starter fertilizers than tilled soils. In summary, soils that have adequate P and K levels are unlikely to benefit from starter P and K applications, but soils that are deficient can show a positive response.

With the advent of larger planting equipment affecting our ability to add 2x2 attachments due to weight restrictions or machine folding operations, pop-up, or in-seed furrow, applications of fertilizers may be the only possibility. Application of pop-up materials is much more restricted because we are putting salts and possibly ammonia forming fertilizers near the germinating seed. So how much fertilizer can be placed with the seed? The general rule of thumb used by Ohio State University is 8 lb of N + K2O per acre with the seed. The main factor determining whether or not salt will be an issue is soil moisture at the time of planting. The wetter the soil the more salt that can be applied without any adverse affects on seed germination. Urea-based nitrogen sources and diammonium phosphate (DAP) can be problematic when applied with the seed due to the formation of free ammonia during their breakdown. This too is dependent upon soil moisture, and the wetter the soil the less likely there will be a problem. The recommendation in place by Ohio State University does have a safety factor because we do not have a really good way to determine soil moisture at the time of planting.

Cereal Rust Mite (or the Timothy Mite) on Timothy

Authors: Ron Hammond, Mark Sulc, Andy Michel, Bruce Eisley

Last week we received a call from the Erie/Huron County area on a problem on timothy. Apparently a pest, the cereal rust mite, also known as the timothy mite, was attacking the crop. The timothy mite, an Eirophyid mite, is more of a problem in states to our east and in the mid Atlantic region. These mites are cold-adapted, and become a problem in mid to late April and early May; they are absent for most part in summer. Damage appears as drought-stressed plants. These mites are microscopic and live in the grooves of timothy leaves. On looking on the web, we quote from various sources, "management is limited". Currently, there are no insecticides or miticides available for use against this pest in Ohio. The only available and effective insecticide appears to be Sevin XLR which is available for use in some states as a 24(c) special local need. Although states to our east have it, including Pennsylvania, the Virginias, Delaware, Maryland, and New Jersey, Ohio does not. Currently we are exploring the possibility of getting a 24(c) label in our state, if not in time for this season, for future years.

Alfalfa Weevil Update

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Heat unit accumulations at Piketon and Jackson in southern Ohio have gone over 350, and with the coming week of warming temperatures, will go higher. This is enough heat units that growers in those areas should already be sampling for alfalfa weevils. Heat unit accumulations at our weather stations at the Western Branch in South Charleston and the OARDC in Wooster are close to 250, and thus, fields in central Ohio should begin being sampled. In the north, at the Northwest Station and Ashtabula, heat units are still around 200. With the higher temperatures this week, we would imagine that fields in northern Ohio should reach the stage where sampling for weevil larvae should begin by the end of this week, early next week.

Seedling Diseases and Soybean Rust

Authors: Anne Dorrance

Planting into cool, cold soils will be extra tough this year on soybean seed. Some seed lots have had challenges passing the cold germination tests that we discussed in earlier issues of C.O.R.N. Producers should really watch the soil temperatures this year and plant soybeans under very optimum conditions to promote the chance of getting the best stands. This is not the year, to plant before forecasted heavy rains. Cracked seed coats, cool wet soils are optimum conditions for two seed and seedling pathogens, Fusarium spp. and Pythium spp. Both of these are common in Ohio soils and love cool, wet conditions – soil temperatures greater than 60 degrees are more favorable for the soybeans and these plant pathogens have a bit of a harder time.

For soybean rust, Texas has had one of the first in season finds on kudzu. But it is at a very, very low level. This is a patch that is heavily monitored. Louisiana, Mississippi, Georgia, and Alabama are all below detection levels. The kudzu is growing very well, but did take a step back last week due to cool temperatures. Some of the sentinel plots that were planted in the south are now greening up and more sentinel plots will go in this next week. At this point, based on the reports, soybean rust is at very low inoculum levels and the risk of rust is low for Ohio.

Soil Quality CD Now Available

Authors: Alan Sundermeier

This Soil Quality CD contains information about the fundamentals of soil quality and active organic matter. The impacts upon soil quality of gypsum, cover crops, tillage, and compaction are discussed. Soil organic matter, nutrient recycling and management practices to improve soil quality are also covered. Instructions for using the Soil Quality Test Kit, which can be ordered separately, are included. Speaker PowerPoint presentations with audio, video of field demonstrations, and university publications are included. For Certified Crop Advisors, the CD also offers CEU credits up to 5 hours in Soil & Water Management in self study exams which can be returned for an additional fee. Order with credit card at

NOAA Weather Update For Ohio

Authors: Jim Noel

A change to a drier weather pattern remains on tack. There will be some isolated showers Wednesday with the passage of a weak front. Another chance for rain will occur on Friday into Saturday. Overall, most of these systems look to bring limited rain. The probability of 1" of rain is between 50-70% and 10-40% for 2" rain for the next 2 weeks in Ohio. Some areas may see less than an inch of rain the next 2 weeks. Everything continues to point to a drier than average May with near to above normal temperatures. It looks like the chances for any more freezes are diminishing with time. An outside chance for a freeze remains for northern Ohio.

Archive Issue Contributors: 

Jim Noel (NOAA), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Robert Mullen (Soil Fertility), Mark Loux and Jeff Stachler (Weed Science). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Ed Lentz (Seneca), Glen Arnold (Putnam), Harold Watters (Champaign), Bruce Clevenger (Defiance), Les Ober (Geauga), Mike Gastier (Huron), Steve Bartels (Butler), Mark Koenig ( Sandusky), Steve Prochaska (Crawford), Gary Wilson (Hancock), Greg Labarge (Fulton) and Todd Mangen (Mercer).

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.