C.O.R.N. Newsletter 2006-06

Dates Covered: 
March 20, 2006 - April 4, 2006
Editor: 
Harold Watters

Wheat Assessment and Considerations

Authors: Edwin Lentz, Pierce Paul, Jim Beuerlein

Even though wheat has begun to greenup across the state, temperatures have been cool enough that little growth has occurred. It is still too early to make adequate assessments of stand survival and response to fertilizer. Assessments should not be made until after the risk of excessive freezing and thawing, which is late March for southern Ohio and first of April for northern Ohio. At that time, first inspection should be for heaving damages.

Heaving is recognized when the crowns of the plants are pushed up out of the soil as the soil freezes and thaws during late winter. Close examination of the plants indicate that the crowns and upper roots are exposed with only a few roots remaining in the soil. These plants will green up and look normal for a while, but within a few weeks heaved plants will turn brown and die. Growers generally describe this as fields 'going backwards'. Heaving is generally worse in fields with compacted, wet, high clay content soils. Generally, heaving is more severe in conventional tilled fields with little surface residue than in no-till fields with residue that protects against wide changes in temperature of the upper inches of the soil. Wheat that is planted too shallow is also more prone to heaving problems than wheat that has been planted at the recommended one and a half inches deep.

At the same time fields are inspected for heaving, plants should also be examined for lower stem and root disease problems. As the soil temperature increases, so does the activity of disease-causing fungi. Disease problems are likely to occur first and be most severe in low-lying areas of the field. Excess soil moisture in these areas keeps soil temperatures cool, increases relative humidity, and exposes young plants to pathogen infection. Some soil-borne pathogens thrive under conditions of relatively cool temperatures, high relative humidity, and wet soils. Disease problems can be identified by examining the roots for lesions and discolorations. Dig plants from the field, wash off all soil and examine the crowns. Peal the leaf sheaths down to expose the inner parts of the crown. The tissues in healthy plants should be a creamy white color. If the internal tissues are brown or discolored, then these plants are likely dead or will soon be dead. Pathogen infection leads to root rots and seedling blights, leaving plants stunted with poorly developed roots and tillers.

Adequate tiller number and proper development are essential for high yields. Yield potential is reduced if tiller numbers fall below 25 per square foot after green up. Fifteen tillers per square foot is considered minimum for an economic crop. The number of tillers per square foot is equal to the number of tillers in 20.5 inches of 7 inch wide rows or 14.5 inches of 10 inch wide rows. Obviously, late planted fields should be visited to determine if adequate numbers of tillers are present, but excessive tillering is unnecessary and may lead to lodging. Fields planted within 10 to 14 days of the Hessian Fly Safe Date using 1.3 to 1.6 million seed per acre (18 to 24 seed per foot of row) with about 20 to 25 lb of actual nitrogen/A applied at planting rarely have problems with low tiller numbers in the spring. In fact they generally have many more tillers than are needed for maximum yield. Our experience from counting heads of wheat in fields prior to harvest indicate that most Ohio fields have from 40 to 60 heads per foot of row. If 20 seed were planted per foot of row then each plant will end up with 2 to 3 head bearing tillers. These are the main tillers that developed during fall growth.

Spring N should be applied now or anytime before early stem elongation (Feekes GS 6). Applications should be made when field conditions are appropriate for equipment traffic. Research data shows timing is not critical for yield as long as N is applied by Feekes growth stage 6.

Nitrogen Recommendations for Wheat

Authors: Edwin Lentz, Robert Mullen

We would still recommend the Tri-State Fertility Guide for N rates in wheat. This system relies on yield potential of a field. As a producer, you can greatly increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum nitrogen rate. Once you have selected a value for yield potential, the recommendation may be based on the following equation for mineral soils, which have both 1 to 5% organic matter and adequate drainage:

N rate = 40 + [1.75 x (yield potential – 50)]

We do not give any credit for the previous soybean crop, since we do not know if that organic N source will be released soon enough for the wheat crop. Generally, we would recommend that you subtract from the total (spring N) any Fall applied N up to 20 lb/A. Before N prices were high, producers often did not deduct this amount. We have had above normal temperature and rainfall for January, so some of this fall N may have been lost, but if temperatures were adequate for nitrification (ammonium N converted to nitrate N) we probably also had N mineralized (released by the soil). Thus we may have gained as much as we lost. In summary, whether you deduct fall N depends how much risk you are willing to take and your anticipated return of investment from additional N.

Based on the equation above and deducting 20 lb from a fall application, we would recommend a spring application of
- 110 lb N per acre for a yield potential of 100 bu,
- 90 for 90 bu potential;
- 70 for a 80 bu potential and
- 40 lb N per acre for a 60 bu potential.
Since greenup has started across the state, price should be the main factor in selecting a N source. Volatilization losses should still be minimal for urea based fertilizers at this time. Potential loss of N from 28% solution may be furthered reduced by applying in a band (dribble bar).

Spring Applications of Manure and Inorganic Fertilizer to Cool Season Grasses

Authors: Robert Mullen, Mark Sulc

Fertilization of cool season grasses with either organic manure or inorganic, commercial fertilizer should be done to optimize the production system and meet your goals as a producer. The goal of this article is to provide some information on fertility management of cool season grasses.

Pre-Establishment Fertilization
Soil testing to determine soil nutrient status is the best way to quantify the amount of phosphorus (P) and potassium (K) you need to supply as a manager. With the cost of these inputs rising over the past few years, routine soil sampling should be utilized. Soil testing should be conducted the same way we recommend for row crop production. Collect 15 to 25 random soil cores to a depth of 8 inches, make a composite sample, and submit it to a soil testing laboratory for analysis. Recommendations for fertilizer P and K based upon soil test levels are available online in the Ohio Agronomy Guide in the Forage Production chapter (http://ohioline.osu.edu/b472/0008.html).

Ideally, P and K should be applied and incorporated prior to seeding based on the recommendation. A small amount of nitrogen (N) should also be supplied prior to planting, whether as commercial fertilizer or as manure, to promote good stand establishment. The amount of nitrogen needed is around 30 pounds per acre. If you are supplying manure for N remember that you are also supplying P and K, so make certain to quantify the amounts you are supplying. Knowing the amount of nutrients you are providing will ensure that they are not at a level that will limit production. Additional information on nutrient content of various manures can be found at: http://ohioline.osu.edu/b604/b604_15.html. Manure applied should be adequately incorporated into the soil, and seeding should not be done immediately after manure application. Seeding just after manure application (especially at high rates) can inhibit seed germination. Avoid gross over-application of both N and K (which includes manure) as they can lead to forage nutrient balance issues, especially early in the spring. Quick growth and excessive K uptake can decrease plant uptake of magnesium (Mg). Ruminant animals being fed this Mg deficient plant material can develop grass tetany. Dry cows being fed a forage high in K can develop milk fever.

Maintaining an optimum soil pH for the grass you are growing is also important for stand longevity. Different grasses require different pH levels so know where you need to be soil pH wise. If soil pH is too low (acidic), lime can be applied to adjust soil pH to the optimum level. Ideally, lime should be applied well before seedling (preferably six months), but if you need to make an adjustment make the application whenever possible. Make certain that the lime is adequately incorporated into the soil so that it can neutralize soil acidity as fast as possible.

Fertilizing Established Stands
Soil test information is the best guide for making fertilizer decisions on established stands. The recommendations for established stands are the same as they are for pre-establishment. When soil nutrient levels are above optimum the timing of P and K application is not critical, it can be done anytime during the growing season. When soil test levels are below the optimum, split applications is the best practice to supply needed nutrients. The recommended split is after the first cutting in the spring and after the final cutting in fall. This is especially true for K due to grass tetany and milk fever concerns. Care should be taken when utilizing manure as the nutrient source in the spring. Remember, manure not only supplies N it also supplies K, so applying manure to get the desired N response can lead to high K levels which can represent risk to fed animals. In addition, avoid smothering the grass with an excessive manure application.

Nitrogen application should also be split to ensure N is available throughout the growing season. The current recommendation is that N be supplied at a rate to match yield potential, and that the total N budget be split between N applied prior to green-up and after each cutting. Forty percent of the total budget should be applied prior to green-up in the spring and 30% of the budget should be applied after each cutting. Nitrogen recommendations for cool season grasses can be found in the Ohio Agronomy Guide in the Forage Production chapter (http://ohioline.osu.edu/b472/0008.html).

Assessing Potential Differences Among Hybrids for Ethanol Production

Authors: Peter Thomison, Allen Geyer, Rich Minyo

We recently collected data on total fermentables in grain of hybrids entered in the 2005 Ohio Corn Performance Regional Tests. Measurements of total fermentables have been widely used to assess the ethanol potential of grain for dry grind ethanol plants. The ethanol plants currently under construction in Ohio are all dry grind ethanol operations. Some of these plants may be purchasing corn grain for ethanol production within the next one to two years. We are grateful to Mike Newland at Greater Ohio Ethanol, LLC for conducting these analyses of total fermentables, expressed as grams CO2 per 100 grams dry weight. Analyses of total fermentables were determined using a FOSS 1241 NIR analyzer.

Total fermentables in grain were collected for three 2005 test sites, South Charleston, Bucyrus, and Hoytville. The average and range in values among hybrids at each location are shown in Table 1 below. Averages for total fermentables across the three sites ranged from 38.4 grams CO2 per 100 grams dry weight of grain at Bucyrus to 38.7 grams CO2 per 100 grams dry weight of grain at South Charleston. Although the range in values for total fermentables in grain was usually less than 5% at any location, these small differences can be highly significant according to operators of dry grind ethanol facilities.

The results of this evaluation suggest that many of the hybrids entered in the Ohio Corn Performance Test would be suitable for use by dry grind ethanol operations. One of the companies currently building a dry grind ethanol plant in Ohio has indicated that it might pay a premium for grain with high total fermentables. Grain with total fermentables of 38.3-38.4 grams CO2 per 100 grams dry weight might receive a premium of $0.02/bu. With higher total fermentables, 38.7-38.8 grams CO2 per 100 grams dry weight, premiums could increase to $0.06/bu. Our measurements of hybrid total fermentables indicated that 68% to 88% of the hybrids entered in the three regional 2005 test locations had levels of total fermentables equal to or exceeding 38.3grams CO2 per 100 grams dry weight; 37% to 50% of the hybrids entered had levels of total fermentables equal to or exceeding 38.7 grams CO2 per 100 grams dry weight.

Table 1. Total fermentables as grams CO2 per 100grams dry weight of grain in grain of hybrid entries at three Ohio Corn Performance Test locations in 2005.

South Charleston
Avg: 38.7 (107)*
Range: 37.6 – 39.4

Hoytville
Avg: 38.5 (123)
Range: 37.5 – 39.5

Bucyrus
Avg: 38.4 (82)
Range: 37.3 – 39.3
* Number of hybrid entries in parentheses

Preliminary data from 2005 also suggests that differences in total fermentables in grain among hybrids were fairly consistent across locations, despite marked differences in rainfall during the growing season. Total fermentables were measured in nine hybrids ranging in maturity from 107 to 112 days planted at six Ohio locations. Hybrids producing the highest and lowest total fermentables were usually the same ones at each test site.

Transgenic Corn Acreage Across the U.S. and Ohio

Authors: Peter Thomison

The percent of corn acreage planted to transgenic hybrids reached a record high 52% in 2005 – double the corn acreage planted to transgenic crops in 2001 (26%). This acreage estimate was based on a survey of transgenic crops conducted by the National Agricultural Statistics Service (NASS) in June 2005. The survey asked randomly selected farmers in the U.S. if they planted transgenic corn, soybean, and cotton seed resistant to herbicides, insects, or both. The survey reported on acreage in states that collectively account for 82% of all corn acres planted. Trangenic corn included Bt hybrids with one or more of the Bt genes that can resist different types of insects (i.e. European corn borer and western corn rootworm). Stacked gene hybrids included only those containing transgenic traits for both herbicide and insect resistance. Conventionally bred herbicide resistant hybrids were excluded (e.g. Imi-corns tolerant to imidazolinone herbicides).

According to the NASS survey, the percentage of US corn acreage planted to transgenic insect resistant (Bt), herbicide resistant corn, and stacked gene hybrids averaged 26%, 17% and 9% respectively in 2005. However, transgenic corn acreage in the Eastern Corn Belt is low, especially in Ohio where total planting of transgenic corn hybrids accounted for only 18% of total corn acreage. In Ohio, corn acreage planted to transgenic Bt, herbicide resistant, and stacked gene hybrids was 9%, 7% and 2% respectively in 2005. Ohio corn growers plant significantly less transgenic corn than any other major corn producing state. In South Dakota, 83% of corn acreage was planted to transgenic corn (30%, 31%, and 22% to Bt, herbicide resistant, and stacked gene hybrids, respectively). In the two major U.S. corn producing states, Iowa and Illinois, 60% and 36% respectively, of corn acreage was planted to transgenic corn in 2005.

Managing Stored Grain as Warmer Weather Approaches

Authors: Curtis Young

Storing grain successfully in Ohio is relatively easy if the grain is managed appropriately from the beginning. Purdue University has encapsulated the steps for successfully storing grain and maximizing grain quality and profits into a four letter acronym: S.L.A.M. S.L.A.M. represents four grain management practices that will increase the potential for storing grain successfully: Sanitation, Loading, Aeration and Monitoring. We have reviewed these practices and benefits of employing them in past CORN articles (e.g., http://corn.osu.edu/story.php?setissueID=103&storyID=609). In summary, the objectives of S.L.A.M. are to maintain maximum stored grain quality by protecting the grain from weather, rodents, insects, self-heating, molds, mycotoxins and pesticide residues. By minimizing grain deterioration, one can limit grain spoilage, quality discounts, and excess storage costs.

As warmer temperatures approach with the coming spring and summer seasons, how one handles their stored grain depends on a number of factors including:

How cold is the grain?
When will the grain be sold and moved out of the bin?
Will the bin be partially or completely emptied when the grain is moved?
Has anything gone amiss while the grain was stored?

In the S.L.A.M. system, it is recommended that grain should be cooled to a temperature of 30-35 F as soon after binning as possible using the aeration fans to move temperature fronts through the grain mass. Temperatures in this range are adequate to control most of the potential grain spoilage agents such as molds and insects that can impact grain quality during storage. As outside temperatures rise in the spring, the outer grain layers and the top and bottom of the grain mass will begin to warm which is expected and acceptable. However if the temperature of the grain mass was taken to levels lower than 30 F (“supercold levels”), problems can develop that are unacceptable. This may not be much of an issue in Ohio this year because of the relatively mild winter we experienced. Yet there was a stretch of cold weather in December when one could have chilled grain to extreme levels. When the temperature difference between the grain mass and the outside air is too large, moisture may begin to migrate in the bin and create spoilage problems. Even more importantly, as grain is moved for feed or sale, condensation on newly exposed supercold kernels may cause mold spoilage.

To assess the stored grain management strategies for this spring, farmers and elevator managers need to consider several points.

Grain below 25 F ("supercold") should be rewarmed at this time to reduce the extreme temperature difference that will otherwise develop between the pile and the average outside temperature. Start warming the grain as soon as air temperatures are about 10 F higher than the average grain temperature. One should rewarm the grain to at least 30-35 F or higher if that is what the farmer normally does. During rewarming it is especially important that the fan be operated continuously and the warming front forced all the way through the pile. Allowing a warming (moisture) front to stop part way through the grain mass could result in major condensation at that point leading to mold growth and spoilage.

Grain that is cold (30-35 F) and dry (14-15%), and is moved out of storage before summer (July 1) does not need to be rewarmed in the spring. Although the grain will warm along the outer layers and on the top and bottom of the pile during the spring, the bulk of the grain will remain cool. To prevent accelerated warming of the grain mass, one should cover the fan intake to avoid the natural "chimney" effect in which the cold air is sucked out through the fan opening and the warm air in through the roof vents. Covering may also prevent rodent and pest access. If an automatic aeration controller is used, it may be necessary to disconnect the fan from the controller to make sure it is not inadvertently turned on.

If grain will be held into the summer (past July 1), the temperature in the grain mass should be raised to 50-60 F by mid-spring. The aeration fan should be operated as soon as the average outdoor temperature is 10-15 F above the average grain temperature. Always run the fan continuously to complete a warming cycle and force the warming front through the entire grain mass. This will prevent deposit of moisture in the grain pile, which encourages spoilage.

Several warming cycles may need to be repeated until the average grain temperature reaches 50-60 F. If an automatic aeration controller is used to manage the grain temperatures, it may be advisable to set the operating window wide enough to prevent too many on-off cycles and to assure adequate operating times for rewarming the grain.

Operators with large bins (60 ft diameter X 60 ft height and larger) can manage their grain differently because of the insulating quality of grain in bulk. Full, large bins can maintain relatively low temperatures throughout most of the grain mass year round as long as the grain mass is protected from air currents. To reduce air currents from occurring on their own, one needs to be sure to seal off aeration fans and other opening around the base of the bin. Ventilation needs to be maintained in the headspace and roof area of the bin to allow moisture to escape and not accumulate within the headspace area. This moisture could condense and drip into the surface of the grain resulting in the stimulation of mold growth, sprouting and heat generation.

Information for this article was obtain from Purdue University Cooperative Extension Service Grain Quality Fact Sheet #17, “Rewarming "Supercold" Grain” written by Dirk E. Maier, Agricultural Engineering. For further details on rewarming grain, read this Fact Sheet at: http://www.ces.purdue.edu/extmedia/GQ/GQ-17.html.

Working Around Stored Grain Can Be Dangerous

Authors: Curtis Young

Stored grain by itself normally does not present many hazards, but when working with grain to move it from one place to another, it can become a “monster” in a split second. People can become caught or entrapped in grain in three different ways: the collapse of bridged grain, the collapse of a vertical wall of grain, and entrapment in flowing grain. Moving or flowing grain is involved in all three. People who work with grain -- loading it, unloading it, and moving it from bin to bin -- need to know about the hazards of flowing grain and how to prevent a grain entrapment situation.

Sometimes when grain is left to go out of condition, mold growth will result in the top layer of grain crusting together. This crust can produce a “bridge” or false floor effect while the grain beneath the crust is drawn out by the unloading auger. The resulting bridge is not strong enough to support the weight of a person. If an operator walks out onto the bridge, it will most likely collapse. The collapse will drop the operator to a lower level and possible cover him/her with grain. If the unloading auger is operating at the time, the operator could be further buried after being entrapped in the flowing grain.

Crusting does not always occur over the surface of the grain mass, depending on the cause of the grain spoilage, it can sometimes setup in a vertical column up one side of the bin. If this column is taller than the operator, it could fall on top of him/her when it is knocked down.

An unsuspecting operator who enters a grain bin with the unloader running may be caught in the grain flow before realizing what has happened. It takes only four or five seconds for a person to sink to the point where he or she is helpless. And it takes fewer than 20 seconds to be completely submerged in flowing grain at the center of the bin. Flowing grain is unstable and will not support the weight of a person. It will pull a person down and into the grain mass as it flows. The "suction" action is strong enough that a person cannot "swim," climb, or walk against it and get out. As grain flows out of a bin the victim will be pulled down and under very quickly with little or no time to react.

A person cannot be pulled from flowing grain without risk of injury to the spinal column if the grain is at waist level or higher. The grain will have a very strong grip on the body. Research has shown that up to 400 pounds of pull is required to extract a body from waist-deep grain. That is more than enough force to permanently damage the spinal column.

To avoid injury, dismemberment, and/or death, follow these safety precautions when working around grain:
- Never enter a grain bin without stopping the auger first and then using "lock-out/tag-out" procedures to secure it. Use a key type of padlock to securely lock the switch for the auger in the off position. Attach a tag to the locked switch so that other people involved can positively identify it.
- Do not enter a bin if there is any chance of a bridge being present.
- If you suspect there is a bridge, do not enter the bin to try to break it up. Use a long pole to probe the bridge.
- Do not enter a bin and try to break down grain which has "set up" in a large mass.
- Attempt to break up the grain mass either from the top of the bin with a long pole on a rope, or from outside of the bin, through the door, with a long pole.
- Expect, and be prepared for, the grain mass to break free at any time and to cascade down.
- Prevent grain from bridging or "setting up" in the bin by storing grain in good condition and avoiding spoilage which leads to this problem.
- Children should not be permitted to work or play in an area where there is flowing grain. It is an attractive nuisance and is dangerous to people of all ages, especially children.
- All workers involved in situations where there is flowing grain should be warned to stay out of the grain.
- Warning decals should be placed at all bin entrances, on all rail cars, truck and trailer boxes used for grain hauling, and on all gravity discharge wagons.
- Never enter a grain bin alone; have at least two people at the bin to assist in case problems arise. Use a safety harness or safety line when entering the bin.
- Install a permanent life-line hanging from the center of the bin for a person to grab on to. Tie slip-reducing knots about one foot apart along the life-line. A life-line in a grain bin does not make it safe to enter the bin and should not lead workers to taking undue risks because of a false sense of security.
- Control the access to grain storage facilities to prevent grain entrapments.

In addition to entrapment and suffocation, other hazards that one can encounter include: inhalation of dust and mold spores, slips and falls from ladders, roofs and equipment, and entanglement in augers, pulleys and PTO drive shafts.

Information for this article was obtained from North Dakota State University Extension Ag Safety Fact Sheet AE-1102, “Caught in the Grain!” written by George G. Maher, Ag Safety Specialist, and Purdue University Cooperative Extension Service Grain Quality Fact Sheet #8, “Grain Storage Problems Are Increasing the Dangers to Farm Operators” written by William E. Field, Agricultural and Biological Engineering, and . For further details on safety around stored grain, read these Fact Sheets at: http://www.ext.nodak.edu/extpubs/ageng/safety/ae1102w.htm, http://www.ces.purdue.edu/extmedia/GQ/GQ-8.html.

Control of Annual Ryegrass as a Cover Crop (Adopted from Mike Plumer, University of Illinois)

Authors: Jim Hoorman

Several thousand acres of annual ryegrass were planted in the fall of 2005 in Ohio as a cover crop. Application of herbicides at the 6-8” plant size or before the first node (vegetative) develops, provides the best control. Control at or after the boot stage is very poor until the plant flowers. If glyphosate is used in late March or early April, be aware that cold weather conditions can reduce control. Apply the glyphosate when temperatures are above freezing for one to two days before and after application. It is not recommended that herbicides be sprayed in the afternoon when temperatures are expected to decrease.

Apply glyphosate at a minimum rate of 1.1 lb ae/A. Previous research shows there may be some differences between glyphosate formulations. Glyphosate rates greater than 1.1 lb ae/A should improve control and may be needed during low temperatures. Be sure to add ammonium sulfate (AMS) at 17 #/100 gallon of spray mixture to the glyphosate for improved control. In corn, apply atrazine at a rate of 2.0 lb ai/A plus paraquat at least at 0.75 lb ai/A plus nonionic surfactant (NIS) at 0.25 %v/v. When using atrazine premix products be sure the atrazine rate is 2.0 lb ai/A. Princep may be added to improve control.

The take home message is to apply herbicides early to obtain the most effective annual ryegrass control. Also use the correct combination of products and be sure to scout the field before planting to determine whether a second burndown application is necessary.

Strategies for Managing Marestail, Giant Ragweed, and Lambsquarters in Roundup Ready Soybeans

Authors: Mark Loux

Marestail, giant ragweed, and lambsquarters remain three of the more challenging weeds to deal with, especially when growers take an over-simplified approach to their herbicide programs. Some of the characteristics that make these weeds problematic:

- They are some of the first weeds to emerge in the spring (marestail emerges most of the year), and burndown treatments need to control them. Failure to do so often results in large, weathered weeds later in the spring that are extremely challenging to control.
- They can emerge well into the growing season, which makes it difficult to know how to time postemergence treatments. Early postemergence applications can provide more effective control of emerged plants and minimize interference with the crop, but may miss later-emerging plants.
- They become more difficult to control with increasing size and age.
- Herbicide resistance reduces the number of control options: ALS resistance is widespread in giant ragweed and marestail and growing for lambsquarters; marestail has developed glyphosate resistance in many fields as well as resistance with ALS herbicides; and our research suggests that lambsquarters and giant ragweed may be developing a low level of resistance to glyphosate (see accompanying article in this C.O.R.N.).

Effectively controlling these weeds in soybeans requires an integrated approach to herbicide programs, utilizing several herbicide application timings and a diversity of herbicides to compensate for existing or developing herbicide resistance issues. Specifically, a consistently effective management program includes an effective preplant burndown treatment, use of residual herbicides, and proper management of postemergence herbicide applications. We can also identify certain practices that place producers at risk of control problems for these weeds, including: failure to apply a preplant burndown, over-reliance on glyphosate to the exclusion of other herbicides, failure to use residual herbicides, applying postemergence herbicides too late when weeds are large, using glyphosate rates too low for the weed size and age, and failure to make a second postemergence glyphosate application where necessary. Our suggestions for effective control of marestail, lambsquarters or giant ragweed in soybeans include the following:

MARESTAIL (horseweed)
- Apply burndown herbicides when plants are small – less than 4 inches tall.

- Most effective preplant burndown treatments include: 2,4-D ester plus glyphosate; 2,4-D ester plus glyphosate plus one of the following - Canopy, SynchronyXP, FirstRate, Amplify, or Gangster. Where plants are less than 4 inches tall, a combination of 2,4-D ester plus Gramoxone (at least 0.64 lb ai/A) plus Sencor can also be effective. Where the soybeans have been planted and 2,4-D ester cannot be used, apply a combination of glyphosate plus one of the following - Canopy, SynchronyXP, FirstRate, Amplify, or Gangster.

- Use a glyphosate rate of at least 1.1 lbs ae/A when 2,4-D ester is not in the burndown mixture and when applying postemergence.

- Burndown treatments applied before about May 10 should include residual herbicides to control later-emerging marestail. Most effective options where ALS resistance is known or suspected – Valor, Gangster, Sencor (minimum of 8 oz/A), and Domain (higher rates). The following are also effective residual control options where the grower knows the marestail are not ALS-resistant – Canopy, SynchronyXP, FirstRate, Amplify, Python.

- Where a postemergence herbicide treatment is being applied in Roundup Ready soybeans to control marestail that have survived a prior treatment of glyphosate, apply the maximum labeled rate of glyphosate and consider the addition of Classic, FirstRate, or Amplify.

LAMBSQUARTERS
- Most effective preplant burndown results from a combination of glyphosate plus 2,4-D ester

- Most preemergence soybean herbicides provide effective control of lambsquarters, often for the entire growing season. Effective preemergence herbicides include: Command, Canopy, SynchronyXP, Python, Gangster, Valor, FirstRate, pendimethalin, Scepter, Sencor (except triazine-resistant), and Domain (higher rates, except triazine-resistant).

- Make postemergence glyphosate applications when lambsquarters are less than 6 inches tall, and use a glyphosate rate of at least 1.1 lb ae/A. Use a rate of 1.5 lb ae/A for plants more than 6 inches tall.

- Avoid making postemergence applications during periods of adverse environmental conditions, such as low temperatures, extended cloudy periods, and drought.

- Make a second postemergence glyphosate application as necessary to control plants that survive an initial glyphosate application. Use the maximum labeled rate in these follow up applications. Maximum amount of glyphosate that can be applied postemergence in one season is 2.25 lb ae/A. So, if you use 1.1 lbs ae/A in the first application, use 1.1 lbs again in the second application.

GIANT RAGWEED
- Most effective preplant burndown results from a combination of glyphosate plus 2,4-D ester.

- Use a preemergence herbicide with activity on giant ragweed, which can reduce the giant ragweed population and suppress growth of plants that emerge in the first few weeks after soybean planting. This can minimize the risk of yield loss from early-emerging ragweed and allow for more flexibility in postemergence application timing. Premeergence herbicides with activity on giant ragweed include: Canopy, SynchronyXP, Scepter, FirstRate, Amplify, and Gangster. Note that the giant ragweed activity is based on the ALS inhibiting component of these herbicides, so control will be reduced in ALS-resistant populations. None of these herbicides will control moderate to heavy giant ragweed populations for the entire season.

- The most effective postemergence strategy is to apply 1.1 lb ae/A of glyphosate initially when plants are about 6-10 inches tall, and apply again at the same rate approximately 3 weeks later. Use a rate of 1.5 lb ae/A when plants are more than 10 inches tall, and make a follow up application as necessary at the rate of 0.75 lb ae/A. Applications to plants more than 12 inches tall can put producers at significant risk of soybean yield loss, especially in dense populations, and large plants that have developed a low level of resistance may be difficult to control with even two postemergence applications.

- Make a second postemergence glyphosate application as necessary to control plants that survive an initial glyphosate application. Use the maximum labeled rate in these follow up applications. Maximum amount of glyphosate that can be applied postemergence in one season is 2.25 lb ae/A.

Evolving Lambsquarters and Giant Ragweed Control Problems – What’s the Cause?

Authors: Mark Loux

Across Ohio and the rest of the Midwest, growers and dealers report that lambsquarters has become more problematic in Roundup Ready soybean fields. We have also observed more giant ragweed in Roundup Ready soybean fields recently, and especially compared to the first 5 or so years after their introduction when these fields were largely weed-free at the end of the season. We know that some instances of poor control can be attributed to generally poor management of glyphosate, due to the tendency for some growers to over-simplify their approach to weed management in order to reduce the number of applications and costs. Lambsquarters and giant ragweed can both be generally tough to control with a single postemergence treatment. Growers who omit preplant burndown treatments, apply when weeds are large and old, and use rates too low for the weed size and age, place themselves at risk for control failures. The accompanying article describes management strategies to help ensure consistent control of these weeds, and the rest of this article outlines out thinking on the evolution of resistance in these two weeds.

We believe that some populations of giant ragweed and lambsquarters are evolving to have a low level of resistance to glyphosate. We expect to see changes in the response of our weed populations to glyphosate based on our intense use of this herbicide, and glyphosate-resistant marestail is already abundant in Ohio. While we typically observe about an 8X level of resistance to glyphosate in marestail, our greenhouse research indicates that the level of resistance in lambsquarters and giant ragweed is more on the order of 1X to 4X. So, plants can survive glyphosate rates up to 3 lbs ae of glyphosate per acre, but they usually suffer substantial injury even at lower rates. We also observe considerable variation in the response of these populations among greenhouse experiments. This might not be unexpected for a low level of resistance, but it makes characterization of the resistance difficult, and also makes it difficult to determine the implication of resistance under field conditions.

In field research we conducted in 2005, the suspect giant ragweed population we were working with was difficult to control. In a small plot study in an area of the field where the population was densest, we achieved better than 90% control only when we applied 3 lb ae/A of glyphosate followed by another 1.5 lb ae/A or when we applied Flexstar (1 pt/A) or FirstRate (0.3 oz/A) followed by 1.5 lb ae/A of glyphosate. In a large-plot study using large application equipment, we achieved an average of at least 90% control when we made two postemergence applications at labeled rates, but the most effective control occurred when we applied 1.5 lb ae/A first, and followed with another 0.75 lb/A (as compared to the other way around). We observed a considerable number of plants that were not completely killed in the large plots, and many of these appeared to have produced viable seed.

We conducted field research at six sites where we suspected lambsquarters to have a low level of resistance. At these sites, we were able to achieve excellent control with two postemergence glyphosate applications, but at several sites we did find a few plants that, although small, were able to produce viable seed. All of our lambsquarters plots received two applications, but we did evaluate control after the first application. Our ratings at that time, along with observations of control in the rest of the field at harvest time that was treated only once, led us to conclude that control would have been less than acceptable at several sites had we not treated twice.

So, what does it all mean? Our working theory at this point is that populations of lambsquarters and giant ragweed in some fields are becoming less sensitive to glyphosate. We consider this to be a low level of resistance, since it has developed over time with repeated use of the same herbicide, and control with glyphosate was initially good in these fields. What are the implications of a low level of resistance for users of Roundup Ready systems? We have tentatively concluded the following:

- while some of the blame rests with mismanagement of glyphosate, the evolution of a low level of resistance is likely to be contributing to the problems that growers are experiencing with control of lambsquarters and giant ragweed;

- continued intensive use of glyphosate, an increase in the acreage of Roundup Ready corn, and a failure to integrate glyphosate with other herbicides will cause resistance to be more widespread, and also drive the level of resistance higher within populations.

- the expression of the low level of resistance is variable, so that the resistant populations may be controlled under appropriate management of glyphosate (small plants, high enough rate, multiple applications) and when environmental conditions are favorable. Conversely, these populations are more likely to be poorly controlled when growers mismanage glyphosate (large, old weeds, low rates, no burndown, etc) or when environmental conditions are unfavorable;

- growers observing poor control of lambsquarters or giant ragweed should not assume that it is the result of poor environmental conditions or other factors alone (although these can be part of the problem). Management strategies in subsequent years should be altered in fields where problems have occurred, with the assumption that a low level of resistance could be present (see accompanying article for effective management suggestions);

- growers who mismanage glyphosate will end up with more instances of poor control where there is a low level of resistance. This poor control can result in increased weed seed production, which increases the number of resistant plants the following year. So, mismanagement of glyphosate can speed the development of resistance problems;

- properly managing glyphosate can slow, but will not prevent the development of resistance. Growers also need to implement practices that reduce selection pressure (i.e reduce the reliance on glyphosate alone for weed control), such as rotation of Roundup Ready systems with non-Roundup Ready systems, use of tillage or a multiple-herbicide burndown program to start the crop weed-free, use of preemergence herbicides, and combination of glyphosate with other postmergence herbicides.

Archive Issue Contributors: 

Pierce Paul and Dennis Mills (Plant Pathology), Mark Loux and Jeff Stachler (Weed Science), Robert Mullen and Maurice Watson (Soil Fertility), Ed Lentz (Agronomy), Mark Sulc (Forage Production), Peter Thomison, Allen Geyer and Rich Minyo (Corn Production), Jim Beuerlein (Soybean & Small Grain Production) and Ron Hammond (Entomology). Extension Agents: Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Curtis Young (Allen), Jim Hoorman (Hardin), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Gary Wilson (Hancock) and Keith Diedrick (Wayne).

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.