C.O.R.N. Newsletter 2013-08

Dates Covered: 
April 9, 2013 - April 15, 2013
Glen Arnold

First Thing We Do, Let’s Kill All The Pigweeds*

We have plenty of glyphosate-resistant weed populations in Ohio.  Resistance currently is known to occur in four weed species here – marestail (horseweed), giant ragweed, common ragweed, and waterhemp - and many of these populations are also resistant to ALS inhibitors.  The good news is that our resistance problems are overall less severe than in the southern United States, where the now widespread occurrence of Palmer amaranth has had a substantial impact on crop yields and profitability of cotton and soybean growers, and forced a semi-permanent change in the amount of herbicide that has to be used.  There are also other parts of the Midwest where the abundance of herbicide-resistant waterhemp results in costly herbicide programs and problems with control.

Waterhemp and palmer amaranth are in the Amaranthus or pigweed family.  The most abundant pigweed species in Ohio are redroot and smooth pigweed, which are essentially identical to each other with regard to identification.  Most preemergence herbicides have substantial activity on these pigweed species, and they are usually well controlled by a combination of preemergence and postemergence herbicides.  We have screened a few redroot and smooth pigweed populations for resistance to herbicides, and so far have observed some ALS resistance but not glyphosate resistance.  Waterhemp, which is present primarily in a few western counties in Ohio, has proven itself capable of developing resistance to almost any herbicide site of action used against it.  Waterhemp populations with resistance to ALS inhibitors, glyphosate, and PPO inhibitors (e.g. Flexstar) are fairly common in Illinois and other states to the west.  Populations with up to five herbicide sites of action – ALS inhibitors, glyphosate, PPO inhibitors, triazines, and HPPD inhibitors (Callisto, etc) – exist in several states.  There is also a waterhemp population in Nebraska that developed resistance to 2,4-D in response to continuous use in a warm-season grass field.

Palmer amaranth (aka Palmer pigweed) has been fairly accurately characterized as “pigweed on steroids”.  In addition to the glyphosate resistance, this weed’s rapid growth, large size, extended duration of emergence, prolific seed production, and general tolerance of many POST herbicides makes it a much more formidable weed to deal with than the other Amaranthus species.  The POST herbicides that have activity on Palmer amaranth - Flexstar, Cobra, Reflex, Ultra Blazer, and Liberty - must be applied when the weed is less than 3 inches tall.  Palmer amaranth has overall more potential to reduce yield if not controlled well, compared with the other pigweeds.  We have at this point confirmed the presence of Palmer amaranth in one large field in southern Ohio, and this population is resistant to both glyphosate and ALS inhibitors.  We also have been informed of another possible site just south of Columbus.  As far as we can tell, the source of the first population may have been a CREP/wildlife type seeding, where the seed of the desirable species was apparently contaminated with Palmer amaranth seed.  There are also substantial infestations of Palmer amaranth in Michigan and Indiana, and the source of these appears to be contaminated cottonseed shipped from the southern US for use as animal feed here in the Midwest.  Manure from these animal operations was spread on fields, and the Palmer amaranth then became established.

A major goal over the next decade for Ohio agribusiness and growers, and OSU weed scientists, has to be the prevention of additional infestations of Palmer amaranth and waterhemp.  Both of these weeds have more potential to impact the profitability of our corn and soybean production than our other resistance problems.  More information on these weeds is available on the OSU weed management website, https://agcrops.osu.edu/specialists/weeds, and the websites of other land grant universities in the Midwest and South.  Steps we need to take to accomplish this:

1.  Identification of new infestations as soon as possible after they occur.  We have posted a brief Powerpoint video on our website that covers identification of pigweeds.  A key characteristic for identification of Palmer amaranth early in the season may be the presence of a very dense population where there were only a few plants the previous year.  Identification needs to occur when the plant is small enough that herbicides are still effective.  OSU weed scientists can help with identification, either via digital photos emailed to us, or with visits to fields.  Special attention should be paid to fields receiving applications of manure from animal operations using cottonseed products as feed.  We would appreciate being informed of any new infestations of Palmer amaranth as soon as possible (loux.1@osu.edu).

2.  Implementation of effective management programs.  Both waterhemp and Palmer amaranth have extended periods of emergence, and a combination of preemergence and postemergence herbicides is required.  We assume that most populations are resistant to glyphosate and ALS inhibitors (although there are waterhemp populations in Ohio that are just ALS-resistant), and this should be factored into the choice of herbicides.  Waterhemp is included in the soybean herbicide effectiveness table in the “Weed Control Guide for Ohio and Indiana”.  Growers in the south are using an approach for Palmer amaranth that includes preplant/preemergence application of residual herbicides, and then a combination of postemergence and residual herbicides when the weeds are less than 3 inches tall (and in some cases another application of residual herbicides).

3.  Prevention of further seed production.  As new infestations of Palmer amaranth develop in Ohio, there are likely to be instances where the problem is identified too late to implement effective control measures (this is typical for any new resistance problem).  Where this occurs, it is essential that growers take all steps possible to prevent weed seed production.  This can include tillage, mowing, and also removal of surviving plants by hand.  Effective removal of plants by hand requires more than just cutting them off.  Experiences in the south are that the plant must be uprooted and removed from the field.  Paying a crew of people to remove plants in mid-season should be considered a viable solution, even at a relatively high cost.  The result of not doing so could be a substantial loss of income in future years.

*with apologies to William Shakespeare

4R Nutrient Stewardship-Spring Placement4R Nutrient Stewardship-Spring Placement

4R Nutrient Stewardship-Spring Placement

In case you have forgotten what 4R Nutrient Stewardship is since the last meeting you attended here is a reminder that we are talking about the right rate, source, timing and placement of nutrient in crop production. Today we want to focus on spring placement of nutrient, specifically phosphorous.

Placement from a crop production standpoint is always a discussion about efficiency of nutrient utilization and crop response. As we look at practices to reduce phosphorus loading from agricultural sources into Ohio waters, spring placement could prove to have an important role.

Researcher that have been investigating Lake Erie’s response to nutrient loading have noted a correlation between the amount of phosphorus loading in the period March through June and the subsequent amount of algae bloom, specifically Harmful Algae Blooms (cyanobacteria) on Lake Erie that appears in the July through September time period. A predictive model for HAB development was released for the first time in July, 2012 and performed well in predicting the 2012 HAB bloom level. The data on March through June total P loads is the primary variable used. (Stumpf et al., 2012)  A weekly HAB forecast system considerer’s water and air temperature on the lake along with wind currents and imagery data. This forecast has been has been provided by NOAA since 2009 can be found at http://www.glerl.noaa.gov/res/Centers/HABS/lake_erie_hab/lake_erie_hab.html

With concerns about spring loading effects on water quality it might be a discussion to closely watch applications in this time of the year.

Avoid unincorporated surface applications. Commercial fertilizers by design are water soluble. The solubility of MAP and DAP are 100% and 0-46-0 is 97-100%. Phosphorus is an immobile nutrient but at the point of application there is a period of time before it is stabilized in the soil. A variety of conditions including soil test levels, pH, and soil factors are among other factors that affect solubility. Losses of this soluble nutrient form with runoff events are one area of concern.

How phosphorus is supplied affects loss potential. Surface-applied phosphorus is at more risk for loss than fertilizer phosphorus that has been incorporated with tillage. A minimum amount of tillage following the application decreases the risk of dissolved reactive phosphorus transport and potential loss. Thus, to minimize the risk of phosphorus transport, some tillage (even minimally invasive) is beneficial (Kleinman et al., 2002). It should be noted here that in a no-till system, while plant residue left on the soil surface can reduce runoff volume, it does not reduce the concentration of phosphorus in runoff (Nicolaisen et al., 2007).

Instead of making a broadcast application of phosphorus, one may consider supplementing phosphorus in a starter blend applied with a planter. If soil test levels are near the critical level, phosphorus can be included in a starter to ensure that it is not limiting. Starter phosphorus responses have also been noted on soils with adequate phosphorus that are in a no-till production system. Phosphorus supplied as a starter is much less susceptible to loss due to the fact that it is placed below the soil surface. The unfortunate trade-off is that liquid forms of phosphorus supplied as a starter are typically much more expensive than broadcast applications on a price-per-pound of phosphorus basis.” (Mullen et al., 2009).

Placement is one BMP that we can implement. In indicating incorporation we also need to realize that tillage that leads to increased soil erosion will increase total P loading and still lead to algae problems.

Mullen, R. et al (2009) Best Management Practices for Mitigating Phosphorus Loss from Agricultural Soils. http://ohioline.osu.edu/agf-fact/pdf/0509.pdf [Accessed March 22, 2013]

Stumpf RP, Wynne TT, Baker DB, Fahnenstiel GL (2012) Interannual Variability of Cyanobacterial Blooms in Lake Erie. PLoS ONE 7(8): e42444. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0042444  [accessed March 22, 2013]

Getting Your Corn Crop Off to a Good Start in 2013 Preplant nitrogen being applied

Getting Your Corn Crop Off to a Good Start in 2013

Mistakes made during crop establishment are usually irreversible, and can put a "ceiling" on a crop's yield potential before the plants have even emerged. The following are some proven practices that will help get a corn crop off to a good start.

Perform Tillage Operations Only When Necessary and Under the Proper Soil Conditions.

Avoid working wet soil and reduce secondary tillage passes. Perform secondary tillage operations only when necessary to prepare an adequate seedbed. Shallow compaction created by excessive secondary tillage can reduce crop yields. Deep tillage should only be used when a compacted zone has been identified and soil is relatively dry. Late summer and fall are the best times of year for deep tillage.

Complete Planting by Early May

The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. However if soil conditions are dry and soil temperatures are rising fast (and the 5 to 7 day forecast calls for favorable conditions), start planting before the optimum date. During the two to three weeks of optimal corn planting time, there is, on average, only one out of three days when field work can occur. Avoid early planting on poorly drained soils or those prone to ponding. Yield reductions resulting from "mudding the seed in" are often much greater than those resulting from a slight planting delay. In  2011 and 2012, many Ohio growers observed that their later planted corn yielded better than early corn due to unusually favorable rainfall and temperature conditions in late July and August.

Adjust Seeding Depth According to Soil Conditions

Plant between 1-1/2 to 2 inches deep to provide for frost protection and adequate root development. Seeding depth should be monitored regularly during the planting operation and adjusted for varying weather and soil conditions. Irregular, especially shallow planting depths contribute to uneven plant emergence, which can reduce yields. See last week’s newsletter article for more on the importance of avoiding shallow planting depths.

 Adjust Seeding Rates on a Field-by-Field Basis

Adjust planting rates by using the yield potential of a site as a major criterion for determining the appropriate plant population. Higher seeding rates are recommended for sites with high-yield potential with high soil-fertility levels and water-holding capacity. OSU plant population studies conducted from 2006 to the present suggest that on highly productive soils, with long term average yields of 190 bu/acre or more, final stands of 33,000 plants/acre or more may be required to maximize yields. Lower seeding rates are usually preferable when droughty soils or late planting (after June 1) limit yield potential. On soils that average 120 bu/acre or less, final stands of 20,000 to 22,000 plants/acre are adequate for optimal yields. On soils that average about 150 bu/acre, a final stand of 30,000 plants per acre may be needed to optimize yields. Seeding rate can be cut to lower seed costs but this approach typically costs more than it saves. Most research suggests that planting a hybrid at suboptimal seeding rates is more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels) and harvest delays occur. When early planting is likely to create stressful conditions for corn during emergence, e.g. no-till in corn residues in early to mid April, consider seeding rates 10 to15% higher than the desired harvest population. Follow seed company recommendations to adjust plant population for specific hybrids.

Plant a Mix of Hybrid Maturities

Planting a mix of hybrids with different maturities reduces damage from diseases and environmental stress at different growth stages (improving the odds of successful pollination) and spreads out harvest time and workload. Consider spreading hybrid maturity selections between early‑, mid‑, and full‑season hybrids‑for example, a 25‑50‑25 maturity planting, with 25 percent in early‑ to mid‑season, 50 percent in mid‑ to full‑season, and 25 percent in full‑season. Planting a range of hybrid maturities is probably the simplest and most effective way to diversify and broaden hybrid genetic backgrounds.

Plant full‑season hybrids first

Planting a full‑season hybrid first, then alternately planting early‑season and mid‑season hybrids, allows the grower to take full advantage of maturity ranges and gives the late‑season hybrids the benefit of maximum heat unit accumulation. Full‑season hybrids generally show greater yield reduction when planting is delayed compared with short ‑to mid‑season hybrids.

Applying Manure to Take Best Benefit of Available Nitrogen for Corn Balzer tanker and Dietrich toolbar

Applying Manure to Take Best Benefit of Available Nitrogen for Corn

Applications of liquid manures have the potential to provide nitrogen that can be counted toward meeting the needs of the corn crop and substituting for 28% or other fertilizer N sources. Research on the application of manure preplant or sidedress to corn has been ongoing in Ohio for several years. Liquid swine and dairy manure were applied to pre-emergent and post-emergent corn at the OARDC Hoytville research station in 2011 and 2012.

The nitrogen content of livestock manure can be determined by submitting a sample for testing. Testing revealed the swine manure source for this research plot contained approximately 38 pounds of available nitrogen per 1,000 gallons.   The dairy manure source contained approximately 10 pounds of available nitrogen per 1,000 gallons.

In 2011, a total nitrogen rate of 175 pounds from all sources was used. An application rate of 4,700 gallons per acre of swine manure was used. A dairy manure application rate of 13,577 gallons provided 135 units of nitrogen with supplemental 28%UAN applied just prior to the dairy manure application to reach the 175#. Corn was planted on June 3rd in 2011. Pre-emergent manure applications were made on June 6th and post-emergent manure applications were made on June 16th. All treatments received 175 #/acre of nitrogen.

In 2012, a total nitrogen rate of 200 pounds from all sources was used. An application rate of 5,200 gallons per acre of swine manure was used. A dairy manure application rate of 13,577 gallons per acre provided 135 units of nitrogen. The dairy reps received additional nitrogen incorporated as supplemental 28%UAN applied just prior to the dairy manure application to reach the 200# N rate.

Corn was planted on April 26th. Pre-emergent manure applications were made on April 27th and post-emergent manure applications were made on May 16th. All treatments received 200 #/acre of nitrogen.

Dry weather in June and early July of 2011 severely reduced corn yields on the 28%UAN side dress plots. The liquid added by the swine and dairy manure likely helped the early growth of the corn. The manure moisture also appeared to improved control of knotweed at the site which may have reduced weed pressure.

The 2012 growing season was also unusually dry. Again, the moisture added by the manure probably benefitted the overall manure treatment yields.

Stand populations were approximately 28,000 plants per acre across all treatments. The manure did not appear to reduce the plot stands in either year.

All manure was applied with a 5,250 gallon tanker and Dietrich tool bar. Surface manure applications were accomplished by simply raising the Dietrich toolbar out of the ground.


2011 & 2012 Corn-Manure Research Plots OARDC Northwest Branch




Two-year average





Pre-emergent treatments




Incorporated 28%UAN




Incorporated swine manure




Surface applied swine manure




Incorporated dairy manure + 28%UAN




Surface applied dairy manure + 28%UAN








Post-emergent treatments




Incorporated 28%UAN




Incorporated swine manure




Surface applied swine manure




Incorporated dairy manure + 28%UAN




Surface applied dairy manure + 28%UAN








Zero nitrogen check





LSD= 16.99


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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.