CFAES Give Today
Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-09

Dates Covered: 
April 15, 2008 - April 22, 2008
Steve Prochaska

Avail – Can It Improve Phosphorus Fertilizer Efficiency?

Authors: Robert Mullen

A new additive to phosphorus fertilizer is currently being marketed in Ohio called Avail. Avail is a polymer that can be used as a coating for dry phosphorus or as an additive to liquid phosphorus fertilizers. The polymer has an extremely high cation exchange capacity (reportedly 1800 meq/100 g) that binds soil cations calcium, magnesium, iron, and aluminum decreasing their ability to interact with phosphorus. Theoretically, application of this material with a phosphorus fertilizer source should improve phosphorus availability at least in the short term.

Data collected at Kansas State University in 2001-2003 showed that Avail coated monoammonium phosphate (MAP) applied at planting increased corn yields in two of the three years compared to uncoated MAP (page 34). The soil test P level was 23 ppm using Bray-Kurtz P1 extractant and not considered deficient.

An additional study conducted at the University of Minnesota reveals that in one out of three years broadcast applied diammonium phosphate (DAP) coated with Avail resulted in a yield increase compared to uncoated DAP. In 2002, Avail added to a starter 7-21-7 liquid material did not result in a yield increase.

The greatest concern regarding Avail is that information limited at present, so widespread use of this product may not be warranted. The other issue to be considered is how high soil P fertility affects response. High P soils are unlikely to benefit from application of this material, but research information is not available at this time

Cold Temperature Effect on Wheat After Green-Up

Authors: Pierce Paul, Jim Beuerlein, Dennis Mills

The forecast is for average night-time temperatures to drop considerably over the next day or so, with lows in the 20s. The wheat in now greening up across most of the state, but in some southern counties, early-planted wheat may already be jointing. Growers, especially in southern Ohio, are concerned that these cold temperatures may damage their crop. Whether or not the wheat crop is damaged by cold spring temperatures and the extent of the damage depend on three main conditions: 1) how cold it gets, 2) the length of time the crop is exposed to the cold temperatures and 3) the growth stage of the crop at the time of exposure. Freezing temperatures are most damaging when the crop is at more advanced stages of development. Once it warms up in the spring and the wheat starts to grow, it looses its cold-temperature hardiness, making it more prone to injury from freezes. Such injuries are most severe when freezing temperatures occur during boot and heading growth stages.

At our current growth stage (tillering to jointing), freeze injuries will likely be less than they would be if we were at boot or heading. Before growth stage 6, the growing point, which is easily damaged by cold temperatures, is near the soil line where it is protected from injury. However, as the crop develops and the growing point extends above the soil surface, freezing temperatures may be more injurious. For instance, temperatures below 12 F are injurious during tillering, where as, during jointing 2 hours of exposure to 24 F may be sufficient to cause injuries to the growing point. For more information on this subject go to During tillering, injuries tend to be greatest if the wheat is lush and actively growing (especially after spring nitrogen application) and are more common in low areas of the field, appearing as light green to yellow discoloration (burning) of the tips of the leaves (early symptoms may be confused with those caused by some viruses and nutrient deficiency). Although these injuries may reduce tiller numbers, at this early growth stage, the wheat crop still has time to recover and produce new leaves and tillers once it warms up.

During the initial stages of jointing, which may be occurring in some southern counties, the growing point is still somewhat protected by vegetation. However, some level of injury may still occur. In addition to discolored leaf tips, the growing point of injured plants will become brownish, with a water soaked appearance. To assess the extent of the injury, remove the leaves, split the stem longitudinally (lengthwise), and examine the growing point, which is located above the uppermost node. Examine both main and secondary tillers from different areas of the field and determine the average number of healthy and injured tillers per foot of row. A healthy growing point is usually white to yellowish-green in color as opposed to off-white or brown. When the growing point is severely damaged, growth of the affected stem stops, even on healthy-looking plants. In extreme cases, the leaves in the whorl die and the affected tiller may not produce a head, however, secondary tillers may remain unaffected and should develop normally and produce grain.

Remember, wheat is a cool season crop and can tolerate temperatures well below freezing. In addition, the forecast is for warmer conditions later in the week, with highs in the mid to upper 60s after Wednesday.

Applying Wheat Herbicides in 28% - How Late is Safe?

Authors: Mark Loux

Since wet weather has prevented traffic in many wheat fields, applications of herbicides and nitrogen fertilizer may occur when wheat is at a more advanced growth stage compared to some other years. Be sure to stage wheat prior to herbicide applications, and consult the “Weed Control Guide for Ohio and Indiana” and herbicide labels for information on herbicides and growth stage. The figure on page 151 of the 2008 guide serves as a quick reference on application timing relative to wheat stage. One of the questions relative to this subject is – how late in spring can wheat herbicides be applied using 28% UAN as the spray carrier? Stated another way, does application of herbicide in 28% UAN increase the risk of wheat injury and yield loss compared with application in water, when wheat is advanced in growth stage?

Herbicide labels often do not provide much information on application in 28% UAN. We conducted one study on this in 2003, where we applied various herbicides in water or 28% when wheat was in the joint or boot stage. Herbicides applied included Harmony Extra, 2,4-D amine, Buctril, and Harmony Extra plus 2,4-D amine. None of the herbicides reduced wheat yield when applied in water or 28% UAN on April 16 to wheat in the joint stage. The major treatment effect we observed for application later in the spring, to wheat in the boot stage on May 9, was a yield loss of about 20% when Harmony Extra or Harmony Extra plus 2,4-D was applied in 28% UAN. Aside from this, for the May 9 application, there was a trend for minor yield loss with the combination of Harmony Extra plus 2,4-D applied in water, and Buctril applied in 28% UAN. Keep in mind that the wheat growth stage on May 9 was far enough advanced that several of these herbicides should not have been applied in water or 28% UAN. For example, 2,4-D labels specify application to wheat prior to joint or boot stage, depending upon the product.

These results indicate that wheat should tolerate application of herbicide in 28% UAN well into April, as long as the restrictions on herbicide labels relative to what growth stage are followed. For products that applied with surfactant, consult labels about the surfactant rate when applying in water vs 28%, since surfactant rates may be reduced to minimize the risk of injury when applying in 28%.

Alfalfa Weevil Update

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Southern Ohio has accumulated enough heat units such that growers should begin sampling for alfalfa weevils. Heat units at our weather stations in Piketon and Jackson are both over 300 as of this time. Central and/or northern Ohio has not reached 300 heat units , although it should reach that point by the end of the week in central OH, and not until next week for northern Ohio locations.

Adjustments to Consider if Corn Planting Delayed

Authors: Peter Thomison, Robert Mullen, Mark Loux

The wet weather we’ve been experiencing recently has raised concerns that we might be looking at a later than normal planting season that could impact yields. Meteorologists are now forecasting drier conditions the remainder of the month. According to one report, high pressure, warming temperatures and low relative humidity will mean good to excellent drying conditions this week and more days will be dry than wet next week. However, in the event rains cause further planting delays or soils are slow to dry, the following are some suggestions to consider in dealing with a late planting season.

Although the penalty for late planting is important, care should be taken to
avoid tillage and planting operations when soil is wet. Yields may or may not be reduced this year due to delayed planting, but effects of soil compaction from “mudding the seed in” can reduce yield for several years to come. Keep in mind that while higher yields are associated with early plantings, planting date is just one of many factors that determine yield in corn. Moreover, average corn yields from past years do not suggest a strong relationship between planting date and yield. Dr. Bob Nielsen at Purdue University has addressed the relative importance of early planting dates in a recent newsletter article available online at

If you originally planned to apply nitrogen and herbicides pre-plant, consider alternatives so that planting is not further delayed when favorable planting conditions occur. Although application of anhydrous N is usually recommended prior to April 15 in order to minimize potential injury to emerging corn, anhydrous N may be applied as close as a week before planting (unless hot, dry weather is predicted). In late planting seasons associated with wet cool soil conditions, growers should consider side-dressing anhydrous (or UAN liquid solutions) and applying a minimum of 30 lb/N broadcast or banded to stimulate early seedling growth. The latter approach will allow greater time for planting and buy time later for sidedressing. Applying starter with the seed increases the sidedress period by supplying some nitrogen to get the crop through the early part of the season meaning that sidedress can occur later with little or no signs of N deficiency. Similarly, crop requirements for P and K can often be met with starter applications placed in bands two inches to the side and two inches below the seed. Application of P and K is only necessary with the starter if they are deficient in the soil, and the greatest probability of yield response from P and K starter is in a no-till situation.

Keep time expended on tillage passes and other preparatory operations to a
minimum. The above work will provide minimal benefits if it results in
further planting delays. No-till offers the best option for planting on time
this year. Field seedbed preparation should be limited to leveling ruts left
by last year’s harvest - disk or field cultivate very lightly
to level. Most newer planters provide relatively good seed placement in
"trashy" or crusted seedbeds. Final tillage passes just before planting can
be beneficial in suppressing weeds, but may not be practical this year.
In many cases, it may be more profitable to complete planting first and apply herbicide afterwards to control emerged weeds. Where this occurs, apply herbicides as soon as possible after planting, so that the crop emerges and develops without interference from weeds. Application prior to crop emergence allows for use of higher rates and more choice in herbicides, which can help ensure effective burndown. Effective burndown treatments that also include residual herbicides will help minimize the potential for major weed problems to develop later in the season, especially where glyphosate-resistant weeds occur.

Don't worry about switching hybrid maturities unless planting is delayed to
late May. If planting is possible before May 20, plant full season hybrids
first to allow them to exploit the growing season more fully. Research in
Ohio and other Corn Belt states generally indicates that earlier maturity
hybrids lose less yield potential with late plantings than the later
maturing, full season hybrids.

With no-tillage or reduced tillage, increase seeding rates 10% over those
used with conventional tillage. Consult seed company recommendations for
specific hybrid planting rates under reduced tillage. Lower yields in
no-till can sometimes be related to sub-optimal plant populations at

Nielsen, R.L. (Bob). 2008. Corn Planting Date is Important, But….Corny News Network, Purdue Univ. [On-line]. Available at (Published 12 April 2008)

Archive Issue Contributors: 

Jim Noel (NOAA), Anne Dorrance and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Ed Lentz (Agronomy) , Mark Loux (Weed Science), and Jeff Stachler (WeedScience). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Harold Watters (Champaign), Wes Haun (Logan), Les Ober (Geauga), Mike Gastier (Huron) Jonah Johnson (Clark), Steve Bartels (Butler), Mark Koenig ( Sandusky), Steve Prochaska (Crawford) and Marissa Mullett (Coshocton).

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.