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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2009-34

Dates Covered: 
October 6, 2009 - October 13, 2009
Curtis E. Young

Handling Frost Damaged Corn

According to the USDA/NASS ( as of Sunday, October 4, 93 percent of Ohio's corn was dented, compared to 100 percent both last year and for the five-year average. Forty-six percent of corn was mature, compared to 79 percent both last year and for the five-year average. Four percent of the corn was harvested, ten percent behind last year and seven percent behind the five-year average.

The growing season for corn in many NW Ohio fields ended last week when a killing frost occurred September 30, 2009. Although this frost may have only been about a week earlier than normal, corn in some affected fields had not yet reached kernel "black layer", the stage at which kernel growth ceases and maximum kernel dry weight is achieved (also referred to as "physiological maturity"). For those growers with questions on the impact of frost damage on grain yield and maturation, one good source of information is "Handling Corn Damaged by Autumn Frost" NCH-57 by P.R.Carter and O. B. Hesterman available online at This publication includes information on the effect of frost on grain development and describes options for handling damaged corn. The following is an excerpt from the publication that addresses effects of frost injury on yield potential and whole plant and kernel moisture.

The effect of frost damage to corn depends on the severity of defoliation, stalk damage, and stage of growth. Tables 1 and 2 provide yield loss and kernel moisture estimates resulting from premature plant death during grainfill. The tables summarize the findings of Minnesota researchers who defoliated plants to simulate frost damage at different kernel development stages.

Table 1: Yield Loss in Corn as a Result of Plant Defoliation at Three Kernel Development Stages.

-Kernel Development Stage- -Percent Grain Yield Reduction-
Soft dough 34-36
Full dent 22-31
Late dent 4-8

Source: Afuakwa, J. J., and R. K. Crookston. 1984. Using the kernel milkline to visually monitor grain maturity in maize. Crop Science 24: 687-691.

Table 2: Whole Plant and Kernel Moisture of Corn at Four Kernel Development Stages.

Kernel Development Stage % Moisture % Moisture
- Kernel Whole Plant
Soft dough 62 >75
Full dent 55 70
Late dent 40 61
Physiological maturity (Black Layer*) 32 53

* Black Layer-indicates end of kernel growth and maximum kernel dry weight (physiological maturity).

Source: Afuakwa, J. J., and R. K. Crookston. 1984. Using the kernel milkline to visually monitor grain maturity in maize. Crop Science 24: 687-691.


Fall and Spring Herbicide Treatments for Management of Marestail - How to Use the Residual Herbicide?

Multiple years of OSU research on fall and spring herbicide treatments have consistently shown that the value and effectiveness of residual herbicides for soybeans is maximized when they are applied in the spring, not the fall. There are articles covering this in the C.O.R.N. archive for the last several falls, so we won't cover the whole story again here. The bottom line is that is can be a big mistake to apply all of the residual herbicide in the fall, with the intent to omit the spring pre-plant treatment and apply just post-emergence herbicides in next year's soybeans. Fall application of chlorimuron products such as Canopy EX/DF can control many summer annual weeds through early June the following year, but the residual control of ragweeds and marestail is often reduced greatly with fall applications, compared with application of residual herbicide in the spring. This is partly due to the prevalence of ALS resistance in these weeds, but a lot of the problem also lies with their biology, and ability to emerge well into the growing season.

Post-emergence control of many marestail populations is close to impossible due to herbicide resistance. The goal of a marestail management program is to ensure that the combination of fall and spring burndown and residual herbicides results in a weed-free seedbed at the time of soybean emergence, and little to no emergence of marestail between soybean emergence and crop canopy closure. Even the most effective marestail management programs can fail to completely achieve this, but they often keep the populations low enough in the soybeans that they are not problematic.

Marestail plants that emerge in late summer or fall are easily controlled with a fall herbicide treatment. However, it's essential to realize that a fall herbicide treatment is not likely to accomplish everything that’s needed in an effective marestail management program. An effective program does not necessarily involve application of herbicide in the fall. A combination of the appropriate burndown and residual herbicides applied in April can adequately control marestail, even those that emerged the previous fall. So, one option in fields where other winter weeds are not a problem is to skip the fall herbicide treatment and apply a combination of burndown and residual herbicides in April when marestail are still small.

In those marestail-infested fields requiring a fall herbicide treatment for management of other winter annual annual weeds or dandelion, it is essential not to apply all of the residual herbicide in the fall. This also applies to those fields that are typically so wet that soybeans cannot be planted until mid to late May. In this situation, the goal of a fall residual herbicide treatment might be just to ensure that marestail are not too large when burndown herbicides are finally applied in May. Regardless of the type of herbicides applied in fall, an effective rate of a residual herbicide should still be applied in the spring, to maximize control of marestail that emerges in May and June. The most effective residual herbicides for spring application include two modes of action, to ensure effectiveness on ALS-resistant marestail. Examples: Envive, Valor XLT, Gangster, Sonic, Authority First, and Canopy DF + metribuzin. However, it should not be necessary to apply something this broad-spectrum or costly in the fall. We suggest one of the following approaches:

1. Apply a combination of glyphosate and 2,4-D in the fall, followed by application of residual herbicide in the spring prior to soybean emergence. At the time of soybean planting, the field is likely to be infested with marestail that emerged earlier in spring, so include effective burndown herbicides (2,4-D, Gramoxone, glyphosate, or Ignite or some combination as appropriate based on herbicide resistance, plant size and time until soybean planting) to control emerged plants.

2. Apply 2,4-D with Canopy DF or EX at fairly low rates (e.g. 1 oz of EX or 2 oz of DF) in the fall, followed by application of residual herbicide in the spring (with burndown herbicides if the residual from fall does not hold marestail through planting). It is possible to follow the fall Canopy application with a spring application of a chlorimuron-containing herbicide, as long as the total does not exceed the maximum labeled rate of chlorimuron for the soil type.

3. In ALS-resistant populations where Canopy will fail to provide any residual control of marestail, it may be possible to substitute a combination of 2,4-D with metribuzin in the fall. This combination should control most emerged winter annuals, but can be weak on dandelion. Follow with application of residual herbicide in the spring (with burndown herbicides if the residual from fall does not hold marestail through planting).

The idea here is to apply an herbicide treatment in the fall that adequately controls emerged weeds, provides some residual if desired, but does not break the bank and allows use of the majority of the residual herbicide in the spring. Options 2 and 3 would be most suitable for fields that are wet well into spring, where the goal is to control at least some of the marestail that emerge in early spring. Canopy certainly provides substantially longer residual than metribuzin, but use of metribuzin preserves the option to plant corn the following spring.

Increase Wheat Seeding Rate If Late Planting Becomes a Concern

The prospect of a late soybean harvest again this year already has some Ohio wheat growers concerned about having to plant wheat later than recommended (Hessian Fly Safe date; between September 22 for northern counties and October 5 for the southern-most counties). Ideally, all the wheat should be planted by the second week of October in order to ensure adequate tiller development before winter dormancy. Due to late soybean harvest, growers in some areas will more than likely be planting wheat well into October. Wheat planted late is at greater risk for poor stand establishment (fewer tillers per foot of row), increased winter kill, and spring heaving. However, this all depends of the weather conditions during the fall and early winter. In any given year, if warmer-than-usual conditions occur during late fall-early winter (freezing weather delayed until early December), even wheat planted as late as the first week of November may still do fairly well.

If late planting becomes an issue, growers should plant at a higher seeding rate than the regularly recommended rate of 1.2 to 1.6 million seeds per acre for 7.5-inch rows (that is about 18 to 24 seeds per foot of row with normal sized seed) to compensate for fewer tiller development in late-planted wheat (during the third and fourth week after the fly-safe date). Plant at a rate of 1.6 to 2.0 million seed per acre instead of the normal seeding rate. The number of seeds per pound and germination rate are important for determining the correct seeding rate and drill calibration. There are fewer seeds per pound of large seeds than per pound of small seeds. The number of seeds per pound can be found on the seed bag. Additionally, late planting also means plants will be smaller than normal when entering dormancy, have smaller and more shallow root systems than normal making them more susceptible to heaving next March. The best heaving control is to place the seed between 1.0 and 1.5 inches deep and to plant no-till. These two practices combined will reduce heaving potential by more than 95 percent. Also, do not increase your fall N rate in an attempt to get more tiller development or larger plants. The recommended 20 to 30 pounds of N will be adequate even at the later planting date. Larger N rates will most likely be lost and not benefit the crop.

Low Western Corn Rootworm Variant Numbers for 2nd Straight Year

Western Corn Rootworm (WCR) Variants are WCRs that will lay eggs in soybean during August and September (the normal oviposition site is corn, which is why we call these "variants"). If these fields are rotated to corn the following year, the first-year corn will be at risk for root damage. Monitoring for this pest is achieved using yellow sticky traps in soybean, with beetles counted every week. If the number of beetles per trap per day exceeds 5, then protection of first year corn is warranted. Ohio State University Extension personnel continued trapping for the WCR variant for the 13th year in a row. The number of fields exceeding the 5 beetles/trap/day threshold decreased, just like in 2008. However, for 2009, none of our fields exceeded threshold, even though we sampled fields with historically high numbers of WCR variant. Most of our fields were not even close to 5 beetles/trap/day, and our average for the entire state was less than 1. Other Midwestern states are reporting similar low numbers.

Why have the numbers decreased for 2 years in a row? There are many intriguing thoughts, including weather factors (cold, wet springs), as well as the possibility of Bt-rootworm corn hybrids having similar effects to that of the European Corn Borer - a wide-scale decline in rootworm populations. However, we do receive reports of first year corn fields that are heavily damaged from the WCR variant, even near fields that were monitored with yellow sticky traps, which suggests that "hot-spots" of WCR variant remain. More data will be needed to make definitive conclusions on the current status of western corn rootworm variant. However, the presence of "variant hotspots" strongly emphasizes the need for individual field scouting, as there seems to be a lot field to field variation.

New Resources on Management of Marestail

Several new resources on marestail management are available from OSU, and these can all be found at our web page - We cooperated with Purdue University weed scientists to write the 2-page fact sheet, "Management of Marestail in No-till Soybeans," which is available as a pdf. We have also posted two video Powerpoint presentations in Flash format: "Marestail Management - the Short Story," a 10-minute video for those who want the basics; and "Marestail Management - the Longer Story," a 30-minute video for those wanting more complete information on biology and the data that supports our recommendations. If not posted already, the video links should be posted within a day or so of when you receive this newsletter.

Feeding Frosted Forages

Sorghum and Sudangrass Forages

Prussic acid poisoning can occur when feeding sudangrass, sorghum-sudangrass hybrids, forage sorghum, or grain sorghum. These species contain varying concentrations of cyanogenic glucosides, which are converted to prussic acid, also known as hydrogen cyanide (HCN). As ruminants consume forage containing high levels of cyanide-producing compounds, prussic acid is released in the rumen, absorbed into the bloodstream where it binds hemoglobin, and interferes with oxygen transfer. The animal soon dies of asphyxiation. Prussic acid acts rapidly, frequently killing animals in minutes. Symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse. Ruminants are more susceptible than horses or swine because cud chewing and rumen bacteria help release the cyanide.

Generally, any stress condition that retards plant growth may increase prussic acid levels in plants. Hydrogen cyanide is released when leaves are damaged by frost, drought, bruising, cutting, trampling, crushing, or wilting. Plants growing under high nitrogen levels or in soils deficient in soil phosphorus or potassium tend to have high levels of cyanogenic glucosides. Species and varieties differ in prussic acid poisoning potential. Sudangrass varieties are low to intermediate in cyanide potential, and sorghum-sudangrass hybrids and forage sorghums are intermediate to high. Piper sudangrass has low prussic acid poisoning potential, and pearl millet is virtually free of cyanogenic glucosides. The management practices described below can reduce the risk of prussic acid poisoning from forage sorghum, sudangrass, and sorghum-sudangrass hybrids:

1) Graze or greenchop only when the grass is greater than 18 inches tall.
2) Do not graze wilted plants or plants with young tillers.
3) Do not graze plants during or shortly after a drought when growth has been reduced.
4) Do not graze on nights when frost is likely. High levels of the toxic compounds are produced within hours after a frost occurs.
5) Do not graze after a killing frost until the plants are dry. Wait 5 to 7 days to allow the released cyanide to dissipate.
6) Do not graze for two weeks after a non-killing frost.
7) Delay feeding of silage for 6 to 8 weeks after ensiling. Fresh forage is generally higher in cyanide than silage or hay because cyanide is volatile and dissipates as the forage dries. However, hay or silage that likely contained high cyanide levels at harvest should be analyzed for HCN content before feeding.
8) Split applications of nitrogen decrease the risk of prussic acid toxicity, and proper levels of phosphorus and potassium in the soil will also help.
9) Don't allow hungry or stressed animals to graze young sorghum grass growth.

Nitrate poisoning can occur under conditions of high nitrogen fertilization, heavy manure applications, drought, overcast weather, prolonged low temperatures, or other stress conditions that retard plant growth. Under these stressful conditions, high nitrate levels accumulate in the crop. Once forage is fed, nitrate is converted to nitrite in the animal. When nitrite levels are high, the animal cannot metabolize it quickly enough, and nitrite inhibits oxygen transport in the blood. Symptoms include rapid breathing, fast and weak heartbeat, muscle tremors, staggering, and ultimately death if corrective steps are not taken.

The same management precautions for prussic acid poisoning will help prevent nitrate poisoning. Although pearl millet does not create a potential problem with prussic acid poisoning, it can accumulate high nitrate levels leading to nitrate poisoning. Also, corn for silage should be monitored for nitrate concentrations under conditions described above. High nitrate levels will persist when forages are cut for hay, but ensiling the crop will reduce nitrates by approximately 50%. If forage is suspected of high nitrate levels, have it tested before feeding.

Archive Issue Contributors: 

State Specialists: Pierce Paul, Anne Dorrance, Bruce Eisley (Plant Pathology), Ron Hammond and Andy Michel (Entomology), Peter Thomison (Extension Corn Specialist), Mark Loux (Extension Weed Specialist), Robert Mullen (Extension Soil Fertility Specialist), Greg Roth Grain (Crop Management Specialist, Penn State University). Extension Educators and Associates: Glen Arnold (Putnam), Roger Bender (Shelby), Mike Gastier (Huron), Wes Haun (Logan), Harold Watters (Champaign), Howard Siegrist (Licking), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Steve Prochaska (Crawford), Les Ober (Geauga), Tim Fine (Miami), Alan Sundermeier (Wood).

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.