C.O.R.N. Newsletter 2006-35

Dates Covered: 
October 17, 2006 - October 23, 2006
Curtis E. Young

How Late Is Too Late To Plant Wheat?

Authors: Dennis Mills, Jim Beuerlein, Pierce Paul

Recent estimates coming in from across the state show that soybean harvest, and consequently, wheat planting are lagging way behind estimates for the same period last year. To date, only about 15-20% (state average) of the soybeans has been harvested and about 10-15% of the wheat planted. At about this same time last year, Ohio’s growers had already harvested about 50% of their soybeans and planted about 45% of their wheat. Given the current weather forecast, we anticipate that a lot more beans will be coming off and more wheat planted towards the end of this week and early next week; nonetheless, many growers will still be faced with having to plant wheat later than usual.

There is no easy answer to the question of how late is too late to plant wheat. It all depends of the weather conditions during the Fall and early winter. Ideally, all the wheat should have been planted by the second week of October in order to ensure adequate tiller development before winter dormancy. Due to late bean harvest, growers will more than likely be planting wheat during the last week to October, and because of contractual agreements and current wheat prices, some growers may still be willing to plant wheat as late as the first week of November. Wheat planted this late is certainly at greater risk for poor stand establishment (fewer tillers per foot of row), increased winter kill, and spring heaving. However, 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.

To compensate for fewer tiller development in late-planted wheat, growers are recommended to 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). Plant at a rate of 1.6 to 2.0 million seed per acre instead. The number of seeds per pound is greater than usual this year, so the pounds of seed per acre will also be larger. 2.0 million seeds per acre is 30 seeds per foot of 7.5 inch row. If there are 13,000 seeds per pound, you will need 154 pounds of seed to get 2.0 million per acre or 123 pounds to get 1.6 million seeds per acre. The following table by Jim Beuerlein (http://corn.osu.edu/story.php?setissueID=102&storyID=605) shows the pounds of seed needed per acre to accomplish various seeding rates using different sizes of seed.

Seed per Millions of Seed per Acre
Pound 1.2 1.4 1.6 1.8 2.0
10,000 120 140 160 180 200
11,000 109 127 145 164 182
12,000 100 116 133 150 167
13,000 92 108 123 138 154
14,000 85 100 114 129 143
15,000 80 93 107 120 133
16,000 75 88 100 113 125
17,000 71 82 94 106 118
18,000 66 77 89 100 111


Soybean Rust found in KY and IL but not OH

Authors: Anne Dorrance

Last Wednesday (10/11), Kentucky reported their first find of soybean rust for the 2006 season. The leaves were pulled from the field on the previous Friday (10/6). Part of the time lag between when the rust was found and this announcement is that leaf samples had to be submitted to the USDA for confirmation of a first find. This find prompted searches throughout the Midwest region. Illinois is still screening leaves, but as of this morning only two counties are positive. The infections in these locations are very light with low incidence throughout the fields and few pustules. Apparently they had good rains during Sept 21-24, which dumped spores across a fairly wide section of Western Kentucky. The main take home message at this point is that there would have been plenty of time to spray in Ohio if this type of advanced rust detection had occurred during the production season.

In response to these finds, Ohio's illustrious soybean sentinel scouts hit the road and hit the fields. Soybean leaves were collected from 18 Ohio counties last week (Paulding, Pickaway, Hardin, Williams, Clark, Fulton, Hancock, Butler, Van Wert, Sandusky, Shelby, Auglaize, Clermont, Defiance, Clinton, Brown, Union, and Logan). All of the leaves were submitted to the C. Wayne Ellet Plant and Pest Diagnostic Clinic. Nancy Taylor examined each of the leaves and no rust was found in the samples. If this had occurred in July, we would continue to sample twice a week, however frost has taken care of our plants for 2006.

In both KY and IL, the disease has moved in too late to have any impact on soybeans for this season. The scouts in these states will continue to search to determine how widespread these spores reached. This is a "great" learning opportunity because it is happening out-of-season, for future years on how soybean rust will move and what to expect from these infections. To follow the developments in rust over the next month, you can see this on the USDA website: www.sbrusa.net.

Frost Damage Can Lead to Prussic Acid Poisoning

Authors: Mark Sulc

Jack Frost is taking his first bites of the year, bringing the potential for prussic acid poisoning when feeding forage from the sorghum family. Those forages contain cyanogenic glucosides, which are converted quickly to prussic acid in freeze-damaged plant tissue. Prussic acid, also known as hydrogen cyanide, can kill animals within minutes if it is present in high concentration.

Prussic acid binds hemoglobin in the bloodstream and interferes with oxygen transfer. The animal basically dies of asphyxiation. 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 from plant tissue.

Sudangrass varieties are low to intermediate in cyanide poisoning potential, sudangrass hybrids are intermediate, sorghum-sudangrass hybrids and forage sorghums are intermediate to high, and grain sorghum is high to very high. Johnsongrass, chokecherry, and black cherry also have potential for prussic acid poisoning. Piper sudangrass has low prussic acid poisoning potential, and pearl millet is virtually free of cyanogenic glucosides.

Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high cyanide potential. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay, because cyanide is a gas and dissipates as the forage cures and dries.

When grazing or greenchopping sorghum species this fall, follow these guidelines:

1) Do not graze on nights when frost is likely. High levels of the toxic compounds are produced within hours after a frost.

2) Do not graze after a killing frost until the plants are dry. Wait 5 to 7 days to allow the released cyanide to dissipate.

3) After a non-killing frost, do not allow animals to graze because the plants usually contain high concentrations of toxic compounds. Once the first frost has occurred, grazing should not begin until 5 to 7 days after a killing frost.

4) Don’t allow hungry or stressed animals to graze young sorghum grass growth.

5) Graze or greenchop only when sorghum grasses exceed 18 inches in height.

6) Do not graze wilted plants or plants with young tillers.

7) Green-chopping the frost-damaged plants will lower the risk compared with grazing directly, because animals have less ability to selectively graze damaged tissue; however, the forage can still be toxic, so feed with great caution.

When making hay or silage from sorghum species this fall, consider the following:

1) Prussic acid content decreases dramatically during the hay drying process and the forage should be safe once baled as dry hay. The forage can be mowed anytime after a frost. It is very rare for dry hay to contain toxic levels of prussic acid. If the hay was not properly cured, it should be tested for prussic acid content before feeding.

2) Forage that has undergone silage fermentation is generally safe to feed. To be extra cautious, wait 5 to 7 days before chopping after the forage was frosted. If the plants appear to be drying down quickly after a killing frost, it can safely be ensiled within a shorter time period from the frost.

3) Delay feeding silage for 8 weeks after ensiling. If the forage likely contained high HCN levels at time of chopping, hazardous levels of prussic acid might remain and the silage should be analyzed before feeding.

Other common forages such as alfalfa, clovers, and cool-season perennial grasses do NOT produce toxic compounds after a frost and can be fed safely. The only concern is a slightly higher potential for bloat when grazing legumes within a day or two after a killing frost.

Soybean Aphid 2007 Prediction

Authors: Ron Hammond, Bruce Eisley

Although somewhat anticlimactic based on comments over the past month, we are now making our prediction official. We expect the soybean aphid's two-year cycle to continue next year, and are predicting the soybean aphid to again rear its ugly head and become a significant problem in Ohio. We had mentioned two or three weeks ago that we had been finding large populations of aphids on buckthorn, but we wanted to wait until we saw fall collections from suction traps in late September. Well, data from those traps are coming in (see http://www.ncpmc.org/traps/index.cfm for a list of sites and the numbers), and as of the two weeks ending September 22 and 29, the numbers of winged aphids have skyrocketed. Thus, based on the movement and numbers of winged aphids that have been collected, along with their heavy presence on buckthorn, we are making the prediction of soybean aphid problems next summer. As always, we could be wrong, but we have called it correctly for the past 5 years! If we are wrong, at least it will be to the growers' benefit.

As we go through the winter, continue reading this CORN newsletter and listening to us at winter meetings on suggestions on how best to manage, and NOT to manage, this pest. We will be further discussing such things as skip row plantings, seed treatments, foliar insecticides, and geographically differences in terms of the aphid in further articles. For an early indication of this, read last week's newsletter about seed treatments for soybean aphid control which we do not recommend.

Save the residual herbicide for the spring?

Authors: Mark Loux

As we have indicated in past C.O.R.N. articles, fall herbicide treatments are an effective tool for management of winter annual weed populations, and are a first line of defense against dandelions, poison hemlock, and wild carrot. The primary value of fall herbicide treatments is control of weeds that have emerged by the time of application, which typically results in a weed-free field next spring, at least until sometime later in April. This can be accomplished with about $6 to $10 worth if herbicide. In the C.O.R.N. article of September 12, we listed effective fall herbicide treatments and discussed the problems with using higher cost treatments. Specifically, be cautious about adding residual herbicides to fall treatments, since many do not help control emerged winter annuals, and their activity may not last long enough to help out with summer annual weed control in next year’s crop. The primary exception to this for soybeans is Canopy, which control winter annuals in the fall, and can control lambsquarters and some other broadleaf weeds into next June (Sencor + 2,4-D also fits here, but has much shorter residual than Canopy). Even Canopy may be better used in spring than in fall, though, especially in fields where glyphosate failed to adequately control giant ragweed this past summer. With regard to corn, the choice of herbicides in the fall does not alter the need for a comprehensive herbicide program next spring.

Our research over the past several years clearly shows that for those weed populations that are either resistant to or not well controlled by glyphosate, residual herbicides are most effectively used in the spring. Some examples from our research over the past several years:

Situation #1. Post-emergence herbicides cannot be relied upon to control many marestail populations, due to the frequent presence of glyphosate and/or ALS resistance. We conducted a number of experiments comparing residual control of marestail with fall vs spring herbicide treatments. While there were some instances where residual herbicides applied in fall controlled much of the marestail through late May, this was much easier to achieve when residual herbicides (metribuzin, Valor, Canopy, etc) were applied in the spring. The most effective approach to marestail control was spring application of glyphosate plus 2,4-D ester plus a residual herbicide (or Gramoxone plus metribuzin plus 2,4-D ester), which controlled emerged marestail up to 6 inches tall regardless of herbicide resistance and gave the best chance for the residual herbicide to control the later-emerging marestail. Since much of the marestail in Ohio is ALS-resistant, it’s fairly important that the residual herbicide contains metribuzin, Valor, or Spartan. These three herbicides have shorter residual in soil, compared to Canopy, and really should be applied in spring when the goal is control of weeds into June.

Situation #2. Giant ragweed was not well controlled by multiple applications of glyphosate in a number of fields in Ohio this year. Our research shows that giant ragweed populations in continuous soybean fields with a history of reliance on glyphosate have become less sensitive to glyphosate. We consider this to be a low level of resistance, and our expectations are that the number of fields where this occurs will probably increase again into next year. We conducted research at four sites this summer to determine whether glyphosate-based programs could still control these populations. We were able to achieve effective control only where we used one of the following programs: 1) a preplant burndown treatment of glyphosate plus 2,4-D ester followed by two post-emergence glyphosate applications - the first at 1.5 lbs ae/A on 6 to 12 inch plants and the second at 0.75 lb ae/A approximately three weeks later; or 2) a preplant application of glyphosate plus 2,4-D ester plus a pre-emergence herbicide followed by two post-emergence glyphosate applications – the first at 0.75 or 1.5 lbs ae/A on 6 to 12 inch plants and the second at 0.75 lb ae/A approximately three weeks later. We used Gangster as the pre-emergence herbicide in these studies, but Canopy, Scepter, or FirstRate would have worked as well. While we did not absolutely need the pre-emergence herbicide to obtain adequate ragweed control, it reduced the weed populations and slowed the ragweed growth, so that we had more time to apply the first post-emergence treatment. One of the fields had received an application of Canopy EX the previous fall, which slowed the ragweed growth in the spring, but even in this field we were not able to adequately control the ragweed with glyphosate alone in this year’s soybeans. Growers experiencing poor giant ragweed control with glyphosate this year should use this approach outlined here in future years, and the pre-emergence herbicides should be applied in spring rather than fall.

We are not suggesting that fields with a history of marestail or giant ragweed problems be left untreated this fall. Many of these fields also have winter annual weed and dandelion infestations, which could merit a fall herbicide treatment. What we are suggesting is that these fields should be treated with residual herbicides in the spring to improve the chances of controlling marestail or giant ragweed in the soybeans. So, it may make more sense to use a non-residual herbicide treatment in the fall (such as glyphosate plus 2,4-D ester), and save the residual herbicide for the spring. We’re guessing that as our problems with glyphosate-resistant weed populations increase, this may have to become a standard practice in the fields where problems occur.

A new podcast has been created for the CORN Newsletter which has several issues already posted online, including two on fall herbicide treatments and use of residual herbicides in fall versus spring. To download the podcast, go to http://www.apple.com/itunes/download/ and download the free iTunes software to your computer. Once you have done that, start iTunes, click on the music store button, select podcasts from the "Inside the Music Store" list and use the search option (it has a little magnifying glass by it) and search for "OSU CORN Newsletter." When iTunes finds the link, click on the subscribe button. The weekly podcast will then be sent to your podcast folder in iTunes every week. You can then listen to the podcast at your computer or burn it to a CD to listen to in your car. This is our first work with podcasts on weed control issues, so they may seem a bit rough, but they should improve with time. Any feedback on this method of communication is welcome.

Transgenic Corn and Need for Refuges

Authors: Ron Hammond, Bruce Eisley

With the possibility that Ohio growers will be planting more Bt transgenic corn hybrids next spring, we thought it best to begin reminding growers about the requirement to plant refuges of at least 20% to non-Bt hybrids. This need is for IRM, Insect Resistant Management, purposes which is an attempt to prevent insects from developing resistant to the Bt gene. These are government regulations that must be followed. Growers who fail to follow IRM requirements risk losing access to Bt corn technology.

There are two different Bt hybrids that could be used, Bt for corn borer and Bt for corn rootworms. There are some similarities and some differences in the requirements for the two. If you are planting a stacked hybrid containing both types of Bt, we recommend following the IRM requirements for Bt corn rootworm

The first requirement is the same for both Bt hybrids. You need to plant a 20% refuge area to non-Bt corn. In Ohio, you have to plant at least 20 acres of non-Bt corn for every 80 acres of Bt corn. In terms of the distance of the refuge from the Bt corn, there is a major difference. For corn borer, the non-Bt refuge can be within 1/2 mile, but preferably it should be within 1/4 mile, of the Bt field. For corn rootworm, the non-Bt refuge has to be in the same field as the Bt corn, or adjacent to it. When adjacent, it can be separated at most by a ditch or a road, but not by another field. When planting the refuge, there are various plantings options, including a separate field refuge (mainly for corn borer), an adjacent field, a separate but adjacent block next to the refuge, a block refuge within the Bt field, the refuge planted along the perimeter, or a split-planter refuge. If planting the refuge using a split planter, the strip width should be at least 4 rows (6 preferred) for corn borer and at least 6 rows (12 preferred) for corn rootworm.

There are two other general areas related to requirements, management of the Bt field and non-Bt refuge, and use of other insecticides. Both areas should be managed in a similar manner. Growers should plant both hybrids close to or at same time, and select Bt and non-Bt hybrids that have similar growth and development characteristics. There are a few other guidelines for corn borer and corn rootworm hybrids related to tillage, rotations, etc, and growers see seed dealer for these.

In terms of insecticide use, there are guidelines for controlling the target insect (corn borer or corn rootworm) and secondary insects in both the Bt corn and in the refuge. The major ones are, for European corn borer, non-Bt corn refuge may be treated with conventional insecticides only if the target pest reaches economic threshold. However, a foliar Bt-based insecticide cannot be used within the refuge. For rootworms, a soil-, seed-, or foliar-applied insecticide for control of rootworm larvae and other soil pests is allowed in refuge. If an aerial insecticide is applied to the refuge for control of rootworm adults, the same treatment must be applied at same time to corn with the Bt trait. As with management guidelines, growers should seed their seed dealer for additional requirements related to insecticide use.

It is of extreme importance that growers follow these guidelines. Not only are we concerned about preventing resistance to the Bt technology, but also to make sure growers do not loose the ability to use this technology because of making wrong decisions.

Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Jim Beuerlein (Crop Production Specialist), Peter Thomison (Corn Production), Mark Loux (Weed Science), Mark Sulc (Forage Specialist), Robert Mullen (Soil Fertility), Ron Hammond and Bruce Eisley (Entomology). Extension Agents: Roger Bender (Shelby), Howard Siegrist (Licking), Harold Watters (Champaign), Curtis Young (Allen), Wesley Haun (Logan) and Greg LaBarge (Fulton).

About the C.O.R.N. Newsletter

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.