CORN
Crop Observation and Recommendation Network

May 28 - June 3, 2002
C.O.R.N. 2002-15

In This Issue:

A) More on Selecting Corn Hybrids for Delayed Planting
B) Prognosis Poor for Corn "Leafing Out" Underground
C) Corn Replant Considerations
D) Herbicide Programs for Non-Roundup Ready Soybeans
E) Some Considerations for Herbicide Programs in Late-Planted Corn
F) Wheat Development and Predictions for Fusarium Head Scab
G) Some Wheat Disease Evident at This Time
H) Slugs
I) Purdue Forage Day

A) More on Selecting Corn Hybrids for Delayed Planting - Peter Thomison CORN Questions

Bob Nielsen, Purdue University, and I have just published an Extension publication entitled "Delayed Planting & Hybrid Maturity Decisions") that details much of the information we have been putting out over the last couple of weeks on the issue of selecting hybrids for late planting. The publication is available primarily over the Web, as an Adobe Acrobat PDF file, and can be downloaded at: http://www.agry.purdue.edu/ext/pubs/AY-312-W.pdf

The publication is also currently linked from the Bob Nielsen's, Purdue University, Chat 'n Chew Cafe web site: http://www.kingcorn.org/cafe

B) Prognosis Poor for Corn "Leafing Out" Underground - Peter Thomison CORN Questions

Early growing season weather and seedbed conditions may create emergence problems resulting in corn seedlings leafing out underground. Seedings, which exhibit this abnormal emergence, may have a twisted appearance because internal leaves start expanding before the seeding has elongated. Several factors (or combination of factors) may be responsible for this abnormal growth. These factors may be characterized as environmental, chemical, or mechanical. Environmental conditions associated with underground leafing include light penetration, cold soils, or heavy rains soon after planting. When plants unfurl below the soil surface, they usually turn yellow and die.

In a cloddy field where soil coverage of seed is poor and irregular, sunlight can reach the germinating seedling and induce leaf emergence beneath the soil surface. Also, heavy rains after planting can cause a hard crust, which makes emergence of small seedlings very difficult. As a result, bending and twisting of the seedling below the crusted layer often occurs. Planting the seed too deep, which may cause poor germination and emergence, may also result in premature unfurling of the corn.

Certain herbicides such as Lasso and Dual, and the various premixes that contain their active ingredients can show similar symptoms (i.e. twisting, abnormal growth) when excessive rates are applied pre-emergence. Besides excessive rates, improperly closed seed furrows can allow the pre-emergence herbicide to come in direct contact with the seed. Excessive soil insecticide dosage or in-furrow placement of insecticide phytotoxic to seed can also cause twisting sprouts and abnormal leaf expansion underground. In addition, anhydrous and aqua ammonia N fertilizer injury has been associated with these symptoms. Certain corn hybrids are also more prone to this problem during emergence when unfavorable environmental conditions occur.

Corn seedlings that exhibit abnormal unfurling symptoms during emergence will be unable to penetrate any but the loosest soil even if the crust is broken mechanically or softened by rain. Prompt treatment with a rotary hoe, weeder, spiketooth harrow or cultipacker may help break the crust and improve emergence. However, even when used carefully, these salvage operations can cause some damage to seedings, which are emerging normally. To minimize poor seedling emergence due to unfurling below the soil surface, watch for cloddy seedbeds, open seed furrows, and crusting surface soils after rains. Also check planting depth periodically and adjust accordingly during the planting operation and monitor herbicide and soil insecticide rates.

C) Corn Replant Considerations - Peter Thomison CORN Questions

Recent frost injury to corn, along with ponding and flooding damage, have resulted in questions about replanting. Don't make a final assessment on the extent of damage and stand loss too quickly. For more information on assessing injury to corn from low temperatures and flooding and ponding, consult last week's C.O.R.N.articles. Replant decisions should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. The following are some guidelines to consider when making a replant decision.

If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:

Original target plant population/Intended plant stand
Plant stand after damage
Uniformity of plant stand after damage
Original planting date
Possible replanting date
Likely replanting pest control and seed costs

To estimate after damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. (Table 1 shows row length needed for various row widths.) Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient.

Table 1. Row length required to equal 1/1000 acre when corn is planted at various row widths.

A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Tables 2 and 3 show effects of planting date and plant population on final grain yield for the central Corn Belt. Table 2 is a newer chart developed by Dr. Emerson Nafziger at the University of Illinois that includes earlier planting dates and higher optimum plant populations. Table 3 is based on older data from the 1970's, but it still provides a reasonable assessment of potential yield losses, especially for planting dates in June. Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.

Table 2. University of Illinois replant chart developed under high yielding conditions (adapted from Nafziger, 1995-96)

Table 3. Central Corn Belt grain yields for corn planted at various dates and population rates, expressed as a percent of optimum planting date and population yield (uniformly spaced within row).

*Adapted from NCH-30 "Guidelines for Making Corn Replant Decisions"

Here's how these tables might be used to arrive at a replant decision (Table 2 will be used in this example). Let's assume that a farmer planted on May 9 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 2, the expected yield for the existing stand would be 79% of the optimum. If the corn crop was planted the next day on May 29, and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting is 81 minus 79, or 2 percentage points. At a yield level of 150 bushels per acre, this increase would amount to three bushels per acre which would probably not justify replanting costs.

It's also important to note plant distribution within the row. Remember that the values in Tables 2 and 3 are based on a uniform distribution of plants within the row! Add a 5% yield loss penalty if the field assessment reveals several gaps of 4 6 feet within rows and a 2% penalty for gaps of 1 3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction.

When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio. For more details on this issue consult previous May 2002 C.O.R.N. articles, as well as a new Purdue/Ohio State publication entitled "Delayed Planting & Hybrid Maturity Decisions"; it's also available online at: http//www.agry.purdue.edu/ext/pubs/AY-312-W.pdf

You also need to review herbicide and insecticide programs under late planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control.

Concerning insect control, if insecticides were applied in the row at initial planting, consider re application if tillage is used before replanting. Also remember that later planting dates generally increase the possibility of damage from insects such as European corn borer, corn rootworm beetle, and black cutworm. Therefore, understand that replanting itself does not guarantee the expected harvest population. Corn replant decisions early in the growing season will be based mainly on plant stand and plant distribution. Later in the season as yields begin to decline rapidly because of delayed planting, calendar date assumes increased importance.

The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is.

Sources: Guidelines for making corn replant decisions. 1990. National Corn Handbook. NCH 30; Illinois Agronomy Handbook. 1995-96. University of Illinois.

D) Herbicide Programs for Non-Roundup Ready Soybeans - Mark Loux CORN Questions

Continued wet weather will cause producers to switch from corn to soybeans in some fields, and there may not be enough Roundup Ready soybeans to meet this added demand. Some things to consider for those fields that have recently been planted or will be planted with non-Roundup Ready soybeans within the next several weeks:

- There may be little need for preplant or preemergence herbicides in many soybean fields, since the majority of this year's weed population has probably already emerged (especially in no-till fields). The reduced weed populations after planting and relatively rapid soybean growth should increase the effectiveness of single-application postemergence herbicide programs. Rainfall usually becomes more infrequent as the season progresses, increasing the possibility that preemergence herbicides will not receive enough rain in time to become active and control the first flush of weeds that emerges after planting.

- To facilitate the implementation of postemergence herbicide treatments, make sure the field is free of weeds at the time of planting. Apply glyphosate or Gramoxone as necessary before soybeans emerge to ensure a weed-free field. While we suggest the use of preemergence herbicides in some situations (see below), be aware that mixing preemergence herbicides with glyphosate can reduce the activity of glyphosate on certain weeds. Large weeds and thistle patches in many fields may require maximum glyphosate activity. Therefore, applicators will have to weigh the advantages versus the possible disadvantages of mixing preemergence herbicides with glyphosate.

- Giant ragweed, common lambsquarters, and waterhemp are weeds that may justify some type of preemergence herbicide treatment, even with the late planting. Although populations of these weeds will be reduced this late in the season, they are still among the most difficult to deal with in postemergence programs. Giant ragweed and waterhemp are weeds that can emerge through mid-summer, so consider a reduced rate of a preemergence product to reduce the population and allow for slightly later postemergence application. Preemergence herbicides with significant activity on giant ragweed include Canopy XL, Scepter, Backdraft, FirstRate, and Gauntlet.

- Control of lambsquarters with postemergence programs requires the use of Raptor or Harmony GT. Controlling lambsquarters with about $6 per acre of preemergence herbicide allows for more flexibility in postemergence herbicide and adjuvant choice, which can result in better control of most other weeds and less crop injury. Some possible preemergence options for lambsquarters control: 4 to 6 oz of Sencor, 1.5 oz of Valor, 2.5 oz of Canopy XL, or 1.4 oz of Scepter (or the rate of Backdraft that provides this amount of Scepter). Pursuit and Extreme should also provide sufficient residual control of lambsquarters through mid-summer.

- In OSU research, late-planted soybeans seem to be most likely to suffer yield loss from excessive herbicide injury, since there is less time to recover from injury compared to early-planted soybeans. Therefore, avoid the use of injurious herbicide mixtures. Applying postemergence herbicides when weeds are less than 4 inches tall improves herbicide effectiveness and reduces the need for "cocktails" that might cause excessive injury.

- Mixing postemergence broadleaf and grass herbicides can result in reduced grass control due to antagonism between herbicides. This is more likely to occur on yellow foxtail, barnyardgrass, and crabgrass, since these are generally more difficult to control than giant foxtail. With regard to grass herbicide choice, antagonism has been most evident for Assure II, and least evident with Select, with Fusion and Poast/Poast Plus somewhere in between. Antagonism will be more likely when nonionic surfactant is the spray adjuvant, so use crop oil concentrate if possible.

- Some producers have switched to Roundup Ready soybeans because of problems with ALS-resistant weed populations. When switching from corn to soybeans, any remaining Roundup Ready soybean seed should be planted in fields with known ALS resistance problems. Where this is not possible, herbicide programs should be built around PPO-inhibiting herbicides such as Flexstar, Cobra, or Ultra Blazer. OSU research has shown Flexstar to be the most consistently effective of these for common and giant ragweed control. The use of Basagran with these products can improve ragweed control.

E) Some Considerations for Herbicide Programs in Late-Planted Corn - Mark Loux CORN Questions

Corn planted in late May or June is likely to be less profitable than early-planted corn, due to the reduced yield potential. However, later-planted corn should also be subject to lower weed populations, since many summer annual weeds have already emerged. While total postemergence programs make sense in late-planted soybeans, the low cost and effectiveness of atrazine keeps many producers using preemergence programs even in late-planted corn.

Total postemergence herbicide programs can be somewhat difficult to successfully implement in corn for a number of reasons. Weeds can interfere with corn sooner after planting compared to soybeans, so there is an increased risk of yield loss when postemergence herbicides are applied too late. Available research indicates that weeds should be controlled in corn before they exceed 4 to 6 inches in height to avoid yield loss. Although the weeds that emerge after a properly timed postemergence application have much less affect on crop yield, they can reduce yield if present at high enough populations. Late-emerging weeds can also reach sufficient size to interfere with harvest and produce seed that causes problems in future years. So, not only is proper timing of application essential to minimize the effect of early-emerging weeds, but it can be important for the herbicides to provide at least several weeks of control after application. Another factor is the relatively narrow window for application of most grass herbicides in corn. While soybean herbicides such as Fusion and Select are effective on weeds that exceed 6 inches in height, corn herbicides such as Accent, Basis Gold, Option, and Lightning should generally be applied when grasses are not more than 2 to 4 inches tall.

Given all of these factors, there should still be some room to reduce herbicide inputs in late-planted corn. At the very least, there should be no need for a full-rate, broad-spectrum preemergence program followed by a postemergence treatment. Some ideas and considerations for corn herbicide programs at this time of the year follow (some of the information in the accompanying soybean herbicide article applies to corn also and is not necessarily repeated here):

- Taking a more flexible approach to herbicide use can allow for a reduction in herbicide inputs. For example, if you reduce preemergence herbicide inputs, you may have to occasionally make a follow up postemergence application if late-emerging weeds become a problem. If you are unwilling to scout fields and make a second application if necessary, than you should probably use labeled rates of a broad-spectrum herbicide program.

- Our experience with atrazine premix products (Bicep, Fultime, etc) indicates that they are not likely to provide acceptable control when applied at reduced rates (50% of labeled) unless followed with a postemergence treatment. The atrazine rate becomes too low to control problem broadleaf weeds, even in late-planted corn. A better approach for about the same cost might be a mixture of atrazine plus Balance, since an effective atrazine rate can be maintained. Some producers have been able to use this combination without a postemergence follow-up treatment in fields with relatively low weed populations. Another approach might be a combination of atrazine plus simazine, although simazine is less effective than Balance on grass and broadleaf weeds. Keep in mind also that late application of persistent herbicides can increase the risk of carryover into the following year.

- Where a reduced-input preemergence program is used, be sure to scout fields soon after corn emergence for weed escapes. A goal of this scouting is to observe the weed escapes when they are small, so that the lowest possible rates of postemergence herbicides can be used.

- When using a total postemergence approach, there can be a benefit to using herbicides that provide several weeks of residual control even in late-planted corn. For example, products that contain rimsulfuron (Basis Gold, Accent Gold, Steadfast) have at least some residual activity on grasses, while products that contain just nicosulfuron (Accent, Celebrity Plus) or foramsulfuron (Option) have almost none. The addition of no more than 1 lb/A of atrazine can greatly enhance the residual control of postemergence treatments.

- When applied to small broadleaf weeds in late-planted corn, the lowest labeled rates of postemergence broadleaf herbicides can be adequate. Some examples: 4 oz of Distinct instead of 6 oz; 3 oz of Hornet instead of 4 or 5 oz; 8 oz of Clarity instead of 16 oz; 2 pints of Marksman instead of 3.5 pints.

- Be aware of the maximum corn size per postemergence herbicide labels, and the growth stage at which corn becomes more sensitive to various types of herbicides. For example, corn becomes more sensitive to growth regulators (dicamba, 2,4-D) when it exceeds 8 to 10 inches or the 5th leaf stage. For most ALS inhibitors (Accent, Basis, Lightning, Hornet, etc), application should be made before the 6-collar stage or before corn exceeds 20 inches in height.

F) Wheat Development and Predictions for Fusarium Head Scab - Pat Lipps and Dennis Mills CORN Questions

Wheat development slowed greatly during last week's colder weather, however, the warmer temperatures over the next week will help advance wheat through the heading growth stages. Most of the wheat south of Pickaway Co. was in flower during last week and many fields in central Ohio were in flower over the weekend. In northwest Ohio fields are just beginning to head and will likely be in various stages of head emergence to flowering over the coming weekend. Here at Wooster, most wheat is in flower except for very late planted fields or fields planted to late maturing varieties.

Wheat that is in flower is vulnerable to Fusarium head scab. Wet conditions during this time period increases the risk of head scab. If you have been reading our reports in this newsletter you probably know we are attempting to make risk predictions for head scab. You can get updated risk predictions from the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease by clicking on Forecasting Fusarium Head Scab of Wheat in Ohio. We are using weather data from a number of locations in the state and to date we have been able to make risk predictions for early and mid flowering dates for most of the locations in the southern section of the state. Fortunately, to date most locations have not had conditions highly conducive for scab development prior to flowering (See table below). Scab risk predictions will be made other locations in the state as the crop advances through flowering and early grain filling periods.

The time period from infection at flowering to when symptoms can be seen on the head is about two weeks; longer if the temperatures are cool. Those fields in the far south, from the Ohio River up through Ross Co., may be scouted this week for beginning symptom development. Symptoms will develop over the next week or more in these areas. Our Scab risk predictions indicate only low to moderate risk for scab in these areas, so hopefully little disease will be detected.

G) Some Wheat Disease Evident at This Time - Pat Lipps CORN Questions

Barley yellow dwarf is very evident in many fields throughout the state at this time. The heading and flowering growth stages are a very good time to see Barley yellow dwarf. It causes the upper half of flag leaves, and other leaves to turn bright yellow or red, depending on the variety. In most cases the affected plants are scattered around fields or near the edges of fields wherever the aphid vectors entered the fields last fall. Please be aware that this is not frost injury. Although the disease may look severe, yield losses will be low unless a high percentage of plants are affected in the field. For a photo of the disease see http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/byd.htm.

Powdery mildew appears to be restricted to a few fields, but has gotten to economic level in only a few fields of the more susceptible varieties. If you have not seen powdery mildew in your wheat by this time you probably do not have to worry about it.

Stagonospora leaf and glume blotch are still a threat to fields especially those in areas that have received consistent rain showers over the past few weeks. Stagonospora is a warm weather fungus and plants become more vulnerable to attack after flowering, so little disease development has occurred so far. Due to the advancing of wheat growth stages in the state, there may not be an opportunity to apply a fungicide for Stagonospora control because of fungicide label restrictions for applications to before full head emergence. Seed producers are encouraged to continue to scout fields through grain fill for symptoms because the disease can affect seed quality. For more information see: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/stagonospora.htm

H) Slugs - Ron Hammond and Bruce Eisley CORN Questions

We are getting reports of slug injury from various parts of the state, with the most severe problems in more central Ohio with lesser amounts in the north. Growers should expect the slug problem to intensify over the next few weeks, and thus, should begin monitoring their situation and taking action if the injury is severe. The use of Deadline MPs, Trails End LG, or another molluscicide bait should be used at the recommended rate of 10 lb per acre. Growers who will be planting soybeans over the next one to two weeks should carefully monitor their situation because the next few weeks is the worst time for slug problems, especially on emerging soybeans. Slugs can be even greater problems if the seeds are planted in less than ideal conditions, resulting in seed furrows that do not close well. Slugs will crawl up and down the seed furrows eating to their heart's content. For those growers who experience a stand reduction because of slugs resulting in the need for replanting, remember that the slugs will not only still be there, but they will be bigger and consuming greater amounts. Thus, a replanting that is necessary because of slug feeding might need a molluscicide bait application even more so!

I) Purdue Forage Day - Mark Sulc CORN Questions

The Forage Day combines educational workshops with live equipment demonstrations. Dr. Keith Johnson, Forage Day Coordinator, says that "Seeing the different pieces of equipment perform side by side is especially helpful. I've always felt that if someone has a need to purchase equipment, the demonstrations would help him or her make a more informed decision."

Forage Day Presentations cover various topics in the production, utilization and marketing of forages. There will also be a Hay Quality Contest. For all the details check the following website: http://www.agry.purdue.edu/ext/forages/forageday/

No pre-registration is required, and there is no registration fee for the general public. Lunch will be provided at a nominal cost.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

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.

Editor: Clark Hutson        Web Editor: Tom Rosati

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

  | C.O.R.N. | Newsletter | Archive | Search | Questions? | Ohioline | Publications |