CORN
Crop Observation and Recommendation Network

For Week of June 1-7, 1998
C.O.R.N. 98-12

In This Issue:

A) Rainfall Needed for Preemergence Herbicides
B) Height Restrictions for Postemergence Corn Herbicides
C) Use Methylated Seed Oils (Mso) in Northern Ohio
D) At This Time, Question the Use of Preemergence Herbicide
E) Black Cutworm in Late Instar Stages
F) Leafhopper and New Alfalfa Stands
G) Warm, Dry Weather and Wheat Development
H) "Patching In" Poor Corn Stands
I) Is Supplemental N Needed for Corn?

A) Rainfall Needed for Preemergence Herbicides - Jeff Stachler CORN Questions

Fields in Northern Ohio which have not received rainfall after the application of preemergence herbicides, should be scouted for escaped weeds!! Many areas have not received enough rainfall to incorporate and activate the herbicides. Do not count on atrazine and Bladex to be taken up by the roots of weeds once significant rainfall occurs, especially if the grasses are over 2 inches tall. In Northern Ohio fields where preemergence herbicides were applied only 2 weeks ago, the use of a rotary hoe can incorporate some of the herbicide and take out very small weeds. For most fields it is too late to rotary hoe, so consider Bladex or atrazine, if grasses are less than 1.5 inches. Corn must have 5 or fewer leaves for Bladex, and less than 12 inches tall for atrazine. The total amount of atrazine must not exceed 2.5 pounds per acre. If grasses are taller than 1.5 inches, then Accent must be used. Research at OSU has shown that Accent may be applied at 0.33 ounces per acre for grasses less than 2 inches, but if over 2 inches then use 0.67 ounces per acre.

B) Height Restrictions for Postemergence Corn Herbicides - Jeff Stachler CORN Questions

With the hot weather throughout the state, corn is growing rapidly. Be sure to check corn height and stage before spraying!! Listed are the restrictions for some postemergence corn herbicides:

• Do not apply Basis beyond 2-collared corn.
• Do not apply Banvel, Clarity, or 2,4-D at 1.0 pint per acre, or Marksman over the top of corn greater than 8 inches tall (or no more than 5 leaves for Banvel and Clarity)
• Do not apply Clarity, atrazine or any atrazine containing premix such as Contour, Buctril/atrazine, and Basis Gold if corn is greater than 12 inches, or before 6 collars for Basis Gold.
• When corn is over 8 inches tall, 2,4-D must be applied with drop nozzles. Clarity or Banvel may be applied over the top of corn after 8 inches, but use 8.0 fluid ounces or less to reduce risk of injury. For maximum crop safety with Banvel or Clarity, use drop nozzles when the corn is greater than 8 inches. When tank mixing herbicides with Banvel or Clarity, it is recommended to use less than 8.0 fluid ounces of Banvel or Clarity, and use drop nozzles to reduce injury risk. The risk of corn injury will also increase if surfactants or crop oils are added to these tank mixes.

More information about appropriate additives and corn height restrictions may be found in The Ohio State University Weed Control Guide, Bulletin 789 (pages 54 and 55), or the herbicide label.

C) Use Methylated Seed Oils (Mso) in Northern Ohio - Jeff Stachler CORN Questions

When using Accent or any ALS inhibiting herbicide during dry conditions, the use of MSO instead of surfactant or crop oil concentrate will provide increased and more consistent control. Research has shown up to 20 percent increase in control of moisture stressed grasses when MSO is tank-mixed with Accent. The use of MSO in a tank-mix of Accent plus atrazine has also reduced the risk of antagonism between Accent and atrazine.

D) At This Time, Question the Use of Preemergence Herbicide - Jeff Stachler CORN Questions

Now that it is the beginning of June, it is recommended to switch from a preemergence herbicide program to a postemergence herbicide program, especially for soybeans. If preemergence herbicides are applied now there is a much greater risk of carryover into next year. This is especially true for products such as Scepter, Canopy, Canopy XL/Authority Broadleaf, and atrazine. Also the chances of rainfall begin to decrease, so that proper herbicide activation may not occur (that has already happened in Northern Ohio). There is a case for still using preemergence herbicides in corn due to postemergence weed control being more difficult, and the usefulness of atrazine, but as stated above significant rainfall is needed for herbicide activation.

E) Black Cutworm in Late Instar Stages - Hal Willson CORN Questions

Corn has been growing slowly during the past week due to hot and dry weather. At the same time, cutworms have been feeding predominantly below ground. Although severe infestations have not been reported, a number of cases of cutworm activity have been reported. Black cutworm larvae collected during the past week were predominantly in the late instar stages of development, which indicates that the larvae will be pupating and additional injury will be minimal. As a result, it should be emphasized that application of a rescue treatment at this point in time will not likely achieve a significant reduction in losses. Treatment of cutworms during their final stages of development may achieve a degree of revenge, but it should be recognized that the bulk of the damage has already occurred.

F) Leafhopper and New Alfalfa Stands - Hal Willson CORN Questions

During the past week, both Mark Sulc (forage agronomist) and I have noted that potato leafhoppers have exceeded the economic threshold level in our new alfalfa seedings. Collection of 8 to 10 adult leafhoppers per 10 sweeps on new stands of 8 inch high alfalfa indicates a potential for economic injury, especially given the stressful growing conditions associated with the current hot and dry weather. Successful establishment of a spring seeding may be adversely affected by leafhopper; thus, stands should be scouted, since timely application of rescue treatments may be warranted.

G) Warm, Dry Weather and Wheat Development - Pat Lipps CORN Questions

Wheat development is advancing ahead of schedule. Temperatures in the upper 80's and dry conditions in most areas of the state have not been favorable for an extended grain filling period. Wheat fields in the southern part of the state flowered over 3 weeks ago and are now beginning to show signs of maturing. The lower leaves of early maturing varieties are dying and the heads are losing the dark green color. This is normal. The potential for high wheat yields is still quite good, especially since the level of disease on the upper leaves and heads is still low throughout the state. Continued hot, dry weather will erode the yield potential of the crop. The good news is there have been no reports of significant levels of head scab in the state at this time! Cooler temperatures and a few showers to relieve drought stress would add more bushels to the crop.

H) "Patching In" Poor Corn Stands - Peter Thomison CORN Questions

When corn stands have been reduced in limited areas of a field, growers will sometimes attempt to plant over the poor stand ("patch in") rather than kill the existing plants and replant at a full population. However, "patching in" is generally of limited benefit unless the surviving plant population is less than half of the intended population. The success of such an approach is even less likely late in the planting season (i.e. after June 1). The later planted corn cannot compete effectively with the remnants of the original plant population for sunlight, water, and nutrients. In these late planting situations, late emerging plants often function more like weeds, and contribute little to grain yield. Moreover some of the areas within fields targeted for "patching-in" this year have been slow emerging due to limited moisture. In this event, it is possible that patching-in may result in final stands substantially higher than the rest of the field. Therefore check for delayed emergence in those areas where you are about to replant.

Corn growers are confronted with a similar problem in fields involving plant stands with uneven emergence. Questions often arise as to whether to replant stands with poor emergence or whether to protect late emerging plants during row cultivation. Research in Illinois and Wisconsin suggest these guidelines for the following questions:

Should you replant stands with uneven emergence?

• If the delay in emergence is less than 2 weeks, replanting will have a minimal effect on yields, regardless of the pattern of unevenness.
• If 50% or more of the plants in the stand emerge 3 weeks late or later, then replanting may increase yields up to 10%. To decide whether to replant in this situation, estimate both the expected economic return of the increased yield compared to your replanting costs and the risk of emergence problems with the replanted stand.

Should late emerging plants be protected during row cultivation?

• If the delayed plants emerge 1½ to 2 weeks late, use shields and avoid burying seedlings during cultivation.
• Protect plants emerging 3 weeks late, if 50% or more of the plants in the stand are late emergers.
• If less than 25% of the stand emerges 3 weeks late or later, it probably will not pay to encourage their survival. Yields will be about the same whether or not these delayed plants are buried during cultivation.

More detailed information on making such replant decisions is provided in National Corn Handbook Chapter 36, "Effects of Uneven Seedling Emergence in Corn".

I) Is Supplemental N Needed for Corn? - Jay Johnson and Peter Thomison CORN Questions

Given our prolonged wet weather and saturated soil conditions earlier this spring, many growers may be concerned about their nitrogen (N) management program. Do I need more N than I put down early in the spring?

A simple "scorecard" has been devised by Mike Schmitt, Extension soil scientist at the University of Minnesota, to help decide if supplemental, or extra, N is needed. We have modified this decision aid for the N forms and placement practices used under Ohio conditions. Keep in mind that good judgment is still important when using this simple decision aid. Also, each field needs to be evaluated individually. This scorecard is intended to serve as guide and not a definitive determination of N needs.

FACTOR 1: What N product was used?

FACTOR 2: When was the fertilizer N applied?

FACTOR 3: What has been the predominate soil moisture status in the field this spring?

FACTOR 4: What is the crop's current condition?

Total the score for the four factors and use the following guidelines:

The "re-evaluation" option is only viable until you no longer have sidedressing options. Illinois research has found that 50 lbs N/acre as a supplemental N rate was satisfactory for a wide range of conditions. While a total score of 17-18 would merit a 40 lb/acre N recommendation. A total score of more than 18 may require a higher N rate.

Readers can subscribe electronically to this newsletter bysending an e-mail message to: listserv@agvax2.ag.ohio-state.edu with the message: subscribe corn-out. A successful subscription message will receive a reply from 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.

Contributors to C.O.R.N. this week include: State Specialists: Pat Lipps (Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Jay Johnson (Soil Fertility), Mark Sulc (Forages); District Specialist: Ed Lentz (Agronomy); Extension Agents: Dennis Baker (Darke), John Barker (Knox), Roger Bender (Shelby), Clark Hutson (Seneca), Dave Jones (Allen), Greg La Barge (Fulton), Larry Lotz (Fayette), Max Mohler (Lima Branch), Steve Prochaska (Crawford), Howard Siegrist (Licking), Barry Ward (Marion).

Editor: Ed Lentz  Web Editor: Nathan Watermeier

Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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.

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