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For Week of April 6-12, 1998
C.O.R.N. 98-4
In This Issue:
A) Wheat in Advanced Growth Stage
B) Update on Disease in Wheat
C) Weed Control in Wheat, More on Wheat Herbicides
D) Tips for Improving Stand Uniformity in Corn - Planter
Maintenance
E) Starter Fertilizer with Seed
F) Mesurol not Legal as a Hopper Box Treatment
Our greatest threat to the wheat crop over the next few weeks is freezing injury. I have no reports of any serious freezing injury at this time. However, leaf tip burn from low temperatures is evident in many fields. I have reports from Kentucky indicating they have already lost about 15% of their early planted, early season wheat crop to freezing injury and about 30% of the wheat acreage has had some level of damage. This could happen in Ohio if temperatures get too low during the time when the growing point and immature wheat heads are above the soil level (anytime after growth stage 6). The data that I have available indicates that death of the developing growing point can result if the temperature stays at 24 F for 2 or more hours when plants are in growth stage 6 (first node visible). There are many factors that may affect the freezing susceptibility of wheat at this growth stage, but we can use this temperature as a rule-of-thumb. In any case, the more advanced tillers will be most susceptible to freezing damage at this time. Once freezing injury occurs it may not be possible to determine the extent of the damage for a week or more after the damage has occurred. Freezing damage is assessed by splitting open the stems above the uppermost node to expose the growing point and developing head. Light tan to brown discoloration indicates damage. Freezing temperatures can occur anywhere in Ohio until the end of April.
The rapid growth of wheat and the relatively cold night time temperatures have held the development of diseases in check over the past two weeks. Powdery mildew and Stagonospora leaf blotch have not advanced during this time. Most reports from around the state indicate that the crop is relatively free of disease at this time. We expect powdery mildew will begin to spread as soon as the temperatures get into the 60-70 F range, especially when the night time temperatures are also warm. We do not recommend any fields be sprayed with a fungicide at this early stage of development. This is entirely too early to spray to achieve maximum economic returns. Fields previously scouted for powdery mildew should be checked again prior to flag leaf emergence for possible application of a fungicide.
1. Correction to wheat herbicide information in the last C.O.R.N.: Buctril and other bromoxynil products labeled for wheat should be applied before boot stage (we had indicated application before jointing in our previous comments).
2. With regard to double-crop soybeans: soybean cannot be planted following wheat that is treated with Stinger, Curtail, or Peak. Other products labeled for wheat should not injure soybeans planted after wheat harvest. Labels of Harmony Extra and Express allow soybean planting 60 days after application.
3. As we indicated previously, control of thistle will vary with the emergence pattern and size of the thistle. Most wheat herbicides have some activity on thistle, but if thistles are extremely small and still emerging at the time of application, thistles may regrow and interfere with harvest. Larger thistle plants are likely to be suppressed by herbicide, and remain stunted through the summer.
4. Following the last issue of C.O.R.N., Novartis sent us a note indicating that Peak is as effective as Harmony Extra on wild garlic. We have to take their word on this, as we have no data on wild garlic control with Peak.
Uneven stands of corn are becoming more common as the move toward planting corn with reduced tillage gains momentum. Fields that exhibit stand uniformity problems are often characterized by tall and short corn, large within-row gaps, and groups of crowded plants. This lack of stand uniformity is a problem involving uneven seedling emergence and within-row spacing of plants. Variable seedbed soil moisture associated with uneven crop residue distribution and weather conditions is a major factor causing uneven corn emergence, whereas high planting speeds (in excess of 6 mph) and poor planter maintenance/adjustment are primarily responsible for uneven within-row plant spacing.
Uneven plant stands characterized by large within-row gaps of 4 to 6 feet can reduce grain yields up to 5%. About 1/4 pound of potential yield can be lost for every ear in a tight grouping of two or more plants. Uneven emergence can also have a major impact on potential yield even if within-row spacing is relatively uniform. If 1/2 or more of a stand is delayed two weeks in emerging, yield losses of 5 to 8% can be expected. If 1/2 or more of a stand is delayed in emerging three weeks or later, yield losses of 20% or more can occur.
Corn sometimes emerges unevenly because of environmental conditions beyond the control of growers. However, timely planter servicing and adjustment, as well as appropriate management practices, can help prevent many stand uniformity problems. The following are some tips for improving the uniformity of seed placement during planting.
1. Avoid excessive tillage trips and tilling wet soils.
2. Check seed depth and seed soil contact periodically during planting.
3. Distribute residues over row areas evenly.
4. Plant at speeds between 4 1/2 to 5 1/2 mph.
5. With plate-type planters, match the seed grade with the correct planter plate.
6. Planters with finger pick-ups should be checked for wear on the back plate and brush,
use a feeler gauge to check tension on the fingers, then tighten them correctly.
7. Check for wear on double-disc openers and seed tubes.
8. Make sure the sprocket settings on the planter transmission are correct.
9. Check for worn chains, stiff chain links, and improper tire pressure.
10. Lubricate all chains and grease fittings.
11. Make sure seed drop tubes are clean and clear of any obstructions.
12. Clean seed tube sensors if you have a planter monitor.
13. Make sure coulters and disc openers are aligned properly.
14. With air planters, match the air pressure to the weight of the seed being planted.
15. Make sure press wheels are adjusted to close the seed slot.
Two publications, "Stand Establishment Uniformity in Corn," (AGRY-91-01 by Dr. Bob Nielsen, Extension Corn Specialist at Purdue University), and "Effects of Uneven Seeding Emergence in Corn" (National Corn Handbook, Chapter 36) provide more details on the effects of uneven plant spacing in corn and ways to prevent these problems from occurring.
The general practice of applying fertilizer in contact with seed is not recommended. Band placement to the side and below the seed is usually superior to any other placement. Some farmers, however, have grain drills or planters that place fertilizer in contact with the seed. In this case, caution should be used to prevent seed or seedling injury from fertilizer salts. For corn, do not place more than 5 lb ( N+K2O) per acre in contact with the seed on low CEC soils (CEC less than 7) and no more than 8 lb (N+K2O) per acre when the CEC is greater that 8. Soybean seed is very sensitive to salt injury; consequently, all fertilizer for drilled soybeans should be broadcast before planting. For small grain seedings, do not drill more than 100 lb of plant nutrients (N+P2O5+K2O) per acre in contact with the seed. Do not apply more than 40 lb N per acre as urea in contact with small grain seed. Young germinating seeds and seedlings are very sensitive to salt injury. Dry weather will accentuate the injury. When seeding forage legumes, do not place mote than 100 lb P2O5 and 50 lb K2O per acre in contact with the seed. If the fertilizer is placed 1 to 1 1/2 inches below the seed, the seeding time fertilizer may include all of the P and up to 150 lb K2O per acre. Broadcast and incorporate any additional fertilizer requirements before seeding. For established legumes, all fertilizer requirements should be top dressed in the fall before plants go dormant (approximately October 1) or after the first cutting in the spring.
USEPA has notified ODA that they intend to reject a Special Local Need (SLN) 24c registration application for Mesurol 50 HBT submitted by Gowan. The intended use applied for had been to use Mesurol as a hopper box treatment on seed corn to control crows, starlings, etc. Labels circulating with this hopper box use listed are not legal. The Ohio Department of Agriculture reminds everyone that this use Mesurol HBT is not a registered label and is thus illegal.
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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: Pat Lipps (Extension Specialist, Plant Pathology), Peter Thomison (Extension Specialist, Corn Production), Mark Loux (Extension Specialist, Weed Science), Jeff Stachler (Extension Associate, Weed Science), Larry Lotz (Fayette Co.), Barry Ward (Marion Co.), Ray Wells (Ross Co.), Roger Bender (Shelby Co.), Gary Wilson (Hancock Co.), Steve Bartels (Butler Co.), Howard Siegrist (Licking Co.), John Barker (Knox Co.), Max Mohler (Extension Associate), Clark Hutson (Seneca Co.), Joanne Kick-Raack, (Extension Associate, PAT), and Steve Prochaska (Crawford Co.).
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.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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