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For Week of August 10-16, 1998
C.O.R.N. 98-22
In This Issue:
A) 1998 Ohio Wheat Performance Tests Are Now Available
B) Smut in Corn
C) Time to Change Those Traps
D) Effects of Stress During Grain Fill in Corn
The Ohio Wheat Performance Tests is now available at your county OSU Extension office. It is also available on line at: http://www.ag.ohio-state.edu/~perf The publication reports the yield and performance characteristics of 64 varieties from 21 seed companies grown at five different locations in the state. Sites of the performance tests were: Northwest Branch (Hoytville), Bucyrus, Wooster, Greenville, and Circleville. Wheat yields were very good across all locations. The average yield for all varieties across locations was 80.2 bu/A. This is the highest average yield reported for this test since the studies began in the early 1980's. The location with the highest average yield was Wooster with 86.2 bu/A and the lowest was Northwest branch with 67.8 bu/A. There is a smorgasbord of other information available in the report including: heading dates, lodging, test weight, flour yield, flour softness rating, plant height, heading date, powdery mildew evaluation and Stagonospora (Septoria) nodorum leaf blotch evaluation, and two and three year yield averages. The varieties are listed in order of maturity, with the earliest varieties listed first.
Growers should use the report to help select varieties for growing this coming year by comparing varieties for different characteristics, not just yield. The top ten yielding varieties, across all locations, listed in order of heading date are: AGRA GR962, Hybritech Q7203, Pioneer brand 25R57, Dyna-Gro DG422, Hybritech Q708, LG Seeds LG1388, Pioneer brand 2540, Pioneer brand 25R26, and Hopewell. The top yielding varieties include both public and private varieties. Wheat producers should also look at lodging scores as well as other performance information before selecting varieties. In particular look at ratings for disease resistance to powdery mildew and Stagonospora leaf blotch, two of the most important diseases affecting wheat in Ohio. Winter hardiness is extremely important for a variety in Ohio, but due to the mild winter that occurred this year all varieties in the test survived well. You may wish to look at the test report for 1997 to find winter survival ratings for some varieties of interest.
There is a lot of information presented in this three page report. Spending half an hour looking over the data and comparing variety performance characteristics will help you choose the best varieties available to help insure those top yields. If you do not have time to look at the test, then remember you have the potential to lose more than the cost of the seed when you grow the wrong variety.
This year we are seeing more common smut, or boil smut, in the corn than usual. The smut fungus produces enlarged galls on various plant parts. Leaves, stalks, ears and/or tassels can be infected. The galls are covered with a greenish-white to silvery-white tissue. As the galls age the inside turns to a mass of powdery, dark olive-brown to black spores. Some galls associated with ears can be quite large, sometimes larger than a softball. We are seeing more common smut because of the stormy weather we had earlier in the year. The smut fungus spores survive in the soil. The spores are splashed by rain or blown by violent winds to the plant surfaces. When severe winds and/or hail cause injury to the corn plant, the open wounds are sites for infection by the rain splashed spores. Infections occur and the fungus develops its characteristic large galls on the plants. Yield loss occurrs when the smut galls affect the ear or when the galls develop on the stalk below the ear. Actual yield loss is proportional the number of plants affected in the field. This smut fungus does not produce any toxins that affect livestock, so there is no problem in feeding affected plants or ears. In fact, in some countries common smut is grown to be eaten and is a highly prized delicacy. Most corn hybrids have a fairly high level of resistance to common smut, except when the leaves or stalks are damaged. There are no recommended control measures since it is only an occasional economical problem when associated with storm or hail injury. .
This week marks the second trap change for those cooperators of the First Year Western Corn Rootworm Survey. Replace the Pherocon or Multigard traps in the field with a fresh trap sometime this week. Don't forget to count the Western corn rootworm beetles on the old traps as soon as possible.
Insect activity in field crops is fairly low this time of year. The following observations have been taken from central, northwestern and southwestern Ohio.
Potato leafhopper can still be found in considerable numbers in alfalfa, causing stunting and "hopper burn," especially on stands not receiving a periodic rain. Weekly inspection of fields for this pest is still appropriate.
European corn borer pressure has remained low to this point, with large and small larvae (3rd-5th instars) from the first generation still being found in corn plants. These larvae will eventually become the adults of the second generation.
Bean leaf beetle in soybeans has been reported to exceed 1 beetle per sweep with defoliation exceeding 10 percent at only a few locations, considerably below the threshold. As soybean plants begin to pod, look for feeding damage (scars) on pods. If damage approaches 8% on pods and adults exceed 2 per sweep, continue monitoring. Consider treatment if pod injury and adult numbers increase.
(from the Purdue Pest Management & Crop Production Newsletter 31 July 1998)
Weather conditions across Ohio during the past week have been a study in contrasts. While parts of NW and West Central Ohio benefited from timely rains, other areas received little or no rain. In those areas where soil moisture is growing deficient, corn is beginning to show symptoms of moisture stress with leaf firing and leaf rolling. With most Ohio corn is well into grain fill, what impact will drought and other stress conditions have on crop performance during these final stages of crop development? The following is an article from the Purdue Pest Management & Crop Production Newsletter written by Dr. Bob Nielsen which discusses effects of stress during grain fill in corn.
While the pollination period is considered to be the most critical yield-determining interval in the corn plant's life cycle, severe stress on the corn plant during the grain fill period can also result in dramatic yield loss. Yield loss during grain fill can occur from 1) stand loss, 2) incomplete kernel set, 3) lightweight kernels, and 4) premature plant death.
Stand Loss During Grain Fill:
Yield loss due to stand loss during grain fill is usually greater than that due to stand loss that occurs during the vegetative phase. When stand loss occurs prior to pollination, ear size (number of kernels) on surviving plants may compensate in response to the lesser competition of a thinner stand. Additional compensation may occur during grain fill in terms of greater kernel weight. When stand loss occurs during grain fill, ear size has already been set. Only kernel weight can compensate in response to the lesser competition of a thinner stand.
Incomplete Kernel Set in Corn:
Kernel set refers to the degree to which kernels have developed up and down the cob. Incomplete kernel set is not always apparent from 'windshield' surveys of a corn field. Husks and cob will continue to lengthen even if kernel set is incomplete. A wonderfully long, robust-looking, healthy green ear shoot can completely mask even a 100 percent failure of pollination or severe kernel abortion.
One of the causes of incomplete kernel set is unsuccessful pollination. Unsuccessful pollination results in ovules that are never fertilized and, subsequently, ears with varying degrees and patterns of incomplete kernel set. Many factors can cause incomplete pollination and distinguishing between them can be very difficult.
Certain insects like corn rootworm beetles and Japanese beetles can interfere with pollination and fertilization by their silk clipping action. These insects feed on pollen and will subsequently clip silks as they feed on the pollen that has been captured by the silks. Unusually early or late pollinating fields are often particularly attractive to these insects.
Drought stress may delay silk emergence until pollen shed is nearly or completely finished. During periods of high temperatures, low relative humidities, and inadequate soil moisture levels, exposed silks may also dessicate and become non-receptive to pollen germination.
Unusually favorable conditions prior to pollination that favor ear size determination can result in ears with an unusually high number of potential kernels per row. Remember that silk elongation begins near the butt of the ear and progresses up toward the tip. The tip silks are typically the last to emerge from the husk leaves. If ears are unusually long (many kernels per row), the final silks from the tip of the ear may emerge after all the pollen has been shed.
Another cause of incomplete kernel set is abortion of fertilized ovules. Aborted kernels are distinguished from unfertilized ovules in that aborted kernels had actually begun development. Aborted kernels will be shrunken, mostly white, often with the yellow embryo visible; compared to normal plump yellow kernels.
Kernels are most susceptible to abortion during the first 2 weeks following pollination, particularly kernels near the tip of the ear. Tip kernels are generally last to be fertilized, less vigorous than the rest, and are most susceptible to abortion. Once kernels have reached the dough stage of development, further yield losses will occur mainly from reductions in kernel dry weight accumulation.
Severe drought stress that continues into the early stages of kernel development (blister and milk stages) can easily abort developing kernels. Severe nutrient deficiencies (especially nitrogen) can also abort kernels if enough of the photosynthetic 'factory' is damaged. Extensive loss of green leaf tissue by certain leaf diseases, such as grey leaf spot, by the time pollination occurs may limit photosynthate production enough to cause kernel abortion. Consecutive days of heavily overcast, cloudy conditions may also reduce photosynthesis enough to cause abortion in recently fertilized ovules.
Decreased Kernel Weight:
Severe stress during dough and dent stages of grain fill decreases grain yield primarily due to decreased kernel weights and is often caused by premature black layer formation in the kernels. Decreased kernel weight can result from severe drought and heat stress during grain fill; extensive European corn borer tunneling (especially in the ear shanks); loss of photosynthetic leaf area by hail, insects, or disease early in grain fill; and killing fall frosts prior to normal black layer development.
Once grain has reached physiological maturity, stress will have no further physiological effect on final yield, because final yield is already achieved. Stalk and ear rots, however, can continue to develop after corn has reached physiological maturity and indirectly reduce grain yield.
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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: STATE SPECIALISTS: Pat Lipps & Anne Dorrance (Plant Pathology), Peter Thomison (Corn Production); DISTRICT SPECIALISTS: Jim Jasinski (IPM); EXTENSION AGENTS: Roger Bender (Shelby), Clark Hutson (Seneca), Barry Ward (Marion), Greg La Barge (Fulton), Howard Siegrist (Licking) and Steve Prochaska (Crawford).
Editor: Clark Hutson Web Editor: David Etzkorn
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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