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For May 3-10, 1999
C.O.R.N. 99-7
In This Issue:
A) Evaluating Frost Injury to Corn
B) More on Burndown Weed Control
C) ApronMaxx Seed Treatment Update
D) Wheat Condition is Excellent; Disease Levels Generally Low
E) Field Crop Pest Activity
F) Why did I get all the CORN messages last week?
When assessing frost injury to corn, don't make a decision on extent of damage and stand loss too quickly. Destruction of leaf area on small corn plants is seldom as serious as appearance might suggest. Young corn seedlings can be severely damaged above ground and still survive with little or no effect on yield. The key to predicting survivability is understanding where the growing point is inside the plant with respect to the stage of plant development. The condition of the growing point is a good indicator of plant health.
The growing point of a corn plant is located deep inside the seedling where all the remaining leaves originate, as does the tassel. You can observe the growing point by digging up a seedling and splitting the stem from top to bottom. The growing point will be located at the top of the pyramid-shaped whitish stalk tissue near the base of the seedling. In corn seedlings that have just emerged, the growing point is located approximately 3/8 inch below the soil surface, just above the crown area. The growing point remains below ground for about 3 weeks or until five to six leaves have fully emerged, after which its position elevates as the stalk begins its rapid elongation phase.
While the growing point is below ground, the corn plant is relatively safe from above-ground damage to the leaves and stem. Severe damage from late frosts, wind blasting, hailstones, anhydrous burn, insect feeding above ground, etc., will usually not kill corn plants younger than the 6-leaf stage as long as the growing point is not damaged. On the other hand, while the growing point is below the ground, the plant is more sensitive to below-ground insect feeding, flooding or saturated soils.
To determine the viability of young corn plants damaged by frost, the simplest advice is to wait for several days after frost injury for signs of regrowth. Generally 2 to 4 days of 70 degree or warmer temperatures are sufficient to stimulate new leaf growth on an affected plant. If temperatures have been cooler than normal, regrowth may not be readily evident. In that event, you can determine plant viability by splitting the stem and looking at the growing point. If the plant is "healthy" the growing point will be firm and white or cream colored. A darkening or softening of the growing point usually precedes plant death.
As the weeds get larger in no-till fields, especially annual grasses, Roundup Ultra, Touchdown, or Gramoxone Extra will need to be added to clean up no-till fields. When weeds get over 6 inches tall, they become more difficult to control with Gramoxone Extra and Roundup Ultra or Touchdown should be used instead. Be sure enough Roundup Ultra or Touchdown is being added to control the weeds present in fields, because as weeds get larger, higher rates of these herbicides will be necessary. If Roundup Ultra or Touchdown are being added just to control small annual grasses, then only a low rate of these products are necessary. Roundup Ultra or Touchdown should be applied at least at 1.0 quart/A or 1.6 pints/A, respectively, to control perennial grasses and higher rates will provide more complete control, especially for tough perennial grasses. Maximum control of perennial grasses is achieved in the boot to head emergence stage.
ApronMaxx RTA will not be available for the 99 soybean production season. The Environmental Protection Agency has recalled the 24C use permit for this product in Ohio. The reason for this action is that one of the inert ingredients, 2-pyrrolidone, 1-octyl does not have clearance on soybeans. While this inert ingredient is approved on cotton and cotton seed oil, soybeans have not been tested. All shipments and distribution of ApronMaxx RTU in Ohio were stopped the week of April 19th. This is the result of a miscommunication between Novartis and the supplier of the inert. Novartis and EPA are still in discussions about any other actions that may be taken. ApronMaxx RTA is combination of Apron XL and Maxim for use as a seed treatment fungicide to control seed and seedling diseases caused by Pythium, Phytophthora, Rhizoctonia, Sclerotinia and Fusarium.
Wheat is in flag leaf emergence growth stage throughout most of the state, with fields in more southern locations having most flag leaves out and those in the north have flag leaves just emerging. Warm dry weather over the past week has limited the development of most leaf diseases.
If you have not detected any sign of powdery mildew in your fields up to this time then probably you will not have to be concerned with it this year. Powdery mildew is still common in many fields of susceptible varieties in the north central and north eastern sections of the state. However, in most cases powdery mildew has not advanced to the third leaf on the stem (flag leaf is leaf 1, second leaf is just below the flag leaf and the third leaf is below the second leaf). Night temperatures in the 50 degree range and day temperatures in the 60 to 70 degree range, with high relative humidity will favor continued development of powdery mildew. It is time to spray for powdery mildew when the second leaf is in danger of becoming infected.
Cutworms: Reports of cutworm detection have been received. On Wednesday last week, we sampled weedy soybean stubble for cutworms at the Western Branch using the soapy water flushing method, but only detected Dingey cutworms which appear earlier than the black cutworm larvae and seldom cause serious problems. However, our pheromone traps at the station average 26 adult black cutworm moths per trap which represents a high moth catch and may indicate a potential problem. As early planted corn emerges under current optimal weather conditions, fields should be scouted periodically to detect early signs of cutworm activity.
Bean leaf beetle: Sweep net sampling of alfalfa has not to date detected any bean leaf beetle activity, which is a general sign of potential activity that may impact early planted soybeans. However, while sampling for cutworm in soybean stubble last week, we did detect a number of bean leaf beetle that presumably had overwintered in the residue. Early planted soybean fields sometimes attract the over wintering adult bean leaf beetles to the point that a rescue treatment is warranted. Once a significant acreage of soybeans has emerged, the problem tends to be dispersed to the point that most fields at not significantly impacted by the over wintering populations.
Alfalfa weevil: Weevil activity continues to be increase in some alfalfa fields. Larvae range from 2nd to 4th instar in development, and pupating larvae should become evident during the forthcoming week. Most alfalfa has developed to a point where early cutting may be the optimal approach to the impact of weevil feeding activity. However, if alfalfa harvest must be delayed until the planting of corn and soybeans is finished, then the alfalfa should be checked in case a timely rescue treatment is needed.
We apologize for all the messages you received last week from the CORN listserv. We have occasionally had a few people try to subscribe to the list and have difficulty. Out of desperation they send an e-mail message to our CORN list that ends up going to all subscribers to the list. Last week a few people inquired about these messages by hitting reply on their e-mail program which sent more messages to the CORN listserv. Thus the snowball started rolling down the hill. In order to assure that we do not send out unwanted messages through the CORN listserv, as of last Tuesday we have limited postings to only CORN editors.
Occasionally you may want to contact someone about CORN or even have a question you would like the specialist contributing to CORN address. We have established an address you can send messages to: corn-questions@postoffice.ag.ohio-state.edu
Another problem that people may have is when we send out tables in the newsletter. Where tables are included every effort is made to transmit the tables so the reader may view them intact. Due to the setup of different e-mail receiving programs, tables may not be readable due to shifts in lines and font sizes etc. Readers can visit our web site when table formats are unreadable. The newsletter is posted on the web site by Tuesday noon at: http://www.ag.ohio-state.edu/~corn/
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
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 (Extension Specialist, Plant Pathology), Anne Dorrance (Extension Specialist, Plant Pathology), Peter Thomison (Corn Production), (Jeff Stachler (Extension Associate, Weed Science), and Hal Willson (Extension Entomology); EXTENSION AGENTS: Roger Bender (Shelby), Larry Lotz (Fayette), Clark Hutson (Seneca), Barry Ward (Champaign), Dennis Baker (Darke), Glenn Arnold (Putnam), Gary Wilson (Hancock), Greg La Barge (Fulton), Howard Siegrist (Licking) and Steve Prochaska (Crawford).
Editor: Steve Prochaska Web Editor: Nathan Watermeier
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
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