CORN
Crop Observation and Recommendation Network

April 17-25, 2000
C.O.R.N. 2000-9

In This Issue:

A) Corn planting - when?
B) Soybean seed quality
C) Soybeans and Inoculants
D) More on winter annuals
E) Wheat growth stage update
F) Weed emergence report - giant foxtail has arrived
G) Field assessment of alfalfa weevil

A) Corn planting - when? - Peter Thomison CORN Questions

In Ohio, corn growers need to begin planting as soon as field conditions will allow. In large part this is due to the fact that during the two or three weeks of optimal corn planting time, there is, on the average, about one out of three days when field work can occur. This means that growers may need to begin planting (if soil conditions are dry) before the optimal planting date to ensure successful crop establishment. Corn planted  10 days or 2 weeks  before the optimum dates may not yield as much as that planted on or near the optimum dates, but it usually  yields more than that  planted  2 weeks or more after the optimum dates. Nevertheless there are risks associated with early corn planting. The following is a recent newsletter article by my counterpart at Purdue University,  Dr. Bob Nielsen, that considers some of these  risks.

Corn Planting Fever! No, it's not the name of my favorite 70's disco song. Rather, it simply reflects a fact of life that warm, dry, sunny days in early spring bring on  daffodils, crabapple blossoms, dandelions and corn planters.  While I do not begrudge those who want to begin planting corn in early April, I feel compelled nonetheless to at least remind them of some of the risks of early corn planting.

An important fact of corn life to remember is that germination and emergence will not occur rapidly or uniformly when soil temperatures are hovering at or below the 50 degree F mark.  In Indiana, soils typically do not warm to temperatures consistently above 50 degrees F until mid-April (south) to early May (north). In fact, bare soil temperatures as I write this article are averaging less than 50 degrees F in central and northern Indiana. [These temperature ranges are probably similar to what we are experiencing in Ohio]. Consequently, it is not uncommon for early April planted corn to emerge three to four weeks after planting.

Early April planted corn will typically yield 4 to 6 percent less than that planted in late April or very early May. Slowly developing seedlings are more susceptible to damage by soil diseases and insects. Slow, uneven germination and emergence results in uneven stand establishment. If uneven emergence or damage by insects or diseases occurs, yield losses can easily increase to as high as 20 percent.

Stand establishment may be so poor as to warrant replanting, which results in greater expense to the producer and possibly less yield than if the field were planted in late April or early May to begin with. By the way, if you have planted prior to April 6 and subsequently need to replant a failed field, don't count on your crop insurance helping with the replant expenses . Check with your insurance agent for details.

The point of this discussion is to simply caution corn growers that there is plenty of calendar time within which to plant the 2000 crop before the proverbial end of the prime planting window in early May. If you are bound and determined to plant corn at the first opportunity, then consider the following tips.

1. Begin planting with the hybrids in your lineup that are rated best for seedling vigor and/or whose cold germination ratings are the greatest.

2. Use one of several available pesticide planter-box seed treatments to hedge against a lengthy period of exposure to soil diseases and insects.

3. Avoid early planting in no-till fields with heavy levels of surface trash, because temperatures will be even cooler in those seedbeds than in more bare fields.

4. Do not plant extra shallow hoping to capitalize on warmer temperatures nearer the surface. A seeding depth of 1 to 11/2 inches remains a viable target even with early plantings. Shallower depths are more susceptible to the effects of soil drying, bird and rodent feeding, and uneven planter depth control.

5. Apply starter fertilizer in a 2-by-2 placement at rates of nitrogen no less than 20 lbs of actual N per acre.

B) Soybean seed quality - Jim Beuerlein CORN Questions

The dry stressful 1999 growing season had a negative effect on the quality of soybean seed available for 2000.  After thorough cleaning and processing, germination percentages for many seed lots are in the 80% to 90% range.  That seed is very fragile and breaks easily when moved mechanically or handled in a rough manner.  Much of the germination loss is due to physical seed damage inflicted at harvest and results in abnormal development of the developing seedling and failure to emerge from the soil.

Soybean seed should be handled with great care to minimize further damage and seeding rates should be increased to compensate for germination percentages lower than 90%.  For germination percentages of 85%, 80%, and 75% the seeding rate should be increased by 6%, 13%, and 20% respectively.  If the germination percent is greater than 90%, no seeding rate adjustment is needed.

Fungicide seed treatments are encouraged to help protect the seed from soil pathogens after the seed is planted and will improve stand counts if the seed is exposed to excessively wet soil or other stresses following planting.  However, fungicides will not help mechanically damaged seeds and may damage those with ruptured seed coats.

1999 grain being saved for seed should be cleaned and checked by professionals for quality and germination.  Many producers have found their saved seed to have very low germination and were forced to buy new seed.  Two Ohio labs that perform such evaluations are: Central Ohio Seed Testing in Dublin, OH (614-792-0334) and Seed Technology in Marysville, OH (937-644-0088).

C) Soybeans and Inoculants - Anne Dorrance CORN Questions

Research at Ohio State University by Dr. Jim Beuerlein, has shown that application of inoculants to soybean seed resulted in increased yields.  Inoculants are comprised of a living organism, a bacterium called Rhizobium.  This bacterium forms a symbiotic relationship with the soybean roots, which results in nodule formation.  The bacterium captures nitrogen and converts it to forms that can be utilized by the soybean plant.  Because inoculants are living organisms they are subject to heat, changes in moisture and some of the ingredients in seed treatments.  Many fields in Ohio need fungicide seed treatment, therefore, the optimum method is to treat seed first, then allow the seed treatment to dry.  The inoculant is then applied shortly before planting.  To maintain the viability of the inoculant once it is applied to the seed it is important to keep it cool and protect it from dramatic changes in the environment.  Novartis is co-promoting their new on farm seed treatment ApronMaxx RTA and Cell-Tech2000, a liquid Rhizobium product for this planting season.  The company reports that the ApronMaxx RTA is safe to mix with the Rhizobium in the Cell-Tech2000. OARDC researchers will be evaluating this combination in field trials during 2000.  However, it should be noted that Apron XL and Allegiance will still need to be applied to seed and allowed to dry prior to adding inoculants.

D) More on winter annuals - Mark Loux CORN Questions

This is a follow-up to last week's article on winter annual weeds.  We failed to mention that Authority and Canopy XL can provide good control of henbit, purple deadnettle, and star-of-bethlehem (but not chickweed). Apply with 2,4-D ester for best results.  We downplayed the effectiveness of 2,4-D on some winter annuals last week, but is does help control a number of weeds (mustards, dandelion, and marestail) and generally improves the activity of other herbicides. 

We concentrated mainly on herbicides to use prior to soybeans last week, and this is because most of our corn is planted following tillage and atrazine tends to help control most emerged weeds.  However, Roundup or Gramoxone can be used prior to corn or soybeans.  These products can be tank-mixed with Sencor (check label for maximum rate) or 2,4-D ester prior to corn planting.  However, be aware than 2,4-D occasionally injures corn when applied around the time of planting, generally when rainfall is plentiful after planting.  Many 2,4-D labels prohibit application within 14 days before through 7 days after planting to minimize the risk of injury. Some dicamba products can also be applied preplant to corn to aid in burndown, but can injure corn, especially in low organic matter, coarse-textured soils.  Balance will also help control a number of weeds prior to planting, but our research shows it to be most effective for burndown when mixed with atrazine.

No-till fields vary greatly in their weed populations at this time of the year.  Some fields are heavily infested with chickweed, deadnettle, mustards, dandelions, etc., and the preplant herbicide selection requires considerable thought.  Other fields may have a sparse population of winter annual weeds and a few summer annuals beginning to show, and their may be little need for Gramoxone or glyphosate.  In these fields, a number of different herbicide programs can be effective, and treatments such as Canopy/2,4-D may be sufficient.  No-till fields should be scouted prior to herbicide decision-making to make sure the  herbicide choice is appropriate.

E) Wheat growth stage update - Pat Lipps CORN Questions

Cold nighttime temperatures last week helped slow down wheat growth. The earliest fields in southern Ohio are approaching flag leaf emergence (growth stage 8), whereas the earliest fields in the northern part of the state are producing their second node (growth stage 7).  Although the growth stages are more advanced than most previous years, plants are probably no more that a week and a half earlier than normal at this time. Warm weather this coming week could promote continued rapid development of the wheat crop.

F) Weed emergence report - giant foxtail has arrived - Jeff Stachler CORN Questions

Common ragweed was over-looked and was present last week in fields. Giant foxtail and velvetleaf are emerging in fields with dark soils in central Ohio. Take this into consideration when applying burndown herbicides. The giant foxtail is still small enough for Canopy and Canopy XL in soybeans and atrazine and Balance in corn to take them out at this time.

G) Field assessment of alfalfa weevil - Hal Willson CORN Questions

Reports have been received that alfalfa weevil is causing economic levels of injury in southern Ohio. In addition, early 1st and 2nd instar larvae can be readily found in alfalfa fields of central Ohio.

Alfalfa weevil is the primary pest of first cutting alfalfa in Ohio. In most years, the weevil does not cause significant injury warranting rescue treatments due to biological control by a complex of beneficial parasites that generally maintain weevil activity at sub-economic levels of activity. However, in some years, the parasites may not maintain weevil populations at a sub-economic level, and application of a timely rescue treatment may be warranted to reduce economic losses due to excessive defoliation.

When weevil activity appears to be above normal, tip injury and weevil larvae abundance of alfalfa stands should be evaluated. The first step of the evaluation should include random selection of a number of stems to determine the percent of tips exhibiting feeding injury.  If tip feeding injury indicates a potential problem, then additional stems should be sampled and shaken into a bucket to determine the number of larvae per stem and confirm whether a serious problem exists and corrective action should be taken.   Levels of tip feeding injury and weevil larvae abundance that should trigger a need for corrective action are given in the following table.

When harvesting early due to weevil, check within one week for re-growth. It should be noted that tip feeding injury only indicates a potential problem and that a decision to apply a rescue treatment should be based on a count of larvae per stem based on a random sample of thirty or more stems.  At the present time, tip injury may be confused with frost injury. In addition, significant tip injury may be visible, but the weevil larvae population may have been decimated by environmental conditions.  Thus, the larvae per stem count is the most important variable in making a decision to treat or not to treat.

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.

Contributors to C.O.R.N. this week include: State Specialists: Pat Lipps and Anne Dorrance (Plant Pathology), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Hal Willson (Entomology), Peter Thomison (Horticulture and Crop Science); Extension Agents: Steve Bartels (Butler), Clark Hutson (Seneca), Barry Ward (Champaign), Gary Wilson (Hancock), Glenn Arnold (Putnam), Bruce Clevenger (Defiance), Howard Siegrist (Licking), Ray Wells (Ross) 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.

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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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