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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2006-21

Dates Covered: 
July 10, 2006 - July 18, 2006
Jim Skeeles

Soybean Rust Update

Authors: Anne Dorrance

The southeast has been very dry and soybean rust has stalled. For all soybean diseases, optimum environmental conditions, lots of inoculum and a susceptible host are needed for disease to develop – this year we were missing 2 of the 3 components. We will continue to monitor these plots throughout the season. In fact, several plots were planted this past week to monitor soybean rust through the fall. Twenty-three of the thirty-seven sentinel locations were scouted last week. More than half are reporting brown spot and two locations reported the presence of Phytophthora stem rot. Frogeye leaf spot (2 lesions) was reported from Morrow County, this was reported in Southern Indiana as well. Frogeye can reduce yields on some susceptible varieties. Scouting in those fields that had Frogeye last year – if they are planted again to soybeans would be worthwhile. Fungicides can limit these losses but spraying is only needed when frogeye is present at readily detectable levels at the R3 growth stage.

Aerial blight is another disease of soybean that is also controlled by fungicides. It has been discussed in some recent radio advertisements. Aerial blight is caused by Rhizoctonia and is prevalent in hot, humid regions, such as southern Arkansas, Louisiana, and Florida. Aerial blight on soybeans has never been identified in Ohio.

Corn Pollination Underway in Many Ohio Corn Fields

Authors: Peter Thomison

During the past week, tassels began appearing in many early planted corn fields. The flowering stage in corn is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Stress conditions such as drought or hail damage have the greatest impact on yield potential during the reproductive stage. The following are some key steps in the corn pollination process.

Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. Under very dry conditions, silk emergence may be delayed, and such “asynchronization” of pollen shed and silking may result in poor kernel set and reduced grain yields. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon.

The tassel is usually fully emerged and "stretched out" before any pollen is shed. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen.

Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.

Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains.

Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.

A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.

Pollen of a given plant rarely fertilizes the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant are pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. As noted above, poor kernel set is more often associated with poor timing of pollen shed with silk emergence – with silks emerging after pollen shed (poor “nick”). However, hybrids rarely seldom exhibit this problem unless they experience extreme drought stress.

Farm Focus Field Day July 18 to Focus on Tillage & Soil

The July18, 2006, Field Day at the Marsh Foundation Farm will focus on the various tillage methods, soil testing and soil fertility and offer wagon tours of the 300 acre research plots. The Field day is hosted by the Farm Focus Committee and The Ohio State University Extension

Free and open to the public, one of the day’s features will be a workshop conducted by Dr. Robert Mullen, an OSU soils specialist who will discuss soil testing and soil fertility. Highlights of the morning and afternoon will be demonstrations on vertical tillage equipment and strip-till equipment.

The Vertical Tillage Equipment Demonstrations will feature Great Plains Turbo-till, Phillips Smart-till 2200, Phoenix Till-lite and Rotary Harrows and Salford RTS. The Strip-till Equipment will have equipment demonstrations from DMI, Remlinger and Trailblazer.

Narrated wagon tours of the various research plots will run throughout the 300 acre Marsh Foundation/Farm Focus site. There will also be free lunch provided by the sponsors of the Farm Focus Field Day. Visitors will have the opportunity to visit with the tillage equipment demonstrators throughout the afternoon.

Sponsors of this summer’s field day include Ag Credit, Archbold Equipment, First Bank of Berne, CNH America, Great Plains Mfg., Homier & Sons, Inc., Heritage Farm Equipment, Kennedy-Kuhn Inc., Phoenix Equipment, Precision metal Fabricating, Remlinger Manufacturing, R&G Manufacturing and Williamson Insurance Agency.

Registration begins at 8:30 a.m. There will be three 45 minute in-field workshops in concurrent sessions beginning at 9:15, 10:30 and 11:45 a.m. The Farm Focus Committee will offer shuttles to run between sessions as needed. Visitors will have the opportunity to attend all sessions if they arrive prior to 9:00 a.m.

Farm Focus is a non-profit organization made up of volunteers from Van Wert County dedicated to continuing agronomic education the tri-state area. The Farm Focus research and clinical trial program is sponsored in part by The Ohio State University Extension, Van Wert County and The Marsh Foundation School Farms.

For more information about the July 18th Field Day, visit the Farm Focus website at or call the Ohio State University Extension, Van Wert County office at 419.238.1214.

Japanese Beetles and Other Defoliators in Soybeans

Authors: Ron Hammond, Bruce Eisley

We are receiving reports from around the state of the presence of Japanese beetles in soybeans in rather large numbers. Along with these beetles, a few reports of grasshoppers have also been received. Added to that, we should begin seeing first generation, adult bean leaf beetles and Mexican bean beetles in the next few weeks, along with perhaps green cloverworm larvae. Needless to say, soybean defoliators will be the next concern for soybean growers.

This fact is important because soybeans are beginning to enter their reproductive stages, with flowers now being found on most plants. In terms of defoliation, it would be unusual for any of the above mentioned insects alone to cause significant defoliation throughout a field. However, a complex of two or more might cause defoliation levels to rise above threshold levels. For fields with large populations of Japanese beetles, remember that these beetles will congregate; finding one Japanese beetle means you will usually find a lot of them in the same area. Thus, at least for this insect, you need to make an extra effort to sample from numerous locations in the field to get a better idea of what is happening across the entire field.

Growers are advised to initiate scouting procedures to prevent defoliation from reaching the 15-20% defoliation threshold during the reproductive growth stages, R1-R5, which then rises to 20-25% during growth stage R6 late in the summer. A list of labeled insecticides for control of all these soybean pests is available at When sampling, check numerous places within the field (again, especially for the Japanese beetle), avoiding the field edges which often tend to have higher levels than the rest of the field.

Potato Leafhopper

Authors: Bruce Eisley, Ron Hammond

Based on our own sampling in alfalfa and soybeans and with the reports we are receiving, potato leafhoppers are occurring in high numbers. Growers are advised to check their alfalfa for potential problems. The threshold on leafhopper-susceptible alfalfa is as follows: when the average number of leafhoppers in a single sample (10 sweeps) equals or is greater than the height of the alfalfa, treatment should be considered if harvest is more than 7 days away. The thresholds are higher for glandular-haired varieties rated as highly resistant to potato leafhopper (at least 50% resistance ratings). The threshold for established stands of highly resistant alfalfa is 3X the regular threshold. This year, these thresholds might be reached because of the larger leafhopper populations we are experiencing. We recommend this threshold for any highly resistant alfalfa that is beyond its first cutting of the seeding year. However, we feel that the regular thresholds should be used for potato leafhopper resistant alfalfa prior to the first cutting of the seeding year, which includes most fields planted this spring.

We mention soybeans because we have observed some injury. In late planted soybeans that are still in the early vegetative stages, we have seen plants with potato leafhopper injury. Injury is evident from the slight yellowing at the tips of some leaves. Although the soybeans will usually grow out of this, growers should be aware of what it looks like to as not to confuse it with other problems.

Western Corn Rootworm Adult and Larval Injury

Authors: Ron Hammond, Bruce Eisley

As is the case in many Midwest states, western corn rootworm adults are beginning to show up in large numbers. With corn silks not yet out, we have already received reports of feeding on leaves in corn fields with large numbers. The beetles scrape off the outer layer of the leaf resulting in a leaf that looks as if it has been burned. We normally are not concerned about this leaf feeding but will be concerned in these fields when the silks begin to emerge because the beetles will move to the silks and begin feeding.

Because of the potential for uneven silking because of patchiness of the corn growth, there may be only a small portion of the field that has fresh silks at any one time. In these cases, the beetles will congregate on those emerged silks and populations per plant may be larger than if the whole field had silked. As more plants silk, the population may become dispersed throughout the field and reduce the beetle numbers per plant and thus the need for treatment. Also, remember that the higher Japanese beetle populations might add to the problem of silk clipping, especially around the edges of the fields. Rescue treatment for rootworm beetle silk clipping is warranted if 5 or more beetles are found per silk mass when 75% of the plants have silked and silk clipping to 1/4 inch or less is observed. Rescue treatment for Japanese beetle silk clipping may be warranted if there are 3 or more beetles per silk mass and pollination has not occurred.

Previous articles have discussed larval injury and possible plant lodging. We are getting reports of fields having significant lodging in Ohio. Before assuming that the lodging is because of rootworm root feeding, growers should dig roots, wash them, and rate the roots for larval injury. There are many causes for plant lodging, rootworm feeding being only one of them. With the poor growing conditions at times this past spring and early summer, along with significant amounts of rain some areas have experienced and then the recent storms and high winds, many fields experienced conditions leading to plant lodging. See the CORN newsletter, 2006-19, for how to dig and rate rootworm injury.

Field Crops Day at Northwest Agricultural Research Branch Station 7/18

Authors: Greg LaBarge

Herbicide, disease, insects and water manegement will be the focus of the Tuesday, July 18 Field Crop Program being held from 6:00 to 9:00 p.m. at the
Northwest Agricultural Research Station, Custar. The Station is located one mile east of SR 235 between Hammansburg and Oil Center Roads in western Wood County.

Soybean Rewards Program
Phil Farmer, Ohio Soybean Council

Preserving Glyphosate Utility in a Continuous Roundup Ready World
Dr. Mark Loux, Horticulture & Crop Science, OSU

Crop Disease Concerns and Management
Dr. Anne Dorrance, Plant Pathology, OARDC

Insect Issues Impacting Producers
Dr. Ron Hammond, Entomology, OARDC

Water Management
Dr. Norm Fausey, Food, Agr. & Biological Engineering and Natural Resources, USDA

For more information contact: Matt Davis at 419-257-2060 or

For a listing of more summer programs being held across Ohio check the Agronomic Crop Team Calendar at

Archive Issue Contributors: 

State Specialists: Ann Dorrance and Pierce Paul (Plant Pathology), Jeff Stachler (Weed Science), Peter Thomison (Corn Production), Ron Hammond and Bruce Eisley (Entomology), Robert Mullen and Maurice Watson (Soil Fertility). Extension Educators: Edwin Lentz (Seneca), Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Steve Bartels (Butler), Greg LaBarge (Fulton), Steve Foster(Darke), Jim Skeeles (Lorain), Mike Gastier (Huron), Keith Diedrick (Wayne), Roger Bender (Shelby), Jim Lopshire (Paulding) and Gary Prill (Van Wert).

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.