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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2011-23

Dates Covered: 
July 19, 2011 - July 26, 2011
Amanda Douridas

Weather Update

No changes from last week. A hot week with some scattered storms and severe weather can be expected.

July 18-25 - Temperatures will average 5-10 degrees above normal with rainfall averaging 0.5 to 1.0 inches. Normal rainfall is near 1 inch per week. Due to the nature of thunderstorms, this means some places will receive 2+" while others get 0.25 inches. Due to the very hot weather ahead this week, thunderstorms will be capable of producing severe weather with damaging winds a real threat. Expect this week to feature highs in the 90s and lows in the 70s.

July 25-August 1 - Temperatures will relax some next week to average 0-2 degrees above normal with rainfall again at or below normal in the 0.5 to 1 inch range with a high degree of variability.

August Outlook: Expect the trend to be your friend with temperatures continuing at or above normal and rainfall at or below normal, but there is no indication of no rainfall for an extended 30+ day period of time, we will at least have chances for some rain even if less than normal in places.

Corn Pollination Overview

During the past week, tassels and silks began appearing in corn fields that were planted during mid-May or earlier. Corn planted in early June may not be not be tasselling and silking until early August. There is usually some variability in pollination within corn fields and the pollen shed period extends from one to two weeks. This year we can expect even greater variability because saturated soil conditions and loss of nitrogen in poorly drained and compacted areas have inhibited corn growth. Soil moisture deficits due to limited rainfall have also resulted in differential plant growth. The pollination period, 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 have the greatest impact on yield potential during the reproductive stage. Past research indicates that four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5 to 10 percent. The potential for yield losses to soil moisture deficits increases dramatically when plants begin to flower. During tassel emergence, four days of moisture stress has the potential to reduce yields 10 to 25%. Silk emergence is the most critical period in terms of moisture use by the plant. During this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. Four days of moisture stress during silk emergence has the potential to reduce yields 40 to 50%. However, the stress conditions we are alluding to over these “four day periods” are severe and involve extensive leaf rolling (characterized by plants with “pineapple” like leaves) throughout much of the day. Also keep in mind that the corn plant is more vulnerable to hail injury during the period from tassel emergence (VT) to silking (R1) than during any other period because the tassel and all the leaves are completely exposed. Complete defoliation of the plant at VT usually results in 100% yield loss.

The following are 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. However, in some years under favorable growing condition, silks may actually emerge before tassels fully emerge and pollen shed starts in certain hybrids.  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. Pollen may be shed before the tassel fully emerges (“stretches out"). Pollen shed usually 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.

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 all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be 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.

For more information on pollination in corn, check out the following references.

Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.

Nielsen, R.L. 2010. Tassel Emergence and Pollen Shed. Corny News Network, Purdue Univ. [On-Line]. Available at

Nielsen, RL . 2010. Silk Emergence. Corny News Network, Purdue Univ. [On-Line]. vailable at at

“Green Snap" Damage to Corn

Breaks in the stalk usually occur at nodes (along nodal plates) below the ear. When soil moisture and temperature conditions are favorable for growth during this stage of plant development, plants elongate rapidly but stalks are unusually brittle. Stalk brittleness is greatest in rapidly growing corn under high temperature, high soil moisture conditions. There is speculation that rapidly growing plants are more susceptible to snapping-off for several days during the few weeks before tasseling because there has been little time for plants to develop lignified tissues at the nodes.

Although we encounter green snap problems periodically in Ohio, it's usually a more serious problem in the western Corn Belt. Vulnerability to green snap damage varies among hybrids. However, all hybrids are at risk from such wind injury when they are growing rapidly prior to tasseling. The use of growth regulator herbicides, such as 2,4-D or Banvel, has also been associated with stalk brittleness, especially if late application or application during hot, humid conditions occur. Once the crop tassels, green snap problems generally disappear. Back in the 1990’s, Nebraska researchers observed that it was often the most productive fields with the highest yield potential that experienced the greatest green snap injury. They concluded that factors promoting rapid growth early in the growing season also predisposed corn to greater green snap injury.

According to Dr. Emerson Nafziger at the University of Illinois… “Yield effects of green snap depend on the number of plants snapped and where the breakage takes place. Stalks that break above the ear will usually produce an ear, but if nearby plants are intact, they will shade the broken-off plants and reduce ear size. When plants break at the node below the top ear, dormancy will break and allow the next ear down to develop, but it may not receive enough pollen to produce a lot of kernels. Plants that break near the ground won't produce yield, of course, but will allow more light to reach intact plants, which in turn will produce more grain. Loss of plants thus typically reduces overall yield less than the percentage of broken plants might suggest.”

For more on green snap, check the following

Elmore, R. 2011. Wind and Corn. Iowa State University Integrated Crop Management Newsletter.

Nafziger, E. 2011. Wind damage in corn. University of Illinois. The Bulletin.
Will this be a white mold year?

Will this be a white mold year?

The historic white mold fields that would be most “at-risk” in 2011, are those that have good canopy closure and have had frequent rains through July and where night temperatures are dipping very low – 60’s to 70’s.  Only a few fields in the state fit this description.  However, the high temperatures predicted for the next few weeks will prevent any development of white mold.  If any infections occurred prior to this, they will just sit there.  In addition, any fungicide applications made will promote flare-ups of spider mites.  High temperatures and poor root development will also limit recovery from herbicides that “suppress” white mold. 

Risk for Two Spotted Spider Mites in Soybean Increases

Risk for Two Spotted Spider Mites in Soybean Increases

Despite the torrential downpours in the spring, many areas of the state are becoming very dry, with little rainfall in the forecast but with very hot temperatures.  Although we have not heard of outbreaks in Ohio yet, there is a risk of mite populations beginning to increase in soybeans given the weather conditions.  Whether mites do become widespread problems is unknown; however, growers in dry areas might want to begin checking their fields for possible mite infestations, especially around the field edges. We would not expect whole field infestations; growers should nevertheless also check areas within their fields.  Additionally, any fields with fungicide applications (which can kill fungal pathogens that keep spider mite populations in check) should be prioritized for scouting.  Early symptoms of two spotted spider mite infestations are yellow stippling of soybean leaves.  Two spotted spider mites are small (smaller than soybean aphids), brown and black and can be seen with a hand lens on the underside of the leaf.  If a leaf is removed and shaken above a white piece of paper, the mites will fall, crawl around and make it easier to see.  See our fact sheet for more information on two spotted spider mites in soybeans.

If mites begin to build up in fields, growers have a few choices in materials to spray (see  which will do an adequate job in control: chlorpyrifos (Lorsban and various other formulations), dimethoate, and bifenthrin (various formulations), and various mixes of different materials including Hero which is zeta-cypermethrin and bifenthrin (active against mites), and Cobalt which contains gamma-cyhalothrin and chlorpyrifos (active against mites). Growers seeing yellowing along field edges should check for mites with a hand lens and consider a field-edge treatment. If the problem exists throughout the field, an entire field spray should be considered.  We would also recommend using materials that offer mite control rather than suppression alone.

Update on Western Bean Cutworm Flight

Update on Western Bean Cutworm Flight

The adult flight of western bean cutworm sharply increased this week, more than tripling the count from last week.  Indiana, Michigan and Ontario have all reported egg deposition in corn, so now is the time to intensify egg scouting in your fields.  Remember, inspect 20 plants in 5 random locations and look for clumped egg masses on the upper most leaves.  Threshold is 5% of plants infested.  Corn that is just about to tassel is most susceptible to egg deposition, but all pre-tassel corn can have eggs, so prioritize your field scouting.  Please report any eggs found to Andy Michel ( or your local county Extension Educator. 

West Ohio Agronomy Field Day

West Ohio Agronomy Field Day

The gates will open at 9:30am to allow attendees time to get checked in and find a seat. The program will begin at 10:00am with a quick welcome. Participants will then rotate through four intensive fifteen minute sessions taught by county educators. Harold Watters, CPAg, CCA, from OSU Extension, Champaign County, will discuss proven agronomic practices for maximizing soybean production. Dr. Ed Lentz, CCA, Crop Production Specialist from OSU Extension, Seneca County, will discuss research based recommendations for soybean fertility. Bruce Clevenger, CCA, from OSU Extension, Defiance County, will discuss on-farm research currently conducted by OSU Extension on max inputs for soybeans. Bruce will also discuss key on-farm research principles for evaluating products on-farm. Justin Petrosino, OSU Extension, Darke County, will discuss management of tough to control weeds like marestail, giant ragweed and waterhemp.

After the morning sessions the groups will break for an excellent lunch sponsored by Asgrow and Cargill. If you cannot make The Great Darke County Fair this year, you will still be able to enjoy a Farmer Brown sandwich. The restaurant’s lunch trailer will provide the famous Farmer Brown sandwiches and fries to all attendees.

To beat the August heat afternoon sessions will be held under the shade of a barn roof. Attendees can relax as they listen to state specialists discuss major issues related to soybean production. Dr. Anne Dorrance, Soybean Pathologist, Ohio State University, will discuss “Soybean Challenges for 2011: The Expected and Unexpected”. Dr. Andy Michel, Field Crop Entomologist, The Ohio State University, will discuss “Insect Threats to Soybean Production.” The field day will conclude with special guest Dr. Shaun Casteel, Soybean Specialist, Purdue University, sharing the secrets of “Improving Soybean Yields Profitably.” 

Registration has begun for the event. Attendees can save $5 by paying the $15 registration fee before 4:30 pm, July 29, 2011. After the 29th and at the door, registration will cost $20. For the registration fee participants will receive publications and handouts, a chance to mingle with county educators, state specialists and sponsors. The event also allows those with a private or commercial pesticide applicators license the chance to obtain recertification credits, and certified crop advisors can earn continuing education credits. To register call the Darke County Extension Office at (937) 548-5215. You may also visit the county website at to print a flier, or visit the Agronomic Crops Website at for more information.

Field Crops Day

Program includes:

Insect Issues for Late Planted Crops – Andy Michel, Entomology OSU Extension

Impact of Late Planted Corn on Agronomic Performance – Peter Thomison, Horticulture & Crop Science, OSU Extension

Water Management and Challenges for Ag And Water Resources – Larry Brown, Ag Engineering, OSU Extenison

Getting the Best Coverage and Deposition from your Sprayer – Erdal Ozkan, Ag Engineering, OSU Extension

No registration needed.  No cost to attend.

Sponsored by Ohio Ag Research & Development Center and OSU Extension.  Call 419-257-2060 for more information.

Ohio Farm Field Day, July 20 & 21

An Ohio Farm Field Day will be held July 20 and 21 in Mercer County, with a line-up of all-star speakers. (Same program each day) The topics are aimed at helping crop and livestock farmers enhance their farming practices at the same time they help the environment.

The Van Tilburg Farm is hosting the field day at 6951 Oregon Road, Celina, OH. The program will run from 9:00-3:30. Registration is only $10. Call 1-855-332-2231 (Toll Free) to register.

Five hours of Certified Crop Advisor CEUs have been approved (3 hrs Soil & Water; 1.5 hrs Nutrient Management; and 0.5 hr Pest Management).

Topics include: Soil quality, strip-till, cover crops, manure management, weed id, earthworms and controlled traffic.


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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.