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Ohio State University Extension


C.O.R.N. Newsletter 2007-22

Dates Covered: 
July 16, 2007 - July 24, 2007
Howard Siegrist

Assessing the Impact of Drought on Pollination in Corn

Authors: Peter Thomison

Reports of short, waist high corn tasselling, as well as uneven flowering within fields, are not uncommon in parts of Ohio which have received negligible rain since May. Many corn growers want to know what impact drought stress has had on corn pollination, the stage in corn development most sensitive to such stress conditions. When severe drought stress occurs before and during pollination, a delay in silk emergence can occur. Sometimes the length of this delay is such that little or no pollen is available for fertilization when the silks finally appear. When such delays in silking are lengthy, varying degrees of barrenness will result. It's very likely that silk emergence will be delayed in drought-stressed corn fields unless we get some significant rain very soon.

There are two techniques commonly used to assess the success or failure of pollination. One involves simply waiting until the developing ovules (kernels) appear as watery blisters (the "blister" stage of kernel development). This usually occurs about 1 1/2 weeks after fertilization of the ovules. However, there is a more rapid means to determine pollination success.

Each potential kernel on the ear has a silk attached to it. Once a pollen grain "lands" on an individual silk, it quickly germinates and produces a pollen tube that grows the length of the silk to fertilize the ovule in 12 to 28 hours. Within 1 to 3 days after a silk is pollinated and fertilization of the ovule is successful, the silk will detach from the developing kernel. Unfertilized ovules will still have attached silks.

Silks turn brown and dry up after the fertilization process occurs. By carefully unwrapping the husk leaves from an ear and then gently shaking the ear, the silks from the fertilized ovules will readily drop off. Keep in mind that silks can remain receptive to pollen up to 10 days after emergence. The proportion of fertilized ovules (future kernels) on an ear can be deduced by the proportion of silks dropping off the ear. Sampling several ears at random throughout a field will provide an indication of the progress of pollination. Severe silk clipping by Japanese beetles and corn rootworm beetles during pollination can also adversely influence pollination. This “ear shake technique” can also provide an early indication of pollination problems due to insect feeding.

Unusually long silks that are still "fresh" period are a symptom that pollination has not been successful. Unpollinated silks continue to elongate for about 10 days after they emerge from the ear husks before they finally deteriorate rapidly. During this period, silks become less receptive to pollen germination as they age and the rate of kernel set success decreases. If you observe unusually long silks in drought stressed field it may be an indication of pollination failure.

Dr. Bob Nielsen, the corn extension specialist at Purdue University, has written a good article, ("A Fast & Accurate Pregnancy Test for Corn"), which includes excellent pictures showing silk detachment and use of the “ear shake technique”; it’s available online at: .

Evaluating Potential for Nitrate Problems in Corn

Authors: Peter Thomison

Hot dry weather across Ohio has raised questions concerning the potential for toxic levels of nitrates in corn harvested for silage. Nitrates absorbed from the soil by plant roots are normally incorporated into plant tissue as amino acids, proteins and other nitrogenous compounds. Thus, the concentration of nitrate in the plant is usually low. The primary site for converting nitrates to these products is in growing green leaves. Under unfavorable growing conditions, especially drought, this conversion process is retarded, causing nitrate to accumulate in the stalks, stems and other conductive tissue. The highest concentration of nitrates is in the lower part of the stalk or stem. For example, the bulk of the nitrate in a drought-stricken corn plant can be found in the bottom third of the stalk. If moisture conditions improve, the conversion process accelerates and within a few days nitrate levels in the plant returns too normal.

The highest levels of nitrate accumulate when drought occurs during a period of heavy nitrate uptake by the corn plant. A drought during or immediately after pollination is often associated with the highest accumulations of nitrates. Extended drought prior to pollination is not necessarily a prelude to high accumulations of nitrate. The resumption of normal plant growth from a heavy rainfall will reduce nitrate accumulation in corn plants, and harvest should be delayed for at least 1 to 2 weeks after the rainfall. Not all drought conditions cause high nitrate levels in plant. If the supply of soil nitrates is in the dry soil surface, plant roots will not absorb nitrates. Some soil moisture is necessary for absorption and accumulation of the nitrates.

If growers want to salvage part of their drought damaged corn crop as silage, it's best to delay harvesting to maximize grain filling, if ears have formed. Even though leaves may be dying, the stalk and ear often have enough extra water for good keep. Kernels will continue to fill and the increases in dry matter will more than compensate for leaf loss unless plants are actually dying or dead. Moreover, if nitrate levels are high or questionable, they will decrease as plant gets older and nitrates are converted to proteins in the ear.

For information on testing and feeding corn with varying nitrate-nitrogen levels, check out the following

Nitrates in Dairy Rations - Maurice Eastridge and Bill Weiss, Ohio State University Fact Sheet AS-0003-99
available on-line at .

Effects of Leaf Midrib Breakage on Corn Yields

Authors: Peter Thomison

Hail storms and thunderstorms accompanied by strong winds may cause extensive damage to corn leaves, resulting in defoliation and breakage of leaf midribs. Late postemergent application of fertilizers and pesticides can also result in leaf mid rib breakage. While effects of defoliation on corn performance are well documented, little information is available on effects of leaf midrib breakage on subsequent corn growth and performance. In OSU evaluations conducted in 2002-2004, breakage of leaf midribs at the leaf collar reduced yields nearly 30% whereas breakage at mid leaf usually had no significant effect on yield. Results of the 2004 evaluation are available online at: .

Yellow Beans?

Authors: Anne Dorrance, Dennis Mills

Droughts provide an opportunity to locate problem areas in fields. Many have noticed and commented about the patches of yellow, stunted soybeans across the state. The areas are not always low, poorly drained areas and the chlorosis ranges from minimal to severe. Could these symptoms be caused by soybean cyst nematode? Areas of fields with high populations of SCN will show signs of stress first. Soybeans in these areas will appear yellow or off-color, begin to wilt and in some cases die before other areas of the field. Normally in Ohio we do not see such severe above ground SCN symptoms, but is the problem being compounded by lack of rainfall? The poor growing conditions combined with SCN is more than some of these plants can stand. You may be able to see cyst females on some of these roots. Carefully dig plants and shake the roots gently, then look for the tiny "pearls" on the roots. This will work much better in the lighter soils. Take notes on these fields - these are the ones that should be sampled for SCN this fall following harvest. These SCN fields must be managed by CROP ROTATION. By keeping the SCN populations low, optimal yields can be obtained.

Soybean cyst nematode has great potential to build high populations which can cause substantial yield losses in a short period of time. The best time to sample soil is in the fall following harvest. The C. Wayne Ellett Plant and Pest Diagnostic Clinic fee for SCN testing is $15.00 per sample. .

Sampling Instructions:

1. Use a 1-inch diameter soil probe to collect soil samples (6-8 inches in depth)
2. Following a zig-zag pattern, collect 10-20 soil cores per 10-20 acres
3. Collect cores from areas of similar soil type and crop history
4. Dump cores from each 10 to 20 acre area into a bucket or tub and mix thoroughly
5. Place 1 pint (2 cups) of mixed soil in a soil sample bag or plastic zippered bag and label with a permanent marker
6. Store sample in cool, dark place until shipped to a lab doing SCN analysis.
7. Samples may be sent to:

C. Wayne Ellett Plant and Pest Diagnostic Clinic
110 Kottman Hall
2021 Coffey Road
Ohio State University
Columbus, OH 43210-1087

Soybean Sentinel Plot Report

Authors: Anne Dorrance

Soybean samples from Ohio are all negative for soybean rust. Brown spot is now fairly established in most locations. Frogeye leaf spot is present but does not appear to be increasing in the areas that did not get rain; however, it is increasing in areas where dews and locations that received favorable moisture. Dry weather is just not favorable for infection and development of disease. For those of you with frogeye, if it continues to be dry, hold off on the fungicide until the weather turns more favorable. On the national level, soybean rust has now been found along the coast of Texas, in a few kudzu plots in Mississippi and more in Louisiana. It is still spotty. Even in these plots that have soybean rust it is still at low levels. This will change over the next few weeks as conditions in the south are more favorable. I would expect that the US map . will continue to have more counties turn red over the next week – but risk for this to reach Ohio in time to impact our normal planted soybeans is still very, very low.

Caution: Fungicide Restrictions on Corn Silage and Soybean Forage

Authors: Pierce Paul, Dennis Mills, Anne Dorrance

Some questions have been raised this past week on cutting corn for silage and soybeans for forage. Some fields have been treated. There are feeding restrictions with some of these fungicides. Below is a brief list with the CURRENT label. If you are going to harvest early and use for feed, please double check your labels to be sure that there are no restrictions.

Product Active Corn Soybeans
Headline pyraclostrobin no restrictions Soybean hay – 21 days
      Soybean forage – 14 days
Quadris azoxystrobin 7 day PHI Soybean hay – 0 days
      Soybean forage – 0 days
Quilt azoxystrobin no more than 28 fl oz Do not use for hay or forage
  propoconazole 30 day PHI  
Stratego propiconazole 30 day PHI Do not use as hay or forage
Domark tetraconazole not labeled Do not use for hay or forage


Field Crop Insect Update

Authors: Bruce Eisley, Ron Hammond

CORN –Adult corn rootworms are being reported to be feeding heavily on both leaves and silks in some corn fields. While the feeding on leaves is mostly cosmetic, feeding on silks can cause yield reductions. Be aware that adult Japanese beetles are also being reported to be feeding on corn silks. 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. For Japanese beetles, rescue treatment is warranted if there are 3 or more beetles per silk mass and pollination has not occurred. Reports suggest that some fields are already being heavily damaged, so scouting now is critical. Additionally, you still have time to check root injury for efficacy of corn rootworm control tactics, and also to determine the presence of the western corn rootworm variant in first year corn. See the CORN newsletter, 2007-19; . for instructions how to dig and rate rootworm injury.

SOYBEAN – The main concern in Ohio as of this week remains two-spotted spider mites, a pest that is becoming more widespread because of drought conditions. We are beginning to see an increase in infested fields in Ohio and surrounding states. See the CORN newsletter, 2007-18; . for information on controlling these mites. Although populations of soybean aphids still are running very low, scouting for aphids the next few weeks is crucial because if it is going to happen, this will be the time for arrival of large numbers of winged aphids and the beginning of economic populations. At this time, we still do expect economic populations to occur, so do NOT let your guard down. For information on the relative levels of soybean aphid in Ohio and surrounding states, see the USDA IPM PIPE website with its weekly soybean aphid reports from locations throughout the U.S. including Ohio. The Pest Information Platform for Extension and Education (PIPE) shows the finds of soybean aphids as well as soybean rust. For the soybean aphid, note that the data presented on the map represents conditions observed in individual fields and does not represent conditions or a need for treatment in any other field. Growers should also remember that defoliating insects are making their presence known, including Japanese beetles and first generation adult bean leaf beetles. Remember that you do not want defoliation going over 15-20% of total leaf area.

ALFALFA – The main insect concern is to keep scouting for potato leafhoppers. In areas under moisture stress (most of the state), remember that the thresholds should be reduced. Under high leafhopper pressure, remember that leafhopper resistant alfalfa also needs watching.

Trapping for Western Corn Rootworm Variant in Soybeans

Authors: Ron Hammond, Curtis Young, Bruce Eisley

It is that time of year to begin monitoring soybean fields for the first year corn rootworm variant that lay their eggs in soybeans. This sampling is especially important in western Ohio because trap results from 2006 indicated a much higher number of adults than in previous years. Thus, it is critical for growers to determine the presence of these insects in 2007. Sampling is done by using Pherocon AM unbaited yellow sticky traps. Two sources of these traps are:

Great Lakes IPM
10220 Church Road
Vestaburg, MI 48891-9746
1-800-235-0285 .

PO Box 44993
Madison, WI 53744-4993
1-800-382-8473 .

Traps should be placed in the soybean fields this week. Growers should attach them to posts slightly above the soybean canopy (6-8”), placing 6 of them at least 100 feet from the field edge and randomly distributed in the field. The traps should not to be too close to an adjacent corn field. Twist tie wires are included with the traps; however we find it more convenient to use cable zip ties. The zip ties are thinner and faster to connect the traps to the posts. The traps should be changed each week for six weeks and a new trap put in its place just above the soybean canopy.

After you change the traps, count and record the number of rootworm beetles on each trap and the number of the days the traps were in the field. The number of beetles/trap/day is determined by adding the number of beetles found on the six traps and dividing that number by 6 and then dividing by the number of days the traps were in the field. Traps should be changed every 7 days if possible but if not be sure to record the exact number of days the traps were in the field.

Catches of 5 or more beetles/trap/day during any trapping week indicates a potential problem with rootworm in the field the following year. Last year, over a quarter of the fields sampled in western Ohio had densities over 5 beetles/trap/day. The management in such fields in 2008 can be to rotate to some crop other than corn, plant one of the Bt transgenic rootworm hybrids, use a soil insecticide, or apply a seed treatment. If you think that there is a potential for severe pressure from rootworm larvae next year, we would recommend not relying on seed treatments. Research has suggested that seed treatments do not provide sufficient protection under heavy rootworm pressure.

Ohio Drought Status

Authors: Jim Noel

Ohio was in a normal to wet regime from late summer 2006 through early spring of 2007. Then the rains shut off. There appears to be many factors driving this. First, the current minor drought formed in the Southeast last summer and autumn when the hurricane season did not materialize. This left that area with a lack of rainfall they typical get during the tropical season. Then came winter, El Nino had formed in the autumn and was expected to bring rain to the Southeast and Tennessee Valley regions. El Nino quickly faded away by January. The result was a dry Southeast into Tennessee Valley region. At the same time, the Ohio Valley was wet especially north of the Ohio River. As we got into the warm season, soil moisture began to play its role. It helped to build an upper level high pressure over the Southeast into the Tennessee Valley. As we went through May into June, this high built further north to combine with a northwest airflow aloft to reduce rainfall drastically over Ohio. It first affected southern Ohio and then spread to the north. In addition, mother nature is now bringing the surpluses of rainfall over the past year into balance, but over a shorter time span. The result has been the perfect storm to affect agriculture. The only impact from this minor drought has really been to agriculture at this point in the state of Ohio.

The question now is what will happen next? Since soil moisture plays its role during the warm season when evapotranspiration is critical, this pattern will likely last at least into August. Evapotranspiration accounts for anywhere from 20-30% up to 50% of rainfall during the warm season based on research and modeling studies. With a reduction in the top soil moisture this likely will result in less evapotranspiration from the corn crop as well. The net result is little change in the atmospheric pattern through August. The driest areas may shift around some though.

The good news is that this drought is mainly limited to agriculture and grass. The bad news is it is affecting agriculture. Long-term conditions remain in the normal category over the 6-12 month period over most of Ohio. However, short term of 90 days or less is much drier than normal. This is putting stress on agriculture, but not on reservoirs, rivers or streams.

Going forward, it will likely not be until the hurricane season and autumn cool season before the pattern can change. There is no clear weather signals now to indicate whether this pattern will persist into fall and beyond at this point. If it were, we would have to become more concerned about next year as subsoil moisture would also be impacted. However, at this point, we will have to wait and see.

We are currently doing research on the relationship between El Nino and La Nina to crops in Ohio. The results are interesting. The short summary indicates that corn and wheat are most impacted by El Nino and La Nina events. 92% of the time when a La Nina occurs, corn crop yields are below normal on average 13% below trend line. For El Nino events, 67% of the time corn crop yields are below normal on average 13% below trend line. During years with no El Nino or La Nina, yields averaged near trend line with the typical spread you would expect above and below the trend line. Results were similar for wheat while little impact was noted on soybeans though La Nina or El Nino events actually increased yields above trend line slightly.

Event Crop Percent of time Yield
    below avg yields Departure
La Nina Corn 92% -13%
El Nino Corn 67% -13%
Neutral Corn 50% 0%
La Nina Soybeans 46% -5%
El Nino Soybeans 42% 0%
Neutral Soybeans 49% -2%
La Nina Wheat 71% -10%
El Nino Wheat 75% -3%
Neutral Wheat 64% -10%


Field Crops Day on July 26

Authors: Alan Sundermeier

The public is invited to attend the Field Crops Day on Thursday, July 26, 2007 at the Northwest Agricultural Research Station. The event will begin at 9:00 am and is free, no registration required. Location at 4240 Range Line Road, 2 miles NE of Hoytville, Ohio in Wood County.

This year's topics include: Managing the Risks of Continuous Corn with Dr. Peter Thomison, OSU Extension Agronomist; Soybean Aphid and other Insect Issues Challenging Agriculture with Dr. Ron Hammond, OSU Extension Entomologist; Meeting the Nitrogen Needs of Wheat & Corn using Livestock Manure with Glen Arnold, OSU Extension Putnam County, and Benefits of Crop Rotation with Alan Sundermeier, OSU Extension Wood County.

Sponsored by Ohio Agriculture Research & Development Center along with Ohio State University Extension. Contact Matt Davis at 419-257-2060 for more information.

Farm Focus Field Day - Please Note Correct Date is July 24

Mark your calendars now to hold Tuesday, July 24th for the 2007 Farm Focus field day at the Marsh Foundation/Farm Focus research farm in Van Wert, Ohio. This years’ field day will include field demonstrations of GPS guidance and auto-steering technologies, as well as one pass tillage system implements. The field day will also include a workshop conducted by OSU entomologists, Ron Hammond and Bruce Eisley, on corn pests with special focus on corn rootworm. This event is hosted by the Farm Focus committee, Ohio State University Extension, and OARDC.

Registration begins at 8:00 a.m. at the site and is open to the public. There is no charge. Certified Crop Advisors will have an opportunity to sign up for continuing education credits of 1.0 hour in the area of Pest Management (PM) and 2.0 hours in the area of Crop Management (CM).

The field day is set up as a series of structured sessions in the morning so that visitors will have the opportunity to attend all the field demonstrations as well as the corn pests workshop. Lunch will be provided at no charge compliments of the financial sponsors for the field day. In the afternoon, there will be time for one on one visits with presenters/demonstrators.

The Marsh Foundation/Farm Focus site is located on the northeast edge on the town of Van Wert at the intersections of US 127 and Route 30 bypass. Just look for the bright orange signs which will take you right to the site. Don’t miss this great opportunity to learn about the latest in GPS technology and tillage equipment.

Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pierce Paul, and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Peter Thomison (Horticulture and Crop Sciences). Extension Educators: Roger Bender (Shelby), Howard Siegrist (Licking), Steve Prochaska (Crawford), Todd Mangen (Mercer), Harold Watters (Champaign), Greg LaBarge (Fulton), Ed Lentz (Seneca), Gary Wilson (Hancock), Alan Sundermeier (Wood), Mike Gastier (Huron), Jonah Johnson (Clark), Keith Diedrick (Wayne), Steve Ruhl (Morrow) Steve Foster (Darke), Glen Arnold (Putnam), Jim Lopshire (Paulding), Wesley Haun (Logan), Curtis Young (Allen), Gary Prill (Van Wert), and Jim Noel, Senior Hydrologist, National Weather Service, Wilmington.

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.