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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2012-17

Dates Covered: 
June 11, 2012 - June 19, 2012
Harold Watters

June Weather Update

The overall trend remains in place. Slightly above normal temperatures and below normal rainfall is the trend that looks to  dominate our overall pattern for the next several weeks.

Except for some rainfall early this week, little or no rainfall is forecast this week. Most places will receive 0.25 to 0.50 inches or less from the early week rains. Temperatures will retreat to below normal for a couple of days around mid-week then return to above normal late in the week into the weekend.

The other headline is the low dewpoints and relative humidity that will grip Ohio for the middle and end of this week creating a huge draw on soil moisture far more than you would expect with temperatures in the low 80s. Relative humidity for middle to late this week will drop to 25-35% with dewpoints dropping into the 40s!

Next week will be more of the same with below normal rainfall and temperatures only slightly above normal with only scattered rains at best.

Temperatures may trend to normal in late June and early July with the below normal rainfall continuing.

Effects of early season dry weather on corn ear formation

Many corn fields across Ohio are experiencing exceptionally dry conditions. Rain early this week will bring some relief but forecasts call for more dry weather later. Moisture stress during the early-mid vegetative stages of corn development is atypical in Ohio. Based on observations made at the end of last week, most corn across the state ranged from about V5 (the five leaf collar stage) to V10 or slightly beyond. Ear formation is probably well underway in fields at the more advanced stages of development. However, as early as the V4/V5 stage, ear shoot initiation is completed and the tassel is initiated on the top of the growing point.  During the rapid phase of corn vegetative growth (which generally starts by V7), ear yield components are being determined. Kernel row numbers per ear are generally established by about V7.

Will the recent moisture stress impact ear formation and yield potential? It takes fairly severe stress conditions during the early vegetative growth stages to impact kernel row numbers per ear. Kernel row numbers are usually less affected by environmental conditions than by genetic background. Therefore, in most cornfields, it’s unlikely that kernel row numbers have been impacted significantly by recent dry conditions. However, unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions. Determination of kernels per row (ear length) is not usually complete until V12 to V15. Severe drought stress during the two weeks prior to pollination can reduce kernels per row and lead to a reduction in grain yield.

Iowa research by Claassen and Shaw on effects of drought on grain yields in corn is widely used in assessing the potential impact of water stress on yield potential. According to this Iowa research, drought stress during early vegetative growth usually has a negligible impact on grain yield. Some corn agronomists contend that mild drought during June may even be beneficial because roots generally grow downward more strongly as surface soils dry, and the crop benefits from the greater amount of sunlight that accompanies dry weather. However, during later vegetative stages, when kernel numbers per ear are determined, plants become more sensitive to stress. According to Claassen and Shaw's findings, 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.


Claassen, M.M., and R.H. Shaw. 1970. Water deficit effects on corn. II. Grain components. Agron. J. 62:652-655.

Nielsen, R.L. 2012. Hot & Dry; More of the Same Not Good for Corn Yield. Corny News Network, Purdue Univ. [URL accessed June 11 2012]. 

Hail damage to corn should be limited

Hail damage to corn should be limited

Last week we received reports of hail storms that damaged corn fields in northwest Ohio.  The impact of hail damage is largely dependent on the corn crop's stage of development. 

Hail affects yield primarily by reducing stands and defoliating plants. Most of the hail damage results from defoliation. Generally, the corn plant is little affected by hail prior to the 6 to 7 leaf stage because the growing point is at or below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to internode elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage with the tassel stage/pollen shedding stage (VT) being the most critical period.

Severe hail damage prior to the 6 to 7-leaf stage can also result in “twisted” or “tied” leaf whorls as injured plants recover and new leaves try to unroll; however, most plants usually grow out of this problem and tied whorls seldom cause major yield loss.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs, if damage occurs prior to tasseling. For this reason, estimates of hail damage should be delayed several days to allow for this period of re-growth.

The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V7 plant according to the leaf collar method would probably correspond to a 9-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Corn growth stages will vary considerably depending on location, planting date, etc.. Moreover, there is also variability in growth within fields because of uneven emergence and development. The growth stages of the corn reported damaged by hail storms in NW Ohio last week were at about V5 or earlier when injury occurred (Fig. 1). Based on estimates of the National Crop Insurance Association (Table 1), at the 7-leaf stage (or about V5), if 50% of the leaf tissue is destroyed by hail, a corn plant loses about 2% of its grain yield potential; if 100% defoliation occurs, a corn plant loses about 9% of its yield potential.

For more detailed information on evaluating hail injury in corn, consult "Assessing Hail Damage to Corn" National Corn Handbook Chapter 1 (NCH-1)." Available on-line at

(verified 6/11/12)


Table 1. Percent yield loss in corn based on growth stage & defoliation

(adapted from NCIA Corn Loss Instructions, rev. 1984)



Percent Leaf Defoliation

Growth Stage*





7-leaf (V5)**





8-leaf (V6)





9-leaf (V7)





11-leaf (V9)





13-leaf (V11)





15-leaf (V13)















*as determined using the hail adjustor’s leaf staging method; ** approximate leaf collar stage within parentheses.

Corn Response to Sidedress Nitrogen

Dry weather in many parts of the state may affect recent applications of sidedress nitrogen. In addition, the growth stage of the corn crop at the time of application is a factor in nitrogen utilization. Many fields in the dry areas are in the V6 stage and the establishment of nodal roots has been slow because of the hot and dry conditions in the top couple inches of the soil.

Fertilizer nitrogen either exists in the nitrate or ammonium form. The plant may utilize either form but the nitrate forms moves with water and ammonium form must be in close contact with roots for uptake. Since sidedress occurs in the middle of the row, either nitrate moves with the water being taken up by the roots or roots have to grow into the area of the nitrogen deposition. Under dry conditions movement of nitrogen by water is limited and root growth is restricted. Until a significant rain event (at least a ½ inch rain), sidedress nitrogen may be not utilized by the crop.

During extended dry periods producers may see some advantage to anhydrous ammonia versus UAN-28%. The vapor movement of the anhydrous will expand into a greater area between the rows where the 28% band will have to wait for rain to move more into the soil profile. As a result, roots may reach the anhydrous band sooner than the UAN band. This generally occurs in years that short supply of rain reduces yield potential.

Corn that has received starter nitrogen may also look better under dry conditions. The first three to four weeks of the crop, the seed generally provides adequate nourishment until the nodal root system takes over around the V5 to V6 growth stage. At this time the nodal roots should be established enough to draw nutrients from the soil. Plants that have starter will be able to reach nitrogen sooner, which becomes important when weather events, such as dry weather, reduce nodal root development.

The use of foliar fertilizers will not be adequate to correct limited nitrogen uptake from dry soil conditions and would be considered a poor input choice. Even under good conditions, university research has shown little benefit to foliar fertilizer applications in Ohio.

Western Bean Cutworm Flight Begins in Ohio

Western Bean Cutworm Flight Begins in Ohio

Last week, OSU Extension Educators in a few counties reported catching western bean cutworm moths in pheromone traps (see updated map under the corn tab at our Agronomic Crops Insects webpage,  Historically, WBC flights did not occur until the 3rd week of June, so, like most other insects this year, we are seeing moths about 1-2 weeks earlier than usual.  As we continue to warm over the next few weeks, our counts will increase and scouting for eggs should begin. 

We anticipate peak flight to be the 1st or 2nd week of July.  Corn that was late planted, including areas of re-planting, will be the priority for scouting, but all corn that remains un-tasseled will likely need scouting until past peak WBC flight. We will have weekly updated counts and maps in the CORN newsletter and our website.  For now, make sure your traps are out, but beware of WBC imitators.  We have had abnormally high catches of yellow striped armyworm (see figure and comparison to WBC at our webpage:  These are not the true armyworms that are causing problems in Ohio wheat and pastures, and are not known to cause significant damage to crops in Ohio.  However, they may cause confusion for proper WBC identification.

Twospotted Spider Mites on Soybeans

Twospotted Spider Mites on Soybeans

This past week we had our first report of twospotted spider mite showing up on soybeans in western OH, as well as similar reports of mites on soybeans in Iowa.  Obviously the warm and dry weather in the state as well as the Midwest has caused spider mites to start showing up on the crop.  Although not causing economic injury yet, if hot and dry weather continues, the likelihood of a mite problem will become greater as the weeks pass.  

Spider mites infestations can first be noticed by yellow stippling on the upper surface of the leaves.  The mites themselves can be identified by examining the critters that will be on the underside of the leaves with a good hand lens.  Please keep us informed via your extension educators on any developing mite populations you come across.  At this time of year, mite infestations might be found not only on field edges, but also throughout the field.  The earlier you recognize mite infestations, the quicker you can deal with them prior to economic losses.  We will further address this concern as it becomes more warranted.  For now, go to for the most recent information on how to identify twospotted spider mites on soybeans, including treatment guidelines. 


Considerations for Double-Crop Soybeans

Ohio wheat harvest may occur several weeks earlier than most years providing the opportunity to double-crop soybeans across the state. Timely rains will determine the success of double-crop soybeans but a producer may increase the probability of success by following several management practices.

Double-crop soybeans should only be planted if the seed zone has adequate moisture for germination and emergence. Soybean seed planted into dry soil will not germinate until adequate rainfall. By waiting to plant until adequate moisture or high probability of significant rainfall, a producer has time to decide whether the planting date is still early enough to expect optimal growth and yield potential.

Even with adequate moisture at planting, the success of double-crop soybeans is heavily dependent upon rainfall in August and late July. Moisture should be conserved by planting without tillage.

Straw should be removed so that is does not interfere with soybean planting.  No more than 12 inches of wheat stubble should be left to provide mulch cover for the soybean crop. Excess straw should be baled or chopped and spread evenly on the field.

Double-crop soybeans will have a shorter vegetative period before flowering is initiated since day lengths will begin to shorten after the summer solstice. To compensate for less vegetative growth a producer should consider variety selection, row width and seeding rate to maximize yield potential.

·      Early maturing varieties should be avoided for optimum yield. In the northern half of the state, Group 3.0 to 3.4 should be adequate and maturity group 3.4 to 3.8 for the southern half.

·      Narrow rows are a must for optimal yields in double-crop situations.

·      Seeding rate should be increased to 4 seeds/foot row in 7 inch row spacing.

Herbicides selected and rates of application used for weed control in double-crop soybeans should kill the weeds present at planting and provide residual control. Additional fertilizer should not be needed, including foliar, if a build up/maintenance program (such as the University Tri-state recommendations) have been followed for the wheat crop and soil pH is below 6.8.

Rainfall will determine the success of double-crop soybeans. By selecting the right maturity group, seeding rate and row width double-crop soybeans may add to a producer’s profits with timely rains.

Agronomic Crops Calendar

Western Agronomy Field Day

Date: 7/18/2012

Time:   9AM - 3PM

Location: 7721 South Charleston Pike, South Charleston, OH 45368, Western Agricultural Research Station, 7721 South Charleston Pike, South Charleston, Ohio 45368

Pre-registration required, lunch included - $20 per person payable at event

To register contact Harold Watters, OSU Extension,  or 937 292-4159 or Joe Davlin, Western ARS Manager, or 937 462-8016


Field Crops Day - Northwest

Date: 7/26/2012

Location:Northwest Agricultural Research Station, 4240 Range Line Road, Custar, OH 43511

More Info: Contact:Matt Davis 419-257-2060


Check the Agronomic Crops Team Calendar for more information as we get closer to both field events:



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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.