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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2009-21

Dates Covered: 
July 7, 2009 - July 14, 2009
Howard J. Siegrist

Yellow Soybeans - What To Do

Authors: Edwin Lentz, Keith Diedrick, Robert Mullen

Reports are beginning to surface about yellow soybeans in north central Ohio (and other isolated spots as well), and the question is what to do about it. Foliar manganese is being promoted in some areas as the reason for the chlorotic beans, but this may not be the solution to the condition.

Prior to a decision being made about what to do one should first confirm the cause of the yellow condition. Manganese can be the culprit on some of the acreage, but it is unlikely the cause over a wide geographic area. Potassium deficiencies are also quite prevalent this year most likely due to the potash price last fall, so on some of that acreage potassium may be the reason for yellow soybeans. Some fields may be experiencing some level of moisture stress (either too much or too little) depending upon where the fields are. Soybean cyst nematode may also be the cause of poor-looking soybeans.

Visual symptoms can be a first indicator as to what is likely occurring. Manganese deficiency will occur on the newer/upper leaves and appear as an interveinal chlorosis. Manganese deficiency is most typical on soils that have a relatively high pH (>7) and soils that have high organic matter levels (peats/mucks). Drought stressed soils can also have low manganese available and subsequent manganese stress. Potassium deficiency appears on either lower or upper leaves (depending upon growth rate) as a yellowing that begins at the leaf tip that progresses to the leaf base along the edge of the leaf. Potassium stress is more likely on soils with low K availability (revealed through soil test) or fields that are drought stressed. Water stressed soybeans appear generally chlorotic and slow growing. Soybeans affected by SCN can appear similar to potassium deficiency. The take home message here is that visual assessment can help with diagnosis, but it alone is unlikely to isolate the underlying cause.

Tissue sampling, soil sampling, and root digs are the next step in diagnosing what is occurring in your field. When sampling soybeans sample the uppermost, fully-expanded trifoliate and remove the petioles (small stem that connects the trifoliate to the main stem). Tissue analysis can confirm whether or not a nutrient deficiency is being encountered. If the problem is not widespread across the field (which they typically are not), collect samples from an unaffected area and an affected area. Collect at least 15 samples per area. Additionally, soil test information can also be extremely helpful, so collect corresponding soil samples as well.

If a foliar manganese application is warranted, some producers may just add it to the glyphosate application in Roundup Ready soybeans. Most glyphosate products are compatible with foliar manganese, but to reduce the instances of antagonism or lessened weed control, pick a chelated manganese product, use the full 17# of spray-grade ammonium sulfate per 100 gallons of spray solution, and use labeled rates of the glyphosate product appropriate to the weed size (consider separate applications of glyphosate and manganese if the weeds are large). Finally, the mixing order of the products should be water first, ammonium sulfate next, chelated manganese third, and the glyphosate product last. As always, refer to the specific product labels for guidance.

Remember, every field is different and the underlying cause for poor soybeans is also different. Applying manganese to a field that is not manganese deficient only decreases economic profit of that specific field, true of any nutrient that is non-limiting. Plant sampling, soil sampling, and root digging may seem like a considerable inconvenience, but the amount of many you may potentially save will be worth it.

Weather Update

Authors: Jim Noel

Last week we saw below normal temperatures and precipitation.

This week we will see a trend from near normal temperatures early in the week to above normal late in the week. Rainfall will be rather isolated through Friday with most places seeing very little. The best chance would be in the west and north.

A more organized cold front will be some rainfall this weekend.

Next week we will see a little more active pattern with scattered showers and storms every few days and temperatures will relax to near normal.

The week of July 20th will trend back to below normal temperatures and below normal rainfall.

Overall, the rest of July will average slightly below normal temperatures and slightly below normal rainfall.

Note: Our computer models suggest below normal temperatures and normal to above normal rainfall but the trend is your friend and our conceptual models in a west to northwest airflow does not support as much rainfall.

Also, with El Nino developing, the trend toward warmer and drier conditions this fall and winter remain in tact. The question now is the drier regime developing now or will it wait until early autumn. We will get answers in the next week or two as our computer models are fairly wet. If those rains do not occur, it would suggest the trend is happening now.

Early Planted Corn Is Tasseling

Authors: Peter Thomison

During the past week, tassels began appearing in corn fields that were planted in late April and early May. Corn planted in late May and early-mid June will probably not be tasselling until early to mid August. 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. Much of the state’s corn looks good now. However, there is concern about the availability of adequate soil moisture when corn begins pollination in areas that have received little or no rainfall during the past three weeks. Moderate temperatures have help minimize effects of lack of moisture. So far, reports of visible drought stress (leaf rolling) have been limited to fields with sandy soils or shallow soils over gravel.

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%. Keep in mind that 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. Fields with scattered plants exhibiting some leaf rolling late in the afternoon are probably not experiencing severe stress.

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. 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.

Dr. Bob Nielsen, the corn extension specialist at Purdue University, has written excellent articles on the flowering stages of pollen shed and silk emergence that contain good images of the pollination process. They’re available online at -

Nielsen, R.L. 2007. Tassel Emergence and Pollen Shed. Corny News Network, Purdue Univ. [On-Line]. Available at .(URL verified 7/6/09).

Nielsen, R.L. 2007. Silk Emergence. Corny News Network, Purdue Univ. [On-Line]. Available at .(URL verified 7/6/09).

Interest In Foliar Fungicide Application Increases As Corn Begins To Tassel

Authors: Dennis Mills, Pierce Paul

Corn is beginning to tassel in some parts of Ohio and tasseling will likely continue during the first three weeks of July. Field surveys and reports coming in from across the state suggest that foliar disease pressure is extremely low at this time, even in continuous-corn fields. This is not surprising given that it has been fairly dry and cool over the last two weeks or so. Remember, disease development depends heavily on the weather, as well as the susceptibility of the hybrid planted and the availability of spores. Most of the foliar diseases of economic importance in Ohio develop best under warm, wet, humid conditions and tend to be more of a concern when susceptible hybrids are planted into or next to no-till corn fields. Warm, humid conditions are required for spore production in crop residue, and rainfall and wind for spore dissemination from the residue to the lower leaves of the plant. High humidity favors rapid spore germination and infection of the leaves and may lead to severe blighting if warm, humid weather persists. Scout fields over the next few weeks (between 15-leaf to tasseling/silk emergence) for foliar diseases to determine how much disease is present. Lesions on the leaves below the ear leaf should be used as guide for fungicide application, especially on susceptible hybrids.

Although foliar disease pressure is very low at this time, some growers are still interested in applying a foliar fungicide to their corn with the hope of increasing yields. Results from fungicide trials conducted in 2006, 2007 and 2008 show very similar trials in terms of yield response across the state and across the Corn Belt. Corn hybrid yield response to foliar fungicides continues to be highly variable and unpredictable. In 2008, several corn fungicide trials were conducted at four locations in Ohio (Western Research Station, near South Charleston; the Northwest Research Station, near Hoytville; the Snyder Farm, Wooster, and the ATI Research Farm in Apple Creek), providing us with a total of 20 trials for disease and yield comparisons. At each location, multiple hybrids with different levels of resistance to gray leaf spot and yield potential were planted, allowing us to evaluate hybrid corn yield response to fungicides for a combination disease pressure, weather, and hybrid scenarios. With the exception of one of the trials conducted at Snyder Farm, all trials were planted no-till or reduced-till into fields previously planted with corn.

In all trials, foliar fungicides were applied between tassel and silk emergence (VT – R1) at label-recommended rates, using high-clearance spray equipment calibrated to deliver approximately 20 GPA. At the time of fungicide application, only trace amounts of foliar disease were observed on the lower leaves (well below the recommended fungicide application threshold), and disease levels remained low through the growing season at all locations. Gray leaf spot and common rust were observed towards the end of the season, especially at South Charleston and Apple Creek. Averaged across the ear leaf and the two leaves below the ear, gray leaf spot severity at the R4 growth stage (dough) in untreated plots of the most susceptible hybrid was 2.9% and 5%, at South Charleston and Apple Creek, respectively, and less than 2% at Wooster and Hoytville.

Yields in the untreated checks ranged from 73.6 to 177.96 bu/A, with an average of 109.8 bu/A, whereas in fungicide-treated plots, yields ranged from 68.19 to 188.49 bu/A, with an average of 109.55 bu/A. In 12 of the 20 trials, treated plots had numerically higher yields than the checks, however, the yield difference varied considerable from trial to trial. Yield differences between treated and untreated plots (treated minus untreated) ranged from -16.70 to 10.53 bu/A across all 20 trials, with an average difference of -0.28 bu/A. Similar fungicide trials were conducted by university researchers across the Corn Belt, with similar results. Depending on the fungicide, average yield differences between treated and non-treated were between -1.2 and 4 bu/A when foliar disease severity was less than 5% and between 1.6 and 10 bu/A when severity was greater than 5%.

How Long Have We Had These Problem Weeds?

Authors: Tom Jordan

We sometime think that just when we eliminate one weed in a field, another one comes along and takes its place. Well that is how nature works. But, have you ever wondered where “new” weeds come from once you solved a weed problem or why when you change tillage practices, you get a different population of weeds? My theory is that we have seen a few new weeds enter the state in the past 100 or so years, but if the new weed is not a grass like Johnsongrass, it probably is not a weed that will majorly impact crops. While many weeds have moved into the state with early settlers or were dropped off of wagons and railroad cars, many of the more problem species are native to the area. A few examples of weeds that were transported into the state as it was being settled are velvetleaf, prickly lettuce, kochia, and Johnsongrass.

Many of the weeds that dominated the state in the past, or the ones that we presently have in fields today, are a result of tillage practices, crop rotations, and weed management programs. In earlier days, prior to tractor-powered deep tillage, corn was usually grown about every third year with small grains and a forage legume crop produced in between. Tillage was shallow, and in the years of small grains and forages there was no postemergence tillage in those crops. Records show that the predominate weeds in Indiana from 1888 – 1929 were primarily crabgrass, a group of annual broadleaf weeds, a few biennials, and some shallow rooted simple perennials (Table 1). More people worried about wild garlic than about Canada thistle. As tractor powered equipment increased, people begin to moldboard plow and go to more monoculture crops like corn, or later a corn soybean rotation. With these practice changes, we began to see a different set of weed problems including annual broadleaf weeds and deep-rooted creeping perennials. Crabgrass was still the dominate grass (Table 2).

In the 1950’s and 60’s both fertilizer and herbicide use increased. This is when we began to see giant foxtail overtake crabgrass as the predominate grass species, and also see the pigweeds, Jimsonweed, and lambsquarter species appear in crops. As herbicide selection allowed us to go to reduced or no-till, a strange thing happened (Table 3). All of those weeds that were present in fields back in the early days (Table 1) begin to reappear. However, we still managed to keep the weeds we had in the tillage years (Table 2). By reducing tillage, those weeds that do not fare well under aggressive tillage were able to survive well under no-tillage. Since those weeds were not the major weed problems present in fields when herbicides were introduced after the early 1950’s, there was little resistance selection pressure on them. Many of the broadleaf weeds that were present during the herbicide years began to show high degrees of tolerance or resistance to herbicides. We have always had our set of major problem weeds. We have just shifted them around with tillage and herbicide use.

Table 1. Major Weed Problems 1888 – 1929
Prickly lettuce Broadleaf plaintain
Daisy fleabane Wild carrot
Buffalobur Mustard species
Horsenettle Downy brome
Cocklebur Crabgrass
Canada thistle Wild garlic

Table 2. Major Weed Problems 1929 – 1950
Cocklebur Bindweed species
Jimsonweed Canada thistle
Velvetleaf Morningglories
Quackgrass Common Milkweed
Johnsongrass Crabgrass
Table 3. Major Weed Problems in No-till
Prickly lettuce Morningglories
Canada thistle Foxtail species
Daisy fleabane Marestail
Horsenettle Common Ragweed
Wild carrot Giant ragweed
Crabgrass Pigweed species
Mustard species Common milkweed
Bindweed species

Cereal Leaf Beetle In Corn

Authors: Bruce Eisley, Andy Michel, Ron Hammond

As mentioned in earlier articles in this newsletter, cereal leaf beetle was a concern this past spring on wheat and oats. Most of that damage was by larvae of the beetle, which was then followed by larval pupation and then more recently, adult emergence. These adults will be the overwintering stage that start populations next year. However, before these adults go into a type of hibernation for the remainder of the summer and then winter, they will feed on available crops, most notable corn. This feeding is often heaviest along the edges, especially in those fields that are across the road or adjacent to wheat or oat fields where the population had built up. This feeding is superficial unless the injury is extremely heavy,. Recommendations for treatment are only when feeding is greater than 50% over the entire plant, the corn is under stress, and beetle populations are extremely large. Because this seldom happens, nothing should usually be done. The feeding will end shortly.

Potential Twospotted Spider Mite In Soybean

Authors: Bruce Eisley, Andy Michel, Ron Hammond

Reports are coming in about areas of Ohio that are beginning to get very dry, and crops that are starting to show moisture stress. If low rainfall conditions continue, we will enter a period where two-spotted spider mites begin to develop on soybean and cause significant injury. We would recommend that growers begin to scout soybeans in dry and crop-stressed areas for beginning mite populations. The best way to scout at this time is to walk fields, especially field edges at this time, for the presence of yellow stippling on top of leaves that suggests mite feeding. Pictures of this injury are available on our new Agronomic Crops Insects web site, . The photos can be seen by going into images under the soybean section. Upon seeding the stippling, turn the leaves over to search for the presence of mites. We will keep growers updated on the situation with mites throughout the summer. If mites are found in your area, please contact us or your county extension educator.

Archive Issue Contributors: 

State Specialists: Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Peter Thomison (Horticulture and Crop Sciences), Robert Mullen and Keith Diedrick (Soil Fertility), and Jim Noel (NOAA). Extension Educators and Associates: Glen Arnold (Putnam), Roger Bender (Shelby), Bruce Clevenger (Defiance), Tim Fine (Miami), Greg LaBarge (Fulton), Ed Lentz (Seneca), Les Ober (Geauga), Steve Prochaska (Crawford), Howard Siegrist (Licking), Alan Sundermeier (Wood), Suzanne Mills-Wasniak (Montgomery), and Harold Watters (Champaign).

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.