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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-25

Dates Covered: 
August 4, 2008 - August 10, 2008
Andy Kleinschmidt

Scouting for Rust by Land and by Air

Authors: Anne Dorrance, Kiersten Wise, Don Hershman

As of today no soybean rust pustules have been found in the Midwest, including Ohio, Illinois, Indiana, Kentucky, and Missouri.

As most of you know, soybean leaves are collected from sentinel plots established throughout the state on a weekly basis and sent to laboratories where they are closely examined for soybean rust. In addition to the sentinel plots, there are numerous spore traps monitored regularly for spores of the soybean rust fungus (Phakopsora pachyrhizae) throughout the US. This year, we are primarily monitoring rain traps in a joint project with the United Soybean Board and USDA-ARS. Each year that these traps have been monitored (2005-2007), they have been positive for spores during June, July and August. This pattern has continued for 2008.

Spores of the soybean rust fungus are killed by UV radiation (sunlight) and by dessication. These are just two of the many research findings over the past few years. Thus, it is highly likely that for most of the spore finds to date, the spores are dead by the time they reach the spore trap, hundreds of miles from the original source. The lack of documented soybean rust in numerous northern states that have had frequent rust spore finds over the past three years is evidence for this statement. Unfortunately, current methodology can only detect the presence of spores, but cannot test for viability. In addition, the spore finds have been light. Thus, if infections did occur it would be in the range of one pustule on one leaf in 10 acres. At this rate, it would take until late September to find the one plant that had the infection.

We have also had a lot of rain this year, especially during June and early July. However, in many areas the “faucet” turned off until recently (or it is still dry), making it very unfavorable for rust development. If any infections were associated with any of the spores finds this years, unfavorable conditions would delay development.

When spore traps indicate that spores of the rust fungus are found, we intensify soybean rust field monitoring efforts. To this end, requests have gone out to the Ohio, Kentucky and Indiana soybean rust sentinel networks to increase the number of soybean leaves collected in sentinel plots, and to increase mobile scouting efforts in areas that have even the slightest chance that favorable weather conditions may have resulted in soybean rust infections.

At this time we are not recommending fungicide applications be made for soybean rust management. If we do find soybean rust this week, it will still not be at the level that requires immediate treatment. This is one of huge difference between Brazil and the Midwest. Our initial levels of soybean rust spores are very, very low compared to Brazil. This gives us extra time to apply fungicides, if they are indeed they needed at all. For April planted soybeans in Ohio and Indiana (May-planted in Kentucky), that are at R5 – these are “out of the woods”. However, we are continuing to monitor fields for soybean rust since later planted soybeans are still at some risk.

If soybean rust infection is suspected in any field, we request that samples be forwarded immediately to the State Extension Specialist for diagnosis. Official confirmation of soybean rust can only be made at the state level, and crop insurance claims cannot be processed without accurate diagnosis. Note: Ohio still has not recorded its first find and must meet APHIS requirements for a new invasive pathogen. If soybean rust is confirmed in a location, extension personnel and CCA’s throughout the state will be notified, and the most current information and management recommendations will be posted on the USDA National Soybean Rust website:

Soybean Aphid Update for Ohio

Authors: Bruce Eisley, Andy Michel, Ron Hammond

We still are finding few soybean aphids in Ohio. However, neighboring states are reporting having received a flight of winged aphids, most likely from states to the northwest including Minnesota and Wisconsin. We would expect that Ohio has also received them. Also, states in the northwestern Corn Belt (northern Iowa, Minnesota, the Dakotas, etc) are reporting economic populations that are requiring insecticide treatment. Thus, growers in Ohio should continue to scout, remembering that the threshold for treatment remains an average of 250 aphids per plant. Do not let your guard down until we get well into August and soybean pod-filling growth stages.

Growers in northern Ohio who have made “insurance” sprays (see article on spraying insecticides on soybeans) should pay extra attention to those fields over the coming weeks. With winged soybean aphids perhaps arriving in these fields, there is a chance, because of having killed all the beneficial, that a relatively small number of aphids will build up to economic levels. Apparently some other states are seeing already seeing this happening. (This is one of the reasons we do NOT recommend insurance spraying).

Twospotted Spider Mite on Soybean

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Although most of Ohio had good soil moisture through early summer, many areas of the state are becoming very dry, with little rainfall in the forecast. During sampling last week in some of these dry areas, we have become aware of the presence of the twospotted spider mites along edges of some fields. Although mites should not become widespread problems, growers in dry areas might want to check their fields for possible mite infestations, especially around the field edges. Although we would not expect whole field infestations, growers should nevertheless also check areas within their fields.

If mites begin to build up in fields, growers have a few choices in materials to spray which will do an adequate job in control: chlorpyrifos (Lorsban and various other formulations), dimethoate, and two of the new materials discussed last week in this C.O.R.N. newsletter, Hero which contains 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.

Spraying Insecticides on Soybeans and Honey Bees

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Although soybean aphids remain at low levels in Ohio, we are aware that many growers are adding insecticides to spray tanks when applying fungicides for plant health purposes and even late applications of herbicides because: “Well, I’m going over the field anyway so I thought I’d add an insecticide for insurance purposes! The insecticide is relatively cheap and soybeans are worth so much!” As we have always stated, we do NOT recommend this practice, and feel an IPM approach is much better for everyone and everything, including the environment. We do NOT recommend an insecticide application unless there is a REAL need.

However, we realize that this is being done. What we need to address is an extremely important and related issue, and that is the need for growers and custom applicators to protect bees when spraying insecticides on soybeans (or any crop or insect pest for that matter). The need to do this is present whether the insecticide is being sprayed for an actual pest, or when being sprayed for “insurance purposes”! Remember that most insecticides have a caution statement on their label about spraying around bees and blooming crops. The typical statement is: “This product is highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops or weeds if bees are actively visiting the treatment area”.

The Ohio Department of Agriculture addresses this concern under Regulatory Divisions & Programs, Plant Industry Division, Pesticide Regulations, Law and Statues, Plant Industry 901:5.

901:5-11-02 restrictions

(B) No person shall:

(15) Apply or cause to be applied any pesticide that is required to carry a special warning on its label indicating that it is toxic to honey bees, over an area of one-half acre or more in which the crop-plant is in flower unless the owner or caretaker of any apiary located within one-half mile of the treatment site has been notified by the person no less than twenty-four hours in advance of the intended treatment; provided the apiary is registered and identified as required by section 909.02 of the Revised Code of Ohio (, and that the apiary has been posted with the name and telephone number of the owner or responsible caretaker.

(16) Apply pesticides which are hazardous to honey bees at times when pollinating insects are actively working in the target area; however, application of calyx sprays on fruits and other similar applications may be made.

We continue to advise that growers and applicators maintain good communications with bee keepers near their fields to prevent and limit unintended problems. A listing of registered apiaries can be obtained from the Ohio Department of Agriculture. The website is The list can be requested via e-mail to the address

Below are some specific recommendations for environmental and pesticide factors that will lessen the potential for injury to bees.

1) Drift of pesticide not only can injury non-target plants but bees or other insects located within the canopy of non-target plants. Follow all precautions related to drift such as wind speed, direction identifying risk potential of neighboring crops. Recently we have seen more fields with filter strips or other conservation areas along borders. Plants in these border areas may be in bloom and harboring foraging bees. Drift or spray overlay has the potential to cause injury to bees and should be considered in pesticide applications.

2) Timing of application can limit bee injury. Applications in the evening or early morning are generally best. Bees are less active at these times of the day. Other times when the blooms are less attractive and lower bee activity are acceptable as well.

3) Formulations of pesticides will make an impact on toxicity. Dust and wettable powders are more toxic than emulsifiable concentrates. Ultra low volume applications versus a regular application are generally more toxic. No repellents can be added to tank mixes that will keep bees away from treated areas.

4) Toxicity of pesticides can differ. Most pesticide have been tested with bees in laboratory settings. Keep in mind there can be differences in field results versus laboratory results due to environmental factors as well as the sensitivity difference in populations of bees.

Evidence of Drought and Heat Stress Appearing in Corn Fields

Authors: Peter Thomison

One of the corn production scenarios we least like (because it often results in below average grain yields) is an exceptionally wet spring followed by a hotter and drier than normal July and August. June 2008 was one the wettest on records in many parts of the state and July was one of the driest in many areas). Unfortunately as the dry weather that started in July persists, such a scenario seems to be a possibility. A combination of high temperatures and inadequate rainfall is beginning to stress corn fields across Ohio. What’s exacerbating this problem are the marginal roots evident in some corn fields. Although I didn’t receive widespread reports of “rootless and floppy corn” this year, I have noticed late planted corn "leaning" and upon examining roots of such plants, have observed small very shallow root systems (especially given the large size of plants). Several factors, including poor planting conditions, shallow planting depths, sidewall compaction and/or excessively wet soil conditions in June have inhibited good root development in many fields. With the onset of drier, warmer conditions in July, these limited root systems have been unable to extract water deeper in the soil profile. Cooler weather and the possibility of storms later in the week may ease drought stress, which is important because many late planted corn fields (planted after June 1) are just entering the pollination period, the stage of development most susceptible to drought. Other fields past pollination are vulnerable to kernel abortion which drought conditions increase.

To estimate the impact of dry hot weather on corn yield potential, let's review the effects of moisture deficits on corn growth and development from the late vegetative stages, prior to pollination, to the dent stage of kernel development. Yield losses to moisture stress can be directly related to the number of days that the crop shows stress symptoms during different growth periods. The following summarizes findings of Iowa research by Claassen and Shaw on effects of drought on grain yields in corn. This Iowa data is widely used in estimating the potential impact of water stress on yield potential.

Vegetative Stages: Although most of Ohio’s corn crop is either pollinating or past pollination, much of the corn planted the first week of June or later is still vegetative. During the 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 5-10 percent. Kernel row numbers on the ear are determined by the 12th collared leaf stage and the potential number of kernels per row is complete about one week before silking.

Tassel Emergence: As the tip of the tassel begins to emerge from the whorl, the upper stalk internodes rapidly elongate and the ears begin to expand. Silks from the base of the ears are also rapidly elongating. Four days of moisture stress at this stage has the potential to reduce yields 10 to 25%.

Silk Emergence to Pollen Shed: At this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. This is the most critical period in terms of moisture use by the plant. Four days of moisture stress at this stage has the potential to reduce yields 40 to 50%.

Blister Through Dent Stage of Kernel Development: About 12 to 36 days after silking, the cobs, husks and shanks are fully developed and the kernels are increasing in dry weight. Moisture stress will reduce kernel fill from the ear tip down. Four days of drought at the blister stage has the potential of reducing yields 30-40%, and at dough stage, 20 to 30%.

Where early season conditions contributed to corn stands with uneven emergence and development, yield losses may be higher depending on various factors such as the length of emergence delays and the percentage and distribution of later emerging plants. Where there is considerable variability in plant size, smaller, stunted plants will be at a competitive disadvantage with larger plants for nutrients, water and sunlight.

Wheat Fungicide Seed Treatment

Authors: Dennis Mills, Pierce Paul

Seed treatments can play an important role in achieving uniform seedling emergence and giving seedlings a good head start under certain conditions. The selective use of seed treatments can protect seeds or seedlings from early-season diseases. Fungicides are available to protect seed and seedlings from many seed-borne or soil-borne pathogens. Seed treatments are most beneficial for seeds infected prior to planting or when cool, wet soil conditions, which delay germination, exist at planting. Seed treatments should not be considered a cure-all for the selection of poor seed lots. Seed treatments will not increase the germination of poor quality seeds – seeds with excessive mechanical damage, seeds stored under poor conditions, genetic differences in variety, or other damage.

Extensive research has shown that seed treatments can increase stands from poor quality seed or when planting conditions are less than optimum. However, seed treatments do not always increase yield. Generally, seed treatments result in increased yield by preventing infection of seedlings by soil borne pathogens which results in frequent skips within crop rows. Grain producers should realize that any one seed treatment will not control all pathogens that may attack seeds and seedlings. Protection is also short lived, generally only lasting as long as it takes for the crop to emerge. Before selecting a seed treatment it is essential for the grower to consider potential problems associated with the seed and the history of problems associated with each field.

It is highly recommended that winter wheat seeds be treated for control of several seed-borne diseases, including loose smut, common bunt, Stagonospora glume blotch and scab. The systemic fungicides Dividend XL and Raxil - Thiram, Raxil XT, and Raxil MD have excellent activity against both loose smut and common bunt at low usage rates (a.i./ cwt). Dividend XL is effective in controlling seed-borne Stagonospora, but it is more effective against seed-borne scab at the higher rate (1.0 fl. oz./cwt) than at the lower rate (0.5 fl. oz./cwt). Products containing Raxil used at the labeled rates are effective against seed-borne Stagonospora and have relatively good activity against seed-borne scab.

Most seed treatment products are combinations of fungicides to provide broad spectrum protection. In years when head scab is severe, or in seed lots with high Fusarium infection, try to avoid planting seeds harvested from scabby fields or from lots infected with head scab. However, if scabby seeds are used for planting, a companion seed treatment fungicide is recommended. LSP Flowable Fungicide contains TBZ (thiabendazole) and provides good control of seed-borne scab. During wet fall weather soil-borne Pythium damping off can cause loss of stands when seeds are planted into cold, wet soils. Dividend XL contains Apron XL (mefenoxam) and Raxil XT and Raxil MD contain Allegiance (metalaxyl) to help prevent seed rot and damping off caused by Pythium. Apron XL, Apron FL and Allegiance are highly specific and only control Pythium damping off, therefore they should never be used alone on wheat.

A table showing the relative efficacy of fungicide seed treatments for management of certain diseases of wheat in Ohio is available at:

Assessing the Success of Pollination in Corn

Authors: Peter Thomison

Many corn growers want to know what impact recent dry weather 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. Although it’s rare, when such delays in silking are lengthy, varying degrees of barrenness will result.

Others may want to determine the impact of silk clipping by corn rootworm beetles and Japanese beetles on pollination. According to corn entomologists, damage by silk clipping insects is usually limited unless the silks are being continuously clipped back to less than 1/2 inch long before pollination is 50 percent complete

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.

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 this problem; it’s available online at (verified 8-4-08)

Cover Crops and Nitrogen – Can I Capture Some Nitrogen for Next Spring?

Authors: Robert Mullen

Nitrogen prices are an issue on most producers’ minds these days. It appears as if the higher prices are going to be with us for a while and you may be thinking of alternative methods of supplementing nitrogen for corn. One possibility is growing a cover crop after your wheat this summer and allowing it to grow into next spring. The question is what kind of nitrogen value might you expect?

Ohio State University has established field trials the last couple of years to help answer this question. Experimental plots have been at OARDC’s Northwest, Western, and Wooster locations. At the Northwest Research Station in 2007 we did not observe any nitrogen contribution from red clover interseeded into wheat for a subsequent corn crop. We did, however, observe a rotational benefit of 18 bu/acre when red clover was established compared to no cover crop. At the Western Research Station in 2007, we did not observe a rotational benefit associated with the establishment of red clover after wheat harvest nor did we observe a nitrogen contribution. From a separate study at the Western Research Station in 2007, we did see what appeared to be a rotational benefit from field pea established in late September, but we did not see similar results for soybeans, early planted field peas (late August), or annual ryegrass. We did not observe a nitrogen contribution from any of the cover crops. At a fourth trial conducted at the Wooster research location, we did not observe a nitrogen contribution or rotational benefit with annual ryegrass seeded after wheat harvest.

Take home message – based upon last year’s findings we cannot definitively identify a nitrogen contribution from the establishment of any cover crop after wheat prior to corn. We did see some rotational benefits (2 out of 4 locations) with legumes, but at the two sites were non-legumes were evaluated we observed no corn yield benefit. There are some research publications from other areas of the U.S. that show nitrogen contributions from legume cover crops, but our research does not corroborate those findings. Establishment of cover crops solely for the purpose of supplementing nitrogen should be approached with caution. Legume cover crops have a greater probability of supplementing some nitrogen (not based on our research, but others have reported this) than non-legumes, but it is not a sure thing. Additionally, establishment of the cover crop is not a guarantee either. The earlier the crop is established the greater the chance of good growth prior to the onset of winter.

OSU Weed Science Field Day: Management of Giant Ragweed with Resistance to Glyphosate and ALS Inhibitors

Authors: Mark Loux

OSU weed scientists will host a field day on August 14 at our research site near Clarksburg, where we have been determining methods for managing a giant ragweed population with multiple herbicide resistance, to glyphosate and ALS inhibitors. The tour will start at 1 pm with a brief discussion of herbicide resistance, followed by a walk through our research plots in Roundup Ready and Liberty Link soybeans. The plot is located on Clarksburg Pike, about 0.5 miles west of the intersection of Clarksburg Pike and State Route 207. Traveling west from this intersection, the plots are in the first corn field on the north side of the road. There is no charge for this event. Contact Mark Loux for more information – (614) 292-9081 or

Western Ohio Agronomy Field Day

The Ohio State University Extension, and Stillwater Watershed and A.C.E. (Agriculture for a Clean Environment) groups are co-sponsoring the Western Ohio Agronomy Field Day on August 13, 2008. The field day will start at 5:30 p.m. and will be held at the Darke County Research Farm located at 5105 County Home Rd. Greenville, Ohio (the farm is located at the southwest corner of St. Rt. 127 and St. Rt. 49, just south of the Darke County Jail). Participants must register prior to August 11th by calling the OSU Extension Office at 937 548-5215 or email: . Pesticide applicator credits will be given for Core, Category 1 (Grain & Cereal Crops) and Category 2 (Forages).

Topics of discussion will include:
• Crop Insect Up-date, presenter, Dr. Ron Hammond, IPM and Entomology Specialist, OSU Extension.
• 2007 Soil Fertility Issues, presenter, Robert Mullen, Soil Scientist, Ohio State University.
• Soil Grid Sample Project, Harvestland Co-op Representative.
• Weed Control Up-date, presenter, Harold Watters, OSU Extension Educator.
• New Corn Technology and Refuge Requirements, Matt Davis, CCA, Pioneer Seed Account Manager.
• 2007 Pesticide Application Issues, Steve Foster, CCA, OSU Extension Educator.
• Field Tours: Low Linolenic Soybean Production Comparison Test Plot, Roundup Ready Alfalfa Demonstration Plot, First Year Corn Rootworm Study, Western Bean Cutworm Study, Soybean Rust Sentinel Plot.

This educational program is open to the public. CCA credits for Certified Crop Advisers and Pesticide Applicator credits (core, categories 1 and 2) will also be provided. For more information contact the Darke County OSU Extension office at (937) 548-5215 or email .

Weather Update

Authors: Jim Noel

The trend toward drier weather continues.

This week: Expect some showers and storms especially the middle part of the week. After a burst of heat temperatures will relax again later in the week.

August: Overall, near normal temperatures with a trend now toward below normal rainfall is underway. Some places will see normal rainfall but the trend now is toward slightly below normal rainfall for August.

La Nina has ended and we will watch to see if an El Nino develops later this year or in early 2009. This could impact our rain patterns longer term.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux (Weed Science), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Robert Mullen (Soil Fertility) and James Noel (NOAA/NWS/OHRFC). Extension Associates and Educators: Gary Wilson (Hancock), Harold Watters (Champaign), Glen Arnold (Putnam), Howard Siegrist (Licking), Mark Koenig (Sandusky), Ed Lentz (Seneca), Mike Gastier (Huron), Jonah Johnson (Clark), Mark Koenig (Sandusky/Ottawa), Steve Foster (Darke), Alan Sundermeier (Wood), Marissa Mullett (Coshocton), Tim Fine (Miami), Les Ober (Geauga), Suzanne Mills-Wasniak (Montgomery), and Todd Mangen (Mercer).

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.