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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2012-12

Dates Covered: 
May 8, 2012 - May 14, 2012
Glen Arnold

Powdery Mildew and Septoria leaf blotch: This Year the Story is Different

Powdery mildew and Septoria leaf blotch are two of the most prevalent leaf diseases in the state of Ohio. Every year some level of both is observed on the lower leaves very early in the season, but rarely do these diseases ever reach the flag leaf early enough to cause yield loss. This is largely because in a “normal” year, mid-to-late-spring temperatures are too high for them to move up the plant. THIS YEAR IS DIFFERENT. With the development of the crop about two to three week ahead of what is considered to be normal for Ohio and temperatures consistently in the 60s and 70s, both diseases are developing rapidly, especially in field with high relative humidity and highly susceptible varieties. They thrive under mild, humid conditions, and Septoria even prefers rainy weather, which spreads spores throughout the field and up the plant.

On susceptible varieties, small white powdery pustules, typical symptoms of powdery mildew (Fig), are already on the flag leaf. Similarly, Septoria blotch is also being reported on the leaf below the flag leaf in fields where highly susceptible varieties are grown. These are our two most important leaves. We need to protect these leaves on susceptible varieties to ensure proper grain fill and high yields.

Plan to apply a fungicide to those fields with susceptible varieties because these are the fields most likely to sustain yield loss. One percent severity (percent leaf area affected, i.e., about 2-3 lesions or mildew pustules) on the second leaf down between growth stages 8 (flag leaf emergence) and 10 (boot) is the threshold level for applying a fungicide. Research has shown that if disease affects the upper two leaves by heading, yield losses can be as high as 25% on susceptible varieties. Scout fields by pulling about 50 individual tillers randomly from throughout the field and look for the small white pustules on the lower leaves and leaf sheaths. In the case of Septoria, look for dark, brownish lesions with grayish centers and black dots in the gray area.

Evaluate individual tillers by looking at the top (flag) leaf, then the second leaf. If the second leaf is already infected, the lower leaves would have a lot of mildew pustules and Septoria lesions on them. Fields that need a fungicide application will have lots of disease in the lower canopy, but these will only become an economic problem if the disease advances to the upper leaves before flowering. That is, within the next week to 10 days. Yield responses to fungicide application are generally dependent on the amount of disease on each plant, how early disease attacks the upper leaves and the level of susceptibility of the variety to the disease.

Remember, for foliar disease management (powdery mildew, Septoria, Stagonospora and Rust) fungicides are usually not needed when resistant varieties are grown. Also, remember that a fungicide applied at this growth stage (boot to heading), even though it is close to flowering will not provide adequate control of head scab. Visit the Ohio Field Crops disease website for an updated list of fungicides registered for wheat disease management

Ponding Effects on Corn and Soybeans

Rainfall was mixed across Ohio during the past week. Although some areas of NW Ohio missed any appreciable rainfall, some fields in central and SW Ohio received up to 4 and 5 inches of rain resulting in localized ponding and flooding of corn and soybean fields. If the ponding and flooding was of a limited duration, i.e. the water drained off quickly within a few hours, the injury resulting from the saturated soil conditions should be minimal.

CORN The extent to which ponding injures corn is determined by several factors including: (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Prior to the 6-leaf collar stage (as measured by visible leaf collars) or when the growing point is at or below the soil surface, corn can usually survive only 2 to 4 days of flooded conditions. Since most of the corn that’s been planted so far is not beyond the V2 stage, it’s especially vulnerable to damage from ponding and saturated soil conditions. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. If temperatures are warm during ponding (greater than 77 degrees F) plants may not survive 24-hours. Cooler temperatures prolong survival so the lower temperatures forecast for the next couple of days should be beneficial. Once the growing point is above the water level the likelihood for survival improves greatly.

Even if ponding doesn't kill plants outright, it may have a long term negative impact on crop performance. Excess moisture during the early vegetative stages retards corn root development. As a result, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. Ponding can also result in losses of nitrogen through denitrification and leaching. Even if water drains quickly, there is the possibility of surface crusts forming as the soil dries that can impact the emergence of recently planted crops. Growers should be prepared to rotary hoe to break up the crust to promote emergence.

For corn that’s emerged, check the color of the growing point to assess plant survival after ponding. It should be white to cream colored, while a darkening and/or softening usually precedes plant death. For corn not yet emerged, evaluate the appearance and integrity of seeds or seedlings that have yet to emerge (likely rotting if discolored and softening). Look for new leaf growth 3 to 5 days after water drains from the field.

Disease problems that become greater risks due to ponding and cool temperatures include pythium, corn smut, and crazy top. Fungicide seed treatments will help reduce stand loss, but the duration of protection is limited to about two weeks. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season.

SOYBEAN (the following is adapted from Palle Pedersen, former soybean extension specialist, Iowa State University) Water logging and poor aeration associated with localized floods and ponding can result in significant soybean yield reduction. The extent of ponding and flood damage to soybean is related to the temperature of the water, the amount of water motion and the duration of the flooding and ponding conditions. 

Soybean prefers adequate soil oxygen for maximum productivity. Oxygen content of water is much lower than air therefore saturated soils and flooding reduces the amount of oxygen available to the plant. Research has shown that oxygen concentration can be close to zero after 24 hours in flooded soil, depending on water movement. Without oxygen, the plant cannot perform important functions like respiration, an important function of plant growth. Soybeans can generally survive for 48 to 96 hours when completely submersed. The actual time frame is dependent upon air temperature, cloud cover, soil moisture conditions prior to flooding, and rate of soil drainage.

Temperatures influence the speed of respiration so high temperatures will be more detrimental to soybean recovery since the faster the respiration is “running” the faster the oxygen is depleted and the plants then start rotting. Cool, cloudy days and cool, clear nights increase the survival of a flooded soybean crop.

Research from Minnesota shows that flooding for 6 days or more may result in a significant yield loss or loss of the entire crop. With temperatures in the 80s, soybean plants may only survive a few days. Ohio researchers found that plants in flooded fields are injured from a buildup of toxins and carbon dioxide, which is up to 50 times higher in flooded soils than in non-flooded soils. They concluded that plants are more injured from the buildup of carbon dioxide than from lack of oxygen. During emergence, soybean fields subjected to flooding and saturated soil conditions are at major risk from Phytophthora and Pythium damping-off.


Nielsen, R.L. 2011. Effects of Flooding or Ponding on Young Corn. Corny News Network, Purdue Univ. [On-Line]. Available at:

Pedersen, P. 2008. Effect of flooding on emerged soybeans. Iowa State University Integrated Crop Management. [On-Line]. Available at:

Soybean Seedling Diseases – What to Look for in 2012

Soybean seed and seedlings are vulnerable to a number of soil borne pathogens in the early spring.  The conditions for these diseases have been quite variable this year in Ohio, with some areas very dry and cool while other locations have been warm and wet.

In previous years where we have seen alternating dry and wet conditions, Rhizoctonia is more prevalent than those diseases caused by water molds.  Rhizoctonia is probably there it just gets outcompeted by the watermolds.  Symptoms can range from no emergence to brick red colored lesions on the area of the stem just below the soil surface.  Those seedlings that survive will produce soybeans but fewer than those that are healthy. 

The watermolds, Phytophthora sojae and Pythium spp., may have a tougher time this year.  The water molds survive year-to-year as oospores in the soil.  To get these oospores to germinate and infect soybean seedlings, we typically need a 2-week incubation period where the soil is moist.  This year, in some areas of the state it has been dry prior to planting.  In addition, saturated soil conditions for 12 to 36 hours, is often needed for many of these to produce zoospores.  Symptoms caused by watermolds are light to dark brown, lesions on any part of the root or cotyledon. 

Other soil borne pathogens that can also infect soybean seedlings are Fusarium graminearum (the same fungus that causes head scab of wheat), Macrophomina (the charcoal rot fungus), and Fusarium virguliforme (Sudden death syndrome fungus).  Symptoms caused by these pathogens can range from pink to brick red to brown and dark brown lesions, very similar to those caused by Rhizoctonia and the water molds.  We are always happy to take a look at these plants collected from fields in Ohio.  So if you do have plants that are infected but not yet dead, please send them our way to Dorrance Lab; Dept. of Plant Pathology, OARDC, 1680 Madison Ave., Wooster, OH  44691.

For management of all of these seedling diseases, host resistance is one of the first strategies,  but there are also seed treatments.  If you have a stand issue, get the problem diagnosed correctly – sampling and recovering the pathogen is the only way to do this.  Next, look at the seed treatment package.  In Ohio, we have a great diversity of pathogens and a single active ingredient will not control all of the different pathogens – so some adjustments in materials will be required for that field in the future.

POST Corn Treatments with Residual Activity

As we mentioned several weeks ago, this may be a year where the benefits of including residual herbicides in POST corn treatments are substantial, even where herbicide were applied at planting. 

Corn planted several weeks ago still has a long way to go until crop canopy development, and we are really just starting into the period when most summer annual weeds emerge.  The addition of residual herbicides can be especially appropriate when the corn is less than 12 to 14 inches tall at the time of the POST treatment.  Residual herbicides are largely not needed in POST applications to corn that is getting close to canopy closure (20 inches or so), with the exception of burcucumber.  Scouting and making the decision before corn is 12 inches tall allows for the most options where residual herbicide is needed, since this is the cutoff for atrazine use.

A list of POST corn herbicide options, with a brief summary of their residual activity follows.  All of these herbicides have activity on emerged weeds as well (Table 4 in OH/IN Weed Control Guide), so that they can improve control and provide some resistance prevention when mixed with glyphosate or Ignite, or can replace these in some instances.

Atrazine – residual control of broadleaf weeds, and more limited control/suppression of grasses.  Also available as premixes with dicamba, which improves control of emerged broadleaf weeds.  Apply when corn is less than 12 inches tall.

Atrazine/acetamide premixes – residual control of grass and broadleaf weeds.  Where an atrazine product was applied at planting, keep in mind that the total amount of atrazine for the year cannot exceed 2.5 lbs ai/A.  Guardsman Max can be applied up to 12-inch corn; acetochlor/atrazine premixes can be applied up to 11-inch corn.

Callisto – residual control of broadleaf weeds.  Up to 30-inch or 8-leaf corn.   Callisto Xtra is a premix of Callisto and atrazine (up to 12-inch corn).

Capreno – residual control of grasses primarily.  Broadcast up to V6 corn.

Halex GT – residual control of grass and broadleaf weeds.  Up to 30-inch or 8-leaf corn.

Hornet – residual control of broadleaf weeds.  Broadcast up to 20-inch corn or 6 collars.

Resolve Q – residual control of grasses, lambsquarters, pigweed, and smartweed.  Broadcast up to 20-inch corn or 6 collars.

Spirit – residual control of some broadleaf weeds.  Broadcast up to 20-inch corn or 6 collars

Herbicides that have to be applied before corn is about V2 or 5 inches have been omitted here since that is really a delayed PRE application, where a comprehensive residual program is needed.  There are some fields that remain untreated with herbicide where corn has emerged but is still small.  Most of the PRE corn herbicide and herbicide premixes can be applied POST to small corn.  Check labels and the OH/IN Weed Control Guide for information on maximum corn size and use of adjuvants and tank-mix partners.

More on Sharpen tank-mixtures:

We heard from several manufacturers after last week’s article about Sharpen labels.  Here’s what we know at this point.  Sharpen cannot be mixed with any product containing flumioxazin, which includes Valor, Valor XLT, Envive, Enlite, and Gangster.  FMC indicates that labels allowing mixtures of Sharpen with FMC Authority products are still valid, and we assume that Sonic is included here.  Contact your dealer or manufacturer rep for more information.

Wheat Scab Update: 7 May 2012

Wheat continues to approach and advance through the critical flowering growth stage across the state of Ohio. Several fields are flowering in the southern third of the state, will begin to flower in central Ohio later this week, and in the northern third of the state within the next 7 to 10 days.

For wheat flowering early this week, the scab forecasting tool ( indicates that the risk for scab is low. This is probably because it has been fairly dry and cool over the last few weeks. The forecast is for scatted showers and possible thunderstorms tonight (Monday May, 7) and tomorrow, which favors scab, but temperatures are predicted to remain in the 60s and lower 70s for all of this week, with nighttime temperatures in the 40s. This will likely cause the risk of scab to continue being low over the next week or so, but keep checking the weather, the growth stage of your crop, and the scab prediction website to get a better estimate of the scab risk in your field.

These cool temperatures may mean low scab, extended grain fill, and consequently, high grain yield and quality. However, cool, humid conditions may also mean problems with other diseases such as powdery mildew and Septoria leaf blotch. These diseases have already been reported on the flag leaves in fields with susceptible varieties. Scout fields and plan to apply a fungicide if your variety is susceptible and lesions are already in the leaf below the flag leaf. However, remember that a fungicide applied before flowering will not provide adequate control of head scab if conditions do eventually become favorable.

Upcoming Weather Forecast


The period of March and April was warmer and drier than average overall, opposite of 2011. At the Ohio Grower Association meeting in January I presented that in many ways 2012 would be the opposite of 2011.

However, May has started out wetter. After a wet Monday and early Tuesday with widespread 0.5 to 1.0 inches and some totals of 2-3 inches, drier and more seasonable weather will return for the week of May 8 to May 13. Normal is about 70 and 50. After some rain Tuesday in the east and south it will be mainly dry until about Sunday or Monday.

The week of May 14-21 will return to warmer than normal with about normal rain of 0.5 to 1.25 inches.
Temperatures will be at least 3-5 degrees above normal.

Overall, May is shaping up to warmer than normal and a little wetter than normal now.

Summer is still on track with warmer than normal June going to normal or slightly cooler than normal August. Rainfall is likely a little drier than normal in June going to a little wetter by August.

Now is the Time to Calibrate Your Sprayer

Higher pesticide costs and new chemicals designed to be used in lower doses make accurate application more important than ever. There is no better time than early spring to take a closer look at your sprayer. Among the things to do is to find out if the sprayer is delivering the proper application rate (gallons per acre) you wish for your spraying situation.

One can determine if the chemicals are applied at the proper rate only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production. While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating ground water and environment. Results of "Sprayer Calibration Clinics" I participated in Ohio, and data from several other States show that only one out of three to four applicators are applying chemicals at a rate that is within 5 % (plus or minus) of their intended rate (an accuracy level recommended by USDA and EPA). Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration.

Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate. Over a decade ago, my colleagues at University of Nebraska conducted an interesting survey. The survey results revealed that there is a direct positive correlation between application accuracy and the frequency of calibration. Approximately 67 percent of the operators who calibrated before every spray operation had application errors below 5 percent. Only 5 percent of the applicators who calibrated their equipment less than once a year (once every two, three, four years) achieved the same degree of application accuracy.

How to Calibrate a Sprayer

Calibrating a boom sprayer is not as difficult as it sounds. It usually doesn’t take more than 30 minutes to calibrate a sprayer, and only three things are needed: a watch showing seconds, a measuring tape, and a jar graduated in ounces. A pocket calculator also will be handy. Usually the ultimate goal when calibrating a sprayer is to find out the actual application rate in gallons per acre. There are many methods to choose from to determine this, but one method that is the easiest, most practical, and requiring few calculations is described in OSU Extension publication on boom sprayer calibration. Here is the URL for this publication:

Calibration may require you change the travel speed and/or spray pressure, and replacing the nozzles with the right size if the changes in pressure and/or travel speed don’t bring the difference between the desired and actual application rate to within  plus or minus 5% of the desired application rate. You need to recalibrate the sprayer after any adjustment is made until the application error is within the allowable range of 5% of the desired rate.  Always keep in mind that changes in spray pressure will help you bring the application rate to what you want, but you may not be getting the size of droplets recommended for a given application. Higher spray pressures cause reduction in droplet size which may increase the risk of spray drift.

One final important point to consider: Getting the right amount of chemicals on the ground is not enough to achieve effective pest control. How the chemical is deposited on the spray target is as important as the amount deposited. Make sure that all nozzle tips are properly aligned. Some nozzles require overlapping adjacent spray patterns. Check the nozzle catalog to determine the overlap required for a given type of nozzle.

Protecting Honey Bees From Pesticides

Protecting Honey Bees From Pesticides.  Extension educators are already getting calls from beekeepers and growers about protecting honey bees from pesticide applications.  Technically, the best place to start is to read the Ohio Administrative Code  901:5-11-02 at

(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, 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.

In other words, anyone planning to make an application of a product that is labeled to be toxic to honey bees to a flowering crop which covers an area over a half acre in size must notify the beekeeper within 24 hours of the application.  However that beekeeper must have the apiary posted with contact information so that the applicator can notify him/her.  Ideally a sign should be posted by a road closest to the apiary stating that an apiary is in the area and contain contact information.  If the beekeeper has registered the location, the Ohio Department of Agriculture (ODA) will have the location on file.  Any grower/applicator can call ODA at 614-728-6373 and obtain a list of apiaries by location.  This file is sent electronically usually within 24 hours of the request.

Beekeepers can help themselves by registering new locations early in the season so that the locations are in ODA’s  data system.  They should also know who owns the properties near the apiary and remind them that the apiaries are nearby.

Ohio law requires that all apiaries are registered by June 1st.  This information is given to the pesticide applicators when they call ODA to obtain apiary locations.  Without the information on this form, the applicator does not know who to contact.  If the contact information is not known or if the location is not registered, the beekeeper has no recourse if the bees are affected by a pesticide application.

If a beekeeper suspects that their bees were affected by a pesticide, they should make the following steps:

1) Contact their County Apiary Inspector.

2) Take pictures of the hives and collect as much information as possible including when the colonies last appeared to be healthy; personality of the colonies (actively flying, signs of nosema,etc.) direction of the wind, crops growing (or to be planted) in fields nearby; present activity of hives; dead drones? Dead pupae being kicked out?...etc.

3) Collect 50-100 bees in or on the bottom board and freeze asap. Do not collect bees that have been lying on the ground as they deteriorate quickly.  Leave ~ 100 bees for ODA to collect.  They will not take bees that have already been collected.

4) Contact the Ohio Department of Agriculture at Reynoldsburg Ohio. – 614-728-6373.   An official will collect samples for testing.   Call them as soon as possible as it may take 24 hours before they can arrive.  They will try to determine the cause of the bees’ death.

Keep in mind that planting a treated seed is NOT considered to be a pesticide application.  The planter is planting a treated article.  The company which treated the seed made the pesticide application, not the grower. The rules discussed do not apply to this situation. 

ODA Apiary Website:

More information:


How to Reduce Bee Poisoning from Pesticides

Scout for Slugs Now

We are receiving numerous reports right now about slugs causing significant feeding injury requiring treatment with baits.  These reports are 2-4 weeks early compared with most years, and is a result of the warmer winter and March.   Slugs have attached out earlier than normal and have reached a size that causes noticeable feeding injury much sooner.  We had addressed this possibility in C.O.R.N. Issue 8, April 10, when we wrote: “Warmer weather and soil temperatures will be causing slugs to hatch earlier and will result in slugs beginning their heavier feeding earlier.  If planting times are normal, slugs will be a bigger and larger threat than normal.  If planting early, perhaps the slug feeding will be more similar to normal conditions.  If planting is late, slugs will be relatively larger and capable of even heavier feeding. “   

Corn and soybean present two different concerns.   With corn’s growing point being below the soil for a few weeks, most of the feeding above ground will be to growing leaves that will be replaced, and not on the growing tip that would kill the plant.  Because of continued growth of corn that will probably occur, there is some leeway in terms of the time required to make the treatment if needed.  But keep in mind that the corn is still relatively much smaller than when feeding normally would be occurring, and thus, presenting a much more serious situation.   

However, the growing point of soybeans is between the cotelydons as they emerge from the soil.  Thus, the slug is easily able to reach and feed on both the cotelydons along with that growing point, making it much easier for slugs to kill the soybean plant as it emerges from the soil.  This fact makes immediate treatment of soybeans perhaps more critical if no leaves have yet emerged and expanded.

For growers who have experienced slug issues in the past, it is critical that fields be scouted NOW.  If plants have emerged and have leaves, look for the telltale signs of leaf feeding.  But for soybeans not yet or just now emerging, or yet to be planted, care should be taken to determine if slugs are present and lying in wait.   This latter situation could require a bait application just prior to emergence. Use your own past experiences with soybean stand reductions caused by slugs to determine whether an early treatment should be made this year. 

The two available baits are those containing metaldehyde (Deadline MPs and others), and those with iron phosphate (Sluggo).  See our slug fact sheet for more information:



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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.