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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-12

Dates Covered: 
May 5, 2008 - May 12, 2008
Todd Mangen

Diagnosing Emergence Problems in Corn

Authors: Peter Thomison, Pierce Paul, Ron Hammond

In some Ohio counties, corn planting is nearly complete and corn is emerging, whereas in others, little or no corn has been planted due to persistent rain and cool soil conditions.

Diagnosing emergence problems early is critical in identifying solutions and developing successful replant plans, if needed. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.
(some of this information has been adapted from a newsletter article by Dr. Greg Roth, my counterpart at Penn State).

- No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.

- Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.

- Seed with poorly developed radicle (root) or coleoptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor. Although corn has just started to emerge or has not yet emerged, growers should carefully inspect seedlings for symptoms of disease. This is especially true in lower lying areas of fields where ponding and saturated soils were more likely. Seeds and seedlings that are brown in color, are soft and fall apart easily while digging are obviously dead or dying. Seeds and seedling roots or shoots that have a weft of white to pinkish mold growing on them are likely victims of fungal attack and will likely die. Pythium and Fusarium are common fungi that attack plants and cause these damping-off or seedling blight symptoms under wet, cool conditions. It is more difficult to diagnose disease damage on plants that also show abnormal growth caused by cold soil conditions or by crusting of the soil surface. However, dark, discolored roots and crowns, instead of a healthy creamish-white appearance, are typical symptoms of seedling diseases problems. So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet.

- Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.

- Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.

- Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.

- Uneven emergence. May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.

Note patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.

Don’t forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). This was widely observed in many fields in 2005 when corn planted in mid April did not emerge until the first or second week of May. As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential can be reduced.

Slugs and Field Crops

Authors: Ron Hammond, Andy Michel, Bruce Eisley

We are now getting into the time of spring when scouting for slugs should begin. Egg hatch is starting in southern OH and will slowly move northwards. Corn and soybean growers who have had problems with slugs in the past should sample their fields over the next few weeks, checking numerous spots in their fields for eggs and juvenile slugs. Slug eggs are usually laid in batches of 3-5 and are found just at or slightly below the soil surface. Growers should move crop residue aside in an area about a foot square, and scrape the soil with a small knife or other instrument.

Nitrogen Accumulation by Annual Grass Weeds in Corn

Authors: Mark Loux

The following article was written by Bill Johnson and Glenn Nice, weed scientists at Purdue University. It appeared in the May 2, 2008 issue of the Purdue Pest and Crop Newsletter, and is reprinted here with minor modifications. A few additional relevant comments by Mark Loux can be found at the end of the article.

It is anticipated that adoption of Roundup Ready and Liberty Link corn will continue to proceed at a fairly rapid pace over the next couple of years in the eastern cornbelt. We have observed many growers making adjustments to their weed control programs, including reduced use of soil-applied acetamide-atrazine premixes, and increased reliance on postemergence applications of glyphosate in Roundup Ready corn or glufosinate (Liberty/Ignite) in Liberty Link corn. So, we are moving from a system which was largely devoid of early-season weed pressure to a system where early-season weed infestations will be common. These infestations will require broad-spectrum postemergence herbicide treatments to obtain effective control and protect against yield loss from weed interference. It is important to understand that weeds are just like crop plants in the sense that they utilize soil nutrients to grow and reproduce. What is not well understood is the extent of nitrogen utilization by weeds, and its effect on crop yields. Over the past several years, several graduate students at Purdue University working under my (Johnson’s) direction have conducted research on nitrogen accumulation by weeds in corn and the impact of this on corn yield. This research will be summarized in several articles in this and future newsletters.

The subject of this article is our research on annual grass weed interference and nitrogen accumulation in no-till, Roundup Ready corn. The objective of this project was to determine the interactive effects of grass weed interference and side-dress N applications on corn and weed growth, N content, and corn yield. The experiment was conducted under no-till conditions in 1999 and 2000 on a silt loam soil with 2.5% organic matter. Preemergence herbicides were applied to control only broadleaf weeds, and grass weeds were allowed to emerge with the corn. The grass weeds present in this study were giant foxtail, barnyardgrass, and large crabgrass, at a combined population density of approximately 30 plants per square foot. Ammonium nitrate fertilizer was surface-applied at 100 lb N/A just prior to planting. We utilized a relatively low or “threshold” rate of nitrogen in an attempt to ensure that we could measure the effects of N accumulation by grass weeds on corn growth and yield.

The grass weeds emerged at about the same time or slightly later than the corn, and were controlled with glyphosate when they were either 3, 6, 9, or 12 inches tall. After the grass weeds were controlled at the specific timings, the plots were kept weed-free for the remainder of the growing season. To determine if side-dress nitrogen could be utilized to overcome the effects of early-season grass weed competition, these weed removal timing treatments were duplicated. In the duplicate set of plots, an additional 40 lbs of N/A was applied when corn was 2 feet tall. Corn and grass weed tissue samples and soil samples (2 feet deep) were collected from weedy and weed-free plots at each application timing and at corn harvest. Plant samples were analyzed for total Kjeldahl N, and soil samples were analyzed for nitrate and ammonium content.

The results showed that grass weeds accumulate a substantial amount of nitrogen on a per area basis. At the 3-inch removal timing, the corn and grass weeds contained similar amounts of N on a per area basis. By the time grass weeds were 12 inches tall, they had accumulated 50 to 63 lbs of N per acre in 1999, and 16 to 32 lbs of N in 2000. This amounted to about three times more N compared with the amount accumulated by corn in 1999, when the grass weeds emerged with the corn. It represented about half as much N compared with N in corn in 2000, when corn emerged about 10 days before the weeds emerged.

The main effect of weed removal height on corn yield was similar in both years. Corn yield and N content of corn biomass were similar to the weed-free control when weeds were 6 inches or less at the time of removal. When weeds were removed at a size of 9 inches or taller, corn yield was reduced and corn accumulated less N compared with corn in weed-free controls. Where weed interference reduced yield, subsequent application of side-dress N resulted in recovery of corn yield in 2000 when adequate late season precipitation was available, but had no effect on corn yield in 1999 when late-season precipitation was limited.

In summary, when grass weeds (a density of 30 plants per square foot in this study) emerge at the same time as corn, they should be controlled before reaching 6 inches in height to prevent them from accumulating excessive amounts of N and reducing crop yield. Surface-applied ammonium nitrate as a side-dress treatment was effective in overcoming the competitive effects of early-season weed interference in corn in a year with adequate late-season precipitation, but was not effective in a dry year. The best opportunity for utilizing side-dress N to recover yield due to early-season weed interference probably involves injection of the N into the soil after postemergence herbicides are applied. This will help ensure that a minimal amount of N is tied up by microbes, as they decompose the weed biomass on the soil surface.


To minimize the influence of grass weeds on N accumulation and corn yield, use residual herbicides in Roundup Ready, glyphosate-resistant, or Liberty Link corn. Many of these can be applied to emerged corn, so if you have already planted, you can still apply residual herbicides by themselves or in a mixture with glyphosate or Liberty. Always check the label or with your retailer or sales rep to see which residual herbicides can be applied to emerged corn, especially when mixing with postemergence herbicides.


Hellwig, K. B., W. G. Johnson, and P. C. Scharf. 2002. Grass
weed interference and nitrogen accumulation in no-tillage corn (Zea mays L.). Weed Sci. 50:757-762.

Additional comments by Mark Loux:
The Purdue research showed that corn could tolerate grass weeds without yield loss as long as the grasses were removed with postemergence herbicides before they exceeded 6 inches in height. It’s important to recognize that, although the results of this study are valid, it was conducted at only two site-years (one location over two years). Previous research that was conducted over a broader range of environments (total of 34 site-years) showed that corn yield was reduced by an average of 6% when weeds (grass and broadleaf mixtures) were removed at a height of six inches. In that research, which was conducted in the absence of preemergence herbicides, maximum yield was obtained when weeds were less than 4 inches tall at the time of postemergence herbicide application. Use of residual herbicides at planting greatly reduces initial weed populations, and delays emergence of late-emerging weeds, which results in postemergence situations where weeds are less likely to reach a height of 6 inches. Use of residual herbicides thus largely prevents weed interference and substantial accumulation of N by weeds. Where residual herbicides were not applied at planting, be sure to apply postemergence herbicides when weeds are no more than 3 inches tall, and include residual herbicides to prevent later season weed infestations and N loss.

Wheat Scab Risk Prediction 2008

Authors: Dennis Mills, Pierce Paul

The 2008 wheat scab risk prediction tool is up and running, and is again available for use in 24 states. As fungicides with some effect on suppressing scab (Caramba, Proline and Proline+Folicur tank mix) become available for use in Ohio, the use of this tool will become very important to help guide application decisions. For foliar disease management, the presence of lesions on the lower leaves often is used as an indication of the risk of foliar diseases spreading up the plant and application decisions are based on the presence of lesions on the flag leaf and the leaf below the flag leaf. For head scab management, however, fungicide decisions must be made well before visual symptoms are seen on the heads, so disease thresholds cannot be used as indicators of scab risk. In fact, by the time scab symptoms are observed, it is too late to apply a fungicide - grain DON content may already be high and all fungicides will be off label.

Head scab develops best when wet, humid conditions occur shortly before and during flowering. So, the web-based scab risk tool uses weather data (temperature, relative humidity and rainfall) from the seven day period prior to flowering to assess the risk of a scab epidemic (> 10% severity) developing. In addition to risk predictions based on actual weather conditions (the default risk map), the risk tool also provides predictions based on forecast weather. Information from weather forecasts is used to generate risk maps that estimate risk 24 and 48 hours ahead of time. The risk model is 80% accurate; however, the level of accuracy may vary from one field to next depending on the uniformity of the flowering date (among other things). Hence, it is important for producers to correctly identify the flowering date in their fields. In fact, since flowering may last for several days in any given field (depending on the weather), it is important to use multiple flowering dates, five to seven consecutive days, to estimate the overall risk in your fields. Walk fields and observe the heads of multiple tillers from multiple locations for fresh anthers hanging out of the florets. Remember, spent, dried up anthers may still be seen hanging from wheat heads well after flowering.

To aid in the assessment of scab risk, we will provide commentaries at the bottom of the risk maps. As the wheat growing season progresses, commentaries will be updated regularly to inform Ohio producers of the risk of scab occurring as weather conditions change and as we summarize data collected from across the state. These comments will help users assess the risk of scab in the state based on the color patterns displayed on the risk map. The commentary will also provide information regarding observations of crop growth, weather patterns and other diseases of importance in Ohio.

More Fungicides Registered for The Suppression of Head Scab in Wheat

Authors: Dennis Mills, Pierce Paul

Last spring Proline (prothioconazole) from Bayer CropScience received a section 3 federal registration for use in wheat for head scab and foliar disease management on wheat. Now, Caramba (metconazole) from BASF and Folicur (tebuconazole) from Bayer CropScience also received section 3 federal registration for use in wheat. In terms of efficacy against head scab and vomitoxin, Proline, Caramba and a tank mix of Proline + Folicur are very comparable. Data from studies conducted across the US show that on average Proline + Folicur, Caramba, and Proline alone, when sprayed at flowering (Feeke’s 10.5.1), had about 50% reduction in scab and about 42% reduction in DON when compared to the untreated check. Proline is recommended at rates between 4.3 – 5.7 fl. oz/Acre, Caramba between 14 – 17 fl. oz/Acre, and the tank mix of Folicur + Proline at 3 fl. oz/Acre of each product (commonly referred to as Proline 3+3).

For scab suppression, the best results were achieved when these products were applied at flowering (Feeke’s 10.5.1), forward and backward mounted nozzles were used to achieve maximum coverage of the heads, and when the products were applied to moderately resistant wheat varieties. With the hope of controlling as many diseases as possible with a single fungicide application, producers may be tempted to apply these products as early as boot (Feeke’s 10). However, for head scab management, treatments applied at Feeke’s 10 are much less effective than those applied at Feeke’s 10.5.1. It should be noted that even when applied at the correct growth stage none of these products will provide complete scab control, especially if prolonged periods of wet conditions occur during and after flowering. The term here is SUPPRESSION. What producers can expect is a reduction of head scab and vomitoxin, but NOT a total 100% control.

For foliar disease management, fungicide recommendations are based on visual disease thresholds. However, for head scab and vomitoxin management, applications must be made well before visual symptoms are seen on the heads. The scab prediction website ( should be used as a guide to assess the risk of scab occurring and to help determine whether or not a fungicide should be applied. As the wheat crop approaches flowering, the prediction tool will be updated frequently with commentary regarding the risk of head scab occurring to help growers make decisions regarding fungicide use.

These new additions bring the list of fungicides currently labeled for use by Ohio wheat producers to nine. The others are Tilt (Syngenta) and PropiMax (Dow AgroSciences) containing propiconazole (triazole type chemistry); Headline (BASF) and Quadris (Syngenta) containing strobilurin type chemistry (the active ingredient in Headline is pyraclostrobin and azoxystrobin is the active ingredient in Quadris); and Stratego (Bayer) and Quilt both containing a combination of a triazole and a strobilurin (propiconazole and trifloxystrobin in stratego and propiconazole and azoxystrobin in Quilt). Currently, all of these materials are labeled for application through Feekes Growth Stage 10.5 (full head emergence) for foliar disease control (read product label for more details).

All nine of these fungicides are very good materials; however they have slightly different activity against the various fungal foliar diseases found in Ohio wheat fields. Tilt and PropiMax at 4.0 fl oz/A and Quilt at 14 fl. oz/A have excellent activity against powdery mildew, Stagonospora blotch and leaf rust. Headline (9 fl oz/A), Quadris (6.2 to 10.8 fl oz/A) and Stratego (10 fl oz/A) are relatively less effective against powdery mildew, but more effective against leaf rust. Proline (4.3 to 5.7 fl oz/A), is very similar to the others in terms of efficacy against Stagonospora and leaf rust, and current trials will determine how effective it is against powdery mildew. Therefore, if you are targeting powdery mildew then choose Tilt, PropiMax or Quilt and if you are targeting leaf rust choose Headline or Quadris. Any of these fungicides would be adequate for the other diseases or disease combinations when applied at the appropriate time. For instance, if a strobilurin is applied alone after infection has occurred, efficacy may be greatly reduced.

Remember, for foliar disease management (powdery mildew, Septoria, Stagonospora and Rust) fungicides are usually not needed when resistant varieties are grown. However, for head scab, under highly favorable conditions, the best results are seen when fungicides are applied to resistant varieties as part of an integrated management strategy.

Weather Update

Authors: Jim Noel

The weather pattern change in early April has yielded 50-100% of normal rainfall for most of the state the last 30 days. Most areas had 2-3.5 inches of rain with 3-4 inches being normal.

The far north has been the wettest. However, soils have been so wet from the last 6 months that even though we have had good drying, even light rains make the soil moisten up quickly.

It appears we will have a pause from the drier than average pattern for the short term of the next 1-2 weeks with the probability of 1-2 inches of rain ranging from 70% south to 90% north. As is the case anytime, isolated streaks will be higher and lower than this. It appears the far north and northwest and possibly the far south have the greatest chance of this heavy rain. The systems will cross the area every few days.

The western cornbelt out towards Iowa, Wisconsin, southern Minnesota and northwest Illinois have been much much wetter than here and are being impacted even more.

It appears the wettest areas will remain west of Ohio the next few weeks.

Research shows most of the time trend line adjusted corn crop yields are below average in La Nina years with a less chance for wheat and more likely average or above average yields on soybeans. We will have to see how this year lines up with research.

The data still supports a trend to drier than average for late May and June but it does looks like at least average rain the next 2 weeks with small areas of above average rainfall mainly in the north.

The weather computer models have a low confidence level so the verification of this wetter pattern the next 2 weeks is still not a guarantee.

A new device to check accuracy of sprayer pressure gauges available now

Authors: Erdal Ozkan

There are many things that affect the end result (efficacy) from a pesticide application. The most obvious ones are: careful scouting (knowing exactly what the problem is); selecting the best pesticide to take care of the problem; applying the right amount of pesticide per acre uniformly on the target; keeping as much of the pesticide applied as possible in the intended area of application; weather conditions during the application; and timing of application.

Other than the weather conditions, you can control all the other factors mentioned above. So, how do we achieve conditions that help us keep the pesticide applied in the application area with maximum deposit on the target? The answer is in the size of the droplets. In general, smaller droplets are more effective, especially for insecticide and fungicide applications. However, small droplets are highly susceptible to spray drift, increasing the risk of losing them. Nozzles not only help us achieve a precise flow rate and the desired spray pattern, they also are a key factor in droplet size.

Pressure gauges on sprayers are there for one reason: measure the actual pressure. They are important accessories of a spraying system because pressure affects both the amount of liquid being sprayed and droplet size. A malfunctioning pressure gauge may result in over or under application of pesticides, and significant changes in droplet size.

Increasing pressure causes an increase in the number of small droplets, and in the flow rate. Decreasing pressure does the opposite, increasing of droplet size and reducing flow rate. For instance, increasing the pressure by a factor of 4 doubles the flow rate.

To accurately regulate spray pressure, it first has to be measured. Use a pressure gauge with a range at least twice the expected operating pressure. A pulsation damper protects and increases the life of a pressure gauge and smoothes pressure pulsations which makes reading the gauge much easier.

There is usually a pressure drop in the spray line between where the pressure regulator valve is located and the nozzles. Therefore, pressure gauges should be located as close to the nozzles as possible, and the pressures at the nozzles should be checked at least once to determine the magnitude of the pressure drop.

Having an accurate pressure gauge is essential to proper calibration of a sprayer. Therefore, compare the readings from your pressure gauge periodically with the readings from another calibrated gauge. Dr. H. Zhu and his co-workers at The Application Technology Research Unit of USDA-Agricultural Research Service in Wooster, Ohio have developed a portable device that can be used to check the accuracy of pressure gauges on sprayers. The device is a revised version of a light weight Model T-621 hydraulic pressure pump from AMETEK Measurement & Calibration Technologies. (Contact 727-536-7831 for details on the Model T-621.)

The testing unit consists of a hand pump, a factory calibrated gauge, a small water reservoir, and a port for the gauge that is to be tested. To check the accuracy of the pressure gauge you have on the sprayer, remove it from the sprayer and screw it onto the port on the side of the tester. Then squeeze the handle, and read the pressure on both gauges. If the pressure readings are the same your gauge is in good condition. If not, replace the bad pressure gauge with one that is accurate to maintain the droplet size and the flow rate desired.

Getting the most out of pesticides depends on many factors. Pressure is only one of these factors, but an important one. For the lack of a good $40 pressure gauge, you could lose thousands of dollars because of lower crop yields. And drift related litigations could reach hundreds of thousands of dollars. I suggest you avoid this risk, and check your pressure gauges now.

New Rules for Getting Around at Farm Science Review

Authors: Chuck Gamble

Be sure to bring your walking shoes for Ohio State University’s Farm Science Review, Sept. 16-18 at the Molly Caren Agricultural Center in London, Ohio.

Beginning this year, visitors to Ohio’s premiere agricultural event may notice a decrease in the number of motorized vehicles on the Farm Science Review grounds. Show organizers have prohibited the use of all types of vehicles, except for golf carts, electric scooters and units compliant with Americans with Disabilities Act (ADA).

The new regulations are part of the organizers’ efforts to promote safety and respond to the growing number of vehicles being used in the exhibit area, at the Gwynne Conservation area and in the demonstration fields.

“For every golf cart rented, someone was bringing in an ATV or other motorized vehicle,” said Chuck Gamble, Farm Science Review manager. “Farm Science Review is intended to be a pedestrian show, and vehicles permitted on the grounds should be limited to those folks who truly need them. If you don’t need it, then don’t bring it.”

Attendees perusing the latest in agricultural research, production and equipment can do so by either taking a stroll, renting one of the show’s golf carts, or bringing their own golf cart or ADA-approved unit. Wagons are available to transport visitors to the Gwynne Conservation Area and demonstration fields.

“The safety of our attendees and exhibitors is our No. 1 priority at Farm Science Review,” said Gamble. “We want to make sure everyone who attends Farm Science Review comes away with an enjoyable experience.”

To learn more about the new regulations, log on to the Farm Science Review Web site at Attendees are encouraged to familiarize themselves with the regulations before attending the show. For additional questions or concerns, contact Farm Science Review headquarters at (614) 292-4278.

Farm Science Review is sponsored by the College of Food, Agricultural, and Environmental Sciences, Ohio State University Extension, and the Ohio Agricultural Research and Development Center. It attracts upwards of 140,000 visitors from all over the country and Canada who come for three days to peruse 4,000 product lines from 600 commercial exhibitors and learn the latest in agricultural research, conservation, family and nutrition, and gardening and landscape.

Regional Crop Reports Available

Authors: Harold Watters

Many of the county Agronomic Crops Team members include their local crop, insect, disease and weather scouting information on the county or regional websites. This information can be used to fill in the holes that can sometimes occur when a state specialist makes a report and recommendations to cover the entire state of Ohio.
The West Central Ohio group of extension professionals have been using a crop and weather blog since last summer, and others use a local county extension website or some have created their own blogs. Please feel free to view the local or regional sites noted below throughout the growing season to get a more localized picture of what may be happening in your neighborhood.

West Central Ohio – covering the counties of Darke, Auglaize, Miami. Mercer, Champaign, Clark, Logan and Shelby:

Northwest Ohio – from Fulton, Williams, Defiance and Paulding Counties:

From Van Wert County:

From Northeast Ohio, covering Geauga, and the Tri-county area:

Archive Issue Contributors: 

Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility) Mark Loux (Weed Science), Jim Noel (NOAA), Erdal Ozkan (Ag Engineering) and Chuck Gamble (Farm Science Review). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Greg LaBarge (Fulton), Steve Foster (Darke), Harold Watters (Champaign), Mike Gastier (Huron), Mark Koenig (Sandusky), Wes Haun (Logan), Marissa Mullett (Coshocton), Jonah Johnson (Clark), Ed Lentz (Seneca), Les Ober (Geauga), Steve Bartels (Butler), Alan Sundermeier (Wood), Gary Wilson (Hancock), Tim Fine (Miami), 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.