C.O.R.N. Newsletter 2005-12

Dates Covered: 
May 9, 2005 - May 17, 2005
Editor: 
Tammy Dobbels

Check Corn Fields for Emergence Problems

Authors: Peter Thomison

Although many fields in Ohio were planted to corn three weeks ago, corn emergence has been limited because of cool wet soil conditions. More recently, as soils have dried, soil crusting has inhibited emergence. Unfavorable growing conditions have also resulted in other factors (such as seeding diseases) adversely affecting growth and poor emergence in corn. Given the potential impact these factors can have on stand establishment and the need to replant, I strongly encourage growers to make stand counts, scout fields, and troubleshoot emergence problems.

My counterpart at Purdue, Dr. Bob Nielsen, commented in his most recent newsletter article (May 8, 2005) that he had visited a number of fields in east central Indiana Friday afternoon that had not yet emerged even though the calendar was approaching three weeks since they had been planted. Bob stated that “apparent seedling disease development in these fields was widespread and eventual stand establishment may be poor enough to merit replanting.” He went on to observe that a common combination of factors among these fields was mid-April planting (5 to 6 days prior to the recent cold snap) followed by the onset of cold soils (too cool to sustain germination), heavy rainfall, short-term ponding, saturated surface soils, surface soil crusts [which sounds familiar to what many of our Ohio fields have experienced], and (eventually) seedling diseases.

Although corn has just started to emerge or has not yet emerged, growers should carefully inspect seedlings for symptoms of disease; especially in lower lying areas of fields where ponding and saturated soils were more likely. Bob noted in his article that the consequences of seedling disease on the success of emergence and initial stand establishment will become more apparent by the end of this week, if not sooner.

Bob’s article “Some Mid-April Planted Corn in Trouble” is available online at http://www.agry.purdue.edu/ext/corn/news/articles.05/StandLossDisease-0508.html and contains some excellent pictures of various symptoms of seedling disease development.

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.

(I’ve adapted some of this information from a newsletter article by Dr. Greg Roth, my counterpart at Penn State).

-No seed present. May be due to planter malfunction, 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.

- 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.

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.

B) Assessing Corn Seedling Emergence and Seedling Diseases - Pat Lipps

Growers are encouraged to spend some time walking fields and digging seedlings to evaluate their condition before making replant decisions. Dig seeds from the seed furrows and wash them off with water. 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. Given a chance to emerge with warmer soil temperatures many of these plants will likely survive. It is best to check these seedlings very closely for dark brown or soft areas on seedling roots and on shoots next to the seed. These immature plant structures should be white to creamy white in appearance. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet. Plants that show disease or damage will likely be slow to emerge even with warmer conditions and also show less vigor. Growers should also remember that uneven emergence and slow growth at this time of year could impact overall yield, but these effects must be weighed with the known impact of later planting on yield potential. A slight to moderate reduction in stand is a better bet than replanting in many instances, especially if you have to decide whether to replant these fields or plant fields that are not yet planted . Of course the later in the season the replanting is done the greater the risk of lost yield potential.

Assessing Corn Seedling Emergence and Seedling Diseases

Authors: Patrick Lipps

Growers are encouraged to spend some time walking fields and digging seedlings to evaluate their condition before making replant decisions. Dig seeds from the seed furrows and wash them off with water. 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. Given a chance to emerge with warmer soil temperatures many of these plants will likely survive. It is best to check these seedlings very closely for dark brown or soft areas on seedling roots and on shoots next to the seed. These immature plant structures should be white to creamy white in appearance. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet. Plants that show disease or damage will likely be slow to emerge even with warmer conditions and also show less vigor. Growers should also remember that uneven emergence and slow growth at this time of year could impact overall yield, but these effects must be weighed with the known impact of later planting on yield potential. A slight to moderate reduction in stand is a better bet than replanting in many instances, especially if you have to decide whether to replant these fields or plant fields that are not yet planted . Of course the later in the season the replanting is done the greater the risk of lost yield potential.

Wheat Yellowing, Is It Nitrogen Deficiency?

Authors: Robert Mullen, Patrick Lipps


While most are concerned with corn emergence and getting soybeans planted, some have reported yellowing of wheat. So is this chlorosis the result of nitrogen deficiency? Most likely it is not, unless you have completely missed your nitrogen application this spring. Up to this point, conditions this spring have not been conducive to loss of nitrogen. Soils were wet (not excessively) a couple of weeks of ago, but soils were also cool which plays into our favor with regard to nitrogen loss. Now that air temperatures are up soils are fairly dry, again this plays into our favor with regard to nitrogen loss. For those considering later applications of nitrogen, make sure what you are seeing is a nitrogen deficiency. If the yellowing is the result of disease pressure applying additional nitrogen will not help the condition. The bottom line is this, if you have made a nitrogen application this spring and your wheat is yellow do not automatically assume that you have a nitrogen deficiency. Assess what you have done up to this point (with nitrogen) and eliminate other possible causes of the yellowing.

For producers considering a late application, remember for the most part potential yield for the field is set at this point. The number of spikes (tillers/heads) per plant is already established as well as the number of spikelets per spike and kernels per spikelet. Late nitrogen applications (after Feekes 6) often do not result in sizeable yield increases. Most of the time late season nitrogen applications result in increased grain protein. If considering this late season application, stay away from flat fan nozzles and utilize streaming or dribble nozzles to decrease the amount of leaf tissue exposed to the fertilizer solution. Selecting the wrong nozzles can result in severe leaf burn. Burning of the flag leaf (which is starting to emerge) can result in yield losses. The amount of yield loss is highly variable and difficult to quantify.

What Is The Risk Of Head Scab On Wheat This Year?

Authors: Dennis Mills, Patrick Lipps, Pierce Paul


The next 5 to 6 weeks is a critical period for the wheat crop in Ohio as this is the time when weather conditions determine the occurrence and spread of wheat diseases. The top yield limiting diseases on wheat in the state include powdery mildew, Stagonospora leaf and glume blotch, leaf rust and Fusarium head scab. To date, there has been little disease pressure in the state, but the return of warmer weather and frequent rain showers could greatly change the situation. Fusarium head scab is one disease that can cause severe yield losses and poor quality grain when weather conditions favor its development. A web-based risk model for Fusarium head scab is available again this year for wheat growers to track the risk of this disease. The Wheat Fuasrium Head Bight Prediction Center can be accessed via the web at http://www.wheatscab.psu.edu/. For those of you that do not have web access, we will be providing the results of the risk forecasts for general regions in Ohio in future C.O.R.N. newsletters.

Growers can access this web site to help them determine the risk of head scab occurring in their wheat fields. Much like a weather forecast, this system predicts the probability of an event, in this case an epidemic of Fusarium head scab. For this system, an epidemic is defined as a head blight severity of at least 10% in the field. For example, severity would b e10% if 10% of the heads were entirely blighted or if 20% of the heads were 50% blighted. Yield would be impacted by this level of disease and it would be highly likely that the mycotoxin DON would be present in the grain

The homepage of this web site provides links to information about the risk prediction model, the biology of the disease and instructions on how to use the 'Risk Map Tool". Obtain a disease risk prediction by clicking on the 'Risk Map Tool'. Within a few seconds you will be asked to provide some basic information to three questions. You need to enter the flowering date of your fields in the calendar to the left of the screen, indicate if you are growing 'spring' or 'winter' wheat (all wheat in Ohio is winter wheat) and if the wheat was planted into corn residue covering 10% or more of the soil surface. After answering these questions click 'OK' and the map of the US will come up. Pointing your mouse to Ohio and clicking will bring up the risk contour map for the state and National Weather Service weather stations represented as blue dots on the map.

At this point you can change the date of flowering by clicking different dates on the upper left calendar, however you can not choose tomorrows date or any future date. The models use only recorded weather data not forecasted weather data. The calendar indicates the chosen flowering date in dark blue and the previous seven days utilized by the model in lighter blue. Assuming that you will be looking at this site before your wheat goes into flower, you can watch the potential disease risk by visiting the site each day or viewing the risk predictions for several different days. Please note that the model predictions run on weather data and a prediction will be generated regardless of if there is wheat flowering or not. The colored contour maps are produced using a source of weather information known as the Rapid Update Cycle (RUC) created by the National Weather Service. The RUC system combines multiple sources of weather information to generate observations on a 12 square mile grid throughout a region. The risk prediction contour maps will be colored red for high risk, yellow for moderate risk and green for low risk. Additionally, you can click on any of the weather station locations to get a risk probability for that location and the web page will provide the risk prediction for the previous seven days in a graph at the bottom of the page. Please note that the predictions for the individual weather stations may not be identical to what is on the contour map predictions. This is because they use different sources of weather information where the weather station uses one information source and the RUC uses multiple sources.

We recommend that you visit and work in the web site to become familiar with it so you understand it when the time comes to obtain risk predictions. Please read the sections on "Model Details" and "Reality Check". You should note that like any mathematical model that relies on weather inputs, this is not a perfect predictor of head scab; the model has been about 80% accurate. Weather conditions that occur after you receive a forecast can impact the level of scab in the field and DON in the grain. Therefore, this prediction is a snapshot of the risk on the date you request the prediction. Use the prediction as another source of information about the probability of disease. Also look at the 7 and 10 day weather forecasts to see if rain will be frequent with temperatures in the 65 to 75 F range. Last year the models adequately predicted the severity of scab but severity levels were not indicative of the DON levels in the grain due to wet conditions occurring during maturation of the grain in the field. In general there is a very poor correlation between head blight severity and levels of DON in the grain at harvest.

Rotary Hoe for Weed Control

Authors: Mark Loux

The rotary hoe can help control weeds in fields where preemergence herbicides did not receive rain soon enough for effective activity. For best results, the rotary hoe should actually be used prior to weed emergence, when weeds have germinated but are still below the soil surface (sometimes known as the “white stage”, due to the absence of chlorophyll). Weeds that have emerged and established a root system may not be as well controlled by the rotary hoe. A timely rotary hoeing can control weeds that are about to emerge, essentially “buying time” for a significant rain to occur, which will promote preemergence herbicide activity.

Controlling Emerged Grasses with Atrazine

Authors: Mark Loux

When adapting atrazine-containing herbicide treatments for early postemergence use, be sure to use the proper atrazine rate and spray adjuvants, and apply when grasses are small. Foxtails should be one inch tall or less if possible at the time of application, before any leaves have fully developed. An atrazine rate of 2.0 lbs active ingredient per acre is most effective. When using atrazine premix products (Guardsman Max, Bicep II Magnum, Degree Xtra, etc), additional atrazine should be added to bring the rate to a total of 2 lbs. Atrazine is most effective for control of emerged weeds, and especially grasses, when it is applied with crop oil concentrate. However, atrazine premix products are formulated with various emulsifiers and surfactants, which may also promote atrazine activity on emerged weeds. Adding crop oil concentrate to these products may increase the risk of crop injury. We suggest consulting with the manufacturer’s representative for specific recommendations on adjuvant use for atrazine premix products when applying to emerged corn.
 

Soybean Rust Update

Authors: Anne Dorrance

Thirty of Ohio’s 46 sentinel plots have been planted and 2 have emerged. We will be monitoring these plots this week to see if they have emerged. The big news this past week was the announcement by Monsanto that PRELIMINARY GREENHOUSE studies indicate that glyphosate may have an effect on the soybean rust fungus. This is interesting and IF proven true could be good news for the north central states. Applications of Round-up in the southern states would help to delay the epidemic. However, several things can impact this – how much rust develops on the kudzu and if in fact this is effective under field conditions. Often responses in greenhouses can not be duplicated under field testing. From numerous discussions with colleagues around the country last week, no one could document where glyphosate had any effect on soybean foliar pathogens. Under no circumstances should producers experiment with this strategy this year – this is one for the scientist. By the time soybean rust gets close to Ohio, we should have data from the southern US.

Bean Leaf Beetle in Soybean

Authors: Ron Hammond, Bruce Eisley

Growers should plan on monitoring emerging soybeans for bean leaf beetles. Although populations were not especially high during 2004, we did see some fields with significant numbers. If early defoliation reaches 50% and plants appear stunted, an insecticide treatment would be recommended. Keep in mind that bean leaf beetles will tend to be most numerous in early-planted fields.

As in past years, there is still concern with the beetle's ability to vector bean pod mottle virus. The bean leaf beetle transmits this virus, especially in early season during feeding by the over-wintering beetle. This concern tends to be greater on food grade soybeans and those being grown for seed where seed quality is an important issue. If growers choose to treat the bean leaf beetle for virus control, they should spray the bean leaf beetle during the VC-V1 stage after the soybeans emerge from the soil and when beetles begin to appear in the field. Recommendations also suggest that a second spray be made in July at the beginning of the first beetle generation.

How to Kill Roundup Ready Corn – Part II

Authors: Mark Loux

Following last week’s article on the potential problem in killing a poor stand of Roundup Ready corn so that the field can be replanted with corn, several readers offered solutions that we had not considered. One of these was to apply Balance Pro to the field, which should kill small, emerged corn and still allow any type of field corn to be replanted in the field immediately. While we assumed that the field would be replanted with Roundup Ready corn, one reader suggested that a different type of corn could be used in the replant. Two suggestions along this line: 1) plant Liberty Link corn and apply Liberty soon after emergence to kill the old stand of Roundup Ready corn, or 2) plant Clearfield corn and apply Lightning soon after emergence to kill the old stand of Roundup Ready corn. Labels for Liberty and Lightning do not restrict replanting of the appropriate type of corn following their application, but labels for both specify application should occur after corn emergence. So, legally, one would have to wait until Liberty Link or Clearfield corn has emerged before applying herbicide to kill the old stand of corn.

Archive Issue Contributors: 

State Specialists: Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Robert Mullen (Soil Fertility), Bruce Eisley and Ron Hammond (Entomology), Mark Loux and Jeff Stachler (Weed Science), Peter Thomison (Crop Science-Corn). Extension Educators: Roger Bender (Shelby), Steve Foster (Darke), Gary Wilson (Hancock), Dusty Sonnenberg (Henry), Howard Siegrist (Licking), Harold Watters (Champaign), Tammy Dobbels (Logan), Glenn Arnold (Putnam), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Todd Mangen (Mercer), Steve Prochaska (Crawford) & Ed Lentz (Seneca)

About the C.O.R.N. Newsletter

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.