C.O.R.N. Newsletter 2004-13

Dates Covered: 
May 11, 2004 - May 18, 2004
Editor: 
Tammy Dobbels

Bean Leaf Beetle (BLB) Emerging

Authors: Ron Hammond, Bruce Eisley

We are getting reports that people are finding bean leaf beetles (BLB) in alfalfa when they are checking for alfalfa weevil. When BLB first emerge from their over wintering sites they will many times move into alfalfa for a sort time to feed. These beetles will be moving from alfalfa into soybeans as soon as they begin to emerge. If there are few soybeans up in an area when the beetles begin to move, they will congregate in these few fields and could cause some damage. Early emerging soybeans should be checked to make sure BLB are not damaging the new emerging plants.

Applying Preemergence Herbicides To Emerged Corn

Authors: Mark Loux

A number of corn fields in the state did not receive a herbicide application at the time of planting, and corn has already emerged in many of these fields. Most preemergence corn herbicides can be applied to emerged corn, although only Degree Xtra and Bullet are labeled for application using 28% UAN or similar solutions as the spray carrier. Degree Xtra and Bullet can be applied in fertilizer solution when air temperatures are less than 85 degrees, and some leaf burn should be expected. Corn should be no more than 6 inches tall if Degree is applied in fertilizer solution, and no more than 5 inches tall for Bullet. The Define label does not prohibit application in fertilizer solution but contains the following statement, “Using fluid fertilizer as a postemergence spray carrier to apply Define SC is not recommended if fluid fertilizer burn is not considered acceptable”. All other corn herbicides should be applied using water as the spray carrier. The following preemergence herbicides should not be applied to emerged corn: Axiom, Balance, Epic, Sencor. With regard to corn size, labels for specific products or active ingredients indicate the following (assuming other herbicides are not included in the mix – if so, check labels for other restrictions):

- Atrazine – corn up to 12 inches tall
- Products containing acetochlor – corn up to 11 inches tall
- Products containing metolachor or s-metolachor – corn up to 5 inches tall (Bicep and Cinch ATZ can be applied to corn up to 12 inches tall in rescue situations, but other herbicides should be added for large weeds)
- Products containing alachlor – corn up to 5 inches tall
- Define – corn up to the 5th leaf collar stage
- Guardsman Max, Outlook – corn up to 12 inches tall
- Lumax – corn up to 5 inches tall

Where soil was tilled prior to planting, two options exist in fields with emerged corn, since weeds and corn will be emerging together. One option is to stay with the full rate of an atrazine premix product, which will control small, emerged grass and broadleaf weeds and also provide residual control. In OSU research, early postemergence application of atrazine premix products, when the first flush of weeds has emerged but is less than about an inch tall, has been consistently effective. Labels vary somewhat, but most atrazine premix products specify application when weeds are less than 1 ½ inches tall or when they have not exceeded the 2-leaf stage. Additional atrazine can be included where weeds are larger, and we suggest atrazine rates of 2 lbs active ingredient per acre where grasses are more than 1/2 inch tall. Mixtures containing Callisto (such as Lumax), Hornet, 2,4-D, dicamba, or other herbicides can improve control of emerged weeds where necessary. Where grasses are more than 1 1/2 inches tall, the addition of a reduced rate of a postemergence grass herbicide (Accent, Steadfast, Option, etc) is suggested. The addition of nonionic surfactant or crop oil concentrate will generally be necessary where weeds have emerged, but check labels for specific recommendations on tank-mixtures and adjuvant use to avoid crop injury.

Heading in Southern OH, What is The Risk Of Head Scab

Authors: Patrick Lipps, Dennis Mills

Wheat in southern Ohio is heading in some fields which means the crop will be flowering soon. In general wheat begins to extrude its anthers from florets of the head within 3 to 4 days after heading. This is a critical time when the wheat plant is most susceptible to Fusarium head scab or head blight. Growers can now access a web site to help them determine the risk of head scab occurring in their wheat fields. We will be providing the results of the risk forecasts for general regions in Ohio in future C.O.R.N. newsletters. So far the risk of scab is very low across the entire state.

The Wheat Fuasrium Head Bight Prediction Center can be accessed via the web at http://www.wheatscab.psu.edu/.

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". Enter the page to get a scab 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 and 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 predicted 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.

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 'real' risk predictions. Please read the sections on "Model Details" and "Reality Check". Also note this is an experimental system and the web site managers will be working with it throughout the season to 'fix' any bugs. If you do not get a prediction for a location, try again in a few hours.

Where are Micronutrient Deficiencies Most Likely to Occur?

Authors: Robert Mullen

With all the attention paid to the big three in soil fertility (N, P, K), micronutrients are sometimes overlooked. Micronutrient levels in Ohio soils are for the most part adequate for maximum crop production. Not to say that micronutrient deficiencies do not reduce yield, but the likelihood of having a micronutrient deficiency in Ohio is generally small. For each micronutrient (and sulfur), field conditions are presented that can enhance the potential for deficiencies.

Sulfur
Sulfur (S) deficiencies would most likely be found in coarser textured soils low in organic matter (S is actually a macronutrient but it is included in this discussion). Because sulfur exists as sulfate (anion – negatively charged) in soil solution, its mobility is similar to nitrate. Sulfur is primarily made plant available by mineralization from the organic fraction and is found readily in rainfall (due to industrial processes). The amount of sulfur found in rainfall varies dramatically across the cornbelt with values as high as 30 lb S/acre and as low as 5 lb S/acre reported. The amount typically used by a crop is approximately 1/10th the amount of N used. If manure application is a part of the fertilizer regimen, the likelihood of seeing a S deficiency is small.

Zinc
Zinc (Zn) deficiencies are primarily confined to areas of the field where erosion has exposed subsoil. Coarser textured soils low in organic matter and high pH soils (> 7) enhance the potential to see Zn deficiencies. Similar to S, if manure is applied regularly as a soil amendment, Zn levels should be adequate for maximum production. Soils with relatively high levels of organic matter are also likely to have adequate levels of Zn. The lower the soil pH the less likely that Zn levels are in the deficient range.

Copper
Copper (Cu) deficiencies are primarily confined to black sands and organic soils (mucks and peats). Mineral soils are rarely deficient in Cu.

Manganese
Manganese (Mn) deficiencies are primarily found in soybeans and oats grown on high pH, high organic matter soils. Mineral soils with pH levels less than 6.5 rarely exhibit Mn deficiencies. Application of high rates of manure can actually enhance the potential of seeing a Mn deficiency, as Mn can be bound in unavailable organic chelates. The likelihood of observing a Mn deficiency in corn or alfalfa is small.

Boron
Boron (B) deficiencies are most likely found in alfalfa grown on coarser textured soils and low organic matter soils. Boron deficiencies are rare in soybeans. Like most micronutrient metals as soil pH decreases B availability increases. Do not apply B as a starter in close proximity to the seed, it can cause seed injury.

Iron
Iron (Fe) availability is strongly tied to soil pH. If soil pH is below 7.3, it is very unlikely that Fe is deficient. Iron deficiency is most probable in calcareous soils or soils with high pH.

Molybdenum
Unlike the other micronutrient metals, molybdenum (Mo) availability increases as soil pH increases. Because of this, Mo deficiencies can be observed on legumes grown in extremely acid soils (pH less than 5.0). However it is more economical to apply lime than to provide Mo as a soil amendment. Molybdenum deficiencies for other non-leguminous crops are extremely rare in this portion of the United States.

Remember, the examples of conditions conducive to deficiency presented above are where deficiencies are most likely to occur, not where they will definitely occur. Generally speaking, soils in this region supply enough micronutrients to satisfy crop needs, thus supplementation of micronutrients by fertilization is unnecessary. Soil testing can indicate whether a micronutrient is deficient or not. If a micronutrient deficiency is suspected, soil and/or plant analysis should be conducted.

Check Corn Fields For Emergence Problems

Authors: Peter Thomison

A number of factors contribute to poor emergence in corn. The following is some information adapted from a newsletter article by Dr. Greg Roth, my counterpart at Penn State, which addresses this topic. With corn emergence nearly complete in many fields in western Ohio, this is the time to take stand counts, scout fields, and troubleshoot emergence problems. Diagnosing emergence problems early is critical in identifying solutions and developing successful replant plans. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.

-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.

- Seed 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. 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.

New Requirements On Labels, Selection of Nozzles For Drift

Authors: Erdal Ozkan

More and more we are seeing specific application recommendations/requirements on pesticide labels, such as: “Apply this product with nozzles producing fine to medium size droplets”. What is a “fine” or “medium size” droplet?, and why did we have to categorize droplets in this fashion? Here are the answers to these and other related questions.

It is all about spray drift. We expect sprayers to perform several important tasks. One of the expectations is that a sprayer should help us reduce pesticide drift to minimum while maintaining optimal efficacy throughout the application site. After wind speed and direction, spray droplet size is the second most important factor affecting drift. Each class of nozzles, even the same type of nozzle with different orifice sizes (flow rates) , or the same nozzle operating under different conditions all will have different droplet size distributions, consisting of droplets ranging from very small to very large at different proportions. To avoid drift, one should choose the best nozzle and operate it under most optimum pressure settings. Almost all major agricultural nozzle manufacturers have recently introduced their version of Low Drift nozzles. These nozzles are designed to create larger droplets at the same flow rate and operating pressure than comparable conventional flat fan nozzles. However, if operated at low pressures, some conventional nozzles can be as effective in reducing drift as the low drift nozzles operating at higher pressures. Mostly for this reason, pesticide manufacturers were not able to recommend one particular type of nozzle for drift control. On the other hand, US EPA has been requesting some type of information on labels which applicators can use to determine nozzle size, type and operating parameters to reduce drift. To help manufacturers of pesticides and regulatory agencies such as EPA, American Society of Agricultural Engineers has developed a standard called “Spray Nozzle Classification by Droplet Spectra” (ASAE S-572).

This Standard defines droplet spectrum categories for the classification of spray nozzles, relative to specified reference nozzles discharging spray into static air. The purpose of classification is to provide the nozzle user with droplet size information primarily to indicate off-site spray drift potential and secondarily for application efficacy. This Standard defines a means for relative nozzle comparisons based on droplet size only. Other spray drift and application efficacy factors (eg, droplet discharge trajectory, height, and velocity; air bubble inclusion; droplet evaporation; and impaction on target) are not addressed by the current Standard. (ASAE S-572).

This Standard identified 6 droplet size categories: very fine, fine, medium, coarse, very coarse, and extremely coarse. Also, a unique color is assigned to each class. (This color should not be confused with the ISO color coding for flow rates). Following table gives the classification categories, their symbols and corresponding color codes. Also shown are approximate VMDs (Volume Median Diameter) droplet sizes associated with each class. The droplet sizes given are for comparison purposes only and should not be used for all nozzles, and operating conditions. Nozzle flow rate, spray pressure, and physical changes to nozzle geometry and operation can affect nozzle classification. In other words, a given nozzle can be classified into one or more droplet size categories, depending on the selection of flow rate, operating pressure, and other operational conditions. To determine the exact drop size classification of a nozzle under a given set of operating condition, one should always check the data given in nozzle manufacturer catalogs.

Classification categories, symbols, and corresponding color codes are the following.

NOZZLE CLASSIFICATION TABLE


Classification Category

Symbol
Color Code
Approx. Droplet Size VMD**
VeryFine
VF
Red
<150micron
Fine
F
Orange
150-250micron
Medium
M
Yellow
250-350micron
Coarse
C
Blue
350-425micron
VeryCoarse
VC
Green
425-500micron
ExtremelyCoarse
XC
White
>500micron





** VMD (Volume Median Diameter) droplet size, is the size of the droplet which divides the spray in two equal parts by volume. Half of the spray volume is contained in droplets smaller than the VMD, the other half of the spray volume is contained in droplets larger than the VMD. (For reference: There are 125,000 microns in one inch. Thickness of human hair is about 75 to 100 micron).

Purple Corn, What Is Going On?

Authors: Peter Thomison, Robert Mullen

When you combine our current cool nighttime temperatures, high radiation levels during the day, and wet field conditions, you are likely to start seeing purple plants in some corn fields. The first thing that may come to mind is a phosphorus deficient soil. This is unlikely the case, especially this early in the year. The purple tint is more attributable to the production of anthocyanins which is a plant response to a stress or a combination of stresses. Cool temperatures, high solar intensity, and water stress (drought and water-logged conditions) combine to inhibit root growth. Other factors including soil compaction, herbicide injury, etc. can make the effect even more pronounced. Purple corn can also be the result of what is known as the “fallow syndrome.” If corn follows a fallow season, a root fungus called mycorrhizae reaches a low population. Mycorrhizal infection of corn aids in phosphorus and zinc uptake. Until the fungal growth is stimulated by the corn roots, which exude starches and sugars, the purple color may persist. Fortunately, the purple tint is short-lived and rarely persists beyond the V6 growth stage. It should not have an impact on the yield potential of the field.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Dennis Mills (Plant Pathology), Robert Mullen (Soil Fertility), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Peter Thomison (Crop Science � Corn), Erdal Ozkan (Ag Engineering), Bruce Eisley (IPM), and Ron Hammond (Entomology); Extension Agents: Roger Bender (Shelby), Ray Wells (Ross), Barry Ward (Champaign), Steve Foster (Darke),Todd Mangen (Mercer), Greg La Barge (Fulton), Howard Siegrist (Licking), Alan Sundermeier (Wood), Tammy Dobbels, (Logan), Glen Arnold (Putnam) Mark Keonig (Sandusky), Harold Watters (Miami), and Dusty Sonneberg (Henry), Mark Koenig (Sandusky), and Steve Prochaska (Crawford)

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.