C.O.R.N. Newsletter 2010-31

Dates Covered: 
September 21, 2010 - September 27, 2010
Editor: 
Wes Haun

Weather Update

The weather outlook is above normal temperatures and below normal rainfall.

Some showers are possible Wednesday with a weak weather system otherwise the week will see temperatures 10-15 degrees above normal. There is a chance for more rain this weekend into early next week but a wide range of uncertainty exists from little rain to a decent chance for much needed rain.

Cooler weather can be expected this weekend into next week. However, the longer term trends support the persistent pattern of above normal temperatures and below normal rainfall through autumn. This pattern is suggested to change by late fall into winter to above normal rainfall and near normal temperatures at that time.

For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is subjected to drought stress during grainfill, photosynthetic activity is reduced. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi. As plants near maturity, this removal of nutrients from the stalk to the developing grain results in a rapid deterioration of the lower portion of corn plants in drought stressed fields with lower leaves appearing to be nitrogen stressed, brown, and/or dead.

Other plant stresses which increase the likelihood of stalk rot problems include: loss of leaf tissue due to foliar diseases (such as gray leaf spot or northern corn leaf blight), insects, or hail; injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium; compacted or saturated soils restricting root growth (recent flooding); and high plant populations.

Most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity. It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot. Although a number of different fungal pathogens cause stalk rots, the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium. For more information on stalk rot in corn, consult the OSU Plant Pathology web site "Ohio Field Crop Diseases" (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/) for more details and pictures of the disease symptoms associated with these pathogens.

The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvest promptly. It’s not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms! Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to weathering, e.g. strong winds and heavy rains.

A symptom common to all stalk rots is the deterioration of the inner stalk tissues so that one or more of the inner nodes can easily be compressed when squeezing the stalk between thumb and finger. It is possible by using this "squeeze test" to assess potential lodging if harvesting is not done promptly. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present.

To minimize losses for stalk lodging rot damage, avoid harvest delays. Identify fieldswhich are at greatest risk and harvest these fields first. Fields which experienced late season drought stress or extensive northern leaf blight or grey leaf spot would be prime candidates for early harvest. This is not the year to allow corn to dry in the field to 15% to save on drying costs!

Planting Wheat After Corn? Here are a Few Things to Consider

Some Ohio wheat growers are thinking about planting wheat after corn to avoid some of the late planting issues we have had to deal with over the past few years. Indeed, timely planting will result in good stand establishment (more tillers per foot of row) and reduce the risk of winter kill. However, planting wheat after corn to ensure that the crop is planted early enough has several disadvantages.

In wheat following corn, being both members of the grass family, both crops may be affected by some of the same pests and diseases. One such disease, and by far the one of greatest concern, is head scab, caused by Fusarium graminearum. This fungus causes ear and stalk rot in corn and even if the cornfield into which wheat is planted did not have a major ear rot or stalk rot problem this year, the fungus still is present in the corn stubble left in the field after harvest. Wheat planted into this stubble is more likely to have head scab and vomitoxin problem next year, especially if late-spring, early-summer conditions are wet and humid. Our studies have shown that when residue is abundant (more spores of the fungus present), only a few days of wet and humid conditions during flowering are needed for head scab to develop and vomitoxin to exceed critical marketing thresholds (2 ppm). We had high levels of scab and vomitoxin in some parts of the state in 2010 largely because most of our varieties are susceptible, there were lots of spores around probably because of the ear rot problem we had in corn in 2009, and conditions were wet and humid during flowering. Planting wheat after corn could lead to similar problems in 2011 if the weather is favorable for scab. Remember, one of the best ways of minimizing losses due to head scab and vomitoxin is to plant wheat after soybeans and not after corn. LET US BREAK THE CYCLE OF VOMITOXIN PROBLEMS!!

 If you HAVE to plant wheat after corn or have already done so, hopefully you have planted a scab resistant variety or will do. Even when wheat is planted after soybean, planting a scab resistant variety is highly recommended. In addition, plow under the corn stubble before planting wheat and be prepared to apply a fungicide next year at flowering if the weather becomes favorable. These approaches will minimize, but will not eliminate the risk of scab in wheat planted after corn.

 

The Hessian Fly-Safe Date is Not Only about Hessian Fly Hessian Fly-Safe Dates in Ohio

The Hessian Fly-Safe Date is Not Only about Hessian Fly

For years, a very standard recommendation for profitable wheat production in Ohio has been to plant wheat after the Hessian fly-safe date. This recommendation is based on the fact that at the dates indicated on the map, Hessian fly adults would no longer be alive.   Adults emerge in later summer, mate, and then oviposit in different types of grasses.   Adult life span is extremely short, perhaps only a week, during which time they do not even feed.  After this short time span, adults die off.   The fly-free date is set at a time when it is expected that the adults have died and are no longer around the area.  As a result, damage caused by this insect will likely much less if wheat if planted after the specific date fly-free date in your area. 

However, in Ohio the Hessian fly-safe date is not only about the Hessian fly. Anxious to take advantage of early soybean harvest and good planting conditions, some producers have already planted wheat or are thinking about doing so before the Hessian fly-safe date. Some argue that they have not seen the Hessian fly in years, so there is no need to worry about planting after the fly-safe date. However, another excellent reason to plant wheat after the fly-safe date is to minimize problems with diseases, especially barley yellow dwarf virus (BYDV).

BYDV is transmitted by aphids and tends to be most severe when transmission occurs in the fall. Research showed that due to unfavorable weather conditions, the aphid population tends to crash after the fly safe date, leading to fewer problems with BYDV. Planting date studies conducted here at OSU a few years ago showed that BYDV problems and yield loss associated with this disease are much higher when wheat is planted well before the fly-safe date. Planting after the fly-safe date also minimizes early establishment of other diseases such as Stagonospora blotch and leaf rust.

Soil Sampling This Fall? Take the Time and Do it Correctly

We often write an article this time of year discussing the importance of soil sampling and providing some guidelines on how to do it.  Those items will be discussed, but we wanted to spend a little time illustrating why a good soil sample is so important. 

Have you ever thought about what a soil sample is?  More importantly, have you ever thought about what it represents?  If you follow Ohio State University Extension guidelines and collect 15 cores to constitute a composite for every 20 acres, you will likely collect around a pound of soil.  Were you aware that the weight of soil over an acre to a depth of 6 inches is around 2 million pounds?  So you are collecting a very small sample to represent the average of a larger area.  Statistics reveals to us that 15 cores are adequate to accurately represent the average soil test level for this larger area, but you do need to make sure that the sample is representative of the bulk of your field.  We often discuss the need to collect samples from “representative areas”.  I am quite confident that you as a producer know where those areas are within your fields, and more importantly you know where the “troubled” areas are.  Those troubled areas should be sampled separately to ensure that they do not influence the average information you are collecting.  This also allows you the opportunity to possibly identify why the “troubled” area is less productive, if it is related to soil fertility.

From a lab perspective, errors associated with soil test estimates can be minimized.  Sample weighing, extraction time (if the sample requires chemical extraction), and instrumental analysis do have errors associated with them, but they can be minimized.  The easiest way to introduce greater uncertainty is to do a poor job sampling.  Beyond what was discussed in the previous paragraph, sampling depth and moisture regime at the time of sampling is critical to the accuracy of the information you collect. Thus sampling to a consistent depth is critical to get an accurate representation of the soil’s actual nutrient supplying power.  There is no preferred sampling time (comparing spring to fall), but be consistent about sampling time.  Additionally, avoid moisture extremes (too dry or wet) when collecting soil samples.

Summary:

  • Collect a minimum of 15 cores per composite.
  • Be consistent about sampling depth.
  • Be consistent about the timing of sample collection and avoid moisture extremes.
  • Avoid contamination.  Use clean probes for sampling and clean buckets for mixing.

After receiving the analysis from the lab, go the Tri-State Fertilizer Recommendations online to determine the rate needed to ensure maximum productivity (http://ohioline.osu.edu/e2567/index.html).  If soil analysis reveals the soil is well above the established critical level, consider not applying that nutrient this fall.  If below the critical level, the nutrient should be applied to ensure it is not yield limiting.

Late Summer Soybean Aphid Update Soybean Aphids on Buckthorn

Late Summer Soybean Aphid Update

As expected, we have been seeing soybean aphids on maturing soybeans that still have some green leaves on them.  This late aphid build-up had been expected following a summer of almost no aphids.  More importantly, we have been begun seeing winged soybean aphids along with a few newly laid aphids on buckthorn, the aphid’s overwintering host.    This has been observed near Toledo as well as in Richland County.  We will continue to search buckthorn for continued build-up of aphids and then for eggs over the next few weeks.   We do expect eggs to be oviposited which, if they do, will suggest a potential for soybean aphids problems next summer.   Keep reading this C.O.R.N. newsletter for continued information on the soybean aphid.

Using Waste Sludges as Liming Materials

Sludges and wastes generated from municipal, agricultural, and industrial activities can be excellent sources of lime for soil neutralization, and land application is an excellent way to recycle these materials.  Due to the variability of waste materials and their neutralizing power, lab analysis of the material is extremely important.  Typical lab analysis should reveal effective neutralizing power (ENP) of the material and heavy metal levels.  Other nutrients such as nitrogen, phosphorus, potassium, and other macros/micros should be reported as well.

Care should be taken when applying these materials as lime sources.  Annual applications of such materials can increase soil pH levels well above 7, so make sure to account for the neutralizing ability of the materials that are applied as well as monitoring soil pH levels determined by soil test.  Raising soil pH levels above 7 can result in decreased micronutrient availability and increased carry over of some herbicides.  Also make sure there is equipment available to evenly spread the waste lime material to avoid future problem pH areas. We all have seen “hot spots” in fields that had pockets of high soil pH showing manganese deficiency in soybeans and wheat or zinc in corn. 

In summary, pay close attention to soil test reports (soil pH specifically) and lab analysis of these waste limes (ENP) when making applications to avoid over-liming. As further caution, you may want to only apply these materials on fields that have pH levels below 6.3. 

For additional information on soil pH and ENP please consult the fact sheet “Soil Acidity and Liming for Agronomic Production”.

 

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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.