C.O.R.N. Newsletter 2011-34

Dates Covered: 
October 4, 2011 - October 10, 2011
Editor: 
Curtis Young

Potential for Corn Ear Rots in Ohio Corn

It is already the first week of October and most of the corn is still not ready for harvest. Some of the earlier-planted fields are being harvested, but at relatively high moisture levels. This is causing some concern among producers as to the potential for ear rot and mycotoxin problems. We have received reports of ear rots in some fields and, understandably, after the vomitoxin problems we had in 2009, producers are asking whether we are likely to see a similar problem again this year. So far the problem does not seem to be widespread, with only a few fields affected, and not every ear rot is associated with vomitoxin contamination of grain. In particular, most of the reports indicate that the affected fields have Diplodia ear rot, which does not result in vomitoxin contamination. However, ear rots could potentially become more of a problem if it continues to rain and the corn remains in the field for an extended period.   

One of the very first steps to determining whether you will have a problem with vomitoxin or other mycotoxins is to know which ear rot you have in your field. Generally, it is fairly easy to tell ear rots apart based on the color of the fungal growth on the ear, where the moldy kernels are located, and how they are distributed on the ear. Other good indicators are the prevailing weather conditions and susceptibility of the hybrids. For the two most common ear rots in Ohio, Gibberella and Diplodia, both of these diseases develop best when wet weather conditions occur during the first few weeks after silking, with Gibberella being favored by slightly cooler temperatures than Diplodia. Unlike 2009 when conditions were cool and rainy during the weeks after silking, conditions were relatively warm and dry this year. For both diseases, spores of the fungus are splashed onto the silk where they penetrate and grow into the ear. However, infection may also occur at the base of the ear, especially if it rains late in the season and the ears remain in an upright position, collecting water at the base between the husks and the kernels.        

Diplodia causes a thick grayish-white mass of mold to grow on the ear, usually beginning from the base and growing toward the tip. With Gibberella, a visible white to pink mold usually covering the tip or more of the ears is characteristic of this disease. The Gibberella ear rot fungus produces mycotoxins that are harmful to animals. These include deoxynivalenol (Vomitoxin) and zearalenone and T-2 toxin, all of which may cause health problems in livestock. Therefore, suspect grain should be tested for these mycotoxins by chemical analysis before being fed to animals. As a general rule do not feed any grain with 5% or more Gibberella moldy kernels. Hogs and young animals are particularly sensitive to these mycotoxins. Diplodia ear rot is less of a concern from a mycotoxin standpoint. There have been no reports of Diplodia producing mycotoxins that are harmful to animals in Ohio, but animals do refuse to eat grain with high levels of Diplodia-damaged kernels. Additionally, severely affected grain has low nutritional value.

Certain hybrids are more susceptible to one or more ear rots than others. Examine ears to determine the presence of ear molds. Make a note of which ear rots are present and hybrids that are most affected. Make future hybrid choices based on this information. Growers are advised to follow certain harvest and storage guidelines to minimize problems associated with kernel rots and mycotoxin contamination:

1. Harvest at the correct moisture and adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in (machine or insect) damaged kernels.

2. Dry harvested grain to 15% moisture and below to prevent further mold development in storage.

3. Store dried grain at cool temperatures (36-44F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.

4. Periodically check grain for mold, insects, and temperature.

5. If mold is found, send a grain sample for a mycotoxin analysis to determine if toxins are present and at what level. For more on moldy grain, mycotoxins, and mycotoxins sampling and analysis visit the following websites:

http://oardc.osu.edu/ohiofieldcropdisease/t01_pageview2/Home.htm

More Late-Season Northern Corn Leaf Blight in Ohio

As was the case in 2009, we are seeing late, but rapid development of Northern Corn Leaf Blight (NCLB) in some Ohio corn fields. Why are we seeing such high levels of NCLB this year and how will this affect our yields? At the time of silk emergence (R1), foliar disease levels were very low in corn fields across the state, but shortly after R3 (the milk stage), lesions of NCLB began showing up on the middle and upper leaves of the plants. As the season progress, lesions continue to develop, blighting as much as 30% of the ear leaf in some fields as the crop approach the dent stage (R5). On most of the hybrids with the problem, the symptoms are very characteristic of a susceptible reaction to the disease, with one-to-six inch long cigar-shaped gray-green to tan-colored lesions on the leaves. 

Since the 2001 growing seasons, we have been seeing a fairly steady increase in the occurrence of northern corn leaf blight in the state. This may be due in part to an increase in the number of acres planted to NCLB susceptible hybrids. The relatively late occurrence of the disease this year was probably due to favorable weather conditions late in the season. NCLB develops best at temperatures between 66 and 80F, accompanied by extended periods of surface wetness (due to rainfall, dew, and high relative humidity).

For an epidemic of northern corn leaf blight (and any other plant disease for that matter) to occur, three basic conditions must be satisfied: 1) the fungus (Exserohilum turcicum) must be present; 2) the hybrid planted must be susceptible to the prevalent races of the fungus; 3) and the environmental conditions must be favorable. In Ohio, the fungus is present because it survives in crop residue in the field and continues to build-up from one year to the next. So when a susceptible hybrid is planted, then the only thing that is missing is favorable weather. We have had cool, wet conditions over the last few weeks. However, when the disease develops late, its impact on grain yield tends to be much less than when it develops early during grain fill.

Make a note of the susceptible hybrids and avoid planting them again next year. Planting resistant hybrids is the most effective method for control of NCLB. Partial resistance, which protect against all four of the known races of the fungus, is common among hybrids and should used to minimize problems in the future. On hybrids with partial resistance, lesions are smaller, of a lighter color, and produce fewer spores than lesions on susceptible hybrids.

Corn Drydown: What to Expect?

Recent wet, cool weather slowed drydown.  By early to mid‑October, dry-down rates will usually drop to 1/2-3/4% per day (from rates of up to 1% per day in September when drying conditions are usually more favorable). By late October to early November, field dry‑down rates will usually drop to 1/4-1/2% per day and by mid November, probably 0-1/4% per day. By late November, drying rates will be negligible.

Estimating dry‑down rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25-20% requires about 45 GDDs per point of moisture. In October, we accumulate about 5-10 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids vary from this pattern of drydown.

Past Ohio research evaluating corn drydown provides insight on effects of weather conditions on grain drying. During a warm, dry fall, grain moisture loss per day ranged from 0.76-0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32-0.35%. Grain moisture losses based on GDDs ranged from 24-29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24-29 GDDs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20-22 GDDs. The number of GDDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.

Agronomists generally recommend that harvesting corn for dry grain storage should begin at about 24-25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear rots, insect feeding damage and wildlife damage. This year growers should be prepared for localized  root lodging and stalk lodging that may slow harvest and contribute to yield losses.

Potential for Stalk Lodging in 2011 Corn Crop

As farmers have started harvesting earlier planted corn fields (those typically planted in mid May or earlier, they've encountered stalk lodging especially in western counties. . Some of these fields received little or no rain since late June until the last couple of weeks, so drought conditions may have contributed to some of the stalk lodging that is occurring.

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; and high plant populations. This year, coupled with drought-like conditions early in the season, northern corn leaf blight towards the middle and later parts of the season has contributed to the loss of green photosynthetic leaf area in some fields, increasing the potential for "cannibalization" and consequently, stalk rot problems.

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, 6-8" 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 fields that 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!

Dry Corn in the Field or in the Grain Dryer

This year's late planting window throughout much of Ohio has led to a late maturing and high moisture corn crop. High moisture corn standing in the field is a dilemma. The question of whether to let corn continue to dry down in the field or harvest and dry through your on-farm grain drying facility (or pay commercial grain drying fees at your local elevator or terminal) is sometimes not an easy one. There are a number of variables to consider as we wrangle with this question. How much dry-down can we expect in the field? What is the stalk quality and can we expect corn to stand while we wait for this dry-down to occur? How much wildlife damage should we expect by letting corn "field dry"? Are there fungal disease issues that are occurring and what can we expect them to do to corn quantity and quality? How much will colder weather in later October and November affect drying efficiency? What is the cost of propane and drying? How many acres have to be harvested in our operation, and is waiting for corn to "field dry" an option given normal weather (or given adverse weather if we want to err on the side of caution) in October and November?

The biggest variables in this whole equation are how much dry-down we can expect in the field and the cost of mechanical drying.

According to Peter Thomison, Extension Corn Specialist, "Corn will normally dry approximately 3/4-1% per day during favorable drying weather (sunny and breezy) during the early warmer part of the harvest season from mid‑September through late September. By early to mid‑October, dry-down rates will usually drop to 1/2-3/4% per day. By late October to early November, field dry‑down rates will usually drop to 1/4-1/2% per day and by mid November, probably 0‑1/4% per day. By late November, drying rates will be negligible."

Armed with this information and near-term weather forecasts, producers can get some idea of what kind of dry-down potential there will be for their high moisture corn. Producers should also check stalk quality in fields that they are considering letting field dry.

The cost of drying is the other important piece in trying to answer this question. With propane costs around$1.50-$2.00 per gallon (depending on quantity purchased and time of purchase) drying costs will be substantial this year with higher moisture corn to harvest. Calculating your own on-farm cost of drying is preferred but if you would prefer to estimate multiply 0.02 times your propane cost.

Example- Harvest Now: Corn Moisture at 25% and propane cost at $2.00/gal. Cost to dry to 14%: $0.44/bushel. (0.02 x 2 x 11 points).

Now let's assume we decide to wait 1 week to harvest and expect a 3 point dry-down to occur with no field loss due to stalk lodging or ear drop. This saves us approximately $0.12/bushel ($0.32 drying cost versus $0.44). Assuming we have ample time to finish harvest and have no field loss in other fields due to waiting, it may be worth considering. For a 150 bushel yield this amounts to $18/acre in savings.

Now let's assume we will sustain a 3 bushel/acre yield loss due to waiting. If corn price is $6/bushel, your $18/acre savings on mechanical drying due to leaving the crop stand an additional week is offset.

This math will look different for every operation and will change each day. Understanding all of the factors and how to properly estimate the gains and losses from each factor will allow you to make the best informed decision when it comes to letting corn "field-dry" or drying it mechanically.

Terminals and grain elevators sometimes offer early harvest season discounts to their drying costs or allow high moisture corn to be delivered with reduced "shrink" due to their need for corn. These incentives are set to prompt growers to deliver corn early and are often advantageous to those who have corn that meets the moisture specifications laid out by the buyer.

Training Program on Herbicide Resistance available online from the Weed Science Society of America

The Weed Science Society of America (WSSA) has introduced a free training program designed to educate pesticide applicators, growers, agrichemical retailers, farm consultants and other stakeholders on herbicide resistance in weeds. The five-module program is available as web-based training, PowerPoint slides or video. WSSA plans to work with grower organizations, government agencies and others to disseminate the materials, with a special emphasis on reaching growers and agrichemical retailers, and is also exploring continuing education credits for those who complete the courses. The new herbicide resistance education program is initially available from the WSSA website at ( http://wssa.net/LessonModules/herbicide-resistant-weeds ) and from the Pesticide Environmental Stewardship (PES) website at ( http://pesticidestewardship.org ). Development of the program was supported by the National Corn Growers Association, the National Cotton Council, and the American Soybean Association. It was funded by WSSA and by the Herbicide Resistance Action Committee, an industry coalition focused on herbicide stewardship.

Newer Bt Corn Options

Last week we discussed the concern with resistance developing in the western corn rootworm to one of the Bt proteins and what this means, if anything, for Ohio growers. A few additional comments should be made when considering Bt transgenic hybrids because a few new choices have come on the market.  

There are two new hybrids from Syngenta, Agrisure 3220 and Agrisure 3122. Agrisure 3220 was released earlier this year and is in our table of current Bt corn products (as of April 2011) on our website ( http://entomology.osu.edu/ag/images/DiFonzo&Cullentrait_April_25.pdf ). Agrisure 3220 is a stacked hybrid with Cry1Ab, Cry1F, and Vip3A Bt proteins providing resistance to many of the various lepidopteran (above-ground) pests, including the western bean cutworm. This product does not offer control of rootworms. Only a five percent structured refuge is required (this product is NOT refuge-in-a-bag). The second, newer product is Agrisure 3122, which contains the Cry1Ab, mCry3A, Cry1F, and Cry34/35Ab1 Bt proteins offering control of both the above-ground lepidopteran pests along with corn rootworms. This product will be marketed as Agrisure 3122 Refuge Renew trait stack requiring only a five percent structured refuge. We would mention that Syngenta has submitted a five percent blended refuge-in-a-bag version of Agrisure 3122 for EPA approval. 

The second group of options comes from Pioneer, who previously had released Optimum AcreMax 1 and Optimum AcreMax RW, the latter being a refuge-in-a-bag product for rootworm. They have recently released two new products, Optimum AcreMax, containing Cry1F and Cry1Ab for lepidopteran or above-ground insect control, and Optimum AcreMax Xtra which includes those same two proteins as well as Cry34/35Ab1 for control of corn rootworms. Both Optimum AcreMax and AcreMax Xtra are integrated refuge products, meaning refuge-in-a-bag; no separate refuge is required. A major difference that growers should be aware of is that while Optimum AcreMax has a 5% integrated refuge, Optimum AcreMax Xtra has a 10% integrated refuge because of the addition of the genes for rootworm control. However, because the refuges are in the bag, no differences in planting will be evident; you open the bag and plant!

Weather Update October 3-October 10

Short term some good news! The first week of October will see a change to warmer and drier weather. Over the next week high temperatures will mostly be in the 60s to low 70s northeast to 70s west. Lows will be in the 40s and 50s. Little or no rain is forecast from Oct. 4-11. Normal temperatures are highs 65 northeast to 70 southwest and lows 45-50.

However, it looks like rain chances will come back in week 2, Oct. 12-19 as moisture surges north from the Southeast. Temperatures will remain close to normal with highs mostly in the 60s and lows in the 40s to low 50s. Rainfall will be normal to above normal. Normal is about 1/2". Expect 1/2-1" with the wettest being in the east and northeast sections. This could impact harvest especially in the north and east.

September was a wet month with above normal rainfall. In fact, some places like Dayton, OH saw their wettest September on record beating 2005.

Additionally, much of the north and south may approach or beat all-time annual rainfall records depending how the year ends. For example, Cincinnati needs about 3" to beat their all-time wettest year. The central section will have a very wet year too but does not appear it will beat all-time records unless we get a lot more rainfall by year's end. 1990 is one of those years to beat!

Looking forward to later October and early November, nothing suggests anything better than normal temperatures and rainfall. In fact there may be a preference for the trend of slightly wetter than normal to return. We will monitor.

Finally, we do not expect an early freeze this year. There is a very low chance of freezing temperatures the next 2 weeks. Wet soils will help to play a factor here by retaining heat.

 

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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.