C.O.R.N. Newsletter 2006-19

Dates Covered: 
June 26, 2006 - July 3, 2006
Editor: 
Greg LaBarge

Flooding Injury to Soybeans

Authors: Anne Dorrance

Several past studies have evaluated the effects flooding on soybeans. Research projects led by Dr. Tara Van Toai of the USDA-ARS and Department of Horticulture and Crop Science. In one study, soybean plants at the V2 and V3 stages were flooded naturally due to excessive rainfall, something we are all familiar with. Two 9-m wide transects across the flooded area within each field were divided into plots of 9 m by 9 m according to flooding duration: no flooding, 1 to 3 d, 4 to 6 d, and 6 to 8 d. Yield was reduced primarily due to reduced plant populations, shorter plants and fewer pods developing per plant. Other studies showed yield losses of 20% when soybean fields were flooded for greater than 2 days, but it should be noted they still had a yield. Some varieties can tolerate flooding more than others. For those fields with greater than two days of total saturation, ponding, can expect to see some long term effects. Secondary factors, such as root rots, will also contribute to the damage. Growers should note the varieties and compared varieties that were flooded for the same length of time. Some varieties will be impacted to a greater degree than others.

Late Replanting Decisions in Soybeans

Authors: Greg LaBarge, Jim Beuerlein

Replanting decision are easy when the crop is completely destroyed and we need to start from scratch. When a partial stand exist then the decision always tougher because we need to take in factors such as the original stands expected yield and what the replanted crop may gain us. In addition, we need to select the proper maturity to allow the crop to maturity before frost in the fall.

Replanting Decision

A step-by-step decision guide for estimating the returns to replanting is shown below. A method to estimate soybean plant stand using a hoop can be found at: http://corn.osu.edu/story.php?setissueID=135&storyID=801

1. Base yield for field ____ bu/a
2. Est. of yield as % of normal from reduced stands (Table 1 below) ____ %
3. Est. of deficient stand yield (Base yield x line 2) ÷ 100 ____ bu/a
4. Projected gross income (line 3 x market price) ____ $/a
5. Weed control cost for poor stand ____ $/a
6. Gross return with no replanting(line 4 minus line 5) ____ $/a
7. Est. of yield as a % of normal from delayed planting (Table 2 below) ____ bu/a
8. Est. of yield for replanting (Line 1 x line 7) ÷ 100 ____ bu/a
9. Projected gross income from replanting (line 8 x $ price) ____ $/a
10. Cost of replanting (tillage, seed, herbicide, labor) ____ $/a
11. Gross returns from replanting (Line 9 minus line 10) ____ $/a
12. Compare gross returns on line 6 and line 11 to determine whether to replant ____ $

Table 1. Yield effects from reduced plant populations with uniform stand and weed-free conditions.

  % of Full Yield
Population (Plants/A) Conventional No-till
160000 100 100
120000 100 98
80000 98 95
60000 90 90


Table 2. Expected yield of soybeans based on planting date.
Planting Date Yield (% of Normal)
May 1 100
May 10 99
May 20 96
May 30 90
June 10 80
June 20 68
June 30 57
July 10 40


Variety Selection

If the decision to replant is obvious or makes economic growers should carefully select maturities to fit the rest of the growing season. Table 3 shows recommended maturity ranges based on area of the state and planting date.

Table 3: Recommended Relative Maturity Ranges for Soybean Varieties Planted in June and July in Northern, Central, and Southern Ohio.
  Planting Date Suitable Relative Maturity Yield Potential
Northern Ohio June 1-15 3.2-3.8 20-45
June 15-30 3.1-3.5 15-35
July 1-10 3.0-3.3 10-25
Central Ohio June 1-15 3.4-4.0 28-48
June 15-30 3.3-3.7 20-40
July 1-10 3.2-3.5 15-33
Southern Ohio June 1-15 3.6-4.2 30-50
June 15-30 3.5-3.9 25-45
July 1-10 3.4-3.7 20-40

More information on replant decisions can be found in the Ohio Agronomy Guide at: http://ohioline.osu.edu/b472/0006.html and Corn, Soybean, Wheat, and Alfalfa Field Guide at http://ohioline.osu.edu/b827/0003.html.

 

Soybean Rust and Plant Health

Authors: Anne Dorrance

The risk of rust is extremely low for Ohio for the foreseeable future (June 26, 2006). We will continue to monitor our sentinel plots, look for other soybean diseases and continue to build our database. The drought in the southeast is the primary reason for the –non-development of rust this year. This then raises several other issues, Section 18 materials, triazoles, should be put in storage. Talk to your rep to see what the conditions are to maintain the effectiveness of the material. Any use of these materials is off-label. For the fungicides that have full Section 3 label, there has been a substantial amount of debate over their use. My colleague at the University of Kentucky, Don Hershman, has a very nice article addressing the numerous issues. He has given us permission to reprint it here.

For those of you that would like to “experiment” with this plant health aspect, here are a few guidelines that I would recommend to give you the best information.

1. Know what the variety is.
2. Have more than one check strip, wider than your combine, and space them across the field. Three should be plenty.
3. In your comparisons, do not include the parts of the field where you have weed escapes or along tree lines, these areas are going to yield less anyways, so this is false data whether it was treated or not.
4. Take averages. When you do harvest your fields, take several strips, both untreated and treated. Then take the average of the untreated strips and compare that average to the treated. Fields are not uniform and with our stand issues this year there is going to be even more variability across the fields.

“PLANT HEALTH” FUNGICIDE APPLICATIONS TO SOYBEAN
By Donald Hershman, Professor and Extension Specialist, University of Kentucky

As I write this article (June 19, 2006) the soybean rust risk in Kentucky soybean is very low. I do not foresee a change in this situation at least through early July. During the next 30 days, many acres of Kentucky soybean will be in the early reproductive stages (R2 – full flowering to R3 – early pod development). This is the target period for “plant health” application of fungicides. These treatments are beingprom oted by a couple of major fungicide manufacturers as a means of promoting enhanced plant health, leading to higher crop yields. Suggested treatments involve strobilurin-containing fungicides, such as pyraclostrobin (e.g., Headline) or azoxystrobin (e.g., Quadris).

In the absence of soybean rust and significant risk of infection by the rust pathogen, the decision to apply a “plant health” fungicide application is not as straight forward as some might believe. There is not general agreement among university and industry scientists regarding the potential for plant health applications to result in economical benefits to producers. By economical, I mean that the $ return per acre exceeds the $ invested in fungicide/application costs.

During 2003-05, the Kentucky Soybean Promotion Board invested a significant
amount of your check-off dollars to determine the potential for “plant health” fungicide applications to result in an economic benefit to producers. Funds were given to the University of Kentucky and WheatTech, Inc. to facilitate independent study of this question. Tests conducted by the University of Kentucky involved both large and small plot studies during 2003-05. WheatTech studied the question in a small plot tests during 2004-05 tests.

The results of tests were mixed, but generally,applications of fungicides to soybean, in the absence of specific foliar fungal diseases, frequently did not produce a statistically significant (i.e., economical) yield response. Specifically, over the three years of study, significant yield results were encountered in six (6) of twenty-four (24) experiments (25.0% response rate). A similar rate of statistically significant treatment responses (26.9%) was seen in 62 replicated experiments conducted throughout the Midwest and Northeast during 2005. These experiments involved both large and small plot tests. All of the experiments referenced so far involved replication of treatments, which gave scientists the ability to statistically analyze treatment results. The ability to statistically analyze treatment results may seem more “ivory tower” than practical, but in fact, just the opposite is true. From a practical perspective, the only way to know, with any
degree of certainty, if one treatment produced a different result than another
treatment is to subject results to the rigor of accepted statistical procedures. Anything less results in one guessing if one treatment really had an impact, or if apparent differences were merely the result of chance and/or inherent experiment variability.

In contrast to the above, results of “plant health” fungicide applications based on a large number of strip plot, side by side comparisons, in grower fields have been much more favorable to potential yield benefits. For example, 162 side by side comparisons, summarized by BASF from Indiana and Ohio in 2005, showed an average yield response to “plant health” fungicide applications of 5.6 bu/ac (3 - 4 bu/ac is considered to be break even, depending on the fungicide and application cost, and the price received per bushel of soybean). Comparisons summarized from 192 fields across the Midsouth in 2005, including Kentucky, were even more favorable with an average yield response of 8.5bu/ac. It is my understanding is that Syngenta can produce similar results from their on-farm trials over the last few years.
There are many inherent problems with non-replicated, side by side, strip plot
comparisons. One major concern is that results typically do not include detailed information on disease activity. Thus, one cannot know if a disease was the reason for the success or failure of a treatment. In addition, treatments in a field cannot be statistically analyzed because there is no in-field treatment replication. Still, large numbers of strip trials with similar results have meaning and value, albeit serious questions still exist about the data generated.

What is one to make of the apparent discrepancy between the results of 84 replicated experiments, conducted by numerous scientists, and the results of non-replicated, but numerous, on-farm treatment comparisons conducted by industry? To be honest, I am not sure. Certainly, the great disparity in results should be a “red flag” to anyone considering making applications of foliar fungicides to soybean in the absence of specific foliar fungal target diseases. On the other hand, very high treatment yields in many strip plot comparisons (and some replicated experiments) over the last few years make it clear that something significant is going on. I have seen enough positive results to conclude that “plant health” applications of fungicides
to soybean cannot not be discarded, offhand. Yet, I have also seen enough negative results to know that there are many, many scenarios where “plant health” fungicide applications simply will not pay for themselves.

At this point, I would simply caution producers who are considering making fungicide applications for plant health benefits, to make those applications with the awareness that a significant economic response is not assured. At this point, we (university and industry scientists) do not have enough information to be able to recommend which fields/situations have a high probability of an economic response and which fields have a low probability of response. In addition, applications of any pesticide in the absence of a specific target pest(s) is contrary to integrated pest management principles. Thus, there may be unintended, long term implications (environmental,
regulatory, and/or sociological) associated with applying fungicides to soybean in the absence of specific target pests. One consequence could be the suppression of native fungi that keep insect populations in check, naturally. There is already some evidence that indiscriminate use of fungicides in soybean has resulted in increased insect/mite activity in some states. Another consequence could be stricter future pesticide laws and regulations. The point is we must be very cautious when we get into the realm of applying fungicides (or any pesticide) to large acreages of soybean (or any crop), even if there is a good rationale for doing so. In this article, I am making it known that the rationale for making “plant health” fungicide applications to soybean is not firmly in favor of making the applications. Thus, caution is advised at
numerous levels.

Sampling Wheat for Deoxynivalenol (DON)

Authors: Dennis Mills, Pierce Paul

Deoxynivalenol (DON) is a mycotoxin produced by some species of Fusarium. Members of this group of fungi (predominantly Fusarium graminearum in North America) cause head scab in wheat and ear and stalk rot in corn. DON is NOT known to be produced by the fungi which cause Stagonospora and Septoria blotch of wheat. Once Fusarium graminearum infects and colonizes the wheat heads and the right set of environmental conditions occur (temperatures between 70 and 85F and moisture levels greater than 20%), DON may be produced. There is a positive association between the amount of scab we see in the field and the level of DON contamination. However, since both the manifestation of scab symptoms and DON accumulation are highly weather-dependent, it is not uncommon to find fields with lower or higher levels of DON than the visual symptoms suggest. In addition, DON may still accumulate in storage if storage conditions are inadequate, leading to levels of the toxin that are high relative to the visual scab symptoms seen in the field. Wheat lots are often docked when DON contamination exceeds certain levels; hence, testing for DON is a common practice when marketing wheat.

Since DON is water soluble, it can be extracted from grain using mixtures of solvents and water (methanol + water, acetonitrile + water). Several different methods are available for testing grain for DON. It is beyond the scope of this newsletter to describe every method in detail, however, it is important to know that they vary greatly in sensitivity (any two tests may give different results), and as such, should all be tested prior to being used. ELISA-based (enzyme linked immunosorbent assay) methods are the most widely used and recommended. Several commercially available test kits are ELISA-based. Regardless of which method is used, it is important to perform the test using a sample of grain that adequately represents the lot being tested. Sample size, number of samples, and location from which samples are taken may all affect the accuracy of the test. Unless the entire lot is heavily infected, the spread of scabby kernels within the lot is highly variable. A single sample taken from a single location within the lot may lead to incorrect conclusions regarding the overall level of toxin contamination. Ideally, multiple samples should be taken at random from multiple locations within the lot. The number of samples will vary depending on the size of the lot.
When the level of scab in a field is high, several precautions should be taken to reduce mycotoxin contamination of the harvested grain (taken from Fact Sheet AC-4-96; Head Blight or Scab of Small Grains by P. E. Lipps):

1. Adjust combine to blow out smaller, shriveled kernels.
2. Dry harvested grain to 13.5 percent moisture as soon as possible after harvesting. The Fusarium fungi cannot grow or produce mycotoxins in grain at this moisture level.
3. Store suspect grain by itself and do not mix with good quality grain. Mixing contaminated grain with good grain will only yield a poor product that may be difficult to sell.
4. Have suspect grain analyzed by a laboratory adequately equip to perform such analyses before feeding to livestock. For more information on mycotoxins and a listing of laboratories that can do the testing visit the field crops pathology website at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/ and click on Moldy Grains, Mycotoxins and Feeding Problems and Mycotoxin Sampling/Laboratories for Analysis.

How Late Can Roundup Ready Soybeans be Treated With Glyphosate?

Authors: Mark Loux

In a recent publication from Monsanto called the “Roundup Ready Soybean Management Guide”, the company has clarified how late in the season glyphosate can be applied to Roundup Ready soybeans. Current wording on Monsanto brand glyphosate products states that glyphosate can be applied to Roundup Ready soybeans “throughout flowering”. The label has been revised to define this more in terms of standard growth stage designations for soybeans. Labels will now state that Monsanto brand glyphosate products can be applied to soybeans through the R2 growth stage (flowering), but not after the R3 growth stage begins. The R3 growth stage begins when one of the uppermost four nodes with a fully developed leaf has a pod that is at least 3/16 inches long. Application of glyphosate to soybeans that have started the R3 stage is not supported by the label (i.e not legal).

We have only infrequently observed injury to Roundup Ready soybeans from late-summer glyphosate applications. However, these label changes would restrict how late glyphosate could be applied and presumably help growers avoid this injury. Our research shows that, when an appropriate management strategy is used to manage weeds in Roundup Ready soybeans, there is little need to apply glyphosate in late summer. Late summer applications are most often needed when the first postemergence application is delayed so long that large weeds are not well controlled, and an even later second application is then required to try to complete control of these weeds. Late season weed control problems are compounded by the slower soybean canopy development that is the result of the extended duration of early-season weed-crop competition in this situation, which results in a crop that is less able to suppress late-emerging weeds. This problem can largely be avoided by making the first postemergence application when most of the weeds are no more than 4 to 8 inches tall, and applying glyphosate again about three weeks later. Use of a residual herbicide at the time of planting allows the initial postemergence glyphosate application to be made 1 to 2 weeks later in the season, which often eliminates the need for a second postemergence application althogether.

The label changes also appear to have the purpose of making growers aware that the label does not support the use of glyphosate to control soybean rust. The publication states that there is insufficient evidence at this time to show that glyphosate adequately controls rust. Should fungicide treatments be needed to control rust, they would often be applied after R3 stage. Restricting the application of glyphosate to R2 or earlier means that the legal application window for glyphosate is not likely to coincide with the timing of fungicide applications. The Monsanto publication states, “Since Asian rust typically requires management at later stages of soybean development, Monsanto wants to emphasize that growers must not delay Roundup agricultural herbicide applications into reproductive soybean growth stages in an attempt to gain additional rust management value.”

We have been asked many times about the possibility of applying glyphosate with an insecticide and/or fungicide late in the season, in order to reduce applications costs. There does not appear to be antagonism between glyphosate and the fungicides or insecticides, and it could make sense to apply them together if there is a need for late-season weed control along with insect or disease control. However, this application would be legal only if soybeans were not past the R2 stage, and not supported by the glyphosate label if soybeans were in the R3 or later stage. As we mentioned earlier, growers who find themselves often having to apply glyphosate in late summer should modify their weed management programs in Roundup Ready soybeans. Late-summer applications are usually not needed where glyphosate is appropriately managed.

 

European Corn Borer Update

Authors: Ron Hammond, Bruce Eisley

We are getting a few reports of ECB damage showing up and in at least one case the percent of plants showing injury is above the threshold level. Remember to check whorls for live larvae if a field is near or over the threshold level. Heavy rains last week may have killed some larvae in the whorl and thus treatment would not be necessary. We would suggest that you pull several whorls and carefully unroll the whorl to look for live larvae. This will also tell whether the larvae or still in the whorl and have not drill into the stalk. If larvae have already drilled into the stalk then the larvae will be harder to kill.

Sampling for Corn Rootworm Larvae

Authors: Bruce Eisley, Ron Hammond

The next couple of weeks will be a good time to check for corn rootworm larval feeding injury. Corn fields to check include fields where corn follows corn or those fields in NW and west central Ohio where corn follows soybeans and the possibility of first year corn damage might be possible. The reason to check in the next couple of weeks is because the maximum larval feeding injury will be during this time and larval feeding will be ending as the larvae pupate and new adults begin to emerge. After larval feeding has ended, the roots on some hybrids will begin to regenerate and when this happens, rootworm larval injury is more difficult to detect.

We suggest the following method to check for rootworm injury:

1. Carefully dig plants, don’t pull them, from the field taking as much soil as possible with the plant.

2. Carefully remove as much soil as possible from the plant without damaging the roots and also look for any larvae that might still be in the soil or on the roots. Rootworm larvae are white, about 1/2 inch in length when full grown with a brown head and brown plate on the tail http://ohioline.osu.edu/icm-fact/images/43.html (see picture).

3. If there is still soil on the roots you can either soak the root system in a bucket to loosen this remaining soil or you can spray the root system with a hose to remove the remaining soil.

4. After the soil has been removed, check the roots for feeding injury, either roots chewed back to the stalk or tunneling in the roots.

Root systems can be rated using either a 1 to 6 scale or 0 to 3 scale. In both ratings, the scale indicates the amount of damage to the root system and can be used to determine if economic injury has occurred.

Iowa 1 to 6 Scale: (Economic injury normally occurs at a rating of 3 to 3.5)

Rating by damage to roots

1 - No damage to the roots.
2 - Slight feeding scars present.
3 - One root chewed to within 1-1/2 inch of the plant.
4 - One node of the roots destroyed.
5 - Two nodes of the roots destroyed.
6 - Three nodes of the roots destroyed.

Modified Node-Injury Scale.

Rating by damage to roots

0 - no visible damage to roots
0.05 - slight scarring
0.08 - moderate to severe scarring, no roots chewed to 1.5 inches of stalk
0.1 - one root chewed to 1.5 inches of stalk
0.5 – half node of roots chewed to 1.5 inches of stalk
1 - one node of roots destroyed
2 - two nodes of roots destroyed
3 - three nodes of roots destroyed

Many areas in Ohio had a lot of rain last week and this may have some effect on the survival of larvae at this time. If you are in an area that received heavy rainfall and have saturated soils, if you digs roots in these areas, see if larvae are still alive at this time.

Potato Leafhopper and Resistant Alfalfa

Authors: Bruce Eisley, Mark Sulc, Ron Hammond

Last week we mentioned the need to begin sweeping alfalfa for potato leafhopper adults and nymphs. We had reports that some second cutting fields have required treatment. Sampling procedures and thresholds were given, with treatment for leafhoppers being based on the number of adults and nymphs found when sweeping versus the height of the alfalfa. Treatment is warranted if the number of adults and nymphs in 10 sweeps equals or exceeds the height of the alfalfa in inches.

We failed to discuss the situation for potato leafhopper resistant alfalfa. Although we expect much less injury to resistant alfalfa, leafhoppers can cause injury in some instances, especially to first year growth or to subsequent cuttings if leafhopper densities are extremely high. Prior to the first cutting during the establishment year when spring planted, research suggests it might be prudent to continue to use the same threshold, that is, when PLH numbers in 10 sweeps equal or exceeds the height of alfalfa. During subsequent cuttings thereafter, or in the first summer following a fall planting, our research indicates you can use a 3X threshold for the varieties that have been demonstrated to be highly tolerant of the pest in yield trials that have not been treated with insecticides (OSU has such trials, see results at http://www.ag.ohio-state.edu/~perf/). For resistant alfalfa beyond the first cutting, treatment would be warranted if the number of leafhoppers in 10 sweeps is three times the height of the alfalfa. Thus, if plant growth were 6 inches, the threshold on resistant alfalfa would be 18 leafhoppers in 10 sweeps.

 

Prospects for "Muddied Corn"

Authors: Peter Thomison

During the past week, localized flooding along stream banks in northern Ohio resulted in partial and complete immersion of nearby corn fields. In some cases, corn plants were under water for up to two to three days. When water drained off fields, plants were covered to varying degrees with a layer of mud. There have been questions about whether corn plants covered by a layer of mud will survive and/or can perform normally.

The layers of silty mud covering plants will limit or prevent leaf photosynthesis. Bacteria deposited in leaf whorls by flooding can result in disease and kill plants. On the positive side, most corn in Ohio has entered a phase of growth that is less vulnerable to flood damage. Corn planted before May 10 is probably well beyond the V5 stage when the growing point is at or below the soil surface and more sensitive to flooding and associated anaerobic soil conditions. Moreover, most corn development in the state has not progressed beyond the 10 to 11 leaf collar stage of development so most leaves on affected plants should not be severely impacted by the mud coatings (assuming that mud in the whorl does not inhibit normal emergence of subsequent leaves). Corn plants produce up to 21 leaves, so at the 10 to 11 leaf collar stage, about half the corn leaves have yet to emerge from whorl.

The leaves that have yet to emerge are the most important for the corn plant because the upper canopy produces most of the corn plant's yield potential. According to the National Insurance Service's defoliation charts, complete leaf loss at the 11 and 13 leaf collar stages results in 13 and 22% yield loss, respectively. However, it's unlikely that photosynthetic capacity of leaves has been completely destroyed in plants covered with mud. Rain forecast later this week will wash silt off leaves allowing for resumption of photosynthesis. It will also help wash mud out of leaf whorls allowing new leaves to emerge.

 

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Mark Loux and Jeff Stachler (Weed Science), Peter Thomison, (Corn Production), Ron Hammond and Bruce Eisley (Entomology). Extension Educators: Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Woody Joslin(Shelby), Steve Bartels (Butler), Steve Prochaska (Crawford), Greg LaBarge (Fulton), Steve Foster(Darke), Mark Koenig (Sandusky), Jim Skeeles (Lorain), Alan Sundermeier (Wood), Mike Gastier (Huron), Bruce Clevenger (Defiance) and Keith Diedrick (Wayne)

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.