C.O.R.N. Newsletter 2013-28

Dates Covered: 
August 27, 2013 - September 4, 2013
Editor: 
Rory Lewandowski
Questions about SDS

Questions about SDS

Our OSU Extension Agronomy State Field Specialist have assembled the following list of questions concerning sudden death syndrome and its widespread development across Ohio this year.  I’ve (Anne Dorrance) done my best to address most of them, although for some the “jury” is still out as we await data from this season’s trials.

Does seed treated with a fungicide reduce the level of infection for SDS?  Particularly fludioxonil which is listed as excellent on Fusarium, and if so, on average what length of protection to soybean seedlings could be expected ( ie. 7 days, 10 days)?

The jury is still out on the use of seed treatments for early season control of sudden death syndrome.  All of my data for seed treatments and Fusarium comes from F. graminearum, which is really a seed rotter.  F. virguliforme, the causal agent of SDS – is a root rotter, and can infect roots over the course of the season.  Seeds and seedlings are the most vulnerable stage to many pathogens, after this time the plants defense mechanisms will hopefully be able to pick up the slack.  There are a number of new seed treatments, including some that are biological, that may have more or longer activity.  We will see how this year’s studies go.

How good are the soybean genetic resistance genes in preventing infection?

In one word, excellent!  There is very good resistance to SDS now and as we can see from our field trials this year it is effective from the early to late season stages.  I need to remind everyone though – disease severity is directly linked to the presence of soybean cyst nematode and new findings indicate root knot nematode as well.  Managing SCN populations is very important to managing SDS.

How many races? I read that preliminary research Identified more than a dozen different Fusarium virguliforme.

There are no races – in the classic terminology in which an isolate will act differentially with a host that has R-genes, like we have with Phytophthora sojae.  Resistance to Fusarium virguliforme is a type of partial resistance and is effective against all strains.  The Leandro lab and colleagues at Iowa State University reported that there is variability within the F. virguliforme populations found in the US which was identified with molecular markers and different levels of aggressiveness (ability to cause disease), but natural variation is expected.

The very strong relationship of SCN to SDS is well documented - is this also true for Brown Stem Rot?

This strong relationship relates to the increase in severity of the disease in the presence of SCN.  Yes, this is also true for brown stem rot.  Brown stem rot and SDS have very similar foliar symptoms.

Plant area/Symptom

Brown Stem Rot

Sudden Death Syndrome

Pith

Brown

White

Tap root

White

Gray, sometimes with blue spores

Root Rot

Absent

Present

 

Studies from Japan, Iowa State and Univ. of Wisconsin all indicate that disease severity of BSR is greater when SCN is present.  However, most of our varieties now have SCN resistance and there is some reduction in overall symptom development – albeit the relationship is quite complicated.

Another facet that also influences brown stem rot symptom development is soil pH.  A study at the University of Wisconsin very nicely demonstrated that severity was greater when soils are low in phosphorus and potassium and soil pH is below 6.5

Malvick from Minnesota found many fields that with plants infected with both SDS and BSR; have found similar results in Ohio?

Numerous times, we have recovered both the SDS and BSR pathogens from the same plant- since 1997.

Seedlings are very susceptible to SDS infection according to Leandro of Iowa, but what about infection in later growth stages when SCN may be more active ?

SCN is very active and can sense the plants as soon as they have been planted.  For our studies with SCN, to get accurate population data – we try to sample within 24 hours of planting or many of the eggs will have already hatched.

When I examine SDS foliar symptom infected plants, the base of the plant may show brick red lesions characteristic of Rhizoctonia; have other pathogens been linked to SDS; or are these likely secondary fungi with Fusarium the primary disease causing agent?

We see this brick red coloration in response to several soybean pathogens, including Sclerotinia, occasionally Phytophthora.  This could be dual infections, all of these pathogens are in the soil and the conditions that favor one also favor these other pathogens.  This could also be part of the plants attempt to defend itself.  Glyceollin,  the key plant compound that is made, is toxic to many fungi and oomycetes.  We often see this red at the edge of the infection sites, the compound turns red once it comes into contact with sunlight.  Our own Dr. Terry Graham – Emeritus Professor in the Dept. of Plant Pathology has done an enormous amount of research on this compound.

The link between soil compaction and SDS is established; Given this link, can we also say that stress on the plant (too wet) may also contribute to SDS?

This relates more to the conditions that favor fungal growth, ability to form spores, and ability to infect plants.  Compaction helps keep the soil wet for a longer period of time, and takes longer to dry out.  The roots have a very difficult time penetrating this.  A very nice study at Southern Illinois University demonstrated that on heavy soils, breaking up that compaction layer reduced overall disease severity. For high yield production systems, field quality, and drainage are key to obtaining high yields.

Why is SDS appearing in new areas and not in areas where it has been observed in the past?

This is quite common with plant diseases, it all relates to the disease triangle.  Is the variety planted in those historic sites resistant to SDS, and are the SCN populations lower than when the symptoms were prevalent the last time.  For SDS to develop in a field, high levels of SDS inoculum AND SCN populations, a SDS susceptible host as well as heavy rains shortly after planting are needed. My thought and recommendation for producers, once you have SDS, always select a variety with resistance to SDS and SCN for future plantings.

Treating aphids at the R5-R6 transition

Treating aphids at the R5-R6 transition

Over the past few weeks, we have seen soybean aphids rapidly increase in population size and have received a lot of questions on whether or not to treat. By now we all should be familiar with the soybean aphid threshold of a rising population of 250 aphids per plant.  But keep in mind that this number is the action threshold, it is not the economic injury level (EIL) at which soybean aphid causes yield loss.  Yield loss occurs when aphids reach 500-600 aphids per plant.  Furthermore, these numbers do not apply to beans at R6 and later.  The thresholds at these growth stages increase to over 1,000 aphids per plant.  So if you are in an R5 stage, and have 250 aphids per plant should you treat?  Here is some information to help you guide your decision:

1) Check again in 3-4 days, are the aphids increasing (remember a RISING population of 250 per plant)? At many sites, natural enemies like lady beetles are keeping aphids down.

2) At this point in the summer, you can expect aphids to double in size in about a week. Do you think you will reach R6 before aphids get to 500 per plant? If so, then it probably won’t pay to treat. Bottom line is predicting when you can get to R6 when thresholds go up. 

3) Do you have to use ground equipment?  Then expect a 2-3 bushel loss on yield which might impact whether or not you see a return on the application cost.

Seems like this year, soybean aphid appeared very late in the season for Ohio, which can sometimes make for difficult treatment decisions.  However, predicting when soybean will reach the R6 stage and frequent scouting will provide the best information on whether or not it pays to treat.  

Estimating Soybean Yield

To estimate yield, four soybean yield components need to be considered: plants per acre, pods per plant, seeds per pod, and seeds per pound (seed size).  A printable worksheet to estimate soybean yield can be found by clicking on the following link: yield worksheet

It is difficult to accurately predict soybean yield because of plant variability, but estimates become more accurate as the growing season progresses.  During last year’s soybean workshops, we calculated soybean yield based on this procedure and compared our results to yield from a plot combine.  The soybean yield estimate method consistently predicted higher yields compared to combine yield.  On average, yield estimates were often 25-50% greater than combine yield.  Why did this occur?  There is a great deal of plant to plant variability and a sample size of ten randomly selected plants may not be a large enough sample size.  The more plants used in yield estimates, the more accurate the estimate becomes.  Also, consider how “randomly” plants are selected for yield estimates.  It’s possible to inadvertently select larger/healthier plants for yield estimates.   

To estimate soybean yield:

1. To calculate plants per acre, count the number of pod-bearing plants in 1/1,000th of an acre.  In 7.5-inch row spacing, count the number of plants in 69 feet, 8 inches of row.  In 15-inch row spacing, count the number of plants in 34 feet, 10 inches of row.  In 30-inch row spacing, count the number of plants in 17 feet, 5 inches of row. 

2. To estimate pods per plant, count the number of pods (containing one or more seeds) from 10 plants selected at random.  Divide the total number of pods by 10 to get the average number of pods per plant.

3. To estimate the number of seeds per pod, count the number of seeds from 10 pods selected at random.  Generally, the number of seeds per pod is 2.5, but this number can be less in stressful environmental conditions.  Divide the total number of seeds by 10 to get the average number of seeds per pod.

4. To estimate the number of seeds per pound (seed size), assume that there are 3,000 seeds per pound.  If the soybean plants experienced stress, seed size will be reduced, and it will take more seeds to make one pound.  Use a seed size estimate of 3,500 seeds per pound if smaller seeds are expected because of late season stress.

Using the above estimates, the following formula is used to estimate soybean yield in bushels per acre: bushels per acre = [(plants/1,000th acre) x (pods/plant) x (seeds/pod)] ÷ [(seeds/pound) x 0.06]

Scout new CREP areas now for Palmer amaranth

Palmer amaranth has been increasing around the Midwest and CREP seedings can apparently be one source of new infestations.  Much of the seed for CREP seeding comes from Kansas where Palmer amaranth and other pigweeds are abundant, and it has become apparent over the past decade that it is possible to have Palmer amaranth seed present in the seed mixtures used to establish CREP areas.  We so far have one major Palmer amaranth infestation in far southern Ohio, and it was our assessment that a CREP seeding about five years ago was probably the source of Palmer amaranth there.  We also identified Palmer amaranth in several other CREP seedings about 7 years ago, but none of these appeared to gain a foothold in nearby crop fields.  We were made aware of the presence of Palmer amaranth in another new CREP area last week, and we are assuming that the source of the Palmer there was also contamination of the seed mix.  The Palmer amaranth infestation in far southern Ohio is definitely resistant to glyphosate, but we don’t yet know whether this new one is resistant. 

One of our assumptions about Palmer amaranth based on experiences in the southern United States is that it will likely develop glyphosate resistance in crop fields when exposed to repeated applications of glyphosate.  It’s important that we err on the side of preventing new infestations of Palmer amaranth in Ohio so that we don’t have similar experiences here.  We are working with several agencies to better determine whether seed used to establish CREP does contain Palmer amaranth seed, and if so, what steps need to be taken to make sure this stops.  Our recommendation at this point for landowners and growers is to scout recently established CREP areas for the presence of Palmer amaranth.  Plants that are not yet producing viable seed (small black seed when you shake or smash seedheads in your hand) should be removed from the field immediately to prevent seed production.  Herbicides applied now are not likely to adequately prevent the development of viable seed.  Where plants are already producing viable seed, it would probably be best to just leave them where they are to prevent spread of seed.  Intensive monitoring of any infested areas and adjacent fields should obviously also occur for the next several years.  There is information on identification and management of Palmer amaranth on the OSU and Purdue weed science websites, including short videos on identification that can be reviewed prior to crop harvest.  Click here to access the OSU Extension page on Palmer amaranth: https://agcrops.osu.edu/specialists/weeds/palmer-amaranth

We would appreciate knowing about any new infestations of Palmer amaranth for the purpose of helping landowners and growers put management plans in place to prevent further spread and mitigate existing situations.

Multicolored Asian Lady Beetle

Multicolored Asian Lady Beetle

One of the consequences of this past summer having been a soybean “aphid year” is the development of large populations of the multicolored Asian lady beetle in soybean fields where aphids were numerous.  When walking through such fields, it is easy to see many lady beetle larvae and adults on top of the plants.  From the soybean’s perspective, this is a good thing because the lady beetles will help to reduce aphid populations that go to buckthorn where they lay their eggs.  This should help to make next year, 2014, a “low aphid year”.  However, we would remind everyone that these lady beetles, as the soybeans mature, will begin going to other crops including fruits and grapes causing concern, especially for wine producers.  At a later date, they will begin showing up in people’s homes and apartments in large number to try to overwinter inside buildings.  These issues have occurred in late summer and the fall every two years following economic populations of soybean aphids, which was characteristic of this past summer. 

Weather Outlook: Mostly warmer and drier

The weather pattern has now shifted to warmer and drier than normal and this will likely be the rule into early September except in northeast sections where more rainfall will occur.

The outlook is for much above normal temperatures for the last week of August with below normal rainfall except in northeast section of the state that will see near normal rainfall.

Temperatures for the last week of August will average 10-15 degrees above normal. Rainfall will average 0 to 0.50 inches with isolated totals especially in the northeast topping 1-2 inches in thunderstorms.

Temperatures will remain above normal for the first week of September but the overall pattern will relax. Temperatures will be about 1-5 degrees above normal. Normal highs are in the upper 70s to lower 80s and normal lows are in the upper 50s to lower 60s. Rainfall will continue to be below normal with most places getting 0.50 inches or less.

The 16-day rainfall outlook from the National Weather Service Ohio River Forecast Center can be seen here:

http://www.erh.noaa.gov/ohrfc/HAS/images/NAEFS16day.pdf

Looking further ahead, indications are it will turn cooler and wetter for the second half of September, but until then it will be warmer and drier than normal in most places.
 

Modified Rely Intercropping Soybeans into Wheat Field Day

Modified Relay Intercropping (MRI) is the planting of soybeans into standing wheat about the time wheat is flowering. In 14 years of replicated trials in North Central Ohio on the MRI system, yields have averaged 76 bushels/acre for wheat and 28 bushels/acre for soybeans. Wheat yields in favorable growing seasons have exceeded 90 bushels per acre and while soybeans have yielded well over 40 bushels per acre.

 In some years, MRI may offer a greater soybean yield potential than traditional double cropping of soybeans after wheat.   Vyn et al, found that relay intercropping of soybeans yielded better than double cropping of soybeans north of I - 70 in Indiana (http://www.agry.purdue.edu/staffbio/AY316.pdf).  

The focus of the field event will be to share information on how the system works, and to view various trials of intercrop soybeans.  Intercropped corn and grain sorghum will also be demonstrated.

The event will be held at the OSU Unger Farm on Sept. 4, 2013 from 6:30 to  8:00 PM.  The OSU Unger Farm is located a quarter mile west of Bucyrus on Bucyrus Nevada Road. Watch for signs.

Organic and Sustainable Agriculture Field Day

Thursday, September 5, 2013.  Time from 5:00 – 8:00 pm.  Meal provided.

Location: Agricultural Incubator Foundation, 13737 Middleton Pike, Bowling Green, OH.  5 miles north of Bowling Green, take St. Rt. 582 exit from Interstate 75, turn west about 2 ½ miles.

The field day is free and open to the public.  No reservations needed.

Agenda includes discussion of OSU Organic Food and Farming Education Research program, scientists will discuss results and seek comments for future research.  Organic Valley organic corn variety test plot, 24 varieties.  Zeolite soil amendment research, USDA long-term organic eco-system services grant results, no-till organic grain production, cover crops, pest scouting and organic controls.

Sponsored by O.A.R.D.C. (Ohio Agricultural Research & Development Center) and OSU Extension

Contact Alan Sundermeier at 419-354-9050 or Sundermeier.5@osu.edu for further information.

PAT Credits offered at Independent Ag Equipment Field Day

Extension will offer both private and commercial PAT credits at a field day sponsored by Independent Ag Equipment, 4341 Sandhill Road, Bellevue, OH 44811. The field day will be held Thursday, September 5, 2013 with PAT sessions beginning at 10:45 a.m.  Although this is a company field day, pesticide training is open to the public. Field Specialist Dr. Steve Prochaska and Huron County Extension Educator Mike Gastier will offer one hour of core training and one half hour in category 2A and 2C ( Category 1 private). Certified Crop Advisor continuing education credits will also be offered. No reservations are required. If more information is needed please call the Huron County Extension office at 419-668-8219.

2013 Soybean Disease and Pest Twilight Meeting

What?

An Ohio Soybean Association membership engagement that will include field tours of insecticide and fungicide trials. Dr. Anne Dorrance, Ohio Agricultural Research and Development Center (OARDC), will speak about frog eye and brown spot. In addition, Dr. Andy Michel, OARDC, will speak about stink bugs and aphids.

Where?

Buck Farm

7632 Wildcat Pike

New Bloomington, OH  44341

When?

September 5, 2013. The program will begin at 5:30 p.m. Dinner will be provided.

There is no registration fee, but limited space is available.  RSVP by calling the Ohio Soybean office at 614-476-3100 or email David Blankenship at dblankenship@soyohio.org.

 

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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.