Posts filed under ‘crop disease’

How Soybean Sudden Death Syndrome Looks at the Root

Most agronomists and farmers are good at identifying soybean Sudden Death Syndrome (SDS) through leaf symptoms (below image courtesy of Glen Arnold, OSU Extension Putnam County):

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However, there is another diagnostic feature that can be used as well.  OSU’s Anne Dorrance will also use blue spores of the SDS fungus on a soybean tap root as a diagnostic feature.  This avoids incorrect diagnosis, that is, diagnosing brown stem rot or interveinal chlorosis from nutrient deficiency as SDS.

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Full podcast here:  

August 24, 2010 at 12:07 pm 1 comment

Precautions for Handling Moldy Grain

Poor quality and mycotoxin infested grain is common this year with some growers reporting very low levels to very high levels.  Purdue University recently published a short article on grain safety handling:

Breathing grain dust is never healthy, and grain handlers should always wear protective masks when they work in grain bins, and when conducting operations that generate dust. Grain damaged by ear rots will have higher levels of dust and fines present, compared to good quality grain. Fungal spores produced by the ear rot fungi will also be in the grain dust. Fortunately, the fungus that causes Gibberella ear rot does not produce a lot of spores. However, there will certainly be spores of other molds in the grain dust. These spores can lead to allergic reactions, which may include flu-like symptoms, if workers do not take precautionary measures to protect themselves from exposure.

Simple safety procedures can be implemented to minimize exposure to grain dust and mold spores. When working with moldy grain, wear appropriate clothing such as long sleeves, pants, and gloves. A dust mask or respirator should also be worn to minimize inhalation risks. People who have a compromised immune system or respiratory ailments should avoid handling or working with moldy grain.

Full podcast here:

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February 17, 2010 at 8:12 am

Soybean Rust – Close to Ohio in 2009 but no Cigar

Dr. Anne Dorrane, OSU Extension Pathologist, recently discussed how close soybean rust came to Ohio in 2009. Excerpted from the January 12, 2010 CORN Newsletter:

Soybean rust was a big topic again at the end of 2009. First detections in Kentucky were in early September and followed a month later on late planted soybeans in Southern Indiana. What was most impressive this year – was the amount of rust that built up in the southern states at the end of the season. A limited number of Mississippi producers had yield losses directly due to soybean rust based on reports from Dr. Tom Allen, their field crop pathologist. In addition to the soybean, the amount of kudzu that was also infected is also becoming an issue. The good news is that again, not all kudzu is susceptible to the current strains of soybean rust we have right now. And the kudzu patches that are Susceptible are getting placed on maps to make the scouting easier in the future.

The biggest announcement that was made at the 2010 APS National Soybean Rust Meeting held in December was that the sentinel plot system would change. And this is a good thing. We know more, we can be more efficient at scouting now that we know where to look and those of us in the north can get better and knowing when to look. There is no point in searching in Ohio, if the southern states are negative. For 2010, we will again be monitoring the maps and commentary from our southern colleagues at the Soybean Rust website (http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi). We will continue to monitor in Ohio as soybean rust continues to approach the middle tier of states. Hopefully it will continue to miss us or arrive to late to have an impact.

January 20, 2010 at 8:15 am

Agronomy Technology Day Planned

The Van Wert County Extension Office, in partnership with agribusinesses, will be hosting an Agronomy Technology Day on January 16, 8:30 a.m. to 2:30 p.m. at the Van Wert County Extension Office.

Farmers are invited to attend this free agronomy technology educational program. “The meeting will focus on several current agricultural topics as well as review some of the great research conducted at Farm Focus in 2009,” said Van Wert County Extension Educator Andy Kleinschmidt.

One of those hot topics that will be addressed is an update on the mold situation in corn. “The moldy grain issue is huge right now, and to address this issue OSU Pathologist Dr. Pierce Paul will provide a videocast update with the latest information on how to deal with moldy grain,” said Kleinschmidt.

Other topics to be covered include: foliar fertilizers and fungicides for corn and soybeans, Kixor herbicide update, marestail and giant ragweed control, corn and soybean seeding rates, and tillage.

This Agronomy Technology Day is free and open to the public. Lunch will be provided, so please RSVP to the Van Wert County Extension office at 419-238-1214 or kleinschmidt.5@osu.edu by January 14.

Full podcast here:

January 5, 2010 at 3:49 pm

More Questions and Answers on Moldy Grain, Mycotoxins

Q. Why is there such a within load variation for vomitoxin ppm? For example, a load can test zero ppm at one elevator and 10 ppm at another elevator.

Response: Variability stems from the fact that there is variation in the number of ears infected within a field and, on any given ear, there is variation in the number of kernels infected, and even more, kernels with similar appearance in terms of moldiness on the surface, may have different levels of internal fungal colonization and consequently variation in mycotoxin contamination. In addition, healthy-looking kernels may also be contaminated with vomitoxin.  Variability is a major issue!!  Because of this variability, sampling needs to be done correctly in order to adequately determine the level of contamination. There are always “hot spots” within the grain lot and if you sample only once or a few time and end up doing so in those “hot spots” then you’ll overestimate how contaminated the grain lot really is. Conversely,  if you totally miss the hot spots then you’ll underestimate contamination. That’s the reason why we always recommend that multiple samples be taken from multiple locations within the lot, then bulk, mix and grind the grain before analysis.

We (OSU) have not used all of the testing equipments that are out there, but most of the highly recommend ones are fairly reliable and consistent. The kits that give you quantitative estimates (1,2,3,15,38 ppm) are generally better that the semi quantitative (more than 5 ppm) or qualitative (yes/no response) kits… but it all depends on what you are using the kit for. In general, the ELISA kits (most of the kits that are out there are ELISA-based) are calibrated against the more sophisticated quantitative lab equipment, and if used correctly (incorrect  use is another potential source of variation) should provide consistent results across elevators. However, test results from one elevator to another are also subject to variation in how the samples were drawn from one elevator to another. Unless the sampling is done correctly and in the same or a similar manner among elevators, it will be impossible to tell whether the differences (0 at one elevator and 10 at another) are due to differences among the testing equipments or to poor and inconsistent sampling protocols among elevators. In fact, the best way (but probably not the most practical) to compare elevators it to send subsamples from the same bulk sample for testing at the different elevators.

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Q. For on-farm separation of mycotoxin infested corn from clean corn, would a gravity table work satisfactorily?

Response: Very moldy kernels are usually lighter than healthy, plump kernels, however, like I in the paragraph above, plump-looking kernels may also be contaminated with vomitoxin. Any method that can be used to remove moldy kernels will help to reduce the overall level of contamination of the lot… moldy kernels are always more contaminated that the most contaminated of the healthy-looking kernels.

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Q. Is there a possibility of the probe itself being a cause for some of the variability in readings? Can the mycotoxin be transferred to clean corn from a probe?

Response: Although the probe can more the mycotoxin-producing fungus around, the probe is generally not a means by with the mycotoxin itself moves from contaminated to clean corn. If the corn is indeed clean (with little or no fungus) and stored correctly, then the small amount of fungal mycelium or spore carried on the probe should not be sufficient to cause major contamination of the healthy lot.  However, on the subject of cross contamination, it is never a bad practice to clean the probe before moving between lots or loads.

Part I of mycotoxin issues can be read at http://wp.me/peijs-p9

Full podcast here:

December 31, 2009 at 7:30 am

Purdue: Soybean Rust Confirmed in Indiana

From: Purdue Plant & Pest Diagnostic Lab (http://www.ppdl.purdue.edu/PPDL/soybean_rust.html)

Soybean rust was confirmed in Indiana September 30th on soybean leaves collected in southeast Posey county.  Posey County is in the extreme southern and western part of Indiana. The soybean field where rust was found was at R7 and rust was detected at very low levels. Pustules were observed on 14 out of 100 leaves. Severity was low, with 1-2 pustules on each infected leaf.

In 2009, soybean rust has been found in 14 states and 293 counties in the United States, and in two states and five municipalities in Mexico.

Soybean rust was found in 392 counties in the United States in 2008. This is the highest number of counties reporting the disease since it was first discovered in the continental U.S. in 2004.

Unfortunately, there are additional hosts that can serve as overwintering reservoirs for the pathogen and allow for build-up of inoculum, in those environs free from freezing temperatures. The pathogen is well adapted for long-distance dispersal, because spores can be readily carried long distances by the wind to new, rust-free regions.

Although impossible to find symptoms this late in the year in Ohio (thanks to the October 1 killing freeze) the latest soybean rust information can always be found at corn.osu.edu

Full podcast:

October 7, 2009 at 11:37 am

Lookalike Soybean Diseases: Brown Stem Rot

Brown Stem Rot is one of the lesser abundant diseases in my area, and is often easily confused with soybean Sudden Death Syndrome (SDS).  I had the chance on September 11 to spend a few minutes in the field with Dr. Anne Dorrance while we examined my brown stem rot plots. Foliar symptoms, when present, consist of wilting, chlorosis, and browning of the tissue between the veins. These foliar symptoms are very similar sudden-death syndrome. Generally, the two diseases can be distinguished by looking at the soybean pith. With brown stem rot, a brown to reddish brown discoloration of the stem pith occurs and can be continuous throughout the stem from the base of the plant upwards.  If the pith appears healthy at first, give a second look for discoloration at the nodes.

When this disease does develop it tends to be in fields that have been in continuous soybeans, short rotations, reduced tillage, or no-till. When disease is severe, yield reductions from 10 to 38% have been reported. The fungus, Phialophora gregata, only infects soybeans and is also residue borne.

Crop rotation and soybeans with resistance are two of the main tools used to combat brown stem rot in soybeans.  Dr. Dorrance’s factsheet on the subject is available here: http://ohioline.osu.edu/ac-fact/pdf/0035.pdf

Anne Dorrance rating brown stem rot in soybeans-Van Wert County September 11, 2009

Anne Dorrance rating brown stem rot in soybeans-Van Wert County September 11, 2009

September 14, 2009 at 8:15 am

Soybean Sudden Death Syndrome

Reports across the midwest (Nebraska, Iowa, Kentucky)  indicate that soybean sudden death syndrome (SDS) is becoming prevalent in some areas.

Image courtesy Ohio Field Crop Diseases and Pat Lipps (retired).

The OSU Pathology group has an excellent resource on crop diseases available at the Ohio Crop Disease website.  Below is from the section on SDS:

Symptoms

  • begin as small pale green to yellow circular leaf spots
  • brown to tan areas develop between the veins
  • pith is white
  • root decay and discoloration of roots and crown

Environment

  • high soil moisture during late vegetative growth stages
  • SCN can increase severity of foliar symptoms

Survival

  • fungal spores overwinter and survive for years in the soil
  • spores have been found on the cysts of SCN

Management

  • reduce SCN populations
  • increase soil drainage by tiling or tillage
  • long crop rotations – soybeans only once every three years

Full podcast available here:

August 26, 2009 at 8:00 am

Two Common Soybean Diseases and Fungicide Recommendations

Observations from my sentinel plot as well as other soybean fields indicate that bacterial blight of soybean is present at low levels in many fields. In Ohio, this disease is not considered yield impacting. Bacterial blight is spread by rain and wind, and favored by cooler weather. Bacterial blight and brown spot are likely to be confused. I took a few quick photos to show the differences.

Bacterial blight symptoms: small, brown lesions that are yellow to brown and often are surrounded by a yellow halo.

One of the most common soybean pathogens in Ohio is brown spot. Brown spot also produces yellow to brown lesions, however, the lesions are typically found in the lower canopy on older leaves and do not have a yellow halo present. (Photo credit: Anne Dorrance)

I had incorrectly identified the symptoms in this image as brown spot. Thanks to John Damicone from Oklahoma State University for correctly pointing out to me that this is NOT brown spot.  The image is of Cercospora blight on soybeans. this symptom is getting some debate right now -- is it Cercospora blight or is it a sunburn type of effect on some varieties.  We have started to a small project to try and identify what this is in response to some samples and feedback from some other regions in the state.

I had incorrectly identified the symptoms in this image as brown spot. Thanks to John Damicone from Oklahoma State University for correctly pointing out to me that this is NOT brown spot. The image is of Cercospora blight on soybeans. This symptom is getting some debate right now, and the question is whether or not this is indeed Cercospora blight or is it a sunburn type of effect on some varieties. Dr. Dorrance has indicated that there is a small project to try and identify what this is in response to some samples and feedback from some other regions in the state.

Key point: Foliar fungicides will protect against brown spot, but are not recommended for management of bacterial blight. Brown spot is considered a minor foliar disease of soybean in Ohio, but yield differences have been documented with fungicide application. OSU research has demonstrated that fungicide applications can reduce the incidence and severity of foliar diseases as well as the minor foliar pathogens found in Ohio. Timing of application is one critical factor in fungicide application. Also, it is important to consider cost-benefit analysis given that a fungicide application may only increase yield by 3 bu/acre.

Full audio podcast available here:

August 12, 2009 at 8:10 am

Foliar Fungicide Application to Corn

Late July through early August used to be a time when things settled down on most farms. The last of the herbicides had been sprayed on soybeans, and wheat has been baled and stored.  During the past couple of years, however, there has been a push to apply foliar fungicides to corn during the critical corn reproductive stage.  Questions remain as to the efficacy of applying fungicides to corn this time of year, and whether or not this practice is warranted.

In this video clip shot July 23, 2009, I am spraying my corn fungicide trial with Stratego @ 10 oz/acre + NIS @ 0.125% v/v. Volume was 15 GPA at 40 PSI with XR11004 on very early VT corn. I noted less than 1% leaf area had rust, no other diseases were present. Thanks to Brent Neate for application and use of the Walker 44.

I am involved with three studies over the past three years looking at this very issue.  I have data to share for 2007 and 2008, and will be releasing the 2009 data following harvest this fall.  Below, I will summarize the results from 2007 and 2008 studies.

The studies from 2007 and 2008 are similar in design.  In both years the study was set up as three treatments with four replications of each treatment in a randomized complete block design. Plot size was 45 feet wide by 1090 feet long. The treatments tested were: 1) Untreated check, 2) Headline at 6.0 ounces per acre + nonionic surfactant (NIS) at 0.25% v/v, and 3) Stratego at 10.0 ounces per acre + nonionic surfactant (NIS) at 0.125% v/v.  Fungicide applications were made with a high clearance ground sprayer in 15 gallons per acre spray volume at 50 psi using TeeJet XR11004 flat fan nozzles.

Due to differences in growing seasons between 2007 and 2008, the application date was different.  In 2007, both the Headline and Stratego foliar fungicide treatments were applied on July 18 with corn at growth stages VT-tassel emergence to R1- silking.  In 2008, both the Headline and Stratego foliar fungicide treatments were applied on August 8 with corn at growth stage R2-blister.

Results of the studies are similar. Data from the trials indicates there were no statistically significant differences between the treatments for corn yield.  Visual inspections during the growing season did not show any significant disease pressures in any of the plots, but the fungicide treated plots did have greener plants later in the season.  Here are the actual yield numbers for 2007: untreated check = 184.6 bushels/acre, Headline = 183.4 bushels/acre, and Stratego = 188.0 bushels/acre.  Here are the actual yield numbers for 2008: untreated check = 118.2 bushels/acre, Headline = 123.9 bushels/acre, and Stratego = 125.5 bushels/acre.  Variability between the yield means is most likely being caused by other outside influences and cannot be attributed to the fungicide treatments based on the statistical analysis.

The complete studies (which include data on hybrid, planting date, fertility, etc.) are available online at: http://farmfocus.osu.edu/corn_foliar_fungicides-07.pdf and http://farmfocus.osu.edu/corn_foliar_fungicide-08.pdf.  For more information on corn diseases and fungicides recommendations for corn, please stay informed with the weekly updates from the OSU Extension Agronomic Crops Team CORN Newsletter at http://corn.osu.edu/.

July 27, 2009 at 8:00 am

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