Fusarium Head Blight

April 24, 2012 in Uncategorized

A few wheat fields in the county have reached the flowering stage.  Flowering typically begins 3-5 days after head emergence, but weather can have an influence on this.  This stage is characterized by extrusion of the anthers, which typically begin in the middle of the grain head.    While there is little risk  for infections right now, the situation should be monitored closely during the next couple of weeks.  The Fusarium Head Blight Risk Assessment Tool for 2012 can be a useful tool which helps determine local risk levels.  Click on the picture below to visit the tool.  As of now, the risk level is low since we have not received rainfall until this past weekend and temperatures are a bit on the cool side.  Again, this could change quickly, so be sure to monitor your wheat fields and watch the weather.  If the decision to make a fungicide application is made, be sure to check out the table below developed by The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184).  Not all fungicides are labeled for Fusarium Head Blight suppression and some are not as effective as others.  Even the most effective fungicides may only provide 50% control.  It is important to remember that fungicide applications that target Fusarium Head Blight need to occur at Feekes 10.51 (when the anthers are first observed on the head) to be most effective.

Wheat Head Flowering.  Photo by P. Sylvester.
Snapshot of Fusarium Head Blight Risk Assessment Tool on April 23.

Fungicide Efficacy for Control of Wheat Diseases. From The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184)

References:

Hershman, Donald E. and Douglas JohnsonA Comprehensive Guide to Wheat Management in Kentucky.  ID-125.  Section 7. Disease Management.  University of Kentucky Cooperative Extension.  Online. http://www.uky.edu/Ag/GrainCrops/ID125Section7.html

Wise, Kiersten.  2012.  Tools Available to Monitor Risk of Fusarium Head Blight (Scab) in Indiana Wheat.  Pest & Crop News, Issue 3.  Purdue Cooperative Extension.  Online.  http://extension.entm.purdue.edu/pestcrop/2012/issue3/index.html#tools 

Wheat Disease Identification

April 17, 2012 in Uncategorized

Below are pictures of wheat diseases that are found in Delaware. The barley yellow dwarf pictures are from this year, all the other photos are from 2011.  Click on any photo to make it larger.

Wheat infected by Barley Yellow Dwarf Virus.  Note the yellow and red discoloration at the tip of affected leaves.  Photo by P. Sylvester.
Wheat infected by Barley Yellow Dwarf Virus.  Typically occurs in patches within a field. Caused by feeding of aphids which spread the disease.  Photo by P. Sylvester

Leaf Rust on Wheat.  Photo by P. Sylvester.

Wheat heads with symptoms of Fusarium Head Blight (scab).  Photo by P. Sylvester

Wheat heads with symptoms of Fusarium Head Blight (scab).  Photo by P. Sylvester.

Wheat heads with symptoms of Fusarium Head Blight (scab).  Photo by P. Sylvester.

Septoria tritici blotch (speckled leaf blotch) on wheat.  Note the dark reproductive structures produced by the fungus in the middle of the tan lesions.  Photo by P. Sylvester
Tan Spot on Wheat.  Note the tan lesions with a dark center surrounded by a yellow margin.  Photo by P. Sylvester.

Powdery Mildew on Barley.  Photo by P. Sylvester.

Phillip Sylvester, Extension Agriculture Agent, UD, Kent County.

Wheat Stripe Rust

March 16, 2012 in Uncategorized

Wheat Disease Identification Publication

February 8, 2012 in Uncategorized

A wheat disease identification publication is now available online.  This multi-state extension publication has great photo’s to help with identification, descriptions of wheat diseases, and management techniques. Limited hard copies are available at  the county extension office.  You can also click on the picture which is linked to the publication.

Source:  University of Nebraska Lincoln Extension.  CopWatch: February 2012. Online.  http://cropwatch.unl.edu/web/cropwatch/home

Fusarium Head Blight (Head Scab) in Saved Seed

August 15, 2011 in Uncategorized

I was recently asked about planting wheat and barley seed saved from Head Scab (Fusarium graminearum) infected fields.  Growers should keep in mind that just because the grain may have been infected this season does not mean the grain will be infected next year.  Rather, the infection of head scab is a result of the pathogen being present on infected residue and favorable weather conditions.  Growers should take precautions before planting infected seed this fall.  The seed should be cleaned with the intent to remove as many of the small, light infected “mummies.”  I would also recommend a germination test after the cleaning to help determine seeding rate and optimal seeding populations.  A seed treatment should also be applied to help prevent seedling diseases. Bob Mulrooney, Extension Plant Pathologist, wrote an article in the June 10th edition of the Weekly Crop Update on the subject. 

Head scab has been observed in barley and wheat this season in varying amounts. Barley is just now arriving at the grain elevators. The amount of scab that occurs is dependent on the flowering time, the presence of the scab spores that infect the heads during flowering and the weather conditions during flowering. Most of the barley and wheat varieties that we grow have little or no resistance to head scab. The fungus can be present on old corn stover, and residues of old barley and wheat crops. What drives this disease is wet, warm weather during the flowering period. If the heads of barley or wheat are infected with the fungus (Fusarium graminearum) that cause head scab, that fungus can produce several toxins that can contaminate the grain. These toxins are often referred to as vomitoxins because they can cause feed refusal in non-ruminant animals. The most common vomitoxin that is produced by the head scab fungus is deoxynivalenol or DON for short. DON production by the fungus is extremely variable depending on environmental conditions. The presence of scab on the grain does not mean that the grain has to have DON nor does high or low levels of scab relate to the amount of DON present. A high level of scabby kernels in the harvested grain means that DON will likely be present.
What about the saving or using seed from scab infected fields? As much scabby wheat kernels as possible should be removed from good seed during combining and seed cleaning. This is not easily done with barley or may not be possible because barley does not get as light as wheat. Saved seed kernels can be infected with Fusarium, and seed treatments can reduce the effects of Fusarium on seed. Fusarium on seed can cause a seedling blight of barley and wheat but the seedling infections do not result in head scab or DON in fields that might be planted with infected seed. In fact some studies have shown a reduction of scab infections in seed during storage. Low levels of scab infected wheat or barley can be saved for seed if properly handled and treated without any risk of scab occurring in the crop from that seed.
Another issue for barley producers is that the threshold levels of DON in wheat may not be the same compared to barley presuming that the barley is not intended for human consumption. The DON threshold for wheat is 1 ppm because of human consumption concerns. Barley for feed can have up to 10 ppm without harmful effects depending on the animals being fed and the proportion of infected grain being fed. In my opinion barley should not be held to the same threshold as wheat depending on its destination or final use. See the following information on DON levels in food and feed.
What are the critical levels of DON for use in food and feed?
The concentrations of DON in grain are expressed as parts per million (ppm). One ppm is equivalent to 1 pound in 1 million pounds, 1 penny in $10,000, 1 minute in two years, or 1 wheat kernel in 80 pounds of wheat. The U.S. Food and Drug Administration (FDA) has established DON advisory levels to provide safe food and feed. Unlike aflatoxin in corn, DON is not a known carcinogen. Furthermore, grain with DON would have to be ingested in very high amounts to pose a health risk to humans, but it can affect flavors in foods and processing performance. Human food products are restricted to a 1-ppm level established by the FDA. This level is considered safe for human consumption. The food industry often sets standards that are more restrictive. DON causes feed refusal and poor weight gain in some livestock if fed above the advisory levels. FDA advisory levels are as follows:
1 ppm: Finished wheat products, such as flour, bran and germ that potentially may be consumed by humans. The FDA does not set an advisory level for raw grain intended for milling because normal manufacturing practices and additional technology available to millers can substantially reduce DON levels in the finished wheat product. However, individual millers or food industries may have stricter requirements than 1 ppm.
10 ppm: Grains and byproducts destined for ruminating beef and feedlot cattle older than 4 months and for poultry, providing that these ingredients don’t exceed 50 percent of the diet.
5 ppm: Grains and grain byproducts destined for swine, providing that these ingredients don’t exceed 20 percent of the diet.
5 ppm: Grains and grain byproducts destined for all other animals, providing that these ingredients don’t exceed 40 percent of the diet.
Taken from NDSU Fact sheet PP-1302, DON (Vomitoxin) in Wheat. http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1302.pdf

From “Head Scab and the Relationship to Saved Seed and Vomitoxin Production.”  June 10, 2011.  Bob Mulrooney, Extension Plant Pathologist, UD.

Wheat Diseases

May 31, 2011 in Uncategorized

Disease resistance varies among commercial varieties and now is a good time to evaluate varieties to help make selections for next year.  While yield is the most important aspect of a variety, disease resistance or tolerance is another tool growers should keep in mind while making selections.  Knowing what diseases are in your field is important.  Below is an article from Bob Mulrooney, Extension Plant Pathologist, UD discussing diseases found in the small grains trial near Sandtown, DE.

The wheat in the Kent County variety trial has tan spot moving in rapidly on some varieties. Most of the varieties are in the watery ripe stage of development and will not likely be adversely affected. Leaf rust was easily seen on a public variety ‘Rumor’. Powdery mildew in general was low in most varieties but was in the upper canopy on SS8302, Milton, Bravo, and USG3770. There is a low level of scab in the trial as well. If scab is going to appear it should be evident now or very soon depending on location. Low levels of scab (less than 1% of the heads infected and most of the infected heads were only partially infected) were present in 8 out of 45 varieties (around 18%).There is some sort of physiological spotting that could look like a disease but is probably a resistance reaction by the variety in response to a fungal infection. This spotting was evident on the following varieties at this Sandtown location: Merl, Sunburst,USG3665, USG3409, USG3251, and Grow Mark FS627.

Photo 1. Fusarium Head Blight in Winter Wheat (Photo by Phillip Sylvester)

Photo 2. Fusarium Head Blight in Winter Wheat (Photo by Phillip Sylvester)

Photo 3. Fusarium Head Blight in Winter Wheat (Photo by Phillip Sylvester)

Article by Bob Mulrooney, Extension Plant Pathologist, UD in Weekly Crop Update Volume 19, Issue 10 – May 27, 2011 http://agdev.anr.udel.edu/weeklycropupdate/ Photographs by Phillip Sylvester, Extension Agent, Agriculture, UD, Kent County. 

Fusarium Head Blight Risk Assessment Tool

April 29, 2011 in Uncategorized

Fusarium Head Blight or Scab is a serious disease that infects wheat which does occur here in Delaware under favorable conditions.  Symptoms include a tan or brown discoloration of the head, and will usually give the apperance of a bleached head before ripening.  The grain is usually of poor quality with a white shriveled chalky appearance.  Another downside of scab is the production a mycotoxin, DON, which can contaminate the diseased grain and make it unmarketable.  Management options include selecting a variety with moderate resistant, fungicides, rotation (avoid planting into high corn residue), and adjusting combine to blow out the small, infected grain.  Fusarium Head Blight favors temperatures between 65-85 degrees and extended periods of moisture (rain or dew).  There is a Fusarium Head Blight Risk Assessment Tool which monitors weather data to predict favorable development found at the link below:

http://www.wheatscab.psu.edu/riskTool_2011.html

Fusarium Head Blight Risk Assessment Tool provided by Penn State University, Ohio State University, Kansas State University, Purdue University, North Dakota State University.  Information from Fusarium Head Blight Fact Sheet, Pennsylvania State University written by Erick De Wolf, Pennsylvania State University and Pat Lipps, Ohio State University. 

Viruses in Winter Wheat

April 4, 2011 in Uncategorized

Viruses can be a problem in small grains on Delmarva .  Right now, some fields in the area are showing stress in certain areas, especially in Barley.  Many times, this is from wet areas in the field or from nutrient deficiencies.  Do not rule out viral infection which can have distinct appearance.  Fields can be sampled and sent to the UD Plant Diagnostic Lab for positive identification.  Below is an article from Bob Mulrooney, UD Extension Plant Pathologist, describing what to look for:


The first winter wheat sample with virus symptoms arrived last week. It was sent for confirmation and was determined to be wheat soilborne mosaic virus. Wheat on the Delmarva can be infected by four possible virus diseases. The aphid-transmitted barley yellow dwarf mosaic virus is probably the most common, depending on how high aphid populations are in the fall and early spring. Often irregular patches of stunted wheat occur in wheat fields and as the season warms up infected young leaves will become yellow, and then turn red. Wheat spindle streak mosaic causes a yellow discoloration to wheat seedlings. This yellow discoloration is often most intense in low areas of the field. Leaves of infected plants have long, yellow streaks that are slightly wider in the middle than at their ends. Symptoms are similar to wheat soilborne mosaic and plants often are infected with both diseases. Winter wheat infected by wheat soilborne mosaic develops a pale-yellow discoloration shortly after breaking dormancy in the spring. The incidence of wheat soilborne mosaic is often greater in low areas of the field where moist soil conditions favor growth of the protozoa that spread this viral disease. Leaves of infected plants often have a mosaic pattern of dark green blotches on a pale greenish-yellow background. Symptoms will normally fade when warm temperatures slow the activity of the virus within infected plants. Control of both these soilborne diseases is by planting resistant varieties.
The least common virus disease of wheat that we see is wheat streak mosaic. Leaves of plants infected with wheat streak mosaic have bright yellow streaking. Symptoms are often most severe near the tip of the leaf. The virus that causes wheat streak mosaic survives in volunteer wheat and spreads by wheat curl mites. The disease is often most severe in areas of a field that are closest to these sources of the disease and mites.

 
Barley yellow dwarf mosaic virus

Wheat spindle streak mosaic virus

Wheat soilborne mosaic virus

Wheat streak mosaic virus
 
(Last three photos from Wheat Disease Identification published by NCERA-184, which will be available soon.)

It can be very difficult to positively identify these virus diseases especially early in the spring. They can look like other diseases or nutritional disorders. Testing of infected plants can help diagnose the problem to avoid repeating it in the future or eliminate other possible causes of the symptoms. Unfortunately by the time you see symptoms of these virus diseases there is no control of any of these diseases.

From Bob Mulrooney, Extension Plant Pathologist, University of Delaware, Posted in Weekely Crop Update, Issue 2, 2011.

Wheat Fungicide Decisions

May 5, 2009 in Uncategorized

The following is an excellent article on wheat disease scouting and fungicide use decisions from Arv Grybauskas, Field Crops Extension Plant Pathologist at the University of Maryland

Maryland Field Crop Disease News

Wheat disease observations and recommendations – May 4, 2009

Wheat is starting to head in many parts of Maryland, which gets us to a tricky decision point regarding disease management with fungicides. There are some out there who like to apply a fungicide product like Quilt at heading, regardless of actual disease pressure at that time. It’s viewed as an insurance policy against late season diseases and in some cases it brightens the straw so that those with a market for straw can have a more desirable secondary product. Fungicide applications at heading can be very effective in management of Stagonospora glume blotch (a.k.a. Septoria glume blotch) and rusts and in some cases still effective against powdery mildew. However, there is new information regarding strobilurin and strobilurin-containing fungicides that impacts this decision.

Recent research indicates that fungicides that have an active ingredient that belongs to the strobilurin class can affect the levels of the mycotoxin, Vomitoxin (deoxynivalenol or DON), which develops in scabby grain. The strobilurin only products that are registered for wheat are Headline and Quadris; and the registered products that contain strobilurins are Quilt, Stratego and Twinline. It has been known for some time that all these products when applied at flowering for scab control can result in increased levels of DON. It is for this reason that they do not have scab suppression on their labels and are not recommended. What has only recently come to light is that the application of these products at heading can also lead to increased levels of DON if scab develops. Remember the mills are actively screening for DON and may reject loads on that basis alone. This unintentional consequence of a risk of increased DON levels due to an earlier fungicide application must be considered when thinking about fungicides at heading.

The stalled front that is fluctuating between Virginia and Maryland with pulses of low pressure systems generating showers this week and last is setting us up for an outbreak of scab. It’s also conducive for all the fungal diseases but let’s first cover scab. The long stretch of wet weather is allowing the fungus that causes scab to grow and develop on previously infected crop debris. In most of our cases this means corn stubble left in the fields. Current conditions are still on the cool side of optimum so the risk of scab if wheat was flowering today is low to moderate. Actually barley may be in flower or very close in some parts of the state and those fields are at risk of a developing some scab. As the weather continues wet and gets warmer we will have increased risk of scab in small grains. The keys are source of spores, 7-day pre-flowering weather and post-flowering weather.

The highest risk of getting scab is in fields that were planted no-till or minimum till into corn stubble. There is an equally high risk of scab in back-to-back wheat or barley crops. The lowest risk is in small grains rotated after soybeans or anything other than corn or small grains. Wheat after double-cropped wheat-soybeans is also a high-risk rotation. There is no zero-risk of scab if the weather is wet and warm for an extended period around flowering but the difference in disease levels that can develop is the difference between manageable and a total loss.

There is a scab forecasting web site http://www.wheatscab.psu.edu/ that provides a map of scab risk based on the 7-day pre-flower weather. I will be providing custom commentary for Maryland at this web site. This is a great way to determine if a fungicide may be needed for scab management. The drawbacks are: you need to check the risk maps frequently as wheat approaches flowering, the forecasts are only possible for a one to three day range, and the recommended products are only available in limited supply. The recommended fungicides for scab management are Prosaro, Caramba or a mixture of Proline plus Folicur. Prosaro is a premix of Proline and Folicur. Nothing else has provided comparable and consistent disease suppression to warrant recommendation.

The bottom line for wheat fungicides at heading for the current season boils down to the following questions. First, is the site high risk for scab based on cropping history? If it is then any strobilurin-containing product is an added risk and I don’t recommend it. In fact in most high scab risk sites a fungicide decision based on scab this season will provide the most return based on my observations of other diseases. Your situation may be different. See the following info on observations and risk assessment of other diseases below. If the site is not high-risk for scab, eg. after full-season soybeans, then what are the risks of the other yield-robbing diseases?

Powdery mildew appears to have gotten a late start this season. I have not heard of any commercial fields with high levels of mildew. There are no reports of the breakdown of resistance in popular lines. In my highly susceptible mildew fungicide trial plots on 30 April there is enough disease there to expect a return from a fungicide especially since the weather is favorable now and is not expected to get hot for a while. Disease there is at 100% incidence and the flag-1 leaf has an average of 4% of the leaf area colonized. Powdery mildew will increase in the next week or two. Only susceptible to moderately susceptible varieties have the potential for enough disease to expect a return from a fungicide this season. If there are several white fluffy mildew growths on the flag-1 leaf between flag leaf emergence and boot (and that means simultaneously much more in the leaves below) then a fungicide can provide an economical return if disease favorable weather continues. If the disease has not reached the flag-1 leaf by boot stage it is unlikely that the flag leaf will be affected by disease to the extent that a fungicide will provide a return.

We have just found our first couple of rust pustules in a susceptible variety at the Wye. This weather is favorable for rust to develop and it’s early enough to be a potential problem. It is possible that we have stripe rust as well as leaf rust. Cool temperatures are optimal for stripe rust while leaf rust prefers warm temperatures. Many of our varieties are susceptible to stripe rust. This may be an isolated find but it is important that people start looking. Fungicide applications up to flower on susceptible varieties when made before significant disease development occurs can be very beneficial.

Glume blotch has been very limited. This disease is favored by driving rains and warm temperatures. We are getting some of the rainy conditions needed for the disease but temperatures are below optimum. Threshold guidelines for glume blotch are based on 25% incidence of the disease on indicator leaves. For plants that are at full flag leaf development through boot, 25 % of flag -3 leaves have to be infected to warrant a fungicide application. From boot to heading 25% of the flag-2 leaf need to be infected. I have only found lesions in some fields near the soil, approx. flag-5, and at less than 25% incidence. In another system there must be an average of 2 lesions per flag-1 leaf to warrant a fungicide application (fig 1). These levels are too low to warrant fungicide applications at this time.

Consider your scab risk before you make a wheat fungicide decision this season.

Arvydas (Arv) Grybauskas, PhD
Associate Professor and
Field Crops Extension Plant Pathologist
Department of Plant Science and Landscape Architecture
University of Maryland

Wheat Disease Reactions – Do You Know How Your Wheat Variety Rates?

October 13, 2008 in Uncategorized

Wheat planting is now in full gear across Delaware. How well do you know your wheat variety, especially disease reactions? The following is a table listing varieties and their disease reactions.

Click on the table for a larger image.