The 2014 Delaware Wheat Variety Trial Disease Ratings have been posted to the UD Field Crops Disease Management Blog by Nathan Kleczewski, Extension Plant Pathologist: https://s3.amazonaws.com/udextension/ag/files/2012/10/Wheat-Variety-Trial-Writeup-2014.pdf
A Fusarium Head Blight update has been posted by Nathan Kleczewski, Extension Plant Pathologist, UD on the Field Crops Disease Management blog. It’s important stay informed as wheat transitions into flowering. The update can be found here: http://extension.udel.edu/fieldcropdisease/2014/05/14/head-blight-updates/
If you would like to learn more about Fusarium Head Blight of wheat, please read this factsheet which was recently published by Nathan: http://extension.udel.edu/factsheet/fusarium-head-blight-management-in-wheat/
Visit the Fusarium Head Blight Prediction Center for the latest commentary: http://www.wheatscab.psu.edu/
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)|
Hershman, Donald E. and Douglas Johnson. A 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 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.
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
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.
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 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 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.
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.