Posts Tagged ‘wheat spindle streak mosaic virus’

Small Grain Disease Update

Friday, April 22nd, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Barley
We are getting more reports of powdery mildew in ‘Thoroughbred’ barley. This variety is very susceptible and growers have been spraying fungicides to control the disease and protect their yields. Tilt or other labeled triazole fungicides work well along with strobilurin combination products like Quilt, Stratego, etc. Folicur, which is a triazole or sterol-inhibiting fungicide, does not have powdery mildew control on the label for barley or wheat. Folicur (tebuconazole) is now available as a generic as Monsoon, Orius, Embrace, Tebustar and others. When small grains are followed by soybeans there are no plant back restrictions but if you are planting processing or fresh market vegetables be sure to check the label for what can be planted if a fungicide is used in barley or wheat.

Wheat
Disease activity has been light so far. Another sample of wheat spindle streak mosaic virus was received this week. See the article titled Viruses in Winter Wheat in WCU 19:2 for more information. The one control option for wheat spindle streak is planting resistant varieties. Seed company literature and web sites can provide that information. The University of Maryland has some ratings for disease resistance from their variety trial plots. Dr. Arv Graubaskas revised the MD list last December and it is online at: http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2011/04/MDWheatDiseaseRatings2010.pdf.

 

Viruses in Winter Wheat

Friday, April 1st, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

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.

Agronomic Crop Disease Update

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat
It has been a tough year for wheat production. The wet fall delayed planting, then large areas have been inundated with water for long periods of time and there has been grazing by geese. Areas of the state where wheat has survived but under very wet conditions may be at risk from Pythium root rot if wet conditions persist. The other threat, as if there wasn’t enough trouble for wheat, is from the fungal transmitted soilborne viruses, wheat soilborne mosaic virus and wheat spindle streak mosaic virus (WSSMV). Wet soils in the fall following planting can result in severe infections of wheat soilborne mosaic virus that appear as irregular stunted areas in low areas of the field. Mild stunting and yellow green mottling, dashes and streaks on the leaves are diagnostic for WSSMV. There are no controls for either disease for the present crop. Resistant varieties for both diseases are available.

Soybean Cyst Nematode Survey
I am waiting on the results of the last two soil samples before presenting the results of the Delaware Soybean Board sponsored survey for SCN in Delaware. The results so far have confirmed a shift of the race composition in Delaware soybean fields and the nasty nematode has not gone away.

Small Grain Disease Update

Friday, April 10th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat virus diseases can be hard to diagnose especially when wheat is not growing quickly due to the cool weather. Both soilborne viruses, soilborne wheat mosaic and wheat spindle streak mosaic virus can cause stunting of plants at this time of the year. Varying degrees of mottling and yellow streaks or dashes may be present. It is hard to generalize what the patterns in the field might look like, but wheat spindle streak can be uniform across the field or in scattered spots that generally coincide with low spots in the field. Soilborne wheat mosaic virus is seen typically in large irregular spots in low or poorly drained areas of the field. A wheat sample sent to the lab last week was positively identified with wheat soil born mosaic virus by ELISA testing at Agdia, Inc. For a list of wheat varieties and their ratings for susceptibility to both virus diseases go to http://www.rec.udel.edu/Update09/wheatdiseaseresistance08.pdf. There is no control for these diseases other than planting resistant varieties. When warm weather returns the plants will generally grow out of the symptoms but the effect on yield can be very variable depending how early the plants were infected. If the symptoms persist until the flag leaf emerges, more yield loss can be expected. For additional information on soilborn wheat mosaic virus and wheat spindle streak mosaic virus see this factsheet from University of Maryland http://www.rec.udel.edu/Update09/wheatsoilbornvirusesMD.pdf.

Another disease that has been seen in the lab is Ascochyta leaf spot. This disease is caused by a very weak pathogenic fungus that infects winter damaged leaf tissue primarily. Most fieldmen and growers get excited when they see this because it looks like Septoria leafspot which does not occur until much later in the season in this region. Ascochyta occurs primarily on lower leaves and begins as small chlorotic flecks that then develop into elongated gray-brown spots that can resemble Septoria nodorum spots. This disease does not warrant fungicide applications and usually disappears once wheat growth resumes wholeheartedly.

Scout Wheat for Diseases

Friday, April 11th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Continue scouting wheat for powdery mildew. The cool weather has been ideal for disease development. In cases where too much nitrogen was applied or extra carry-over from last year was not taken into consideration, resistance can be overcome. Lush wheat should definitely take priority when scouting. In areas that had good moisture in the fall keep an eye out for wheat spindle streak mosaic virus. This virus is vectored by a root infecting fungus that needs plenty of water in the fall when the initial infection takes place. We have had reports of it occurring but have not seen any plant samples yet in the lab. Wheat generally grows out of it once warm weather gets here and stays. Symptoms on leaves appear as yellow-green mottling, dashes, and streaks. It can occur widely in fields not just wet areas. Wheat soil-born mosaic virus can often be confused with WSSMV but is generally more limited to wet spots in the field.

wheat spindle streak mosaic virus

Wheat spindle streak mosaic virus