Posts Tagged ‘wheat soil-born mosaic virus’

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.

Small Grain Diseases

Friday, April 25th, 2008

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

Barley
There are low levels of the spot form of net blotch beginning to appear as well as low levels of scald. With most of the barley in head and flowering, it is too late for any fungicide applications. The levels observed so far for these diseases do not appear to be yield limiting.

Wheat
Wheat samples submitted to the Plant Diagnostic Clinic with virus symptoms continue to appear. So far we have had positive diagnoses of soil borne wheat mosaic virus and wheat spindle streak mosaic virus. These can be very difficult to tell apart without a lab diagnosis. So far barley yellow dwarf mosaic has not been identified. Noting the fields where these viruses occur and planting resistant varieties the next time wheat is planted in those fields will manage the disease. Continue to scout wheat for powdery mildew at this time.

 

Soil borne wheat mosaic virus

Soil borne wheat mosaic virus

Small Grain Diseases

Friday, April 18th, 2008

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

Barley
We have had reports of increasing amounts of powdery mildew on barley. Looking at my evaluations of the barley variety trials that Bob Uniatowski conducts yearly, ‘Thoroughbred’ looks to be the most susceptible in the trials but there has never been enough disease present to warrant spraying. Regionally we have no data to evaluate fungicides for control of barley diseases because barley rarely needs to be sprayed for diseases and the cost has been prohibitive. Times have changed and if the heads are emerging and the top two leaves are infected there may be some benefit to controlling powdery mildew on a susceptible variety if the weather continues to favor powdery mildew. Stratego, Tilt, Quilt (10.5- 14.0 oz/A) would be suggested for control if necessary. A beneficial non-target effect will be brighter straw if straw is being baled.

Barley Powdery Mildew

Powdery mildew on barley

Wheat
This week the diagnostic lab received more wheat samples with virus symptoms. The first results have come back and the virus detected was soilborne wheat mosaic virus. SBWMV is a virus that is transmitted to the wheat in the fall by a soil born fungus called Polymyxa graminis. Symptoms range from mild green to prominent yellow leaf mosaics and streaking. Stunting can be moderate to severe. In this region the symptoms are found on plants in areas that are generally wet or poorly drained. Virus symptoms often diminish when the weather gets warm and symptoms are confined to the lower leaves. Symptoms on the upper leaves can look identical to wheat spindle streak mosaic virus. Planting resistant cultivars is the best solution for fields with a history of SBWMV.

I would suggest waiting until early head emergence before applying fungicides to wheat if disease levels do not warrant spraying now. Delaying until head emergence is the last opportunity to apply most fungicides and that application can carry the crop through harvest if glume blotch, tan spot, or rust should appear at or after heading. Another benefit is sooty mold control if we have poor weather during harvest. In most cases disease levels are low in wheat except where high nitrogen carry-over or over fertilization has occurred. That has resulted in more powdery mildew.

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