Posts Tagged ‘barley yellow dwarf virus’

Small Grain Diseases

Friday, May 2nd, 2008

Bob Mulrooney, Extension Plant Pathologist;

Several diseases are present at this time. Powdery mildew, which we had reported earlier, seems to be found primarily on the variety ‘Thoroughbred‘. The spot blotch form of net blotch is also present in some varieties at low levels that should not affect yields. The latest “new” disease that appeared at heading is loose smut. This fungus is present in the seeds at planting and grows with the germinating plant and systemically infects the head and replaces the seed with its dark brown spore masses. Grain harvested from infected fields should not be used for seed unless it is treated with a systemic fungicide such as Baytan, Dividend, and Raxil. Because the spore masses weather and are absent during harvest the fungus does not cause surface contamination of the harvested grain so the feed value is not affected. Plant certified smut free seed and/or treat with a fungicide for loose smut control.


Loose smut of barley caused by Ustilago nuda

 Spot blotch and net blotch

Spot blotch on left two leaves, net blotch on right two leaves


Barley scald caused by a fungus Rhynchosporium secalis.

The last disease that I am seeing in barley is scald. This disease overwinters in old barley debris or can be seed borne. Look for the water-soaked gray-green spots that appear initially. As the lesion the dries out the center becomes bleached then tan with a brown margin (see photo). Some lesions can be very large and several spots can merge and kill the leaf. Rotation and use of resistant varieties is the best control method.

Powdery mildew is still the most prevalent disease present. Continue to scout and remember that the end of flowering is the last opportunity to apply a fungicide for control. We have not confirmed it yet but I believe we have seen barley yellow dwarf mosaic virus (BYDMV) in wheat this week. A late fall infection or early spring infection produces symptoms of off-color wheat, which may be stunted in varying degrees, as well as red-purple flag leaves (the uppermost leaf). Since this virus is aphid transmitted, fields that are early planted or have had high aphid infestations are the most at risk. The later the infection occurs the less the effect on yield. Aphid control, including seed treatments, may prevent BYDMV as well as avoiding early planting.


Barley yellow dwarf causing reddened flag leaves

Flowering has begun for many wheat fields due to the warm weather last week. The remainder will be flowering in the next week or two. If you want to check the Scab Forecasting website visit: for more info. Right now the risk for scab statewide for the next 48 hours is low.

Management of Aphids: Barley Yellow Dwarf Transmission and Direct Aphid Damage in the Spring

Wednesday, March 26th, 2008

Joanne Whalen, Extension IPM Specialist;, Bob Mulrooney, Extension Plant Pathologist; and Gordon Johnson, Extension Ag Agent, Kent Co.;

We are starting to receive questions regarding the need to spray for aphids in late winter and early spring in regards to both barley yellow dwarf virus (BYDV) transmission and direct aphid damage. Although fall conditions were favorable for aphids (warm and dry), we did not see an increase in populations in many wheat fields until late November and early December. In addition, there have been reports of a second period of population increase in late January and early February.

All of the aphids found in Delaware wheat fields are capable of transmitting BYDV. However, the virus strains that cause barley yellow dwarf are generally transmitted to the wheat in the fall or early spring before growth stage 4. For aphids to successfully transmit the virus in the most efficient manner, they normally need between 12 and 30 hours feeding to acquire the virus, and then 4 or more hours of feeding to transmit it. However, aphids are capable of acquiring the virus after feeding on infected plants for only 30 minutes. Once they acquire the virus and it is allowed to incubate for one to four days, they can transmit it to healthy plants for the rest of their life. (more…)