Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Barley
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 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.
Wheat
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: http://www.wheatscab.psu.edu/ for more info. Right now the risk for scab statewide for the next 48 hours is low.