Oklahoma Wheat: Powdery Mildew, Rust, and Barley Yellow Dwarf, with Some Streak Mosaic

    As expected, over the last week the disease situation has change significantly. Wheat around Stillwater is mostly nearing complete heading to starting of flowering (Feekes’ GS 10.1 to 10.5.1).

    In Jackson County (far southwestern Oklahoma), Gary Strickland (Extn Educator; Jackson County) indicated he has seen wheat as far along as ¼ berry, but most of the wheat is in flowering. 

    Across southwestern Oklahoma, Heath Sanders (Area Extn Agron Speclst, SW District) indicated wheat he has seen mostly is in the flowering stage. Wheat at the Lahoma Station (15 miles west of Enid) was mostly between heads emerging to 3/4ths emerged, and according to Greg Highfill (Extn Educator; Woods County) wheat in the Alva area (northwest OK) was mostly just emerging from the boot as of last Tuesday (11-Apr).

    Around Stillwater, powdery mildew (PM) is the primary foliar disease, but it is staying low in the canopy. A sparse scattering of stripe rust can be found, but it is extremely sparse. Leaf rust also is sparse, but is at a higher level than stripe rust. Barley yellow dwarf (BYD) symptoms are common, but it seems to me there is more yellowing than can be totally attributed to BYD (but I’m not sure of the cause).

    Gary Strickland indicated that leaf rust is predominate in southwestern OK, but that stripe rust also can be found. He also is seeing widespread BYD symptoms and higher levels of tan spot (in no-till fields) up higher on the canopy than he has observed in previous years. Southwestern OK has received more moisture over a longer period of time than the rest of Oklahoma, which explains the higher incidence of foliar diseases.

    Gary did not see many aphids over the fall and winter, and so like me, he is surprised at the amount of BYD symptoms.

    Heath Sanders indicated he has seen a lot of powdery mildew but again, so far restricted to the lower canopy. He does feel that the PM has resulted in thinner wheat in some fields due to secondary tiller death/sloughing, which PM can do. He also indicated as did Dr. Brett Carver (OSU Wheat Breeder) that wheat at the Chickasha Station (about 50 miles southwest of OKC – central OK) is showing severe levels of leaf rust and (especially) stripe rust.

    In more northwestern/north-central OK, only light levels of stripe and leaf rust were observed at the Lahoma Station, and Greg Highfill indicated that the variety trial near Alva, OK was “clean.” He did indicated that west of Alva he had received reports of light levels of stripe rust.

    The other disease that is definitely making a presence this year is wheat streak mosaic (WSM). So far the lab has received 16 samples that have tested positive for Wheat streak mosaic virus. These samples have primarily come from central and west-central Oklahoma, and typically have been associated with lack of controlling volunteer wheat in the field itself or in an adjacent field.

    Controlling volunteer wheat prior to the emergence of seedling wheat in the fall is critical to limiting WSM. Once infection occurs, especially if it is a fall infection, wheat likely will be damaged in the spring (Table 1).

    For more information on mite-transmitted wheat viruses such as WSM, please see OSU Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) available here.

    fig1

    Stripe rust and leaf rust on wheat in experimental trials at the Experiment Station at Chickasha, OK (photo courtesy of Dr. Brett Carver).

    fig2a

    A commercial field of wheat showing severe WSM symptoms

    fig2b

    A close-up view of WSM on an individual leaf

    fig2c

    Field immediately adjacent to a commercial wheat field in which abundant volunteer wheat had not been controlled until spring

    table1

    Table 1. Effect of time of infection by Wheat streak mosaic virus on the severity of wheat streak mosaic (WSM) and yield of three wheat varieties. [Taken from Hunger, et al. 1992. Effect of planting date and inoculation date on severity of wheat streak mosaic in hard red winter wheat cultivars. Plant Disease 76:1056-1060.]




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