Crown or Leaf Rust (fungus – Puccinia coronata f. sp. avenae): This fungus overwinters on volunteer and wild oats. Alternate hosts of this rust are species of Rhamnus.The disease appears as tiny, round, yellowish-red pustules on either surface of the leaf blade (See Photo). These pustules produce tiny yellow-red spores that are spread to other plants by wind currents and germinate in free moisture from dews and rains. Crown rust, like other rusts, is caused by a fungus that attacks the leaves and leaf sheath of oats and related grasses. Grazing the infected crop is a suitable means of salvaging value from the crop when damage is heavy. Some varieties have resistance (See Table 1 Below).
Halo Blight (bacterium – Pseudomonas coronafaciens): Lesions or spots appear on leaf blades as oval to oblong water-soaked spots that are buff to light brown in color. A light-yellow zone forms a halo around the brown lesion. The bacterium enters the leaf tissue through stomata or an insect puncture. Suggested controls are seed treatment, crop residue management and rotation.
Leaf Blotch, Victoria Blight, Culm Rot (fungi – Drechslera avenacea, Bipolaris victoriae, Bipolaris maydis): Three species of fungi cause economically significant diseases of oats. With leaf blotch, oblong, linear blotches appear on the leaves. The blotches are light-yellow at first, later turning red to brown. Victoria blight is a seedling blight and sometimes seedlings are killed soon after they emerge. In other cases, plants are stunted, leaves turn red and lower leaves eventually die. Culm rot is a basal stem and root rot. Seed treatment (See Table 2 Below) and crop rotation will help prevent this disease.
Powdery Mildew (fungus – Erysiphe graminis): This fungus disease appears as patches of white, fluffy growth on the lower leaves and leaf sheaths (See Photo). No practical control measure is available. Grazing excessive growth will allow light and air to keep the plants dry, thus reducing the severity of powdery mildew.
Septoria Leaf Blotch (fungi – Septoria sp.): Leaf blotches are gray to dark-brown and run together. Spots on the stem are black and may cause the plant to lodge. The hulls of grain may sometimes become infected and turn black. Use crop rotation and bury crop residue.
Smuts (fungi – Ustilago avenae and Ustilago kolleri): Loose smut (Ustilago avenae) and covered smut (Ustilago kolleri) are two of the most common and widespread of the smut diseases of oats. The smut balls of loose smut form in the oat panicle usually destroying most or all of the seed and hulls. Wind and rain usually dislodge most of the spores soon after they appear and infected panicles are often inconspicuous in the field. The smut balls of covered smut do not ordinarily destroy the outer hulls and the spore masses remain more or less intact inside the hulls until threshing time. Seed treatment with recommended fungicide (See Table 2 Below) will prevent both type smuts.
Stem Rust (fungus – Puccinia graminis f. sp. avenae): The pustules of stem rust are usually oblong and dark reddish-brown. The epidermis is ruptured and often pushed up around the edges and through the center of the pustules so that it is easily visible. The dark color of the stem rust pustule distinguishes it from the light, orange-yellow crown rust.
Barley Yellow Dwarf Virus: Plants are dwarfed and can be either brilliant red or yellow. Symptoms usually appear following a high population of aphids and small grain greenbug. For more information see Yellow Dwarf of Barley in the Barley Section.
Table 1: Oat Varieties
|Variety||Crown Rust||Stem Rust||Halo Blight||Winterkill|
|R = Resistant, MR = Moderately Resistant, MS = Moderately Susceptible, S = Susceptible|
Table 2: Seed Treatment for Oats
|General Seed Treatments||Bipolaris Seed Treatments|
|PCNB, Carboxin, Triadimenol||Mancozeb, Thiram, Carboxin, Imazalil, Carboxin + Thiram|