Current samples
Bur Oak Blight
Peng Tian and Pierce Taylor
Across the Midwest, Bur Oak Blight (Tubakia iowensis) is a fungal pathogen infecting the Bur Oak (Quercus macrocarpa). Affected plants display chlorosis and fruiting bodies on the leaf vein and petiole in mid to late summer. The small-acorn variety of bur oak (Quercus macrocarpa var. oliviformis), is affected more severley than other varieties. The disease can reinfect trees year to year and can eventually cause death after several years of defoliation.
Symptoms and signs: Typical symptoms include necrosis(death) occurring around the leaf veins, as well as the tip. Eventually the fungus occurring on leaf veins result in tissue death. The presence of fruiting bodies can be seen along the veins on the underside of the leaf and around the petiole as a purple discoloration. Due to the death of foliage, Bur Oak Blight is often confused with Oak wilt or Anthracnose disease. These fruiting bodies, or pycnothyrium, presence on the petiole and the tree retaining its leaves over winter are symptoms of Bur Oak Blight which differentiate it from similar diseases. The conidia spores of Tubakia iowensis are microscopic and cannot be seen unaided, thus proper identification requires analysis with a laboratory microscope. Tubakia spp. have a pycnothyrium that composes of a shield like scutellum of radial projected hyphae. The scutellum is supported by a short columnar stalk that bears the round to ovoid conidia spores.
Learn more about the life cycle, damage and management of this disease:
Oak Wilt Disease
Peng Tian and Pierce Taylor
Oak Wilt is a fungal pathogen infecting oak trees, primarily of the Red Oak family. The causal agent is a fungus called Bretziella fagacearum that infects and kills oak trees in parks, woodlands, and residential areas across Missouri. Oak wilt was first detected in Wisconsin during the 1940’s and has since spread across the United States. Red oaks, trees with pointed leaf lobes, are affected more than white oaks, trees with round lobes. This pathogen is usually fatal to oak trees, with death occurring within the season following infection.
Symptoms and signs: Oak wilt affects the vasculature of the tree, resulting in a timely decline. In Red oaks, symptoms generally appear in late spring or early summer and include sectional canopy dieback at the top of the tree and thinning of the entire canopy. As entire sections of branches die off, leaves begin curling and desiccating from the outside inward. Leaves die due to a lack of vasculature within the branches of the tree, and by the end of the summer most leaves will fall off. In branches affected by Oak Wilt, brown staining can be observed under the bark. In White Oaks, symptoms are generally milder. Flagging of the leaves occurs in scattered patches and leaves generally become light brown in color. White Oak trees may die after one year of infection, but it can take several seasons for the tree to slowly decline.
Learn more about the life cycle and management of this disease:
Wheat Streak Mosaic Virus
Pierce Taylor and Peng Tian
Wheat streak mosaic virus (WSMV) is a plant virus that infects wheat and other cereal crops, causing significant economic losses in many regions of the world. WSMV is a serious threat to global food security, as it can significantly reduce crop yields and limit the availability of wheat and other cereal crops for food and feed. WSMV is part of the family Potyviridae, which includes many other economically significant plant viruses. WSMV is transmitted by a tiny, winged insect called Wheat Curl Mite (Aceria tosichella) (WCM), which can easily spread the virus from plant to plant.
Symptoms and signs: Symptoms of WSMV infection include characteristic yellow streaks on the leaves of infected plants. As the infection progresses, leaves take on a mottled appearance which can eventually lead to stunted growth, reduced yields, and even plant death in severe cases. Severity of the disease depends on plant age at the time of infection, environmental conditions. Warm (75-80°F, 24-27°C), dry weather promotes infection by stressing plants and encouraging the proliferation of the primary vector, the WCMs.
Learn more about the life cycle and management of this disease:
Wheat Spindle Streak Mosaic Virus (WSSMV) and Soil-borne Wheat Mosaic Virus (SBWMV)
Pierce Taylor and Peng Tian
Both Wheat Spindle Streak Mosaic Virus (WSSMV) and Soil-borne Wheat Mosaic Virus(SBWMV) are soil-borne viruses that infect wheat and other cereal crops, causing significant yield losses in many parts of the world. As the name suggests, SBWMV is primarily transmitted through soil, either through direct contact with infected plant debris or via soil-dwelling vectors like Polymyxa graminis, a fungus-like organism that can spread the virus to new plants.
Symptoms and signs: Symptoms of WSSMV and SBWMV infection can vary depending on the strain of the virus and the stage of plant growth, but can include yellowing, mosaic or mottling patterns on the leaves, stunted growth, and reduced grain quality. WSSMV can cause light green to yellow spindle-shaped streaks and necrosis of leaves, reduced heading, and slight stunting while the symptoms of SBWMV are chlorotic mosaic or irregular mottling and streaking, and even resetting in some very susceptible cultivars. Symptoms are most prominent on early-spring growth and rarely appear in the fall.
Learn more about the life cycle and management of this disease:
Barley Yellow Dwarf Disease of Wheat
Pierce Taylor and Peng Tian
In Missouri, barley yellow dwarf (BYD) is a disease that can infect a wide range of cereal crops, primarily barley, wheat, oats, and rye. The disease is a significant threat to cereal production worldwide, with estimated losses of up to $1 billion annually, causing yield loss between 11% and 33% and sometimes up to 80% (Miller and Rasochová 1997). Viruses that cause this disease are commonly referred to as barley yellow dwarf virus (BYDV), maize yellow dwarf virus (MYDV) and cereal yellow dwarf virus (CYDV) and belong to different genera in the same family Luteoviridae (Walls III et al). This disease primarily spread by over 20 types of aphids, which feed on infected plants and then transmit the virus to healthy plants as they move between fields.
Symptoms and signs: Symptoms of infection includes yellowing or reddening of leaves, stunted growth, and reduced yield and quality and can vary depending on the crop and the severity of the infection. Vigilant monitoring and management practices are essential for minimizing the impact of the disease on farmers and food security. Typically, BYD disease causes discoloration at the leaf edges and midrib before the leaf tip. Leaves become light green or yellow and may have apparent purple staining.
Learn more about the diagnosis and management of this disease:
Sample highlights archive
Check out previous highlights from the Plant Diagnostic Clinic.