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Red Clover Rust

Morgan Goodnight and Peng Tian

The weather of this spring has been cooler and wetter than the past, which provided great conditions that favor many different types of fungal diseases. As one of important foliar diseases of a broad range of hosts including field crops and ornamental plants, rust diseases weren't left out from this party. The staff at MU Plant Diagnostic Clinic recently received a red clover sample that was confirmed being infected by a rust disease, which was added to an already-full list of these fascinating basidiomycetes.

red clover rust

Symptoms and signs: Symptoms usually begin as yellow spots all over the leaves and stems (Figure 1). Once they become mature, these spots turn red or brown and develop into pustules that are about 2 mm long (Figure 2). These pustules can develop along the stem and over/under the leaves, and cause twisting of the stem, leaf distortion or defoliation in some cases.

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Japanese Maple Scale

Morgan Goodnight and Peng Tian

Insect damages of Japanese Maple Scale were confirmed on a Chinese Holly and a Kwanzan cherry tree that were submitted to The MU Plant Diagnostic Clinic. Contrary to the name, Japanese maple scale has a wide range of hosts and can cause damages on trunk, branches, and leaves of many landscape and nursey plants in the United States.

japanese maple scale

Morphology: Japanese maple scale belongs to the armored scale family (Hemiptera: Diaspididae). The armor is called test that is covered with a white wax and can protect the soft body from the environment. Japanese maple scale is about 1 to 2 mm long. The males and females look almost identical, except that the females are slightly larger. The bodies of male and female scales and eggs are purple in color underneath the test.

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Anthracnose on Maple Tree

Morgan Goodnight and Peng Tian

The MU Plant Diagnostic Clinic recently received a maple leaf sample with dry, dark brown irregular spots that follow the leaf veins. After examination, we confirmed that the symptoms match the anthracnose disease, which could be caused by several different fungi. While the sample we received is from a maple tree, this disease infects a wide range of hosts throughout the US.

leaf blotch

Symptoms and signs: This disease affects new, younger leaves when they have a thin layer of water on them (Figure 1). The symptoms are dark brown blotches or spots that are vein-associated and irregular in size and shape. They are often confused with heat stress or drought, because both symptoms have scorch marks. The young infected leaves curl or cup in response to the disease, while mature leaves do not. Infection normally occurs when the younger leaves are starting to grow and are wet. Infection is more severe on the lower branches where there is more humidity. Severely infected trees can lose their leaves early in the spring and will develop new leaves in midsummer. Anthracnose may be a more serious concern if the hosts are not well established or are suffering from environmental stresses (drought, heat, or winter injury). Although this disease does not kill the host, numerous seasons of infections causing defoliation may greatly reduce the overall growth of the tree.

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Dothistroma Needle Blight

Morgan Goodnight and Peng Tian

The MU Plant Diagnostic Clinic staff found a pine tree with needle blight and dieback problems. After examination of the symptomatic needles, we confirmed the presence of Dothistroma Needle Blight, which is a fungal foliage disease infecting pine needles and can even kill the tree in extreme cases. While this disease effects many varieties of pine trees throughout the Midwest, its primary host in Missouri is Austrian Pine.

dothistroma needle blight

Symptoms and signs: This disease overwinters in the infected needles and disperses during the wet season of the early spring to fall. The first symptoms are the formation of dark spots or bands on the needles (Figure 1). Then, the needle dies back starting at the tip. As it progresses, the whole needle turns brown, dies and falls off the tree. Once the spores are mature, they emerge from the black fruiting bodies in the spots or bands on the needles can be spread by rain or wind. The black fruit bodies are called stromata or pycnidia. They normally appear in the fall when the disease become prominent, but spores aren’t released until the next spring.

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White Mold Disease

Peng Tian

The MU Plant Diagnostic Clinic recently received an alfalfa sample and a tomato sample. Both of them were diagnosed with white mold disease caused by Sclerotinia sclerotiorum.

white mold disease

Overview: The white mold disease on tomato is also called timber rot while on alfalfa, it is called Sclerotinia crown and stem rot. This disease can also affect soybean, clover and many vegetables. In the cool and moist condition, the pathogen affects the crown and stem tissues of the plant. As the disease progresses, white mold spreads inside and outside of the stem, causing stem and crown rot. When humidity and temperature becomes favorable for this disease, black and hard structures with irregular shapes, also known as sclerotia, are produced among the white mold. They are the overwinter survival structures that can stay in the soil for many years, making it very difficult to control this disease.

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