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Bacterial Canker Disease of Tomato

Morgan Goodnight and Peng Tian

With the weather getting warmer in Missouri and garden season approaching, the MU Plant Diagnostic Clinic wants to bring attention to the Bacterial Canker Disease of Tomatoes. This disease can persist in the soil for long periods of time, so prevention is key.

bacterial canker disease on tomato

Symptoms and signs: Symptoms of the disease vary based on the age of the tomato plant, different environmental factors, and the type of infection developed. As a result, a diagnosis of the disease on symptoms alone can be difficult and a sample may need to be sent to a diagnostic clinic to confirm the presence of this disease. Symptoms of seedlings include leaf edge discoloration, necrosis and wilting. The leaves on a mature tomato plant become discolored with interveinal chlorosis and necrosis (Figure 1). The stem develops brown streaks in the vascular tissue and often splits forming brown cankers. The fruit develops small, creamy, white and raised spots with tan or brown centers and white margin.

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Stigmina Needle Cast on Blue Spruce

Morgan Goodnight and Peng Tian

The MU Plant Diagnostic Clinic received a Colorado Blue Spruce sample in March that showed symptoms of needle discoloration and barely distinguishable black spots running along the needles. It was diagnosed as Stigmina Needle Cast disease.

stigmina needle cast

Symptoms and signs: Symptoms of Stigmina Needle Cast progress slowly over a three-year course and eventually develop into needle discoloration and severe needle drop on the lower canopy of the tree. The first sign of the disease are black spots along the needles that are nearly invisible to the naked eye. About one year after the initial infection, symptoms start to become more severe and work their way up the tree to the newer foliage. Needles start to become darker and discolored, ranging from yellow, purple, and brown hues. Severely infected trees under other environmental or cultural pressure may die in the third year.

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Bacterial Leaf Scorch on Oak

John W. Howard II and Peng Tian

Bacterial Leaf Scorch (BLS) disease is caused by the bacterium Xylella fastidiosa, which infects the xylem of susceptible trees. This disease is transmitted by insect vectors, primarily sapsucking leafhoppers, though infection by root grafts are known to have occurred. Xylems infected with BLS eventually become blocked and are unable to transport water and nutrients from the tree roots to leaf tips. There is no cure for BLS and an infected tree will progressively decline and reach mortality in 5-8 years.

bacterial leaf scorch

Xyllela fastidiosa affects a variety of oak species, elm, maple, mulberry, sweetgum, and sycamore. Symptoms of BLS include marginal scorching that slowly spreads inward towards the main veins, further leading to twig dieback (Figure 1). BLS symptoms are similar to drought stress and can be difficult to distinguish between them. Timing of onset of symptoms is generally a differentiation between drought stress and BLS as drought stress injury occurs soon after an environmental event whereas BLS symptoms tend to develop in mid-summer and progressively worsen into fall. A variety of hosts may also exhibit a halo type ring at the scorched boundary. Indeed, BLS symptoms are also often confused with those of Oak wilt and Tubakia leaf spot.

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Cercospora Leaf Blight of Soybean

Morgan Goodnight and Peng Tian

In 2021, the MU Plant Diagnostic Clinic received seven soybean samples diagnosed with Cercospora Leaf Blight (CLB). These disease samples were collected from the counties including Vernon, Cooper, Montgomery, Chickasaw, Clark, and Johnson, and most of them were submitted to the MU Plant Diagnostic Clinic toward the end of the growing season. Symptoms of this disease present as severe leaf dropping and premature death. In addition to CLB, we also found other diseases such as charcoal rot, potassium deficiency and anthracnose present on several soybean samples.

cercospora leaf blight

Symptoms and signs: The symptom of this disease begins as purple, brownish spots on leaves. As it progresses, these leaf spots deepen in color and combine to form large necrotic areas that eventually lead to premature defoliation (Figure 1). In addition to significant yield loss resulted from defoliation, this disease can also cause purple seed stain which severely affects the product quality. Cercospora kikuchii produces septate conidiophores with size of 200-300 µm long and 4-5 µm wide while the size of conidia is 170 to 190 µm long and 3 µm wide.

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Black Canker of Weeping Willow

Peng Tian

Black Canker of weeping willow is caused by a fungus called Glomerella miyabeana and this disease is one of common willow diseases. Glomerella miyabeana and the other fungus Venturia saliciperda, the causal agent of willow scab disease together can result in a serious disease called willow blight.

black canker

Symptoms and signs: Symptoms usually begin as brown to black lesions on the leaves in the early spring. As the disease progresses, these lesions expand to the whole leaf and spread to the petiole. The leaves turn brown and wilt and eventually fall off the stem. Once the lesion spread to the stem or twig, this disease can cause black colored cankers with various size, normally in the junction position of twig and petiole (Figure 1). Once these cankers become mature, black fruiting bodies called acervuli developed on the canker and produce asexual spores called conidia.

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