Alternaria Leaf Spot of Horseradish. Alternaria leaf spot of horseradish is caused by the fungus Alternaria brassicae. This disease is characterized by distinct spots with concentric rings on leaves. In wet conditions dark dusty fungus growth develop on the spots. This disease was first reported from Illinois in 1999.

Bacterial Rind Necrosis of Watermelon. The bacterial rind necrosis of watermelon is caused by an Erwinia species. The disease causes a brown, corky, dry necrosis of the interior of the rind, which rarely extends into the flesh. The affected area may vary from a single small spot to the entire rind. The symptoms resemble those attributed to boron and calcium deficiencies. There are rarely any external symptoms on watermelon. In the case of the severe internal necrosis, the fruit may be misshapen. This disease was first reported from Illinois in 2000.

Tobacco Etch Virus on Tomato. Tomato plants infected with Tobacco etch virus (TEV) appear somewhat stunted with mildly mottled, slightly distorted foliage. Plants infected at an early age are severely stunted. The fruit are mottled and do not achieve marketable size. TEV is a potyvirus, consisting of long, flexuous particles about 760 x 12-13 nm. This disease was reported from southern Illinois in 2000.

Plectosporium Blight of Pumpkin. Plectosporium blight (Microdochium blight) of pumpkin is caused by the fungus Plectosporium tabacinum. All parts of the plant may be affected. Spindle-shaped, tan to white lesions develop on stems, leaf veins, petioles, and peduncles. Stem and petiole lesions can result in the death of attached leaves, and defoliation can occur in severe infection. Infected stems are dry and brittle. On fruit, the fungus causes white or silver russeting. Individual lesions are less than 1/4 inch long, but often coalesce to form a continuous dry, scabby surface. This disease was first reported from Illinois in 2000.

Root Knot Nematode of Horseradish. Root knot of horseradish is caused by the nematode Meloidogyne incognita. Characteristic symptoms of the disease appear on the roots. Infected roots swell at the point of invasion and develop into the typical root knot galls. Several infections take place along the same root, and the developing galls give the root a rough, clubbed appearance. Root knot nematode of horseradish was first identified in Illinois in 2001.

Bacterial Fruit Blotch of Watermelon. Bacterial fruit blotch of watermelon is caused by the bacterium Acidovorax avenae subsp. citrulli. The characteristic symptom of this disease is a dark olive green stain or blotch on the upper surface of the fruit. The blotch is first noticeable as a small water-soaked area, but it rapidly expands and covers much of the fruit surface. As the blotch increases in size, the area around the initial infection site becomes necrotic. In advanced stages of the lesion development, the epidermis of the rind ruptures. Fruit lesions rarely extend into the flesh. Rapid extension of fruit lesions usually occurs during the few weeks prior to harvest. The pathogen also infects leaves, but the symptoms on the leaves may be inconspicuous. Leaf lesions are small, dark brown, and somewhat angular. This disease was first reported from Illinois in 2001.

Dodder. Dodder (Cuscuta spp.) is a parasitic plant and affects the growth and yield of infected plants. Orange or yellow vine strands grow around the stems and the other aboveground parts of the plants. The growing tips reach out and attack adjacent plants. Dodder-infested patches in the field continue to enlarge during the growth season. During late spring and in the summer, dodder produces massed clusters of white, pink, or yellowish flowers, which soon form seed. Dodder was observed in several farms throughout Illinois in 2001.

Southern Blight of Pepper. Southern blight of pepper caused by the fungus Sclerotium rolfsii. Characteristic symptoms of this disease are sudden wilting and death of the plant. The stem is rotted at ground level, and there may be some discoloration of vascular tissue part way up the stem. Often, particularly in wet weather, there are fan?like webs of whitish mycelium around the rotted stem. These will develop sclerotia that look like mustard seed. On fruit near or on the ground there is a rapid rot with abundant mycelium and sclerotia. This fungus is a soilborne pathogen and has a broad host range. The disease was observed in one bell pepper field in central Illinois in 2002.