Diseases and Pests

by Heather Prince

Star-of-Bethlehem (Ornithogalum umbellatum) is a perennial bulb with thin grass-like foliage and starry white flowers. An aggressive spreader, they often appear in lawns or become so thick in beds that they out-compete desired plants. The flowers are usually branched open clusters of bright, waxy, white blossoms with 6 petals and a characteristic green stripe on the underside. They bloom April through June and are about 8 to 12 inches high. The leaves resemble crocus foliage but are far denser in growth. Seed pods are formed after flowering and then plants die back to the bulbs until the next year. Numerous bulblets spring from the parent plants. Rhizosphaera infection

You can hand-dig the bulbs for removal but avoid tilling an area with Star-of-Bethlehem as it helps spread the bulbs throughout the site. In lawns, herbicide options include sulfentrazone, carfentrazone, or 2,4-D (either alone or in a 3-way product). Plan on at least two consecutive years of treatment to eradicate. These postemergent herbicides must be applied to the leaves and since the leaves wither in early summer, proper timing is important. In landscape beds, spot treatment using glyphosate shows marginal results, so hand-digging is your best option. Vigilant weed control is the best way to eradicate Star-of-Bethlehem.

Clients may call alarmed by an unusual pattern of damage resembling lines or clusters of round dots on leaves of plants in the mint and aster family, among others. Four-lined plant bugs (Poecilocapsus lineatus) have been out and about. These tiny insects are named for the four black lines that run down the leathery part of the adults’ wings. The lines of the adult bug can be bright green to bright yellow. The body of the nymphal stage can be bright red and develops the four lines as it matures. As a true bug, their piercing sucking mouthparts allow them to feed on plant fluids, producing dark round sunken spots on the leaves after feeding. The characteristic Poecilocapsus lineatus spots may be clear then form a depression as the plant bug sucks out the chlorophyll. Eggs overwinter in the stems of favored plants, with one generation produced each year. The tiny adults tend to hide in leaf axils, making damage the most reliable tool for diagnosis.

There are no fungicides that effectively control this disease. The best chance of tree survival is to prune diseased branches as soon as suspected fungus is confirmed. Cut back all diseased branches to the nearest living laterals or to the trunk. Avoid injuring bark and clean pruning tools between cuts to reduce fungus spread. Do not prune when affected trees are wet, as spores exude from cankers onto the surface of the bark. Trees under stress are more likely to become infected, so keep trees mulched, fertilize lightly in spring, and water in dry periods, especially going into winter.

University of Illinois Extension Service https://web.extension.illinois.edu/state/ horticulture/index.php 217-333-0519 The Morton Arboretum http://www.mortonarb.org/Plant Clinic: http://www.mortonarb.org/trees-plants/ tree-and-plant-advice/ 630-719-2424 Chicago Botanic Garden Plant Information Service: https://www.chicagobotanic.org/ plantinfoservice 847-835-0972

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