There may be a yellow halo or concentric rings around the spots. Verbena Bonariensis also goes by various other names such as Purpletop vervain, Argentinian Verbena, Tall Verbena as well as Pretty Verbena. Both flowers and leaves will become stiff and discolored. Scale can be eliminated by treating the verbena with insecticidal soap or horticultural oil. Her previous jobs include reporter, photographer and editor for a weekly newspaper. True bugs are juice-sucking pests that steal vital nutrients from plants. & Ruempl.) This will lead to defoliation and twig or branch dieback. One way to test for thrips infestation is to hold a piece of paper under the plant and shake the foliage. & Broome) Ferraris Chalara elegans Nag Raj & Kendr. Some varieties of Verbena are resistant to powdery mildew, such as the Aztec, Laskar and Tukana series. Even though thrips cause unsightly damage to plants, they generally do not harm the plant. Tiny, soft-bodied insects covering the buds and underside of leaves, aphids suck the plant’s fluid by piercing stems and leaves with their slender mouths. Flanigan has written for various publications, including WV Living and American Craft Council, and has published several eBooks on craft and garden-related subjects. This variety originated from South America where it is a common sight in most of the warm regions of … Verbena is a warm-season plant that grows in Sunset Climate Zones H1, H2 and 8 through 24. Powdery mildew, as the name suggests, resembles a white, powdery coating on leaf surfaces. They provide pure, bright colors or delicate, pastel shades and generally grow like gangbusters. This innate vigor protects them from some of the disease problems that require a debilitated host. All Rights Reserved. Large infestations of whiteflies are difficult to control even with yellow sticky cards, horticultural oil and insecticidal soap. The best defense against caterpillars is prevention and handpicking the insects off the plants. These common pests are not insects and are in fact a part of the arachnid family. The gall midget is a tiny fly that resembles fungus gnats. However, larger infestations will result in yellow, withered leaves, which drop prematurely. Pests Of Verbena. Alternaria Leaf Spots. Black root rot Thielaviopsis basicola Chalara elegans [synanamorph] . Like many other plant pests, scales secrete the sticky honeydew, which leads to powdery mildew growth. The best treatment against broad and cyclamen mites is predatory insects that feed on them. She currently works as a writer and copy editor. Some varieties of Verbena are resistant to powdery mildew, such as the Aztec, Laskar and Tukana series. They generally are identified by an X or triangular-shape on their back and leave excrement drops that look like varnish spots on the leaves. Disease Symptoms Pathogen/Cause Management; Botrytis Blight: Tan spots develop on leaves. Some thrips are beneficial insects and feed on pests that can damage plants. A whitefly infestation generally occurs when their natural enemies -- such as ladybugs and lacewings -- have been eliminated. The spots may merge into a V-shaped area. Also, place yellow sticky cards around the plant to catch flying adult mealy bugs. If thrips are infesting the verbena, some pests will land on the paper. The leaves turn yellow, become necrotic and fall off. Other thrips feed on plants causing scarring and distorted plant parts as well as stunted plant growth. Most of the insect and mite pests that affect lantana and verbena are similar. Other species of gall midgets bore into the plant’s tissue. As the spots mature, they begin to sink and turn brown. The fungus Alternaria causes small water-soaked spots on the lower, older leaves of Verbenas. The first signs of powdery mildew on Verbenas are dusty gray or white circular patches on the lower leaves. Alternaria leaf spot : Alternaria sp. Copyright Leaf Group Ltd. // Leaf Group Lifestyle. . The fungus Alternaria causes small water-soaked spots on the lower, older leaves of Verbenas. Even though these pests can cause slow plant growth or premature leaf dropping, leafminer infestation is generally not fatal to the verbena. Spider mites suck the cell content from the verbena leaves, leaving discolored dots on the leaves. Diseases of Verbena (Verbena × hybrida Groenl. Intervention can help manage the injury and stimulate the plant to continue blooming on its regular cycle. For larger infestations, use horticultural oil, insecticidal soap or beneficial predators such as ladybugs. Although lantana and verbena can survive most pests, you may need to intervene if the plant is attacked heavily. Established plants rot at the crown. Galls look like colorful or distorted swellings on the verbena. These sap-sucking insects will cause leaf discoloration, stunted growth and eventually kill the leaves. Shaking the plant lightly will result in a cloud of whiteflies flying off the plant. A close examination of the spots reveal pinkish to orangish sporulation oozing out of the lesions. They appear raised as spores are produced. The spots merge into large areas of necrotic tissue. Save For Later Print. Caterpillars that feed on plants will leave chewed holes in the foliage and consume buds and flowers. Cercospora is a fungus that causes light-green sunken spots on the leaves of Verbenas. Controlling these pests with insecticides is difficult since they feed on the plants buds and inside distorted plant tissue. If left untreated, the patches join together and cover entire leaves. Verbena is rarely affected by diseases, and if properly cared, it will never happen at all. Place annual Verbenas at least 12 inches apart. 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