Yellow Markings on My Rozanne Geranium Leaves

Rozanne geraniums are herbaceous perennials and members of the Geraniaceae family. This lovely flower is easy to grow in well-drained soil in full sun or partial shade. However, Rozanne geraniums are susceptible to thrip infestations which can cause discoloration of the leaves, flowers and stems.

Identification

• Thrips are very tiny insects that measure from 1/16 to 1/8 inch in length and are a variety of colors. This pest feeds on the leaves, flowers and buds of flowers and plants. Thrips are highest in number during the spring and cause damage to many types of ornamental plants. The gladiolus thrip is a serious pest of geraniums, gladiolus, lilies, carnations, freesia, tomato, begonia, snapdragon, chrysanthemum, primula, tigerflower, poker plank and amaryllis.

Effects

• Gladiolus thrips cause yellow marks on Rozanne geranium leaves and flowers, which causes the bulbs to decay. Geranium flower buds will fail to open and damaged bulbs turn soft. Geraniums infested with thrips often have specks of brown excrement on the underside of leaves.

Diagnosis

• Thrips can be diagnosed by shaking geranium leaves and flowers over a white sheet of paper. Use a strong magnifying glass to detect the presence of this tiny insect. Thrips can also cause skin irritation if they come into contact with human skin.

Control

• There are many natural predators that feed on thrips, keeping them under control. Lacewings, predatory mites and parasitic wasps are just a few predatory insects that feed on thrips. When placing predatory insects in your landscape for thrip control, avoid using insecticides as this kills the predatory insects. Sticky traps are often effective in monitoring thrips and other insects. Chemical sprays may be applied for heavy thrip infestations and should be applied once each week for optimal control. Once desired control is achieved, monitor your geraniums for thrips and apply insecticides if re-infestation occurs.