Informational table showing disease name, symptoms, pathogen/cause, and management of Geranium diseases. Disease Symptoms Pathogen/Cause Management Alternaria Leaf Spot Water-soaked spots on underside of leaf enlarge to 1/4 - 1/2 inch. Concentric rings of dark tissue form in spots. Alternaria alternata Avoid overhead watering. Remove and destroy crop debris from benches, pots, and walkways. Apply a fungicide to protect plants. Bacterial Blight Two types of symptoms may develop: 1) Small spots (less than 1/4 inch) develop on underside of the leaf and become sunken and well defined. The leaf wilts and dies as the bacterium spreads through water-conducting vessels of vein and petiole. V-shaped areas form with wide part of V on leaf margins and point of V on veins. 2) Lower leaves wilt at margins while the blade and petiole remain turgid. The vascular tissue of the main stem on the side of the affected portion of the plant is discolored gray-brown. Lower leaves die and fall. Xanthomonas campestris pv. pelargonii Purchase culture-indexed cuttings or grow plants from seed. Immediately discard infected plants after a positive diagnosis is made. Avoid overhead irrigation. Discard all unwanted geraniums at season's end. Do not take cuttings with knives. Wash hands frequently when breaking out cuttings. Or disinfest the cutting knife frequently and thoroughly. Bacterial Fasciation Short, thick, fleshy, aborted stems that form at base of main stem at or below soil level are pale green or green-yellow. The rest of the plant appears healthy. Rhodococcus fascians Purchase culture-indexed plants. Discard infected stock plants and cuttings and infested media. Blackleg Cuttings first develop a brown water-soaked rot at the base. The coal black rot proceeds 3-4 inches up stem and kills the cutting rapidly. Pythium Use sterile propagation media. Discard infected cuttings since affected rooted cuttings later develop root rot (see Pythium Root Rot). Keep hose ends off the ground. Botrytis Blight Flowers turn dark and fall prematurely. Where infected petals land on leaves, an irregular leaf spot forms. Cutting stubs have a brown rot that may extend down stem. Cuttings develop a dark brown rot near the base. Botrytis cinerea Avoid damaging plants in any way. Do not leave large cutting stubs. Remove and destroy fading flowers and leaves. Heat, ventilate, and space plants to ensure good air circulation and low humidity. Apply a fungicide to protect plants. Exclusive use of one chemical can result in the development of populations resistant to the chemical. Do not rely on only one chemical. Edema Small water-soaked pimples or blisters form on the underside of lower leaves. Blisters become corky brown. Severely affected leaves fall. This physiological disorder is favored by cool, cloudy weather. Space plants to provide good air circulation. Plant in well-drained mix. Avoid overwatering during cool, cloudy weather. Pseudomonas Leaf Spot Elliptical, water-soaked 1/4 - 1/2 inch spots form on leaves. Spots become dark brown to black and irregularly shaped. A yellow halo may or may not surround each spot. Pseudomonas cichorii Purchase disease-free cuttings. Do not irrigate overhead. Keep leaf surfaces dry at all times. Pythium Root Rot Symptoms: Root tips appear translucent and water-soaked. The outer layers of root tissue strip off when pulled from soil leaving the central core of vascular tissue bare. Pythium Pot in sterile media. Keep hose ends off the ground. Discard blackleg-infected cuttings even if well rooted. Apply a fungicide to protect plants. Rust Chlorotic specks on upper leaf surface appear directly opposite pustules of rust-colored spores on underside of leaf. Spores erupt in concentric rings forming a "target" spot. Puccinia pelargonii-zonalis Purchase rust-free cuttings. Do not irrigate overhead. Discard unwanted geraniums at season's end. Apply a fungicide to protect plants. Southern Bacterial Wilt Lower leaves wilt, yellow, and fall. Vascular tissue of affected stems turns brown or black. Ralstonia solanacearum Purchase culture-indexed plants. Do not bring ground-planted geraniums into the production area or propagate from them. Destroy infected plants. Verticillium Wilt Middle and upper leaves collapse, dry, and fall. Vascular tissue of affected stems is browned. Symptoms are readily confused with those of bacterial blight. Verticillium albo-atrum or V. dahliae Purchase culture-indexed cuttings. Use sterile potting mix. Destroy infected plants. Viruses Symptoms vary with virus, cultivar, and growing conditions. Symptoms include: mottling, ringspotting, leaf cupping, yellowing of veins, leaf malformation, leaf spotting, and loss of zonation. Many viruses occur singly and in various combinations in plant tissue. Purchase virus-indexed cuttings. Maintain strict insect and mite control.

Alternaria leaf spot.

Bacterial fasciation.

Gray mold (Botrytis) on leaf and flowers.

Edema.

Bacterial blight (Xanthomonas).

Typical wilting Leaf spotting phase.

V-shaped area on leaf.

Net vein symptoms due to virus infection.

Leaf crinkling due to virus infection.

Pseudomonas leaf spot.

Rust.

Black leg.

Prepared by Gary W. Moorman, Professor of Plant Pathology