1974 — “The newly discovered Pierce's disease bacterium could destroy large numbers of grapevines and render parts of California unfit for the culture of common grape varieties.

“Since 1884, this disease has been periodically investigated with the belief that it was caused by a virus…. This study reports for the first time the isolation of a rod-shaped, gram-positive bacterium from the disease-spreading leafhopper Draeculacephala minerva.

“A group of noninfective leafhoppers were fed on healthy grapevines, Vitis vinifera cv. Mission, then they were transferred to plants with Pierce's disease. Excreta (spittle) of 10 leafhoppers was collected after they were fed at first on healthy plants, and then additional excreta samples were taken from the same vectors after they had fed on diseased plants. Each sample of excreta was streaked on an enriched bacteriological agar medium.

“Bacteria grew as small white colonies on the media streaked with the excreta of the leafhoppers which had fed on a diseased grapevine. No such colonies appeared on media streaked with excreta from leafhoppers which had fed previously only on a healthy grapevine.

“These experiments have demonstrated that a gram-positive bacterium is the etiological agent of Pierce's disease in grapevines, and not a virus, as previously believed. The organism has been successfully cultured on artificial media. By using the leafhopper vector injected with the cultured and purified bacteria, the disease symptoms can be consistently reproduced in healthy grapevines and the same organism reisolated from clean leafhoppers fed on these plants and on naturally infected plants from the field.”

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