News and Views

Disease: Xanthomonas leaf spot
Pathogen: Xanthomonas campestris pv. poinsettiicola
Host: Poinsettia (Euphorbia pulcherrima)

Poinsettias. The very name conjures up visions of Christmas. Yet poinsettias are also afflicted by various diseases. One of the most severe of these diseases is Xanthomonas leaf spot caused by a bacterium. The disease was first found in India in 1951 and found in the US in 1960. Pin point spots start out a dull gray to brown water soaked area that rapidly enlarges into yellow, tan and scattered across the leaf surface. The disease is easily spread by water and can be very serious whenever plants are watered by overhead irrigation. Severe disease can lead to the leaves falling off of the plant.

Most, if not all of the cultivars of poinsettia are susceptible. Although a few bactericides containing copper are partially effective, they are rarely effective in controlling the disease when in the outbreak phase. Thus, the disease is most severe to production companies because the bacteria spread easily. The most effective way to control the disease is by using pathogen-free propagating materials.

For additional information on poinsettias, their history, and their diseases, see the December, 2001 APSnet Feature at: http://www.apsnet.org/online/feature/xmasflower/

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