Cranberry Pest Management Red Shoot Disease of Cranberry

Red shoot, caused by the fungus Symptoms and spindly with red or yellow Exobasidium perenne, is a rela- leaves that are slightly more tively minor disease of the culti- Signs round than typical oblong cran- vated American cranberry Symptoms Þrst appear in the berry leaves (Figures 1Ð3). By (Vaccinium macrocarpon) and the spring on current yearÕs shoots mid summer the lower surfaces wild small cranberry (Vaccinium that occur singly or as a cluster of leaves become covered with oxycoccus). The red shoot fun- arising from a node on a buried white, powdery fungal spores. gus is related to the fungus that runner. Affected shoots do not Shoots wither after the fungus causes red leaf spot. Red shoot produce ßowers but rather are has shed its spores. Diseased has been reported in Wisconsin, shoots break off easily from the Massachusetts, the PaciÞc Northwest, and in the Atlantic maritime provinces of Canada. Red shoot is not an economi- cally important disease, and speciÞc control recommenda- tions have not been developed. However, the distorted, red or yellow shoots have sometimes been misidentiÞed as a weed, making growers think that an herbicide should be applied. The fact that red shoot is a dis- ease has been conÞrmed by tak- ing fungal spores from infected plants and inoculating them Figure1. Clusters of red shoot in a bed of ‘Searles’. The orangish-rust col- onto healthy plants; the inocu- ored shoots to the left are not affected by red shoot, but rather a different lated plants then developed red problem such as upright dieback. shoot symptoms.

Figure 2. Early symptoms of red shoot compared to Figure 3. Later symptoms of red shoot compared to healthy uprights (at left). healthy uprights (at left).

buried runner, but if dug care- Disease Cycle Control fully from the ground, one can The fungus overwinters in dis- Red shoot is generally not eco- observe that the shoots originate eased cranberry runners. nomically important, and con- from nodes along the runner Infected shoots arise from trol measures have not been (Figures 4 and 5). nodes, often where infected developed. shoots were attached in previ- ous years. Spores are produced on the undersides of leaves and Patricia McManus shed during mid to late summer. Department of Plant Pathology University of Wisconsin-Madison How spores go on to cause fur- April, 1998 ther infections is not known.

Figure 4. Red shoot-afflicted Figure 5. Closer view of afflicted uprights (red arrow) attached to below- uprights attached to below-ground ground node on a runner (blue arrow). node on a runner.