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Gardening suggestions for growing vinca and petunias year after year

Author: Cathy Cromell
Issue: November, 2013, Page 137
Image courtesy of W. Atlee Burpee & Co.

Vinca



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Q -We’re having problems with flower beds that are planted in the summer with vincas and in the winter with petunias. Some of the new plantings survive, but many wilt and die. The native soil was supplemented with generous amounts of commercial compost and planting mix. How do we manage this problem?

A - Vincas (periwinkle) are very susceptible to fungal root rot diseases, including Phytophthora sp. and Rhizoctonia solani, notes University of Arizona Maricopa County Master Gardener Cathy Rymer. Find details at the Extension Plant Pathology’s site Ag.Arizona.Edu/PLP/plpext/diseases/turf/periwinkle/periwinkleRhizoctonia.shtml. Garden beds infested with Phytophthora should not be planted with vinca for at least two years. Vinca should not be replanted in areas where Rhizoctonia occurs. Consider growing something else, such as marigold, which is more tolerant. The viruses that most often affect petunias are tobacco mosaic virus and tomato spotted wilt, which are transmitted by insects called thrips.

Selecting substitute bedding plants for two years, along with fungal management, seems to be the best course of action. It is essential to have an accurate diagnosis before treating, because other pathogens may cause similar symptoms. For diagnostic assistance, contact the Master Gardener office nearest you. You can find them at cals.arizona.edu/maricopa/garden/html/mgs/satellite.htm. In the future, do not use the same bedding plant (or plants within the same family) in the same place year after year. Instead, practice “crop rotation” with different species, which helps inhibit diseases that strike specific plant families.
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