There's a fungus among us. In fact, there are quite a few. The warm, wet month of May provided perfect conditions for numerous fungal problems _ especially root rot diseases. Many of the pathogens that cause root rots are naturally present in Florida soils. However, they become a problem only when plants become stressed. In very wet weather, that stress can be a poorly drained soil. Few plants will survive in soil which is saturated with water for an extended period because the roots are deprived of oxygen.
Some plants are notoriously intolerant of poor drainage _ ligustrum, avocado, poinsettia, viburnum, pittosporum and citrus, for example. Others, like bottlebrush, oleander, red maple, sweet gum, wax myrtle and hollies, will tolerate wet or dry sites. If the drainage cannot be improved, the best bet is to replace declining plants with ones that don't mind wet feet.
Question: I am completely baffled by the biological condition of the soil around my house that seems to be responsible for the destruction of two dozen periwinkle (vinca) plants that wilt and die 10-14 days after planting. Could soil pH and a heavy wood chip mulch be the problem? I have impatiens and other flowers adjacent to the periwinkles that are the envy of neighbors. Boris Uzenoff, Sun City Center
Answer: Periwinkles (Vincas) are a wonderful, heat resistant and drought tolerant annual. However, wet weather or wet soils stimulate a number of fungus diseases that wreak havoc on them. Heavy mulch would aggravate disease.
The symptoms you described are usually caused by fungi that survive in the soil. The only way to get rid of them is to fumigate the soil (but this would damage the roots of existing shrubs) or to treat with a fungicide like Aliette or Subdue. Both of these are very expensive. Try periwinkles in a drained bed that receives full sun.
Sydney Park Brown is an urban horticultural specialist. Write her in care of the Hillsborough County Extension Service, 5339 State Road 579, Seffner, Fla. 33584.