AboutMike Mascio Expertise I have been an avid gardener since 1985 and an AllExpert volunteer since 1998. I specialize in soil preparation, seed starting and plant propagation, flowers, vegetables, and general landscaping. I am a strong advocate of the square foot method of gardening and the use of organic controls for pests and diseases.
Question The petunias in our window boxes have contracted a fungus/disease. The leaves are covered with small white specks and it is killing the plants. These plants do not get rainfall due to an overhang so they are watered manually. Any thoughts? We live outsie of Boston and weather has been cloudy and rainy most of the month.
Answer I am assuming you used a sterile potting soil in the window boxes and not soil from the garden. If so, this would rule out a soilborne disease. It also means the disease was probably spread through the air or from an insect.
Your only option at this time is to spray the plants with an all-purpose fungicide. It can be either sulfur or copper based. If the disease is not too far along, it should halt it from spreading. However, there is always the possibility that it cannot be reversed. Either way, I would try the fungicide and hope you caught it in time. I would also discard the soil after this season and sterilize the boxes with a mixture of two tablespoons of bleach per gallon of water.
Good luck, and please write again if I can ever provide assistance.
