Phlox (Phlox paniculata) is a cheerful perennial with bushy clusters of blooms in shades of pink, lavender, rose, red, purple and white. Phlox generally begins blooming in mid-summer to late August, and it can grow as tall as 3 feet. Because of its height, phlox is often used as a background plants in landscaping or in narrow borders.
Powdery mildew shows up as white, powdery spots on the foliage of phlox. The spots often cover the green foliage, and eventually move onto the flowers. Powdery mildew is caused by poor air circulation, so do not plant your phlox too closely to other plants, along fence lines or alongside a building. If you notice a problem with powdery mildew, treat it with a fungicide containing sulphur or chlorothalonil.
The spider mite sucks the sap from phlox's foliage, causing the leaves to dry out and turn brown. Spider mites prefer to attack during hot, dry summers. Healthy plants can sometimes overcome a spider mite infestation, if the plant is kept well-watered and fertilized. Spider mites can be treated with an insecticidal soap spray, especially if you catch the infestation early. For more severe problems, choose an insecticide with Kelthane, a miticide for use on flowering perennials. Use insecticides as early as possible in the day, else the plants could suffer more damage.
Verticillium wilt is a fungus that lives in the soil indefinitely, according to the University of Minnesota Extension. Symptoms, which usually appear in July and August, include leaf scorch, dieback of shoots, small foliage, yellow foliage and heavy seed crops. There is no chemical cure. Remove any plants infected with verticillium wilt, wrap them in plastic and place in the trash. Do not put discarded plants in the compost bin, as the wilt will spread into the compost.