Causes of White Spots on Hosta Plants
The Hosta (Hosta spp.) genus consists of between 50 and 70 species of shade-tolerant, mounding plants, many of which are cultivated in the home landscape for their lush, elliptic or heart-shaped leaves. If white spots appear on a hosta plant's foliage, it is a sign that the plant is struggling with a disease or with a pest infestation. Following proper cultural care guidelines will help to prevent foliage problems.
Anthracnose is the most common foliage disease that afflicts hostas, according to the Iowa State University Extension. Anthracnose is a fungal disease that causes irregular white to light tan spots with a brown border. As the disease progresses, spots broaden and split, giving leaves a disheveled, tattered appearance. The disease prefers humid, wet conditions. Spacing plants about a foot apart will help allow for proper air circulation. Heavily infected leaves should be removed and destroyed.
Leafhoppers are slender, hopping insects that suck juice from hosta foliage, leaving behind stippled dots all over the leaves. Leaves may turn brown, and shoots may curl up and die. Leafhoppers, along with their shed skin, can often be found on the underside of leaves. The University of California Integrated Pest Management Program does not recommend control methods for an infestation of adult insects, as they are very difficult to effectively control. Evenly applying insecticidal soap to the undersides of leaves can help reduce juvenile populations.
Viruses can cause a host of foliage symptoms, from white dots and splotches to shriveled leaves, irregular patterns and chlorosis. There are no control methods available for controlling viruses; infected plants should be dug up and destroyed to prevent infecting healthy plants. To prevent viruses, only buy healthy, disease-free hostas from reputable sources. The Missouri Botanical Garden warns that some nurseries may accidentally sell spotted or patterned hostas as novelty plants without knowing that they are infected.
Healthy hostas are less likely to succumb to foliage diseases and pests than plants that are stressed due to improper cultural conditions. Hostas generally do best in U.S. Department of Agriculture plant hardiness zones 3 to 9, where they grow well in shade or filtered sun. Hostas prefer fertile, well-draining soil that is moist, but not wet, to the touch. Maintain a weed- and plant debris-free garden, as viruses and pests can linger in plant matter.