Problems With Pieris Japonica

The Pieris japonica is prone to many of the same problems as rhododendron plants. This evergreen shrub, also known as Japanese andromeda or Japanese pieris, has the same planting requirements and is susceptible to the same pest problems. As long as the pieris japonica is planted correctly, pests and fungal diseases that attack the plant can be treated.

Pieris japonica grows in U.S. Department of Agriculture plant hardiness zones 5 and warmer. This shrub needs well-drained, acidic soil. Pieris japonica does not like full sun exposure, and grows best in partial shade conditions. Leaves that turn yellow between the veins may be a sign of alkaline soil. Soil can be made more acidic by mulching with sphagnum peat, applying aluminum sulfate or using an acidifying fertilizer. If your Pieris japonica is located in full sun, or if it is planted in soggy soil, you may need to move the plant to a better location. Any of these stressors will make a Pieris japonica more susceptible to insect infestations and fungal diseases.

Lace bugs are the most common pest of Pieris japonica. They live on the bottom side of the plant's leaves, sucking the sap and nutrients from the plant. Damage to the leaves from lace bugs shows as mottled yellow foliage. Lace bugs are visible as small, 1/8-inch-long black insects. Young lace bugs can be controlled by spraying the plant with water and knocking the bugs off the plants. Insecticide is needed to eliminate adult lace bugs. Use an insecticide safe for rhododendrons and follow label directions for application. To kill the lace bugs, spray the bottom sides of the leaves as well as the top sides.

Southern red mites and scale occasionally present problems for Pieris japonica. These insects can be controlled by use of an insecticide. Use an insecticide that is safe for rhododendrons and follow the label directions for application.

Phytophthora root rot and phytophthora canker are fungal infections that result from soggy soil or over-watering. The phytophthora fungus causes whole branches to wither and die and a general decline of the Pieris japonica. If you suspect phytophthora, look for reddish-brown cankers at the base of the branches. If only one or two branches are affected, you can stop the spread of the fungus by pruning away the diseased branches. A fungicide approved for use on rhododendrons will also help control the infection. Leaf spot, also caused by various fungi, is caused by wet leaves and will usually resolve itself once conditions improve. If leaf spot continues after the weather dries, use a fungicide to control the fungi.