Disease in Pieris Japonica
This broadleaf evergreen is used as a border shrub, as a hedge, or as a focal point in landscape design. It is a slow grower, but at maturity can reach a height of up to 7 feet with a spread of 5 feet. Japanese pieris prefers partial shade and moist, rich, well-drained acidic soil. It is susceptible to leaf spot, chlorosis, and Phytophthora stem infestations. Japanese pieris can also be infested by pests such as lacebug, scale, mite and nematode.
Phytophthora root rot
Phytophthora root rot begins below ground level with a fungal attack on the fine roots of the shrub. The fungi cause the fine roots to die. The fungus then proceeds to spread to the larger roots, moving up to the root crown. Eventually, the disease spreads up through the stem destroying the root and stem tissue.
Phytophthora root rot Symptoms
This destruction causes the leaves to become chlorotic (turning a lighter color and wilting). The appearance of above soil level symptoms may not occur in some shrubs, other plants can have symptoms for approximately a year before they die. The best way to prevent the disease is to maintain a healthy plant, most importantly it should be planted in well-drained soil and not overwatered.
Japanese pieris is very susceptible to infestation by the lacebug, especially when the shrub is growing in full sun. Lacebugs have piercing, sucking mouthparts. The lacebugs overwinter on the leaves of the shrub, its eggs are embedded in the leaf tissue. They hatch in mid-March begin to feed on the underside of the leaves–sucking the juice from the leaves. They leave behind brown fecal drops. Soon the upper surface of the leaves show signs of destruction and will appear yellow and mottled.
If the shrub is healthy, the infestation is cosmetic in nature and there is no severe damage to the plant. Severe infestations on unhealthy plants will cause the leaves to fall off and the plant will be weakened. The way to avoid lacebug infestations begins with site selection–the Japanese pieris should not be planted in full sun. Early detection is also important. Lacebugs can be eliminated by chemical insecticides when necessary.
Chlorosis is a lack of green chlorophyll in the leaves, thus the leaves appear yellow in color. There are several causes of chlorosis: bad soil drainage, damaged or compacted roots, soil that is highly alkaline, as well as nutrient deficiencies of iron, manganese or zinc. Chlorosis treatment will depend upon the reason for the disease. You may have to add nutrients to the soil, or if soil compaction is the reason, you may need to do core aerification or till the soil.
There are several other pests that can infest the Japanese pieris, and they are: scale, mites, and nematodes. Scales and mites feed on plant juices. These sucking pests are quite small, the damage that they do to plants and shrubs is wilted leaves, growth reduction, and dying branches. They can be managed by the use of insecticides. Nematodes are small, roundworms, or soil pests that live within the spaces between soil particles on wet surfaces. They feed on the fine roots of the Japanese pieris–there is no chemical control solution for nematodes.