Hinoki dwarf cypress (Chamaecyparis obtusa) and Sawara dwarf cypress (Chamaecyparis pisifera) are commonly called false cypress. The plants are excellent varieties for container growing and bonsai, but many varieties, like Reis Dwarf, the fernlike Filicoides, bright yellow Lemon Thread and golden-leaved Nana, are eye-catching specimens outside in the garden, as well. Generally resistant to diseases and pests, dwarf cypress can occasionally suffer from insect, bacteria or cultural problems that cause the foliage to turn brown.
Aphids, scale insects and spider mites may infest dwarf cypress plants. The insects suck the juices from the foliage, often turning it yellow or brown. These insects are tiny, but can damage large sections of the plant. Spider mites weave tiny webs that may be visible on the foliage. Scale insects leave behind a sticky substance called honeydew that attracts ants and often grows sooty or black mold, further harming the plant.
Juniper blight, caused by Phomopsis juniperovora, turns the tips of the cypress needles brown. New growth turns brown and dies during its first summer. The plant begins to die back as the infection girdles one stem after another, progressing to the main stem. If the plant's main stem is less than 1/2 inch thick, the fungus can girdle the stem and kill the entire plant. If the brown needles begin turning a dull gray, the problem might be juniper blight.
Conifers like dwarf cypress may suffer from various forms of rot that turn the foliage brown. Rhizoctonia and Phytopthora root rots infect the underground parts of the plant, affecting the above ground parts. Both infections may cause damping off, which causes seedlings to die.
Dwarf cypress plants that turn first turn yellow, then turn brown and die may be suffering from chlorosis. Chlorosis may be caused by lack of iron or other nutrients in the soil, injury, stress or improper watering. Dwarf cypress requires full to partial sunlight, good drainage and plenty of water. Too much or too little light or water can cause the plant to turn brown and eventually die. Take a soil test to be sure the plant has access to the proper nutrients. Apply a foliar spray to help the plant green more quickly.
Treatment and Prevention
Keep dwarf cypress healthy to help it resist or recover from disease and insect attacks. Re-evaluate your fertilization, watering and pruning practices to be sure the plant has the proper care and you are not accidentally wounding it with gardening tools or lawn mowers. Keep plant debris cleared away from the soil beneath the dwarf cypress to eliminate any insects or fungal spores that may be lurking. If the plant has a fungal infection, prune away and destroy infected areas. Use a copper-based fungicide or a fungicide containing macozeb to treat the infection. Check the label for application and use instructions. To eliminate aphids, spider mites and scale, first try spraying the cypress with the garden hose. Use a strong stream of water to knock the adult insects and larvae off the plant. If that doesn't work, use insecticidal soap to smother the insects.