The Japanese cedar (Cryptomeria japonica) belongs to the Taxodiaceae family. While not a true cedar (Cedrus), this oval-shaped species reaches a height of 40 to 50 feet with a spread of 15 to 20 feet. The straight trunk has a reddish-brown bark that peels. Cryptomeria japonica suffers from diseases and insects that affect the root system, branches and leaves.
Smaller Japanese Cedar Longhorned Beetle
The smaller Japanese cedar longhorned beetle (Callidiellum rufipenne) can attack weak or felled trees and hasten death. This wood-boring beetle measures 6 to 14mm long and 3 to 4mm wide. Physical characteristics include a brown head and thorax on a flattened body and slender antennae. In a 16- to 18-day lifespan, the beetle can fly to a host tree, bore into sapwood, feed on phloem and cambium tissue, and create larval galleries and pupal chambers. Signs include frass, or powdery waste from the beetle, brittle branches, and cracks and depressions on the bark.
Phytophthora Root Rot
A funguslike organism, Phytophthora infects through the root system and leads to plant death. Phytophthora thrives in wet soils above 12.2 degrees C. This pathogen spreads by contaminated soil, splashing rain, contaminated irrigation and water runoff, insects, equipment and handling. According to the University of California Statewide Integrated Pest Management Program, young Cryptomeria japonica trees with relatively small roots and crowns are susceptible.
This disease kills the inner bark and reaches stems or branches. Visible symptoms include a dark layer of sapwood in areas around the upper root and crown and stressed leaves that can turn yellow-green or red-purple. A dying, bronze tree may result. Trees may die in one season or decline over years.
Phomopsis Twig Blight
The fungus Phomopsis juniperovora infects young needles of the Cryptomeria japonica and spreads to the stem tissue. This pathogen thrives in spring and summer with wet, warm conditions. Spores in fruiting structures provide the source of infection in shoots from the earlier season. Insects, wind, handling and pruning can spread the spores.
The disease first manifests with yellow spots at shoot tips. Infected new shoots change from light yellow to red-brown to ash-grey. Watch for lesions on stems and cankers between healthy and infected tissues. As twig blight progresses, stems and needles show dried areas with black spots.
Armillaria Root Rot
The fungus Armillaria attacks the roots and stems. This pathogen can cause wood decay, reduce growth, and kill already weakened trees. The fungus spreads filaments through the roots. This disease progresses to the root collar, tree trunk and sapwood. According to Natural Resources Canada, as sap flow ceases, the tree declines. Resin and soil can encrust infected roots. Needles turn yellow-green then brown prior to falling. This disease causes white rot; infected wood may change from light yellow to white with black lines. Wood texture may feel soft or stringy.
Junghuhnia Root Disease
The fungus or funguslike Junghuhnia vincta produces root rot and butt rot of the stem. This disease occurs in Australia, New Zealand, Hawaii and Gulf Coast region, according to the National Information Center for State and Private Forestry. Symptoms include patchy crowns and white or pink fungal tissue pads at the tree base or on roots. Pink encrustation can appear on lower stems. Foliage turns progressively yellow and brown. Infection spreads by airborne spores and contact with infected plants. Results include white, spongy wood decay and thin black zone lines.
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- Scion Forestry in New Zealand: Pests and diseases of Japanese cedar Cryptomeria japonica
- Natural Resources Canada: Armillaria root rot
- Canadian Food Inspection Agency: Callidiellum rufipenne (Motschulsky) - Smaller Japanese cedar longhorned beetle
- National Information Center for State and Private Forestry: Junghuhnia vincta
- University of California IPM: Phytophthora Root and Crown Rot in the Garden