The predominant symptoms include needle chlorosis and reddening of shoots (called "flagging") that later die. Cankers or lesions that form on the trunks can turn the bark yellow or dark brown and cause resin to exude. Stems may die and get crystalized in resin-soaked lesions. Resin is generally produced in plants to protect against pathogens. Sometimes, the tissue above the canker dies, causing girdling of the stem. The severity of the disease depends on weather conditions and may require moisture and insect wounds or hail to infect the trees. Some insects such as bark beetles, spittle bugs, weevils, pine tip moths, and needle midges may vector the disease into the tree. "F. circinatum" was used to inoculate "P. e." var. "densa" trees to try to increase resin production for extraction, but this approach was ineffective.