Only if the pest is not controlled by these actions, use insecticides. Do not use fungicides. In most cases, where fungus infection is supposed, the proper action is to repot, since very likely the reason is inproper soil condition, or cultural mistreatment. Camellias have a long dormancy period of about three quarters of the year, they do not immediately indicate mistreatment like dry roots or other damage, and six to nine months later twigs dye back or leaves wilt. With this delay, the original cause is forgotten and not related to the disorder, and fungus is suspected.
Yellow leaves result most oftenly from a soil with too large water retention and over watering.
Since watering habit can be controlled only after years of experience, change the soil to insure better draining. The best advice in any unclear camellia disorder is to repot. Commercial growers cannot give their plants this intensive care, and they depend on insecticides and fungicides, but they have the proper equipment and knowledge to use them adequately. We try to establish a diagnostic guide for camellia deseases and disorders. Be patient, this takes time.