What is normal for the plant?

Plant characteristics are variable enough that what is perfectly healthy for one plant may be a sign of a serious problem for another. A good example can be found in deciduous conifers such as bald cypress, dawn redwood, and larch. These three trees bear cones and needles, and neophyte plant lovers may think they are evergreens.
However, they are indeed deciduous, with fall colors ranging from spun gold to reddish-brown, followed by the leaf drop. Many a bald cypress has felt the bite of the saw from new homeowners who notice a completely brown-leaved tree in their new landscape in late fall. Indeed this total browning of foliage would be a sign of almost certain death on a true evergreen conifer, such as pine. Knowing how to identify these deciduous conifers and understanding that their fall color and leaf drop is normal can be all you need for proper diagnosis.
Similarly, knowing that some yews, such as Taxus ‘Helen Corbit’, naturally have needles trimmed in bright yellow should give a horticulturist pause if someone wonders if the yellowing is due to photosynthetic-inhibitor herbicide injury. Knowing that leaves of Naruto Kaede trident maple (Acer buerganum ‘Naruto Kaede’) naturally curl-up along the edges will reduce the chances that the leaf curl will be diagnosed as being caused by moisture stress, herbicide injury, or aphids. Knowing that the needles of dragons-eye pine (Pinus densiflora ‘Oculus Draconis’) naturally have yellow banding will help prevent a recommendation to treat for a needle-caste disease. Knowing that the greenish, strap-like bracts on lindens naturally turn brown after flowering is key to responding to a concern that the browning is associated with some type of fungal disease.