Oriental Lily Turning Yellow
The leaves on my oriental lilies ('Stargazer') are turning yellow from the top down. Some have developed brown spots. Leaves further down appear splotchy. It's been very wet this Spring and Summer. The lilies face south and west, though it's a rather shady location. I've had them for a few years; they survive and have some blossoms though not thriving as they would in a sunnier location. I knew this would be this case when I planted the bulbs - wanted a little color in this shady garden.
There may be several reasons why your oriental lily leaves are browning. It certainly has been a wet season so far and the plants could be suffering from root, stem, and crown rot. Further information on this condition can be found here: https://extension.umd.edu/hgic/root-crown-and-bulb-rots-flowers
There are two viruses that are common to lillies: 1. Lily Symptomless virus and 2. Cucumber Mosiac Virus. These viruses are transmitted by aphids. Lily leaves develop white to yellow mottled, striped, or flecked pattern (the pictures you provided show yellowing in a stripe pattern). There is no effective treatment for viruses, therefore infected lilies must be removed and destroyed. Aphid management is possible with mechanical removal using a garden hose or insecticidal soap - follow instructions on package.
General guidelines for growing lilies: slightly acidic, well drained, fertile soil in full sun to partial shade; regular watering of 1" weekly with soaker hose to avoid wetting soil; use layer of organic mulch to retain consistant moisture.