DMR's seasonal folder gives the plains calendar: white button November to February, oyster September to May, milky February to April and July to September, paddy straw July to September. In the mid hills oyster runs all year and button runs September to March.
The documents do not always agree. That folder starts button in November, while the 2011 manual's round the year chapter says October to February. Treat the one month as the margin of the estimate and settle it with your own weather record.

