We have investigated the brown dwarf ( BD ) and stellar disc fractions in the Upper Scorpius OB Association ( USco ) and compared them with several other young regions .
We have compiled the most complete sample of of all spectroscopically confirmed BDs in USco , and have made use of the Wide Field Survey Explorer ( WISE ) catalog to identify the disc candidates .
We report on the discovery of 12 new BD discs in USco , with SpT between M6 and M8.5 .
The WISE colors for the new discs are similar to the primordial ( transition ) discs earlier detected in USco .
Combining with previous surveys , we find the lowest inner disc fractions ( \sim 20-25 % ) for a wide range in stellar masses ( \sim 0.01-4.0 M _ { \sun } ) in the USco association .
The low disc fractions for high-mass stars in USco ( and the other clusters ) are consistent with an evolutionary decline in inner disc frequency with age .
However , BD disc fractions are higher than those for the stars in 1-3 Myr clusters , but very low in the \sim 5 Myr old USco .
Also , primordial BD discs are still visible in the \sim 10 Myr old TW Hydrae association , whereas the higher mass stars have all transitioned to the debris stage by this age .
The disc frequencies for BDs do not show any dependence on the stellar density or the BD/star number ratio in a cluster .
We also find no convincing evidence that any of the well-known disc dispersal mechanisms for stars are active in BD discs .
We suggest that the large differences in the observed BD disc fractions between regions may well be due to different BD formation mechanisms and therefore different initial disc fractions/properties .

We also present a WISE SED classification scheme , based on the K _ { s } and WISE bands of 3.4-12 \micron .
We have determined certain thresholds in the WISE spectral slope versus spectral type diagrams to distinguish between the red population of Class I/II systems and the Class III sequence .
We have found the WISE [ 3.4 ] - [ 12 ] color to provide the best distinction between the photospheric and the disc population .
Our work includes a comparison of the sensitivities of WISE and Spitzer disc surveys .
We estimate that WISE can be incomplete for discs at spectral type later than M8 in distant clusters such as SOri .
WISE should be able to recover the M8-M9 discs in the nearby young clusters .