Cleon
Legend
What about blight? It's along the lines of horrid wilting, but we already have some fairly high-level SLAs. Blight could come in at a lower age category and more times per day. What about the last thing being heat or fire related? Heat metal might be thematically appropriate.
Oh I forgot about blight. Not sure I like it, since it seems more a disease/affliction than a desert dehydration effect and I'd rather have something that doesn't only affect plants.
Adding heat metal is a good idea though.
As for the level of the SLAs, let's do a quick comparison.
Red Dragon: locate object (2nd/3rd), suggestion (2nd/3rd), find the path (6th), discern location (8th).
Gold Dragon: bless (1st), geas/quest (6th), sunburst (8th), foresight (9th) plus non-standard luck bonus (2nd), detect gems (2nd).
Silver Dragon: feather fall (1st), fog cloud (2nd), control winds (5th), control weather (7th), reverse gravity (7th/8th)
Dune Dragon #1: X (???), heat metal (2nd), hallucinatory terrain (4th), move earth (6th), whirlwind (8th)
If we made the additional spell something low level, like say whispering wind or pass without trace. That'd give its SLAs a range of levels roughly similar to the Silver Dragon.
Giving it horrid wilting for the highest level SLA works better for me than whirlwind though, e.g.:
Dune Dragon #2: X* (1st or 2nd), heat metal (2nd), hallucinatory terrain (4th), move earth (6th), horrid wilting (8th)
*whispering wind or pass without trace.