Blimey, that was tough! It didn’t help that I’m nursing a hangover from last night (beer tasting event) but I think I’d have struggled anyway. Took about 45 minutes, but I had to use reference books to finish it.

Across
1 TRIP,OD=do rev.
5 AP(PRO)ACH(e) - I totally misread this at first, looking for AC(e) inside a type of native American, meaning detail.
9 PARSI,FAL - an opera by Wagner. I had to look up Parsi, as I thought it was just a language. The Fal is a river in Cornwall.
10 RESCUE - R.E.’s cue.
11 CHAMPIONSHIP - as the English football 2nd division is now called.
13 ANNA - an obsolete Indian coin.
14 N(I,COT)INE - I had to check this in the dictionary - a cot is a small cottage.
17 STA(R,FI)SH
18 PARE - sounds like “pair”, and an anagram of 2d.
20 NUCLEAR WASTE - hidden, but at first I tried to make it an anagram of “menu clear was”.
23 ETH(the*),I,OP - the capital of Ethiopia is Addis Ababa, but maybe it gets shortened to Addis. Would be odd though, as the name literally means “new flower”.
24 INFERNAL - i.e. FERN inside nail*
25 F(RAGMEN)T - which might get him into trouble with colleagues at the Guardian!

Down
2 REAP - confirmed as it has to be an anagram of 18ac, but I don’t get the wordplay. As it’s Araucaria, my best guess would be A in REP, with REP meaning sure, but the dictionary doesn’t back that up. [ As has been pointed out, it's hidden in "InsuRE A Possible" - d'oh! ]
4 DEFRA,Y - DEFRA is the Department for Environment, Food and Rural Affairs.
5 A SLAP ON THE WRIST (whips as tolerant)* - not sure about “hardly” as an anagram indicator, but it makes for a good &lit.
6 PERFORCE - PERFORATE, with AT removed, around C (number).
8 C(AU,TIONA)RY - TIONA being (into a)*
12 INS,TRUC=curt rev,TOR
19 US,EFUL=fuel* - with source as the anagram indicator? Pfui.
22 WA(I)N

One of Dac’s easier puzzles I think, but none the worse for that. Consistently excellent clueing as usual.