Pretty easy one to start the week! 4D is a fun clue, and some nice words in 15D and 25A that were clued very fairly.

Across

1

Odds and ends related to overhauling pesticide bans (4,3,6)
BITS AND PIECES — anagram (overhauling) of PESTICIDE BANS

8

Brief detail regarding French cheese (4)
BRIE — BRIEf without last letter (detail)

9

Autodidactic Left's changed nothing (4-6)
SELF-TAUGHT — anagram (changed) of LEFTS, AUGHT (nothing)

10

Cyber crim arrives by chopper (6)
HACKER — double def.

11

Utter havoc, realise leaders must go! (8)
VOCALISE — haVOC reALISE without first letters

12

Sort of school that's mostly awry after a short time (9)
SECONDARY — AwRY (mostly awry) after SECOND (a short time)

14

Fellow's son could sound like a snake (4)
HISS — HIS (fellow's) S (son)

15

Welsh emblem visible on the back of the keel (4)
LEEK — reversal (on the back of) of KEEL

16

To put English off underwear, try science (9)
CHEMISTRY — CHEMISe (underwear) without e (English), TRY

20

Sing about hood looking angry (8)
SCOWLING — CHEMISe (underwear) without e (English), TRY

21

Shy about a B&B being run-down (6)
SHABBY — SHY around A BB

23

Sid refused to disinfect debts so they're going viral (10)
INFECTIOUS — disINFECT without sid, IOUS (debts)

24

Is prostrate in the face of falsehoods (4)
LIES — double def.

25

By similar standards, lumberman gets cosy deal (13)
COMMENSURABLY — anagram (deal) of LUMBERMAN COSY

Down

1

Bombardment of pub fury (7)
BARRAGE — BAR (pub) RAGE (fury)

2

Fine tune the first faint signal (5)
TWEAK — T (first letter of the) WEAK (faint signal)

3

Confident fool devoured half (7)
ASSURED — ASS (fool) URED (half of devoured)

4

Do as promised. Take the offal out of the merchandise? (7,3,5)
DELIVER THE GOODS — cryptic def.

5

Trendy discretion is not impaired (6)
INTACT — IN (trendy) TACT (discretion)

6

Lecture is about nasty deeds (9)
CRUELTIES — anagram (about) of LECTURE IS

7

Half the school miss out on doctrinal splits (7)
SCHISMS — SCH (half of school), anagram (out) of MISS

13

Finished with hollow tree, it'll be too much (9)
OVERWHELM — OVER (finished) WH (with without middle letters) ELM (tree)

15

Sparing with words after an accident with colic (7)
LACONIC — anagram (accident) of AN COLIC

17

One who maltreats Scrooge takes us in (7)
MISUSER — MISER (Scrooge) with US inside

18

Polish cored berry till tough and stretchy (7)
RUBBERY — RUB (polish) BERY (berry without central letter)

19

Prudence, for one, would call out dodgy victualler (6)
VIRTUE — anagram (dodgy) of VIcTUallER without call

22

Even Mandela is starting to brag off script (2,3)
AD LIB — ADLI (even letters of Mandela is), B (first letter of brag)