Thank you to Filbert. Definitions are underlined in the clues.
Across
1. Pharma giant getting into development of magical pesticide, perhaps (12)
AGROCHEMICAL : ROCHE(a large pharmaceutical company/pharma giant) contained in(getting into) anagram of(development of) MAGICAL.
Defn: An example of which/perhaps is a pesticide for agricultural use.
9. Screen that opens in silence, say (7)
SHUTTER : SH!(a request or demand for silence from whom it is addressed to) + UTTER(to say aloud).
10. Coach breaks work schedule for coffee (7)
ROBUSTA : BUS(a road vehicle transporting passengers, a coach being one used for longer journeys) contained in(breaks) ROTA(a work schedule, showing when each person in a group has to do a particular job).
Defn: … from the beans of a widely known kind of coffee plant.
11. Underline M representing magnitude in report (9)
EMPHASISE : Homophone of(… in report) [ “em”(for letter M) “for”(representing/in place of) “size”(magnitude/extent) ].
12. What leads Veronica into temptation? Affection, ironically (5)
LURVE : 1st letter of(What leads) “Veronica” contained in(into) LURE(bait/temptation).
Defn: An ironic term for fatuous love/affection.
13. Doctor sips at aperitif (6)
PASTIS : Anagram of(Doctor) SIPS AT.
Defn: Aniseed-flavoured ….
15. Intensify stock cube using chicken (8)
HEIGHTEN : EIGHT(the cube of the number 2) contained in(stock … using) HEN(chicken, a domestic egg-laying fowl).
18. Pale green used by teenage Auden illegibly (3,2,3)
EAU DE NIL : Hidden in(used by) “teenage Auden illegibly”.
Defn: … colour.
19. On the radio, maybe hear America’s checking who’s in the country (6)
CENSUS : Homophone of(On the radio) “sense”(to perceive/be aware of by using, say/maybe one’s faculty of hearing) + US(abbrev. for America).
Defn: An official survey of the population/….
21. Leave egg where food is served (5)
HATCH : Double defn. 1st: To emerge from its egg, said of, say, a baby bird; and 2nd: An opening in a kitchen wall through which food is served.
23. French composer recalled job on island in Ireland (4,5)
ERIK SATIE : Reversal of(recalled) {[ TASK(a piece of work/job) plus(on) I(abbrev. for “island”) ] contained in(in) EIRE(Irish name for Ireland) }.
25. Husband and wife changing in tent, perhaps are too hot (7)
SWELTER : “h”(abbrev. for “husband”) replaced by(… and … changing) W(abbrev. for “wife”) in “shelter”(an example of which/perhaps is a tent/a portable shelter).
Answer: To be too/uncomfortably hot.
26. Let back in to lecture at American uni (7)
READMIT : READ(to say out loud and dramatically the words from a piece of writing/to lecture) plus(at) MIT(abbrev. for the Massachusetts Institute of Technology, an American university).
27. Mincing Spanish males marketing art (12)
SALESMANSHIP : Anagram of(Mincing) SPANISH MALES.
Defn: …/the skill of selling and promoting commercial products.
Down
2. Bellyache from drinking rum punch (5)
GRUMP : Hidden in(from) “drinking rum punch”.
3. Exclude East German breed taking lead in Crufts? (9)
OSTRACISE : OST(German for “east”) + RAISE(to breed/to rear) containing(taking) 1st letter of(lead in) “Crufts”.
4. Someone who has quit company misusing HR time (6)
HERMIT : Anagram of(misusing) HR TIME.
Defn: …/forgone contact with other people.
5. Gunman maybe spinning barrel before start of roulette (8)
MURDERER : Reversal of(spinning) DRUM(a cylindrical container/barrel) + ERE(before a specified time) + 1st letter of(start of) “roulette”.
Defn: An example of whom/maybe is a gunman.
The clue is a nice allusion to Russian roulette.
6. Intriguing group from California set up research establishment (5)
CABAL : CA(abbev. for California, the US state) + reversal of(set up, in a down clue) LAB(or laboratory, a research establishment).
Defn: …/a small group of people plotting intrigue.
7. Girl hosts banal ceremony before popping off (4,5)
LAST RITES : LASS(a young woman/girl) containing(hosts) TRITE(banal/commonplace).
Defn: …, that is, before dying.
8. To run successful budget, introduce limits? (4,4,4)
MAKE ENDS MEET : [MAKE(facilitate/arrange) for two or more parties to MEET](to introduce to one another), in this case, the parties are the ENDS(limits/the most extreme parts).
Defn: …./not to spend more than budgeted.
9. Taps in expensive rental run with water periodically (12)
STEEPLECHASE : CH(abbrevs. for, respectively, “cold” and “hot”, describing the water taps for, say, one’s bathtub) contained in(in) [ STEEP(expensive/having to pay an excessive amount) LEASE(rental/a contract for the use of something in exchange for payment).
Answer: A racetrack/run with water jumps at intervals/periodically.

14. Wicket-keepers perhaps, who can be difficult to get out? (9)
SQUATTERS : Double defn. 1st: What you might/perhaps call wicket-keepers who adopt a squatting position, in the game of cricket); and 2nd: People who unlawfully occupy empty buildings or unused land and who can be difficult to evict/get out.
16. These perhaps disturbed eelgrass catching prey finally (4,5)
GREY SEALS : Anagram of(disturbed) EELGRASS containing(catching) last letter of(… finally) “prey”.
Defn: These creatures could have/perhaps disturbed eelgrass, a marine plant with long eel-like leaves, before finally catching their prey.

17. Tailors around close to Royal Academy’s area (4,4)
FINE ARTS : FITS(adjusts or modifies to make suitable for a person or purpose/tailors) containing(around) NEAR(close to/within reach).
Defn: The area/field of interest of the Royal Academy, or, in full, the Royal Academy of Arts.
20. Car repairs botched with loss of power (6)
SIERRA : Anagram of(… botched) “repairs” minus(with loss of) “p”(symbol for “power” in physics).
Defn: …manufactured by the Ford Motor Company.

22. Permit I see to put up tiny building on Park Lane? (5)
HOTEL : Reversal of(… to put up, in a down clue) [ LET(to permit/allow) + OH(expression to convey “I see”/”I comprehend what you’re saying”).
Defn: I take “tiny building” as an ironic term, as indicated by “?” for something in Park Lane, a site for luxury hotels.
24. Police force raised detective’s rates (5)
TEMPI : Reversal of(… raised, in a down clue) MET(short for the Metropolitan Police in London) + PI(abbrev. for “private investigator”/private detective).
Answer: Plural of “tempo”/the speed of motion.
The definition in 22d will be a reference to Monopoly, where a hotel is one of the (tiny) buildings you could have on Park Lane.
Thanks to Filbert and scchua
Beaten by two: even with the crossers, MAKE ENDS MEET which I was sure was ‘something one’s something’. I was nowhere near spotting the cryptic def. And FINE ARTS where, of all things, I was thrown by the simple word ‘to’ which I did not identify as a linker. tbh, it is not my favourite linker – I understand the argument for using it but it sits uncomfortably. And, of course, in this case it had me trying to incorporate an L and possibly some A’s into my solution. I was also thrown by the ‘tiny building’ in HOTEL which I took as a Monopoly reference in the end but I feel the clue would have worked as well without the confusion that it introduced.
GREY SEALS, STEEPLECHASE, HERMIT, SALESMANSHIP and HEIGHTEN my faves. Thanks both
Like PostMark, MAKE ENDS MEET defeated me (and FINE ARTS was my LOI – mostly thanks to my far-too-frequent problem of not paying attention to the enumeration and trying to make an 8-letter word fit). I fairly confidently put in SAVE ONE’S BEST for 8d, which fits all the crossers and I think works on both a cryptic and literal level – but probably isn’t quite a phrase in its own right.
Thanks both!
Loved ‘M for Magnitude’.
Also liked CENSUS, MAKE ENDS MEET, FINE ARTS and GREY SEALS.
Thanks Filbert and scchua.
Funny how different solvers have different difficulties. Having got ROBUSTA as my foi, I immediately got MAKES ENDS MEET as my second answer. A few hold-ups along the way but got there in the end, just as I like it. The only clue I didn’t care for was 23a. I didn’t feel the surface properly clued the reversal of EIRE. I felt the “on island” effectively ended the “recalled” bit. Maybe that’s just me?
Just had second thoughts. Reading “TASK on I” as ITASK and then reversing that makes it work.
I needed help with FINE ARTS too for the same reason as PostMark. I didn’t know Satie was an Erik rather than an Eric till I worked out the wordplay. STEEPLECHASE was my favourite.
A smashing blog worthy of this smashing puzzle.
Quite a few clues had me scratching my head, until the pennies dropped.
In 25(ac), SWELTER, the letter-substitution play didn’t quite gel, I thought “wife kicking husband out of tent” or somesuch more “pleasing”.
26(ac), READMIT, is not very disguised ( “let back in”), and lecture = READ is a bit meh.
STEEPLECHASE, 9(d): interestingly ( or not!) in jumps racing these days, the water jump is taken only once, even in the Grand National, so periodically wouldn’t work…well done scchua for selecting the right image!
So much to admire in the way the clues are crafted, e.g. “Russian roulette” in 5(d), it’s a simply superb crossword.
Big thumbs up, Fil & scchua