The most common and most likely answer to this crossword clue is the 9 plus 6 letter word SCAVENGER BEETLE
I've seen this crossword clue in The Times
S
C
A
V
E
N
G
E
R
B
E
E
T
L
E
Buddy explains!
The straight part
We know that "Screen vegetable on the turn for one?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case screen vegetable on the turn for one? = scavenger beetle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.