The most common and most likely answer to this crossword clue is the 8 plus 6 letter word COLORADO BEETLE
I've seen this crossword clue in Financial Times
C
O
L
O
R
A
D
O
B
E
E
T
L
E
More clues leading to the result COLORADO BEETLE
- State vehicle that ruins crops
- Cripes! Trouble with root vegetable amongst cabbage? Possible culprit
- Trouble over root vegetable left in faulty cooler? It’s a pest
- Bug state car, one with black and yellow stripes
- Pest unfit to be cool leader
- Perhaps King Edward’s affliction or state, maybe, worker let out
Buddy explains!
The straight part
We know that "It’s a pest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s a pest = colorado 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.