The most common and most likely answer to this crossword clue is the 5 plus 3 plus 7 letter word DUTCH ELM DISEASE
I've seen this crossword clue in The Guardian
D
U
T
C
H
E
L
M
D
I
S
E
A
S
E
More clues leading to the result DUTCH ELM DISEASE
- Killer of wife smiled wickedly in repose
- What causes the middle to rot?
- Training aided the muscles, producing withering complaint
- Suffering such mal, trees died right away
- I scheduled teams for treatment for tree blight
- Samuel ceded this propagated deadly fungal growth
- Killer in wood, wife smiled devilishly in repose
- Fungal problem — mate is scheduled for treatment
- Wife seems ideal to disperse fungal problem
Buddy explains!
The straight part
We know that "withering complaint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case withering complaint = dutch elm disease.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.