Possible Clues:

• Tree blight spread by bark beetles
• Wife seems ideal to disperse fungal problem
• Fungal, usually fatal, ailment of certain trees
• From Holland to the Spanish mainland, foremost detectives with no difficulty produced a threat to those in 24 across
• What causes the middle to rot?
• Training aided the muscles, producing withering complaint
• With time secluded ash rots, producing a threat to the forest
• Mate is scheduled to be treated for infection of limbs and trunk
• It's bad news for the countryside as Luddite scheme goes to pot
• Puzzling over death, missed clue leading to killer