Possible Clues:

• Disease - pest
• This disease finishes in the opposite way 13 across starts
• Withering disease (in plants)
• Air pollution, for instance
• Disease or fungus that withers plants, say potatoes
• What a pest that it loses weight if you take the top off
• Plant disease; urban eyesore
• Fungal disease - destructive force
• Crop attacker
• Shrivelling disease