Can anyone tell me what pest is cutting through the stems of the all the unripe strawberries and leaving the fruit untouched on the ground by the plant? It is only unripe fruit and just before they start to turn red. They are netted and inside a polytunnel. I have grown strawberries for a few years but never had this problem before. Unless I can deter the culprits, from 40 plants, I will not have any strawberries to eat at all this year! I couldn't find anything useful in my books or on the web. HELP! Thanks.