Is it too late to put grease on my fruit trees.

[Mark /\]

Hello all. I have 2 apple trees, a pear tree and a plum tree all around 7 - 8 years old. Last year all my pears were rotten and looked like they had been eaten from the inside. I have just found out you can apply some tree grease around the tree  to stop the insect climbing up the trunks. You are supposed to first apply it October-ish

All I want to know is it too late to apply some now or was the crucial time to apply it at the back end of last year.

Thanks for  any help.

[Mark /\]