Stan, when I started making bows(many years ago) what I read always said to winter cut your bow wood when the sap was down. Since then I realized it doesn't matter all that much because you will be drying the wood anyway. I prefer to cut whitewood during the growing season so I can just peel the bark off to expose the bows back. With woods like osage, mulberry and black locust it really doesn't matter when because you have to get the bark and sapwood off anyway. I guess for these woods there is less of a chance of them checking with lower sap content...but I cut bow wood when it is available, winter, spring summer or fall!