How to send vendor notifications manually on demand
First you will need to create a custom order status, that will not be a part of standard Magento sales order workflow, and enable it in order state "processing".
Edit app/etc/local.xml and add right before the last
If you have Magento cache enabled, refresh it.
Next, configure uDropship to use this new custom order status to send the notifications to vendors.
Go to System > Configuration > Drop Shipping > Vendor Options. Find Make Available to Dropship on Order Status(es) multiselect, and choose only Ready To Ship status.
Now, when a new order comes in, to notify and make it available for vendors, you will need to change the order status manually to Ready To Ship.