What is the best time of year (what month?) in Raleigh NC to start applying spider control products?
The time to start doing some preventive treatments is once you start noticing any kind of flying insect activity. White flies, gnats, midges, moths and other flying insects are all spider food and if the food is active, so too will be the predator's.
To get more specific, we're located just outside Atlanta GA and typically I'll have to start treating in April. But given the mild winter we've had, I've seen several spiders already so I'll be doing some applications this week.
I also keep a boat at a local lake and it too is already showing newly formed spider webs which is a sure sign there is activity. To get ahead of all these pests, you need to treat early on in the season. And based on where Raleigh NC is in relation to Atlanta, I wouldn't be surprised if things are nearly as active in your region as they are here so I'd say to start now.
Outside Spider Treatments: http://www.brownrecluse.com/brown-recluse-spider-control/spiders-outside