When do I spray my yard to prevent stickers growing? What product?

i would talk to your LOCAL nursery.. and ask them... they will know what you should use for best results and when to apply it.

If the stickers are in the lawn you can use a product called Spectracide broad leaf herbicide. It's a weed killer that only targets broad leaf plants. Spray on a dry sunny day when there's no wind. It will take about three days before the plants to start dying.

http://homeguides.sfgate.com/product-can-use-kill-sandburs-not-grass-96655.html

There are some things that seem impossible to get rid of and stickers is one of them. That is why we use a professional lawn weed control specialist...TruGreen! We spent just as much on buying chemicals and trying to do it ourselves but never really got the job done! We have 8 treatments a year for weed control, fertilize, pre-emergence (which keeps the seeds from germinating in the spring) and lime! The cost is just under $40 per visit and we don't have to worry about protective gear and making sure we have the right products!

Here's an article I found that should help. Wishing you the best!

http://929nin.com/how-to-get-rid-of-those-pesky-stickers-in-your-lawn/

It’s effective anytime the stickers have leaves on them, the more the better because the leaves are what feeds the roots. But on a sunny day, not if it’s rainy. Never let them flower; and if they do, cut and dispose of the flower stalks in a way that they can’t go to seed and spread. When I lived on a farm I put them in a fire pit to dry and then burned them.