You might try using the garden hose with high pressure, to blow the dirt back inside. Then it might spray normally. You could see if the dirt can make it through the spray nozzle after that.
Or try removing the spray button from a spray can of Windex, and push the top right into the spray nozzle. The high pressure from the can should blow the dirt and any fluid back through the line cleaning it out.
If you can remove the sprayer line somewhere under the hood, you can probably just blow it out.