Whether a one-time spray treatment to control mosquitoes is enough depends on multiple factors. Often, you’ll notice a big difference after one application. However, mosquitoes are likely to return if you don't reduce attractive standing water habitats. This usually takes four to eight weeks if it’s still prime mosquito season.

Yes, Johnsongrass is a hard weed to kill. It has the ability to grow fast and spread even quicker, so it requires a detailed plan and thorough application to eliminate it. The best plan of action is to kill Johnsongrass while the weed is establishing itself by hiring a lawn care professional or following the steps above. 

The most effective way to eliminate quack grass without killing the grass nearby is to overseed the area, keep the seed wet until it grows, mow often, and regularly fertilize the area to promote healthy grass that can choke out the invasive weed.

Jet washing can wash away weeds without bending or kneeling to pull them. However, the results will likely be fleeting because the weeds will return unless you use a stronger method that takes them out at the root. Use a jet washer for short-term weed removal, but use a stronger method if you want to get rid of weeds for good.