There are several varieties of ryegrass that grow throughout the United States. Annual ryegrass is perhaps one of the most troublesome of the ryegrass varieties. This cool-season grass can reach up to 3 feet in height, and once established it spreads quickly. But even heavily infested areas can be managed. Studies at Virginia Tech (2000) have shown that the best way to kill annual ryegrass is with the broad-spectrum herbicide Roundup.
Mix the herbicide. According to Virginia Tech, annual ryegrass requires 3 pints of Roundup per acre for effective control. The amount of water required depends on the type of sprayer that you will be using. Boom sprayers require 16 gallons of water per acre. Handgun and knapsack sprayers need roughly 50 gallons of water per acre. Fill your sprayer's tank with half of the required water. Add the required amount of Roundup and mix well. Then follow with the second half of the water.
Spray the ryegrass. Wait for a day with no wind and no rain forecast for the next 48 hours. Then coat the ryegrass evenly with Roundup, just before the point of runoff.
Respray any remaining ryegrass with the same amount of Roundup in six weeks.