Field grass, when out of place in a turf lawn, becomes a pesky grassy weed problem. Control of field grass is threefold. Cultivation practices will reduce the likelihood that field grass will grow in your lawn. If cultivation fails, pre- and post-emergent herbicides will reduce field grass population in the lawn. Determine whether the grass is annual or perennial by observing its living patterns or by sending a sample to your local university extension office.
Mow your lawn so that you only remove one-third of the grass blade at a time. This will encourage a dense grass growth with deep roots. A dense turf will prevent field grass seeds from entering the lawn and growing. Mow grass at a length of 2 1/2 to 3 inches to prevent sunlight from germinating new seeds, says Colorado State University.
Fertilize your lawn using 1 lb. of nitrogen per 1,000 square feet of lawn two to three times a season to increase grass growth. Spring, early fall and November are the ideal times to fertilize.
Apply a pre-emergent herbicide prior to seed germination at the end of April, says the Minnesota Department of Agriculture. Apply according to label instructions, then water into the lawn using 1/4 to 1/2 inch of water.
Spray existing field grass using a post-emergent herbicide according to the packaging instructions. Use a liquid spray and apply on a day that has little to no wind and no chance to rain. This prevents herbicide from killing desired grass.
Reseed patchy areas of the lawn by hand, spreading a small amount of turf grass seed over bare patches to prevent field grass growth. Water daily until the seeds germinate.