Bermuda grass (Cynodon spp.) is a warm-season turfgrass grown across the milder climate regions of the southern half of the United States. When temperatures drop below 70 Fahrenheit, Bermuda grass goes dormant, turning thatch brown. Traditionally, gardeners over-seed this dormant lawn with cool-season rye grasses so the lawn is green in the cool, moist winter months. Once rye grass seeds are present, they will sprout and look like sporadic weeds in a Bermuda grass lawn, especially in winter.
Bermuda grass is favored by gardeners since once it is established it is a durable, drought-tolerant and low-maintenance lawn. Ironically, if you do not have a Bermuda grass lawn, a rogue Bermuda grass plant in any other type of lawn is seen as a troublesome weed. Plenty of resources are available online to deal with weedy infestations of Bermuda grass into other lawns, but not so much for instructing how to rid a Bermuda grass lawn of annoying fescue plants.
Where winters are cool and mild and summers long and hot, Bermuda grass lawns are a good choice, especially for athletic fields. TruGreen Lawn Care mentions that once temperatures drop below 60 degrees Fahrenheit (F), Bermuda grass goes dormant. When temperatures remain above 80 F, the grass is green, lush and vigorous. Clumps of fescue sprout in bare spots in the Bermuda grass lawn and grow deep green, contrasting the brown lawn vividly. If allowed to flower and set seed, fescue plants continue to sprout.
The key to diminishing fescue weeds in Bermuda grass is a maintenance regime that is inhospitable to the former and advantageous to the latter. Fescue relishes cool, moist soils that are fertilized in fall, winter or early spring. Bermuda grass doesn't require these conditions when dormant from fall to spring. According to North Carolina State University turf specialists, do not fertilize a Bermuda grass lawn from fall to winter--this promotes the growth of weeds, including fescue. In summer when fescue plants may still linger in the actively growing Bermuda grass, mow at a height of 1 to 2 inches and fertilize to promote its rapid, dominant growth. Fescue grasses are stressed and diminished when cut at a height below 2 to 3 inches.
Along with seasonal fertilizing and mowing considerations, appropriate watering of a Bermuda grass lawn helps control fescue plants. In summer, add only 1 to 1-1/4 inch of irrigation to the Bermuda grass weekly as needed to supplement natural rainfall. Do not over-water because it benefits fescue. From mid fall to early spring, do not irrigate the lawn so seeds and plants of fescue grow well. Only irrigate Bermuda grass in winter if you are in a drought or excessive winds are excessively drying the top layers of soil.
Prior to the start of Bermuda grass dormancy in fall, an application of pre-emergent herbicide, according to label directions, prevents the sprouting of fescue from seeds. Additional applications are done during the rest of winter and spring. If fescue is perennial and appears from its dormant roots in fall, a post-emergent herbicide, such as glyphosate, is used. Read product labels carefully to learn if the herbicide will also harm the Bermuda grass. Spot-treat only the areas with fescue. Persistence is important to eradicating fescue. Employ both maintenance strategies as well as hand-pulling, digging, and spot application of contact herbicides to eliminate fescue. As long as fescue doesn't flower and set seed, the numbers of weeds will lessen over time.