Season, Zone Dictate Weed Control in Seeded Tall Fescue and Bluegrass

Weed control during establishment of tall fescue and Kentucky bluegrass from seed is difficult for many reasons. First, many herbicides normally considered safe on fully established stands of both grasses can be detrimental to newly developing seedlings. Herbicides containing broadleaf herbicides, such as 2,4-D and dicamba, can injure developing seedlings so severely that if applied to seedlings under the wrong conditions, a delayed turfgrass development can occur.

Second, failure to control weeds from the onset can out-compete developing seedlings and devastate stand development. Weed competition is especially destructive in seeded conditions in spring. The high-density tillering and rapid spread of crabgrass (Digitaria spp.) can out compete and eventually kill tall fescue and Kentucky bluegrass seedlings. Weed competition during fall seeded establishment is less competitive. However, weeds like common chickweed, mouse-ear chickweed and speedwells (Veronica spp.) also can slow the developing turfgrass.

Through common agronomic practices and the timely use of herbicides, weeds can be successfully managed during establishment of tall fescue and Kentucky bluegrass from seed.

Cultural practices and competition

The competitive advantage in a developing turfgrass stand can be shifted easily from the developing seedlings to the developing weeds. First, get the seeding rate right.

Tall fescue should be seeded at about 6 pounds to 9 pounds per 1,000 square feet. Kentucky bluegrass should be seeded at 2 to 3 pounds per 1,000 square feet. Being frugal on seed can leave a thin, open turfgrass canopy that is easier for weeds to encroach. Overapplying seed can cause the turf to be thin and immature making the seedlings more susceptible to disease. Diseased seedlings can die quickly leaving empty areas for weed invasion.

Second, improper fertilization timing and rates can shift the competitive advantage from the turf to the weeds. Fertilization at seeding should focus mainly on phosphorus (P), potassium (K) and the micronutrients — in other words, fertilize at seeding according to soil test. Nitrogen fertility is not needed until two to four weeks after emergence because nitrogen can be lost to the environment in bare soil conditions. Nitrogen fertility then can be supplemented on a month-by-month basis depending on your climate zone and the time of year you are seeding. Northern climates can fertilize more through the summer months while those in the mid-South should avoid nitrogen fertility in the summer due to brown patch severity.

Last, mowing practices play a crucial role in shifting the competitive advantage from turf to weeds. Tall fescue should be mowed at approximately 3 inches, while Kentucky bluegrass should be mowed at a height no lower than 1.5 inches.

Decreasing below these heights can cause the turf stand to self thin and can be harmful to a developing turfgrass stand. Similarly, mowing excessively high can cause the lower leaves to senesce (turn brown), decreasing the density of the turf stand. Infrequent mowing can lead to scalping of the turf. Remember sticking to the "1/3 Rule" (remove no more than one-third of the leaf tissue at each mowing) can save the turf a lot of stress.

Chemical weed management

Despite your best efforts of managing weeds using the best cultural practices, you are still going to have to deal with a certain level of weed infestation more often than not. The weed spectrum will vary according to the time of year you choose to establish tall fescue or Kentucky bluegrass from seed.

In the mid-South and for many other northern climates, seeding in late August to early September is best. With a late-summer to early-fall seeding, your primary weeds will be primarily winter annuals with some late-germinating crabgrass. Herbicide options are available for control of these weeds during a fall seeding.

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