Author Topic: Introduction to Seed Selection  (Read 1965 times)

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Introduction to Seed Selection
« on: April 15, 2011, 01:49:18 PM »

An important factor in turf quality is the selection of grasses and the overseeding program. Not all cool-season grass varieties are created equal, and the requirements of lawns and athletic turf can be very different. Seed selection depends on such factors as the effort, time and money available; the purpose the turf will be used for; and the amount of maintenance that can be dedicated to the grass. Natural fertility can be incorporated into the seed mix by including leguminous (nitrogen-fixing) broadleaf plants such as clovers and trefoil. These plants increase diversity and durability, and naturally supply nitrogen to the lawn.

Athletic Turf
When it comes to selecting seed, there are advantages and disadvantages to each seed type. As a general rule for athletic turf, use a blend of perennial ryes and bluegrasses in your overseeding mix. There are two basic blends that you can use, depending on the condition of each field, the season of the year, and budget concerns. You must take into account the growth characteristics and performance of the grass, as well as seasonal temperatures and available moisture. Let’s look briefly at the two grasses and what they have to offer.

Bluegrass spreads by means of rhizomes, which is an advantage to us because it competes with weeds as it thickens. It has excellent recuperative potential, which is the ability to rebound from damage or normal wear and tear. It has average wear tolerance, but that is offset by its rhizomatous nature. Bluegrass mixes well with other grasses and exhibits good drought, heat and cold tolerance. It can be successfully mown at three inches, the optimum pH is 6.5 to 7.0, it requires two to six pounds of nitrogen per 1,000 square feet, and it has a germination time of roughly 21 days.

Perennial ryegrass increases in size by means of tillers and is more of a clump-forming grass. It has excellent wear tolerance and fair to good recuperative potential. It also mixes well with other grasses and has good drought and heat tolerance, but it can sometimes suffer winter damage due to its poor tolerance of heavy icing conditions. Perennial ryegrass can be mown at three inches, the optimum pH is 6.5 to 7.0, and its nutritional needs are similar to those of bluegrass (two to five pounds of nitrogen per 1,000 square feet). One distinct advantage of perennial ryegrass is that most of the newer cultivars have naturally occurring fungi growing within them (endophytes). The grass plant and fungi live in a symbiotic relationship. The turfgrass supplies carbohydrates to the fungi, which in return give the grass alkaloids and other chemicals that have a beneficial and protective effect on the grass. These alkaloids have been shown to act as an insecticide, controlling several surface-grazing insects. (The fungi live in the veins of the sheath and are not found in the root.)

Recent studies have shown that the grass may receive other benefits from the endophytes, such as some disease resistance, drought resistance and a growth retarding effect on surrounding plants. This growth retarding effect may be a valuable tool for the turf manager to consider in the future. Note that the alkaloids in endophytic grasses are toxic to grazing animals such as horses and cows.

Lawns
For lawns and park areas, two other grass types, tall fescue and fine fescue, extend the range of options.

Turf-type tall fescue[/b[, Festuca arundinacea, is a bunch-type grass that has wider leaves and deeper roots than the other cool-season grasses, which makes it exceptionally heat and drought tolerant. It is also more shade tolerant than bluegrass or ryegrass, though not as shade tolerant as the fine fescues. It requires moderate fertilization and is well suited to being mowed high, above 2-1/2 inches. Tall fescue stands up to wear, but because it is a bunch-type grass that doesn’t spread much, it requires regular seeding to stay competitive in a heavily trafficked lawn. Its blades grow rapidly and may require more frequent mowing. It is not prone to excessive thatch.

Tall fescue is most successful when established from seed in early August (several weeks prior to establishing other cool-season grasses), because it is less winter-hardy in the seedling stage than are other grasses. While generally not recommended, spring establishment can be successful when soils warm and the seeding rate is increased slightly to compete with weed growth.

The fine fescues comprise a group of lawn grasses that includes:

   • Creeping red fescue (Festuca rubra)
   • Chewings fescue (Festuca rubra var. commutata)
   • Hard fescue (Festuca longifolia)
   • Sheep fescue (Festuca ovina)

The fine fescues are the most shade tolerant of the cool-season lawn grasses. Their leaves are medium to dark green and narrow, almost needlelike. They are primarily bunch-type grasses, except for creeping red fescue, which can produce rhizomes. Fine-leaf fescues grow very slowly, require little or no fertilizer and should be mowed at two inches or higher.

These grasses are well adapted to infertile, acidic soils. They are not good for high-traffic areas because they do not tolerate abrasion, and like other bunch grasses, they are slow to fill in damaged spots. The fine fescues are the most aggressive thatch producers of the cool-season grasses, and thatch can become a significant problem if they are not managed properly. This is primarily because fine fescues’ leaf stems are high in lignin (which is slow to break down) and not because these grasses are aggressive growers. In fact, the slow-growing nature of the fine fescues often slows establishment, especially for sheep and hard fescue. Traditionally, the fine fescues are used in mixtures with Kentucky bluegrass and/or perennial ryegrass. However, growing interest in low-maintenance lawns has made blends of fine fescue cultivars increasingly popular.

The low-maintenance approach assumes that quality expectations and foot traffic will be reduced, as the fine fescues will assume a “brown haze” appearance in full sun and dry conditions. Still, the benefits of reduced mowing and fertilizer applications, while still maintaining a dense lawn, seem a fair trade.

The sheep and hard fescues are better adapted to the low-maintenance approach, while chewings and red fescue perform better in traditional lawn mixtures that receive regular fertilizer applications. The fine fescues have few major pest problems. However, under wet conditions they can be attacked by red thread and leaf spot. Like ryegrasses, certain fine fescue cultivars have endophytes to repel surface-feeding insects, but they are susceptible to white grub infestations.
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