• improper cultural practices;
• drought, heat, or cold stresses;
• weeds, insects, or diseases;
• excessive thatch;
• unfavorable growth environment (shade, poor soil conditions); or
• general neglect, abuse, or overuse.

One or more of these conditions may exist. If the cause for poor turf is not obvious, consult a turf expert for assistance.

Turf Improvement Programs

Once the cause of turf decline is identified, select a turf improvement program that will best upgrade the turf by taking into consideration the existing conditions and the desired turf quality. Select a turf improvement from these three:

• Initiate a program of sound cultural practices.
• Renovate turf by planting into existing live or dead vegetation
• Totally reestablish the turf area.
  

In each program, the turfgrasses, soil conditions (fertility, pH, and drainage/aeration), thatch levels, environmental conditions (light quantity, quality, and duration), and existing perennial grassy weeds are evaluated.

I. Initiate a program of sound cultural practices

Many lawns and turfgrass areas can be brought to acceptable quality levels by simply altering turf management practices. Turfgrasses that can be improved in this fashion have many acceptable characteristics, but are in an undesirable condition due to improper mowing, irrigation, fertilization, cultivation, and/or pest control practices. For this program to work effectively, the existing turf area must be comprised of an acceptable turfgrass species and/or cultivars, have adequate density (or be capable of becoming more dense), have acceptable soil conditions, have a moderate thatch level (one-half inch or less), have adequate light, and have perennial grassy weeds in small quantities.
To implement this program, evaluate current management practices, and make changes in them to produce healthy, vigorous turf. Integrate proper mowing, irrigation, fertilization, cultivation, and pest control practices with existing environmental conditions and turf species to bring turf into desired condition. Consult a turf expert for assistance in developing a program of proper turf culture.

II. Renovate turf by planting new grass seed (overseeding) into existing live or dead vegetation

Often, poor turf requires more than improved cultural practices to reach an acceptable quality. In such a case, planting new seed into existing live or dead turf can be beneficial. This program can upgrade turf by bettering turf appearance, density, disease resistance, wear tolerance, and shade and drought tolerances.
To overseed into live existing turf, proper soil drainage/aeration, pH, and fertility should exist, thatch levels should be less than three-quarters inch thick, and perennial grassy weeds (e.g., nimblewill or quackgrass) should only be present in small numbers. When the area in need of improvement has large populations of perennial grassy weeds, use a nonselective herbicide (e.g., glyphosate) to kill the existing turfgrasses and other vegetation in the area, and then plant through the dead plants. When soil conditions are unacceptable, or if excessive thatch is present, use total reestablishment techniques.

General recommendations for planting into live or dead turf

Timing: As in establishing turf from seed, there are two periods when renovating by seed is most successful. In Illinois, the best time of the year to overseed is in late summer and early autumn. See Table 1 for specific dates throughout Illinois. Seeding at this time allows cool-season grasses to develop adequate root systems before the onset of heat and drought the following summer. There is also less competition from annual weeds. Spring seeding is an alternative. During the spring, however, annual weeds can be troublesome. Also, supplemental irrigation may be necessary to keep spring-seeded turfgrasses alive during hot and dry summer weather.

Selecting grass seed: Use high-quality seed in adequate quantities to successfully complete the operation. Table 2 gives seeding rates. In general, Kentucky bluegrass, because of low seedling vigor and slow germination, does not perform well when overseeded into dense, actively growing Kentucky bluegrass or Kentucky bluegrass/perennial ryegrass turf. Alternatively, renovating with Kentucky bluegrass can be very successful when it is planted into live turf that lacks density due to insects, diseases, or drought or into dead turf.
Perennial ryegrass works very well when planted into live or dead turf and is normally planted into Kentucky bluegrass or Kentucky bluegrass/perennial ryegrass mixtures. Perennial ryegrass seed is large, germinates vigorously, and its seedlings can compete adequately when seeded into other turfgrasses. Kentucky bluegrass and perennial ryegrass mixtures can be used to seed into dead turf or turf that is open.
Tall fescue seed is also large and germinates well. It is useful for planting into established tall fescue turf to increase density, or it can be planted easily into dead areas of tall fescue turf. In Illinois, it is not recommended that tall fescue be planted with Kentucky bluegrasses, perennial ryegrasses, or fine-leaf fescues.

Soil/seed contact: It is critical for successful overseeding, whether planting into live or dead turf, that seed be placed into contact with the soil. Seed scattered on top of live or dead turf rarely produces a decent stand. Several methods of placing seed in contact with soil exist. Soil in damaged or small, dead areas can be roughened with a hand rake to open soil to accept seed. After raking and broadcasting seed, use the rake's back side or a stiff-bristled broom to work seed into soil.
To open soil for seeding in large areas, use gas-powered vertical mowers, slicers, core aerifiers, spikers, or slit-seeders. These types of equipment are often available from rental outlets. Vertical mowers have vertically arranged, rotating blades that can be lowered through the turf to scratch the soil. Scratch soil 1/4 to 1/2 inch deep, and work soil in two directions to produce a crisscross pattern. In large areas, seed is broadcast and worked into the soil by hand, or by using a drag made of a piece of chain-link fence or cocoa mats. Slicers are similar to vertical mowers, but make intermittent slits into the existing vegetation and soil.
Core aerifiers open soil by inserting hollow tines into soil and removing plugs of soil. When using a core aerifier for overseeding, it is important that at least 20 plugs per square foot be extracted. Depending on the type of core aerifier employed, multiple passes may be necessary to achieve this number. After broadcast seeding, allow the plugs to dry and use a drag to work seed into soil and crumble the plugs. Spikers are similar to core aerifiers, but use solid tines to open soil and do not remove soil plugs.
Slit-seeders or mechanical overseeders are considered to be the most convenient method of placing seed in contact with soil. The machine combines a vertical mower with a seed spreader. A slit-seeder opens the soil with a vertical mower, and seed is then metered at a predetermined rate from a holding hopper through feeder tubes and dropped into the slits made by the vertical mower. Machines often have a roller that firms the soil after seeding. Adjust the slit-seeder to one-half the desired seeding rate, and plant the area twice using a crisscross pattern to obtain uniform seed distribution.

Available moisture: To renovate successfully, adequate water must be available from seeding through completion of germination. Try not to allow newly overseeded areas to dry once watering has commenced. Initially, maintain a constantly moist seedbed with frequent waterings of short duration. As newly germinated seedlings begin growth, decrease the frequency, and increase the of watering duration to encourage rooting.
Steps in repairing small areas of dead or damaged turfgrasses

1. Roughen the area's soil using a hand rake.
2. Broadcast enough seed into the area to provide approximately 10 to 20 seeds per square inch.
3. Use a rake to work seed into the soil.
4. Begin irrigating. Continue until germination is complete.
5. As new seedlings grow and develop, begin mowing at normal timing, removing no more than 1/3 of the grass blades at any one mowing.

Steps in renovating by overseeding into large areas of live or dead turf

1a.When overseeding into live turf, mow existing vegetation to one inch or less.

1b.When overseeding into dead turf, use a nonselective herbicide (e.g., glyphosate) to kill existing vegetation. Always read, follow, and understand all label instructions for the safest and most efficient pesticide use. Wait at least seven days, and then mow existing dead vegetation to one inch or less.

2. Open soil to accept seed by hand raking, vertically mowing, core aerifying, slicing, spiking, or slit seeding. Unless slit seeding, broadcast adequate seed into seedbed (Table 2).

3. Mat or rake to obtain good soil-seed contact.

4. Begin irrigating. Continue until germination is complete.

5. Two weeks after germination has begun, fertilize with 1/2 pound of N per 1,000 square feet.

6. As new seedlings grow and develop, begin mowing at normal timing, removing no more than 1/3 of the grass blades at any one mowing.

III. Total turf reestablishment

In some cases, existing turfgrasses are in such poor condition or the environment is so unsuitable for supporting turfgrass growth that it is necessary to go through a process of completely reestablishing the turf area. This drastic method of turf improvement is necessary when soil conditions are unsuitable to sustain turf growth and health, when thatch levels are excessive and uncontrollable, or when the existing vegetation (turf or weeds) is in unacceptable condition and cannot be improved. General reestablishment steps include the following:

1. Use a nonselective herbicide (e.g., glyphosate) to kill existing turf and weeds.
2. Correct soil pH, drainage, and/or fertility problems by properly preparing the planting bed.
3. Select and plant new turf by seeding or sodding the area.
4. Supply proper culture for establishment and long-term health.

Turf in Shade

Inadequate light quality, quantity, or duration can lead to turf decline and poor quality. Use shade- tolerant grasses wherever turf is desired and shade exists. If possible, selectively prune or remove shade-producing plants to open the area and allow additional light to reach the turfgrasses. When shade is desired and existing light is inadequate to support turf growth, select an alternative, shade tolerant ground cover (e.g., Japanese spurge, hosta, English ivy, or purpleleaf winter creeper), or an organic or inorganic mulch to cover the area.

Summary

Turf improvement can result in healthy, vigorous turfgrass that betters an area's appearance, value, and sport or recreation value. When turf falls below an acceptable quality level, determine the reason for decline, and then select a program of upgrading the turf. After the improvement program is in place, use good turf culture to maintain turf health.

Table 1. Probable best times for seeding cool-season turfgrasses in Illinois.

Table 2. Overseeding rates in pounds of seed per 1,000 square feet.