Growth Regulators as Overseeding Aids

Clint Waltz, Milling Blalock and Ted Whitwell

Department of Horticulture, Clemson University

Introduction

Overseeding a cool season turf species into a warm season turfgrass sod is a practice used to provide color and improve playability. Earlier overseeding dates are used because of the competition for the fall and winter golfing market. Warm season turfgrass may still be vigorously growing and may reduce the success of an early overseeding. The cool season species is at a disadvantage due to the more aggressive warm season species. Traditional overseeding dates take advantage of natural factors such as reduced temperatures and shorter day lengths to slow warm season turf growth and to aid in establishment of cool season species. In recent years,

growth regulators are used to slow the growth of the warm season turf and enhance the establishment of the overseeded species. However, little is known about how the growth regulators affect the overseeded species.

Objectives

The objective of this project was to determine the effects of various growth regulators on overseeding establishment.

Procedures

Primo Rate Study:

A three year study was completed at the Clemson University turf plots investigating various rates of Primo as an overseeding aid. Plots were established on Tifway `419' bermudagrass (Cynodon transvaalensis Burtt-Davy x C. dactylon (L.) Pers.) maintained at 0.5 inches in height. Plots were 6.6 feet x 6.6 feet, arranged in a randomized complete block design with 4 replications. Primo was applied one week prior to overseeding dates of September 26, October 11, and October 26, 1995. Three rates (0.24, 0.45, and 0.75 oz/ 1000 ft²) of Primo were applied prior to each overseeding date and compared to a nontreated control. Applications were made with a CO2 backpack sprayer set to deliver 30 gallons per acre. One week after application plots were mowed, clippings removed, and seeded at 10 lb/ 1000 ft². A perennial ryegrass (Lolium perenne L.) mixture, (Greenland, Barrage, Pinnacle and Premier cultivars), was overseeded and irrigated. Plots were evaluated for bermudagrass color and injury, ryegrass visual density, height, and seedling counts. Ryegrass seedling counts were determined by averaging the number of ryegrass plants in 1 inch plugs of 5 subsamples.

A second study compared three growth regulators (Cutless, TGR, and Primo) as overseeding aids. Plots were established on Tifway `419' bermudagrass maintained at 0.5 inches in height. Plots were 6.6 feet x 6.6 feet, arranged in a randomized complete block design with 4 replications. Plant growth regulator treatments were Primo at 0.5 oz/ 1000 ft², Cutless at 1.1 oz/ 1000 ft², and TGR at 0.2 oz/ 1000 ft². An untreated control was included for comparison. Applications were made one week prior to three seeding dates; September 26, October 11, and October 26, 1995. Applications were made with a CO2 backpack sprayer delivering 30 gallons per acre. One week after application, plots were mowed, clippings removed, and seeded at 10 lb/ 1000 ft². A perennial ryegrass mixture, (Greenland, Barrage, Pinnacle and Premier cultivars), was seeded and plots were irrigated. Plots were evaluated for bermudagrass color and injury, ryegrass visual density, height and seedling counts. Ryegrass seedling counts were determined by averaging the number of ryegrass plants in 1 inch plugs of 5 subsamples.

Results and Discussion

Primo Rate Study:

Primo on bermudagrass had various effects on turf color and ryegrass density. Primo at all rates for the early seeding date reduced bermudagrass color at 4 and 5 weeks compared to the untreated. Color was also reduced by the higher Primo rates 4 and 5 weeks after initial treatment after the October 11, seeding date. Visual ryegrass density was generally unaffected by Primo treatments within a seeding date. Primo treatments did not affect ryegrass plant counts within a seeding date but fewer plants were noted from the last seeding date.

PGR Comparison Study:

Primo and TGR did not adversely affect the color of bermudagrass at the early and mid overseeding dates. Cutless, however, did reduce bermudagrass color at the early seeding date. Bermudagrass was injured by Cutless at most evaluation intervals and Cutless reduced ryegrass density at all seeding dates (Table 5). Within individual seeding dates, there was no difference in ryegrass plant counts for any of the treatments (Table 3).

When using growth regulators to assist cool season turf establishment, timing of seeding appears to play the most important role in overseeding success. Plant counts indicate that no treatment enhances or inhibits ryegrass establishment, but a later seeding date can suppress visual density. The use of growth regulators as an overseeding aid does not replace proper timing and preparation of the overseeding bed to obtain adequate soil to seed contact.

Table 1. The effect of three rates of Primo on bermudagrass color.

Table 2. The effect of three rates of Primo on ryegrass visual density in overseeded bermudagrass.

Table 4. The effect of three growth regulators on bermudagrass color.

Table 6. Bermudagrass injury as the result of growth regulators.