Date of Award

5-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

McCarty, Lambert B.

Committee Member

Liu , Haibo

Committee Member

Whitwell , Ted

Committee Member

Toler , Joe E.

Abstract

Hybrid bermudagrass [Cynodon transvaalensis Burtt-Davey x C. dactylon (L.)
Pers.] is the preferred turf for golf courses and athletic fields across the southern United
States because of its dark green color, fine texture, good wear and drought tolerance, and
excellent recuperative rate. Despite its many attributes, bermudagrass goes dormant and
turns an unsightly brown color when soil temperatures fall below 10-13oC (50-55super>oF).
Perennial ryegrass (Lolium perenne L.) is often overseeded into bermudagrass in the fall
to sustain acceptable turf quality through the spring months. However, perennial ryegrass
aggressively competes with the bermudagrass for resources in the spring and potentially
releases disruptive allelochemicals into the environment. This competition and inhibition
complicate the spring transition, impair the bermudagrass base, and result in unacceptable
turf quality. Field studies were conducted to determine the best treatment(s) to optimize
the spring transition and ensure continuous acceptable turf quality. Growth chamber
studies were conducted to investigate potential ryegrass inhibition/allelopathy on
common bermudagrass seedlings.
The field experiment utilized an overseeded soccer field to monitor the spring
transition under different mowing heights, fertility rates, and trifloxysulfuron
applications. Two mowing heights (1.2 and 2.5 cm), two nitrogen rates [18 kg N ha super>-1
week super>-1(low) and 36 kg ha super>-1weeksuper>-1 (high)], and three herbicide rates and application dates
[trifloxysulfuron at 0.005 (low) and 0.017 kg ai ha super>-1 (high) April; low and high May; and
untreated] were examined. Turf responses measured were turf quality (TQ), percent
perennial ryegrass (PRG), shoot dry weight (SDW), root dry weight (RDW),
bermudagrass shoot counts (BSC), and percent bermudagrass (PBG). Trifloxysulfuron
(TFS) had a significant effect both years on all measured responses except 2006 RDW.
In 2006, untreated and 2.5 cm low April TFS treatments sustained acceptable turf quality
while all other treatments experienced unacceptable quality for a minimum of 2 weeks.
However, both 2.5 cm low April TFS and control treatments possessed unacceptable
PRG at study's end, 30 June 2006. In 2007, untreated and 1.2 cm low May TFS
treatments at both fertility levels maintained acceptable (>7) quality for the duration of
the study. All TFS treatments had 0 PRG and 100 BSC and PBG ratings at study's end, 1
July 2007.
The first growth chamber experiment utilized pots seeded with bermudagrass that
received irrigation water contaminated with various concentrations of perennial ryegrass
roots or shoots. The potential allelopahic/inhibitory effects of two sources of
contaminant (perennial ryegrass roots or shoots) and four amendment rates (0, 5, 10, 20 g
L super>-1) on bermudagrass germination and growth (root length density, root mass density,
specific root length, root ash weight, dry shoot weight, bermudagrass shoot number, and
bermudagrass tiller number) were examined. No bermudagrass inhibition or yield
reductions were observed for any of the ryegrass irrigation solutions.
The second growth chamber experiment utilized pots that contained bermudagrass
seeded in soil amended with various rates of perennial ryegrass root or shoot. The
potential allelopathic/inhibitory effects of two sources of amendment (perennial ryegrass
roots or shoots) and four amendment rates (0, 2, 12, 23% per 25g soil) on bermudagrass
germination and growth (root length density, root mass density, specific root length, root
ash weight, dry shoot weight, bermudagrass shoot number, and bermudagrass tiller
number) were examined. The highest concentration of ryegrass shoots per mix (23%)
reduced bermudagrass shoots, tillers, shoot weight and ash weight.
In conclusion, cultural practices must be coupled with herbicides that aid spring
transition to achieve a complete, timely spring transition in Clemson, SC. Under normal
spring and summer conditions, best overall transition in Clemson, SC followed 1.2 cm
mowing height, 36 kg N ha super>-1 week super>-1 and 0.005 kg ai ha super>-1 mid-May trifloxysulfuron
treatments.
Perennial ryegrass shoots amended into the soil inhibited bermudagrass seedling
emergence and subsequent growth. Reductions in germination, size, and weight of
bermudagrass seed and seedlings are evidence of allelopathic/inhibitory effects by
perennial ryegrass (Inderjit and Keating, 1999; Rice, 1974). Therefore, allelochemicals
are potentially leaking from severed and decaying perennial ryegrass shoots and
inhibiting/altering bermudagrass growth and development.

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