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 Academic
Programs
Certificate
Program
Classes
by Phil Busey
Degree
Requirements
Golf
and Sports Turf
Grass
Biology
Landscape
IPM
Living
Lawn
Turfgrass
Culture
Research
Interests
Weed
Science
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Weed
Science
Tropical
Signagrass 2: Preemergence Control
A
very serious weed problem in both St. Augustinegrass and bermudagrass
is also frequently misidentified.
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| Hoeing
tropical signalgrass on a sod farm. |
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Tropical
signalgrass, Urochloa subquadripara, (syn. Brachiaria
subquadripara, Bayer code BRASU, also called smallflowered Alexandergrass),
is the most serious weed in south Florida St. Augustinegrass, Stenotaphrum
secundatum, turf, according to sod producers. It is the
second most serious weed in bermudagrass golf turf, based on survey
of 236 south Florida superintendents. Though confused with
crabgrasses (Digitaria spp.), tropical signalgrass leaves
are more shiny and less flexuous.
In
new sod fields, tropical signalgrass germinates more rapidly than
crabgrasses, remaining appressed to the ground while stolons form.
Stolons interweave with cultivated St. Augustinegrass, then
grow on top, creating an unsightly appearance. It is killed
by frost. Tropical signalgrass fills voids left by other weeds.
In a preemergence herbicide experiment, there were more (P
< 0.05) tropical signalgrass seedlings in plots treated with atrazine
at 1.1 kg ha-1 (90.1 seedlings m-2) than in untreated plots (62.6
seedlings m-2). The most effective preemergence treatments
were oxadiazon at 2.3 kg ha-1 and pendimethalin at 3.4 kg ha-1 applied
8 days after plug planting, providing early postemergence control
of 2-leaf seedlings. The most effective management of tropical
signalgrass was preemergence herbicide and early, 25-30 days postplanting,
applications of asulam at 1.2 kg ha-1. Seedling numbers were
reduced by 90-95%, but hand hoeing and spot treatment were still
required.
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