Vol. 54—2000 - NorthEastern Weed Science Society

CREEPING BENTGRASS SEEDLING TOLERANCE
TO HERBICIDES AND PACLOBUTRAZOL
J.E. Kaminski andP.H. Dernoeden'
ABSTRACT
Thetolerance of creeping bentgrass (Agrostispalwtris Huds.) seedlings to most available
berbicides hasnot been studied in the traosition wne climate of the mid-Atlantic region. This
type of research is needed due to the increaseuse of creeping bentgrass as a fairway turf in the
region. Theprimary objectives of this investigation were to detennine: I) bentgrass tolerance to
these chemicals when applied at various stages of seedling development; 2) establishment rate;
and 3) gennination andestablishment of new seedlings fullowing treatment of the test site with
glyphosate andre-seeding the following spring. Thestudy was initiated on a mature standof
'Penncross' creeping bentgrass grown on a modified sandy mix with a pH of6.2. Thestudy area
was treated with glyphosate on 14 September1998. Thesite was then verticut andseeded with
'Crenshaw' creeping bentgrass at 1.0 lb. seedllOOOfl'on21 Sept. 1998. Turfwas mowed to a
beight of 0.60 inches. Treatments were applied two (Le., 12 October), four (i.e., 28 October),
and seven weeks (i.e., 17 November) after seedlings hademerged. Sprayable herbicides were
applied in 50gpa with a Co, pressurizedsprayer equippedwith an 8004E nozzle. Siduron 3.1G
was applied with a shaker hottle. Plots were evaluated fur seedling injury, percent bentgrass
coverage, percent bareground,andoverall quality between 28 Octoher 1998 and8 Apri\ 1999.
To evaluate the potential soil residual of the compoands, the test site was treated with glyphosate
on 23 April 1999, and monitored fur seedling emergence andestablishment (i.e., 20 May to 17
June 1999). Thesite was verticut and againseeded with Crenshaw on 6 May 1999. Plots
measured 5 by 5 ft and were arranged in a randomizedcomplete block design with four
replications. Data were subjected to aua1ysisof variance andsignificantly different means were
separated by the least significant difference test (JRl.05).
Test results indicated that caution should be used when applying certain herhicides or
paclobutrazol prior to and following the seeding ofbentgrass. Data showed that ethofumesate
(0.75Ib aUA) and paclobutrazol (0.125lb aUA) weretoo injurious to apply two weeks after
seedling emergence. Some reduction in bentgrass cover alsooccurred when bensulide (7.5 lb
ai.lA) and siduron (6.0 lb ai./A) were applied to seedlings two weeks after emergence. Plots
treatedwith the afurementioned herbicides, however, exhibited acceptable cover before spring.
Chlorsulfuron (0.125 lb aU A) was extremely phytotoxic to bentgrass seedlings when applied at
two or fuurweeks after emergence. Bensulide(7.5lb aUA), siduron (6.0 lb ai./A),
ethofumesate (0.75Ib ai.lA), and paclobutrazol (0.125lb ai.lA) were generally safe when
applied four weeks after bentgrass emergence. Applying ethofumesate (0.75 lb ai./ A),
prodiamine (0.32Ib ai./A), orethofumesate + prodiamine (0.75 + 0.32lb ai./A) seven weeks
after seedling emergence was not injurious. Thestudy site was treated with glyphosate on 23
April 1999 andoverseeded 6 May 1999. Thesoil residual ofprodiamine applied on 17
November 1998 caused a significant and commercially unacceptable level of seedling death. No
other treatments applied in October or November, 1998 (i.e., ethofumesate alone) caused
unacceptable seedling emergence in plots overseeded in May 1999.
'Graduate research assistant and Professor, Department of Natural Resource Sciences and
LandscapeArchitecture, Univ. ofMary1and, College Park, Md. 20742.
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