Vol. 51—1997 - NorthEastern Weed Science Society

178
ty's main campus that Rhizoctonia blight (brown patch) in
son grasses seemed to be a chronic problem when certain
ence herbicides were being utilized, particularly the
triazin s, atrazine and simazine (A.R. Mazur, personal
communc'ation). This observation led to research by Mr. Steve
Millett for his M.S. degree in plant pathology.
experim
1.1 and
oxadiaz
0.54 k
treatm
'Tifwa
St.
strain
origin
progre
treatm
had
of
oxadia
applic
genera
centip
Mi lett examined several herbicides in greenhouse and field
nts. Herbicides examined were atrazine and simazine, at
2.2 kg a.i./ha, pendimethalin at 1.7 and 3.4 kg a.i./ha,
n at 2.25 and 4.5 kg a.i./ha, and dithiopyr at 0.27 and
a.i./ha. His experiments also included no herbicide
ts. In each experiment, swards of hybrid bermudagrass,
II', centipedegrass 'Oklawn' or 'Tennessee Hardy', and
stinegrass 'Raleigh' were inoculated with a virulent
of Rhizoctonia solani, obtained from bermudagrass
lly. He rated disease over time, to construct disease
s curves, and analyzed the curves for differences by
nt. In most instances, the grasses treated with triazines
ater disease incidence and/or recovered from the effects
ase slower than other treatments. Pendimethalin and
on also sometimes led to increased disease, but dithiopyr
tions did not apparently influence disease (Millett). In
, the magnitude of the increases observed were greater on
de and St. Augustinegrass than on hybrid bermudagrass.
Au
gr
dis
other herbicide-pathogen system we have investigated
s plant parasitic nematodes. In the well-drained, highly
ed, sandy soils in the Southeastern United States, plant
ic nematodes are endemic and cause significant problems on
Itivated plants, including turfgrasses. Common nematodes
use problems in turf include the sting nematode
laimus longicaudatus), lance (Hoplolaimus galeatus),
root (Trichodorus spp.), ring (Criconemella spp.), and
es certain species of root-knot (Meloidogyne spp.).
occasionally cause problems if infestations are unusually
ing nematodes are particularly damaging to turfgrasses.
They a e relatively large nematodes (up to a millimeter in
lengt ), and have a tendency to prefer root tips as a feeding
site. They also have a relatively long stylet used to probe root
tips, and cause significant damage at low numbers. In South
Carol'na, the current threshold is 20 nematodes per 100 cc or ml
or so'l. They are only found in relatively sandy soils, and are
commo in the coastal sandy soils and in sand ridge (Sandhill)
regio s of the Southeast. Also, they do quite well in putting
green constructed with high percentages of sand in the rootzone
mix.
even
the
early
s
have observed that sting nematodes are present and feeding
efore bermudagrass visually comes out of winter dormancy in
ring. In the Coastal regions of South Carolina, this is in
March. This is also the time (late February to mid-March)