Vol. 51—1997 - NorthEastern Weed Science Society

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177
Interact~ons Between Herbicide Use and Turfgrass Diseases
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Bruce Martin
Plant Pathology and Physiology
Clemson University
Dee Research and Education Center
Florence, SC
Herbici4es are valuable tools for the maintenance of quality
turfgrass st~nds. During development of herbicides, turfgrasses
are screenedithoroughly for tolerance to the materials before
labels are o*tained. Good tolerance to healthy stands of grasses
for which th$ materials are labelled is usually obtained.
However, occasionally, unforeseen or unusual stress conditions
may lead to iurfgrass injury. Sometimes the stress can
predispose t~e plant to greater susceptibility to pathogens, and
sometimes th¢ herbicide adds to environmental stress or interacts
with the host turfgrass plant to influence susceptibility to
pathogens. i
Herbicir'es and plant growth regulators don't always cause
problems wit diseases. For example, some triazole fungicides,
such as fena imol (RUBIGAN), have herbicidal and/or growth
regulator chrracteristics as well as fungicidal activity. In the
Southeasterni U.S., fenarimol is utilized as a preemergence
herbicide fo~ Paa annua control as much as for its fungicidal
properties. I_In other cases, herbicides or plant growth
regulators a~fect nontarget organisms and may predispose
turfgrasses ~o greater damage from pathogens, as well as inhibit
the recoverY) of the turf after "active" disease has subsided.
Some oiJ the affected non-target organisms may be stimulated
or inhibited by herbicides. The effects can be direct or
indirect, fqr instance, by influencing a pathogen's virulence
through eff~cts on mycelial growth, spore germination, or
sclerotium ~urvival (Altman and Campbell, Hodges). It is also
possible th~t herbicides can act indirectly by modifying the
relationship between the pathogen and certain antagonists, or the
pathogen's ~nvironment. However, usually, documented effects
have been iq the realm of "predisposition" where the host
physiology ,nd susceptibility to pathogens is altered.
There ~as not been much research in turf concerning
herbicide-t~rfgrass disease interactions. However, Madison
observed a $evere attack of brown patch in Kentucky bluegrass
following afplication of 2,4,S-T and disodium methyl arsenate.
Turgeon, et~al., reported increasing incidence of stripe smut of
Kentucky bl~egrass following bandane application. Karr et. al.
found in grfenhouse investigations that benefin and bensulide
slightly inpreased severity of Rhizoctonia blight and dollar spot
in bermudagrass and pythium blight on annual ryegrass. Other
examples ari in the literature.
It wasi observed in the turfgrass plots at Clemson
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