Vol. 16—1962 - NorthEastern Weed Science Society

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'WEED CONrROLBY DIME1'HYt..:mRACHL6ROl'E1lEPHl'~'1'l!:
ALO~ ANDIN
CEm'AIN CCJ.lBINATJ:otlS
L. E. Limpel, Paul H. Sohuldt, acdl n&tYid Lamont 1/
[
Dimethyl tetraohloroterephthalate in pre-emergenoe applioation onto
freshly oultivated soil pos ses8S II remarkable residual aotivity against lIIaby .
annual grasses, e.g., orabgrass (pigitatia spp.),' tbll foJCtails(SetaEia sW.),
and barnyard
weeds, e. g.
grass [Eornoo~o: orus-galli
purslane (JlrtiJ:C _ olenoea
(L.) Beauv.] and some broadleaved
L.) and lambsquarters (Chenopodium
~ L.). However, at reoommended dosages, it is ineffeotive for oontrol of
ragweed (Ambrosia spps ) and Gal1ns~a spp, and usually provides only partial
oontrol of pigweed (Amaranthus app- and smartweed (Polygonum spp.). The
utility of this ohemioal would be greatly inoreased if it effectively controlled
these latter weeds, but none of many experimental formulations has
enhanced activity. In a continued effort to broaden the uses of this herbicide,
it has been combined with several other materials used in pre-emergenoe
applications.
There are two ways in whioh combinations of weed killers can improve
weed control I (1) The mixture lIID.ybe synergistic, i.e., a given weed speoies
may be far more susceptible to the mixture than it is to either of the oanponents
applied alone. (2) The mixture, in a simple additive fashion, may
control a broader speotrum of weed speoies. It would be expected that oases
of true synergism would be rare, and unless there was an antagonistic interaction,
simple addition of spectra of aotivity would tend to be the rule.
h order to take full advantage of this type of addition, the two herbicides
to be combined ought to be as dissimilar in this respect as possible.
Cbviously, such combinations would be restricted to use on crops which
tolerated all components.
MATERIAISANDMETHODS
The herbicidal materials used in these studies are listed in the table
on the following page.
In the greenhouse test, soil contained in metal flats 12" X 8" X 3"
deep was broadcast seeded both to pigweed (bmaranthuB retrof1exus L.) and to
barnyard grass. Each species was restricted to a specific area of the soil
so that pure stands would be present. The seeds were lightly covered with
soil, and the following treatllB nte were then immediately sprayed onto tho
s oil surface I dimethyl tetrachloroterephthalate, CDEC, and NPAeach at
2 lb./acre, dimethyl tetrachloroterephtha1ate + CDlOOat 2 + 2 1b./acre, and
dimethyl tetrachloroterephthalate + NPAat 2 + 2 1b./acre. The treatments
were replicated three times and three untreated nats were included as checlcs.
The flats were retained in the greenhouse untill good growth had occurred in
the checks at which time total fresh weight of the aerial parts of each
speoies was determined. Per cent control was calculated on the basis of
reduction in fresh weight as compared to the checks.