The Rural Voice, 1978-08, Page 29First noticed in Bruce
Weeds herbicide resistant
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Lamb's -quarters, a troublesome weed m field crops, has developed a
resistance to atrafine. the herb/cede that ,s commonly used to control
Weeds that have built up resistance to
herbicides have been relatively rare in
Canada. But that picture may be changing.
In 1974, a corn field in Bruce County.
was found infested with lamb's -quarters
after it had been sprayed with atrazine. a
weed killer that had always proved
effective in eliminating the weed.
The field had been sprayed with atrazine
with good success for 10 years. Tests on
the lamb's -quarters showed that, com-
pared to a sample of the weed from another
area, it was resistant to the herbicide.
Since then. more than 2,500 acres of
atrazine -resistant lamb's -quarters have
been reported in Ontario and it is
estimated the actual figure is much higher.
scientists now are keeping a sharper
Zook -out for the problem, and cases have
been reported from Quebec, the Annapolis
Valley in Nova Scotia and from Washington
State.
Included in the reports are cases of other
weeds, such as red -root pigweed, ragweed
and goose foot, showing a similar
resistance to the triazine herbicide family
to which atrazine belongs.
Two Aericulture t.an'+rta wPPn
specialists, Suzanne Warwick with the
ELDER ENTERPRISES
Biosystematics Research Institute in Ot-
tawa and Paul Marriage at the depart-
ment's Harrow, Ont., Research Station
have been studying this weed control
problem.
"The triazine herbicides work by
preventing photosynthesis in the weed.
They normally kill off all the weeds except
a few grass species. For the last 15 years
they have been the most commonly used
weed killers in corn fields. Resistant
lamb's- quarter are able to prevent the
herbicide from inhibiling photosynthesis."
The continuous planting of one crop
coupled with repeated use of the same
herbicide created an ideal situation for the
development of resistance.
"A closely related plant, the goose foot,
commonly found in orchards, but some-
times in corn fields, has also been
exhibiting a resistance to triazine
herbicides. We plan to do a closer study of
this species to check the extent of the
problem," Dr. Warwick says.
She says if resistance to triazine
herbicides becomes a problem in corn
fields, farmers should use an alternate
herbicide or rotate weed killers.
"Dicamba or 2,4-D could be used
for control by themselves or rotated with
atrazine to prevent a build-up of re-
sistance. The other alternative, if possible,
is for farmers to rotate crops," Dr.
Warwick cave
Urged to test soil
lhere are dollar savin o be had tor
farmers who test their before fall, a
f^tinratory rl+rertnr with the Ontario Soil
,. ,....o v.»LV. vperateu for the
Ontario Ministry of Agriculture and food at
the University of Guelph says.
The laboratory is encouraging farmers to
consider taking soil samples in summer
because there are dollar savings to be had
in knowing the most efficient use of
fertilizers from early test results.
Professor T. E. Bates, laboratory
director says many farmers who plan to
test soil in the fall are rushed with the
harvest and neglect to do this.
If farmers could test between June and
August then the problem would be solved.
"This is the time to sample soil in hay
fields, pastures and fields designated for
winter wheat. With legumes in hay and
pasture, it's important to apply potash in
late August, if needed. For planting winter+,
wheat in September and October, so..'
samples should be in before August 1," he
Instructions ror soil testing and soli
sample boxes can be obtained from your
local county office of the Ministry of
Agriculture and Food.
THE RURAL VOICE/AUGUST 1978 PG. 29
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