Differential Susceptibility of Conyza bonariensis Biotypes to Glyphosate and ALS-Inhibiting Herbicides in Argentina
Conyza bonariensis is a weed annual broad-leaved species in the Asteraceae family
native to South America, present in fallow in autumn and spring in Argentina.
It spreads by producing high numbers of wind-dispersed seeds. It prefers
undisturbed sites and is a particular problem in low-tillage systems such as
orchards and plantations but also in some agricultural crops.
In no-tillage fallow, control of annual weeds increases by applying
residual herbicides combined with glyphosate. Many of the residual herbicides
for Conyza spp. control are acetolactate synthase (ALS)-inhibiting herbicides,
particularly chlorimuron-ethyl, metsulfuron-methyl and diclosulam. Mixtures of
such herbicides with glyphosate may control biotypes resistant to glyphosate.
Other herbicides included in this group consist of mixtures containing
sulfometuron or chlorsulfuron and are less studied, so the dose for adequate
control is not clear.
The aim of this study was to compare control of three stages biotypes
(rosette, bolting, and reproductive stage) of Conyza bonariensis glyphosate susceptible biotype (S) and tolerant
biotype (T) to glyphosate with glyphosate and mixtures of acetolactate synthase
(ALS)-inhibiting. Seeds of C. bonariensis
were collected in ten fields sampling at least 100 plants combined into a
single composite simple per field. Correlations were made between C. bonariensis using visual evaluations
and plant weight. The data of plant injury were subjected to a normality test
before ANOVA.
For glyphosate, the dose-response curves confirmed that injury of
the biotype T relative to biotype S was significantly lower for both rosette
and bolting stages. Resistance index (RI) for this herbicide was approximately
4 for both weed stages. At bolting, for both biotypes doses much higher than
the recommended dose were required. For acetolactate synthase (ALS)-inhibiting
herbicides, at the rosette stage, control of both biotypes was excellent with
doses significantly lower than the recommended rate. All herbicides within this
group showed a very low I50 relative to the recommended rate.
These results indicate that biotypes difficult to control with glyphosate
at the rosette and bolting stage may be controlled using acetolacte synthase
(ALS)-inhibiting herbicides. Control for the reproductive stage was poor. A
management program based on the combination of glyphosate with pre- and
post-emergence acetolactate synthase (ALS) herbicides may be effective to
control the weed.
Article by Eduardo
Puricelli, et al, from Argentina.
Full access: http://t.cn/E4qLPLx
Image by Javier Pelayo, from
Flickr-cc.
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