Zusammenfassungen der Arbeitskreisbeiträge - Die DPG

hibitors (HRAC: B; WSSA: 2), which normally can not applied
selectively in oilseed rape. Predominantly the herbicide effect
passes by leaf absorption. Imazamox controls weeds like charlock
(S. arvensis), wild radish (R. raphanistrum), common
amaranth (A. retroflexus), fat-hen (C. album), black bindweed
(P. convolvulus), shepherd‘s-purse (C. bursa-pastoris), common
chickweed (S. media), black nightshade (S. nigrum), red
hemp-nettle (G. ladanum), green bristle-grass (S. viridis) and
grain volunteers with an application rate of 40 g a.i. ha –1. A
considerable endorsement of the herbicide activity can be realised
by the add-on of adequate adjuvants.
In Germany, the admission is being expected for the herbicide
“Clearfield”. Clearfield is based on the former standard
herbicide Butisan Top ® for postemergence treatments. In this
way the Clearfield herbicide is fitted with three active components
(metazachlor 375 g l –1 +quinmerac 125g l –1 + imazamox
6.25 g l –1 ) by an application quantity of 2.0 l ha –1 in
combination with the adjuvant Dash ® 1.0 l ha –1 as an postemergence
treatment. The previous experiences with Clearfield
reflected a good selectivity in Clearfield-hybrid cultivars and
are characterised by a good efficacy against important weeds
in oilseed rape. In this way the control of Brassicaceae weeds,
effected till now by products containing clomazone in pre
emergence treatments, can be realised hereby in post treatments.
It is not able to control Clearfield-volunteers with ALS inhibiting
herbicides, especially sulfonylureas, in following crops.
For this reason the Clearfield-volunteers have to be controlled
intensely after harvesting by mechanical and chemical
methods. The spread of volunteers by soil preparation equipment
and harvesters must be avoided extensively. Herbicides
which don’t belong to the HRAC-B-Group have to be preferred
in the crop rotation. Inadvisable is the planting of Clearfield-colza
in crop rotation with sugar beet. The Clearfield-Technology
can be an option in oilseed rape rotations
with cereals to control special weeds like shepherd‘s-purse,
field penny-cress (T. arvense), hedge mustard (S. officinale)
and hill mustard (B. orientalis). The sustainable use of Clearfield
technology requires the accomplishment of particular
safety rules. This is a precondition to avoid the undesired
propagation of resistance properties as well as the development
of the selection of ALS-resistant weeds like black-grass
(A. myosuroides), loose silky-bent (A. spica-venti) or scentless
mayweed (M. inodora). An intensely consulting will be necessary
for every farmer, who aims to cultivate Clearfield oilseed
rape.
Clearfield production system for winter oilseed rape
Dirk Wolber
Landwirtschaftskammer Niedersachsen, Pflanzenschutzamt
Hannover
Imidazolinone tolerant winter oilseed rape varieties and imazamox
containing herbicide are under development in the
moment. Advantage and disadvantages are discussed controversely.
Plant protection services in Germany do not recommend
using the Clearfield system in oilseed rape at actual
status due to the lack of knowledge in several fields of interest.
One question is if it will be possible to grow oilseed rape with
and without imidazolinone tolerance in the same region and
avoid significant gene and seed flow between different fields.
If this is not possible, the question arises who will pay for
damages if damages occur. Futhermore, more experience is
needed to make sure how to control volunteer oilseed rape in
following crops and how to use imazamox in oilseed rape to
control problematic weeds.
J.Plant Dis.Protect. 2/2011
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: 89
Consequences of introducing imidazolinone-tolerant winter
oilseed rape varieties for weed management
Christoph Krato
University of Applied Sciences Bingen, Berlinstr. 109,
55411 Bingen
On commercial field sites in Rhineland-Palatinate several field
trials were conducted to evaluate the consequences of introducing
imidazolinone-tolerant winter oilseed rape varieties
for weed management within the crop rotation.
An application of the CLEARFIELD ® system was done at two
different locations under practical conditions. The complementary
herbicide BAS 79801 H was applied at two different
application timings (early post-emergence: BBCH 09-11 and
post-emergence: BBCH 12-14). The herbicide efficacy as well
as the oilseed rape yield was measured during and at the end
of the trial period. The herbicide treatments controlled the
occurring weeds successfully and even a high density of volunteer
cereals could have been captured as well. But Matricaria
sp. as a major weed was only controlled at a high level when
the herbicide was applied early post-emergence. Oilseed rape
yields were between 43 dt ha –1 and 64 dt ha –1 depending on
the location and soil tillage.
Three major sources of imidazolinone-tolerant volunteer
oilseed rape can be named: (i) The loss of seeds before and
during the actual harvest, (ii) outcrossing between imidazolinone-tolerant
and susceptible oilseed rape varieties and (iii)
The dispersion of seeds due to the corporate use of combine
harvesters. Sources named under (ii) and (iii) were quantified
in two-year field trials.
The highest outcrossing frequencies were observed at the
closest distance of 2 m between imidazolinone-tolerant and
susceptible varieties and were between 0.6 and 2.1% depending
on the year and direction. Frequencies decreased significantly
with increased distance to the pollen source but single
outcrossing events were still found at the widest sampling
point of 45 m. A genetic analysis of F1 plants confirmed the
transfer of both tolerance genes and a heterozygous genotype
in most of the cases.
A dispersion of rape seeds during the harvest period was
simulated using a contractor. Immediately after oilseed rape
harvest the contractor harvested a defined area of winter wheat
on commercial field sites of the University of Applied Sciences
in Bingen in 2009 and 2010. In the first year the dispersion of
seeds was evaluated counting emerged volunteers after multiple
soil preparations while in the second year the amount of dispersed
seeds was measured using plastic shells. A maximum of
267 seeds m –2 (2009) respectively 787 seeds m –2 (2010) were
observed. The seed entry decreased with increased distance
but seeds were still found at the last sample point.
Oilseed rape has a high status within the crop rotation.
Although the occurrence of volunteer oilseed rape in subsequent
crops winter wheat and sugar beet can’t be prevented, a
successful control with selective herbicides (primarily ALS-inhibitors)
was possible without restrictions. While introducing
imidazolinone-tolerant oilseed rape the herbicide regime to
control volunteer oilseed rape has to be adjusted.
Herbicide trials under field conditions have shown that only
few ALS-inhibitors still have the potential to control tolerant
volunteers. Yet the efficacy is quite variable and strongly
depends on environmental conditions, sowing time and competitiveness
of the crop. In contrast herbicides outside HRAC B
showed a high efficacy against imidazolinone-tolerant in winter
wheat. In the subsequent sugar beet effective tank mixtures
(several herbicides; adjuvants) have to be considered for a complete
control. If conditions are unfavorable the herbicide efficacy
can decrease and additional applications may be required.