Weed management in wheat crop
management in wheat crop
WEEDS constitute the
single greatest cause of crop loss in Pakistan. Because
their effect on yield tends to be under estimated, their
presence is often tolerated. The reduction in wheat
yield due to weeds ranges from 15-35 per cent. The crop
totally fails in the field that is infested with weeds.
quality of produce from weed infested field is inferior
due to mixing of weed seeds with wheat grains. Weeds
also act as an obstacle in the cultural practices e.g.
harvesting. Some weeds also help in the spread of
diseases and act as multiplication places.
Integrated weed management makes use of a combination of
different agronomic practices to manage weeds, so that
the reliance on any one weed control technique is
reduced. Reducing the reliance on one or two specific
weed control techniques means that those techniques or
tools will be effective for the future use. The object
of integrated weed management is to maintain weed
densities at manageable levels while preventing shifts
in weed populations to more difficult-to-control weeds.
Losses caused by weeds will be minimised without
reducing farm income.
Controlling weeds with one or two techniques gives the
weeds a chance to adapt to those practices. For example,
the use of herbicides with the same mode of action
(belonging to the same herbicide group) year after year
has resulted in weeds that are resistant to those
herbicides. The continuous production of certain types
of crops also gives weeds a chance to adapt.
Integrated weed management uses a variety of control
techniques to keep weeds “off balance”. Weeds are less
able to adapt to a constantly changing system that uses
many different control practices, unlike a programme
that relies on one or two weed control tools.
An integrated weed management system that combines
cultural and chemical weed management practices is the
most effective and economical way to manage weeds in
wheat. Although several effective herbicides are
available to control broadleaf weeds and grasses in
wheat, herbicides should be viewed as an additional
tool, not as a remedy. Often, when one control method,
whether chemical or mechanical, is used continuously, a
shift in the weed population toward a difficult to
control species will occur. Herbicide resistant plants
within a species can be selected from a susceptible
species and can increase in number. Most commonly,
tolerant species can replace sensitive ones that have
been eliminated by herbicides.
This problem can be avoided by integrating as many
control measures as possible such as crop rotation,
using mixtures of herbicides with different modes of
action, and by rotating herbicides from one season to
the next. A properly prepared seedbed can significantly
reduce weed infestation. If possible, germinate the
weeds before beginning tillage operations using
irrigation. Plough as deeply as possible to break up
soil compaction and reduce risk of herbicide carryover
if wheat is planted after other crops. The tillage
should be just before planting wheat so that any
germinated weeds do not have a competitive advantage.
Good field sanitation is essential for weed control.
When possible select field free from hard-to-control
weeds. Clean planting, harvesting, and tillage
implements prior to entering a field to eliminate
introducing new weeds. Keep field perimeters weed free
because they serve as an initial reservoir for seed to
infest the field.
Planting wheat seed contaminated with weeds is one of
the most common ways to introduce weeds into wheat
field. Plant certified wheat seed. Certified seed is
slightly higher priced, but it is cheap compared with
managing a weed problem that can result from seed
contaminated with weeds.
Weed infestations can be reduced by rotating to crops
with a different life cycle or ones in which different
cultural and chemical practices are used. Crop rotation
regularly changes the crop in each field, the soil
preparation practices in that field, subsequent tillage,
and weed-control techniques. All these factors affect
weed populations. Rotating wheat with summer crops
having allelopathic potential such as sorghum is a very
logical weed control practice.
Management practices which encourage a healthy and
vigorous wheat crop will reduce losses from weeds. Some
of these practices may include: seeding at the proper
depth; seeding at the appropriate rate and time;
selecting the correct amount, timing, and placement of
fertilisers; using adapted cultivars.
The importance of herbicide use is closely related to
the cost and availability of labour. Herbicides are one
of the first labour saving technologies to be adopted as
labour costs rise. As a consequence, the use of
herbicides varies considerably between countries. Weed
management is not accomplished by using cultural
practices exclusively. Some weeds are favoured by the
same management practices that favour wheat. Herbicides
offer an additional tool to control weeds in conjunction
with cultural practices, but are not intended as a
replacement for proper management practices.
The success of a herbicide application is dependent upon
weed species, the timeliness and thoroughness of
application, conditions at the time of application,
herbicide rate, and crop management after the
application. If the decision is to use a herbicide,
carefully read the label. Following the label will
reduce the like hood of crop injury, reduce off-target
movement of herbicide, and maximise weed control.
A number of herbicides are registered for broadleaf weed
control in wheat. However, only few of these herbicides
are effective for controlling weeds. These herbicides
are MCPA, dicamba, bromoxynil (Buctril) and
thifensulfuron + tribenuron.
Several herbicides have been developed primarily for the
control of grassy weeds in wheat. These include
fenoxaprop-P-ethyl, clodinafop-propargyl + safener
cloquintocet, mesosulfuron-methyl, triallate,
difenzoquat, diclofop, and imazamethabenz.
Courtesy: The DAWN