Introduction
- Providing a weed-free environment is absolutely essential
to realise the full potential of new varieties and to make
best use of the key production factors like nutrients, moisture
and other natural resources.
Damage
- During the initial 90 100 days period much of the
soil, space, sunlight etc, are left unutilised by the sugarcane
crop. Taking advantage of this situation, weeds grow luxuriantly
and cause serious damage.
- Due to shading, sugarcane tillering is affected. This leads
to inadequate initial population which ultimately results
in lower stalk population. Weeds also exhaust the soil nutrients
and water.
- Weeds remove four times of N and P and 2.5 times of K as compared
to sugarcane during the first seven week period.
- Weeds absorb more soil moisture. Weeds present in one hectare
of land can remove as much as 750 to 1250 tonnes of water.
Losses
- In India, the reported cane yield losses range from 12
to 72 per cent. If weeds are not properly controlled in the
initial stages, the yield loss could go upto 17.5 t/ha. Twining
weeds which sprout at later stages and twine around clumps
affect cane growth and cause around 25 per cent loss in yield.
The total cane yield loss in the country per annum is around
25 million tonnes (equivalent to 2.5 million tonnes of sugar)
valued around Rs.1500 crores.
- Poor growth of sugarcane resulting from weed infestation also
causes quality depression in sugarcane. The twining weeds
also cause serious harvesting problem. Weeds harbour certain
disease and insect pests that attack sugarcane and thus lead
to indirect losses.
- Bermuda grass (Cynodon dactylon), the cogan
grass (Imperata cylindrica) and eight other graminacious
weeds are known to be alternate hosts to ratoon stunting
disease (RSD) of sugarcane.
Important weeds in sugarcane ecosystem
The major weed flora observed are:
- Cyperus rotundus (sedges),
- Cynodon dactylon (pers),
- Sorghum halepense pers.
- Panicum spp.,
- Dactylocternium aegyptium pers, (grasses),
- Chenapodium album L.,
- Convovulus arvensis L.,
- Amaranthus viridis L.,
- Portulaca oleraceae L.,
- Vicia spp.,
- Commelina bengalensis L., and
- Trianthema portulacastrum L., (broad leaved weeds).
Twining weeds like Ipomea spp. are becoming a problem in many sugarcane growing areas.
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Weed Management Practices
- Effective weed control in sugarcane can be achieved by
adopting various known approaches of weed management. The
various approaches are:
- 1. Mechanical methods
- 2. Cropping and cultural practices
- 3. Chemical control by using weedicides (herbicides), and
- 4. The integrated approach.
Mechanical method
- In the sugarcane fields even now the mechanical methods
of weed control is the most popular and effective method.
One of the important objectives of pre-planting tillage operations
is to control weeds.
- Deep ploughing and collection of grass weeds, particularly,
the nut grass and Haryali is an effective method of controlling
problem weeds.
- Primary and secondary tillage operations also help in burying
the weed seeds deep in the soil and thus making them ineffective.
- Hand weeding and hand hoeing operations are very effective
in controlling weeds in early stages of crop growth. In recent
years, labour shortages are being felt. In addition to hand
weeding and hand hoeing, bullock drawn or tractor drawn implements
can be used for earthing up and hoeing which also control
weeds.
Cultural practices
- Weed control could be achieved through crop rotations,
crop competition, mulching, clean cultivation, trap cropping,
etc.
- Crop rotation practices help in breaking weed chain and thus
help in the destruction of particular type of weeds. For example,
growing paddy in rotation needs a puddled soil condition by
which effective reduction of monocot weeds is possible, which
are otherwise difficult to control. Several twining weeds
can be controlled by growing paddy in rotation.
- Intercropping also provides another means of reducing weed
population. Fast growing short duration intercrops are useful
for this purpose. Mulching using sugarcane trash helps in
suppressing weeds substantially.
Herbicides
- Herbicides (weedicides) are being extensively used for
weed control in many sugarcane growing countries of the world
for the following reasons:
- Labour is becoming scarce and costly
- Conventional methods are inefficient
- Initial weed growth cannot be controlled by conventional methods
- Timely weeding is becoming difficult by conventional methods,
and
- Conventional methods are becoming time consuming and costly.
- Pre-emergence and post-emergence applicaiton of 2, 4-D at
1.0 to 1.5 kg/ha has been found highly effective in controlling
most of the dicot and other broad leaved weeds.
- Pre-emergence application of simazine at 2 kg/ha was found
to be most effective on a wide range of monocot and dico weeds.
Pre-emergence application of triazine compounds (simazine,
atrazine, ametryne, prometryne) resulted in high mortality
of weeds in sugarcane fields.
- Metribuzine, diuron, metoxuron, 2, 4-D sodium salt, dalapan,
paraquat, alachlor, isoproturon, isouron and glyphosate have
also been found to be effective.
- A large number of experiments throughout the country have
indicated that for solo crop of sugarcane, atrazine is the
most effective herbicide at dosages ranging from 2.0 to 5.0
kg /ha. It controls most of the seed germinated dicot weeds
and grasses when applied as pre-emergence spray.
- In Tamil Nadu it is recommended at 2.0 kg /ha. It has become
a very popular herbicide throughout the state. It gives a
more or less complete weed free condition for about 30 to
45 days.
- Pre-emergence application of a herbicide is essential to control
initial weeds. This is done soon after planting on the third
or fourth day. Later on, another application around 25
30 days with a post-emergence herbicide may be required.
- For controlling twining weeds such as Ipomea spp., application
of atrazine or sencor may be done after final earthing up,
around the cane rows.
- Dosage of herbicides varies with soil type. Usually heavy
soils require a higher dosage than a light soil. Pre-emergence
application of herbicide in sugarcane is done as a blanket
spray soon after planting i.e. on the 3rd or 4th day. The
post emergence application is usually applied as directed
spray on to the foliage of the weeds.
- The quantity of herbicide (Commercial product, Q) required
per ha is calculated as follows:
Q = Dosage in a.i./ha / Percent a.i. in the product x 100
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- The quantity of spray liquid required per hectare
is best decided by a simple calibration because
the quantity depends upon the type of sprayer used,
spray quantity discharged by the nozzle used, the
herbicide applicator (the person), and the extent
of weeds present. The calibration could be done
by spraying a small area (about 100 m2) with water
and converting the quantity per hectare.
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- For example, if 7 litre water is required to cover an
area of 100 m2, then the quantity required per ha is calculated
as follows:
Test spray area (Ta)100 m2
Water required to spray the Test area (TW)7 litres
Water required per hectare (=10,000 m2)
=TW/Ta x 10,000
=7/100 x 10,000
=700 litres
Herbicidal control of weeds in intercropped sugarcane
- Pulse crops (mung, cowpea), daincha, groundnut, sunflower,
maize, wheat, potato, gram, mustard, onion etc. are grown
as intercrops in sugarcane. In such situations, herbicide
recommended for solo crop of sugarcane cannot be used. Atrazine
is harmful to black gram, soybean and sunflower. Therefore,
it cannot be used. 2, 4-D is harmful to all the dicot and
broad leaved intercrops.
- The herbicide used must be harmless both to the sugarcane
and the intercrops. Alachlor at 2.5 litre/ ha was found useful
under intercropping of pulses. Oxyfluorfen (Goal) at 1.20
litre / ha is useful when pulse is intercropped, when applied
as pre-emergence spray.
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Integrated Weed Management
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- Complete weed control cannot be achieved by using
any one method. To have more dependable, economical
and desirable weed control without environmental problems,
it is advisable to have a proper combination of agronomical,
cropping, rotational and biological methods with supplemental
use of herbicides.
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- By continuous use of herbicides, in addition to the residual
problem there is every possibility of a major weed becoming
a problematic one. Several of the effective herbicides are
either non-available or prohibitively priced and therefore
their use is restricted. An integrated approach wherein only
supplemental use of herbicide is resorted to is highly desirable.
- Integrated weed management involves use of all feasible control
measures such as mechanical, cultural, cropping, biological
and chemical, in proper combination at different stages of
weed and crop growth to get the most practical and economical
results.
- The objective of the integrated approach to weed management
in a crop-weed community is to shift the balance in favour
of crops to the point where weeds are no longer economically
important.
Mechanical control
- In integrated weed management, mechanical and cultural
methods assume great importance. One of the most important
aspect of weed management is checking the weed seed dispersal.
This calls for destroying weeds before they flower and set
seeds. Mechanical destruction is an effective measure.
- Keeping the irrigation channels clean helps in checking transport
and dispersal of weed seeds. A thorough tillage, besides providing
a good seedbed to the sugarcane crop, also destroys weeds.
Agronomic practices
- Growing the crop with proper agronomic practices will
make the crop more competitive. Maintaining adequate crop
population and application of optimum doses of nutrients are
important.
- In ratoon sugarcanes, gaps favour weed growth. An adequate
ratoon population must be achieved by stubble shaving, off
barring and gap filling.
Pre-emergence herbicide
- Use of a pre-emergence herbicide is essential to control
the weeds during the germination phase of the crop.
- Post-Emergence Management of Parasitic weed Striga Asiatica
in Sugarcane is new practice developed by TNAU in which pre-emergence
application of atrazine 1.0kg/ha on third day after planting
+ hand weeding on 45 DAP with an earthing up on 60 DAP combined
with post-emergence spraying of 2,4-D sodium salt 5g/litre
(0.5%) + urea 20g / litre (2%) on 90 DAP for complete control
is adopted. So that complete control of parasitic weed Striga
Asiatica is ensured. Seed production by the weed is also avoided.
This is a environmentally safe technology.
Hoeing and hand weeding
- Hoeing the inter rows using a ridger would help control weeds besides being
able to earth up the cane rows. Hand weeding of the weeds in the cane rows is still necessary
Irrigation
- Avoiding excess irrigation reduces the build up of weeds and damage to the soil.
Mulching
- Sugarcane trash can be profitably utilised for moisture conservation, weed control and to
enrich organic matter status. Trash mulch reduces weed growth.
Intercropping
- In sugarcane, black gram, green gram, soybean, sunflower, groundnut etc.
can be grown as intercrops, and they help in smothering weeds.
Crop rotation
- Rotating sugarcane with other crop reduces the incidence of certain weed species,
for example, puddling and growing paddy helps in reducing the incidence of several grass and
broad leaved weeds.
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