Introduction
- Weeds are unwanted plants growing in combinations
with crops.
- They compete for the nutrients, water, space, light
and other essential requirements.
- Weed plants serve as alternate host for several pests
and diseases.
- The dominant weeds of this crop in the plains are
given below.
Major weeds of Potato
Scientific name
|
Common name
|
Amaranthus
viridis L |
Pigweed
|
Anagallis
arvensis L |
Pimpemel
|
Avena
fatua L |
Wild oat
|
Chenopodium
album L |
Lambsquarters
|
Convolvulus
arvensis L |
Field bind
weed |
Cyperus
iria L |
Yellow
nutsedge |
Cyperus
rotundus L |
Purple
nutsedge |
Melilotus
alba Desr |
White sweet
clover |
Melilotus
indica L All |
Yellow
sweet clover |
Phalaris
minor Retz |
Canary
grass |
Pea
annua L |
Blue grass
|
Setaria
glauca (L) Beauv. |
Fox tails
Carpet weed |
Trianthana
monogyna L |
Carpet
weed |
- Wider spacing, frequent irrigation and liberal use
of manures and fertilizers create favourable conditions
for taking an early start of weeds well before the crop
emerges.
- It creates a growth margin in favour of weeds, and
if unchecked, causes serious harm to the crop.
- Early weed competition usually reduces crop yield
more than late season weed growth.
- Weed management is the process of limiting the weed
infestation so that crop could be grown profitably.
Top
Commonly used Herbicides
Basalin (Fluchloralin)
- N-(2-Chloroethyl) - 2, 6-dinitro-N-Propyl- 4-(Trifluoromethyl)
aniline.
- It is applied before planting and mixed with the soil.
- It is available as emulsifiable concentrate or as
granules, belongs to dinitro-anilines group and is volatile.
- It is more or less susceptible to photo-degradation
and therefore be quickly incorporated into the soil
before planting of potato crop.
- It is absorbed by the root and translocated throughout
the plant system.
Pendimethalin (Stomp)
- N-(1-Ethyl Propyl)-2, 6 dinitro-3, 4- xylidine.
- This compound also belongs to dinitro-anilines and
available as an emulsifiable concentrate and as granules.
- Under normal environmental conditions, it persists
for less than a year at phyto-toxic levels in soil.
- Pendimethalin is absorbed more rapidly by very small
broad leaf weeds than by the grasses.
- In potato, it is applied as a pre-emergence application
when the weed flora has not yet germinated.
Linuron (Afalon)
- N' - (3,4 - dichorophenyl) - N- methoxy - N - Methylurea.
- Linuron is a substituted urea compound and selective
pre-emergence herbicide for medium to heavy soils under
medium rainfall conditions.
- Linuron appears to be the best persistent of this
group with no detectable residue after 4 months and
hence is useful in situations where same weed germinates
at later stages of crop growth viz. Poa spp.
- Linuron at 0.5 kg/ ha gave the most effective weed
control in potato at Ludhiana.
- In potato, it controls both broad leaf and grassy
weeds like Echinochloa crussgalli, Digitaria spp,
Setaria spp, Amaranthus spp, Chenopoduim album, Melilotus
spp. Anagallis arvensis, Vicia sativa and Funaria parviflora.
Atrazine
- 2-Chloro - 4 ethylamino - 6 isopropylamino - 1,3,5
- triazine.
- It is applied in Potato to control annual grasses
and broad leaf weeds.
- It is also absorbed through roots and translocated
to other plant parts.
- It is an effective herbicide against Digitaria
spp., Echinochloa spp., Cyperus rotundus L., Chenopodium
album L. and Avera fatura L. etc. Since it is more
soluble than Simazine, it is best suited in areas of
low rainfall.
- It also takes less moisture to carry it into root
zone or activate it.
- It effectively controls both monocot and dicot weeds
and has no residual effect on succeeding crop of wheat.
Simazine
- 2 chloro - 4, 6 - bisethylamino - 1,3,5 - trazine.
- It is a systemic herbicide absorbed by the roots and
translocated to other plant parts.
- It does not prevent germination but kills the seedling.
- It is primarily used to control annual grasses and
broad leaf weeds in potato crop and is effective against
Digitaria spp, Setaria spp, Chenopodium album, Amaranthus
spp.
Metribuzin
- 4- amino - 6 t - butyl - 3 (methylthio) - 1,2,4 -
traizin = 5 (4H).
- Among the triazine herbicides, it is the most effective
herbicide.
- Its persistence in soil is less than the other triazine
herbicides.
- It is usually applied as pre-emergence. Sufficient
moisture is required for it's effectiveness.
- It is both root and shoot mobile herbicide with prolonged
soil residual activity upto 6-12 weeks.
- It is very effective against annual grasses and many
broad leaf weeds in potato particularly Chenopodium
album L., Anagallis arvensis L., Melilotus spp, Vicia
sativa L., Trainthena monogyna L, Poa annua L. etc.
Paraquat
- 1 , 1' - dimthyl 1- 4, 4' - bipyridylium.
- It belongs to bi-pyridylium group and is formulated
as emulsifiable concentrate.
- Its foliar application causes wilting and rapid destruction
of the weed foliage within a few hours.
- For best results in the field, it should be sprayed
in the late afternoon or mid-day rather than in the
morning.
- This allows some internal transport of herbicide during
night before development of acute phyto-toxicity induced
by light which could limit movement of herbicide.
- As the high light intensifies it increases the rate
of development of phyto-toxicity symptoms.
- It has no residual activity as it is rapidly absorbed
and inactivated in the soil.
- It is the best herbicide used as directed spray for
the control of annual and broad leaf weeds.
- Paraquat may also be absorbed through skin.
- Therefore at the time of spraying, breathing of the
spray mist and prolonged skin or eye contact should
be avoided.
Propanil
- N - (3, 4 - dichlorophenyl) propionamide.
- It belongs to amide group of herbicides and is formulated
as emulsifiable concentrate.
- Propanil is a selective post-emergence herbicide and
is used in potato to control several annual grasses
and a limited number of annual broad leaf weeds and
sedges.
- It is effective against Cyperus rotundus L., Digitaria
spp., Echinochloa spp etc.
- The ideal time of it's spraying is at 1-3 leaf stage
of the weeds.
- As propanil is a contact spray, uniform coverage is
essential.
- It is applied as a foliar spray therefore soil type
has no effect on its action.
- Propanil is rapidly broken down in the soil thus has
no residual effect on the succeeding crops.
- It is absorbed mainly though leaves. Do not apply
it when rain is expected within next 5-6 hours.Alachlor
: X-chloro - 2', 6' - diethyl - N (methoxymethyl) acetanilide
:
- It belongs to amide group of herbucider and is formulated
as an emulsifialite concentrate and granules.
Alachlor
- It is more effective in medium textured soils than
the heavy soils. It resists leaching.
- In medium textured soils with moderate moisture, herbicidal
effectiveness usually lasts for about 6-10 weeks.
- After the application of alachlor, the early seedling
and root growth are inhibited and weed seedlings do
not emerge from the soil.
- The grasses absorb the herbicide mainly through the
shoots whereas broad leaf plants absorb it through the
roots.
Top
Different weed management practices in Potato may
be classified
- Crop competition methods
- Physical methods
- Chemical methods and
- Integrated weed management practice.
Crop Competition Methods
Crop Weed Competition
- One of the most favourable crop production technique
consists of crowing out the weeds.
- It directly induces healthy growth of Potato plants
and indirectly maintains a crop environment that is
detrimental to weeds.
- Vigorous and fast growing potato varieties like Kufri
Badshah and Kufri Jyoti are better competitors
due to their adequate crop canopy to smoother weeds.
- High competitiveness is obtained with the adoption
of proper crop management practices such as
Proper crop rotations
- Inclusion of smother crop like cow-pea and green manure
crop eliminates weeds by depriving them of sunlight.
- The weeds are also buried along with the green manure
crops and destroyed.
- It also improves the fertility status of the field
on decomposition.
Hot weather cultivation
- Some perennial weeds such as Cynodan doctylon L,
Cyperus rotundus are simply reduced by ploughing
the field deep during the summer months (May-June).
Good seed bed preparation
- It gives the good start to the crop by ensuring quick
emergence of potato.
Proper and timely planting
- Planting of well sprouted tubers at sufficient soil
moisture, proper depth, time and maintaining high plant
densities per unit area helps in growing competitive
potato crop.
Application of light irrigation
- The crop planted in the month of September experiences
high temperature.
- The furrows formed for sowing get dry very quickly.
- This hinders germination of Potato.
- Therefore, application of light irrigation at short
interval helps sprout the tubers rapidly.
- It should be taken care that the water level in the
furrow should rise half the furrow depth i.e. it should
remain below the seed placement level of the ridge.
Placement of manures and fertilizers
- Application of manures and fertilizers in bands near
the root zone of the crop reduces the nutrient loss
by weeds considerably by depriving the weeds of nutrients.
- It also promotes the crop growth and plant vigour.
This in turn smothers the weeds.
Physical methods
- These methods are also called manual and mechanical
methods of weeds control.
- These methods do not involve chemicals but require
manual energy, animal power or fuel to run implements
that dig out the weeds. These methods include:
Manual weeding
- Pulling out the weeds by hand, hand hoe, spade etc
is a very common practice in Punjab and India.
- This method is also useful for the destruction of
weeds growing within the rows where they can not be
controlled by cultivation.
Mechanical methods
|
- Single bottom animal/tractor drawn ridger is
used for earthing-up of crop while the weeds growing
along the side and base of furrow are uprooted
and destroyed.
|
Mulching
- Reduces the growth of annual weeds in potato.
- It has a smoothering effect on weeds by excluding
the light from photosynthetic portions of plant and
thus helps in inhibiting the top growth.
- It also provides an effective barrier to weed emergence.
- In addition it helps to conserve moisture and maintain
temperatures which results quick in emergence of potato.
- Mulching can be done by the use of dry straw, grasses,
other plant parts, paper, plastic and polythene films.
- Mulch should be thick enough to prevent light penetration
/ transmission to suppress photosynthesis by weeds.
- The mulch of straw in potato should be all out 5-10
cm thick.
- Timely hoeing and weeding keeps the weed plants under
check.
- The potato crop develops crop canopy in about four
weeks after crop emergence and if the weeds are controlled
by this time, the crop gains a considerate competition
advantages.
- There is a need to avail full advantage of hoeing
and weeding and it should by followed immediately by
earthing-up.
Chemical methods of weed control
- Weed control through chemical results in better growth
of crop and often in improved yield of tubers than manual
and mechanical means.
- This is due to the elimination of mechanical damage
to the plants.
- Chemical weed control is quick, less laborious and
a large area can be covered in a short time.
- Besides, chemical weed control in seed productions
program is of great practical utility for the production
of healthy seed grade potato as it minimizes the spread
of mechanically transmitted viruses x and s by omitting
some of the cultural operations during the crop growth.
- Several herbicides have been recommended for weed
control in potato and these are used according to their
availability, cost, weed flora and the cropping pattern.
- The herbicides used in potato can be grouped in these
categories.
- Pre-planting application
- Pre-emergence application
- Post-emergence application
Chemical weed management practices of potato
Herbicides
|
Dose per hectare |
Time of Application
|
Stamp
30 EC (Pendimethalin) |
2.5 litres
|
Pre-emergence
application after the application of first irrigation. |
Tafazine
|
500 gm
|
- do
- |
Atrataf
|
500 gm
|
- do
- |
Sencor
|
1 kg
|
- do
- |
Lasso
/ Tok E-25 |
5 litre
|
- do
- |
Tok E-
25 / Lasso + Tafazine |
(2.5
litres + 250 g) |
Mixing
of two herbicides gives better weed control than their
individual applications. Apply this mixture as pre-
emergence after first irrigation. |
Stam
F-34 |
2.5 litres
|
When
weeds attain the height of 5-7 cm and then do the
spray. |
Gramaxone
|
1.25
- 2.0 litres |
When
tubers germination various from 5-10 percent and if
the weed population is less than 100 plants per sq
m. |
Note
- Normally these chemicals are applied using 500 litres
of water .
- But adjust the water quantity as per the type of sprayer
used to obtain equitable distribution of the spray.
- When potato is to be followed by cucurbits (musk melons,
beetle gourds), then don't use Tafazine weedicide as
this group has a long persistance period and these crops
could be injured if grown soon after potato.
Top
Efficient use of Herbicides
- Application time and method of application is very
important and determines the effectiveness of the chemical
applied. Therefore select the appropriate weed management
practice.
- Soil should be well prepared and brought to fine tilth
before spraying.
- Do not disturb the field after spray as the residual
effect would be reduce.
- Apply recommended dose of herbicides for effective
weed kill.
- Select the herbicides according to the weed problem.
- Volatile herbicides should be applied to the soil
before making ridges.
- Apply contact herbicides like Gramaxone (Paraquat)
only when weeds appear.
- Select a suitable sprayer for spray.
Top
Calibrations
- The application of herbicides at rates other than
the recommended levels proves either harmful or of little
use.
- Therefore calibration of the amount of herbicide,
water to be applied, the speed of walking, pressure
to be maintained etc. are very critical for obtaining
thorough weed-kill in the crop. Calibrations can be
done by using the following calculation.
Time Required
|
Total
distance travelled |
D metres
|
Time
taken for travelling the distance D m Walking speed
|
T minutes
(DxS)/T metres / minutes |
Swatch
of spray nozzle |
S metre
|
Area
covered in time T over distance D |
D x
S metre |
Time
required to spray 1 ha |
(10000xT)
/ (D x S) minutes |
Quantity of chemical solution
required
|
Amount
of solution discharged at the given pressure over
area DxS |
Y litre/
min. |
Rate
of discharge / m2 |
Y /
[D x S ] litres/m2 |
Amount
of solution required per ha at the given pressure
Y |
(Y
x 10000) / (D x S) m2 |
Since
1 ha = 10000 m2 |
Z litres
solution required per ha |
Calculation of herbicides for application
- The herbicides are available in the market under the
trade names and the recommendations are given as per
active ingredient (ai) per ha.
- Therefore it is necessary that the requirement of
commercial products is worked out. The following formula
is used for calculating the finally commercial product.
Weight of commercial product required
- (Weight of chemical to be applied/ha) / (percentage
of ai in commercial product) x 100
- This is equal to X gm or litre of commercial product.
- The X gm or litre the commercial product should be
dissolved in Z likes of water required / ha.
Agitation and avoidance of drift
- Settling of herbicides during application should be
prevented especially when suspension of wettable powders
is used to avoid the variation in concentration during
spraying.
- To avoid drift it is recommended to stop spraying
when the wind is too strong (more than 10 km/hr).
- For wind of 5-10 km/hr, the height of the nozzle should
remain constantly downwards and near to the ground throughout
spraying.
Top
Integrated Weed Management
- Integrated weed management approach involves the
reduction of weed infestation below the economic threshold
level by the judicious combination of all feasible means.
- Growing competitive crop of potato with appropriate
agronomic practices for rapid growth of potato plants,
practicing proper crop rotation, summer cultivation and
combination of cultural and chemical methods of weed control
are some of the practices which can be integrated to reduce
the weed infestation in potato crop.
- For best results, preference should be given to the
integrated weed management approach. It not only eliminates
the weed flora but also counts to be cheap and provides
regular workload to the farm labours.
|