Basically cotton is a drought resistant crop because of its
very deep root system.
Drought may occur at any time of the growth period, but the
timing and intensity of drought play an important role in cotton
production.
A moderate drought in the early season may some times be beneficial.
Drought at pre flowering stage has been some times observed to increase
subsequent rate of flowering and yield.
Drought during the early stages reduces the vegetative growth and
finally the yield.
Drought at reproductive stage results in square and boll drop because
it decreases the rate of photosynthesis and stimulates the ABA and Ethylene
production in young bolls.
Ameliorative Measures
Sowing of crop on ridges.
Cultivate drought resistant varieties.
Maintain optimum plant stand
Conserve soil moisture by soil mulching.
Conservation of plant water by the use of anti transparents.
Both under irrigated and/or rainfed conditions when cotton crop
is grown in vertisols, the problem of excess water leading to
water logged conditions are very common, in the beginning of the
crop season and during the crop growth period due to south west
monsoon rains.
Associated Problems
Continuous and/or intermittent rains may delay sowing due to excess
soil moisture conditions.
If rains are received immediately after sowing germination gets effected
due to anaerobic conditions - optimum plant stand could not be established.
Heavy weed infestation is the problem due to moist soil conditions
and mechanical/physical control measures could not be under taken
Excessive water stagnation in the field cause wilting of crop plants
which is otherwise called as physiological wilt due to anaerobic conditions
of soil.
Physiological wilt is caused due to retarding respiratory activity
by roots.
Management strategy
Layout the field into ridges and furrows and sow seed on ridges.
Provide channels across the ridges and furrows at intermittent intervals
to drain out excess water.
Weed control by chemicals by pre emergence application.
Moderately excess moisture conditions can be made good by application
of urea as top dressing immediately after stopage of rains.
When plants wilt due to excess soil moisture and lack of soil aeration.
Spraying of urea 2% or Multi K 2% or polyfeed 2% at 10 days intervals
an foliage helps the plants to require their turgidity.
Premature shedding of floral bud and young bolls is very serious
physiological problem hampering cotton production.
The cotton plant is able to produce only about one third of
its flowers into harvestable bolls
A general shedding of about 60% in the form of squares, 8 per
cent in the form of flowers and 5% in the form of bolls is common.
Physiological shedding of buds and bolls is much less than
the damage caused by insect pests.
The degree of shedding depends on environmental as well as
hereditary factors.
Squares are more sensitive than bolls to physiological injury
due to its complex growth pattern.
Causes for bud and boll shedding
Imbalance between source (Photosynthetic surface) and sink (flowers
and bolls).
Differences in photosynthetic efficiency
Poor drainage or flooding during or after flowering under excessive
moisture conditions, functional activities of roots are sufficiently
impaired.
Lack of aeration also adversely effects fruiting activity.
A decline in maximum relative humidity from 95 to 65% together with
a rise in maximum temperature from 87 to 95°F rapidly increases the
rate of boll shedding.
Zinc and Boron deficiency
Prolonged drought and moisture stress.
Insufficient soil moisture during reproductive growth in cotton promotes
bolls shedding.
Water stress during early flowering cause shedding of squares before
they are flowered while late stress at flowering reduces the rate of
flowering and boll retention.
High temperature during flowering and boll development. Around 38°
or above causes boll shedding.
Cloudy weather
Adequate sunlight is an important factor and an interruption in high
sunlight intensity accelerates boll shedding in cotton. Excessive shedding
of young bolls during rainy weather is a common experience.
Closer spacing
In a closely spaced crop of cotton reduction in light intensity below
the canopy causes boll shedding. This is more pronounced in varieties
with excessive leafiness and bushy growth.
Partial sterility of pollen or unsuccessive pollination.
Excessive application of Nitrogen favours vegetative growth and results
in more shedding of buds and bolls.
Insect or disease incidence
Heavy boll load (Cut out)
Availability of assimilates (source and sink relation)
Hormonal imbalance
Rate of production of auxins - provokes the formation of a thin abscission
layer across the peduncle of the bud or boll.
Mechanical injury.
Physiological reasons for boll shedding
Abscisic acid (ABA) is the major factor for boll shedding in cotton.
Boll shed is more when abscisic acid content is about 0.002 mg (effective
range).
Early shed of bolls occur after about 5th day of anthesis then (ABA)
concentration reaches effective range.
Other bolls shed after 6th - 8th or 10th day at the latest.
In retained bolls, the ABA concentration is much below the effective
range.
Differences in shedding of young bolls among varieties depends on
the level of endogenous abscisins, auxins, gibberellins and cytokinins
produced with in the boll.
Endogenous substances interact in the boll and form abscission layer.
Boll shedding in relation to flowering
Shedding of bolls was higher in a variety that produced large number
of flowers.
Yielding capacity of a cotton variety therefore can not be judged
by its profuse flowering.
Number of mature bolls retained at the end would be the correct measure
of productivity irrespective of the number of boll shed.
Management of cotton after severe square shed
Ascorbic acid (0.1 mm & 0.6 mm) and Napthalin Acetic acid (0.1 mm),
increased kapas yield eventhough there is no improvement in boll setting.
Maximum response was obtained when 5% sucrose was mixed with 0.6
mm AA or 0.1 mm NAA.
The pattern of boll shedding was shifted to higher nodes with these
treatments.
Responses of varieties to these growth regulators varied.
Spraying of AA @ 40 ppm, and/or CCC @ 250 ppm and micronutrients
viz., Zinc, Boron and Magnesium @ 10 ppm each gave good response.
Growth regulators were more effective under irrigated fertile conditions.
Under rainfed and low fertility conditions better response was observed
with Napthalin acetic acid (NAA).
Ikisan- Crisis Management In cotton- Red Leaf Disease of cotton
Red leaf in cotton
Reddening of leaves in cotton generally described as red leaf
disease, red blight and yellow-red disease.
The common symptoms are the rapid development of deep pink
to red colour in leaves which commences when the crop is at about
50 to 60 days.
This spreads rather rapid and is generally associated with infection
by jassids.
Barbadenses and Hirsutum varieties are mostly pre-disposed to this
physiological phenomenon.
The loss is severe if it occurs at early stages of growth.
Causes for Reddening
Nitrogen deficiency.
Water logging or water stress.
Drop in temperature below 21°C.
Symptoms and Biochemical changes due to reddening
The reddened leaves show low chlorophyll content with high anthocyanin
pigment.
Total Nitrogen, Magnesium and Zinc are generally low in leaves with
high level of calcium.
Low nitrogen, phosphorus, magnesium and Zinc and copper and high
amounts of potassium and calcium in the soil.
Magnesium deficiency is primarily associated with reddening.
Precautions and correction of deficiency
Optimum supply of nitrogen.
Sowing dates may be strictly adhered to avoid low night temperature
of less than 21°.
Water logging may be prevented, since this results is non availability
of Magnesium.
Application of Mg SO4 at 20-25 kg/ha to the soil or foliar spray
with 5 per cent MG SO4 and 1% urea as soon as the reddening symptoms
appear in leaf reduces this disorder.
Select a variety or hybrid recommended / suitable to soil and climate
of your region.
Test the seed for its germination percentage well in advance before
sowing.
Take up seed treatment as per recommendation as per the situation.
Ensure there should be sufficient moisture at sowing.
Sow HYV or hybrids preferably on ridges.
Deep sowing should be avoided (3 - 5 cm optimum depth).
For short duration varieties reduce spacing in between and within
rows (75 x 75cm2 or 90 x 90cm2) and for long duration varieties give
wider spacing between and within the rows (105 x 105cm2 or 120 x 120cm2)
Fill the gaps within ten days after sowing (grow cotton seedlings
in the polythene bags on the day of sowing - fill the gaps with these
plants to avoid age difference).
Inter cultivate 2-3 times with a blade harrow in between rows within
30 - 40 days after sowing (Rainfed cotton) helps in reduction of evaporation
losses and better infiltration of water into the soil (if there is rain)
since the soil is loose. In irrigated cotton after each top dressing
and irrigation, run the blade harrow between the rows of cotton.
Thin out excess seedlings at 20 days after seeding - keeping one
seedling per hill (Hybrids) and two seedlings per hill (varieties).
To avoid / reduce square and flower drop - spray NAA twice @ 1ml
/ 4lit of water at 45 and 65 DAS full coverage of squares and flowers.
Fertilize crop at
Nitrogen - 30, 60 and 90 days after sowing in equal splits (irrigated
cotton)
Phosphorus - Last ploughing
Potash - 30, 60 days after sowing in equal splits
Use only recommended doses of fertilizers, pesticides and other chemicals
if any at right time in right method.
Placement / pocketing of fertilizer at 7 - 10cm away from plant at
7 - 10cm depth.
If Nitrogen deficiency is seen in standing crop spray 2% urea twice.
If Magnesium deficiency is observed spray 1% MgSo4 (10g of MgSo4
in one litre of water) at 45 and 75 days after sowing.
If Zinc deficiency is seen apply 50kg ZnSo4 in the last ploughing.
If soil application could not be taken up spray 0.2% ZnSo4 (2g of ZnSo4
in one litre of water) twice at an interval of 4 - 5 days.
If boron deficiency is observed spray 0.1% (1g of Boric acid in one
litre of water) at 60 and 90 days after sowing.
Schedule the irrigation promptly.
Avoid excess irrigation.
Sufficient soil moisture should be there at the time of top dressing
of N fertilizer.
Careful monitoring of crop for pest/disease incidence.
Take appropriate plant protection measures.
Save first flowering at any cost - otherwise-excess vegetative growth
leads to reduction in yield.
Spray pesticides on bottom of the leaves for sucking pests
Spray pesticides on flower, fruits and vegetation in case of borers.
Use pyrethroids only under extra - ordinary conditions only once
or twice during crop period.
Use of alternate methods (BT, PV, Chrysopa, Trichogramma & Neem products)
instead of insecticide use when ETL level is reached.
Use of Neem products and Endosulphan initially when insecticide use
is warranted. Both are relatively safer to natural enemies.
Top the plant to arrest excess growth after putting 15 - 16 sympodial
branches for every plant.
Quality of first two pickings is high - keep the produce separately
for higher price.
Do not mix undeveloped lint, insect or disease damaged lint or spoiled
lint with quality lint.
Remove cotton stubble's after last picking. Defoliants like Dropp
@ 150 - 200 g / ha in 600 lit of water applied at boll bursting stage
hastens the maturity of cotton and vacation of fields 12 - 15 days earlier
for double cropping under irrigated conditions.
Crisis Management
