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Saturday, August 22, 2009

Pests of Fibre Crops

Cotton (Gossypium hirsutum, G. herbaceum, G. barbadense and G. arboreum)



1. Cotton aphid Aphis gossypii Glover (Aphididae: Homoptera)

Distribution: It has a world wide distribution. It also attacks Lady’s finger, brinjal, guava, gingelly etc.

Nature of damage: The greenish brown soft bodied small aphids infest the tender shoots and the under surface of leaves in very large numbers and suck the sap. Severe infestation results in curling of leaves, stunted growth and gradual drying and death of young plants. Black sooty mould develops on the honey dew of the aphids which falls on the lower leaves affecting photosynthetic activity. The Economic Threshold Level (ETL) is 10% affected plants counted randomly.

Life history: The alate as well as apterous females multiply parthenogenetically and viviparously. In a day a female may give birth to 8 – 22 nymphs which become adults in 7 – 9 days.

Management strategies:(i) Spray application of dimethoate 0.03 % or methyl demeton 0.025 % or monocrotophos 0.04 % or imidacloprid 0.01 % affords protection.
(ii) Include also imidacloprid seed treatment for sucking pests @ 3 – 5g /kg seed that protects the crop around 30 – 45 days or so.

2. Cotton leaf hopper Amrasca biguttula biguttula Ishida (Cicadellidae: Homoptera)



Distribution: It is distributed in all cotton growing areas. It is also found to breed on brinjal, potato, lady’s finger and sunflower.

Nature of damage: Both the nymphs and adults suck up the plant sap from the under surface of leaves. The leaves show symptoms of “hopper burn” such as yellowing, curling, bronzing and sometimes drying up, and these symptoms are expressed differently depending on how the different varieties react to the toxic saliva of the insect. The vigour of the plants is impaired to a great extent. The ETL is 2 Jassids or nymphs per leaf or yellowing in the margins of the leaves.

Life history: The female leaf hopper inserts about 15 eggs inside leaf veins and the incubation period ranges from 4 to 11 days. The nymphal period occupies 7 - 21 days depending on the weather conditions.

Management strategies:
(i) Spray application of dimethoate 0.03 % or methyl demeton 0.025 % or monocrotophos 0.04 % or imidacloprid 0.01 % affords protection.
(ii) Include also imidacloprid seed treatment for sucking pests @ 3 – 5g /kg seed that protects the crop around 30 – 45 days or so.

3. Cotton whitefly Bemisia tabaci (Gennadius) (Aleyrodidae: Homoptera)



Distribution: It is widely distributed in India and particularly serious on cotton and brinjal. It is very important as a vector of leaf curl virus disease of crops like tobacco, cotton, etc. and vein clearing disease of lady’s finger. It also breeds on a variety of plants such as hollyhock, lady’s finger, tobacco, safflower, Achyranthes aspera, Lab – lab niger, topioca.

Nature of damage: In cotton the nymphs are found in large numbers on the under surface of leaves and drain of sap due to sucking. Severe infestation results in premature defoliation, development of sooty mould on honey dew excreted, and shedding of buds and bolls and bad boll opening. The ETL is 5- 10 nymphs or adults per leaf before 9 A.M.

Life history: The female whitefly lays the eggs on the under surface of tender leaves. The egg and nymphal periods occupy respectively 3 - 5 and 9 - 14 days during summer and 5 - 33 and 17 - 73 days in winter. The pupal period is 2 - 8 days. The total life-cycle ranges from 14 - 107 days depending upon the weather conditions.

Management strategies:
(i) Spray application of acephate 0.075 % or imidacloprid 0.01 % or acetamiprid 0.01% or neem oil 0.3 % brings about control of the pest.

4. Spotted bollworms Earias insulana Boisd. and E. vittella (Noctuidae : Lepidoptera)



Distribution: Widely distributed in India, Myanmar. It is also found to attack Bhindi.

Nature of damage: The initial infestation takes place on 6 week old crop in which the larva causes detopping (drooping and drying of the shoot) due to its feeding by boring into it. In the later stages of the crop, the buds, flowers and bolls are damaged and a larva may migrate and attack fresh parts. Heavy shedding of early formed flower buds due to the pest is a common feature in cotton fields. The lint from attacked bolls will not be clean. The ETL for this pest is 5% damaged fruiting bodies or 1 larva per plant or total 3 damaged squares / plant taken from 20 randomly selected plants.

Life history: The moth of E. vittella has green fore wings with a white streak on each of them whereas that of E. insulana is completely green. The female moth deposits 2 or 3 eggs on bracts, leaf axils and veins on the under surface of leaf. The egg is crown-shaped, sculptured and deep sky blue in colour. A female may lay about 385 eggs and the incubation period is about 3 days. The larva becomes full grown in 10 – 12 days. The larva of E. vittella is brownish with a longitudinal white stripe on the dorsal side and without finger-shaped processes on its cream coloured body and orange dots on prothroax. The boat shaped tough silken cocoon is dirty white brownish and may be found on plants or on fallen buds and bolls. The pupal period is 7 – 10 days. The total life cycle ranges from 20 to 22 days.

Management strategies:
(i) The infested portions as well as shed buds and bolls should be removed and destroyed.
(ii) Periodical spray application of compounds like phosalone 35 EC @ 1.5 to 2.5 l/ha or carbaryl 50 WP @ 2.5 to 3.0 kg./ha or endosulfan 35 EC @ 1.5 to 2.0 l/ha or monocrotophos 40 SC @ 1.0 to 1.25 l/ha or profenofos 50 EC@ 0.75 to 1.0 kg /ha or thiodicarb 75 WP@ 625 g/ha etc. has been reported to be effective.
(ii) The synthetic pyrethroids fenvalerate and permethrin @ 100 - 150 g a.i./ha, cypermethrin @ 80 g a.i./ha, and deltamethrin @ 12.5 to 15 g a.i./ha are very effective in controlling the bollworms of cotton which may be alternated with other groups of insecticides.

5. Pink bollworm Pectinophora gossypiella Saund. (Gelechiidae: Lepidoptera)



Distribution: This is a well known pest of cotton found distributed all over the world. Alternate host plants of this pest are Lady’s finger, hollyhock and Thespesia populnea, etc.
Nature of damage: The larva enters the developing boll through the tip portion and the entrance hole gets closed up as the boll matures. It feeds on the seeds and moves to adjacent locule by making a hole through the septum. The infested flower buds shed prematurely. A typical rosette-shaped bloom when examined will contain the larva. The infestation results in the seeds being destroyed in addition to retardation of lint development and weakened lint and staining of the lint both inside the boll and in the gin. Further, infested bolls open prematurely and expose it to invasion by saprophytic fungi. The seeds from damaged bolls show lower germination. The infestation ranges from 40 to 85 %. The ETL for pink bollworm is 8 months / trap per day for 3 consecutive days and the traps are to be installed @ 5/ha. or 10% infested flowers or bolls with live larvae.
Life history: The adult is a small dark brown moth and a female lays flattened and striated eggs on the bolls or in between bracts or on buds and flowers, the average being 125 eggs. The egg period varies from 4 - 25 days. The 15 mm long pinkish larva with dark brown head and prothoracic shield becomes full grown in 25 - 35 days and pupates in a thin silken cocoon among the lint, inside a seed or in double seeds, in between bracts or in cracks in the soil. The pupal period is about 6 – 20 days. Both short – cycle larvae and long-cycle larvae occur in Northern India and hibernation during winter takes place in the larval stage. In South India the insect is not known to hibernate in any stage of its development.

Management strategies:
(i) Need based spray application of carbaryl 50 WP @ 2.5 kg/ha or quinalphos 25 EC @ 2 - 3 l/ha or profenofos 50 EC @ 1.5 - 2 l/ha based on ETL.
(ii) Fumigation of seeds with methyl bromide at 1.5 kg/100 cu. m. for 24 hours or with aluminum phosphide at 18 tablets/100 cu. m. or heat treatment for a few minutes at 60°C kills hibernating larvae in seeds.

B. Jute (Corchorus olitorius & C. capsularis)

1. Stem girdling beetle Nupserha bicolor postbrunnea (Lamiidae: Coleoptera)

Distribution: Corchorus olitorius and C. capsularis are the two species of Jute cultivated in Assam, West Bengal, Orissa, Tripura and Uttar Pradesh which are attacked by this pest. It is particularly serious on C. olitorius.

Nature of damage: The adult beetle girdles the stem at two levels before it starts oviposition. This causes withering, drooping and death of the portion above the lower girdle to a length varying from 5 - 50 cm thus resulting in loss of fibre yield.

Management strategies:
(i) Spray application of phosalone 0.07% or endosulfan 0.07 % at fortnightly interval.
(ii) Removal and destruction of drooping stem portions and stem casings containing the larvae in diapause.
(iii) Growing of C. capsularis jute which is not preferred by the insect.

2. Jute weevil Apion corchori Mshll. (Apionidae: Coleoptera)

Distribution: The insect occurs in a serious form on jute in Bihar and U.P.

Nature of damage: The adult weevil excavates a small hole on the stem and oviposits. The grubs tunnel into the pith. Due to damage a gall-like swelling is formed. C. capsularis is more susceptible to attack than C. olitorius.

Life history: The weevil is dull black or dark brown in colour and a female is capable of laying up to 675 eggs during an oviposition period of about 4 months. The egg, larval and pupal periods last for 3 – 5, 8 – 18 and 4 days respectively.

Management strategies:
(i) Spray application of phosalone 0.07% or endosulfan 0.07 or cypermethrin 0.005%.

3. Spodoptera exigua (Noctuidae: Lepidoptera)

Distribution: Has worldwide distribution which includes Europe, South Africa, America and the oriental region. In India, it is quite widespread, found attacking jute, indigo, Lucerne, lentil, cabbage, maize, cotton and gram.

Nature of damage: The caterpillars, on hatching, gather on the leaf surface, the epidermis of which they eat. At this young stage, they are also in the habit of webbing together either several leaflets or the margin of the same large leaf. At times, these webs give a shabby look to the crop. Within these webs the young larvae live gregariously only for two or three days and thereafter they separate and spread out.
The feeding activity of grown up larva is generally confined to a few morning hours i.e. 9 to 11 a.m. and then again after 4 p.m. or so. They are very voracious and quite large patches of foliages are quickly stripped.

Life history: The adult lays eggs on leaves in clusters of up to 200 eggs each. Each egg is spherical like a poppy-seed in shape and size but with radiating lines. These egg-clusters are often covered with buff-coloured hair which are also present in-between the eggs. The egg-period ranges between 24 - 36 hours. The adult stage is a typical small noctuid moth with dark –spotted forewings and white hind wings. The colour of the larva is very variable, depending on the crop on which it has been feeding. When full-grown and full fed the caterpillar seeks shelter usually on the soil surface at the base of the plant, under stones or among leaves and such other debris. Also when necessary, a small amount of webbing is produced as a covering and a very rough cocoon is formed with bits of leaf and other material. The larval period is completed in 12 – 14 days. Inside this cocoon the larva pupates and the chrysalis is of the usual noctuid type with a double spine at the tip of the abdomen. The pupal period may be as short as five days and the whole life-cycle can be completed in less than three weeks. But the life-cycle can be very much lengthened, depending upon the environmental temperature and humidity.

Management strategies:
(i) Collection and destruction of egg masses.
(ii) Spray application of phosalone 0.07% or endosulfan 0.07% or cypermethrin 0.005%.

(Compiled by Harsh saxena)

 
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