Pest Management

The bollworms cause damage by feeding on the bolls of the cotton crop. The damaging stage is the larval stage.

Fig. 1: General life cycle of cotton bollworms

1) Red Bollworms
Description: The eggs are blue when freshly laid and later turn to grey when approaching hatching. They are laid on all parts of the plant and often in obscure sites.

Damage: The larvae feed only on cotton and will attack all development stages of the boll,

Control: carbaryl, cartep, Larvin and synthetic pyrethroids. Karate, Fenvelerate

2) Heliothis bollworm (Helicoverpa armigera)
Description: The freshly laid eggs are a whitish-yellow colour (off white colour). Are generally laid on the upper half of the plant.

Damage: Larvae feed on buds, flowers and young bolls
One larvae can damage about 12 bolls during its life cycle.

Larvin, Karate, fenvelerate,

3) Spiny bollworm
Description: The eggs are very small and green and difficult to see on the crop.
The caterpillars are spindle shaped greeny-brown with long spines on each segment.

Damage: The larva feeds on a wide range of malvaceous plants, including Hibiscus, and is found inside growing points, buds, flowers and young bolls of the cotton plant.
Control: carbaryl, karate, fenvelerate, larvin

4) Pink bollworm.
Description: The eggs are very small and are laid between the boll and bracts which surround the boll. The hatched larvae immediately bore straight into the boll and spend their entire life in that boll.
Damage: A damaged boll often may not show any external damage signs. Because the egg and larvae control is not effective after a crop has been infested.
Control: The best control is to ensure a ‘closed season’. This period is when no living cotton plants are allowed for at least 66 days. The closed season is implemented by legal cotton destruction and planting dates.

Sucking pests
1. Jassids
Description: Wedge shaped (or boat shaped) yellowish green, fast moving insects found on the underside of the leaves.
Damage: Jassids prefer smooth-leafed varieties because hairy-leaves give mechanical resistance to jassid attack.

Threshold: 36 on all hairy varieties (all current commercial varieties are hairy); 24 on smooth varieties.
Control: carbaryl, cypemethrin, dimethoate, fenvalerate, karate, carbofuran, deltamethrin, larvin
2. Aphids
Description: Aphids are usually found on the underside of leaves and on the soft growing points of the plant.
Damage: Aphids feed on growing tissues by sucking sap from the plant.
Control: Foliar insecticides – acetamiprid, marshal/carbosulfan, dimethoate, carbofuran,
3. Whitefly
Description: The adults are minute, white in colour and appear in large numbers. The scale-like nymphs are more difficult to see.
Damage: These nymphs secrete a sticky honey-dew which provides a substrate for black sooty mould and if this develops on open cotton, the grade will be adversely affected.
Control: acetamiprid, imidacloprid, dimethoate, fipronil, diafenthiuron, cypermethrin
4. Lygus
Description: The lygus is a small, active green-brown bug which is difficult to see. Only the damage signs are seen.
Damage: These are a characteristic tattering of the leaves or the rapid shedding of new buds, leading to abnormal vegetative growth with short fruiting branches.

Plate: Characteristic leaf tattering caused by lygus
Control: dimethoate
5. Cotton stainers
Description: Cotton stainers are easily recognized by their markings, which are red and black when they are adults, and bright orange red when they are first hatched.
Damage: Stainers feed on the seed both in developing and developed bolls.
Control: carbaryl, cypermethrin, deltamethrin, dimethoate, fenvalerate, karate, triazophos, cyfluthrin, bifenthrin
6. Red Spider mite
Description: Only the adult female mites are readily visible to the naked eye. These appear as reddish brown dots, about the size of a pin head, on the underside of leaves. .

Damage: The pest is very destructive under hot and dry conditions. The mites suck sap from the underside of the leaf at the points where the main veins of the leaf join.
Control: amitraz, tetradifon, hostathion, dimethoate, dicofol, profenofos, propargite

7. Mealy Bug
Description: Mealy bugs are cottony white, fluffy, scale like insect, known to damage the plants by sucking cell sap.

Damage: Feed on plant sap, normally in roots or other crevices. Severe infestation resulted in stunted growth, premature leaf fall, incomplete opening of bolls and reduction in fibre quality.

Control: Field sanitation, destruction of cotton stalks, minimize movement from infested fields to healthy fields, drench ant colonies with chlorpyriphos. Chemical control: cabaryl, malathion, larvin, profenofos etc.

Pesticide application rates, spray volumes and other specifications

Table : Recommended insecticide and acaricide application rates per hactare.

Amount of pesticide application /ha
Pesticide Unit Plants up to 0.4 m Plants 0.4-0.9 m Plants Over 0.9 m
Carbaryl G 390 785 1 175
Thionex 50EC ml 475 950 1430
Larvin 37. 5% FW ml 365 735 1 100
Talstar 10% E.C. ml ** 200 300
All other pyrethroids ml ** 135 200
Dimethoate 40% ml 85 165 250
Goneton 10% EC ml 70 140 280
Pirimor 50% DG G 40 80 160
Hostathion 40% EC ml 120 235 350
Curacron 50% E.C. ml 135 265 400
Cartep 500SP G
Nuvacron or azodrin 40% EC ml 170 335 500
Tedion 8% El ml 400 800 1 200
Mitac 20% ml 500 1000 1 500

A. To mix one litre of spray make up the quantities of chemical and molasses shown to 1 litre with water. B. Spray Volume
Volume of mixtures shown in column A to be applied.
Pesticides Pesticide Molasses
ml Litres per hectare
Plants up to 0.4 m Plants up to 0.4 – 0.9 m Plants over 0.9 m
Carbaryl 85% WP 215 200 1.7 3.3 5.0
Thionex 35EC 285ml 250 1.7 3.3 5.0
Larvin 37.5% FW 210ml 175 1.7 3.3 5.0
*Agrithrin 20% E.C. 40ml 350 – 3.3 5.0
*Karate 5% E.C. 40ml 350 – 3.3 5.0
*Mavrik 25EC 40ml 350 – 3.3 5.0
*Talstar 10% E.C. 60ml 350 – 3.3 5.0
Dimethoate 40% E.C 50ml 350 1.7 3.3 5.0
Hostathion 40% E.C. 70ml 350 1.7 3.3 5.0
Curacron 50% E.C. 80ml 350 1.7 3.3 5.0
Tedion 8% E.C. 240ml 250 1.7 3.3 5.0
*these chemicals must not be applied to cotton before 25th December or after 1st March in S.E. Lowveld or before 1st February in the remainder of the country. Plants should, therefore, be more than 0.4m tall by these dates.