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Control of insect pests

Pests in tobacco nursery

Before sowing seed beds, chloropyrifos 1.5% dust is mixed @ 40 gm per 10 sq. m. bed in the top soil to prevent damage to seeds and tiny seedlings from soil pests like ants, mole crickets, earthworms etc.

The pests that infest in the nursery are

(1) Caterpillars and Cut-worms (2) Stem borer (3) Grass-hoppers and (4) Whitefly

Caterpillars & Cutworms

Four species of Caterpillars viz., Spodoptera litura F., Laphygma exigua HB., Agrotis ypsilon Rott. and Plusia signata F. are known to infest tobacco nurseries. Of these 4 species Spodoptera litura F. commonly known as tobacco caterpillar is the most important pest.

Tobacco Caterpillar : Spodoptera litura F

The young caterpillars are light green with black head or black spots and mine on the leaf tissues. The well grown caterpillars are grey or dark brown with `V' shaped white mark on the front portion of the black head. They feed voraciously along the veins of leaves and also cut the stems of small and tender seedlings. Hence they are also known as cut worms. There will be about 80 to 100% loss due to this pest.

Control Measures

For preparing 10 litres of 1% NSKS 100 gm of neem seed kernel powder is taken and placed in a small muslin cloth bag.

The bag is dipped in a bucket (or any vessel) containing 10 litres of water and the bag is squeezed for 15 minutes to obtain a light brownish liquid. This suspension can be directly sprayed on tobacco seedlings.

For preparing 2% NSKS of 10 litres, 200 gm of neem seed kernel powder is to be taken and prepared as above.

Spraying 50 litres of 1% NSKS on 3 week old seedlings and 60 litres of 2% NSKS on 4 week old seedlings or 1125 litres of nuclear polyhedrosis virus (NPV) solution prepared by 250 NPV infected larva by mixing with 250 g rice powder or starch powder during evening times or Bacillus thuringiensis var. kurstaki @ 1.0 kg in 1125 litres of water per hectare controls the pest.

If the number of seedlings damaged by Spodoptera exceeds 6 per sq.m. area spraying any one of the following insecticides from 4 weeks onwards is recommended.

(a) Emamectin benzoate 5 SG @ 5 g in 10 litres of water

(b) Novaluron 10 EC @ 10 ml in 10 litres of water.

During cyclonic weather, tobacco caterpillar, S. litura can also be controlled by putting jaggery and rice bran baits. This is prepared by dissolving 6.25 kg jaggery in 12.5 litres of water and adding to this chlorpyriphos 20% 2 litres. To this 25 kg rice bran is slowly added by mixing it thoroughly with a smooth stick so that the bait is made into small balls. The bait is broadcasted on the nursery beds during evening hours to effectively control the caterpillars.

The other 3 species of caterpillars viz., (1) green caterpillar, L. exigua (2) green looper P. signata and (3) black caterpillar, A. ypsilon that sometimes infest the tobacco nurseries can also be controlled by spraying any one of the above insecticides.

Stem borer

The stem borer is the larva of a tiny brown moth called Scrobipalpa (Gnorimoschema) heliopa Low. The tiny caterpillars bore inside the stem and midribs and feed on internal tissues. As a result swelling appears where the borer stays. It causes stunting and unusual branching of the seedlings. It affects the nursery mostly. At times the planted crop is also affected by this.

Control Measures

Whitefly: Bemisia tabaci Gennadius

White flies are small fly like insects seen on the underside of leaves. They will fly immediately when the plant is disturbed. The adult fly sucks the sap from leaves and transmits the leaf curl virus disease from infected to healthy seedlings.

Control Measures

PESTS IN THE PLANTED CROP

The major pests that affect tobacco crop in the field are whitefly, leaf eating caterpillars, tobacco aphid/green peach aphid and capsule borer. Control measures for these major pests are detailed below.

Leaf eating caterpillar : Spodoptera litura F.

In the field crop the pest incidence is generally confined to few border rows. The female moth lays about 2000 eggs on the under side of the leaves in bunches. After 2-3 days of incubation light green tiny caterpillars with black head emerge in hundreds. They eat the green matter of the leaf and turn to grey or dark grey or black in colour. The grown up larva feed voraciously on the tobacco leaf making lot of holes on the leaf causing damage to an extent of 10 to 15%.

Ten pheromone traps per ha are installed 20 days after planting. The leaf is critically examined for egg masses and tiny caterpillars which are later collected and destroyed. If the infestation is severe, the hot spots are sprayed thoroughly with 0.5% neem seed kernel suspension or nuclear polyhedrosis virus 250 LE in 1125 litres of water per ha by mixing with 250g rice powder or starch powder or any one of the following insecticides.

a. Emamectin benzoate 5 SG @ 5 g in 10 litres of water.

b. Novaluron 10 EC @ 10 ml in 10 litres of water

Whitefly : Bemisia tabaci Gennadius

These tiny white flies cause leaf curl disease. The leaves of curled plants are twisted, puckered and thickened with abnormally prominent veins. The plants show stunted growth and the yields are reduced.

Control Measures

Spraying is done preferably in the evening hours (4 to 6 pm) with high volume sprayers ensuring that the both sides of leaves are covered. Further, the spraying schedule has to be adopted by all the tobacco farming community in the endemic area. Spraying should be given 10 days after planting.

Tobacco aphid : Myzus nicotianae Blackman

Green peach aphid: Myzus persicae Sulz:

Aphids are louse like insects which are green or pinkish to brown in colour. In case of heavy infestation hundreds of them can be seen on the underside of leaves. By constantly sucking the sap from leaves they make the plant pale and sickly and thereby retard the growth. They secrete sugary juice known as `honey dew' on the leaves due to which sooty mould develops rendering the leaves unfit for curing. In addition they also transmit virus diseases like rosette or bushy top.

Control Measures

During early winter, for control of aphids when 2% of the plants are infected, any one of the following insecticides is sprayed once.

or

If the infestation is observed later, spraying is taken up only on the infested plants. Subsequently spraying is done only on aphid infested plants once in 8-10 days. A gap of one week is left between spray and harvesting of leaf to avoid excess pesticide residues in cured leaf. If more than one spray is required the insecticide is changed. Spraying is to be done preferably in the evening hours.

Capsule borer : Heliothis armigera Hb

The larvae of this species are greenish or pale brown with broken dark-brown stripes along the body. They bore the capsules and feed on the seeds inside. They feed on top leaves also when the infestation is heavy.

The incidence of capsule borer is observed after December under favourable conditions, preferably after heavy rains in untopped fields. The incidence is seen from 30 days after planting. Generally one larva is seen on the terminal bud. From 30 - 50 days it feeds on the terminal bud and then on the young leaves and causes loss to the crop. More than one borer per plant are seen after the flowering and then it feeds on the developing seed of the capsules.

 

Control measures

Care to be taken while using pesticides

There are strict regulations regarding the pesticide residues in tobacco through out the world. The residues must be within the prescribed limit. In all the tobacco growing countries DDT and other chlorinated hydrocarbon pesticides (except endosulphan) are banned for use on tobacco. Pesticides should not be used indiscriminately. The following are the recommended and banned pesticides on tobacco.

 

Pesticides recommended                             Pesticides not to be used

   Emamectin benzoate                                           Monocrotophos

   Imidacloprid                                                           Dimethoate

  Thiamethoxam                                                       Quinolphas

  Flubendiamide                                                       Phosphomidon

  Neem seed kernel suspension                         Dieldrin

  Pongamia cake powder                                       DDT, Oxydemeton-methyl

  Neem cake powder                                               Profenophos

  Nuclear polyhedrosis virussolution                   Parathion dust, BHC or lindane

  Bacillus thuringiensis var. kurstaki                    Paramar dust, Ekalox dust etc.