SOIL PESTS                    1. Cut worms (Lepidoptera:  Noctuidae)                 BACK

2. White Grub (Coleoptera: Scarabaeidae)

Species complex

1.      Brahmina coriacea

2.      Brahmina cirnicollis

3.      Brahmina flavoserica

4.      Melolontha indica

5.      M. furicauda

6.      Holotrichia longipenis

7.      H. repitita

8.      H. rustica

9.      H. serrata

10.  H. conferata

11.  H. excise

12.  H. nototiocollis

13.  Anomala dimidiate

14.  A. lineatopennis

15.  A. polita

16.  A. rugusa

17.  A. rufiventis

18.  A. communis

19.  A. nathani

20.  Xylotrupes Gideon

21.  Phyllognathus Dionysius

22.  Lepidiota stigma

            B. coriacea                                B. flavoserica                H. longipennis                B. crinicollis                                A. lineatopennis                    A. lineatopennis                                            Lepidiota stigma

Distribution: Cosmopolitan in distribution

Host range:

Polyphagous, damage almost all the vegetable crops, pulses, oilseeds, cereals, millets, potato, tobacco, sorghum, groundnut, maize, soybean, chillies, ornamental plants, forest nurseries, etc.

Nature of damage and symptoms:

• The damage to potato is caused only by the grubs which feed on rootlets, roots and tubers. The first stage grub can survive on the organic matter present in the soil but roots are preferred as and when encountered.
• Older second instar and third instar grubs are more damaging, which make large, shallow and circular holes on tubers.
• Potato grown during summer as rainfed is prone to attack by these grubs.
• Due to concealed feeding white grubs generally remain unnoticed and at harvest a large number of tubers are found infested/damaged.
• Sometimes up to 80 % of the crop may be lost.
• Adult beetles feed on the foliage of many trees

                White grub damaged tuber and roots                                         Holes on damaged tubers

Identification:

• Freshly laid eggs are creamy white which turns dirty white before hatching.
• Full grown grubs are 35-38 mm in length and often coil to “C” shape when disturbed.
• Fully grown grub makes an earthen cocoon and changes to pupa.
• Beetles are of different colours.

C- shaped white grubs                            Pupa inside earthen cocoon

Figure. Identifying features of adult beetle.

Life cycle:

• Each female lays 4-40 eggs singly (in 2-7 installments) in soil in its life span. Incubation period is 7-12 days (Fig below).
• There are three larval instars.
• The duration of respective instars is about 20, 30 and 75 day.
• Total larval duration is about 125 days.
• Pupal period ranges from 12-20 days.
• Adult longevity ranges between 15 - 145 days.
• Overwintering as grub in earthen cells (Fig below).
• There is only one generation in a year. Optimum conditions for white grub growth and damage humid and wet climate with a temperature range of 20- 32ºC with a relative humidity of more than 70 per cent.

                                                        Figure. Life cycle of white grubs.

                Figure. Seasonal activity pattern (life cycle) of white grubs.

Management:

Bird predation after ploughing

·         Two to three deep ploughings immediately after harvest or before potato planting, to expose the resting stages to birds or other natural enemies.

·         Collection and destruction of grubs from soil while ploughing.

·         Collect/trap adult beetles via light traps during May-June at night and kill them.

·         The beetles can also be collected by shaking or jerking the host plants during night. The fallen beetles should be collected and destroyed by putting them either in kerosinized water or by burning.

·         Application of well rotten FYM only. The use of nitrogenous fertilizers, especially ammonia and urea, at higher doses kill the first instar grubs.

·         Removal of weeds from crop vicinity. The host trees (Rubinia, Polygonum, Kaithe and temperate fruit crops) of adults (beetles) should be lopped or pruned.

·         Seed potatoes should be planted little deep (8-10 cm) instead of normal depth (6 cm).

·         Cattle urine extracts of botanicals like Melia, Urtica dioca, Nerium, Eucalyptus etc. @5 % provides good control against white grubs if applied well in time (during sowing, earthing up and tuber formation stage).

·         Spraying the crop and ridges with this biopesticide Bacillus thuringiensis (Bt @ 10⁹ spores/ml) gives a good control. Several strains of the bacterium, Bacillus popilliae, have been found that attack white grubs.

·         Application of Entomogenous fungus, Metarrhizium anisopliae Meld, Beauveria bassiana and B. brongniartii Sacc. @ 5gm/lit of water. 

·         Conservation of the existing populations of natural enemies or by introducing and establishing the known bio-control agents obtained from new localities.

·         Application of Phorate 10G (10-15 kg/ha) near plant base at the time of earthing up or drenching of ridges with Chlorpyriphos 20 EC @ 2.5L/lit when 2% plant damage is noticed or when adult beetles appears.

·         Spray host trees with Chlorpyriphos 20 EC @ 2.5 ml/lit of water immediately after first monsoon shower.

·         Potato crop should be harvested immediately after required maturity i.e. by September. Crop left beyond September suffers more.

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