WHITE GRUBS IN SUGARCANE

Prelude

Sugarcane crop is affected by several spe-cies of Scarabaeid beetle grubs. The economi-cally important major species occurring in IndiCtare Holotrichia consanguinea Blanch in Bihar,Uttar Pradesh and Rajasthan, H. serrata in UttarPradesh, Karnataka, Tamil Nadu and Maharash-tra and Leucopholis lepidophora Brum, inMaharashtra. The adults of these species feedon host tree foliage like neem, Ailanthus sp. andAcacia sp. The grubs of these beetles feed onroots and underground portion of cane causingdrying of clumps or entire crop in a field depend-ing on the population of grubs present.

Nature of injury

The beetles emerging from pupae remaininactive in the soil till the first heavy summerrain in April, by which time their reproductivesystems fully mature. These beetles on emer-gence during nights congregate on their foodtrees and feed on the newly emerging leaves. Atday break, they move back to the soil and layeggs. The first instar grubs on hatching fromthese eggs feed on organic matter in the soil andon small roots of grasses or other plants. Thesecond and third instar grubs feed voraciously onthe roots and underground portion of canecausing drying of clumps. Visible symptom ofdamage is expressed only when sufficient damagehas been done to the roots and undergroundportion of cane. The cane leaves in a clump, apart of the row or a patch of field show yellowingand drying and ultimately all canes dry inaffected regions. The affected clumps can bepulled out without much effort and grown upgrubs can be seen below the clumps.

Losses

Generally the damage by the grubs tosugarcane crop is in patches but the loss canbe as high as 80-100 per cent during epidemics,when the entire crop in a field is affected.

Life cycle

Most species of white grub beetles haveone year life cycle with egg, three larval instarsand a pupal stage. In H. consanguinea, H.serrata and L. lepidophora, the egg period variesfrom 8-30 days, larval period from 56-292 daysand pupal period 10-35 days. The maximumdevelopmental period is required by L. lepido-phora. The total life cycle is completed within

96-357 days. Though pupation takes place byabout October-November, the beetle emer-gence occurs only after the next first heavy summershowers.

Factors influencing pest build up

Deforestation has forced these forest dwell-ing insects to migrate to cultivated crops. Thegrubs are polyphagous and have a wide adapta-bility to different host plants and can survive ongrass roots as well. Availability of adequatemoisture and abundant roots in sugarcane for along time, tend to increase white grub build upmarkedly. Presence of. host food trees for adultfeeding around the cultivated fields, further facili-tates the pest build up. Though the attack issevere in moist sandy soils, these grubs canthrive in clayey as well as black cotton soils.They can withstand drought by remaining inearthern cells for about 100 days in first instarand upto 112 days 'in grown up stages. Highmoisture and waterlogged conditions are detri-mental to the grubs. Heavy rains force the grubsto come to the surface of soil.

Natural enemies

The grubs of H. consanguinea and H. ser-rata are parasitized by two Scoliid parasites,Campsomeris collaris F. and Scalia aurepennisLep.

The grubs, pupae and adults are predatedupon by the common crow (Corvus splendensVeill), mynah (Acridotheres tristis W) and thesparrow (Passer domesticus Linn.), when theseare exposed at the time of ploughing. Thebeetles are predated at night by the Indian hoopoe(Upupa indica Nivah) and the toad (Buto mela-nostictus Schn.) feeds on grubs and adults. Thecarabid beetle (AnthiCisexguttata Ho.) feeds onthe beetles of Holotrichia sp. and the carabid,Pheropsophus sobrinus Dej. feeds on the grubs.

Pathogens affecting the beetles are, thegreen muscardine fungus (Metarhizium anisop-liae Metch.),two white muscardinefungii, Beauveriabassiana (Sals.) Vuill., and B. brongniartii (Sacc.).The milky disease bacterium, Bacillus popilliaeDutky occurs naturally on grubs. A nematodebelonging to Rhabditis sp. parasitizes the eggsand first instar grubs.

Control

Mechanical: Large scale collection of beetlesmay be done from their food trees at nightswith the help of bright torches immediately after

first summer showers on a compaign basis forabout 15 days. The beetles thus collected maybe destroyed in kerosinated water.

Cultural: Frequent ploughing of affectedfields to expose grubs and pupae to predatorybirds may be done immediately after harvest ofsugarcane crop.

Ratooning of sugarcane in affected fieldsmay be avoided and paddy can be planted asthe next rotation crop. This would facilitate killingof grubs in submerged conditions.

Chemical: Application of HCH 10 per centdust @ 100 kg/ha mixed with equal quantity offarmyard manure along the rows and irrigatingthe field to kill newly hatched grubs are useful.

Timely application of 2.5 kg a.i.lha of qui-nalphos granules as side dressing after diggingthe field to expose the grubs. Foliarapplication of Carbaryl/gamma HCH may alsobe done on host trees to kill the beetles.

Recommendations:

Since white grubs are not controlled effec-tively by any single method, an integratedapproach comprising of the following measuresmay be adopted.

i. Mechanica! control by large scale collec-tion of beetles at the time of their massemergence.

ii. Repeated ploughing at the time of landpreparation to expose grubs to preda-tory birds.

iii. Crop rotation with paddy.

iv. Avoiding ratooning in affected fields.

v. Timely application of insecticides syn-chronising with beetle emergence andegg laying.

Publication: No. 33 (1991)

by: Dr. K. Mohan Naidu,Director,Sugarcane Breeding Institute,Coimbatore - 641 007

Script by . Shri K. Ananthanarayana

Prepared by : Dr. R. Thiagarajan andDr. S. Arulraj

Extension

Published

SESHAN. CBE