Plassey borer, Chilo tumidicostalis Hmpsn., is an important, though sporadic, pest of sugarcane in some areas of West Bengal, Bihar and Assam.
The incidence of this borer in a field can be easily spotted by the presence of dry crown of leaves on the infested canes. The injury due to borer in the cane is of two types :
(a) Primary infestation, and (b) Secondary infestation.
(a) Primary infestation. It is caused by the newly hatched larvae congregating in the top 3 to 5 internodes of a cane. More than 100 caterpillars may be collected from a single cane. Fresh frass which is shining red in colour, is usually seen coming out of the holes in the top internodes. The leaves of such canes ultimately dry up. The affected internodes break off easily. The nodes adjacent to the infested internodes throw out elongated sett-roots which envelop the stalk below. Sprouting of side-shoots also sometimes occurs.
(b) Secondary infestation. The grown-up caterpillars migrate to the adjoining canes or to the lower healthyportion of the canes showing primary infestation (each caterpillar entering a separate cane), and give rise to the “secondary attack”. Cane tops do not dry up in this case though individual caterpillars may sometimes bore up to 5 internodes in a single-attacked cane.
Seasonal history and extent of loss.The pest remained active from later half of February to about the middle of November, and passed through 5 to 6 generations in a year. There was overlapping of generations from April to October when all stages of the pest were simultaneously met with.
The pest exhibits polymorphismin larval stage, and 4 distinct types of caterpillars can be seen. However, a typical larva can be identified by the presence of 4 pinkish-brown stripes on its back and a complete circle of the crochet on its prolegs.
During August-September, one life-cycle of the pest is completed in 39-64 days; egg stage lasts for 7 days, larval stage 26-46 days and pupal stage 6-11 days.
In severe cases of infestation, losses may vary from 30 to 50 tonnes of cane per hectare in different varieties. Sugar recovery is also appreciably reduced.
(a) Mechanical. Collection of moths at light traps, removal of cane tops showing primary infestation, and collection and destruction of egg-masses, prove effective in bringing down the pest population and its damage.
(b) Chemical. Spraying the crop with Endrin emulsion at about 1 kg a.i./ha gave promising results in Plassey area.
The internode borer, Chilo (Sacchariphagus) indicus Kapur, is a major pest of sugarcane in peninsular India causing considerable reduction in tonnage and sucrose content of cane. It has been reported from certain pockets in north India and in Madhya Paradesh and Orissa also. The pest remains active throughout the crop season under south Indian conditions, and its attack is particularly severe in Tiruchirapalli, Tanjore and South Arcot districts of Tamil Nadu where the incidence may be as high as 70 percent in some fields. The special season crop which is planted in July-August, suffers more seriously than the January-February planted crop.
Young newly hatched caterpillars prefer the top portion of the cane for their early feeding. Soon after the emergence they feed by scraping the leaf spindle. Subsequently they bore into the tender cane-crop.
The attack of the pest in young shoots is more commonly found in the late-planted crops and in the ratoons. In grown-up canes the damage by the larvae can be observed only when the leaf-sheath is removed. Fresh excreta can also be seen sticking outside the larval holes on the internodes. The larva is sufficiently grown in size by then and is highly migratory in habit at that stage; it often transfers itself from one internode or cane to another.
Seasonal history.Under south Indian conditions the internodes borer remains active throughout the year, and all stages of the pest are met with throughout the year. On account of overlapping of different stages, it is difficult to determine the excat number of generations in a year under field conditions. Studies in the laboratory revealed that the pest completed 6 generations in a year. The moths lay eggs in masses usually on the upper surface of the leaves. After the first moult which takes place on the third or the fourth day of hatching, the larva becomes more activeand starts feeding voraciously on the tender unopened foliage at the top. The grown-up caterpillars bite holes in the internodes through which they enter and subsequently makes tunnels in the stalk.
Before pupation, a fully-grown larva comes out of the tunnel and takes their shelter underneath a tightly fitting leaf-sheath on the cane. It constructs a silken cocoon there in which it later pupates.
(i) This pest is carried over to the succeeding crops though the leaf-sheaths which along with the pupal cocoons sticking to them, are quite often left in the fields as trash after harvest; moths emerging from these pupae fly to the neighbouring fields to lay eggs on the fresh crops.
(ii) Leaves bearing unhatched egg-masses (and left over as trash in the field) also in the carry-over of the pest. Young ines hatching out from these eggs easily find their way to late tillers or to ratoon sprouts nearby.
In Tanjore area (Tamil Nadu) where cane crops are available in the fields all the year round, and where trash conservation and mulching is a regular agronomic practice, the carry-over of the internode borer to the succeeding crops is very much facilitated.
It has been observed that sugarcane varieties with soft rind generally have a higher incidence of the pest than those with a hard rind. The young larva prefers to bore into the top tender portion rather than the well-formed hard internodes. Varieties with close-fitting leaf-sheaths show higher incidence than the loose-fitting and self-detrashing varieties. It has further been observed that the incidence of the borer is less in detrashed crops as compared to crops where no detrashing has been done. Since the newly hatched borer larvae generally remain inside the leaf-sheaths in the initial stages before feeding their way slowly into the cane, and since the grown-up caterpillars usually pupate in-between the stalk and the leaf-sheath, varieties with close fitting leaf-sheaths are preferred by the pest. The crop in water logged fields usually suffers more seriously from the attack of this pest, probably because moisture conditions in such fields are favourable for multiplication of the pest.
(a) Mechanical. Detrashing of canes (and burning of the trash) with a view to destroying the larvae and pupate attached with the leaf-sheaths, proves helpful and is generally recommended for controlling the internode borer.
(b) Chemical. In preliminary trials conducted in Tanjore area of Tamil Nadu, spraying the crop with Endrin 0.1% emulsion 3 times at 4-weeks interval during December-March gave encouraging results against the pest.