Nature and Symptoms of attack

The root borer infected the young shoots as well as grown up canes. When attack occur during the early stages of crop growth, dead-hearts are formed and often one or two leaves adjacent to central leaf whorl also dry up. Dead-heart cannot be pulled out easily and don't emit any offensive smell. There is any one entry hole near the base of the shoot. In the growth up canes, yellowing of leaves occurs and no other external symptoms are discernible and canes have to be dug out to detect its attack. In the underground portion of canes 3-4 holes can be seen.

Extent of Losses

As a result by the infection of the larvae of first brood, 52 percent of the affected shoots produces no tiller, 30 percent produce only one tiller and 18 percent two tillers. through the plant damaged by the larvae of second brood form millable canes they show a decrease of 73 percent in weight as compared to healthy canes. Canes damaged later in the season by the larvae of 3rd brood show a reduction of 17 percent in weight, where as in the cane attacked by the fourth brood there is no effect on the yield and quality. The work done at karnal show that there is no effect on yield and quality due to attack of 3rd and 4th brood of root borer. The percent reduction weight in root borer infested canes over healthy canes ranged from 1.0 to 4.0 % in cultivars viz., Coj 64, Co 7717, Co 77314, Co 1148, Co 8334 and Coj 78. recent studies conduct at Karnal have also show that in commercial cultivars Co 89003 and Co 8347 the reduction in yield due to root borer was 1.0 to 3.7 %.

Seasonal History

The studies conducted at SBIRS, Karnal have show that root borer passes through 4 over planning generations and is active through out the year. Months emerge from the over wintering pupae in the month of April. Maximum emergence occurs in the evening hours between 8 to 12 p.m. . Mating occurs in the late evening hours. Eggs and laid singly on the dorsal side of the leaves along the mid-rib. On the hatching larvae crawls to the base of the stem and enter it by making a hole through the crevices about 3-4 cms below the ground level in the young shoots. In the old canes, 2 to 7 hole cane be seen below the ground level. The larvae feeds in irregular semi-circular pattern along the side of the cane. The population of the root borer which is peak level during Sep- Oct month when the mean ambient temperature is around 34 °C and RH about 65+5 %. In the last week of Nov, The larvae brood enter in to diapause's in to the silken tunnels majority with there heads directed down words. Before population larvae cuts an opening to exterior facilitate easy emergence of adults. Larvae of different sizes under grown diapause's. The full grown larvae pupate in the first week of April. Since root borer and early shoot borer occurred simultaneously during May-June and both produced dead-hearts in young plants, Ratio of root borer and shoot borer was found to be 1:9.

Life-cycle

The studies conducted at SBIRS, Karnal have shown that male and female ratio is 1:1 and adult longety is 2-4 days. On an average about 150 eggs are laid by one female. Incubation period varied  from 7 to 12 and 5 to 8 days, While pupal  period varied from 7 to 18 and 8 to 12 days at 27 °C and 33 °C respectively. Larval period ranged from 38-52 days during may-June at temperature below 15 °C adults laid very few eggs, eggs did not hatch and pupae didn't developed in to adults. total Duration of life cycle varied from 54-68 days during May-June.

Factor favoring pest build up

The root has been observed to be active at temperature around 34 °C and RH of 65+5 percent i.e. condition prevailing during July-August are very conducive for its multiplication. It is tolerant to rain to some extent but heavy rain reduces its incidence by about 30-35 percent. Rotation and plant crops both are equally affected by root borer. Incidence is generally high in a sandy loam soil and affluent water irrigated soils. Cultivation of early and highly susceptible varieties like Coj 64, Co 7314 and with less fiber like Co 89003 enhance the build up of the pest.

Management

i) Cultural and mechanical

1. Digging and destruction of infected shoots at weekly intervals.

2. Deep harvesting of canes which are to be ratooned.

3. Digging of stubble after harvest.

4. Installation of black light traps at a distances of about 50 meter in the field during April-May  is very helpful in monitoring and trapping of large number of months in the fields. This will reduces the population in the subsequent in the generations. Light traps may be set at a distance 20 to 30 meter and these traps can be shifted in the field every 15-20 days.

5. Flooding the field for 24 hrs once a month from may onwards also reduces the population by 30%.

6. heavily infested field by root borer may be rotated with paddy crop for 2 seasons as far as possible. 

7. Varieties susceptible to root borer attack should be harvested early by Nov-Dec.

Chemicals

Application of chlorpyriphos 20EC or confider 17.8EC of furadan 3G @ 1.5 kg a.i./ha during the last week of august helps in reducing the incidences of root borer. application of insecticide should be followed by a light irrigation.

Resistant Varieties
Varieties Cos 767, Co 7717, Cos 8436, Bo 91 and Co 1148 are relatively resistant to root borer attack and should be grown in areas where root borer problem is severe.