Carrot is adversely affected by several pests, diseases and nematodes. Among them northern root knot nematodes, Meloidogyne hapla poses a serious threat to carrot cultivation in hilly region as it is able to survive in low temperature.
The primary symptom is the formation of galls on side roots of tubers, formation of forked roots, split carrot tubers and spindle-shaped enlargements on tap and side roots causing yield losses.
The root-knot nematodes complete most of their life cycle within their host roots. The infective second stage juveniles hatch from the eggs and move through the soil in search of suitable host plants.
They usually penetrate the host roots just behind the root tip region and establish their special permanent feeding sites (giant cells) on the vascular tissues of the root.
The giant cells provide nutrients for the sedentary nematodes which continue to feed, enlarge and moult three times.
Root cells around the feeding sites are also induced to enlarge and form galls and often extensive secondary root formation and branching of the main root is seen.
Depending upon the host and soil temperature, the entire life cycle may be completed in 35 to 60 days. Mature females deposit eggs (550 to 1000) on the root surface.
The nematodes damage the xylem vessels and affect the uptake of water and nutrients. Apart from these injuries caused to root, they facilitate easy entry of other soil borne pathogens which cause root dieback disease.
— Summer ploughing and exposing the soil to sun prior to planting for 1-2 months.
— Growing crops such as marigold. Soil application of Farm Yard Manure at 20 t/ha and Neem cake at 500kg/ha at the time of the ploughing.
— Soil application of Azospirillum and Phosphobacteria at 2kg/ha each at the time of the sowing.
— Rotation of carrot with non host/ poor crops like spinach, radish, barley and wheat.
— Soil application of Pseudomonas fluorescens at 2.5kg/ha mixed with 50 kg of FYM and application of carbofuran 3G at 33kg/ha.
& E. I. Jonathan
Horticultural Research Station, Kodaikanal and Centre for Plant Protection Studies, TNAU, Coimbatore