Polyhouse technology for growing high value crops is gaining popularity among the farmers of Tamil Nadu.

But the soil conditions are highly conducive for nematode infestations of the crops. The most economically important nematode is root-knot nematode.

This nematode causes characteristic galls in the roots resulting in damages and dislocation of xylem vessels which impair the movement of water and minerals. The characteristic symptoms are stunted growth and formation of small and chlorotic leaves.

Main cause

In most cases, problems arise from contaminated soil or soil mixture used as a component of the growing medium, monocropping and infested planting materials.

Commonly followed nematode management practices such as summer ploughing, fallowing and crop rotation which are meant for nematode suppression in field crops are not practicable in polyhouses.

Therefore, nematode management here must be considered primarily as exclusion or avoidance. Once nematodes are introduced it is difficult to manage them.

Some measures

-Drenching the soil with 0.5 per cent formalin at 100 ml/kg soil followed by covering with polythene tarps for two weeks before sowing/planting.

-Growing cowpea (trap crop for root-knot nematode) closely to the main crop and removing the plants out of polyhouse at 45 days after sowing.

-Raising marigold (antagonistic to nematodes) and incorporating in situ after plucking flowers.

-Adding well decomposed farm yard manure at rate of 20 tonnes per hectare to enrich soil.

-Incorporating neemcake at 250 kg/ha soil two weeks before sowing/planting. — Filtering irrigation water using mesh sieves before usage.

Applying Pseudomonas fluorescens/Trichoderma viride @ 2.5 kg/ha mixed with 50 kg farmyard manure ten days before sowing/planting and use chemical pesticide like carbofuran 3G at rate of 1 kg./ha

(Dr. S. Ramakrishnan and K. Devrajan are Professors, Department of Nematology, Mobile: 9442007597, email: nemarama@yahoo.comand kdevarajan@yahoo.co.in, TNAU, Coimbatore.)