BP Singh

224 Rajanvarious chemical solutions at different temperatures. Hastings(1933) quoted Weiss of the U.S. Department of Agriculture whohad shown that active stages of D. dipsaci escaping into the waterof the bath could survive even after four hours at 43.3°C and hadproposed the addition of one or two per cent formalin to the water.Several workers have found that Formaldehyde is not verynematicidal at low temperatuIes but becomes much more so astemperature rises. Hot-water formalin treatments at 43.3°C havealso been used in U.S.A. against D. destructor in iris bulbs andAphelenchoides fragariae in lily bulbs.D. ,dipsaci, in tulips and narcissus can be controlled bydipping the bulbs in the organophosphate thionazin, the treatmentbeing 2500 ppm for ~;5-3 h. Dips of banana sets are a regularpractice, best control being reported with fenal1).iphos at 100 ppmfor 5 min. (Decker et aI., 1971). .(b)SeedsThe seed transmitted nematodes can be controlled byfumigation with methyl bromide in an air tight chamber, but thedosage (concentration * time product) required will depend on theoil and moisture content of the seed. In onion seed, dosage in, excess of 800 mg h/L needed to control the cryptobiotic stage ofthe stem nematode, are phytotoxic, but lucerene seed will toleratedosage upto 2500 mg h/L which is in'excess of the effective dosage.Methyl bromide has been shown to be effective against Anguinaagrostis in bent grass. Generally seeds should be at about 10%moisture content to avoid phytotoxic damage by methyl bromide.(c)Bare root dipsDipping seedlings and transplants in non volatile chemicalsis an effective method of controlling nematodes. M. hapla Chitwoodin roses was controlled by a dip in phenarruphos or ethoprophos.at 100 PPll'l: for 30 min; and the immersion of seed potato piecesin fenamiphos at 1800 ppm was very effective against severalnematodes. Dipping ,tobacco transplants in oxamyl is a good wayof checking introduction of several nematodes.Total control of M. incognitl1; was obtained with fensulfothionand thlonazin (1000 F\Pm) on peach plants (Ponchillia,1973). Boththe treatments were, not phytotoxic. Thionazin at 2000 ppmapparently eradicated the n~matode, M. hapia on peony roots