Importance of osmotic potential as a component of the total potential of the soil water on the movement of nematodes.

Larvae of Ditylenchus dipsad moved at similar speeds through sands of particle size 250 µ. to 500 µ wetted with distilled water or urea solution. Movement in both moisture regimes was related to the moisture characteristic and was fastest when the pores of the sand were draining. Movement in sand depends on the forces holding the soil water in the pore spaces and is independent of the osmotic pressure of the soil water, until the solute concentration is high enough to cause incipient plasmolysis of the nematodes. The length of larvae suspended in urea solutions decreased as the osmotic pressure of the solutions increased. Shrinkage was greatest in the range 0.001 M to 1.0 M concentration and the larvae reached their minimum lengths at approximately pH= 4.1. The solute concentration required to kill nematodes is about the same as that which causes permanent wilting of plants and so it is unlikely that soil additives such as sugar which act only osmotically, would be useful nematicides.
RESP-4542