Abstract
The significance of soil moisture in relation to aeration and larval emergence from cysts of Heterodera schachtii Schmidt is discussed. The rate of larval emergence increased as oxygen concentration increased. A comparison of the moisture characteristics of a mass of cysts and of sand of about the same particle size showed that water was removed from between both the cysts and the sand particles at 12–16 cm. of water‐pressure deficiency. There was an indication that water was removed from between the eggs within the cysts at 100–135 cm‐ of water‐pressure deficiency. The rate of larval emergence showed a gradual decline is suction was increased beyond 20 cm. of water‐pressure deficiency, approaching zero at 175 cm. of water‐pressure deficiency. Results suggest that egg hatch is not directly dependent on pressure deficiency and that the presence of free larvae within the cyst inhibits further egg hatch. A technique is described for measuring larval motility in sand. There is a decline in motility when most of the water has been removed from the sand pore‐spaces. It is suggested that the relatively low rates of larval emergence at high‐pressure deficiencies are due to inhibition of larval migration from the cyst by the surface forces of the water film.
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