and mating. The enlarged abdomen of the fecundated female, the
so-called cyst, remains in the soil. It contains 300 fertile eggs
on an average, and by means of its hardened outer wall it can
persist in the soil for years, releasing newly hatched larvae
whenever conditions are favourable. Apart from that, during the
same summer a second generation emerges from up to 200 eggs
which are laid into a mucuous mass outside the vulval region.
Under favourable conditions, even a third generation may complete
its life cycle before harvest of the sugar beets (DECKER 1969).
By the formation of the giant cells (syncytiae) in the root-
lets, transport ways for water and nutrients are blocked. the
root body remains small, and yield decreases heavily. During
periods of warm and dry days in summertime, the water which is
evaporated by the leaves cannot be replaced by the roots in
sufficient amounts, and therefore the leaves begin to lose
their turgor, and slack down. Because the nematode cannot move
very far in the soil by itself, it is mostly spread passively,
and so it occurs in patches in the field, which can be recognized
by the infested, slackening plants being surrounded by non-infe-
sted, turgid plants. Generally, the leaves keep their dark-green
colour, and become turgid again for a short period after rain
showers or irrigation.
As can be understood from these brief biological explanations,
the multiplication rate of those harmful organisms is an enormous
one. Farmers and sugar companies alike suffer from steadily
increasing economic losses. Countermeasures like planting sugar
beets every three or four years only, and no other host plants,
such as rapeseed, in between, have shown to be unsuccessful in
bringing down the population rate below an economically bearable
level. Only recently, the possibility of applying chemical soil
fumigants effectively has been realized by the development of new
technical application equipment.