Sources and Spread
There are two main sources by which a cereal crop might be infected
1. By non-migrant wingless aphids already present in the field and which colonise newly-emerging crops. This is known as "green-bridge transfer".
2. By winged aphids migrating into crops from elsewhere. These then reproduce and the offspring spread to neighbouring plants.
Read more about this topic: Barley Yellow Dwarf
Famous quotes containing the words sources and/or spread:
“The American grips himself, at the very sources of his consciousness, in a grip of care: and then, to so much of the rest of life, is indifferent. Whereas, the European hasn’t got so much care in him, so he cares much more for life and living.”
—D.H. (David Herbert)
“Cap off
and then what? The brains as
helpless as oysters in a pint container,
the nerves like phone wires.
God, take care, take infinite care
with the tumor lest it spread like grease.”
—Anne Sexton (1928–1974)