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)
“A little quaker, the whole body of him trembling,
His absurd whiskers sticking out like a cartoon-mouse,
His feet like small leaves,
Little lizard-feet,
Whitish and spread wide when he tried to struggle away,”
—Theodore Roethke (1908–1963)