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:
“No drug, not even alcohol, causes the fundamental ills of society. If we’re looking for the sources of our troubles, we shouldn’t test people for drugs, we should test them for stupidity, ignorance, greed and love of power.”
—P.J. (Patrick Jake)
“Everywhere, spread all over in characters of living light, blazing on all its ample folds, as they float over the sea and over the land, and in every wind under the whole heavens, that other sentiment, dear to every true American heart,—Liberty and Union, now and for ever; one and inseparable!”
—Daniel Webster (1782–1852)