What happens to the farm animals and vegetation? What causes this sudden change?

In chapter 1, Rachel Carson presents a dire prediction for the death of domesticated animals and crops, as well as song birds and vegetation, in the form of a fable. In chapter 2, she briefly presents this apocalyptic vision as the result of pesticide use. Her prose draws power from the combining harsh words and hyperbole with our familiar childhood language of fairy tales.
The changes that befall the idyllic rural community are caused by “a strange blight” and “some evil spell.” The silent countryside, under “a shadow of death,” is “deserted by all living things.” Inexplicable diseases strike the farm animals:

mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death.... On the farms the hens brooded, but no chicks hatched. The farmers complained that they were unable to raise any pigs— the litters were small and the young survived only a few days. The apple trees were coming into bloom but no bees droned among the blossoms, so there was no pollination and there would be no fruit. The roadsides, once so attractive, were now lined with browned and withered vegetation as though swept by fire. These, too, were silent, deserted by all living things.

In chapter 2, she provides a scientific explanation but still inserts unscientific language: pollution initiates “a chain of evil” or “a chain of poisoning and death.” The chemical attack on living tissues causes universal contamination. Some is nuclear residue, as Strontium 90 enters the earth through rain or fallout, then “lodges in soil, enters into the grass or corn or wheat grown there….” But a more constant, widespread problem is the result of pesticide use, which reaches the soil directly or through the water, where it affects animals and humans alike:

[C]hemicals sprayed on croplands or forests or gardens lie long in soil, entering into living organisms, passing from one to another in a chain of poisoning and death. Or they pass mysteriously by underground streams until they emerge and, through the alchemy of air and sunlight, combine into new forms that kill vegetation, sicken cattle, and work unknown harm on those who drink from once pure wells.

No matter what the target, they “linger on in the soil” and are so toxic they should be called “biocides.”