Visualizing Environmental Science

366 CHAPTER 14 Agriculture and Food Resources

Lawrence Migdale/Photo Researchers, Inc.

1965

California red scale density

1400

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20

0

1966 1967 1968 1969

Untreated control trees

DDT-treated trees

Economic injury level

Year

Adapted from Debach, P.

Biological Control by Natural Enemies.

New York: Cambridge University Press (1974).

© Graphic Science / Alamy

a. Red scale infestation—shown here on oranges—

makes the fruit unappealing and unfit for market.

b. Scientists understand that the red scale

infestation is a direct result of DDT spraying. This

graph compares red scale populations on DDT-treated

trees (red line) and untreated trees (blue line).

use of a pesticide has resulted in a pest problem that
did not exist before (see What a Scientist Sees).
Another problem associated with pesticides is that
they do not stay where they are applied but tend to move
through the soil, water, and air, sometimes traveling long
distances (Figure 14.17). Pesticides applied to agri-
cultural lands wash into rivers and streams, where they
can harm fishes. Pesticide mobility is also a problem for
humans. About 14 million U.S. residents drink water
containing traces of five widely used herbicides, and
some people living where the herbicides are commonly
used face a slightly elevated cancer risk because of their
exposure.

Alternatives to Pesticides

Given their many problems, pesticides are clearly not
the final solution to pest control. Fortunately, pesti-
cides are not the only weapons in our arsenal. Alterna-
tive ways to control pests include cultivation methods,
biological controls, pheromones and hormones, repro-
ductive controls, genetic controls, quarantine, and irra-
diation (Table 14.1). A combination of these methods

Mobility of pesticides in the environment

Uʈ}ÕÀiÊ£{°£ÇÊ

A helicopter sprays pesticides on a crop—and everything else in

its pathway—in California.

in agriculture, often including a limited use of pesticides

as a last resort, is known as integrated pest management

WHAT A SCIENTIST SEES

Pesticide Use and New Pest Species

An infestation of red scale insects on lemons occurred in California after
DDT was sprayed to control a different pest. Prior to DDT treatment, red
scale did not cause significant economic injury to citrus crops.