to farm strawberries and tomatoes in a cost-effective way without the use of these
harmful chemicals.^57Persistence FactorsPersistence is an important part of pest control, since successful pest control
requires knowledge of the persistence period to make subsequent applications. A per-
sistent chemical is advantageous for long-term pest control because fewer applications
are needed.
Commercial applicators must be familiar with the persistence of each pesticide that
may be applied to soil, especially where adjacent areas may be affected or where
treated soil is used to grow other plants. When different plants are rotated in the
same soil, phytotoxicity, or unintentional pesticide damage to plants, can be a prob-
lem. This is because a pesticide used to control some pests on one plant may leave
residues in the soil that will damage or kill another plant. Information on the persist-
ence of a given pesticide can be found on its product label.
Phytotoxicity results in abnormal growth, leaf burn and drop, and discolored,
curled, and spotted leaves. If phytotoxicity is severe, the plant may die. Phytotoxicity
often resembles other problems such as insect damage, plant disease, and poor grow-
ing conditions such as insufficient moisture and improper fertilization. As with phy-
totoxicity, pesticide persistence beyond the intended period of pest control
contributes to accidental plant injury.^58An Important Enzyme DiscoveryResearchers at the University of North Carolina at Chapel Hill have found that an
enzyme (CaaD) inside a bacterium that grows in the soil of potato fields can—in a
split second—break down residues of a common powerful pesticide, 1,3 dichloropro-
pene, used for killing worms on potatoes.
Although it is expensive for farmers, if this particular enzyme were not in the soil, it
would take 10,000 years for just half of the widely used pesticide to decompose. Also,
the chemical would remain in the soil of the potato fields where it is now used in huge
amounts, contaminating groundwater and posing a threat to human and animal health.
An unusual collaboration between an undergraduate student and a distinguished
biochemistry professor at the university resulted in this important discovery. Dr.
Richard V. Wolfenden, Alumni Distinguished professor of biochemistry and biophys-
ics at the University of North Carolina School of Medicine, stated: ‘‘The half-life of
the pesticide is longer, by several orders of magnitude, than the half-lives of other
known environmental pollutants in water. The half lives of atrazine, aziridine, para-
oxon, and 1,2-dichloroethane, for example, are five months, fifty-two hours, thirteen
months, and seventy-two years, respectively.’’ In contrast, he noted, the half-life of
the potato pesticide residue, chloroacrylate, is 10,000 years, the same as the half-life
of plutonium-239, the hazardous isotope produced in nuclear power plants.^59214 | Pesticides