Horticulture Principles and Practices

1
2
YEAR
3
4
FIGURE 8–5
cycle.
A crop rotation
1
Sweet
potato
Cabbage
Corn
Bean
PLOT
2
3
Bean
Corn
Corn
Cabbage
Cabbage
Sweet
potato
Sweet
potato
Bean
4
Cabbage
Sweet
potato
Bean
Corn
Corn
Cabbage
Bean
Sweet
potato
to transfer the ability to resist diseases and pests from the wild into cultivated species and
from cultivar to cultivar within the species. Sometimes resistance is even transferred
across species and genus boundaries (see biotechnology). Resistant cultivars exist for
most of the major pests of horticultural plants.
8.8.4 HOST ERADICATION
Host eradication is often a drastic preemptive method of pest control that involves the elimination
of all susceptible hosts when a pathogen is known to have been introduced into the
production area. This tactic is used to forestall an eminent disease epidemic. For example,
all citrus trees in a production area where a pathogen has been introduced may be completely
eradicated. On a small scale, host eradication is conducted in nurseries and greenhouses by
rouging (removing off types) infected plants. Certain pathogens require two alternative hosts
to complete their life cycles. In such a case, the less economically important host should be
eliminated to interrupt the developmental cycle of the pathogen. For example, Cronartium
ribicola requires pine and currant plants to complete its life cycle.
8.8.5 MULCHING
Plastic mulching has the capacity to trap heat, which causes the soil temperature to
increase. The high temperature destroys some soil pathogens, including Verticilium.
8.9 LEGISLATIVE CONTROL
Various regulatory or legislative restrictions are placed on the movement of live plants and
produce from one place to another. Controlling the spread of plant pests through laws is
called plant quarantine. The purpose of such laws is to prevent the importation and spread
of pathogens and insect pests into areas where they do not already occur. In the United
States, the Plant Quarantine Act of 1912 established the laws that govern such restricted
movement of materials. International and local (with and between states) restrictions are
designed to curb the spread of diseases and pests that are associated with specific plants.
Enforcement is especially strict with regard to plants that are of high economic importance.
Plant Quarantine
The use of legislation to
control the import and
export of plants or plant
materials to prevent the
spread of plant pests and
diseases.
8.9 Legislative Control 259