Horticulture Principles and Practices

Plant breeding efforts may succeed in developing resistant cultivars to certain pests and diseases.
However, the production enterprise can be wiped out with the introduction of a new
strain of the pathogen from another country or region. When imports are detained in quarantine
procedures, the inspectors observe the materials over a period of time (at least for
the duration of the incubation period of the insect or pathogen), after which plants are
released, treated, or destroyed, depending on the results during the detention.
Quarantines are not foolproof since their success depends on the experience of the
inspectors. Further, pathogens may escape detection if they exist in less conspicuous stages
in their life cycles, such as eggs or spores. Where plants are treated, certain latent infections
may exist in seeds and other plant materials even after a period of growing plants in the field.
8.10 MECHANICAL AND PHYSICAL CONTROL
Pests may be controlled by a variety of mechanical or physical methods, as outlined here:
1. Traps. A number of mechanical control measures may be adopted to control
pests in the greenhouse and field. A fly catcher is a strip of paper or polyethylene
(commonly yellow in color) that has been coated on both surfaces with a sticky
substance. Insects that land on the paper get stuck to it and eventually die
(Figure 8–6). Larger mechanical traps are used to catch rodents. Certain lights are
designed to attract insects, which then become trapped by other devices installed
for that purpose.
2. Handpicking. In a small garden, caterpillars and other large bugs may be handpicked
(not necessarily with bare hands) and destroyed.
3. Barriers. Rodents can be kept out of a garden by fencing it. A band of sticky
paper (similar to a fly catcher) wrapped around the base of a tree prevents
crawling insects on the ground from climbing up the tree.
4. Tillage. As a pest-control measure, tillage (cultivation) is used to remove weeds
from the area.
5. Mulching. Mulching can be a method of mechanical control because a material
such as plastic prevents weeds from growing through the material.
FIGURE 8–6 Polyethylene
trap. (Source: George Acquaah)
260 Chapter 8 Principles and Methods of Disease and Pest Control