Horticulture Principles and Practices

TABLE 8–3
Selected Examples of Biological Control of Horticultural Pests
Biological Agent
Ladybug
Bacillus thuringiensis
Bacillus popillise
Green lacewing
Parasitic wasp
Nedalia beetle
Tilleteopars
Talaromyces flavius
Some Pests Controlled
Aphid
Colorado potato beetle and caterpillar
Japanese beetle
Aphid and mealybug
Tomato hornworm and cabbage looper
Citrus cottony scale
Powdery mildew
Potato wilt and verticillium wilt
In addition to these organisms, the use of resistant cultivars, plants with repellent scents, and crop rotation are other nonchemical
methods of pest control.
Disadvantages
The major disadvantages of biological control include the following:
1. Availability and application are limited to relatively few crop species.
2. Handling of organisms is less convenient than chemicals, often requiring special care.
8.7.2 OTHER EXAMPLES OF BIOLOGICAL CONTROL
A variety of beetles have been identified as predators of pests of cultivated crops:
1. The European seven-spotted lady beetle (Coccinella septempunctata) preys on
aphids.
2. The ladybug (Crystalaemus montrocizieri) destroys mealybugs.
3. The larvae of the Japanese beetle feed on the larvae of other beetles.
In addition to beetles, the bacterium Bacillus thuringiensis is known to infest and
kill a variety of insects, including the larvae of butterflies, moths, and corn borers, while
being harmless to plants. Other examples are presented in Table 8–3. Figure 8–4 presents
examples of various organisms in effecting biological control. These exhibits represent
only a select few examples.
8.8 CULTURAL CONTROL
A variety of strategies are employed to implement cultural control of diseases and pests
in plants.
8.8.1 CROP ROTATION
As indicated in the introduction to this chapter, monoculture and repeated cultivation of
one species on the same area of land encourages the buildup of the diseases and pests
that plague the cultivated species. Crop rotation is a strategy whereby no one species is
perpetually planted on the same plot of land (Figure 8–5). Additionally, a species is not
followed by its relative. Instead, species with different soil requirements or use are
rotated in a definite cycle (e.g., corn to tomato to bean to corn, or a four-year rotation).
Note that the rotation has a cereal, a solanaceous species, and a legume. A rotation consisting
of, for example, potato, tomato, and eggplant (all solanaceous species) certainly
violates the rule of not following a species with its relative. Similarly, cruciferous plants
(e.g., cabbage, broccoli, mustard), leguminous plants (e.g., beans, peas), onions
(e.g., garlic, leek), and Curcubitaceous plants (watermelon, squash) are groups of plants
affected by similar diseases. Rotation of crops is effective in reducing the populations of
8.8 Cultural Control 257