Three Steps to Pest-Proof Plantings
15 May, 2008 By: Janet Aird Get Growing Healthy azaleas outgrowing pest pressures. Photo Courtesy: Don Dale |
What chance do ornamentals have against insects and disease? A pretty good one, according to Brian Maynard, professor of Horticulture at the University of Rhode Island. In 1991, the university and the Rhode Island Nursery and Landscape Association installed the URI Botanical Gardens. Since then, they’ve lost only one or two plants to pests, he says, and both pre-dated the garden. They’ve never used pesticides.
They’ve managed this in large part by planting ornamentals that are well-adapted to the area. The plants are healthy and very pest-tolerant.
Step 1
The first step in having pest-tolerant ornamentals is to choose the ones that will flourish on the site. Choose ones that grow naturally in the same kind of climate, soil, moisture and light conditions, and with heights and widths that maturity fit the space.
Some plants have characteristics to protect themselves from insects, like hairs that prevent them from reaching the leaves, or thick leaves they may not be able to penetrate.
“Plants also have active defense mechanisms. They respond to being attacked,” he says. Some drop leaves, removing the pests’ source of food. Others grow tougher leaves. Many release chemicals that repel pests and keep additional ones from attacking.
When a plant is under attack from pests ‑ either insects or diseases ‑ it releases stress hormones. These chemicals signal to the plant that it needs to change to fight the threat. The chemicals also communicate with other plants nearby, letting them know a threat is nearby.
“That takes energy,” Maynard says. Healthy plants have good energy reserves, so they can both defend themselves and bounce back from an attack.
Plants that are stressed by conditions that are too hot or cold, sunny or shady, wet or dry, are more prone to insects and diseases. In fact, there are pests, for example, bark beetles, that actually seek out ailing plants.
Some plants can change and grow in response to a stressful environment. Red maples in a flooded swamp are stressed at first, Maynard says, but they put out new roots that are adapted to water. Once they’ve done that, the stress disappears.
Step 2
The second step in having a pest-tolerant landscape is to find out which pests are already in your local area and choose ornamentals that aren’t susceptible to them. For example, Maynard says, some varieties of crabapples do very well in Rhode Island, but the same varieties do badly in North Carolina and Ohio. The difference? North Carolina and Ohio both have fireblight, a bacterial disease that attacks them. Rhode Island has none.
Step 3
Third, aerate the soil before planting. A landscape design may be beautiful, but if the soil is compacted, ornamentals will always be stressed because of the poor drainage and lack of air. And once they’re in the ground, he says, it’s very difficult and time-consuming to improve the soil.
This article has been excerpted from a full article that will appear in the May/June issue of Livescapes magazine.
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