Maintenance III: Insect and weed control


A pest is any organism that is out of control – such as weeds, insects, fungi, bacteria, and viruses - and that destroys the health, minimizes the vigor, or ruins the aesthetics of the plant.

Weeds are aggressive, prolific, exotic species that are opportunistic and grow obstinately in exposed soil.  When trying to conserve water in your garden, keep in mind that any plant out of place can be called a weed since it uses water and nutrients intended for other plants.   Eliminate weeds before they set seed to reduce future weed problems.  Also, mulching your garden can reduce weed seed germination by preventing their exposure to sunlight.

Common ways of removing weeds include hand picking, which is simply to dig up the weeds, either with bare hands or with a hoe.  Manual weed removal can be effective when weed populations are low.  In extreme cases, chemical control through herbicides may be necessary.  Herbicides are chemical agents used to destroy or inhibit plant growth and can be effective with weeds.  However, be careful when applying them as any herbicide that kills weeds can just as easily also damage and kill your desired plants.

Generally speaking, healthy plants have a natural ability to ward off insects and diseases, but urban environments can increase the potential for insect problems in trees and shrubs due to urban stress conditions.  These include extreme temperature and moisture fluctuations, air pollution, and acid rain.  Shrubs and trees in poor condition are likely to attract insect pests and are susceptible to damage when attacked.  Incorrect maintenance practices also create plant stress.  To prevent these problems, follow proper planting, pruning, irrigation and weed control practices. 

Careful diagnosis is necessary to determine the cause of any problem.  Consider whether the plant is getting enough or too much water, if it has been over-fertilized or sprayed with pesticides or herbicides, and what is its maintenance history.  Note the list of symptoms and consult a qualified person to diagnose the problem.  Scout for insect and disease pests before you spray.  Control pests when they begin affecting the appearance and overall health of a plant.  Target your control measure to the affected plants and avoid spraying the entire landscape if the pest problem is confined to a small area.

Alternative methods of dealing with pests and disease include what is known as the Integrated Pest Management (IPM) program.  This new approach to pest management acknowledges the presence of problems as natural components of gardens.  Consequently, it gives priority to the use of natural and mechanical [?] controls, and only resorts to using chemicals as a discretionary second choice.  IPM therefore aims at keeping pests in check through natural forces such as predators and weather, thus allowing plants to deal with problems on their own.

Before deciding whether or not to control a pest, determine which part of the plant is being affected.  If it is a part that is to be harvested, you should not use a pesticide.  Also, determine whether the pest can be ignored, and whether the plant is healthy enough to tolerate the damage.  Vigorously growing plants can tolerate some leaf loss without permanent damage.  If the pests are insects, note if they are young enough or if it is early enough in the season for the insects to potentially cause more injury later on.  If this is the case, a more aggressive response may be necessary. Keep in mind that pests often are detected when they are in a terminal state and about to stop feeding.  By then it is too late to do anything that would be of any use.

Plant disease  (image credit: Dalia al-Husseini)

Plant disease

(image credit: Dalia al-Husseini)

This article is part of a series of articles prepared by the Center for the Study of the Built Environment (CSBE) on water conserving landscapes. 

For additional information on water conserving gardens, visit the CSBE web site at

Support for the CSBE project on water conserving landscapes is provided by WEPIA (Water Efficiency and Public Information for Action), a program being implemented in collaboration with the Ministry of Water and Irrigation and funded by the United States Agency for International Development (USAID).