Combating Common Garden Pests
4/10/01

By Joshua Dake
Operations Manager, Miramar
Wholesale Nurseries

One problem all Southern California landscapers have in common is pests in their landscape. Diagnosing the problem early and using the proper techniques to eradicate the pest will ensure that your plant remains healthy — and so does the rest of your garden. A little prevention can keep problems from spreading to the rest of your plants.

Pests come in a variety of forms, from insects to bacteria or fungi. Using the proper pesticide is crucial to target your specific pest. Outlined below are five of the most common pests found in Southern California landscapes.

GIANT WHITEFLY
Despite its name, the Giant Whitefly is only about 1/16th of an inch long. This tiny, white-winged insect lays eggs on the underside of the leaf. Both adult and larvae suck sap from the leaf. Adults excrete a sticky fluid known as “Honeydew” which drops down to the lower leaves and can develop a sooty mold fungus giving the leaves a black appearance.

The plant should be treated with Diazinon, Malathion, or Orthene depending on the type of plant. In severe infestations, webs may form on your plant. If you notice this, cut off the infested part of the plant to encourage fresh new growth.

APHID
Aphids are tiny insects varying in color from pale green to dark brown. They cluster on stems and leaves and can reproduce very quickly in the warm seasons. Aphids feed on plant sugars sucked from leaves, stems, and flower buds. Ants may congregate where there is an aphid infestation as they feed on the undigestable sugars in the aphid’s excretions.

For food crops, try Malathion or Diazinon to eradicate the aphids. On ornamental shrubs, Orthene Systemic Insect Killer provides a defense for the plant over a longer period of time.

THRIP
If you notice deformities in your flowers, fruit, or foliage, it is likely that you have a thrip problem. These slender insects are tan to dark brown to black in color. Both young and adults feed by scraping or rasping the plant tissue and sucking out plant sap. You may notice your flowers become discolored.

Apply Malathion, Diazinon, or Othene Systemic Insect Killer once a week or as often as permitted according to the pesticide label to control newborn thrips. You may notice that new growth is also deformed after the insect is eradicated. Just continue to prune to promote healthy, vigorous new growth.

BOTRYTIS
A common fungus on both fruit trees and general ornamentals is Botrytis, also known as Gray Mold, or Bud and Flower Blight. The disease is caused by any of several varieties of the Botrytis fungus and develops on fallen plant debris, or dead or inactive plant tissue.

Once established, Botrytis spreads to healthy parts of the plant, attacking foliage, flowers, and fruits both before and after harvesting. The fungus will cause spotting and rapid decay of flowers and fruits. Botrytis is common in most soils, but thrives in moist conditions.

In order to prevent your plants from becoming infected with this fungus, be sure to keep all dead limbs pruned and clean up any fallen debris around the base of the plant, especially if it is in contact with moist soil. If your plants do have Botrytis, spray every 10-14 days with Daconil, or any other fungicide containing chlorothalinol. Also, be sure to water your plant at the ground level to prevent the regeneration of spores on wet foliage.

POWDERY MILDEW
Another fungus, which can affect nearly all plants in the garden is Powdery Mildew. It grows on the outside of the leaves forming a whitish gray powder composed of spores. These spores are primarily spread by wind and are active in both wet and dry conditions. If allowed to thrive, Powdery Mildew will turn plant leaves yellow and can eventually kill the plant.

To combat, try spraying with Ortho Funginex or another fungicide containing copper, sulfur, or lime. Remember to keep your plants pruned and thinned to promote good circulation of air.

Always remember when using these and other pesticides, to follow the directions on the label carefully, as certain levels can be toxic to your plants as well as to yourself and the environment. Also be sure that the plant you are spraying is listed on the label of the pesticide you use. For your protection, pesticides should be applied using the necessary safety equipment noted on the pesticide label.

Joshua Dake is the Operations Manager of Miramar Wholesale Nurseries, Southern California’s leading supplier of landscape plant materials and supplies.