They can be a gardener’s nightmare, damaging garden plants and – in worst cases – killing them.
They are damaging garden insects. Your first instinct may be to reach for the container of pesticide. But before you do, remember that pesticides can also kill the good insects in your garden. These are the insects that are natural predators of the destructive bugs.
They range from lady beetles and lacewings to Syrphid flies, and their presence in your garden can help control an infestation of undesirable insects.
Since you want to protect the good garden bugs, pesticides should be your last resort. So here are some methods for controlling various undesirable pests without pesticides.
Adult whiteflies are tiny, white insects that damage the leaves of certain plants by sucking the sap out of them. Whiteflies leave a sticky honeydew on leaves and fruit. Other signs of a whitefly infestation include deposits of white wax and yellowing or dying leaves with whitefly nymphs on them. The young oval-shaped nymphs can be found on the undersides of leaves. If you’ve ever grown zucchini and hit their leaves and saw a bunch of white insects flying off them, they were most likely whiteflies.
If you have a whitefly infestation, hose off the adults with water or use a hand vacuum to remove them. Immediately remove and destroy any isolated, infested leaves. Remove and destroy any infested annual plants once they’re done flowering or fruiting. Use a ready-to-use sticky coated yellow trap for each vegetable plant.
Codling moths are the cause of those worms you may find in apples on your tree. The moths lay eggs, which when they hatch, the emerging caterpillars bore into apples and pears.
Up to four generations of codling moths can occur in a year, so remove and destroy any infested fruit on the trees or that have dropped to the ground to help reduce their populations.
If you have a problem with codling moths, there’s an easy way to protect your fruit by simply bagging them. Cut a 2-inch slit in the bottom of a paper lunch bag. When the fruit is ½ to 1 inch in diameter, slip the fruit through the slit and tape or staple the bag shut, sealing out moths to prevent them from laying eggs on the fruit. When the fruit begins to ripen, remove the bags.
Snails and slugs
These mollusks feed on plants and chew holes in leaves, flowers and even some fruit. Since they like moist dark hiding places, try to reduce moist surfaces and place your garden in a sunny location if possible.
Destroy any slugs or snails you see.
You can also construct and use a wooden trap. Instructions can be found at www.ipm.ucdavis.edu.
Create a copper barrier around raised beds, planters and trees to repel snails and slugs. Copper repels them because the slime from these mollusks is believed to interact with copper, disrupting their nervous system and giving them an electrical shock-like experience if they try to cross over the copper.
Aphids are generally only damaging in large infestations. They can curl large leaves and leave sticky honeydew, but they will rarely kill plants. And they can easily be shaken off, or hosed off plants with water.
To decrease aphids in your garden, you can prune out and destroy any infested leaves. Get rid of any ants on your plants since they prevent predators, like lady beetles and lacewings from getting to the aphids.
And if you do resort to insecticides, use less harmful insecticidal soaps or horticultural oils first and make sure the product you select is registered for use on your insect and plant.
Insecticidal soaps contain potassium salt of fatty acids. The soap can disrupt the cell membrane of the insect, and could remove protective waxes covering insects. To be effective, the soap must entirely cover the body of the insect.
Horticultural oils work by smothering insects to death, and by disrupting their feeding on the plant.
For more information on soaps, oils, less toxic pesticides, and how to deal with other damaging pests, check out University of California, Davis Integrated Pest Management website at http://www.ipm.ucdavis.edu.
Kathy Low is a Master Gardener with the University of California Cooperative Extension office in Fairfield. If you have gardening questions, call the Master Gardener’s office at 784-1322.