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Master gardener in training: Battling bugs

June 2, 2010 |  8:32 am

Caterpillar 1, bean plant 0.

In the UC Extension Master Gardener class, I've learned about the romance of seeds and seedlings, the chemistry of compost and mulch. Now it's time to face the less pleasant realities of the garden: pests -- more specifically, expert recommendations for fighting them off your vegetable crops.

Some bugs do more than eat my food. In the process they weaken the plant, making it susceptible to disease and environmental stress. The bugs aren't evil, just hungry.

Bugs2 Although pests can include vertebrates such as opossums, raccoons and gophers, in class our primary focus has been on insects, the good and the bad. Of the million species documented so far, fewer than 0.1% are considered pests. And by "insect," I'm only talking about bugs with six legs, three body parts and two antennae. Spiders and mites are arachnids. Pill bugs are crustaceans. Snails and slugs are in a weird little group of their own -- hermaphroditic, cannibalistic and living in a world defined by mucus.

Aphids, white fly, mealybugs and other pests move in gradually, almost invisibly. Most aphids are female and don’t need fertilization; put a meal in front of them and they become a baby factory, dropping eggs on the undersides of leaves and in buds. They excrete dew on the undersides of leaves, a sugary treat for ants that over time can become a petri dish for sooty mold. Psyllids do the same. A tomato horn worm, on the other hand, is not so subtle. It can reduce a healthy tomato plant to a stump overnight, starting at the top and chomping its way down. Caterpillars can be shockingly destructive because the irregular holes in the leaves are often blamed on snails and slugs, delaying proper diagnosis.

That's the first step: identifying the problem. How extensive is it? Then you should decide your threshold: How many aphids are too many? Pest and weed specialist Cheryl Wilen talked to my class about integrated pest management, an environmentally aware and holistic approach promoted by the UC Cooperative Extension. The IPM rules are flexible and friendly to organic gardeners: Set a threshold, identify and monitor pests, prevent if possible, and as a last resort, control.

Identifying your problem is tricky. Here are questions to consider:

Is the source of the problem biotic, caused by something alive? Or abiotic, caused by weather, site location, lack of minerals or poor gardening (usually over-watering)? Is the culprit pest or disease?

Bugs3 Inspect leaves for bugs and check roots for grubs or nematodes. Pests will typically go for the youngest, most succulent new leaves and shoots, so look there first.

If you're battling a bug, which bug? One of the best resources for identification is "Insects of the Los Angeles Basin," available from the Natural History Museum of Los Angeles County. Spider mites will leave a webbing on the leaf. Thrips will hide in the buds. Piercer-suckers such as white fly may leave yellow leaves behind, a sign that dead cells no longer have the potential for photosynthesis. The roly-poly pill bug is good and bad -- indispensable to decomposition and building a healthy soil but also capable of gnawing through the stem of a vibrant pea shoot.

And before you deploy some kind of control, realize that by the time you notice a problem, the pest may already have departed for greener pastures. Get some hanging sticky traps -- not to stop an infestation but to diagnose. Inspect every plant -- leaves and roots -- you bring into the garden. After it goes into the ground, monitor. If you keep an alert eye, you’ll notice pests before they become an infestation.

If you have a garden service, ask workers to use your mower, if possible. Clean tools -- especially clippers -- with a diluted bleach solution (one part bleach to nine parts water) to avoid passing diseases. Keep your garden cleared of refuse where bugs hide, and water early so leaves and stems are dry at sunset. If you’re adding beneficial insects such as ladybugs and praying mantis, remember there’s a lag before you’ll see any effect.

-- Jeff Spurrier

Photos, from top: A caterpillar leaves a telltale pattern on young leaves; pill bugs can enrich soil but also eat tender seedlings; the potato bug, or Jerusalem cricket, looks daunting but rarely poses a threat of infestation. Credit: Ann Summa

RELATED: An early spring talk with bug expert James Hogue

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