Regional Gardening Reports :: National Gardening Association

In the Garden:
Southern California Coastal & Inland Valleys
February, 2010
Regional Report

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Aphids love early spring's succulent, nitrogen-rich plant flesh.

First-Of-Spring Pests

With our gardens waking up from their winter slow-growing slumber, new greenery attracts aphids and whiteflies. Between quickening growth and high-nitrogen fertilizers, succulent new growth is just what they love.

PROBLEM: If foliage is crumpled, curled, and yellow, and shiny and sticky with honeydew, or looks blackened with sooty mold, aphids are enjoying themselves. Aphids thrive on new, young growth and excessive nitrogen in the soil.

SOLUTION: Add raw, carbon-rich organic matter such as straw or sawdust to the soil to put the excess nitrogen to work. Aphids are "herded" by ants, who "milk" them for their honeydew and can be blasted from their perches by a forceful stream of water. Spray them with a garlic/onion/paprika mixture or a biodegradable insecticidal soap and water solution. If the foliage looks dull and wilted after two days, rinse it off so that the plant can breathe again. Crush the aphids on branches, leaves, or flower buds - these "corpses" and "bug juice" warn off current and later generations. Dust the aphids with diatomaceous earth. Place aluminum foil or white plastic on the soil or mulch under the plant foliage to reflect sunlight - this disorients the aphids and they'll settle elsewhere to feed. Sticky traps can be made easily from yellow plastic can lids. Paint the lids with a thin solution of honey or sugar and water, and set them outdoors near an infested area. When they have attracted and trapped many pests, wash the lids off, reapply the sweet solution, and set them in place again. Encourage ladybird beetles, lacewings, praying mantids, and syrphid flies. Aphids stay away from nasturtiums, spearmint, and stinging nettle.

PROBLEM: Leaves that are slightly curled and wilt, yellow, dry, and may look shiny from honeydew or blackened from sooty mold may harbor whiteflies. If white flecks fly into the air when the foliage is disturbed, their presence is confirmed.

SOLUTION: Hose off both sides of all leaves on infested plants every few days with an insecticidal soap solution. Destroy heavily infested plants. On plants which are still productive, remove lower, heavily infested leaves. Provide traps of yellow sticky boards. Whiteflies are attracted by a lack of phosphorus (plant foliage is a purple-green) or magnesium (plant foliage is yellow between the veins). In the greenhouse or other enclosed area, utilize Encarsia formosa predatory wasps that don't attack people or pets. Also, use a sticky yellow cardboard to attract and trap them. Add wood ashes, bone meal, blood meal, fish emulsion, or poultry manure tea to increase the phosphorus in the soil, and dolomitic limestone to increase the magnesium. It's a good idea to do a soil test first to see what nutrients your soil may be deficient in. Plant nasturtium and marigold as repellents.

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