Wednesday, April 16, 2014

Garden doctor: How do I get rid of aphids?

Greenpeach aphids are seen in a cluster. Aphids have long, slender mouth parts used to pierce stems, leaves and other tender plant parts and suck out plant fluid. Courtesy photo

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What: Yolo County Master Gardener information table at Picnic Day

When: 9 a.m.-3 p.m. Saturday, April 20

Where: Plant and Environmental Sciences Building, UC Davis

Question: How do I get rid of the aphids on my ornamental garden shrubs?

Answer: As the weather begins to warm, gardeners start to see tiny clusters of aphids on all types of plants. Aphids can be white, black, yellow, brown or red and can infect all types of shrubs, trees and even vegetables. In fact, the UC Davis Integrated Pest Management website,, notes there is some type of aphid for just about every plant.

Aphids are small, pear-shaped, soft-bodied insects with long legs and antennae. They have long, slender mouth parts used to pierce stems, leaves and other tender plant parts and suck out plant fluid. It is often difficult to distinguish aphids from other small insects without a magnifying device but they are seldom seen alone, always in clusters.

A telltale sign of aphids is the discharge of honeydew (a sticky substance) that attracts ants. While feeding on the honeydew, the ants inadvertently spread the aphids, causing an even larger infestation. The honeydew often turns black, causing the growth of a sooty mold fungus.

While a few aphids do little damage to plants, a large infestation can cause any number of problems from curling, yellowing, distortion of leaves and stunting of shoots. Some aphid species inject a toxin into plants, which further distorts growth. A few species cause gall formations.

It is best to get an early start controlling aphids during our spring weather by unleashing a strong spray of water on sturdy plants early in the morning. The aphids are knocked to the ground and for the most part unable to return to the plant. Being diligent with regular spraying, every few days, should keep the aphids under control.

Insecticidal soap and neem oil are chemical controls recommended by the IPM site. These sprays kill aphids and their natural enemies. However, they leave no toxic residue. Be sure to read and follow label directions on all chemical controls. Also, as noted above, refer to the IPM site on aphids for a thorough, in-depth summary of the uses of insecticidal soap and neem oil.

Many predators also feed on aphids. The most well-known are lady beetle, lacewing and syrphid fly. Naturally occurring predators work best, especially in a small backyard situation. Weather plays an important part in the life cycle of aphids. Days with temperatures between 65 to 80 degrees are the prime time for aphids.

Question: Can drip watering be used for shrubs, annuals and vegetables?

Answer: Yes drip irrigation can be used on all these plants very effectively. Like any process, planning is essential. Remember that the goal in watering is to water deeply and infrequently, providing water to the entire root zone and a little beyond. Many plants will root deeper when watered just beyond the root zone, which is particularly beneficial to shrubs and perennials. This deep watering also reduces salt buildup and greatly reduces conditions for diseases that thrive with excessive evaporation due to watering shallowly.

Drip watering or irrigation is composed of three components. You will have a control head that includes a control and a filter. There is also the transmission system of pipes and hoses that deliver the water and then there are the emitters. Pay close attention to the emitters for the volume of water you want delivered in a given amount of time such as a half-gallon an hour or a gallon an hour.

Drip watering also allows you to use taller, low emitting sprayers, but you don’t want to mix emitters with sprayers. Keep emitters on one line (source of water) and sprayers on another. This way you’ll have a more even water pressure running through the lines.

This system can be put on timers so that watering takes place in the early morning hours when there is less evaporation. You will have to adjust the amount of time and the frequency for your particular garden. To get you started during the spring and fall months, 15 minutes daily should be adequate to reach the root zone and during the summer it will be about an hour daily. You can adjust from these points.

Also, you can change out the emitters so that more or less water is being delivered to a particular plant. Shrubs will need the larger volume while annuals and vegetables probably will do fine with a lower-volume emitter and they can all be on the same line.

Like any irrigation system, it is only as good as how it is managed. Because the openings are tiny, you will want to routinely check your emitters to be sure they aren’t clogged with dirt or silt. The advantage to using this type of system for watering is that the water is delivered efficiently and directly to the root zone.

From the University of California Agriculture and Natural Resources website, you can order numerous publications, one of which is “Drip Irrigation in the Home Landscape,”

— Send questions, addressed to the “Garden Doctor,” by email to, voice mail to 530-666-8737 or regular mail to UCCE Master Gardeners, 70 N. Cottonwood St., Woodland, CA 95695. Be sure to include your contact information, because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you.

You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at

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