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Marin IJ Articles

Protect your plants from sucking pests

  • Nanette Londeree
  • Are your roses sporting new leaves that glisten in the sunlight and are slightly sticky to the touch? Seeing a trail of ants crawling up the trunk of your plum tree? How about powdery black stuff on your camellia bush or the garden furniture next to it? All are indicators that sucking insects may have arrived and need your attention.

    There’s a group of soft-bodied insects - aphids, mealybugs, soft scale and whiteflies being the most common, that feed by sucking juices from plants. The direct damage they inflict on the plant can cause spotted, bleached or curled foliage and stunted growth. Indirect damage comes from the waste they produce. The pests can’t utilize all the sugar in the rich sap they draw from the plant, and excrete the excess in the form of honeydew, that looks just like drops of honey on foliage. When pest populations build-up, the sticky honeydew can drip from one part of the plant to another, or to anything around it – other plants, walls, walkways and more. And if that wasn’t bad enough, that honeydew provides the perfect growth medium for sooty mold, a black or dark gray coating on the surface of plant leaves and stems (or other non-living surfaces). This unsightly fungus doesn’t attack plants directly but can weaken them. Then there are the ants. They love honeydew and will fiercely protect those soft-bodied producers, especially aphids, from predators, in order to keep that sugary stuff coming.

    Aphids are small green, yellow, white, brown or black pear-shaped insects. Most species have a pair of tube-like structures projecting from their hind end – differentiating them from other insects. They attack a huge range of plants with roses, apples, flowering plums and many vegetables being favorites.

    Little oval insects with a waxy, white, cottony appearance, mealybugs are slow moving and usually found in clusters along leaf veins, on the underside of leaves, and in hidden areas at joints. They thrive in trees and shrubs, both indoors and out, and love all types of citrus.

    Up to 1⁄4 inch-long, soft scale are named for the shell-like covering that conceals their bodies. They can be found on the stems, twigs, trunks, foliage, or fruit of a wide range of trees or shrubs.

    Whiteflies are tiny with yellowish bodies and whitish wings. They develop rapidly in warm weather; they fly up in a cloud if you disturb an infected plant. Fuchsias, geraniums, many herbaceous ornamentals, tomatoes and most vegetables are some of their favored plants.

    You can save yourself a whole lot of energy and protect your plants by preventing sucking pests from getting established. Some general measures include:

    • Purchase pest-free plants.
    • Inspect plants often for the presence of honeydew producers, honeydew, sooty mold or ants crawling up woody plants or trees.
    • Don’t overfertilize; high levels of nitrogen fertilizer can over stimulate new plant growth, attracting pests.
    • Encourage natural enemies; provide habitat conducive to their needs - a variety of nectar and pollen producing species, shelter, and some pests to feed on.

    If you do see any of the honeydew producers, act quickly. Light infestations can usually be eliminated with a minimum of effort. Start by knocking pests off plants with a strong spray of water and repeating every few days as needed. Prune out any shoots, leaves, twigs or other plant parts that are infested and discard. Where ants are visible, wrap the trunk of the plant or tree with sticky tape to catch the ants and prevent them from tending to the sucking pests.

    Sucking pests are difficult to control with pesticides; developing and maintaining healthy populations of natural enemies, both predators (lady beetles, lacewings and soldier beetles) and parasites, is a more effective long-term management strategy.
    Oh, and if you do find sooty mold (and have removed the source of honeydew), it will gradually weather away, or can be washed off with a strong stream of water or soap and water.