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Check your garden for pests

  • Jane Scurich
  • How's your garden these days? If you're a regular reader of this column, you know Master Gardeners recommend monitoring your garden — strolling — observing, seeing what's happening. I try to live by this advice and have to admit I have recently discovered some really disturbing problems!

    Phormiums are among my favorite plants for adding a bit of drama to the landscape and containers. These New Zealand natives are upright, striking, eye-catching, drought tolerant, and until recently I thought they were indestructible. I was dismayed to discover a disgusting layer of thick, white, furry stuff on the base of the sword-like leaves of two container plants.

    That was not the only damage I found. A tall, strong, beautiful dahlia, robustly blooming in a container on my deck, was considerably less attractive thanks to strangely mottled leaves. Worm-like squiggles transformed the dahlia leaves into road maps with ever-changing and overlapping routes.

    But nothing could prepare me for the devastation to my beloved birch tree. For 35 years I have looked out my window to view distant hillsides through the graceful limbs of my beautiful birch. Suddenly a few weeks ago, I was looking at ravaged limbs, stripped of bark — wounds open to the elements.

    I knew I needed help. I suspected mealybugs were the culprit involved with the phormiums but the other two problems were perplexing. For help accurately identifying the pests and preparing a plan of action, I turned to the University of California (UC) "Pest Notes," an online database that supplies UC's official guidelines for pest monitoring (www.ipm.ucdavis.edu).

    Research confirmed the phormium problem to be mealybugs. I have found an occasional mealybug on my indoor orchids and have been successful treating them by dipping a cotton swab in alcohol and gently rubbing the infected area as recommended by the American Orchid Society.

    This phormium pest was a challenge on a much larger scale. High populations of mealybugs can inhibit plant growth, not to mention create an unsightly appearance. I tried the alcohol swab process and the integrated pest management (IPM) recommended strong blast of water and then an insecticidal soap. I'm keeping a close watch on these plants as it will probably take several weeks of treatment to eradicate the pests. Interestingly, only my container grown phormiums have suffered this infestation.

    I identified the dahlia leaf culprit as leafminers. The larvae feed just beneath the surface of the leaf, leaving an obvious trail. The good news is that this damage is mostly cosmetic and usually does not kill the plant. I followed the recommendation to remove the infected leaves and keep the plant well irrigated. My dahlia does appear a bit naked, but it is continuing to bloom and new leaves are emerging from the leave nodes.

    Imagine when I learned that the damage to my birch tree has been done by my some of my favorite entertainers — the tree squirrels who fly through the neighboring cypress and scamper across my fences. I do not have a solution to this problem. The tree specialist who has skillfully pruned my birch for many years was as surprised as I to see this damage. His research was quite similar to what I learned on the IPM website; "the squirrels strip the bark to feed on the cambium layer causing injury to the tree." The cambium is a thin layer of living tissue just under the bark.

    Recommended squirrel control methods include the use of pellet guns or dogs running free. Unfortunately, neither of these remedies is likely to work in my neighborhood. Squirrels are a part of life in Mill Valley.

    So, what is the result of my garden observations? I need to continue observing. Every day is different. Some pest challenges are easily corrected, some are more challenging, and some I just need to learn to live with.