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Bring the Houseplants Inside; Leave the Bugs Outside

Bug 1: Wax Scale

One of the problems of moving houseplants outdoors during the summer months is that they often become infested with insects. You’ll want to control those bugs before bringing your plants back indoors.
    A Bay Weekly reader sent me a sample of Christmas cactus that had been outdoors along with her other houseplants. She wrote that the plant had not been growing and, despite her care, continues to decline. On the five-inch-long piece of stem in the envelope, I counted 12 scale insects.

Gardeners’ Tip: Feed Your ­Azaleas Ammonium Sulfate

  During the winter months, the flower buds on azalea plants will be enlarging. If there isn’t adequate nitrogen in the soil, the nitrogen from the leaves will migrate from the leaves, generally starting lower. Loss of nitrogen results in the leaves turning yellow and dropping to the ground. By spring, the azalea plants will only have clusters of leaves surrounding the buds at the ends of the branches.
  To prevent this, spread 1⁄4 cup of ammonium sulfate under the drip line of the azalea plants soon after the first frost, which has already come in some parts of Chesapeake Country. If the azaleas are mulched, cultivate the fertilizer into the mulch and irrigate.


    Her Christmas cactus had been infested with wax scale, which appears as a glob of white wax the size of a pencil eraser with a pointed tip. If you scrape the insect from the stem, you will find that the underside is pink.
    The horticultural oils that are safe and effective in controlling other scale insects are ineffective on wax scale. I recommended she use a butter knife to scrape off each scale and either burn them or flush them down the toilet.
    After removing all the scale, examine the plant daily for small white threads — the pest’s crawler stage — crawling on the stem. If they’re present, treat the plant with insecticidal soap.
    I also advised her to check her other plants while still outdoors for wax scale, for I strongly suspect plants surrounding her house or on the ­nearby piazza are also heavily infested. Wax scale are not particular as to what they feed on. They love holly, pyracantha, yews, roses and cherry laurel to name a few. The only effective means of treating a heavy infestation on landscape plants is to spray with insecticidal soap (or malathion on the crawlers). This means inspecting the plants weekly and spraying as often as needed.
    Since last winter was mild, wax scale over-wintered. When we have severe and cold winters, wax scale and its crawlers are killed — only to migrate back from areas south of us.
    Next week, I’ll introduce soft-shell scale, mealy bugs and spittle bugs and spider and cyclamen mites and how to combat them.

Farewell, Tree Stumps

Q    I read in your column in Bay Weekly that tree stumps can be treated with chemicals within the first week after being cut. I had several large trees cut down three weeks ago. Is there anything I can still do to treat the stumps?
     –Lynn Whitall, via email

A    Take a hatchet and make cuts every couple of inches along the outside edge of the stump. Treat the cuts with a 1:1 blend of Weed-B-Gone or Trimec and water. Use an oil can or old paint brush to apply the chemical.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.