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Insect Survivors Are Waking

Spray horticultural oil now to control them

The mild winter is likely to be followed by early invasions of scale insects, spider mites and other bugs that over-winter in the cracks and crevices on the bark of trees and shrubs. Roses, Alberta spruce, blue spruce and roses are the most susceptible species for spider mites. Scale insects will attack euonymus, crab apple, cherries including cherry laurel, oak and pine. Wax scale insects especially like hollies.
    A thorough spraying now with a four percent concentration of horticultural oil will help considerably in reducing the insect population when the growing season starts.

Witches Broom On Roses

Last summer I noticed a deformed branch or two on my Knock Out Rose bushes. My husband and I pulled the plants. Now what? Do I have to pull all of the 18 other roses out? Can I help the other bushes not to catch it? Can I plant more roses in the same spot?
    –Jean Scott Wagner, by email

This is a classic case of witches broom on roses. It is my first time to see it on Knock Out roses. The virus can be transmitted to other roses with pruning tools and by sucking insects such as aphids and spider mites.
  Should you get this virus on your roses, you must dig up the plant immediately and burn it or discard it in the municipal trash. Do not throw it in the compost or over the bank. Sterilize your tools: Pour boiling water over both sides of the shovel blade. Sterilize your pruning tools by spraying them thoroughly with rubbing alcohol. When pruning roses immediately adjacent where the infected plant stood, sterilize the blades of your pruning tools frequently, preferably before making each new cut.
  During the growing season, check your plants weekly for aphids and spider mites. Aphids can be controlled by spraying insecticidal soap or Malathion; spider mites with summer or horticultural oil. Morning applications of sprays are more effective than evening applications.
  Witches broom on blueberry plants should be treated similarly.
Ask Dr. Gouin your questions at All questions will appear in Bay Weekly. Please include your name and address.

Gardening through the Seasons

Fans of The Bay Gardener will want the bound volume of his wisdom. Enough Said: A Guide to Gardening Through the Seasons, compiled by the Annapolis Horticulture Society, is on sale for $20 at Greenstreet Gardens in Lothian and at Grauel’s Office Supplies in Deale. For direct orders — — add $6 postage. The Bay Gardener will inscribe your book and send it by return mail.

    Horticultural oil or summer oil are very safe and are used by organic gardeners to control insects. When plants are dormant, the oils should be applied at four percent concentration for maximum effectiveness. A four percent concentration requires adding 30.7 ounces of water to 1.3 ounces of oil, which makes a quart of spray. For a larger volume, add five ounces of oil to 123 ounces of water.
    Spray both the foliage and the stems of plants thoroughly to achieve uniform coverage. The oil spray should not be applied if temperatures are likely to drop below freezing within 24 hours of treatment.
    If you have either euonymus or Alberta spruce growing in your landscape, it is a must that you spray them to control euonymus scale and spider mites. If you had spider mites on your roses last fall, you are guaranteed to have spider mites on them now. Soon after you prune the roses, spray the stems thoroughly with a four percent concentration of horticultural oil.
    Horticultural oil and summer oil can also be used during the summer months to control spider mites at two percent concentration: 0.7 ounces of oil in 31 ounces of water or 2.5 ounces of oil in 125.5 ounces of water. During summer, never apply the oils when temperatures are 80 degrees or above. Otherwise, you’re courting foliar burn.
    On spruce, horticultural oil will cause the foliage to lose its blue color until next spring. The oil dissolves the waxes that coat the needles and give them their blue color.