Q I planted some magnolia shrubs, varieties of the Little Girl hybrids, in full sun about six years ago. One has never grown as well as its sibling. In the summer it is covered in small brown bumps. I used to remove these in the winter, when they would flake off and sometimes leave a cobweb-y residue. The bumps returned last year and before winter I pried some off. They were pink and had a soft texture. They cluster around the branching points and merge into a fibrous mass.
Ladybugs flock to the magnolia, presumably to feed off the pests. Can you tell me what they are and what to do about them?
A Your magnolia has a pest named magnolia scale. The large dry scales are the dead remnants of female scale insects, and the powdery contents are eggs for the following year's batch of scale insects. Like all so-called soft scales, magnolia scales excrete copious amounts of honeydew. A dark fungus grows on this and is called sooty mold. This is often the first sign of their presence.
The scale is sedentary, but the crawler stage is mobile. The ladybugs are after the crawlers but may not be able to reduce the pest to an acceptable level.
Magnolia scale, assembled in sufficient numbers, draws a predatory caterpillar that spins a silken web around the colonies of scale insects and eats its way through them at its leisure. The caterpillars are seldom seen, but your description of them merging into a fibrous mass makes me think that they may be at work on your magnolia.
Many factors predispose plants to scale attack. Generally, newly planted specimens that are growing in an open, exposed location are more troubled by scale insects.
Excess nitrogen fertilizer and frequent watering also produce soft, rampant growth that allows more scale insects to survive on the plant.
Wait to see what happens this summer. If they continue to be a problem, spray the plant with horticultural oil when the crawlers are present, generally in August or early September. Verify their presence by tapping an infested branch over a white piece of paper.
I planted chives in an herb garden two years ago. They have spread, not just in the herb garden but to other ornamental beds. I have tried spraying the greens with Roundup and rubbing them with gasoline. Neither has worked. What would you suggest?
Chives spread slowly by seed, and the resulting seedlings are easily pulled. The plant you are fighting most likely is wild garlic, which is a common weed. Wild garlic plants look a lot like chives but have a pungent garlic odor when bruised. The weeds may lie as deep as one foot in the soil. The bulbs go dormant in summer, and foliage appears in the autumn. The leaves continue to grow through the spring. The plants go dormant again by the beginning of July.
Don't use gasoline as a weedkiller. It is smelly, dangerous and not particularly effective. Roundup, or any other herbicide containing glyphosate, is quite effective, but timing and application technique are critical. The best time to treat wild onion is in April and May when the foliage is fully grown and actively pumping carbohydrates into the tiny bulbs deep in the soil. The foliage is very waxy, and must be bruised first to allow any herbicide to penetrate. You can use a leaf rake or your (gloved) hand to do the job. To prevent injury to other plants, wipe the herbicide on the garlic, don't spray.
It is also possible to eradicate wild garlic by digging the clumps of bulbs out of the soil. This is best done when the soil is moist. Inevitably, you will miss some of the small bulbs, so plan on checking the beds every spring and fall to remove any stragglers.
Scott Aker is a horticulturist at the U.S. National Arboretum.
