Gardening: Mysterious white lines brown her columbines

  • Article by: NANCY ROSE , Contributing Writer
  • Updated: January 24, 2001 - 10:00 PM

QI planted columbines two years ago. The first year they looked fine, but last year most of the foliage had curving white lines all over it and several plants turned brown and died. What's the problem?

AIt sounds as if your columbines (Aquilegia sp.) suffered from two problems that sometimes occur on these pretty perennial flowers. The white lines are caused by an insect pest known as the columbine leaf miner. These insects can cause foliar damage, and severely infested leaves may eventually die and drop off. However, they probably are not responsible for your columbines turning brown and dying. That probably was caused by a disease such as crown rot.

The adult leaf miner is a small brownish fly, but the damage is caused by the insect when its in the larval stage. Adult females lay eggs on the undersides of columbine leaves, and right after the tiny larvae hatch they burrow into the leaf. The larvae create winding trails as they feed on the inner leaf tissue. If you hold a damaged leaf up to a bright light you can see the larvae at the end of the tunnels. Mature larvae emerge from the leaves, develop into adults and repeat the cycle. There may be four or more generations over the growing season.

Leaf miners are difficult to kill because they are protected within the leaves for most of their life cycle. Systemic insecticides, which are taken up into the plant instead of just sitting on the surface, can be effective if applied fairly soon after the foliage emerges. Make sure the product is labeled for herbaceous perennials and follow label instructions carefully. A non-chemical alternative is to cut off and destroy any leaves that show leaf miner damage. If you religiously keep up with this nonchemical approach you may be able to break the generational cycle of this insect pest. However, if a neighbor has untreated columbines, the leaf miners from those plants may continue to infest yours.

Sudden browning and death of the plant is usually an indication of a disease such as crown rot, which is caused by a fungus and can quickly kill an entire columbine plant. Columbines require excellent drainage, especially over winter, and they are prone to crown, root and stem rots if they are planted in a poorly drained site. Improve the drainage of your soil by adding lots of coarse organic matter before planting columbines, or grow them in raised beds.

The unique nodding habit and jewel-like colors of columbine flowers make them popular perennials, but they are almost always fairly short-lived. An individual plant may last three or four years but that's about as long as you can hope for in most gardens. Many columbines hybridize readily and reseed throughout the garden. I usually allow a number of columbine seedlings to grow in my perennial beds each year. The colors range from deep purple to light pink and, because seedlings of most hybrid columbines do not turn out the same color as the parent plant, I get different colored flowers every year.

QI grew a yellow carrot named 'Sweet Sunshine' from the Burpee seed catalog. It is tasty, but it does seem to have lower germination than other carrots. Are there other yellow carrots available, and do they have different growing requirements than orange carrots?

AWhile orange is the standard color for carrots, there are also white, yellow, red and purple carrots. Cultivated carrots were developed in the region that now stretches from India and Afghanistan to Turkey. Early carrots were yellow or reddish purple. Carrot cultivation moved into Europe, but it wasn't until the 1600s that orange carrots were bred and became the dominant choice in cultivated carrots. The flavor of white, yellow, red and purple carrots doesn't vary much from orange carrots.

I went through the listings for carrot (Daucus carota subspecies sativus) in the Andersen Horticultural Library's Source List of Plants and Seeds looking for yellow carrot cultivars. There don't seem to be many readily available other than 'Sweet Sunshine.' I did find references to several yellow carrot cultivars including, 'Yellowstone,' 'Lubiana' and 'Jaune du Doubs' on European gardening Web sites (check http://www.seedsofitaly.sagenet.co.uk) . Perhaps more U.S. seed companies will develop and sell yellow carrots in the future.

I'm not sure why your yellow carrots did not germinate as well as the orange ones. Sometimes certain unusually colored hybrids (such as white marigolds or yellow petunias) grow less vigorously than those with standard colors. But all carrot seeds are tiny and the equally tiny seedlings can easily fail to emerge if the garden soil is at all crusted. It's also very easy to wash away those tiny seeds with a blast of water from the hose, so keep the soil moist, but do so by using a misting attachment or a fine-droplet sprayer.

-- Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. She spends her spare time gardening, inside or outside, depending on the weather. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.

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