Columbine Muncher Is Likely Sawfly, Not Rabbit

Q: My columbine leaves are devoured. Could it be a rabbit? A: If the leaves on your perennial flowering columbine are completely gone, it could possibly be a rabbit, but there is more than likely another cause. Small green caterpillar-like larvae of the columbine sawfly eat thoroughly and constantly, munching leaves out of existence. A columbine in my garden was reduced to a few leafless stalks by this creature. They are the same color as the edges of leaves and it's necessary to observe closely to see them.

According to Sharon Collman, Washington State University Extension entomologist emeritus, sawfly larvae look like moth or butterfly larvae but aren't the same family. They cannot be attacked by the biological insecticide that affects lepidopterous larvae, B.t (sold under Thuricide and other names.) People frequently make the error of trying to treat sawflies with B.t and do not get any effect. The adult sawfly is a relatively unobtrusive gnat-like creature, less than 1/4-inch in length. Several generations of larvae may hatch in one season; pick them off when you see them.

The columbine will usually send up new shoots and leaves after one set has been destroyed. Keep them watered and monitor the new shoots for columbine sawfly.

Q: How can I keep squirrels from digging in newly-planted bulb beds? A: The Eastern gray squirrel gets the rap for the most disturbance to bulb plantings. These busy diggers will excavate crocus, tulips and anemones and bite into the bulbs. Often, they don't eat them, but take a bite or two and discard the damaged bulbs.

If squirrels are a persistent problem consider planting daffodils. Everything in the narcissus family contains toxins that animals refuse. Grape hyacinth (muscari species) also seems to be somewhat squirrel- resistant.

Planting in containers will help. Some gardeners fashion baskets with fine-mesh hardware cloth (about 1/2 inch mesh), folding and crimping the edges to line planting holes for crocus and tulips. Others plant in nursery cans, providing a plastic layer that protects the bulbs from underground digging.

Cover the ground over plantings with chicken wire, and place a mulch over the wire. This seems like a lot of trouble, more in the engineering department than in gardening, but it is necessary if squirrels are to be deterred from unplanting fall bulbs. Some gardeners report that cayenne pepper sprinkled on the ground deters squirrels, but my experience with this bit of folk wisdom was disappointing. It's expensive and the squirrels seemed to regard this as crocus goulash, and went on digging.

Do not leave unplanted or boxes of bulbs outside where squirrels can find them. Several years ago I did this and the result was that I trained a generation of squirrels to appreciate and eat crocus bulbs. They located the box of bulbs where I had left it, and reduced the contents to scraps, bits and outer skins. They then proceeded to spend the winter digging up every crocus they could find in the garden, having developed a taste for them. The Eastern gray squirrel has driven out nearly all the native Northwestern squirrels, including the red squirrel.

Gardening runs Friday in Scene and Sunday in Home/Real Estate, as space is available. It is prepared by Mary Robson, area horticulture agent; Holly Kennell, Washington State University/King County Cooperative Extension agent, Susan Miller, integrated-pest-management specialist, and volunteer Master Gardeners.