Volume 16, Issue 24 - June 12 - June 18, 2008

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The Bay Gardener by Dr. Frank Gouin

Battling Bagworms

Bag these pests now before they grow too long

If you or your neighbors had bagworms last year and did nothing to control them, you’re likely to have bagworms again this year. The fertile female that lived in that bag all winter is loaded with hundreds of eggs.

When those eggs begin to hatch in late May and early June, the tiny caterpillars will drift with air currents and attach themselves to nearby junipers, arbor vitae, cedar, pine, spruce or fir trees and begin feeding. By mid to late June, their bags will be between one-fourth to one-half inch long, dangling from individual needles or tips of branches. They are visible with the naked eye — but you will need to be searching for them and ready to take action.

The most effective control of bagworms is BT, sold as Thuracide or Dipel, which are applied as a spray. BT is a bacteria that destroys caterpillars such as bagworms, cabbage looper, tomato hornworm, corn earworm, tent caterpillars and more. Spray at the right time, as BT is only effective in controlling bagworms until the bags are about one inch long. As the bagworm approaches maturity, it becomes immune to BT.

Use only fresh BT. Spray that is more than two years old, even stored in a cool dry place, is worthless and should be discarded. Purchase BT in small containers to avoid having to discard it. Old BT can be dumped in an active compost pile.

Once the bags of bagworms become one inch long or longer, you will need to use a hard pesticide such as Sevin to gain control.

Or you can pick the bags by hand from the plants.

If you elect to pick the bags from the plants, just throw them on the ground. They cannot spread, and it will encourage the bagworm’s natural predators to become established in your area.

You Can’t Divide an Azalea

Q Can you split a large azalea that has outgrown its space?

–Bea, by email

A You can cut it back hard to old wood and it will sprout new branches. But do it now, right after blooming.

Q I wish to split a well-established evergreen azalea potted in a large container. The root ball is now far too big, and I wish to split it into three plants and replant them again into tubs. Can this be done?

[email protected], by email

A I have never heard of a successful splitting of an azalea. The problem is being able to capture sufficient roots on each stem. You will find that most of the roots will be on only one stem. The remaining stems will have few roots.

The second problem with splitting azaleas is the stem-rot disease that will invade the stems at the point of division. Either Phytophtora or Botrisphyra root rot will invade the vascular system of the weakened plant.

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

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