Creosote-Treated Wood Is Safe For Use In Gardens

Q. My tomatoes were planted about a foot away from railroad ties. Are they safe to eat?

A. Yes. Wood treated with creosote is quite safe to use around the garden. It can leach into the soil a bit, but it doesn't move far. It may damage or even kill roots, but it is not absorbed by them. It will not be present in your tomatoes.

Old railroad ties are often used for terracing or for building raised beds. Don't plant any closer than 4-6 inches from them and you shouldn't have any problem. To be extra safe, you could paint the side of the tie that will contact the soil with a sealer such as urethane or shellac. Or, line that side of the bed with plastic.

Of real concern with creosote are the oozing and vapors that occur, especially in hot weather. The tar-like ooze can quickly make a mess of your clothes. The vapor is usually a problem only if you create a cloche or plastic row cover over the bed. Trapping vapors in with plants will cause crop damage. For the same reason, creosote-treated wood should never be used in greenhouses.

Q: I've got little green worms eating up young transplants of red acre cabbage. What should I do?

A: There are a number of little green worm-like caterpillars that feed on plants in the cabbage family. They can be cabbage loopers (or inchworms), imported cabbage worms, or diamondback moth caterpillars.

Cabbage loopers and diamondback adults are small brownish or grayish moths with white or silver markings. Adults of the imported cabbage worm are white butterflies with a few black markings on the wings. The adults appear in the spring and the females soon begin laying their eggs on the leaves of cabbage, broccoli, kale, cauliflower, and other members of the cabbage family. The caterpillars hatch out of the eggs within a week and begin to feed on the leaves of these plants. As the caterpillars get bigger, so do the holes in the leaves. When the caterpillars are fully grown, they enter a pupal (or cocoon) stage and emerge again as adults.

There are ways to control these pests without using synthetic pesticides that may disrupt the work of wasps, birds, and beetles feeding on the caterpillars.

-- You could control them by physically removing the caterpillars and destroying them in a can full of soapy water, but this can get to be very tedious in short order.

-- The best control is to exclude them from the plants they want to eat. Many garden stores carry a very lightweight fabric used for floating row covers. The fabric must enclose the plants, and be tucked carefully in the soil all around the edge of the plot. Make sure no pests are on the plants before you install the covers, and remove them only to weed or check for pests - including slugs. You can water right through the cloth.

-- Since all of these caterpillars are the immature stage of moths, a control that will be very effective is the bacterial toxin produced by Bacillus thuringiensis kurstaki (B.t.). This is a very selective poison that targets only moths, but might control the imported cabbage worm (a butterfly) also. It does not damage beneficial insects, nor is it toxic to humans or their pets.

To be effective, the young caterpillars must eat the poison, so be sure to spray products containing B.t. on leaves where they are actively feeding. Repeat the treatment at 5-7 day intervals. To get the best control and greatest safety, please read and follow the label directions carefully.

Gardening runs Friday in Scene and Sunday in Home/Real Estate. It is prepared by Mary Robson, Master Gardener program director, Holly Kennell, Washington State University/King County Cooperative Extension agent, Susan Miller, integrated pest management specialist, and volunteer Master Gardeners.