Q We seem to have become inundated with Japanese beetles. We have traps in which we use the sex pheromone lure, and the pests are so plentiful that we need to empty the traps every day. I was told that we could plant something called rue and it would repel them. I have not been able to find a source and am thinking it might be under some other name.
What you are thinking of is Ruta graveolens (common rue or garden rue), which is purported to repel many insects and other pests. The Encyclopedia of Natural Insect and Disease Control, published by Rodale Press of Emmaus, Pa., lists garden rue specifically as a repellent for Japanese beetles.
A plant enhanced by its fragrant blue-green, finely cut foliage, it is often used as a specimen plant in herb landscaping. It is listed and pictured in James Adams's excellent book, ``Landscaping with Herbs,'' published by Timper Press, Portland, Ore. We also find it included in a catalog from Companion Plants, herb growers at 7242 North Coolville Ridge Rd., Athens, OH 45701.
There is a variegated type as well as the ordinary one, which is sometimes called herb of grace. Rue has yellow flowers with buttonlike centers. Incidentally, the plant commonly called meadow rue is not rue (or Ruta) at all, but Thalictrum.
Another good control for Japanese beetles is milky spore, a bacteriacide. It is available at garden stores, and now that winters are growing milder, it retains its strength through the cold weather and will remain in the soil for years. It is harmless to human beings and wildlife, acting on Japanese beetle grubs only.
Q I was surprised to read in your column that you recommend allowing cats to eat spider plants.
In several of my gardening magazines, I have read that these plants absorb toxic gases in their leaves. In a recent article, it said that several spider plants in a home would absorb any formaldehyde and other pollutants.
I suggest you retract your statement.
Bryant Pond, Maine
All green plants take in carbon dioxide and other impurities and give off oxygen.
Although plants absorb harmful gases such as formaldehyde, we do not need to be concerned that they will be toxic to pets. The remarkable capacity of plants to purify water and air should alert humans to do more to protect plants on our planet.
We should educate children to appreciate the role plants play in our environment. It is extremely important that humans recognize the absolute necessity of plants to ensure our survival.
Doc and Katy Abraham are nationally known horticulturists.