QUESTION: We are planning to have our house tented for termite fumigation, and I am concerned about the herbs and raspberries planted up against the house. Will this contaminate the plants, and how will these chemicals affect the soil?
--S.C., Los Angeles
ANSWER: According to Donald Reierson, a staff research associate in UC Riverside's Department of Entomology, the most commonly used fumigant for termites is sulfuryl fluoride (Vikane), which has just about replaced methyl bromide.
Sulfuryl fluoride shouldn't "contaminate" plants or their roots (it is not absorbed) but may damage or kill them if they come in direct contact with the gas.
The manufacturer, Dow Agro-Sciences of Indiana ( 258-3033), says plant roots can be protected by thoroughly wetting the soil right before the tent goes up because water is an effective barrier to the gas.
When the tent is taken off, this lighter-than-air gas "goes straight up," they said, dissipating very quickly--not down into the soil. Plants will only be harmed if the escaping gas actually hits some foliage.
Plants that are three feet from the house or closer may be burned or killed by the gas, but careful handling of the tent can minimize this. There are no known short- or long-term effects on the soil, other than it will kill any creatures it contacts during the tenting.
Tenting a house is still considered the best way of killing dry-wood termites, which are the termites usually found in house timbers, in dead tree limbs and in patio furniture.
If you have wood patio furniture--even redwood--make sure you put it inside the house before the tent goes up so it gets fumigated too.
Wait for Warmth Before Pruning Tall Begonias
Q: Could you tell me the correct time and procedure for pruning angel-wing begonias?
A: Cane-type or angel-wing begonias such as "Irene Nuss," with its big, drooping clusters of coral pink flowers and dark red leaves, should be cut back in March or April, according to Lew Whitney of Roger's Gardens in Corona del Mar.
This means you'll have to look at a bedraggled plant all winter, but you want to avoid a late cold snap, which will "really fry any new growth," said Whitney.
I cut off only the top third of the canes, just above growth nodes, because I like tall angel wings and mine get 3, 4, even 5 feet tall. Whitney prefers them shorter and bushier, so he cuts off the top two-thirds.
Either way works, and they'll bounce right back if you start fertilizing right after pruning. "They are voracious feeders," said Whitney.
Make sure you save those pieces you cut off. In a shady spot, you can easily root them in potting soil, if you don't keep them too wet, and you'll soon be supplying the neighborhood with baby begonias.
Spray Olive Trees to Halt Fruiting
Q: I have an annual problem with the tremendous amount of olives that fall from two trees, causing much extra heavy labor and, of course, a source of carpet staining when crushed olives are tracked into the house. Do you know of any way we might keep trees from bearing fruit?
--G.P., Simi Valley
A: Nurseries sell fruit eliminator sprays, such as Florel (ethephon), that you can spray on the trees when they are at mid- to full bloom. It effectively stops olives from forming. It works on other trees too, from carobs to cottonwoods, but is commonly used on olives.
The only trick is to make sure that the spray reaches the flowers, which is not too difficult on an olive since it is a fairly short tree. A good hose-end sprayer should do the trick.