Questions on: Insecticides

Ron Smith, Horticulturist, NDSU Extension Service

Q: What is the name of a common insecticide that has bacillus thuringiensis in it to kill moths and caterpillars in a vegetable garden? The places I called can't seem to come up with a product. (e-mail reference)

A: Biobit, Dipel, MVP, Steward, Thuricide and, of course, just plain Bt. Someone should have one or more of these.

Q: I finally resorted to using a handheld mosquito fogger in my yard because I could not access my perennial garden due to those nasty skeeters. I fog when the bees and butterflies are not active. I got to thinking that the chemical I am using, which is the standard weak dose of Resmethrin (0.2 percent) available at hardware stores, might kill the things that are eating my plants, such as thrips, leaf rollers and miners, aphids and spider mites. Would it be effective to just fog the perennials and annuals in hopes of insect control without having to spray liquid chemicals or soaps? The commercial label was not specific on this, referring only to insects that bother humans and not plants. (Moorhead, Minn.)

A: I am certain that the fogging you do to wipe out the mosquitoes also will do a number on many of the plant-munching bugs as well. Your intention is mosquito control, but flies, thrips, and leafhoppers also are bound to be affected.

Q: What stock borer would get into squash vines about two to three inches above the soil line and cause the plant to die? When and what should be used for treatment? (e-mail reference)

A: This sounds like the squash vine borer. There are a couple of ways to combat this pest. Place collars around the vine stem and then slit the stem where the borer has entered. Remove the offending larvae and destroy. Bury the stem in some fresh soil to encourage new root development (it may work!). There are pheromone traps available, but I have no experience with their effectiveness. Sevin is a registered insecticide for control.

Q: I read an article recommending Lindane as a control for the birch borer, but I have been told it has been taken off the market. Do you have an alternative chemical spray? (e-mail reference)

A: A long-residual insecticide (endosulfan or permethrin) can be applied to infested areas. Apply the first treatment in late May, with additional treatments in mid-June and again in late June. Apply only to trees showing noticeable top thinning accompanied by visible insect galleries. Trees that have already been killed back should be removed rather than treated. Thorough spray coverage is essential for control. Imidacloprid, a soil applied product, can be applied once a year for season long control. Try to keep the tree growing vigorously with regular watering when rainfall is lacking and spring fertilization. Lindane is off the market due to its relatively high mammalian toxicity. It has long been implicated in cancer and environmental degradation.

Q: My father has several plum and apple trees that produce abundant fruit, but most are infected with insects that make most of the fruit inedible. In the past he has tried various products, such as the sticky residues, with very little success. He has purchased "Oil-Away," which is 94 percent cottonseed oil. Several of his garden magazines recommend spraying the trees with this product or another called "Eco-Oil". Do you have any experience with this or similar oil products? When is the correct time to spray and how many times would it be necessary to control the various fruit insects, such as apple flies and aphids? (Bismarck, N.D.)

A: Eco-oil is another name for a vegetable based oil that can be used when trees and shrubs are in full leaf. If your dad wants worm-free fruit, he will have to employ a number of tactics: Good sanitation--picking up fallen fruit every year; pruning out excessive twigs and branches, and any that are broken or diseased. Pheromone traps--these are sex attractants that pull the males into the trap, preventing them from mating with the females, which then cannot bear young or lay viable eggs. Spray program--use Sevin at blossom time, after blossom drop, and again about 10 days later. Once he breaks the cycle of infestation, he can then employ organic methods such as the sticky trap, pheromone traps, dormant oil sprays, sanitation, etc., to effect control.

Q: I’ve heard that one can make an inexpensive insect spray by putting some liquid soap in water, using a spray bottle. Is this true? If so how much soap can one use in a quart without hurting the plant? I'm after the white flies on my hibiscus. How often should they be sprayed? The hibiscus defoliated last month, but last week one had seven blossoms. Is it normal for them to cycle occasionally? (E-mail reference, Brookings, S.D.)

A: I do not recommend making up your own soap solution insect spray. The soap manufacturers are guided by economics for their formulations, not what would be good for plants or not good for insects. You could get something that would end up killing your plant. Formulations of insecticidal soap that are available commercially and safe for both indoor and outdoor plants. I suggest using that material to control your insects. Spray as often as necessary to kill the white flies. Good luck--they are tough ones to get rid of. I suggest cutting your hibiscus back--hard--to give it a resting period. Back off on the water for a few weeks, watering just enough to keep it alive. Then gradually increase the watering and fertilizing and new growth should begin to appear. Give it plenty of light; summer it outdoors.

Q.  I have been told that there was a show on PBS on which a gardener was showing how to make organic insecticide and fertilizer. He was using chewing tobacco, soap and beer. I have not been able to locate any information on this. Have you heard about any of this? If you have, I would appreciate any info you could give me. (e-mail)

A. Yes, I have heard of such a mixture, although I did not see the program. Chewing tobacco is a source of nicotine, one of the oldest insecticides known to mankind; the soap is a wetting agent, and the beer, as far as I'm concerned, is a waste. One is better off drinking it. (Just kidding!) Actually, the beer acts as an attractant.

A better one that I have tried is hot pepper spray and garlic, although some would argue that this too is a waste of a good resource, but if it works, why not try it? Get some habanero peppers (Be sure you are wearing plastic gloves.) and liquefy. Add to 2 cups of water, strain and spray. Guaranteed to toast `em! The garlic works pretty much the same way. Get about a dozen garlic cloves, and finely chop them up. Soak them in 1 pint of mineral oil overnight, strain and spray, or dilute with water and add a drop or two of liquid soap.

In both instances, these concoctions are most effective with direct contact on the target insect. Hope this helps.

Q: I have been noticing that most of the chemicals for white grub control list halofenozide as the main ingredient and say it can be used anywhere. Is it really that
safe? (Crookston, Minn.)

A: Halofenozide is a new class of insecticides known as an insect growth regulator (IGR). The chemical’s function is to interfere with the normal molting
process of the target insect. It is considered safe to fish, birds and animals when used at label rates.

Another one to consider is Dipel (or Bt), a biological material that kills by gradually making the grubs sick. Then they stop feeding and die. It is also
very safe.

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