Ask Us About Insects

March 5, 2008 - 16:00

Q What is this, and how do I get rid of it?

A You wouldn’t believe what people will bring to me in a jar or bag — all manner of containers — and want me to identify it following one of my presentations. I know my colleagues have certainly had the same experience. Two such occurrences recently have reminded me that it is very important to get those nagging pests identified.

One was a branch of a perennial brought to me in a baggie that was full of a small scale insect. At first glance, it looked like a serious problem, but under a microscope, I noted that almost every scale body had been parasitized. In addition, the scale insect was not on the part of the plant that was going to be marketed.

That is a very good example of something that you want to leave alone and not treat because treating will certainly upset the balance and cause an outbreak of the pest. In addition, after investigating I found that it was an annual occurrence, which further suggests that they be left alone.

A second example was a 1-gallon Nandina that was full of an infestation of cottony cushion scale. Again, at first glance it appeared to be something serious because many of the leaves had immature stages of the pest, and the grower said that they were treating often. Upon closer inspection, under almost every immature were one or two Vedalia beetle larvae, Rodolia cardinalis, a very effective predator of the scale. If left alone, I am confident the problem will disappear in short order.

Obviously, some situations will necessitate treatment because of the need to ship immediately or to comply with intra or interstate shipping agreements, but these two situations were well suited for natural control.

Q What is a synergist?

A This question was in response to my suggestion that a grower perform a cleanup application of pesticides to contain an out-of-control population of thrips. His treatment program wasn’t quite what it should have been, so I suggested an organophosphate+pyrethroid tank mix as a synergistic combo to clean up the crop prior to introducing a program that could be more efficient against thrips.

Typically, when we mention a synergist, we are speaking about a chemical that will essentially knock out the detoxifying metabolites or enzymes in an insect’s body. We have these metabolites in our bodies too, and we can detoxify many of the pesticides in the same manner. Some insects, however, possess genes that modify the amount of metabolites or enzymes and render the insecticide ineffective.

The use of a synergist will break down, use up or block the metabolites, which helps the insecticide succeed in killing the insect. Therefore, synergists are typically used to restore the effectiveness of a pesticide to which an insect has become metabolically resistant.

One of the more common synergists is PBO, piperonyl butoxide, and it is commonly used to enhance the effectiveness of the pyrethroid insecticides. Even the homeowner can find pesticide products on the shelf that are synergized with PBO. Look at the active ingredients on the side of the can, bottle or bag.

The organophosphate+pyrethroid tank mix mentioned above acts in much the same manner as a synergist+pyrethroid mix. One or the other compound will take out the detoxifying metabolites in an insect’s system, and the other will kill it.

About The Author

James A. Bethke is floriculture and nursery farm advisor at the University of California Cooperative Extension in San Diego County, Calif.

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