Ask Us About Pests

June 5, 2009 - 07:21

Q What’s the latest on thrips control?

A Honestly, not much. Conserve (spinosad) is still the best product out there against thrips, and it is typically effective at very low rates. However, there are clear indications of resistance appearing in both agriculture and ornamental production, and I still hear of growers using it at higher than recommended rates when things get tough. That’s not a good idea. Most of us working on thrips resistance issues think it is important to hold Conserve for the more important occasions, and you and your pest management advisers will have to decide when that may be. In some of our research here, we have observed that the new product from Valent, Overture (pyridalyl), has had some effect on Conserve-resistant thrips, so it makes sense to add this new product to your rotations. Our suggestion is to rotate your products carefully, using the softer more suppressive products during the early or off-season and use the more effective products like Conserve for the height of the season when you know you are going to need help controlling thrips. With the addition of Overture, there are now numerous classes of chemicals (see chemical class charts by Syngenta or OHP) to choose from that are labeled for thrips and added to rotations including older chemicals like organophosphates and pyrethroids, Avid, IGRs, and newer products like some of the neonicotinoids that are showing promise.

Q Spraying scales weekly still doesn’t eliminate them. Suggestions?

A I was visiting a grower recently that showed me a scale insect problem on a euphorbia. They were relatively large white scale insects on dark-green foliage, so they were very noticeable, and I know that it’s pretty tough to sell plants that look like that. He was treating them quite often and assumed that they were spreading, and from all outward appearances, they were. He plucked a few off of the plant to show me that they were still yellow underneath the hard scale cover, which he assumed were alive. Good point. Unfortunately, that’s still an assumption because there were many that were not yellow but black underneath and certainly killed. I took a large sample back and put it under the microscope, and every scale that I turned over was dead regardless of color or size. Without magnification, however, he assumed that he needed to keep spraying or do more. It is critical, when the goal is to reduce pesticide use and use pesticides judiciously, to be sure that the pesticide is necessary.

Scale insects, especially hard scales, are one of those types of pests that will not just disappear when they are killed. The dead bodies or scale coverings will remain on the stems and foliage unless you wash them off, and sometimes just washing with water will not be enough to remove them.

I recommended to one of my woody ornamental growers to go out and purchase an inexpensive dissecting microscope so that they could make good treatment decisions. The grower thought that he had a mealybug problem, but when I took the samples back to the lab and looked under the scope, I found more than two species of mites, two species of whitefly and mealybugs among other things. I took one of our stereoscopes to his facility to show them what they were missing, and they promptly purchased a dissecting scope. It is well worth the investment for those that want to make good treatment decisions.

About The Author

Jim Bethke is floriculture and nursery farm adviser with the University of California Cooperative Extension in San Diego County.

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