What to do about greenhouse thrips on salal?

Asked May 15, 2017, 11:23 AM EDT

Based on what is known about the life history of greenhouse thrips, what do you think I should do to deal with the white-leafed salal in my back yard? Shall I be cutting it back and keeping the leaves out of compost? Do the thrips have a ground phase? Should I be clearing areas around the base of the plants? I tried a sticky "thrip trap" that has not seemed to work yet?

I found an article about experiments at UW back in 2004--but no results, do you know what they determined?
http://www.washington.edu/news/2004/03/04/gardeners-do-battle-with-tiny-foe/

Curry County Oregon insect issues greenhouse horticulture

3 Responses

hello, to let you know that i was away for three days, but called several folks at the UW as well as forwarding on your concerns to others who have been involved at some level with this issue here in Oregon during the final hour or so that i was here on Monday. There is no easy or fast answer for you, and i will reopen this case when i have time to pull the info together, but it probably won't be until the end of next week. I apologize for the delay, but as i have shared with other folks, there is nothing at present that i am aware of in regards to treatment on salal at this point.

Oh, and thanks for that lead! i did a number of searches and could find no further info or results with the approach that was taken.

So, here's the further info that I've received from others to forward back to you. It appears that cutting the foliage back may be helpful, and spraying would most likely have to be ongoing:
Dear all:

Last year, I also tried to contact personnel at U of W regarding the greenhouse thrips outbreak there but never got any response to my e-mails or phone messages.

As Scott says, the present damage is probably from last year. A sample taken by ODF near Coos Bay in February had one live thrips on it, so it appears they may have overwintered in at least small numbers. Whether this is the “norm" or is the consequence of the more typical winter temperatures this year, we don’t know. The greenhouse thrips can have numerous generations in a season, so it could be that the large numbers we found last year were the eventual result of small overwintering populations.

I’ve seen pictures of almost completely defoliated salal (from Bandon) with buds beginning to swell and break, so it appears that plants can survive at least some dramatic defoliation. However, Chris Hedstrom and I observed salal in the Florence area last fall that had apparently succumbed following repeated defoliation.

As best we know, the greenhouse thrips does not shelter in the ground or on shed leaves. If it does not, there is no point to removing leaf litter or keeping such out of compost and there wouldn’t appear to be any value in clearing litter and leaves around the base of the plants. However, we know so little about the overwintering behavior of this insect that I am not comfortable stating definitively one way or the other. From what I could see from the image of the recovering plant in Bandon, I don’t know that cutting the plant back would help.

While adults can fly, I suspect these thrips normally confine their movements to crawling on stems to new leaves or by crawling between leaves in contact. The only “thrips sticky trap” I know of is a yellow sticky card used to determine whether thrips are present by trapping adults flying from plant to plant, which does not control overall thrips numbers. If that is the trap referred to below, it will have little or no effect.

Chris and I are planning to survey for the thrips this summer, including looking for natural enemies. I appreciate any reports, particularly north of Florence, of suspect damage. In that vein, please remember that azalea lace bug has been found attacking salal in the Willamette Valley, sometimes pretty heavily, so there is always the possibility it could be involved as well. In that vein, Scott mentioned lace bug damage to azaleas in Azalea Park in Brookings. Scott, if you could get me some samples, particularly with live lace bugs or at least dead adults (pretty early in the season yet), I’d really appreciate it.

In terms of solutions, Chris and I will be looking into the prospects for biocontrol using a parasitoid that appeared effective in California. There are numerous questions to be addressed in this regard, among them whether the agent is still commercially available, whether it would survive here, whether it would be effective if it survived here, and the population dynamics of the greenhouse thrips itself.

Hope this helps. Please let me know if anyone has any questions.

Jim



from the Grounds Supervisor I
UW Campus Grounds Operations

Hi Scott

I wish I had better new for you in regards to Greenhouse Thrips. We continue to have trouble with Thrips in years with a mild winter. Years with winter temperatures below freezing we have almost no damage from Thrips.

Our standard practice is to remove affected plants material ( we cut they to the ground and let them re-sprout ) including all leave and debris then mulch the area. It is not surprising to find Thrips along roadsides, We also found that we added to the problem by not covering our load we took to the dump, spreading Thrips along the way, we now cover our loads going to the dump. We don’t use pesticides to control Thrips, it comes down to a timing issue by the time you realize there is a problem it is too late to spray. If you have any question contact me and I will try to help the best I can.

From the the IPM and sustainability coordinator for the campus.

Thrips can be very difficult to control. It can take multiple sprays every month. UC Davis recommends that we spray in the beginning of spring to protect the new growth and remove all infected leaves. We found similar results from the 2004 study. We have had little success with spraying but have found removing infected growth diminishes the severity of the outbreak. The main plants that we have problems with our salal and some of the viburnum species. I have attached the UC Davis IPM page for reference.

http://ipm.ucanr.edu/QT/thripscard.html



I hope this helps answer your questions and will make a difference in dealing with your issues what has become a major pest.
Scott