Any new news about how to deal with thrips on landscape salal?

Asked April 11, 2020, 5:03 PM EDT

It's shaping up to be another bad year for greenhouse thrips on the salal in my yard, and so I am wondering if there is any updated news about how to deal with them. In particular, I am wondering what to do with all the bleached foliage that I want to cut back. Is it OK to pile it up in the back 40, or should I try to burn or dispose otherwise? Back in 2017 when there was a bad salal year, it was reported that there was still too little known about the thrips life cycle and wintering habitats in landscape plants to make a recommendation. THANKS!

Curry County Oregon

4 Responses

i have the question into ODA and found their annual report on plant and pest issues, but could not locate the specific info re your situation. I have also seen this condition again. It was hard to determine if the salal that was affected in the past came back as vigorously as previous.

It would be interesting to hear from you what you did in the past, if anything, and especially how this plant recovered--if you cut it back. One interesting point of note is to ascertain where the pest is going once the damage has occurred and that is also a question that I have, and it could be that this is an issue that we will see as an ongoing cyclic problem that there is no real remedy for--especially given how much of this appears to be happening on public land.

I will get back to you with what I find, but it would also be interesting to know how you treated this situation last time it occurred. This type of information might be very useful to folks at the ODA, and it would also be helpful to those of us who work for Oregon State University.

Hi Scott, Thanks for your response. Last time (2017?), I pruned back the damaged leaves (pretty much pruning back near to the ground) in one area of hedge (it's interspersed with rosemary) that is very visible from my windows. I threw the leaves away in a garbage bag because I didn't want to inadvertently spread the thrips. In other areas in my yard, I did nothing. I did not document this well --so I am going only my memory. That year, and in intervening years, the hedge salal did just fine --I think because we had some good winter freezes, but not this past winter.

What I am finding now is that I am having thrip damage, bleaching, again in the hedge where it was before. In the wilder areas where I did no pruning, there is now some dead wood (presumably some of the salal was killed off either by GT or by drought?) but plenty of green leaves underneath -- last year's growth that does not yet seem to be affected. I don't really see many new leaves. However, it may well be a result of aspect/ soil/ moisture rather than any result of what I did.

If you want to give me some guidance about what to look for/ pay attention to/ what to do, perhaps I could be more helpful or do a useful experiment. I just trimmed down the salal in that hedge again (have leaves out in the lawn for now) --and there is another area very close by that is all bleached.

Again the wilder area--about 20-30 feet away, has no sign of bleaching (mostly in shade), yet.

Like you, I have also seen this damage in our local state park :( . I LOVE this plant with its pretty leaves and flowers and fruit--so I hate to see it in trouble. I will appreciate any more info you can provide.

I was hoping for something more solid to offer in terms of treatment, but all the ODA could suggest are the methods and agents in the Pacific Northwest Insect Management guide from OSU (listed below, although there are no treatments available for household use).

The state entomologist at ODA suspected these will be of limited effectiveness, particularly in a landscape context. He had no idea whether cutting salal to the base will reduce the thrips populations to non- or less-damaging levels. Given his suspicions about the probable pest load in the overall environment (especially since they’ve found them on a number of other evergreen shrubs), He's a bit dubious about the efficacy of that approach. He forwarded my message to the new state entomologist in charge of biological controls (Some of the current controls are also listed below, and these would most likely not be available to you, and might be in the natural environment.). I was waiting for feedback from him before sending this information back to you, and if anything should come my way, I will let you know.

Greenhouse thrips (Heliothrips haemorrhoidalis)

Pest description and crop damage The insects are very small with fringed wings. Monitoring is usually made by visual inspection for the thrips or their damage. Their damage is usually evident as a scraping of the epidermal layers of the plant leaf. Thrips are vectors of a serious disease. Tomato Spotted Wilt Virus (TMSV) and Impatiens Necrotic Wilt Virus (INSV) can have devastating consequences in susceptible crops.

Biology and life history They tend to prefer very tight spaces and are particularly attracted to flowers with pollen.

Scouting and thresholds Thrips can be very difficult insects to detect. Use blue or yellow sticky traps to assess infestation and control efforts. An aggregation pheromone for thrips, Thripline ams, is available for monitoring.

Management-biological control

When there is potential for vectoring disease and/or low tolerance for direct damage from thrips, biological control may be inappropriate as a tactic. There must be some tolerance for a pest in order to sustain biological control organisms. Where viruses are not a factor or damage tolerance higher, biological control may provide several benefits, including pesticide resistance management, improved worker safety, and reduced re-entry intervals.

Management-biological control

Natural enemies include:

  • minute pirate bug, Orius insidiosus
  • predatory mites, Typhlodromips (Amblyseius) swirskii; Iphesius degenerans; Neoseiulus (Amblyseius) cucumeris; Neoseiulus barkeri
  • predatory thrips, Thripobius semiluteus
  • soil-dwelling predatory mite, Hypoaspis miles-Feeds on pupal stage in soil.

At this point, it's hard to say if there would be any affect on dumping the yard waste in the back forty, and burning it would probably make little difference at this point. i believe some of the methods of control listed above would be for larger agricultural use.

Much thanks for trying to track down an answer, Scott. Too bad that there is no better guidance from ODA! I realize they are up against lots of pests and probably need to prioritize the ones that hit farms, but beyond bleaching out my hedge, these landscape scale GT could be really bad for wildlife in general-- and also could be bad for the floral foliage industry, which harvests salal. I'll probably continue to prune the most bleached areas in my hard, hoping that greener leaves will return (and will aim to take better notes about what happens). Please let us know if you learn more!