Pear Leaf Blister Mites - late stage

I did some reading around the forum about Pear Leaf Blister mites, and want to make sure I have this right.

I only see them on one limb of the tree which was grafted last year. The rest of the tree currently has marble sized E pears (unknown) on other limbs. I am guessing the grafted variety (Ubileen) is more susceptible to these pests.

Will the same limb be susceptible next year, meaning I need to spray that limb with Lime Sulfur spray (or maybe they will just not return naturally)?

Given where we are in the season, do I understand correctly: remove the affected leaves and don’t worry about any treatment?.. or should the leaves be left to help that graft from last year grow? I might have to remove most of the leaves on the graft.



Last year I had a serious case of pear blister mite on a 5 out of 8 pear trees. I did not remove leaves since almost all of the leaves were affected. By August infected leaves were nearly black and tree looked quite awful although it still produced some fruit.
This winter/spring I sprayed those 5 trees with Lime Sulfur at dormant, green tip, and finger bud stage (3 sprays). I have no blister mite on those 5 trees.
One of the pears I did not spray seems to have a mild case of blister mite this year.
So I am concluding that 1) pear blister mite can spread and 2) that Lime Sulfur is effective.


The usual control based on literature is an early oil spray before first growth. Beware of anecdotes, they are as likely incorrect as correct. PBM often appear one year and are absent the next- even without treatment.

How we love our anecdotes, but science is tricky enough. Over the years I’ve found fault in scientifically derived info, but my own anecdotal observations are more fallible still.

Sulfur is not a first resort for me because it also kills predatory mites and other beneficials and I don’t believe someone should have to make 3 apps of anything just to control PBM. I recommend only using hort oil just before first growth.


Thanks all, great info. It sounds to me like maybe a progressive approach is best:

  1. See if they recur next year (given they are not rampant).
  2. If so, try horticulture oil before first growth
  3. If that does not work, try Lime Sulfur, knowing it will also affect beneficials.

It also sounds like if attempting to treat once in the leaf, Lime Sulfur is likely the only option.

Is it likely they will spread more, untreated, this year, or once established that’s it for the season?

You are right that the first dormant spray is narrow range oil. The second ‘green tip’ spray is Lime Sulfur. The third ‘finger bud’ spray is micronized sulfur.
I was following the below UC IPM protocol for pear blister mite, pgs 63-64.


Here’s an anecdote that corroborates your post :wink:

I had pear blister mite bad on my seckel pear last year. Sad because it was its first year really bearing. I picked off many leaves, but would have had to remove nearly all of them if I wanted to get all of the blisters. The crop was essentially a loss.

This late winter I sprayed dormant oil with copper and so far this year there is very little blistering. Way better than last year, in fact if I weren’t looking for it I may not have noticed any. Of course only 4 or 5 pears on the whole tree this year :frowning: At least maybe they will size up a little.

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Where does it say you can treat it with lime sulfur once it is in the leaf? Even synthetic miticides are supposed to be futile once that happens. The last spray in the UC Davis program, based on what CD said, is before the trees leaf out. I would have preferred a link directly to their guidelines on PBM. Too tired in spring, just came back from 8 hrs of pruning peach trees while I thin them. Tedious that thinning hr. after hr. day after day. Funny, I never get bored with pruning.

Anyway, oil alone should do the trick. Been dealing with them a long time- many seasons, many sites.

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It was a Scott comment I saw in another thread…maybe I misinterpreted.

“Usually I use lime-sulphur which is more potent against things inside leaves as it enters the tissue. Lime-sulphur works very well in the growing season, it should be used more often then but it has this reputation as a dormant spray that it can’t shake.”

Fair enough on the Hort oil, as I’d like to minimize use [of chemicals] where possible.

Edit - found reference

Yes I have used it in the past and it is effective.

These days I do one lime sulphur plus oil as a delayed dormant spray (swelled buds) and that is the end of that. The combo is a one-two punch.

And you can’t really know which punch is landing. I only use oil for pear blister mites and have never used anything else and get full control if it goes down early enough. The problem is that the ideal time to oil apples is later than pears, so when I see some PBM damage it is always where I’ve sprayed the oil too late for pears.

I am surprised you can spray sulfur and oil together, but I assume you can because you apply it so early. I would not have dared combine them if any green was showing at all.

At any rate, you are not suggesting it can penetrate the leaves to kill PBMs, and that should be clear. Little mistakes with oil can create a lot of damage, whether it is combined with sulfur or just frost.

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Me either!
I think it’s because it is somewhat like sculpture - and the artist in me likes that. I always look forward to it, even if I botch a lot of it!


The way I read “more potent against things inside leaves” was that it would kill the mites in a developed leaf that has been infected. @scottfsmith, has that been your experience, or I’m missing it here? Just want to make sure in the future I don’t use something without the potential for benefit.

Yes I have used it to kill mites inside leaves. Lime sulphur is an unusual compound, I have heard it can penetrate like a systemic but not very far. Whatever it is doing exactly, it can kill the mites.


Would this be the correct stage? Or is it a little too late? I’m sorry to be asking such basic questions. But I know that given a little too late, it can damage the leaves. Thank you

How do you know it killed the mites? Did you identify dead mites with a microscope? I don’t see how else you could tell, given the damage usually stops by mid-spring anyway.

I’m not asking to be difficult but in order to believe your claim I need to understand how you arrived at it. You are contradicting the literature I’m familiar with so I’d like to know the full basis of your belief.

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Yes, I identified them with a microscope. Then I wrote a paper about it. It appeared in J. Fruit Pathology.

Just kidding!! :grin: I sprayed, then in a few days the red spots turned to brown and there were no more mites that season. They have multiple generations so it seems like something must have been killed if they did not re-appear.

I’m not sure how it works but … it seems to work. The galls that mites create in fact are holes in the leaves and it could be the chemical can get to the mites through the microscopic holes. Or who knows what. These mites are uncommon in commercial orchards since a lot of sprays will kill them, and I don’t think they are very well studied for that reason… no $$ there.

I looked to find more information and could not find anything. I did notice that lime-sulphur seemed more common than oil as a recommendation, but indeed l-s will reduce the predatory mite population. I never have mite problems myself so it is not a big deal for me.


Thank you. I’m just trying to sustain some border between belief and fact because this is really hard- so much that occurs in the orchards I manage defies any established scientific explanation but I draw some sense of order by dividing what I think I think from what I think I know.

I’m surprised that the old Cornell book on commercial recs doesn’t include lime-sulfur in its list of materials to fight PBM- apparently it is high on the U.C. Davis list of controls although I’m unable to locate even that. Usually university recs take very seriously the collateral damage of beneficials.

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I’ve never understood how some sprays can give you mite flare-ups… the sprays killing the beneficial mites should equally well be killing the bad ones so it keeps the playing field level. It could be that there are pockets where it happens that there are no beneficial ones left only bad ones so there could be isolated spots of mite damage. Anyway, I’ve never seen it happen myself.

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It does seem to defy logic. However some mites are completely impervious to pyrethroids. At least the efficacy charts and labels show no efficacy. Then there are miticides which have very little insecticidal activity. Technically mites are not insects but arachnids. Apparently their biology is different enough that some insecticides don’t work on them.

I’ve also read that in some cases a compound will kill both mites and mite predators, but the problem occurs because mites can build back populations very quickly, whereas predators are very slow to build back populations, leaving the potential for mite explosions.

I’ve had some mite flares with apples. It’s a challenge to try to keep the stink bug down, yet keep the mites at bay. I’ve used 1% oil mixed with an insecticide, which seems to help.

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I would have led with that- an essential tenet of IPM. In nature, predators usually do reproduce more slowly than prey species. How relevant that is in the context of mites, I haven’t a clue, but that doesn’t mean I haven’t a hunch.