Japanese Andromeda/Pieris japonica & Rhodo issues

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by pirhan, Apr 26, 2022.

  1. pirhan

    pirhan Active Member

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    Hello,

    I have moved and inherited a new garden. It's a newer build and the soil doesn't seem the greatest. The previous owner had these plants and they are looking quick sickly. I fertilized last year and amended the soil again with steer manure, but the leaves seem to be worse. There is a shrub next to the fence on the strata and it seems to have no leaf issues, so maybe this is fungal? Any help would be appreciated.

    The rhodo was new last spring. I didn't realize how much the snails/slugs/critters would enjoy it - any suggestions on helping it as well?

    Lower Mainland, zone 7a
     

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  2. vitog

    vitog Rising Contributor 10 Years

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    I'm not sure about the other plants, but the rhodos need acid soil; and manure tends to raise pH levels, unless it is very old. Most websites advise against using it for rhodos.
     
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  3. pirhan

    pirhan Active Member

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    Oh! I had no idea. I have two hydrangeas, one near the rhodo, so I will look at amending the soil to be more acidic.
     
  4. Pieter

    Pieter Active Member 10 Years

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    I doubt it's slugs or snails nibbling on your rhodie, probably weevils.
     
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  5. pirhan

    pirhan Active Member

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    Thanks! I always see plenty of snails and slugs around, but never any weevils, so I assumed they were the culprit. Anything I can do or it's what it is?
     
  6. Margot

    Margot Generous Contributor 10 Years

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    I haven't time to write much right now but will this evening. The 2 pieris almost certainly are being attacked by lacebug and the rhodo by root weevils. You can find a lot about both problems online but I will get back to you later.
     
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  7. pirhan

    pirhan Active Member

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    Thank you very much. The pieris are very small so it will be difficult to spray under the leaves to get rid of the lacewings. Pesticide was the other option but as I am trying to plant many pollinator friendly plants, I don't think this would be a good idea.

    Do the weevils also like primula? I planted some primulas and they've been nibbled down to nothing. I also had a rabbit eat all my lilies last year...

    I could see about transplanting the rhodo and piers (both quite small) to another location in the strata which would give me a chance to spray the underside of the piers. I'm actually not particular to them, but particular enough not to outright toss them. Since I live in the lower mainland (zone 7), I like to have some structural pieces for the winter time.

    The garden in question is 8x7 and 6x7 (the walkway to the front door separates the two). There are two hydrangeas in either corner, four piers in total (two on each side of the walk), the rhodo, a camellia and a boxwood. I have various perennials - dicentra, lupin, helleborus, lilies, lungwort, viola, tulips, gladious, two tiny roses, heuchera and some ferns. There was a bee balm there but I don't think it survived with the lack of sun. (The previous owner put those and the roses in when the house was on the market.)

    Zone 7, north facing, part sun (morning and late afternoon direct sun only), cheap garbage "soil"
     
  8. Pieter

    Pieter Active Member 10 Years

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  9. Georgia Strait

    Georgia Strait Generous Contributor

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    Did I miss what area you’re in?

    to have a sickly Pieris japonica is saying something … I consider them the common shrub and generally happy (and useful landscape plant) at the coast — they are for sale at the supermarket right now … that’s how common

    I like Pieris and there are many names these days — they can be messy with leaves etc naturally dropping — tho this plant is evergreen, like a rhodo.

    more info about your sun exposure and climate location and wind exposure etc will be helpful

    are these sentimental garden plants ? (Example - this garden was planted by a friend / relative)

    if not — your best option in several ways (money / time / upkeep in future etc) might be start over with a design you like and plants in good health from reputable sources
     
    Last edited: Apr 27, 2022
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  10. pirhan

    pirhan Active Member

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    Thank you for the info.

    Lower Mainland, zone 7(a) with north facing part sun, total area approximately 100sq ft, part of the garden is under the eaves

    I've really no emotional connection to the plants other than I hate the waste in tossing them. They were planted by the previous owner. I could plant them elsewhere in the strata as there are spots that are empty from other dead rhodo/piers. There are many other piers around the entire complex and others look very sickly too. With that, I am thinking perhaps it's best that I replace them with something else - if I do treat them for lacewing, it's likely that they will be reinfected. I suppose I will purchase another boxwood as that seems very happy in its spot, but I'm open to any other option for an evergreen.

    The garden is split down the middle with the front walk way and one side is 8x7 and the other 6x7.

    Shrubs: 4x piers, rhodo, boxwood, 2x hydrangea, 2x rose (very tiny as they don't get enough light - planted by the previous owner), one camellia

    Perennials: dicentra, lupin, hellebores, lilies, lungwort, viola, tulips, gladiolus, heuchera & some ferns

    Edit: Would this be a soil pH issue at all? I did touch the leaves looking for lacewings and debris came off.
     
    Last edited: Apr 27, 2022
  11. Margot

    Margot Generous Contributor 10 Years

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    The late Harold Greer, who wrote the article on rhodo pests you cite, was a very well respected authority in the rhodo world so I'm shocked at what is written about Lacebug. First of all writing the word 'Lacewing' beside 'Lacebug' implies they are the same insect when when they are absolutely NOT.

    Lacewing is a beneficial insect, not at all the same as Lacebug which is very damaging to Pieris and, to a lesser degree, Rhodos.

    Secondly (I think this must be an old article) the pesticides Malathion and Orthene, Greer recommends to control lacebug on rhodos are now known to be harmful to the environment. Malathion is banned and probably Orthene as well.

    In any case, we don't know for sure that it is Lacebug causing your Pieris leaves to become mottled.

    Here is an article I wrote about lacebugs for another BC Rhododendron Society. There is a paragraph explaining how to figure out if your plant's leaves are afflicted by lacebugs.
     

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    Last edited: Apr 27, 2022
  12. Margot

    Margot Generous Contributor 10 Years

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    Hello @pirhan. Have you taken a look yet at the undersides of your Pieris? Do you see any tell-tale black specks or actual larvae? If you're not sure, you could put a few leaves in a plastic zip-lock bag and take them into a garden centre. Make sure you ask someone who knows what they're talking about - like a lot of businesses these days, garden centres are sometimes hiring less-than-qualified people.

    If the problem with the leaves is not Lacebug, then I don't know what else to suggest.

    If you're sure it is Lacebug, your options are limited as I explained in the article above because it's difficult to get completely rid of an infestation even with the use of chemical insecticides. As @Georgia Strait said, your best option may be to replace them with something you like better. There is evidence that Lacebugs can move from Pieris to Rhodos.

    As for the Rhodo, those notches around the edges of the leaves are caused by root weevils whose larvae overwinter in the roots of the plant. Often most real damage is caused by larvae eating the leaves. It used to be that people drenched the soil with Diazinon or some other awful insecticide but not any longer - most such chemicals are now banned.

    The notches you see on your Rhodos' leaves were chewed last year. It will soon be time for new leaves to appear, co-ordinating nicely with the emergence of adult root weevils all ready to climb up into the branches at night and feast on the leaves.

    Three good, non-chemical ways to prevent leaf damage are -
    1. Put a light coloured sheet under the Rhodo and then go out after dark, shake the branches and see the weevils fall onto the sheet. You can decide how best to dispose of them.
    2. My favourite deterrent is also awkward because it involves wrapping tape or a plastic band around the base of the trunk(s) and smearing it with a product such as Tanglefoot. This prevents the weevils from climbing up into the branches but you have to be sure they can't climb across from other nearby shrubs either.
    3. Drench the soil with special nematodes which eat the larvae before they mature. It's getting late to do that and weather conditions need to be just right. It's also expensive.

    These and other solutions can be found on the Rhododendron Society website: Root Weevils: Troublesome Rhododendron Pests
     
  13. Georgia Strait

    Georgia Strait Generous Contributor

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    Oh those old names you cite @Margot — I recall a few nice tasty chewed up rhodos for which I purchased half of DuPont (or ortho?) re: similar issues as described by original poster here

    Some people still have those products in the dark recesses of sheds / carports

    the trouble is - disposing of chemicals properly safely these days -

    Back to topic - the price of a new Pieris at the box store is around 20$ … who doesn’t appreciate instant garden gratification :)
     
  14. Margot

    Margot Generous Contributor 10 Years

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    That's an excellent price these days. I really like Pieris - the new leaves are as colourful as many other shrubs' flowers.

    The arrival of Lacebug is a big concern though - it had begun showing up on the Lower Mainland before we left 16 years ago and is becoming more prevalent here on Van Island now as well. It's a bit of a dilemma . . . putting up with it on Pieris risks it spreading to rhodos.
     
  15. pirhan

    pirhan Active Member

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    Thank you everyone for the help.

    I have seen lacewings in my garden but I've never seen lacebugs. I have the usual millipedes, centipedes and rollies. I made some containers for the front and found these bugs in the soil, but their wings don't seem intricate enough for lacebugs. I've attached a photo of those as well as more of the leaves. I didn't see anything on the undersides. There was debris, but it may be mud from the rain kicking up the soil. (It's consistent with what's splattered on the house.) I also have a dicentra that I planted last year that has yellowing leaves. Is this a nutrient deficiency or perhaps too basic a pH? Only the one hydrangea bloomed last year and it was a rusty pink colour.
     

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  16. Margot

    Margot Generous Contributor 10 Years

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    Great to know that you have lacewings - those guys are keepers! You wouldn't normally see lacebugs unless you looked on the underside of leaves where they were active. They don't circulate in the garden at large the way lacewings do.

    The dark markings on the backs of Pieris leaves in your photos look like lacebug damage to me. Seeing as they are last year's leaves, it isn't surprising not to see adult lacebugs or larvae. You should keep an eye on the tender new leaves which are probably unfolding now to see if there is any activity on them.

    As for the dicentra, it looks to me as though it could use more nitrogen but advice on growing them suggests that they should not need much, if any, fertilizer if they are grown in a rich, organic soil amended every year with a top dressing of leaf mold. Having said that, I don't think it would do any harm to give them a one-time drink of a balanced liquid fertilizer - 14.14.14 or 20.20.20, diluted according to directions on the package.
     
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  17. vitog

    vitog Rising Contributor 10 Years

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    Pink Hydrangea blossoms indicate alkaline soil. It would be useful to check the soil pH to verify that it is in the preferred range for each plant. It's easy to lower the pH by adding sulfur.
     
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  18. Georgia Strait

    Georgia Strait Generous Contributor

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    I have a good experience thru all this heat smoke cold snow with a certain boxwood (buxus) in large planters —- I don’t have time to look up name right now tho I will later

    easy water
    Easy trim
    A pleasant rounded shape (I don’t prune it; I like loose style

    you might also consider a rosemary in pots — research the hardiest … supposed to be Arp but my plants labelled Arp died this past winter on pots

    lavender ?

    i will get back to you about Boxwood
     
  19. pirhan

    pirhan Active Member

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    Thank you so much everyone.

    I think the best course of action would be to remove the piers. I know several empty spots around the strata that they can go. On the fence about the rhodo as the spouse picked that out for the flowers. (Which have not come in this year.) Since the larvae hide in the roots, I could take a garbage bag over the roots during transplant and knock off the soil?

    I'm open to any weird or unusual small sized shade-ok evergreens. I live in the lower mainland and often go to Art Knapp which is in White Rock/South Surrey.


    @Georgia Strait - I like loose style too and I think I'll get another boxwood so that I have structure and greenery over winter. They would be in the ground. The back is part shade and the only full sun I get is the front patio which I put the containers - I should have specified this. (Catnip, sedum, some salvia and a lemon cypress... also picked out by the spouse.) I have been keeping my eye out for a cold hardy rosemary for years. An acquaintance of mine had one in a zone 4 and I find that unbelievable. I do have a lavender still in a pot; I'll put that in one of the empty holes from the piers.

    @vitog - I was thinking of doing a test. Do you have recommendations on any meters or do you think the DIY vinegar/baking soda works?

    @Margot - Thank you so much for your help. I don't think the soil is the best. I was digging a hole and there was plastic, a bag? and a few other plastic bits. I put some steer manure down about a month ago and I might get some mushroom compost, but that might be overkill.
     
  20. vitog

    vitog Rising Contributor 10 Years

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    For pH tests there are electronic meters and coloured test strips available, both quite inexpensive. I believe that the test strips are more accurate, but I haven't used them. I checked the accuracy of a meter that I bought, and it seemed to be reasonably accurate when dipped in dilute vinegar water. However, I eventually found that it was not very accurate when the probe was just pushed into sandy soil. I found that I could improve the accuracy of the soil reading by making a small depression, filling it with dechlorinated water, stirring the resulting mud around, and then dipping the pH probe into the mud.
     
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