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I'm in the Willamette Valley in Oregon, USA, (USDA zone 8b) and I have a Vaccinium ovatum, Vaccinium parvifolium, and a Vaccinium membranaceum in a section of my garden. They're shaded up until noon by a row of Leyland Cypress 10 feet to the east and then get full sun after noon. The Vaccinium membranaceum gets a little more sun than the others because of its placement on the hill.

Since the beginning of July, the Vaccinium membranaceum's leaves have been turning red, then black, and then crispy, starting mostly from the edges. This started from the top of the plant on the east side (nearer the shade) and is proceeding to the rest of the plant's leaves.

Healthy leaves at the base Healthy Leaves at the Base

Discolored Leaves at the Top Discolored Leaves at the Top

Black Crispy Leaves on the Shaded Side Black Crispy Leaves on the Shaded Side

Defoliated Branches Defoliated Branches

  • I planted the other Vaccinium varieties last year. They're doing fine.
  • I planted the V. membranaceum in the early spring this year when it had no foliage. I planted it with chunks of dead wood, compost, and mulch. It grew a lot of healthy bright green foliage up until July.
  • The pH of the soil is acidic (blueberries also grow well here).
  • The lawn is about 2 feet to the west. I've applied weed and feed and lime to it with a drop spreader.
  • All three varieties are on the same drip system and receive roughly the same amount of water. A moisture meter indicates that the soil is moist to wet. The plant experienced heavy prolonged rains in the spring and seemed to do fine with that.

Any ideas what could be causing this?

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  • Has it been hot dry and sunny since July?
    – Bamboo
    Jul 24 '18 at 15:06
  • It has been. There's been little rainfall and temperatures in the lower 60s at night and up to the upper 90s in the day. Some days the high is in the lower 70s.
    – watkipet
    Jul 24 '18 at 15:55
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I suspect the problem is drought related - you say you planted it in early spring this year, and that it is exposed to more sun than your other plants which went in a year ago, yet they are all receiving the same amount of water. There are healthy looking growth buds on the bare stems in your photo, which makes it less likely to be an infection or infestation.

A shrub planted earlier this year will require more water than those planted a year ago; this is particularly critical if the weather is hot and dry and the plant receives a good amount of direct sun. Given you're using a drip system, I don't know if its possible to alter how much this particular plant receives without increasing the water supply to your other plants. If it isn't possible, then I suggest you make sure to give this particular plant a couple of gallons a day on top, especially right now, and ongoing up to Fall, unless the weather is cool and damp.

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I don't believe this is a drought or watering problem - I believe it is a fungal infection caused by possibly too much moisture or humidity. If the plant defoliates and is slowly dying as time progresses I would definitely remove it, isolate and possibly even remove most of the soil immediately in/around it's planting area. Fungal diseases can be most easily spread from rainwater rebounding onto plant leaves and branches from infected soil or ground litter. A clean soil surface (use sterile mulch and replace frequently) is the best defense. Some plants can withstand an application of lime sulfur when dormant but I am not sure I would use it on membranaceum - and if used, only when the plant is fully dormant.

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