A pieris japnioca in my back garden has some dead areas this season. It's had spider mites since I moved into my east Vancouver house 5 years ago. Maybe the mites have taken their toll? In spring the troubled plant usually has chartreuse leaves and has done well despite the spider motes till this year. It's right beside another flourishing pieris (with new leaves that are red) that also has spider mites. Both are quite large and I have not known how to effectively treat the mites ....Any suggestions?
Get some Safer's Soap spray at any garden ctre and follow label directions. Do it again in 5 days, and 5-7 days after that (to get all the eggs). What are the chances that you can move the plants into light shade, where they may do better, be less dry and hot, and the mites won't want them anymore? You'd have to wait til Nov. to do it however.
You mention one of them has reddish new growth. Pieris formosa forrestii and its more common hybrid 'Forest Flame' have extra colorful young leaves which pass through a long, pale, mottled phase that looks like mite injury (stippling) before becoming green. I wonder if that is actually what you have going on, and not really mites? This would explain failures with mite control you may have attempted. Otherwise, mites certainly could kill individual sections of foliage if heavy enough (do you have webbing?). Pieris are also prone to water molds, which kill individual branches, as are their relations rhododendrons.
I have the red tip variety (Mountain Fire) and the leaves are very pale and spotty, and never seem to get dark green and shiny. I also both the white and prink (Valley Rose) flowering variety which also unhealthy looking leaves - pale, spotty and some of the leaves have folded in half length wise. They receive sun much of the day and are in good, mulched soil. How can I get them to keep healthy dark green leaves?
