Problem with Nova Zembla rhododendron

Asked August 20, 2019, 10:08 AM EDT

My rhododendron is dropping green leaves (mostly only browning at the petiole and base of the leaf) and others on the plant are curling up. Some of the stems look fine, others near the curling leaves are green but look wrinkly/spongy, and a few have turned brown and died. It's planted on a slight slope, about 10 feet away from 2 other rhodos that aren't showing any of these symptoms.

Do you have any idea why it's having trouble, or is there a good way to diagnose the problem? I just bought it this spring at a local nursery - could it be sudden oak death?

Lehigh County Pennsylvania

3 Responses

The fungus Phytophthora causes one of the most common disease problems in the landscape for rhododendron. This fungus is a “water mold,” and thrives in poorly drained or wet conditions. A wilted plant is usually the first sign of trouble. Rhododendron leaves will curl inward and droop. Drought can cause similar symptoms. Roots of affected plants appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion.This disease is favored in poorly drained areas or when plants are set too deeply.

Can you determine if the soil of the new plant location or the drainage pattern is significantly different from your other rhododendrons? You may need to consider relocating the plant if it is poorly drained or is compromised by heavy clay content.

Thanks! The wrinkled stems and wilting made me wonder if it was too dry, but the problem might be that it's too wet.

Of the three rhododendons in close proximity to one another, this one is the closest to the bottom of the slope (although still a few feet from the low point at the bottom), so I assume the soil might be wetter -- never really soggy/waterlogged on the surface, but it is definitely clay soil once you get down a few inches below the topsoil. I just planted it in the yard a few months ago, so would digging it up and replanting in the same spot with the soil mounded up a bit higher be a potential fix? Or will the fungus continue living in the plant even if I do that?

Replanting is probably worth a try but you will need to replace the clay soil content if you observe the roots are soggy or blackened. Be careful not to plant too deep (dig a wide shallow hole and displace as much clay as possible) and use a soil mixture that is half soil and half moist sphagnum peat moss. After planting, mulch with wood chips, pine needles, or shredded oak leaves. Mound the mulch to form a bowl to capture rain but keep the mulch away from the bark of the plant. These materials are mildly acidic and help maintain the desired soil pH. Additionally, sprinkle a small amount of sulfur around plants on an annual basis. Good luck with the transplant and I hope it survives and brings you satisfaction in the future years,