PJM Rhododendron Fungas?

Question: I went on vacation for a couple weeks. When I came back some of my PJM rhododendrons were looking sickly with leaves turning yellow/brown/reddish with some spots. I've attached a pictures of the whole group, the single worst affected bush and a close up of a portion of the bush.

What do you think it is. What steps should I take to restore their health?

Thank You

responder: An Ask Extension Expert Replied July 26, 2024, 3:29 PM EDT
response: Hello,  Based on the images you sent and the symptoms you’re describing on your PJM rhododendrons could be indicative of several potential issues.  Here are a few possibilities and the steps you can take to address them:  Cercospora Leaf Spot: This disease causes circular to irregular brown spots up to 1/2 inch in diameter on leaves, especially lower leaves. The spots may become tan in the center and may have a yellow halo. Management: Inspect new plants for infection, rake and destroy fallen leaves, avoid overhead irrigation, and apply a fungicide to protect leaves before infection in the spring. More information at this link:   Azalea and Rhododendron Diseases (psu.edu)  Phytophthora Root & Crown Rot: This is a common disease caused by a fungus that thrives in poorly drained or wet conditions. Symptoms include wilting, curling of leaves, and discoloration of the wood near the soil line.  Prevention & Treatment: Ensure good drainage and avoid planting in areas where water can collect. Select resistant varieties and avoid setting plants deeper than the original soil level. Raised beds can help, and do not plant in sites where previous plants have died from root rot. More information at this link:   Azalea & Rhododendron Diseases | Home & Garden Information Center (clemson.edu)  Iron Deficiency: When rhododendron or azalea leaves turn yellow while the veins remain green, it’s often due to iron deficiency, which can occur if the soil pH is too high. Management: You may need to lower the soil pH to the optimal range for rhododendrons, which is 4.5 to 5.5. This can be done by applying soil amendments like sulfur or using fertilizers formulated for acid-loving plants.  More information at this link:   FS1146: Rhododendrons and Azaleas: Injuries, Diseases and Insect Damage (Rutgers NJAES)  Botryosphaeria Canker: This canker causes rough, sunken, dark-brown areas on the bark, leading to wilting and death of branches. Management: Water plants to prevent drought stress, prune infected branches back to healthy tissue, and disinfect pruning shears frequently. No chemicals adequately control this disease, but some hybrids may have resistance. More information at this link:   Azalea and Rhododendron Diseases (psu.edu)  Powdery Mildew: This fungal infection may cause yellowish-green or purplish-brown spots or blotches on the upper surface of leaves. Management: Ensure good air circulation and remove affected leaves. Fungicides can be applied as a preventive measure. More information is at this link:  Rhododendron: Powdery mildew | Hortsense | Washington State University (wsu.edu)  It’s important to correctly identify the issue before taking action.  Therefore, I highly recommend you get a confirmed and precise identification of the problem. I recommend you send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab. The experts there can also provide you with the best treatment options.  Their email is <personal data hidden> - Please include your name – The lab will let you know if they need a sample sent. FYI – The lab may also ask for additional images too.  Their website is at this link:  Plant & Pest Diagnostics (msu.edu)  Their Contact Information is at this link:  Contact Us - Plant & Pest Diagnostics (msu.edu)  This link will explain the details on submitting a sample to MSU Plant & Pest Diagnostics Lab:  Submit Samples - Plant & Pest Diagnostics (msu.edu)  Regular monitoring and maintaining good cultural practices are key to preventing these issues.  I hope this helps!

responder: The Question Asker Replied July 27, 2024, 4:09 PM EDT
response: Thanks I sent to pics in as you suggested.  Sent from my iPhone On Jul 26, 2024, at 3:29 PM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: An Ask Extension Expert Replied July 28, 2024, 5:39 PM EDT
response: Hello again,  You are welcome - Thank you for letting me know!  I also want to send this information to you.  For PJM rhododendrons in Michigan, the ideal site and growing conditions include:  Zone: They are suitable for USDA zones 4 to 8.  Sun: Partial shade is best for these plants.  Soil: They prefer well-drained organic soils. The soil should be acidic with a pH range of 5.2 – 5.5, highly organic, and never completely dry.  Moisture: While they can withstand dry conditions, they should not be left completely dry.  Height and Width: PJM Rhododendrons typically grow to a height of 4’-6’ and have a similar width.  Bloom: They are known for their winter flowers, blooming in February in some regions.  It’s important to note that while PJM rhododendrons are adaptable and can withstand cold and harsh sites, they do best in partial shade and well-drained, acidic soils.  Additionally, be mindful of common pests like Phytophthora root rot and root weevils.  Have a great day!