Phytophthora control for Rhododendron

Asked July 25, 2016, 11:08 AM EDT

Hi I recently submitted photos of my large Rhododendron [7' high X 5' wide] and the dead branch section. It seemed that phytophthora was the most likely cause and some chemical suggestions were given. I appreciate that but have a couple follow up questions now that I am treating the plant. The chemicals are shockingly expensive but I was able to obtain a pint of Agri-Fos which lists the fungicide as control for the disease. The directions are more written for commercial operations and are a bit confusing for the homeowner. So far I have cut out the bad branch and raked a few of the leaves underneath the plant, Near dusk I did a foliar spray using 2 tsp per 1/2 gallon mix which was just enough to wet down the plant leaves. The directions also reference a soil drench but it is unclear whether I should mix up another batch just to drench the soil under the plant. [they speak more to dipping plant roots for small nursery plants]. The weather is hot and they do mention caution if plant is heat stressed. Mine does not appear to be, it is in some shade being located under a large oak tree and I water each morning in this heat. I also waited until dusk when it cooled down somewhat before applying the fungicide. I plan on spraying again in 4 weeks as indicated in Agri-Fos instructions. I also had a knockout rose just next to the Rhodo which completely died and I have removed and also wondered if a soil drench would be suggested? Would appreciate any suggestions as I try to keep my Rhododendron alive. I plan on going down fighting especially after what I paid for the fungicide! [grin] Thank you, Jack Barnes

Worcester County Maryland shrubs rhododendron

1 Response

We are not sure how you received a diagnosis of phytophthora on your rhododendron. Certainly, there is something going on other than usual leaf drop. https://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG51_IPM_Azaleas_an... We do not know why your knockout rose died, but there is no need to drench that spot. Agri-Fos will retard phytophthora, but will not kill it. Frequently new bushes are cheaper than fungicide. Phytophora usually occurs in areas where there is a lot of water. Make sure you do not have standing water, but also make sure it is watered deeply in time of drought. vw