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

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. 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