I had the entire yard landscaped and only the gold mounds are doing poorly. The plant starts with brown tipped leaves and within 2-3 days the entire plant looks dead. I am in southwest FL and have sprinkler system. They have been in 10 weeks and this happened suddenly and before they were perfect. I thought grubs and found the in grass. All areas have been treated with dylox product and fertilized but to no avail for these plants, all others look great. What to do? I have 18 of these and each day another seems to go brown.
Certified GKH Gardening Expert
Unfortunately, it sounds like fire blight. There is no cure for it and can spread through spirea rapidly. Confirm this with your local nursery. If they agree, you will need to do the following. Remove and destroy all dead plants. Aggressively prune back any dead areas on the remaining plants. To try to really stop it in its tracks, you may want to consider removing any infected plants.
This article on this disease will help you: https://www.gardeningknowhow.com/plant-problems/disease/fire-blight-remedies-and-symptoms.htm