The question: What has ravaged bottlebrushes (above) and many other plants since the devastating freeze of early January?
I've been promising a tip sheet on phytopthora, and here it is. (It's also spelled phytophthora, but we'll stick with phytopthora.)
This is going to be simple and straight-forward advice, because I think the academic detail or "university jargon" used in scientific papers is about as boring as watching paint dry!
I believe this disease has ravaged many plants in the area, especially bottlebrush (Callistemon) and Japanese blueberry (Elaeocarpus). Basically, phytopthora is a root-rot disease (similar to cotton root rot) brought on by the wicked combination of a wetter-than-normal fall and a wetter-than-normal January and February. And the brutal freeze in early January didn't help.
After talking with experts at Texas A&M, and hearing what folks like Bob Patterson at Southwest Fertilizer are seeing and recommending, my advice is to spray the plant and drench the soil with Garden Phos Systemic Fungicide from Monterey, previously known as Agri Fos. The most important part of this is the soil drench.
Now, I know that you're not going to find Garden Phos everywhere. So if you can't locate any, look for Captan for the soil drench and use any liquid systemic fungicide for the foliar spray.
And it's critical to do this application more than once. In fact, it should be on a monthly basis until new growth is no longer ravaged by the disease.
Bob Patterson also recommended making sure to pull the mulch away from the plants at the base. He also suggests using something like a spading fork to carefully poke holes of 4-6 inches into the soil so the liquid penetrates to the root zone — quite literally getting to the root of the problem — where the phytopthora actually exists.
Lastly, if you plan on replacing any plants that died from this root rot, be sure to drench the area fully before replanting.