I received the following question and thought that it would be useful for all of you to know as well:
Hi Stacey. I have Japanese hollies as my foundation planting on the front of my house. They have been developing brown, dying to dead areas and I’m concerned that there is something wrong with them. I noticed that my annual vinca plants that were planted in the same bed didn’t do well this summer either. Sorry I don’t have any pictures but I’ll try to get them to you soon. Do you have any ideas as to what this could be?
Steve, first of all thanks for e-mailing me…this is exactly the reason that I started this blog; to help gardeners solve the problems that they are experiencing. With that being said, I’m afraid that I don’t have any encouraging news to offer. I’m pretty sure that black root rot (Thielaviopsis basicola) or BRR for short, is to blame. Japanese Holly is otherwise known as Ilex crenata and the entire crenata species falls prey to BRR. Annual vinca (Catharanthus roseus) is also on the list of plants that BRR enjoys. While chemical controls are always an option, I’m not a fan for many reasons. My advice is to remove the shrubs and take as much soil with them as you can; in other words, don’t shake the soil from the rootball as you remove them.
Black root rot is ubiquitous which means that it is virtually everywhere. When viewed under a microscope it looks like little Tootsie Rolls in the soil.
Those “tootsie rolls” are known as chlamydospores and there sole purpose in life is to remain dormant until the next little root comes growing by. At that point, the infection starts all over again.
But there is good news from all of this…there are many plants that are resistant to BRR and can grow very well in areas that have been contaminated. Some of the shrubs include Nandina, Chinese holly (Ilex cornuta) and Boxwood (Buxus spp.). If you are looking for annuals that can tolerate a BRR infestation, consider Mexican heather (Cuphea spp.) or Lantana but steer clear of vinca, petunia, pansies and geraniums (Pelargonium).
I hope this helps you Steve and anyone else who may have Japanese hollies that are floundering in the landscape. This speaks volumes about monoculture but I’ll save my time on my soapbox for another day. If there are any pest or disease issues that you’d like me to help you with, please let me know at firstname.lastname@example.org.