I have a Toronto garden (part sun, ammended sandy loam, irrigated) that I planted with Euounymus coloratus several years ago. It was badly infected (and I mean BAD) with crown gall, so I have removed it…at least 250 sq. ft. of it. I would like to replant the area with vinca and Hiil’s yew, as well as perennials.
Q. 1..Should I worry about the bacteria infecting the yew and vinca too? I can remove the top several layers of soil, replacing with fresh soil if you recommend this.
I unwittingly spread the disease to other euonymus coloratus, about 150 sq. ft. in another area of the garden (by clipping with infected tools), but the disease has not progressed as far there. The galls (I correctly removed them) were very sparse, quite young and small, located very close to where we clipped.
Q. 2..I would like to remove this euonymus as well, but am concerned that in doing so I will severe the roots of a nearby Chinese dogwood and infect it too. Should I be concerned about that?
Thanks for your advice and answering my questions.
Thank you for your inquiry to Toronto Master Gardeners.
Your first question is about spreading disease to future plants. Yes, Crown Gall is an extremely infectious disease of the soil, and it is easily spread through pruning with contaminated tools, according to Bill Hlubik, a Professor and Agricultural and Resource Management Agent for Rutgers Cooperative Extension- The New Jersey Agricultural Experiment Station, Rutgers University. You can read more about this on the University’s Agricultural Experiment Station website: http://www.ifplantscouldtalk.rutgers.edu/planttalk/article.asp?ID=4
Because of this, I have researched which plants might be most resilient to the disease. An excellent source of information is the University of Illinois Extension program website: http://hyg.ipm.illinois.edu/pastpest/200211b.html In this linked article you will find a list of plants that you can be more certain of using in the future. Yew is one of these.
Before you start replanting, I would like to pose a question for you about using Vina minor (Periwinkle). Are you aware that it is on the list of invasive plants in the Toronto area? Especially on hills and near ravines, Vinca can take over from and choke out our native plants. I know that you can purchase it at nurseries (Go figure!) but the same can be said of a few other invasives, such as Goutweed (Aegopodium podagraria). City of Toronto advises against its use. https://www1.toronto.ca/city_of_toronto/parks_forestry__recreation/urban_forestry/files/pdf/Controlling_Invasive_Plants.pdf
Removing the soil would not guarantee complete eradication. Instead, I would recommend that you improve the existing soil with two inches of compost every fall. There’s no need to work it in, as the worms and microbes will do the work, and you avoid any unnecessary soil and root disturbance. As with people, plants thrive and can fight off infection with better nutrition.