Agrobacterium tumefaciens is the bacterium responsible for crown gall. Crown gall affects many species in the rose family (Rosaceae). Rapid growth of infected cells produce galls primarily on the roots, but galls may also occur on twigs and branches. The galls can be unsightly if above ground level, and crown gall anywhere on the plant can disrupt the flow of nutrients causing stunting or plant decline.
The bacteria that causes grown gall is typically found in soil naturally and is able to infect the plants through mechanical damage (ie. when planting, aerating, root feeding insects). Be careful when planting trees from a nursery because the soil can become contaminated if the nursery stock is infected.
Part of the crown gall broken off the root. Pear trees with crown gall on roots restrict nutrients and water flow. Extensive grown gall, forming woody galls on exposed injured roots.
Case study
Crown gall is an interesting disease that we do not see super frequently. It can be hard to diagnose since it is mostly underground. I first found it on an ornamental pear tree in decline and it took quite some time to identify the culprit. The only above-ground symptom on the pear tree was an extremely thin canopy. Everything else looked healthy. I poked around the roots, knowing most urban tree issues start in the soil, and found many unusual woody growths.
Treatment/Mitigation of Crown Gall
There is no cure for this disease and it can persist in the soil for years. Galls can sometimes be pruned out to improve aesthetics and infected plants can live for years. If you know that crown gall is a problem on your property you need to use caution when you plant new trees and shrubs. The bacteria responsible can persist in the soil for a long time and will continuously infect new plants.
A list of plants shown to have resistance to the disease include: barberry, hornbeam, true cedars, ginkgo, golden raintree, tulip tree, mahonia, spruce, linden, boxwood, catalpa, beech, holly, larch, magnolia, black gum, pine, Douglas fir, bald cypress, hemlock, birch, firethorn, redbud, smoke tree, sweet gum, deutzia, serviceberry, yellowwood, yew, and zelkova.
Sterilization of infected soil is an option but it is costly and usually not a good option for homeowners.
If your trees have a problem or you want to make sure they don’t, give Wellnitz Tree Care a call.
