What is killing my Bee Trees is a question we get from time to time. The answer varies considerably from species to species so, I will try to cover some of the more prevalent causes. There are a number of insects and diseases that are common to trees in North America. Some are species specific and others are generalists that attack anything under stress. The following descriptions are not restricted to Bee Trees but apply to most common lawn trees. Before treating anything, get a diagnosis from your states Extension Service. Treating with the wrong product can actually cause more harm than good.
Soil borne fungi also known as root rots are common. Phytophora is a water borne fungus that is particularly hard on Chestnuts and Sourwoods. Both of these trees need good drainage and perform best on high ground and sloping ground where water does not stand after a rain. Do not over water newly planted Chestnuts and Sourwoods. Banrot is a suggested fungicide in Tennessee. Check with your state Extension Service for recommended products for Phytophora in your state
The Korean BeeBee Tree- Evodia daniellii or Tetradium daniellii is a much desired tree by beekeepers for its productive flowers. This tree has been around for many years but has never been popular in the nursery trade possibly because it is so attractive to bees but more likely because there are so many well known trees already available. This scarcity means there is not much known about the culture of growing these trees. There is little research into actual practice of making them grow into healthy productive trees.
Having grown BeeBee Trees for several years now in the nursery we have had reach out to our State and USDA plant services to diagnose some of the diseases to which they are are susceptible. We just this summer (2018) have had diagnosed what was suddenly killing some of our trees.
We sent samples off and they were diagnosed with rhizoctonia and our USDA Research Station recommended a solution.
There is a soil born fungus called Rhizoctonia that attacks the roots and the bark at the base of the tree. This is the same fungus that causes Damping Off of young transplants in the vegetable garden and flower beds. Rhizoctonia is basically everywhere but only causes disease when conditions are right for infection. Plant stress is the biggest issue with infection. Damaged roots at transplant ( which cannot be entirely avoided), drought stress, and too much water are all factors that can lead to infection. This disease is not always fatal but will decrease vigor and overall growth. From what I have heard from customers, the trees seem most susceptible the first few years. Older trees seem to be able to resist catastrophic infection.
Symptoms are a sudden yellowing and drooping of the foliage and a blackening of the bark at the base of the tree. The disease progreses rapidly and tree death can occur in 7 days from the onset of symptoms. The fungus can also cause cankers on the bark. These would be treated with a foliar fungicide application. See the label for application instructions. The symptoms of over watering and underwatering are similar which adds to confusion. (See pictures below)
The solution for Rhizoctonia, as recommended by our extension service here in Tennessee is a fungicide soil drench of Thiophatate Methyl. This fungicide is available through several brands, Banrot, Greenlight, Fertilome, Scotts and Bonide to name a few. Follow the directions exactly and if follow up applications are recommended then do them to stop later reinfection. Check with your state Extension Service for recommended products as not all states allow all products.
The BeeBee Tree is not the only tree susceptible to Rhizocontia and there are other soil fungi that affect other trees. Many garden plants can be killed by this fungus as well.
Other pests we have seen are Ambrosia Beetle, Leafhoppers and Giant Swallowtail Caterpillars.
Ambrosia Beetle attacks stressed trees and are attracted to the ethanol emmitted by a tree under stress. The Beetle drill into the tree pushing strands of sawnust out of the hole they drill. It is a distinctive sight to behold, deposit an egg and inoculate the tree with a fungus to feed the larvae. The fungus kills the tree. If rain washes the sawdust strands away, a pencil lead sized hole will be left in its place. Death is sudden and complete. This insect is widespread through the Eastern US and attacks are random. One tree will die and the others around it be unscathed. Ambrosia Beetles are a hard nut to crack. They can be killed with Permethrin which is a contact poison. Check with your states Extension Service for products recommended for your state. (See pictures below)
Leafhoppers and Aphids feed on the sap in the leaves which causes yellowing ang brown leaf tips. Leafhoppers also spread plant viruses that can cause leaf distortions. Several common pesticides, some organic ones, will take care of Leafhoppers. Aphids exude honeydew which bees actually feed on during the summer months.
There are several tip borer moths that can kill the growing tips of new growth in spring. They generally do not cause permanent harm to the tree but, may require some pruning and retraining of a leader in the tree.
I don’t consider Giant Swallowtail Caterpillars to be a pest but where they live, you will see their larvae on youe BeeBee Tree. Many moth and butterfly larvae feed on our native trees. We try to leave these alone unless they are causing serious damage.
Then there are leaf fungi. Powdery Mildew, Anthracnose, Leaf Blights and others. A light infection won’t hurt much but, in a rainy year, leaf fungi can defoliate a tree.