Walnut Trees and Thousand Cankers Disease
Having grown
up on a Midwest farm, I have always had a strong desire to “raise something” in
addition to a family.
Back in 1973, I read an article in Farm Journal about tree rustlers stealing walnut trees from Iowa farms. I knew then that walnut trees must be worth raising if the value is so great that someone wants to steal them. I thought to myself, ‘Growing trees seems like a possibility for me!’
At the same time, the U.S. Forest Service’s (USFS) Forest Inventory and Analysis (“the forest census”) predicted that there was not going to be enough black walnut in its native range to meet projected global demand for walnut veneer and lumber. With these USFS data, my desire to buy land to raise black walnut trees was solidified.
So 40 years ago I bought 30 acres of forestland which had some walnut on it along with a mixture of other hardwoods and red cedar, typical of north Missouri. My daughter and son enjoyed the outdoors and helped with some pruning and brush clearing efforts while they were growing up. They retain some ownership and pride in our Tree Farm to this day.
Our land has been certified with the American Tree Farm System® for several years now, and has been a destination for community tours and tours of the National Walnut Council (WC) and Missouri State Chapter Tours.
I’ve been a member of WC for more than 35 years. WC has been a great source of information in managing the growth of quality logs of black walnut. Other members and I share experiences in all phases of walnut growth, from site selection and planting to pruning techniques, thinning, and most importantly managed timber sales.
Walnut
timber growth and production is really a multi-generational process, as the
growth cycle is at least 55 to 70 years. Raising walnut trees is a legacy and I
do not expect to physically harvest the younger trees that I pruned and managed.
Unfortunately, a walnut grower’s worst nightmare is threatening to ruin everything that woodland owners are working for.
Thousand cankers disease (TCD) is a recently discovered tree disease that once subsisted on the Arizona walnut but has moved north and east onto other walnut species like my native eastern black walnut.
A tiny walnut twig beetle is a vector of the fungal organism that causes small cankers to form under the bark of branches and small limbs high in the crowns of walnut trees. Humans are the other vector that moves both the beetle and the fungal spores when diseased walnut logs, slabs, turning wood, or firewood with bark attached are hauled great distances.
The symptoms of this deadly disease are not noticeable for possibly up to eight years after a given tree has been attacked by beetles that carry the spores. Symptomatic trees show wilting and bronzing of leaflets on a couple branches high in the crown.
As more cankers form and coalesce, more leaves die but typically hang on to the twigs as the leaflets are not getting enough sap flow to sustain growth. Dying of the crown may take a couple more years and then basal epicormic sprouts may emerge from the lower trunk as the whole tree dies in 10 years or so.
As walnut growers, my family is defenseless to thousand cankers disease (TCD). There are no fungicides or insecticides that could economically or feasibly be used to protect our walnut trees against this disease. I can only hope that no one hauls around diseased firewood, logs, or pretty slabs of walnut with diseased bark.
If a new point of introduction of TCD is not contained, the beetles will multiply exponentially and will spread the fungal disease a couple miles per year. I am desperately hoping that current research on biological insect control techniques may identify native predators or parasitoids that could be mass reared and released into zones of new TCD detections to suppress the beetle population and slow the spread of the disease.
Harlan Palm is past president of the National Walnut Council and of the of the Missouri state chapter of WC. The Walnut Council is a 501(c)(3) not for profit corporation that promotes sustainable forest management and utilization of American black walnut and other high quality fine hardwoods. Check out Harlan’s black walnut story in this recently released video. Photos courtesy of Harlan Palm.
