What is in this article?:
- More research needed for TCD in California walnuts
- Threat to English walnut industry
- TCD management: detection
- At least 60 cases of thousand cankers disease are confirmed in California; about half each in commercial English walnut orchards and native black walnut trees in residential and riparian areas.
- TCD occurs after the walnut twig beetle carries spores of the fungus Geosmithia morbida on the insect’s body into the tree where it bores holes in the tree bark and disrupts the phloem tissue.
TCD management: detection
Most of the TCD confirmed finds in northern California are in black walnut so far. The disease has been confirmed in about a dozen English trees. Surveys are needed to determine the extent of TCD in English walnut.
“The only management for TCD right now is detection,” Hasey said. “Growers need to be aware of this disease but not be alarmed.”
If TCD is suspected in an English walnut tree, Hasey says contact the local UCCE farm advisor. E-mail a digital photo of the tree to the advisor. Hasey notes that sudden branch death during the summer can be the result of branch wilt, not TCD.
For trees confirmed with TCD, Hasey recommends removal if the entire tree is diseased. In partially diseased trees, remove the upper branches to the green wood.
Burn infected wood on site according to local restrictions. Chipping wood will not kill the bug but will interfere with the insect’s egg-laying cycle. Do not sell infected wood for firewood or woodworking.
Hasey says TCD is not a quarantine issue since then disease is widely found.
In Tulare County, UCCE farm advisor Elizabeth Fichtner first found TCD in English walnuts in Fall 2009. To date, at least 10 cases are confirmed in English countywide. Fichtner has found TCD in the varieties Tulare, Chico, and Chandler, and on Paradox and black walnut rootstocks.
“I was in an orchard looking at trees for a different problem, turned around, and saw it,” Fichtner said. “It was very dramatic. The tree had all of the stereotypical TCD characteristics.”
Fichtner has found the disease in mature English trees, not in new plantings.
Unlike Hasey’s finding of the disease only in declining trees, Fichtner has found TCB in healthy English walnut trees. Hasey and Fichtner have confirmed cases on English walnut with and without bleeding.
Additional research is needed to learn more about the disease, vector, and fungus.
“Funding is tight right now in the research realm with a lot of financial cutbacks in Washington, D.C.,” Bostock said.
Bostock is a plant pathology professor at UC Davis and serves as executive director of the National Plant Diagnostic Network (NPDN). The NPDN is an award-winning program established in 2002 and funded by USDA to enhance agricultural security through training of first detectors and diagnosticians, and support for diagnostic laboratories.
The NPDN seeks to create infrastructure and processes to enable the rapid detection and identification of new and emerging pest problems in crops before they can become established or widespread.
“Unfortunately, the NPDN budget has been cut by 39 percent for 2011,” Bostock said. “One of the diseases we are concerned with nationally is thousand cankers disease.”
Bostock says funds are needed to better understand the biology of the pathogen and the insect in all walnut species. Down the road, resistance development through walnut breeding may offer the best possible solution.