- Author: Kathy Keatley Garvey
Entomologist Vonny Martin Barlow of Blythe, formerly of the UC Division of Agricultural and Natural Resources (UC ANR) and the UC Statewide Integrated Pest Management Program (UC IPM)--and who most recently served an entomology project consultant with the UC Davis Department of Entomology and Nematology--passed away unexpectedly Dec. 9 in a Palm Springs hospital. He was 55.
Dr. Barlow, known for his expertise in insect pest management, including pests of rice, cotton and alfalfa, was the third graduate student of the late Larry Godfrey (1956-2017), Cooperative Extension entomologist, UC Davis Department of Entomology and Nematology.
In an email to friends and colleagues, Sonia Rios, area subtropical horticulture advisor, UC Cooperative Extension, Riverside and San Diego counties, related that Dr. Barlow "passed away unexpectedly on Dec. 9 from a massive heart attack." Services (limited to five people due to the COVID-19 pandemic precautions) will take place Dec. 28 in Palm Springs.
Born May 18, 1965 in Mountain View, Calif., Vonny received a bachelor of science degree in biological sciences, with a special emphasis in entomology, from San Jose State University in 1993; a master's degree in plant protection and pest management from UC Davis in 1997; and a doctorate from Virginia Polytechnic Institute and State University (Virginia Tech) in 2006.
"From there, I went on to North Carolina State University where I gained extensive research and extension experience as a tree fruit post-doc," he related on Linked In. "I worked on evaluating the 'whole-farm' approach to mating disruption used in apple orchards to manage codling moth and oriental fruit moth. I then joined the Agriculture and Natural Resources Division of the University of California in 2009 as an entomology/IPM/crop production farm advisor for Riverside County until 2018. I worked in an area predominated by 75 percent alfalfa rotated with other crops like cotton, mixed melons, lettuce and broccoli."
Dr. Barlow left UC ANR in 2016 to become a pest management consultant, working both with industry and agricultural partners. He served as an affiliated IPM advisor from 2012 to 2017, and was a leader and author of the rice, cotton, and alfalfa Pest Management Guidelines. He did research on biological control and IPM of invasive insects and plants of field and forage agroecosystems.
At UC Davis, where he received his master's degree, he served as a graduate research assistant in the Godfrey lab. His master's thesis project "involved studying the impact of early spring weeds on Lygus bug population dynamics and their natural enemies in the alfalfa hay cropping system," he wrote on LinkedIn. "Alternative sources for feeding and reproduction (e.g., weedy plants) have shown to have a profound impact on Lygus bug populations. I was able to develop recommendations for management of weedy plants in alfalfa that had a two-fold benefit. The first is reduction of crop loss in susceptible crops (e.g., cotton) to Lygus bugs in adjacent fields. The second is reduction of the amount of pesticides used to control Lygus bug populations."
Dr. Barlow co-chaired the Godfrey celebration of life on June 7, 2017 at the Putah Creek Lodge, UC Davis, with distinguished professor and IPM specialist Frank Zalom of the UC Davis Department of Entomology and Nematology.
He is survived by his mother, Janice, and a brother, Cary, both of San Jose.
- Author: Kathy Keatley Garvey
The article, “Status and Impact of Walnut Twig Beetle in Urban Forest, Orchard and Native Forest Ecosystems,” published in the Journal of Forestry, updates the spread of the disease, and chronicles the role of the bark beetle, Pityophthorus juglandis, and the canker-producing fungus, Geosmithia morbida, in killing walnut trees, especially black walnuts.
Native to southwestern United States and northern Mexico, the bark beetle, about half the size of a grain of rice, “has invaded urban, orchard and native forest habitats throughout the United States, as well as Italy,” said lead author and forest entomologist Steven Seybold of the Pacific Southwest Research Station, USDA Forest Service, Davis, and a lecturer and researcher with the UC Davis Department of Entomology and Nematology.
Walnut twig beetles (WTB) tunnel into branches and trunks of walnut (Juglans) where they create galleries for mating and reproduction. They carry spores of the fungus into their galleries, and the resulting fungal infection causes formation of cankers, which coalesce and girdle branches and stems.
Between 2005 and 2016, the disease killed nearly 60 percent of the 210 specimens of southern California black walnut mature trees in the USDA Agricultural Research Service's National Clonal Germplasm Repository Juglans Collection near Winters, Seybold said. “This is only an estimate and the true proportion of the mortality is likely much higher, as only six of the 210 trees were rated as having healthy crowns in August 2016."
Seybold estimated that the E Street tree is about 150 years old, "maybe older" and around 50 feet in height. It measures almost 65 inches--or just over five feet--in diameter.
“The walnut twig beetle is also significant because it is the consummate invasive species; it is small enough to travel under the bark of modest-sized pieces of barked wood and it can withstand relatively dry conditions that it might encounter during transit,” Seybold said. “We believe that it has moved from isolated Arizona black walnut trees along creeks and rivers in the desert Southwest to nearly the entire western USA wherever walnut trees of any species have been planted or grew naturally. It has also been transported to Europe and established significant populations in Italy.”
Seybold noted that the disease is “unique because of its multifaceted negative impact on walnut trees involved in landscaping, food production, and forestry. Walnut trees are valuable ecologically and for food and timber, so the walnut twig beetle is a good model in which to study the impact of a bark beetle on forest and agro-ecosystem services.”
Other co-authors are Professor William Klingeman III of the Department of Plant Sciences, University of Tennessee, and forest entomologist Tom Coleman with the USDA Forest Service's Southern Region, Asheville, N.C..
UC Davis doctoral student Jackson Audley of the Seybold lab and Richard Bostock lab (Plant Pathology), contributed photos of dead and dying walnut trees in the Davis area, along with UC Davis doctoral student Corwin Parker and Hishinuma. Audley, who is researching an ensemble of behavioral chemicals that repel the walnut twig beetle from landing on English walnut trees, conducts his research in a commercial orchard near Winters.
“WTB is one of a few invasive bark beetles in North America where expanding distribution and impact have been pronounced enough to affect other species, communities, and ecosystems to the extent that services provided by urban forests, agroecosystems, and wildland areas have been altered,” the co-authors concluded in their paper. “We envision that ecological impacts of WTB will continue to unfold across a wider geographic area to affect various types of key services, i.e., provisioning (e.g., timber and nontimber products); regulating (e.g., air and water quality/quantity, climate regulation); and cultural (e.g., recreation, aesthetics, shade) services.”
Scientists first collected the beetle in North America in 1896 in New Mexico, 1907 in Arizona, 1959 in California, and 1960 in Mexico, but never considered it a major pest of walnut trees until black walnuts began deteriorating and dying in New Mexico in the early 2000s. Walnut tree mortality that occurred in the early 1990s in the Wasatch Mountains of Utah and in the Willamette Valley of Oregon is now attributed to TCD.
“Currently, good cultural practices and sanitation of infested materials are the primary strategies for disease management within orchards and also for prevention of spread of the disease and vector to regions with low rates of infection,” according to the UC Statewide Integrated Pest Management Program (UC IPM)>
UC IPM recommends that trees with less than 50 percent live crown be removed to reduce the buildup of walnut twig beetles and inoculum in the trunk and larger scaffold branches. "Chemical control with either fungicides or insecticides is not recommended for management of thousand cankers disease," UC IPM says.