Research Continued from Page 7
Yolo County reported 71 to 403 acres af- fected between 2017 and 2022, with some years seeing more than others. No cases have been reported this year, according to Yolo County Agricultural Commissioner Humberto Izquierdo. UCCE farm advisor Brenna Aegerter, who serves San Joaquin County, saw branched broomrape in two adjacent to- mato fields in the Sacramento-San Joaquin Delta in 2014. The growers rotated those fields out of tomatoes into almonds and rice, which are not host crops. She has not seen broomrape in the county since. Gene Miyao, UCCE farm advisor emer- itus for Yolo and Solano counties, found the related Egyptian broomrape in three Solano County fields about six years ago. It marked the first time the weed had been found in the United States. The fields were fumigated, and there have been no addi- tional finds. Orobanche weeds are obligate para- sites, meaning they depend entirely on their hosts for survival. Several species are found worldwide, but branched broom- rape is the one currently causing head- aches in California. In spring, tan to brownish seeds small- er than grains of sand germinate in the soil. When the parasitic weeds come in contact with tomato roots, they typical- ly latch on, sucking water and nutrients.
A flag in a Woodland tomato field, above, marks the location of a branched broomrape weed. At right, researcher Brad Hanson examines the weed, which has caused tomato yield losses of up to 80%.
After blooming, plants may produce more than 100,000 seeds that are easily spread and can remain viable in the soil for years. Because broomrape weeds spend much
of their life underground or entwined around lower portions of tomato plants, scouting for them is difficult. In the Woodland field, UC Davis re- searchers are employing drones and hy- perspectral imaging—a technology that captures a wide spectrum of light beyond what human eyes and normal cameras can detect, allowing for in-depth analysis. “Different characteristics of plants re- flect light in a different way, which results in them appearing in different colors,” UC Davis doctoral student Mohammadreza Narimani said in a statement on the on- going research. “We can monitor different levels of nutrients in the plant and identify if there are any signs of broomrape.” Doctoral student Matt Fatino, who is part of Hanson’s lab, is looking at how to modify broomrape management systems from other countries with Mediterranean climates and apply them to California. The goal is to develop an integrated program California growers could use should the pest become widespread. Part of Fatino’s research involves test- ing different herbicides, application rates and timings to find ones that control broomrape but cause minimal damage to tomatoes. One that passed the muster was Matrix SG from Corteva Agrisciences, which already was registered for other weeds in tomatoes. It received a special local need registration for broomrape in late 2022. For three seasons, Fatino also screened the most common commercial tomato varieties for broomrape resistance in UC Davis’ quarantine greenhouse. He found few differences. In addition, Fatino conducted small- scale tests on research and breeding lines and noted potential resistance in some of them. Hanson and his team will work with interested seed companies to conduct fur- ther testing. “The seed companies are starting to
take this seriously as a breeding objective,” Hanson said. On a related front, Davis postdoctoral researcher Pershang Hosseini is preparing to conduct experiments in the quarantine greenhouse this winter looking at alternate broomrape hosts. Scientific literature re- ports a wide host range, but Hanson said little is known about the parasite’s prefer- ences in California. At the infested Woodland site, Hanson has found broomrape on nightshade, a weed in the Solanaceous plant family that also includes tomatoes and potatoes. Although sunflower is reported as a host, Hanson said he hasn’t seen it in that crop. Safflower also is considered a host, but he said most of California’s crop is grown in the winter when soils likely are too cool for the weed. In addition, Hosseini is working with UCCE plant pathologist Cassandra Swett to test whether a handful of sanitizers can kill broomrape seed and several to- mato pathogens, reducing their spread on farm equipment. Last year, they worked with processors on sanitizing tomato harvesters. Building on that work, they are focusing on tomato trailers this season. Cristina Davis, professor of mechanical and aerospace engineering, is leading ef- forts to develop a sensor to detect broom- rape. It measures volatile organic chem- icals infected plants emit as alert signals. (Vicky Boyd is a reporter in Modesto. She may be contacted at vlboyd@att.net.)
8 Ag Alert October 11, 2023
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