- Author: Richard Smith
- Author: Steven T. Koike
Clubroot disease can be a serious production issue for broccoli, cauliflower, and other brassicas in the Salinas Valley. The disease is caused by a unique organism (Plasmodiophora brassicae) that is closely related to ciliate protozoans but is classified in its own taxonomic group. It survives over 20 years as resting spores in the soil that are released as the clubbed root tissue decays. At temperatures above 65 °F, the resting spores release zoospores that swim to host plant roots and infect through root hairs. Once inside the plant, the organism grows into a large multinucleate plasmodium (a multinucleate mass of protoplasm) which stimulates changes in the plant hormones, resulting in enlarged root cells and the characteristic clubbing of the roots (Photo 1). Root infections by the clubroot pathogen can occur in both acid and alkaline soils; however, acidic soil conditions favor the development of the root symptoms. In addition to the main brassica crops, Plasmodiophora can infect arugula, radish, mustard cover crops, and weeds such as shepherd's purse and even some grasses. Plants that develop severe root swellings will exhibit above ground symptoms (Photo 2) indicative of non-functioning root systems, which includes yellowing, wilting, poor growth and stunting, drying and death of lower leaves, and eventual plant death.
Clubroot in the Salinas Valley is mostly controlled by maintaining soil pH above 7.2 to 7.3 by liming. The high pH does not kill the pathogen but inhibits the formation of the root clubs. Soils where control of clubroot by liming is achieved are called “responsive” soils. However, soils where liming is less effective are called “unresponsive” soils.
In 2020 we had calls regarding the incidence of clubroot on brassicas. In each situation the grower/PCA had soil lab results that indicated that the soil pH was greater than 7.2. To investigate this situation, a small study was conducted. At three fields soil was collected from symptomatic and asymptomatic areas of the crop and soil pH was determined using a pH meter at the UCCE or UC Davis Analytical Lab. The results shown in Table 1 indicate that clubroot was more severe in soils with lower soil pH levels. These findings are consistent with what we know about clubroot, that higher pH soils should have less concern with this disease.
So why did clubroot occur in soils that had test pH values greater than 7.2? It is important to keep in mind that soils have a great deal of inherent variability. The goal is to determine if the soil pH for a 5 or 10 acre field is ≥7.2. This is typically done by collecting 15 – 20 soil cores from various parts of the field and mixing them together as a composite sample. However, if sample collection by chance missed areas of lower soil pH, the lab results may be skewed to represent areas of the field that had relatively higher pH values. If this is the case, such a sample could have an artificially high pH (greater than 7.2) while some parts of the field may have a lower pH value. One way to have greater confidence in the soil pH is to collect more soil cores in fields where clubroot disease has been noted in the past.
At present, we have not seen evidence in Monterey County that soils are unresponsive to liming or that the liming treatment is failing to control clubroot, given variability in soil pH and pH testing. In our intensive vegetable production system, soil pH tends to decrease over time through the use of ammonium fertilizers. The loss of calcium, magnesium and potassium from crop removal and leaching can also contribute to lower soil pH on lighter soils. Given the longevity of clubroot resting spores in the soil, it is important to maintain a liming program to assure that soil pHs are above 7.2 to 7.3 to thoroughly suppress clubroot throughout the field.
Table 1. Three evaluations of soil pH in clubroot affected fields
Site |
Soil pH |
Crop |
Location |
Soil Type |
|
Symptomatic |
Asymptomatic |
||||
1 |
6.01 |
6.25* |
Broccoli |
Blanco |
Pacheco clay loam |
2 |
6.60 |
7.58 |
B. sprouts |
Eastside |
Chualar loam |
3 |
7.13 |
7.67 |
Cauliflower |
Near river |
Metz complex |
* These plants were also affected but to a lesser degree.
- Author: Pamela Kan-Rice
Schilder named director for UCCE Ventura and Hansen REC
Annemiek Schilder joined ANR on Aug. 1, 2018, as director of UCCE Ventura County and Hansen Agricultural Research and Extension Center. She hails from the Netherlands, where she grew up in an extended family of dairy and field crop farmers. Her grandfather, who farmed well into his 90s, inspired her to follow a career in agriculture.
Schilder studies small fruit pathology, mycology, applied virology, plant disease diagnostics, integrated pest management and organic and sustainable disease management.
She joins UC ANR from Michigan State University, where she was associate professor from 2006 to 2018 and an assistant professor from 1998 to 2005 in the Department of Plant Pathology and Department of Plant, Soil and Microbial Sciences. At MSU, Schilder was responsible for research, extension and teaching of sustainable disease management in small fruit crops, such as grapes, blueberries, strawberries, raspberries and cranberries. She studied the diagnosis, epidemiology and integrated control methods for major fungal and viral diseases of these crops, and worked closely with entomologists, horticulturists, plant breeders, agricultural economists, extension educators, and growers to develop a holistic approach to plant health. Schilder also holds an adjunct faculty appointment in the Department of Plant, Food and Environmental Sciences at Dalhousie University in Nova Scotia, Canada.
From 1994 to 1997, Schilder was a postdoctoral fellow at the International Institute of Tropical Agriculture in Ibadan, Nigeria, researching legume and cassava diseases, seed health, and plant quarantine issues, and gaining an appreciation for the challenges faced by African farmers.
Schilder earned a Ph.D. and M.S. in plant pathology (cereal diseases) from Cornell University and a B.S. in agronomy from the University of Louisiana at Lafayette. She also studied plant sciences for a year at Wageningen Agricultural University in The Netherlands.
Schilder is based in Ventura and can be reached at (805) 662-6943 and amschilder@ucanr.edu.
Humiston named 2018 California Steward Leader
“I was really involved in the 1990s in trying to figure out how agriculture and environmental interests find common ground, as well as building bridges between rural and urban sectors," Humiston said. "In the 2000s, I started focusing on economic development and sustainability. In my current job, I'm bringing all of those together around the reality that sustainability truly has to be a triple bottom line. We've got to develop ways for people, the planet and prosperity to all thrive and enhance the synergies between them."
In nominating Humiston for the award, Sonoma County Supervisor James Gore wrote, “Glenda is a powerful and relentless advocate for triple bottom line prosperity. She has championed and delivered in every position I have seen her in. As one of the co-chairs/Steering Committee for the Economic Summit, she has ensured that working landscapes remains a driver for rural prosperity.”
“Glenda embodies what CA Forward and the California Stewardship Network are all about: empowering regional hubs to own their own future,” added Gore, who served with Humiston at the U.S. Department of Agriculture as presidential appointees under President Obama.
As co-chair of Elevate Rural California, Humiston is working on three main areas: biomass, rural broadband and water infrastructure. “We identified those issues at last year's summit and worked this year to identify where the opportunities were as well as options to pursue,” she said. “We're bringing that information to the summit this year to get people to really rally around those three issues and move forward working on implementation.”
Steve Koike, emeritus UCCE advisor in Monterey and Santa Cruz counties and current lab director of TriCal Diagnostics, has been awarded the 2018 Outstanding Contribution to Agriculture Award from the California Association of Pest Control Advisers (CAPCA).
CAPCA gives the prestigious award to people who have made a meaningful difference in support of California agriculture.
“This honor recognizes the plant pathology research and problem-solving expertise that Steve provides to growers, PCAs and others in the agricultural industry,” said Mike Stanghellini, TriCal research director. “Steve's priorities, previously with UC Cooperative Extension and now with TriCal Diagnostics, are to be scientifically and technically correct in the lab as well as practical and useful in the field. He is pleased to continue to provide diagnostic services to the agricultural industry in California and other states, and he remains engaged in plant pathology research and investigations.”
- Author: Pamela Kan-Rice
After 28 years of service, Steven T. Koike, UC Cooperative Extension plant pathology advisor in Monterey and Santa Cruz counties, plans to retire from the University of California at the end of 2017.
Koike, who joined the UCCE Monterey County office in 1989, conducts an extension research and education program on diseases of vegetable, fruit and ornamental crops. He focused on diagnosing plant problems, investigating the epidemiology of diseases, evaluating fungicides and other disease control methods, identifying and characterizing new diseases, and advising clientele on disease management approaches.
Koike created and operated the university's only county-based, fully equipped diagnostic lab for plant diseases, located in Salinas.
Using his diagnostic skills, Koike was instrumental in identifying a new virus that damaged the celery crop on California's central coast from 2007 through 2009. Tracing the virus back to poison hemlock, he and Oleg Daugovish, UCCE advisor in Ventura County, advised growers to remove the weed to protect celery, parsley and cilantro crops.
In 2009, downy mildew began causing spinach leaves to turn bright yellow and then brown in the Salinas Valley. By testing samples of diseased spinach from throughout the state, Koike and his counterparts at the University of Arkansas determined there were four new races of the mildew causing the outbreaks. Revelation of the new fungus strains in 2012 helped the industry develop resistant spinach cultivars.
In response to foodborne illness outbreaks, he collaborated on field studies involving foodborne bacterial pathogens, including E. coli survival in vegetable fields.
During his UCCE career, Koike published 381 peer-reviewed and 711 non-peer-reviewed publications, including his 450-page book Vegetable Diseases: A Color Handbook.
Koike has received many awards, including the UC ANR Assembly Council Fellowship for Advanced Studies in 1997; a 1999 Resolution from the Monterey County Board of Supervisors for excellence in service and research; 2000 Award for Outstanding Achievement from the California Friends of Agricultural Extension; 2005 Joseph M. Ogawa Research & Teaching Endowment Award; the Milton D. and Mary M. Miller Plant Science Awards in 1993, 1998 and 2006, from the UC Davis Department of Plant Science; 2011 Oscar Lorenz Award, Dept. Plant Sciences, UC Davis; UC ANR Distinguished Service Awards for Outstanding Research in 2002 and 2011; and the American Phytopathological Society's National Award for Excellence in Extension Plant Pathology in 2013.
In announcing his retirement, Koike thanked the many people who assisted and encouraged him in his extension career: growers, pest control advisers and other agricultural professionals; fellow UCCE academics from throughout the state; research technicians and support staff from his Salinas office and other university and USDA researchers.
In January 2018, Koike will become the lab director for TriCal Diagnostics, which is building a new laboratory, in Hollister. His new position with TriCal Diagnostics will involve operating a commercial diagnostic lab for plant diseases, supporting research on soil-borne plant pathogens, and providing plant pathology information to clientele who grow or work with various agricultural commodities.
- Author: Jeannette E. Warnert
The story, which featured USDA plant pathologist Carolee Bull, detailed one of her recent investigations, conducted with Steve Koike, UCCE advisor who specializes in plant pathology. They sought to determine what pathogen was putting spots on broccoli raab and other cruciferous crops in the Salinas Valley.
Once the correct identification and classification of the pathogen was completed, an environmentally sound and affordable way of dealing with it could be developed.
“We create our own puzzles,” Bull said, “and then we solve them.”
- Author: Jeannette E. Warnert
Steven Koike, UC Cooperative Extension farm advisor in Monterey County, has received the 2013 Excellence in Extension Award by the American Phytopathological Society, reported the Salinas Californian in a lengthy profile article written by D.L. Taylor.
Koike is considered by his grower clients as a problem solver who identifies new plant diseases and controls outbreaks. He is the primary resource person for coastal plant pathology issues.
“Steve’s program provides another service to the university: it is an academic model for outstanding scholarship in the UC Cooperative Extension system,” said Maria de la Fuente, director of UCCE in Monterey County. “His vision and creativity encourage county-based academics to expand our horizons beyond historically limited roles as advisors.”
Koike’s research involves dozens of host crops and many factors that cause plant diseases, such as fungi, bacteria, viruses, as well as chemical and physical factors in the environment, the article said. For example, following the 2006 E. coli O157:H7 outbreak on California spinach, he engaged in food safety research and conducted studies on E. coli and Salmonella ecology and survival under field conditions in the Salinas Valley.