- (Focus Area) Agriculture
- Author: Michael D Cahn
Introduction
Traditional winter cereal cover crops planted in the Salinas valley have many potential benefits including, scavenging nitrate in the soil profile, increasing organic matter in the soil, and protecting the soil from erosion during storm events. However, when grown for 3 to 4 months during the late fall and winter, cereal rye, triticale, or barley can accumulate 5 to 6 tons of dry matter biomass that must be incorporated into the soil before planting a spring vegetable crop. Tilling in a high amount of cover crop biomass can be disruptive to spring planting schedules. Consequently, only a small fraction of the vegetable ground in the Salinas valley is cover cropped each year.
Previous studies demonstrated alternative strategies can limit the biomass growth of these cereal cover crop species so that they can more easily be tilled into the soil, and therefore less disruptive to spring planting schedules. After fall land preparation, the cereal cover crops are seeded into listed beds and/or in the furrow bottoms. After they become established they can reduce runoff and protect the soil from erosion during early winter storm events. Before the cover crops grow too big, they are terminated with an herbicide to limit the amount of above ground biomass that needs to be incorporated in the spring. For organic systems, planting a mustard cover crop on listed beds or furrows which can be terminated mechanically by mowing is another strategy to limit biomass. A good target for these low biomass cover crops is between 0.5 to 1 ton of dry matter per acre by the date of termination. Once terminated, the biomass begins to decompose. However, the residue on the surface continues to protect the soil from erosion and can significantly increase infiltration from rain events. This helps to leach accumulated salts in the soil as well as recharge groundwater aquifers. The remaining decomposed residue can easily be incorporated into the soil during bed preparation in the spring.
One risk of this low biomass approach is accessing fields during the winter to terminate the cover crop. If soil conditions are too wet or if there is not enough available labor, it may be difficult to fit in a spray application or to run a flail mower. This termination step also increases the cost of managing the cover crop. A possible solution is to use species that grow slowly during the winter when temperatures are cold. Sudangrass and sorghum-sudangrass hybrid are warm season adapted species that could be used in this low biomass approach to managing winter cover crops.
Field trial with warm season adapted cover crop species
A field trial was conducted with sudangrass and sorghum-sudangrass in the 2023-2024 winter to evaluate biomass growth, and the effect on storm water runoff and soil erosion compared to bare-fallow plots. The site was located on an Arroyo Seco gravelly loam soil with a slope of more than 5%. Plots measuring 1050 ft in length by four 40-inch wide peaked beds were planted with either sudangrass, sorghum sudangrass hybrid, or left bare fallow. Treatments were replicated 4 times. The cover crops were seeded at 60 to 80 lbs/acre on October 4th and were subsequently sprinkle-irrigated several times. Total water applied for establishment was 2.6 inches. One application of the herbicide Bromoxnil (Maestro) was applied about 45 days after planting to kill emerged broadleaf weeds. Air temperature and rainfall were monitored at the field site and flumes were installed in late November at the end of each plot for measuring runoff during winter storm events (Fig. 1). The flumes were equipment with automated sampling pumps that could collect runoff during storm events. Runoff samples were evaluated for sediment and nutrient concentration at the UC Davis Analytical Laboratory.
Results
Above ground biomass, N uptake, and carbon accumulation
Both cover crops had limited biomass growth, accumulating only 0.35 to 0.5 tons/acre of dry matter by early January and less than 1 ton/acre by mid March (Table 1). Growth was set back by cold conditions that occurred from mid November through early January, occasionally reaching freezing temperatures which caused damage to leaves (Fig. 1). However, the freezing temperatures lasted only a few hours and were not severe enough to kill the cover crops (Fig. 2). By March 13th the cover crops had taken up 45 to 55 lbs N/acre and had a carbon to nitrogen ratio of 15. The C:N ratio of 15 would suggest that after soil incorporation the residue would slowly break down and release N for the following vegetable crop.
Runoff, rainfall infiltration, and control of soil erosion
Total rainfall measured at the trial site was 10.2 inches for the winter season. The most intense period of rainfall occurred in late January and early February which resulted in several runoff events (Fig. 3). During this period about 50% of the rainfall in the bare fallow plots was lost as runoff compared to 15% lost as runoff in the cover crop plots (Fig.4). Over the entire winter season, runoff was reduced by an average of 70% under the cover cropped plots compared to the bare fallow plots, and significantly more rainfall was infiltrated into the ground in the cover cropped plots. In addition, suspended sediment concentration was 90% and 77% less in the sudangrass and sorghum-sudangrass cover crop plots, respectively, compared to the bare plots. Turbidity, total P, and total N concentration in the runoff were also reduced under the cover crop plots compared to the bare fallow plots (Table 2).
Seasonal soil erosion losses could be calculated based on the volume of the runoff and sediment concentration in the runoff. The total loss of sediment averaged more than 3500 lbs per acre in the bare fallow plots during the winter, while erosion losses were reduced by 96% to 98% in the sorghum-sudangrass and sudangrass plots (Fig. 5). Total N losses were reduced by 83% to 86% in the cover crop plots compared to the fallow plots, and total P losses were reduce by 81% to 85% in the cover cropped plots compared to the bare fallow plots.
Conclusions
The use of warm season species such as sudangrass and sorghum sudangrass hybrids as winter cover crops provides several advantages compared to planting winter cereal cover crops. The biomass growth through the winter is self-limiting due to the cold conditions that typically occur in the Salinas Valley. Because the biomass would likely be limited to less than 1 ton per acre, these species can be planted on listed beds in the fall rather than on flat ground. This means that in the spring, the remaining cover crop can be lillistoned into the peaked beds a few weeks before final bedshaping and planting. Cover crops planted on flat ground and have high amounts of biomass require many tillage passes to prepare ground for planting. Despite, having less biomass than traditional winter cereal species, sudangrass and sorghum-sudangrass hybrid provided excellent erosion control compared to bare ground, and increased infiltration of rainfall during storm events. Also these species may be able to scavenge significant amounts of nitrogen from the soil which can limit nitrate leaching during the winter months.
Acknowledgments
This project was funded by the California Leafy Greens Research Board.
![Figure 5. Rainfall volume infiltrated and lost as runoff in the cover crop and bare treatments during late January and early February 2024. Figure 5. Rainfall volume infiltrated and lost as runoff in the cover crop and bare treatments during late January and early February 2024.](http://ucanr.edu/blogs/SalinasValleyAgriculture/blogfiles/108695.png)
![Figure 6. Total sediment loss in cover crop and bare-fallow plots during the 2023-24 winter season. Figure 6. Total sediment loss in cover crop and bare-fallow plots during the 2023-24 winter season.](http://ucanr.edu/blogs/SalinasValleyAgriculture/blogfiles/108696.jpg)
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- Author: Kathy Keatley Garvey
The seminars begin Monday afternoon, Sept. 30 and continue every Monday through Dec. 2.
Nematologist Amanda Hodson, assistant professor of soil ecology and pest management, is coordinating the seminars. All, except one, will be held in Briggs Hall. All, but one, will be on Zoom.
The Zoom link:
https://ucdavis.zoom.us/j/95882849672.
Michael Hoffmann, professor emeritus, Cornell University, will deliver the Thomas and Nina Leigh Distinguished Alumni Award Seminar in the Putah Creek Lodge at 4 p.m. on Oct. 14. (See below)
The list of seminars:
Monday, Sept. 30, 4:10 to 5 p.m., 122 Briggs
Kyle Wickings
Department of Entomology, Cornell University
Title: “Composition and Function of Soil Invertebrate Communities in Residential Greenspaces”
Monday, Oct. 7, 4:10 to 5 p.m., 122 Briggs
Juliana Rangel Posada
Professor of Apiculture, Department of Entomology, Texas A&M University
Title: “Don't Compromise: Food Lipid Content Shapes Protein-Lipid Regulation in Honey Bee (Apis mellifera) Nurses”
Monday, Oct. 14, 4 p.m. to 7 p.m. Thomas and Nina Leigh Distinguished Alumni Award Seminar
Michael Hoffmann
Professor Emeritus, Cornell University
Title: “Our Changing Menu: Using the Power of Food to Confront Climate Change”
This will take place beginning at 4 p.m. in the Putah Creek Lodge and will include a social, lecture and dinner. Reservations closed. (See more)
Monday, Oct. 21, 4:10 to 5 p.m.,122 Briggs
Andrew Corbett
Research Affiliate, UC Davis Department of Entomology and Nematology (formerly with the lab of UC Davis distinguished professor Jay Rosenheim, now emeritus)
Title: "In Silico Experiments with the Effect of Natural Habitats on Biological Control in Agricultural Landscapes."
Monday, Oct. 28, 4:10 to 5 p.m., 122 Briggs
Jolene Saldivar
UC Davis Chancellor's Postdoctoral Fellow, lab of Professor Louie Yang
Title: "Disturbance in Coastal Sage Scrub and the Implications for Migratory Butterflies”
Monday, Nov. 4, 4:10 to 5 p.m., 122 Briggs
Eliza Litsey (exit seminar)
Litsey, a former graduate student in the honey bee lab of Elina Niño, UC Davis Department of Entomology, received her master's degree in entomology in June 2024 and is now a laboratory technician at the lab of research entomologist Julia Fine, USDA/ARS, Davis. Litzey also holds a bachelor's degree from UC Davis.)
Monday, Nov. 18, 122 Briggs (in-person only; will not on Zoom)
Andre Custodio Franco
Assistant Professor, Indiana University Bloomington
Title: "Deciphering the Soil Macrobiome: Belowground Communities Driving Ecosystem Responses to Global Change”
Monday, Nov. 25, 4:10 to 5 p.m., 122 Briggs
Christine Sprunger
Associate Professor of Soil Health at Michigan State University
Title: "Nematodes as Bioindicators of Soil Health and Climate Resiliency”
Monday, Dec. 2, 4:10 to 5 p.m., 122 Briggs
Inga Zasada
Research Plant Pathologist, USDA-ARS
Title: "How an Applied Nematolgist Uses Genomic Tools to Address Plant-Parasitic Nematode Research”
For more information, contact Hodson at akhodson@ucdavis.edu
![Honey bees will be among the topics at the UC Davis Department of Entomology and Nematology fall quarter seminars. This bee is heading toward gaura in early morning. (Photo by Kathy Keatley Garvey) Honey bees will be among the topics at the UC Davis Department of Entomology and Nematology fall quarter seminars. This bee is heading toward gaura in early morning. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/108697.jpg)
- Author: Bodil Cass
F\ig Wax Scale has recently been detected in the environment in the San Diego County. This insect is commonly intercepted at ports of entry, especially on shipments of palms, but has not previously established a reproductive population in California to our knowledge.
Fig wax scale is an A-rated, actionable invasive pest by CDFA, due to its high potential to damage fresh fruit production through lowering yield, increased production costs, disruption of export markets, and vectoring of plant viruses including grape vine leaf-roll virus. It is a polyphagous phloem feeder and a potentially devastating pest of many high-value crops including almond, grape, citrus, pistachio, avocado, cotton,fig,palms,pear,and ornamentals.In the USA it is currently only found in Florida, although it is distributed throughout much of the rest of the world and frequently affects citrus and fig production in Europe. The environmental conditions throughout much of California are considered favorable for this scale to establish if it is not eradicated and prevented from re-entering.
For more on this scale and other recent topics, check out the Topics in Subtropics Newsletter:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=60446
![fig wax scale ant feeding fig wax scale ant feeding](/blogs/blogcore/blogfiles/108401.jpg)
![fig wax scale female fig wax scale female](/blogs/blogcore/blogfiles/108402.png)
- Author: Ben A Faber
Statewide citrus bearing acreage relatively stable for past three seasons
The Pacific Regional Office of the USDA's National Agricultural Statistics Service (NASS) conducts an acreage survey of California citrus growers as funding is available. The purpose of this survey is to provide bi-annual citrus acreage, which includes information on new plantings and removals. It is the continuation of a long series of industry-funded Citrus Acreage surveys.
This report consists of two parts:
- Table 1 shows estimated statewide bearing acreage for the 2020-21, 2021-22 and 2022-23 seasons.
- Tables 2, 3, 4 and 5 show detailed acreage data by type, variety, and year planted -- as voluntarily reported by citrus growers and maintained in NASS' database.
With perfect information, the estimated statewide bearing acreage and the detailed acreage data would be the same. Generally, this will not be the case for the following reasons:
- A voluntary survey of approximately 5,000 citrus growers is unlikely to ever attain 100 percent completeness.
- It is difficult for USDA/NASS to detect growers who are planting citrus for the first time.
Click here for a larger image.
Click here to read the full report.
Source: ccqc.org/wp-content
![lemon tree image lemon tree image](/blogs/blogcore/blogfiles/108270.jpg)
- Author: Dylan Beal
Hello everyone, I'm the new UC IPM Entomology Advisor serving the communities of Monterey, Santa Cruz, and San Benito Counties. Born and raised in the Santa Clarita Valley, I'm excited to return to my home state of California.
Inspired by a lifelong passion for insects, I pursued bachelor of science in degrees in Entomology and Plant Pathology at Cornell University in Ithaca, NY. At Cornell, I was first exposed to the world of cooperative extension, working in a lab to study and support natural enemies of spider mites, aphids, thrips, fungus gnats, and whiteflies in greenhouses.
In partnership with Montpellier SupAgro and the Università degli Studi di Torino, I received a Master of Science degree in Viticulture and Enology. For my master's thesis, I worked with Italian grape growers on understanding the ecology and management of leafhopper vectors of the pathogen responsible for European grapevine yellows (Flavescence dorée phytoplasma).
For my PhD, I studied Environmental Science, Policy, and Management at the University of California, Berkeley. At Berkeley, I worked with grape growers and cooperative extension advisors in Napa and Sonoma county to understand the role of spittlebug insect vectors in spreading Xylella fastidiosa, the bacteria responsible for Pierce's disease of grapevine.
After Berkeley, I have worked as a postdoc at Washington State University with cherry and blueberry growers to adapt and adopt innovative and internationally recognized practices for sustainable management of Spotted-Wing Drosophila (SWD). As part of that work, I have closely partnered with growers, pest control advisors, USDA scientists, cooperative extension advisors, and industry representatives on SWD projects related to biological control, cultural control, behavioral control, and pesticide resistance screening and management. Additionally, I was part of a team that worked to coordinate SWD management with the management of the leafhopper vectors of X-Disease phytoplasma in cherry.
With 15 years of experience in New York, California, Washington State, France, and Italy, I'm excited to collaborate with you all to support the development and adoption of innovative, cost-effective, and sustainable insect pest management practices. I aim to develop partnerships, lifelong relationships, and projects that center and elevate grower voices, experiences, and leadership. Together, I hope that we can not only address the threat that agricultural insect pests pose to our three counties but also help to support the many communities and ecosystems that interface with our agricultural livelihoods. Please feel free to reach out to me at 831-759-7359 or djbeal@ucanr.edu. The Bug Doctor is in to look at any insects you may find!