- Author: Emily Dooley
- Posted by: Gale Perez
Hanson and team battle invasive species
At first glance, Orobanche ramosa looks like an interesting blossoming plant, one that could add a unique flair to flower arrangements. But it's a parasitic weed that attaches to roots, sucks out nutrients and is threatening California's $1.5 billion processing tomato industry.
The weed's tiny seeds — smaller than finely ground pepper — can survive in soil for many decades and be carried by wind, water, soil transfers and even footwear. If found attached to crop plants and reported to the state, farmers are required to destroy the field before harvest, taking large losses not covered by crop insurance.
Its resurgence concerns state regulators and industry, which is helping fund multidisciplinary research at the University of California, Davis, on ways to detect, manage and fight the weed.
“Most of the damage occurs before you can see it,” said Brad Hanson, a professor of Cooperative Extension in the Department of Plant Sciences. “There's a lot of ripples to the problem. We could see it spread to other crops and other regions in the state if it's not managed.”
Across three colleges at UC Davis, researchers are working on ways to detect the pest, manage it in the field throughout its life cycle and develop long-term solutions to minimize the threat to California agriculture. The work is happening in labs and the field, using drones, human spotters and new techniques to sniff out volatile organic chemicals that are emitted when the weed is present.
They are also testing ways to sanitize farm equipment to reduce the risk of spreading seeds from contaminated fields to clean ones. And they are testing dozens of other crops to see if they are susceptible or could be used as false hosts to kill off the Orobanche seeds in the soil.
Invasive species alert: A weed resurgence in California agriculture
The California Department of Food and Agriculture and industry had a program from the 1950s through the 1970s to eradicate the weed, which is commonly known as branched broomrape. But the weed showed up again in Yolo County in 2017.
“Believing it to be eradicated, the industry moved on to other challenges,” said Zach Bagley, managing director for the California Tomato Research Institute Inc., or CTRI. “We've been aggressive, with this as our top priority, and we've been putting the funding behind it.”
CTRI's research budget for 2022 and 2023 is nearly $1 million, and half of that money has gone to fund six researchers and their teams at UC Davis and UC Davis Chile, as well as some work at University of Wisconsin.
“Unfortunately, or fortunately, tomatoes are going to have to be the tip on the spear of trying to address this,” Bagley said. “UC Davis has relationships with industry. They have the expertise in the areas we need for this problem.”
Last year, CTRI, Corteva and Hanson's team got state permission for an herbicide treatment that, in trials, has reduced Orobanche emergence fourfold. “That management treatment has been used extensively by growers this year,” Bagley said.
The CTRI funding has helped leverage other money, bolstering the research capability.
“It shows the power of the university,” Hanson said. “It shows the kind of things we can do with the research and extension expertise in a land-grant university. When something like this arises, we can spring into action.”
Severe regulatory triggers impact California tomato farmers
It's hard to know quite how far Orobanche has spread.
Yolo County farmers reported 71 to 403 acres affected between 2017 and 2022, with some years seeing less and others more. No cases have been reported this year, Yolo County Agriculture Commissioner Humberto Izquierdo said.
But Orobanche weeds could be sprouting up elsewhere.
“The issue with this pest is that growers are very reluctant to report it and it's not an easy issue to spot,” Izquierdo said. “The regulatory requirements are very strict. Once it's found, we limit harvesting on that field.”
Izquierdo works with canneries and the CTRI to promote good sanitation policies, so the weeds don't spread. But with a limited number of inspectors, it's hard to get a handle on the extent of the problem without consistent reporting.
“If we don't know where the problem is, we can't deal with it,” he said. “It really takes cooperation from industry to be able to move forward.”
Hanson says it's likely that there are more infested fields in Yolo County than what has been reported, and there's no obvious reason Orobanche could not spread to other tomato-producing regions. But the harsh repercussions for reporting can be a barrier: “Do the right thing, lose hundreds of thousands of dollars,” he said.
The low reporting numbers combined with the hardiness, number and sheer longevity of Orobanche seeds requires more than regulatory action.
“This is not something you're going to sweep under the rug,” said Matt Fatino, a Ph.D. student researcher in Hanson's lab. He has been working on chemical control strategies, including on projects with counterparts in Mediterranean climates, where the weed is more prevalent.
Field research on tomato plant diseases promotes sustainable agriculture
A local grower recognized the issue needed research and allows Hanson, Fatino and other UC Davis scientists access to a 3-acre plot in Woodland where tomatoes are planted in infected soil. There, researchers test out different ways to control the weeds on the ground and others take to the air to scan for evidence of the pest.
A half dozen other weeds also clustered around that one tomato plant, attached at the roots underground by what looked like an undifferentiated mass once unearthed.
In the distance, students and other lab members kicked at the tomato plants, searching for the weeds and placing tiny flags to mark their presence.
In Fatino's experiment, different herbicides of varying concentrations have been applied via irrigation to the rows in an attempt to gauge what may work best controlling the Orobanche. The chemicals must be authorized with the state and have restrictions on use.
Every week, spotters arrive with differently colored flags to mark their latest finds. In past years, 800-900 flags were planted in the 1-acre experiment.
“It's a needle in a haystack project,” Hanson said.
At that same plot, Ph.D. student Mohammadreza Narimani and others from the Digital Agriculture Laboratory, which is run by associate professor of Cooperative Extension Alireza Pourezza, use drones equipped with special cameras and technology to scan the field.
The lab, which is housed in the College of Engineering and College of Agricultural and Environmental Sciences, specializes in using digital technology and data analytics to support sustainable agriculture.
The team has divided the field into quadrants, flagging spots with and without Orobanche weeds. Four drones fly over the field, equipped with Light Detection and Ranging, or LIDAR, scanners, RGB, multispectral and hyperspectral cameras. As the drones fly, real-time images appear on a laptop, filling in the screen square by square with images and data from the camera's sensors to be analyzed later in the lab.
“Different characteristics of plants reflect light in a different way, which results in them appearing in different colors,” Narimani, the drone pilot, said. “We can monitor different levels of nutrients in the plant and identify if there are any signs of broomrape.”
Secure lab research on plant pathology and broomrape weed
Back on campus, the weeds are carefully studied in a secure environment known as the Contained Research Facility, or CRF, which is dedicated to studying invasive plant pests, ranging from pathogens and weeds to nematodes and certain invertebrates like spiders and insects.
The facility is the first of its kind in the west and houses labs, greenhouses and growth chambers. People working in the space must adhere to strict protocols meant to ensure none of the pests escape the space. Waste is sterilized on site and people, plus phones and other personal items brought inside, must shower out to leave the facility.
In a small space set aside for Orobanche, postdoctoral scholar Pershang Hosseini has a handful of projects; Hosseini also is in the Department of Plant Sciences. One of her projects is testing whether certain sanitizing chemicals can kill the seed, removing the threat of Orobanche and other pathogens spreading on farm equipment. Hosseini is working on that project with plant pathologist Cassandra Swett, an associate professor of Cooperative Extension.
Another project involves planting more than two dozen crops to see whether they are susceptible to Orobanche or if they could serve as false hosts, causing the seeds to die out because they germinate but don't find a suitable host to parasitize.
Along those lines, Hosseini is also studying a chemical that is similar to a natural substance in tomato plants that signals Orobanche to germinate when no host exists, essentially causing the seeds to commit suicide.
“No seeds can germinate twice, so this could be a way to directly reduce the amount of seed in the soil seedbank,” Hosseini said.
Innovative plant disease detection: Sniffing out broomrape in tomato plants
Other professors are also using the space for related research, and one project involves smelling volatile organic chemicals.
“We're basically sniffing out diseases or infections or parasites,” said Cristina Davis, professor of mechanical and aerospace engineering.
Davis and her lab director and staff researcher Mitchell McCartney developed a sensor to detect Orobanche by measuring odors emitted from plants affected by the weed.
“The plants tend to off gas an alert signal around themselves to warn other plants,” McCartney said. “There's all this information that's being passed around us in the air, but the human olfactory nerve isn't sensitive enough to pick up on those changes.”
At the Contained Research Facility, tomato plants are enclosed in an airtight space and fresh air is pumped in, while a sponge-like sensor collects what is emitted into the air. Back at their home lab in the College of Engineering, Davis and McCartney superheat the sponges to release volatile organic chemicals.
“It captures a snapshot of odor,” he said.
If a unique chemical signature can be isolated, fields could one day be sniffed for Orobanche weeds, serving as an alert system.
Biological innovations in plant breeding could mean solutions for California farms
“The goal is to figure out if there are very early gene expressions when plant roots are attached by broomrape,” Sinha said. “Early response is where we feel resistance will lie.”
Brady is looking at if the cell types of tomato plant roots could be modified to create a barrier to the weed from attaching.
“It's a combinational approach to attack from all these different points in the life cycle,” Brady said of the UC Davis research. “It's attacking the attacker.”
For Hanson, the research is among the most collaborative that he's been a part of and shows how real-world problems can be addressed when industry, regulators and researchers work together.
“We're making progress on a major threat to California agriculture,” he said, “and it's really rewarding to be a part of the research team.”
Media Resources
- Brad Hanson, UC Davis Department of Plant Sciences, bhanson@ucdavis.edu
- Emily C. Dooley, College of Agricultural and Environmental Sciences, ecdooley@ucdavis.edu
- Amy Quinton, UC Davis News and Media Relations, 530-601-8077, amquinton@ucdavis.edu
Media kit of images for download.
Original source: UC Davis Dept. of Plant Sciences
Emily Dooley is a Communications Specialist with the College of Agricultural and Environmental Sciences at UC Davis.
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- Author: Lauren Fordyce
Tomatoes are ripening all over California right now keeping many gardeners and tomato lovers busy picking, canning, and eating. But what may not make gardeners happy are seeing curled leaves and not knowing why. There are many reasons why your tomato leaves may be curling or rolling. Being able to narrow down possible causes takes a bit of detective work, but using this article and UC IPM's Plant Problem Diagnostic Tool can make it achievable!
Tomato leaf curl can be the result of:
Environmental stressors
Leaf curl on tomato is often caused by environmental stress, not necessarily pathogens or insects. Too much or too little water or nutrients, can make leaves curl. A wet spring, followed by warm weather can cause physiological leaf roll. Leaves may roll downward and become firm and leathery. Usually, the lowest leaves are affected most and the plant appears healthy otherwise. When conditions become more favorable, like more water if the plant hasn't been getting enough or consistent watering, environmental stressors will often resolve themselves and the plant will recover.
Plant pathogens
Several viral infections can cause tomato leaves to curl. Curly top virus causes leaves to cup downward, become thick and brittle, and stunts plant growth. Tobacco mosaic virus results in mottled leaves that appear stringy and distorted. Tomato spotted wilt virus causes downward-cupped leaves and necrotic spots. It is important to note that viruses can be transmitted to tomatoes, and other garden plants, by sap-sucking insects. Therefore, their control is important in preventing these viruses. There is no treatment for virus-infected plants, so it is best to remove and dispose of them.
Insects
Aphids, whiteflies, thrips and other sap-sucking insects can cause leaves to curl by sucking plant juices out of the leaves. Check the undersides of leaves to look for these insects. Once you have identified the culprit, see the UC IPM fact sheets (Pest Notes) on various methods for managing them.
You may see some ‘good bugs' around the garden too. Many natural enemies will feed on these pest insects, so keep an eye out for lady beetles, lacewings, and minute pirate bugs. Also look for signs of parasitization (like aphid mummies) from parasitoid wasps!
Herbicide injury
If you recently applied an herbicide near your tomato plants, their leaves could be curling from herbicide drift or contamination. When tomato plants come in contact with herbicides, like 2,4-D, their leaves may curl or cup and become distorted.
How can you prevent tomato leaf curl?
- Choose pathogen resistant tomato varieties.
- Harden off plants or wait for the weather to warm up before planting outside.
- Ensure tomatoes receive consistent and adequate water.
- Use the correct amount of fertilizer.
Visit the UC IPM website for more information about tomato pests, issues, and cultural controls. If you have additional questions, please contact your local UC Master Gardeners for more information.
- Author: Melissa G. Womack
Almost any home gardener will tell you that one of the most versatile and rewarding plants to grow in a summer edible garden is a tomato. In fact, a 2023 study by the National Gardening Association revealed that 86 percent of gardeners grow tomatoes. It is understandable that the tomato plant is a popular home vegetable garden staple, tomatoes offer thousands of different varieties options and flavors. Plus, nothing beats the bursting flavor of a ripe tomato straight from the garden.
When properly cared for, a single tomato plant can produce 10 to 15 pounds (4.5 to 6.8 kg) or more of fruit. As with any gardening journey, sometimes there can be obstacles or challenges to overcome. If tomato yields aren't what was expected, or the fruit is damaged, it could be due to a number of abiotic disorders, diseases or pesky pests.
Abiotic disorders result from non-living causes and are often environmental, for example: unfavorable soil conditions, too much or too little water, extreme temperature, physical or chemical injuries, and other issues that can harm or kill a plant. Using research-based information from UC Agriculture and Natural Resources (UC ANR) publication, Growing Tomatoes in the Home Garden.
Here are five of the most common abiotic disorders of tomatoes and how to address them:
- Sunburn or Sunscald: Yes, just like humans tomatoes can also suffer from sunburns because of overexposure to the sun. Sunburnorsunscald occurs on the side of the fruit exposed to the sun, which turns brown and becomes leathery in texture. Solutions:
- Maintain the plant canopy to produce adequate leaf cover for the fruit.
- Avoid overpruning.
- Provide partial shade during peaks sunlight hours.
- Leaf Roll: You might find that the older leaves on your plant suddenly roll upward and inward, becoming stiff, brittle and tough to the touch. This is typically caused by high light intensity and moist soil, especially in staked and heavily pruned plants. Solutions:
- Choose less-susceptible varieties.
- Maintain even soil moisture.
- Provide partial shade during peaks sunlight hours.
- Blossom End Rot: This condition appears as a water-soaked spot at the blossom end of the fruit, which enlarges and darkens, creating a sunken, leathery appearance. It's more prevalent in sandy soils and is primarily caused by calcium nutrition imbalance and inconsistent water levels. Solutions:
- Maintain even soil moisture.
- Amend planting area with compost to improve water retention.
- Avoid heavy applications of high-nitrogen fertilizer.
- Soils deficient in calcium may be amended with gypsum.
- Fruit Cracks and Catfacing: Rapid growth during high temperatures and excessive soil moisture can lead to circular concentric cracks around the stem end, radial cracks shooting out from the stem, and malformation and cracking at the blossom end, a phenomenon known as ‘catfacing'. Solution:
- Keep soil evenly moist.
- Maintain good leaf cover or provide partial shade during hours of most intense sunlight.
- Mulch around the plant 3 to 7 inches deep to maintain soil moisture and temperature.
- Solar Yellowing and Green Shoulders: This problem is marked by the tomato turning yellow or yellow-orange instead of the normal red color, with the upper part of the fruit stubbornly staying green even though the lower part appears red and ripe. It's a result of high temperatures and intense light. Solutions:
- Maintian plant vigor to produce adequate leaf cover.
- Avoid overpruning.
- Provide partial shade during hours of most intense sunlight.
A variety of insects and pests can cause other damage to tomato plants. Some examples of common pests, include: hornworms, tomato fruitworms, tomato pinworms, stink bugs, white flies, and leafminers. For information about identifying and managing pests in your edible garden visit the UC Integrated Pest Management (UC IPM) website, ipm.ucanr.edu.
Navigating the ups and downs of growing tomatoes might seem daunting, but don't forget, every seasoned gardener has been in your shoes once. We've explored the common abiotic diseases and challenges you might encounter in your tomato-growing journey, and hopefully armed you with solutions to keep these issues at bay.
If you have additional questions or need more help, don't hesitate to reach out to your local UC Master Gardener Program. We have a team of volunteers trained and eager to help you have a bountiful harvest! mg.ucanr.edu/FindUs
Source: Growing Tomatoes in the Home Garden Publication 8159 http://anrcatalog.ucanr.edu/pdf/8159.pdf
- Author: Amber Vinchesi-Vahl
- Posted by: Gale Perez
Myself, Cooperative Extension Specialist Cassandra Swett, and UC IPM collaborated on creating this document directly from stakeholder input and funding from the Western IPM Center. Below I have highlighted the documented critical needs for managing weeds in processing tomato production in California (more detail on each can be found in the PMSP, cited below). These needs were prioritized by growers, PCAs, academics and industry for the state, the northern growing region and the southern growing region and include research, regulatory and education priorities.
“Statewide Critical Needs for Weeds
Research
- Develop and identify management methods (including, but not limited to, herbicides) that work for difficult-to-control and perennial weeds, particularly nutsedge and field bindweed.
- Better understand weed biology and how to influence weed biology for the purposes of weed management, especially methods to break the dormancy of belowground structures (especially field bindweed and nutsedge).
- Develop effective, affordable methods to eradicate branched broomrape from processing tomato fields, prevent its spread, and manage infestations if it becomes well established in California (see Northern Region Critical Needs for Weeds for more information).
- Identify effective and practical sanitation methods, especially for eliminating broomrape seed on harvesting equipment (See Statewide General Critical Needs #3).
- Develop methods to detect branched broomrape and Egyptian broomrape in tomato fields more easily.” (p. 12).
“Northern Region Critical Needs for Weeds
Research
- Develop integrated weed management methods (including herbicides) for difficult weeds such as fleabane, horseweed, groundcherries, velvetleaf, nightshades, and glyphosate-resistant ryegrass and sunflowers.
- Conduct necessary efficacy research to register herbicides as described in the Northern Region Critical Needs for Weeds, Regulatory Needs.
- Identify environmental conditions and production practices that produce different weed problems, including soil quality and water management, and the efficacy of cultural practices to manage such weeds.
- Determine effective management practices for broomrape infestations.Research management practices (including herbicides) that control nightshades and reduce reliance on the costly practice of hand weeding.Research management practices (including herbicides) that control nightshades and reduce reliance on the costly practice of hand weeding.
- Determine the efficacy of methyl bromide alternatives (e.g., metam sodium/metam potassium, solarization, conventional herbicides).
- Identify biological control agents that may attack broomrape and test potential options.
- Determine or confirm how broomrape spreads from field to field, and ways to prevent its spread.
- Test efficacy of more postemergence herbicides (particularly those that can be sprayed over the top of the crop) and herbicides available for fallow bed weed control.
Regulatory
- Add or expand herbicide registrations.
- Register more fallow bed and preplant herbicides and increase application options (especially aerial and helicopter applications) to give growers weed control options to use in wet preplant conditions.
- Explicitly register herbicides for fallow bed management, not just preplant use.
- Identify and register herbicides that can be used near almond orchards.
- Register herbicides for difficult weeds such as fleabane, groundcherries, horseweed, nightshades, velvetleaf, and glyphosate-resistant ryegrass and sunflowers.
- Pursue 24(c) labels or Section 18 exemptions where necessary and possible.
- Register postemergence herbicides that are safe to apply over the top of the tomato crop to kill late-season weeds.
Education
- Educate growers and pest control advisers on how to reduce herbicide drift. Many of the herbicides registered in processing tomato (e.g., carfentrazone) have drift issues.
- Conduct outreach to growers and pest control advisers about impacts of soil quality, water management, and other conditions that produce specific weed problems and how to avoid them via cultural practices.
- Educate growers and pest control advisers on how to reduce and manage glyphosate-resistant weeds (especially ryegrass, fleabane, and sunflower).” (p. 17).
“Southern Region Critical Needs for Weeds
Research
- Develop effective alternatives to glyphosate, especially those that are systemically translocated.
- Enhance cultivation methods for removing weeds, such as via finger and torsion weeders or robotic technology.
- Increase efforts to find effective biological control agents for weeds (e.g., research the effectiveness of the herbivorous mite that attacks Russian thistle).
Regulatory
- Register any effective and viable alternatives to glyphosate, especially systemically translocated herbicides.
Education
- Educate growers on whether or how natural enemies can be used to manage Russian thistle and other relevant weeds.” (p. 17).
Weeds come up frequently in other areas of the PMSP, especially in relation to insect pest management.
You can also find descriptions of common weed problems on page 45 and weed management practices are included in the Farming and IPM Practices section starting on page 58. There is a weed occurrence table on page 75 in Appendix I, and efficacy tables for herbicides and nonchemical management starting on page 93 in Appendix II.
Martin, T., C. Swett, A. Vinchesi-Vahl, and S. Parreira. 2021. Pest Management Strategic Plan for California Processing Tomato Production. https://ipmdata.ipmcenters.org/documents/pmsps/2021_07_22_Processing_Tomato_PMSP_final.pdf
2021 07 22 Processing Tomato PMSP final
- Author: Matthew Fatino
- Author: Bradley Hanson
- Posted by: Gale Perez
Rimsulfuron, marketed as Matrix SG by Corteva, is registered on tomatoes in California is widely used both PRE and POST for nightshade and other broadleaf weed control. Based on research conducted in Italy that showed promising broomrape control with rimsulfuron applied in the irrigation water through surface drip lines (Conversa et al.), we did pilot studies in 2021 and 2022 in California.
With initially promising results, the California Tomato Research Institute submitted a 24c label (“Special Local Need”) request to California Department of Pesticide Regulation. The request was to add a chemigation application technique specifically for management of broomrape. The 24c label was approved in September 2022 and is available.
A breakdown of the 24c describing the approved chemigation application process is below.
From Corteva Matrix Label (https://ucanr.edu/blogs/UCDWeedScience/blogfiles/97715.pdf):
- For use on processing tomato for management of broomrape (Phelipanche ramosa, aka Orobanche ramosa) and Egyptian broomrape (Phelipache aegyptiaca). For management of broomrape, apply Matrix SG through buried- or surface-drip irrigation tubing to transplanted tomato. Apply at an application rate of 1.33 oz/A for up to 3 applications per season at approximately 30, 50 and 70 days after transplanting.
- Refer to product label for Matrix SG for Use Precautions, Mixing and Application directions.
- Surface or buried drip irrigation applications simulate banded applications.
- The amount of water and injection time may vary depending on soil type and irrigation system used. Introduce Matrix SG into the irrigation system at approximately the midpoint of the irrigation set to limit movement of the herbicide beyond the tomato root zone, where broomrape germination and attachment occurs, which may improve broomrape control. Factors such as soil type, irrigation system, injection timing and length, drip tape placement, etc. may affect weed control when Matrix SG is used through the drip irrigation system.
- After Matrix SG has been evenly applied across the field, flush the irrigation system prior to ending the irrigation.
- Do not apply more than a total of 4.0 oz/A Matrix SG (0.0625 lb ai/A rimsulfuron) on tomato during the same year.
- Do not make more than 3 applications of Matrix SG per year.
- Preharvest Interval: Do not apply within 45 days of harvest.
- This label must be in the possession of the user at the time of application. Follow all recommendations and restrictions on the Matrix SG Section 3 labeling.
It is important to note that when using rimsulfuron as a chemigated material following the label, you are using the yearly maximum rate of 4 oz/acre. For growers that do not use rimsulfuron as a PRE or POST product, this will not change current weed control programs. However, if growers currently utilize rimsulfuron as a PRE or POST product in their current programs, it will need to be excluded to avoid going over the annual 4 oz/acre maximum. This may affect general weed control, as rimsulfuron is often used to target nightshade species. Research into alternatives to rimsulfuron for general weed control in processing tomatoes will begin in 2023.
As with any pesticide, it is important to read and follow the most current label instructions for application.
We would like to thank the California Tomato Research Institute for funding ongoing broomrape management research and coordinating the 24c request, Corteva Agrisciences for providing product for the research and internal data from the US and Europe to CDPR, and our cooperators who hosted herbicide research trials that support the entire processing tomato industry.
Matt Fatino is a UC Davis Ph.D. student with Brad Hanson's Lab.
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Matrix SG Section 24c