- Author: Michael Hsu
In 20-year study, UCCE specialist Mitchell, colleagues, growers advance no-till and cover cropping practices
In the 1990s, long before “regenerative agriculture” was a buzzword and “soil health” became a cause célèbre, a young graduate student named Jeff Mitchell first learned about similar concepts during an agronomy meeting in the Deep South.
Mitchell was astonished to hear a long list of benefits attributed to practices known internationally as “conservation agriculture” – eliminating or reducing tillage, cover cropping and preserving surface residues (the plant debris left after harvest). Potential positive impacts include decreasing dust in the air, saving farmers money on fuel and equipment maintenance, improving soil vitality and water dynamics and a host of other ecosystem services.
“All of these things start adding up and you kind of scratch your head and say, ‘Well, maybe we ought to try some of this,'” recalled Mitchell, who became a University of California Cooperative Extension cropping systems specialist at UC Davis in 1994.
In 1998, Mitchell launched a long-term study of those practices at the West Side Research and Extension Center (REC) in Five Points, Fresno County. “We started this because, way back when I first began my job, nobody was doing this,” he explained. “This was brand-new, uncharted territory for California.”
For the next 20 years, Mitchell and his colleagues studied changes to the soil and ecosystem, learned from their failures and successes, and shared those hard-won lessons with fellow scientists and farmers across the state. A summary of their findings was recently published in the journal California Agriculture.
Conservation agriculture in California: ‘No trivial undertaking'
Mitchell and the Conservation Agriculture Systems Innovation Workgroup – a network established in 1998 comprising farmers, researchers, public agency personnel and members of private entities and environmental groups – started with a virtually blank slate. According to Mitchell, surveys at the beginning of the 21st century found that conservation agriculture practices were used on less than one-half of 1% of annual crop acreage in California.
Although no-till is common in the Midwest and Southeast of the U.S. and across wide swaths of the globe, it was almost unheard of in the Golden State. With the development of irrigation infrastructure in the 1920s, California farmers saw continually phenomenal growth in yield over the last century – and thus had little incentive to deviate from tried-and-true methods that relied on regular tillage.
Nevertheless, intrigued by the potential benefits of conservation agriculture, Mitchell wanted to see which of those practices could be feasibly applied to California cropping systems. During the 20-year study at West Side REC, the researchers grew a rotation of cotton-tomato, followed by a rotation of garbanzo, melons, and sorghum, and finally tomatoes.
But at first, it was a struggle to grow anything at all – as they had to master the basics of how to establish the plants in a no-till, high-residue system.
“This was no trivial undertaking,” Mitchell said. “Early on we struggled – we failed the first couple of years because we didn't know the planting techniques and we had to learn those. There was an upfront, very steep learning curve that we had to manage and overcome.”
Then there was the long wait to see any measurable improvements to soil health indicators, such as the amount carbon in the soil.
“For the first eight years, we didn't see any changes whatsoever,” Mitchell said. “But then they became strikingly different, between the no-till cover crop system and the conventional field without cover crops, and the divergence between those two systems became even starker.”
The two-decade time horizon for the West Side REC study is one major reason why it has been so valuable for growers and scientists alike.
“It's so hard to capture measurable changes in soil health and soil function metrics through research because those changes are really slow,” said Sarah Light, UCCE agronomy farm advisor for Sutter, Yuba and Colusa counties and a co-author of the recent California Agriculture paper. “Often in the course of a three-year grant you don't actually get statistically significant differences.”
Reaching, teaching and learning from farmers
The study site on the west side of the San Joaquin Valley also has been a vital teaching resource. Even though Light works with farmers in the Sacramento Valley, she has conveyed findings from that research with her clientele and uses soil samples from the site to vividly illustrate a significant benefit of conservation agriculture practices.
In one demonstration, she drops soil aggregates – which look like clumps of soil – into two containers of water. One clump, from heavily tilled land, falls apart quickly and the water becomes dark and murky. The other, comprised of soil that has been no-till and cover cropped for 20 years, holds together – a sign of healthy, resilient soil – and the water remains relatively clear.
“It's a really simple demo, but it's very effective because it shows how easily soil aggregates break apart with water – or not,” Light said.
That aggregate stability is a key factor in soil's ability to both move water (infiltration) and hold onto water (retention). Those dynamics are crucial for farmers to avoid ponding in their fields, preserve water for drier months, and generally endure the flood/drought whiplash of climate change.
Over the years, Mitchell has hosted thousands of visitors at the West Side REC study site to showcase the potential benefits of adopting soil-health management practices.
“I don't think I'm exaggerating in saying that this is probably the most-visited agricultural field station project in the history of UC ANR (UC Agriculture and Natural Resources),” he said.
Both the West Side REC – and Mitchell himself – are greatly valued by the local grower community.
“Jeff is a microcosm of the university's applied research on the West Side of the San Joaquin Valley,” said John Diener, who grows almonds, fresh market garlic, canning tomatoes, cotton, masa corn and wheat for production and seed on land adjacent to the field station.
Growers adopt, adapt and adjust practices
Tom Willey, a retired farmer and longtime collaborator with Mitchell, has actively encouraged peers to visit the Five Points site – especially in the early years.
“It was very innovative and there weren't many examples of that anywhere in the state,” Willey said. “So, I helped encourage people to go out there and learn and possibly think about doing similar work on their own farms.”
Willey himself was a pioneer in experimenting with no-till practices in organic vegetable cropping systems.
“As organic farmers, we were probably more tillage dependent than conventional farmers because it was the only method we had for weed control; we weren't able to use herbicides,” Willey said.
Despite early struggles, he persisted in trying different techniques and mechanical means of weeding. And Willey later partnered with a group of progressive vegetable growers and UC and California State University Chico personnel to secure a Conservation Innovation Grant from the Natural Resources Conservation Service to support more on-farm trials and share their experiences.
In the end, however, no-till proved too risky to continue, given the losses they incurred. One tricky issue is nutrient cycling. The organic growers found that after mowing down a cover crop and spreading compost, leaving those nutrients on the surface without incorporating into the soil through more vigorous tilling (or adding synthetic fertilizers, as conventional growers could do) results in lower yields. In the short term, farmers simply did not see yields that could sustain their operation.
“It's very difficult in vegetable systems, and particularly difficult in organic vegetable systems,” Willey said. “I would say a number of us have learned to diminish the over-reliance that we had on tillage, but not to completely eliminate it.”
Cover cropping is also a challenge for some farmers, with certain cover crops making a perfect haven for devastating pests such as lygus bugs and stink bugs, according to Diener.
“We do everything we can to eliminate the host crop from which they come, so why am I going to bring the enemies to my house?” he said. “It's about making enough money to be there next year. You're not going to be there next year with these pests. It's just not a practical management option, in light of our significant pest pressure and disease hosts for our crops of value.”
Instead of planting cover crops, Diener said he opts for mixing in grain crops that can similarly contribute to soil health – while generating revenue at the same time. According to Diener, a longtime collaborator with Mitchell, the best way to adopt conservation agriculture practices is to tailor them to specific localities and each grower's circumstances. And in his corner of the San Joaquin Valley, that means not following the template of the high-precipitation, no-till systems found in the Midwest.
“We've adapted Jeff's principles to our program; it won't look like Iowa to you, which is what everybody comes to expect to see. It ain't how it works, folks,” Diener said. “It's a different methodology. We do those things that fit our environment and that's why that West Side field station is important – because it's our environment.”
Promoting and enhancing soil health, one step at a time
More widespread adoption of soil-health management practices can be driven by a variety of factors. With the rise of drip irrigation in tomatoes, for example, more growers began using no-till or reduced till to minimize disruptions to the delicate driptape in their fields.
And, according to Mitchell, the dramatic increase in no-till practices in dairy silage production – from less than 1% to over 40% – was the result of entrepreneurial efforts by a small but extraordinarily dedicated group from the private sector that worked with farmers, one by one.
Because optimizing these practices requires close and intensive attention – and no small amount of courage and gumption – Mitchell and Light understand that growers might need to take an incremental approach. Even one fewer pass over the field, or cover cropping every other year, can provide some benefit for soil health, Light said.
“The value is that when you can prove the concept, then you can motivate every step of the way,” Light explained. “Jeff is showing the shining light of the goalposts, and that can motivate us to take every challenging step along the way.”
Shannon Cappellazzi, who helped with the data analysis on the recently published California Agriculture paper, agrees that there is value in taking a stepwise approach in building soil health.
Cappellazzi was the lead project scientist on the Soil Health Institute's North American Project to Evaluate Soil Health Measurements, which looked at 124 different long-term soil research sites across the continent – including the Five Points site.
After analyzing 2,000 samples from the various study sites, Cappellazzi said the evidence suggests that layering on each component of a conservation agriculture program – doing no-till, adding cover crops and then integrating livestock, for example – can have additive, cumulative benefits for soil health.
“I think having the data to show the long-term benefit makes people willing to do the short-term change, even if it's a little bit hard for a couple years,” Cappellazzi said.
The research at the West Side REC also produced another key takeaway.
“To me, what really stood out was that for most of the soil health indicators, cover crops had a huge impact. Both the cover crops that had no till – and the cover crops that had standard tillage – had considerably higher carbon and soil health indicator measurements than those without cover crops,” said Cappellazzi. She added that the data also indicated improvements in how the water moved into the soil, and how the soil held that water.
Vital research drives an enduring legacy
Water management and conservation, of course, will be paramount in California's increasingly volatile climate reality. Mitchell's Five Points research – and related studies across the San Joaquin Valley by UC Davis agroecologist Amélie Gaudin and others – contributed data that overturned a long-held belief about winter cover cropping.
“There's a lot of preconceived ideas about cover crop water use,” Mitchell said. “One of the things that we learned was that compared to bare soil water loss in the wintertime, cover crop water loss during that same growing period – from about November through March – tends to be almost a wash.”
That crucial finding provided researchers and soil health advocates with invaluable evidence to preserve the practice as an option for farmers.
“They've needed to go around and give a dog-and-pony show to a lot of Groundwater Sustainability Agencies (GSA) that had been on the brink of banning the growing of cover crops because the perception out there is that they use a lot of water,” said Willey, the retired vegetable grower. “But over the winter months, cover crops don't use a lot of water. In fact, they may not use any net water at all.”
The young researchers who studied cover-crop water use represent another important legacy of the Five Points study site. It has been an experiential training ground for many of the next generation of soil scientists, agronomists and ecologists.
“The number of students who have been trained by and through this study has been really phenomenal,” said Mitchell, noting that they have worked on topics ranging from air quality to soil carbon related to no-till and cover cropping.
Their contributions will be essential in continuing to refine and optimize these practices that are fundamental to conservation agriculture. On Diener's concerns about lygus bugs and stink bugs, for example, Cappellazzi – in her new role as director of research at GO Seed – is studying and breeding cover crops with an eye on characteristics that make for less hospitable habitats for certain pests.
Indeed, while the California Agriculture paper effectively wraps up the 20-year study at Five Points, its lessons will continue to resonate and inspire for years to come.
“This is a step in a long journey,” Light said. “It's a launchpad – this paper might be able to tie a bow on it in terms of the data collection, but in terms of the extension impact, this is really just the beginning.”
And for Willey, the omnipresent climate crisis compels the entire sector to pick up the pace along that journey.
“We've got a lot of pressure now to evolve agriculture very rapidly in response to climate change and I don't think we can sit around and twiddle our thumbs,” he said. “We know the directions we need to be heading – with more natural systems mimicry and less reliance on toxic inputs and synthetic fertilizers – and we need to figure out how to incentivize and support farmers in moving in those directions.”
/h3>/h3>/h3>/h3>/h3>/h3>- Author: Saoimanu Sope
Although training is required to become a University of California Master Gardener, the benefits of gardening can be experienced by anyone and everyone.
“As long as you're willing to get your hands dirty,” said Laurie Menosky, a UC Master Gardener volunteer in Orange County, “you can learn to grow all sorts of things.”
In early April, Menosky partnered with ETN Medical Infusion (a clinic in Orange County) and the Sustainability Program for Student Housing at UC Irvine to teach students how to grow tomatoes. Menosky welcomed all in attendance, including families with toddlers who seemed fascinated by the 60 tomato plants atop one of the tables in the room.
The UC Master Gardener Program is a part of UC Agriculture and Natural Resources. During her presentation, Menosky taught participants how to choose varieties that fit their taste and growing environment, how to cultivate a thriving environment, and how to control pests and diseases using integrated pest management practices.
“We have 16,000 residents at UCI and sustainability is one of our values. One of the ways we engage students is through on-campus gardens,” said Rachel Harvey, sustainability program manager for UCI Student Housing and a UC Master Gardener volunteer in Orange County.
UC Irvine has one teaching garden reserved for undergraduate learning, and three gardens operated and maintained by graduate students. “I was on the waiting list for a garden plot for a while, but it was totally worth the wait,” said Johanna Rinaman, a fifth-year Ph.D. student studying physical chemistry.
While the highlight of the event for many people was the opportunity to take a tomato plant home, another important takeaway was how gardening can be a good activity for your mental health. Sarah Nghiem, family medicine specialist at ETN Medical Infusion, who worked closely with Menosky, was instrumental in developing the mental health content for the day, encouraging attendees to attempt gardening with a mental health perspective.
Nghiem and her team received funding from the Orange County Health Care Agency through the Mental Health Services Act to work with transitional aged students (15-24 years-old) on understanding the importance of mental health, which led to the collaboration between UC Irvine, her alma mater, and the UC Master Gardeners of Orange County.
“I didn't do any gardening during the winter, and I felt a lot more anxious and depressed during that time,” Rinaman said. “I know gardening improves mental health because I've immediately felt a difference whenever I spend time with plants.”
Rinaman, whose father taught her a lot of what she knows about gardening, said that having access to a 4 feet by 6 feet plot to grow her own food is one of the many things she loves about UC Irvine.
Like Rinaman, Menosky turns to gardening to decompress, especially during the long days of summer. Teaching others about the physical and mental benefits of gardening gives her an opportunity to share her experience and, hopefully, help others find new ways to manage stress.
“We often have attendees come back years later telling us how our information has helped them and how much more they are enjoying their time in their gardens,” she said.
To conclude her presentation, Menosky instructed participants to line up for their own tomato plant. Attendees took their plants outside to transfer them from a small pot to a grow bag – a type of container that helps root structure development.
Cassie Ekwego, a third-year transfer student studying civil engineering, couldn't hide her excitement after carefully lifting her plant. “I don't think I realized how attentive you need to be when working with plants,” said Ekwego, reflecting on what she learned from Menosky's presentation.
Now that she has her own plant to care for in her own home, Ekwego is eager to put her new knowledge to the test. “I love tomatoes, but this is going to be a huge responsibility for me,” she said.
Randy Musser, UC Master Gardener program coordinator for Orange County, said that while he enjoys talking to avid gardeners, bringing gardening to new people in the community is special to him. “This tomato workshop is particularly exciting for me because it is an opportunity for the UC Master Gardeners to grow our connection to UCI and young people just starting off on their gardening journey,” said Musser.
With a generous contribution from UC Master Gardener volunteer Sheila Peterson, Musser was able to purchase enough supplies to help attendees, like Ekwego, jumpstart their gardening experience.
Students, whose stress levels can skyrocket throughout the school year, value opportunities to be outdoors, try something new and be in community. “The garden is a different type of classroom. It's a place where students can learn and experiment, hopefully in a way that reduces stress,” said Harvey of UCI Student Housing.
Ekwego, who tried gardening for the first time while volunteering at UC Irvine's teaching garden, is just one of the many students inspired by their experiences. “Gardening reminds me that it's OK to get my hands dirty,” Ekwego said.
- 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