As sorghum plants cope with drought conditions, the plants' roots and adjoining microbial communities are communicating in a chemical language that appears to improve the plants' chances under water stress.
“It's amazing,” said Peggy Lemaux, UC Cooperative Extension specialist. “We know there are lots of microbes in the soil and, for the most part, ones in the surrounding soil stayed the same under drought conditions. We only saw changes in those microbes closely associated with the roots.”
The role of drought in restructuring the root microbiome was the first published discovery to come out of a sweeping drought research project underway since 2015 in the fields at UC Kearney Research and Extension Center in Parlier. The five-year study, funded with a $12.3 million grant from the Department of Energy, aims to tease out the genetics of drought tolerance in sorghum and its associated microbes. Using sorghum as a model, scientists hope the research will help them understand and improve drought tolerance in other crops as well.
The new research results from the lab of USDA's Devin Coleman-Derr at UC Berkeley, published April 16, 2018, in the Proceedings of the National Academy of Sciences, document the fate of microbes associated with sorghum roots under three distinct irrigation regimens. Because the San Joaquin Valley generally sees no rain during the growing season, it is the ideal place to mimic drought conditions by withholding irrigation water.
All plots received a pre-plant irrigation to initiate growth. In the control plots, sorghum was irrigated normally, with weekly watering through the season. In the plot simulating pre-flowering drought stress, the plants received no additional water until flowering, about halfway through the season. The third treatment was watered normally until it flowered, and then water was cut off for the rest of the season.
Beginning when the plants emerged, the scientists collected samples from each plot on the same day and time each week for 17 weeks. In a mini, in-field laboratory, roots, rhizosphere (zone surrounding the root), leaves and soil samples from 10 plants in each plot were immediately frozen and transported to Berkeley, where they were disseminated to collaborators, who investigated the plant and microbial responses at the molecular level.
“When a sorghum plant is subjected to drought, it starts sloughing off metabolites, nutrients and amino acids from the roots. The compounds appear to communicate to the neighboring microbial community that the plant is under stress,” Lemaux said. “That selects out a certain population of microbes. Certain types of microbes increase, others go away. When you add water back, the microbial community returns to its pre-drought population in just a few days.”
The researchers cultured two specific microbes that were enriched in the rootzone under drought conditions. They coated sorghum seeds with the microbes and planted them under drought conditions in a growth chamber. This treatment encouraged the plant to grow more roots.
“The microbes appear to improve plant growth during drought,” Lemaux said. “Those microbes appear to be helping plants survive drought. We didn't know that was happening before we got these results.”
Lemaux said the research might lead to future field use of the research breakthrough.
“A lot of companies are interested in the microbiome,” she said. “Some are already selling microbes to coat seeds.”
Pests have always been a bane of human existence. Modern society has developed effective pest management, “but there is no kind and gentle way to kill things,” said Brian Leahy, the director of the California Department of Pesticide Regulation, in remarks at the April 2018 IPM Summit.
The ever increasing incidence of invasive pests and the concerns about how to manage them will be a continuing challenge. Leahy said society is on a pest treadmill; and the best way to address it is with integrated pest management (IPM).
The concept of integrated pest management emerged 60 years ago when scientists recognized that imposing a harsh chemical on a natural system threw it off kilter, often causing unexpected, usually negative consequences. They realized that combining an array of pest control methods – such as careful supervision of insect levels, promotion of beneficial insects, and using less harsh products – would be more effective, safer for families and farmworkers, and kinder to the environment in the long run.
And yet, pesticides are still widely used in agricultural, horticultural and structural systems.
“We need to make IPM more robust,” said Pete Goodell, UC IPM advisor emeritus who spent 36 years as an IPM researcher, leader and teacher. “We need to make IPM easier to adopt.”
The meeting in Davis brought together nearly 200 people engaged in the science, business and regulation of pest management. They were assembled to address the tensions around pesticides and their alternatives, and usher in a new generation of researchers and practitioners to maintain and expand on six decades of progress in integrated pest management.
The IPM Summit is the final chapter of a collaborative effort titled “The Pests, Pesticides & IPM Project,” which was funded by DPR to enhance dialog about pest management. The project leader is Lori Berger, UC IPM academic coordinator.
“This project addresses the challenges pests pose to society,” Berger said. “We want to increase adoption of IPM practices on farms, and also in schools, homes, museums and golf courses. We're all in this together.”
One example of urban IPM efforts was presented by the IPM Summit keynote speaker Kelly Middleton, director of community affairs for the Greater Los Angeles County Vector Control District. She outlined the substantial public health concerns associated with pest control in California's largest urban area. A primary target is mosquitos.
“In the early 1900s, vector control started with concerns about malaria and mosquito populations,” Middleton said.
Over decades, the vector control district worked behind the scenes to keep mosquito populations in check. But in recent years, new species of mosquitos capable of spreading Zika, West Nile encephalitis, chikungunya and yellow fever have made their way to LA, intensifying concerns.
A key IPM tool in Los Angeles is minimizing standing water where mosquitos can breed. With year-round water flow irrigating vast landscapes and concrete drainages that inhibit infiltration, the vector district is faced with mosquito breeding grounds created by “urban drool,” Middleton said.
Trash rife with nutrients – such as discarded food and plant materials – are perfect nourishment for immature mosquitos, a condition referred to as “urban gruel.”
Higher temperatures predicted because of climate change only threaten to exacerbate the problem.
“A warming world is a sicker world,” Middleton said.
An effective IPM approach to mosquitos is short-circuiting their reproduction opportunities by enlisting residents to maintain swimming pools, drain any receptacles that can capture rainwater or irrigation, and be vigilant about basins containing water in their environments.
These efforts are emblematic of the societal collaboration that can tackle pest problems without pesticides.
In his IPM Summit presentation, Goodell called for public sector investment in basic research, applied research, extension and education to find IPM solutions and encourage implementation. He appealed for IPM outreach to include community organizations, home owners associations and other non-traditional partners. He suggested agriculture take advantage of farmworkers' presence in the field for early pest detection.
“Technical pest management skills are critical, but it's connections with people that are key to bringing about change,” Goodell said.
Help the environment on Earth Day, which falls on Sunday, April 22, this year, by growing insectary plants. These plants attract natural enemies such as lady beetles, lacewings, and parasitic wasps. Natural enemies provide biological pest control and can reduce the need for insecticides. Visit the new UC IPM Insectary Plants webpage to learn how to use these plants to your advantage.
The buzz about insectary plants
Biological control, or the use of natural enemies to reduce pests, is an important component of integrated pest management. Fields and orchards may miss out on this control if they do not offer sufficient habitat for natural enemies to thrive. Insectary plants (or insectaries) can change that — they feed and shelter these important insects and make the environment more favorable to them. For instance, sweet alyssum planted near lettuce fields encourages syrphid flies to lay their eggs on crops. More syrphid eggs means more syrphid larvae eating aphids, and perhaps a reduced need for insecticides. Similarly, planting cover crops like buckwheat within vineyards can attract predatory insects, spiders, and parasitic wasps, ultimately keeping leafhoppers and thrips under control.
Flowering insectaries also provide food for bees and other pollinators. There are both greater numbers and more kinds of native bees in fields with an insectary consisting of a row of native shrubs planted along the field edge (called a hedgerow). Native bees also stay in fields with these shrubs longer than they do in fields without them. Therefore, not only do insectaries attract natural enemies, but they can also boost crop pollination and help keep bees healthy.
Insectary plants may attract more pests to your plants, but the benefit is greater than the risk
The possibility of creating more pest problems has been a concern when it comes to installing insectaries. Current research shows that mature hedgerows, in particular, bring more benefits than risks. Hedgerows attract far more natural enemies than insect pests. And despite the fact that birds, rabbits, and mice find refuge in hedgerows, the presence of hedgerows neither increases animal pest problems in the field, nor crop contamination by animal-vectored pathogens. Hedgerow insectaries both benefit wildlife and help to control pests.
How can I install insectary plants?
Visit the Insectary Plants webpage to learn how to establish and manage insectary plants, and determine which types of insectaries may suit your needs and situation. If you need financial assistance to establish insectaries on your farm, consider applying for Conservation Action Plan funds from the Environmental Quality Incentives Program (EQIP) offered by the Natural Resources Conservation Service.
- Flower flies (Syrphidae) and other biological control agents for aphids in vegetable crops. (PDF)
- Good news for hedgerows: no effects on food safety in the field.
- Hedgerow benefits align with food production and sustainability goals.
- Habitat restoration promotes pollinator persistence and colonization in intensively managed agriculture. (PDF)
- Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops.
The changing climate predicted for California – including less rain and higher day and nighttime temperatures – is expected to cause chronic stress on many street tree species that have shaded and beautified urban areas for decades.
Realizing that popular trees may not thrive under the changing conditions, UC Cooperative Extension scientists are partnering with the U.S. Forest Service in an unprecedented 20-year research study to expand the palette of drought-adapted, climate-ready trees for several of the state's climate zones.
“The idea is to look at available but under-planted, drought-tolerant, structurally sound, pest resistant trees for Southern California that do well in even warmer climates,” said Janet Hartin, UCCE horticulture advisor in San Bernardino County.
Hartin, a 34-year veteran advisor, said the project is her first to stretch to 20 years; it will likely extend past her tenure with UCCE.
“I'd like to retire in five or six years,” she said. “But I'm very excited about being a pioneer in a study that will continue with my successors. I think it's important for our children and our children's children, as well as for the environment.”
At the end of 2019, with three years of data on tree health and growth rates, the scientists expect to be able to publish the first results and make them available to arborists, urban foresters and residents throughout the regions of the study.
Twelve tree species were selected for each climate zone in the comparative study, with several area parks used as control sites. Hartin and her Southern California research collaborators – UCCE advisors Darren Haver of Orange County and Jim Downer of Ventura County – worked closely with UC Davis plant biologist Alison Berry, UC Davis research associate Greg McPherson and USFS research urban ecologist Natalie van Doorn to select promising species.
They looked for trees that are already available at local nurseries, but are underutilized. The trees in the project exhibit drought tolerance and disease resistance, plus produce minimal litter. The researchers also sought trees that would provide ample cooling shade for a long time – ideally 50 years or longer.
The varieties come from areas around the world with climates similar to California. Two trees planted in replicated plots at the UC Riverside Citrus Field Station are native to Australia, two are native to Oklahoma and Texas, one is native to Asia and two are non-native crosses of other trees. Three of the trees are native to California: the netleaf hackberry, Catalina cherry and island oak.
“Trees are a long-term investment,” Hartin said. “A tree will live 50, 70, 90 years. The proper selection is very important to help ensure longevity.”
Making the long-term investment with the proper selection yields considerable returns. In a warming world, trees are natural air conditioners.
“Urban areas create heat islands, with dark asphalt surfaces reradiating heat. Cities can be 10 to 20 degrees warmer than the surrounding environment,” Hartin said.
Other tree benefits include soil health and stability, wildlife habitat and aesthetic beauty.
Following are a sampling of trees that are part of the comparative study:
Acacia – A 20-foot-tall, 20-foot wide evergreen that is drought resistant, and withstands moderate irrigation. Native of Australia.
Brazilian cedarwood – A native of Brazil and Paraguay, the deciduous tree grows to 50 to 65 feet. The tree produces pale yellow tubular flowers in the spring.
Catalina cherry – Native to the chaparral areas of coastal California, the Catalina cherry grows to 30 feet high. The evergreen tree tolerates drought when mature. It produces sweet purple-to-black edible fruit.
Chinese pistache – A deciduous tree with beautiful fall color. Grows to 35 feet tall, 30 feet wide. Drought resistant, but tolerates moist soil. Native to central and western China.
Desert willow – Growing to 30 feet tall and living 40 to 150 years, the desert willow tolerates highly alkaline soil and some salinity. A deciduous tree, it boasts large pink flowers all summer that attract hummingbirds and other wildlife. Native to the southwestern U.S. and northern Mexico.
Escarpment live oak – Native to west Texas, this tree is cold hardy and drought tolerant. Typically evergreen, it can be deciduous in colder climates.
Ghost gum – Very tall at maturity and drought tolerant. An Australia native.
Indian laurel – Commonly called a ficus, this is a 35-foot-tall, 35-foot-wide tree at maturity that is drought resistant and tolerates highly alkaline and saline soils. Shade potential is high. Native of Asia and Hawaii.
Ironwood – A southwestern and northern Mexico native, Ironwood is semi-drought resistant once mature and tolerates alkaline soil. Ironwood, which grows to about 33 feet tall, can live 50 to 150 years.
Island oak – This tree is native to five of six California off-shore islands. Drought tolerant, it grows to nearly 70 feet tall when mature.
Maverick mesquite – Native to the southwestern U.S. and northern Mexico, this tree does well in full sun and is drought resistant once established. The tree grows to 35 feet tall. The Maverick mesquite is a thornless variety.
Mulga – A versatile and hardy tree that grows 15 to 20 feet in height, the mulga – a Western Australia native – tolerates hot and dry conditions. The leaves are evergreen and the tree has yellow elongated fluffy flowers in spring.
Netleaf hackberry – A California native, the netleaf hackberry grows to 30 feet. Its deep root systems and heat resistance makes the tree idea for urban conditions.
Rosewood – Native to southern Iran, Indian rosewood grows to 65 feet tall, and 40 feet wide. Evergreen. Semi drought resistant and intolerant of alkaline soil.
Shoestring Acacia – Evergreen and 30 feet tall when mature, shoestring acacia is drought resistant and thrives in slightly acidic to highly alkaline soils. Native to Australia.
Tecate cypress – A native of Southern California and Mexico, the Tecate cypress is very drought tolerant. Its foliage is bright green. Young trees are pyramidal in shape, becoming more rounded or contorted with age.
Partners in the tree study are Los Angeles Beautification Team volunteers, LA Parks and Recreation team, Chino Basin Water Conservation District, and Mountain States Wholesale Nursery.
Funding and other support is provided by LA Center for Urban Natural Resources Sustainability, ISA Western Chapter, Britton Fund, USFS Pacific Southwest Research Station, and the UC system.
Because periodic droughts will always be a part of life in California, the UC California Institute for Water Resources (CIWR) produced a series of videos to maintain drought awareness and planning, even in years when water is more abundant.
The final video of the three-part series, which focuses on drought strategies for citrus, was launched April 6 on the UCTV Sustainable California channel. The first episode, which centered on alfalfa production, premiered Feb. 2 on the UCTV Sustainable California channel. The second video, on almonds, was launched March 2 on Sustainable California. A trailer with clips from all three episodes is here.
The videos are inspired by a collection of 19 drought tips produced by CIWR in collaboration with UC Agriculture and Natural Resources researchers during the drought of 2010-16. The tips cover a broad spectrum of California crops, from alfalfa to walnuts. Topics also include salt management, use of graywater in urban landscapes, and the use of shallow groundwater for crop production.
The drought tips collection and the drought tip videos were sponsored by the California Department of Water Resources. Following are links to each of the videos:
The CIWR drought tip series opens with Cannon Michael of Bowles Farming in Los Banos. The alfalfa grower works with UCCE specialist Dan Putnam. “There's a lot of misunderstanding about alfalfa as a crop,” Michael said. “It does take water to grow it, as with anything, but you get multiple harvests of it every year.”
The second episode features almond producer Raj of Meena farms. He works with David Doll, UCCE advisor in Merced County. “One positive of this drought,” Meena said, “is that it has forced us all to be more efficient in how we use our water.”
The series finale features Lisa Brenneis of Churchill-Brenneis Orchard in the Ojai Valley of Ventura County. She worked with UCCE advisor Ben Faber to install a new water-efficient irrigation system. “Irrigation is the only job we really have to do,” Brenneis said, “and we have to get it as right as we can.”
For a complete list of drought tips, see http://ucanr.edu/drought-tips.