Posts Tagged: pest
Almond crop yields threatened by disease new to California
Detection of fungus causing red leaf blotch spurs call for grower vigilance
Symptoms of red leaf blotch (RLB), a plant disease caused by the fungus Polystigma amygdalinum, have been observed for the first time in California across the Northern San Joaquin Valley.
Molecular DNA testing by the laboratory of Florent Trouillas, University of California Cooperative Extension fruit and nut crop pathology specialist, has detected P. amygdalinum. Pest identification was confirmed by the California Department of Food and Agriculture and U.S. Department of Agriculture.
The disease, named for the characteristic orange-to-dark red blotches that appear on infected leaves, is typically nonlethal for trees but has been a long-standing problem for almond-growing regions across the Mediterranean. Causing trees to lose their leaves prematurely, the fungal pathogen can significantly diminish crop yields in the current year and the next.
“It is one of the most severe diseases of almonds for Spain and the Middle East,” said Trouillas, an associate professor in the UC Davis Department of Plant Pathology. He recently co-authored an explanatory article on the UCCE San Joaquin Valley Trees and Vines blog.
With symptomatic trees seen in multiple orchards across Madera, Merced, San Joaquin and Stanislaus counties, Trouillas said RLB is already “somewhat widespread.”
“From the first observations so far, it seems like it affects some of the most-planted cultivars, like Nonpareil and Monterey,” he added. “We've observed it in a diversity of cultivars already.”
UC Cooperative Extension specialist urges taking preventive measures
According to Trouillas, RLB caused by P. amygdalinum is “highly specific” to almond trees, and generally only affects their leaves. Infection typically happens at petal fall, when small leaflets are first emerging and most susceptible to disease. After the pathogen's latent period of about 35 to 40 days, the first symptoms appear – small, pale-yellow spots on both sides of the leaves.
Those blotches become yellow-orange and then reddish-brown in the advanced stages of the disease during June and July. Now, with RLB symptoms becoming more prominent, Trouillas and UC Cooperative Extension advisors across the Central Valley have seen an uptick in calls.
“PCAs [pest control advisers] have been confused because they've never seen anything like this,” said Trouillas, noting that the yellow-orange-red blotches are symptoms unique to RLB and cannot be confused with other known almond diseases.
Applying fungicides after RLB symptoms appear is ineffective, Trouillas said. The best thing growers can do at this point is to report symptomatic trees to researchers so they can track the prevalence and distribution of the disease.
Growers who see signs of this new disease in their orchard should contact their local UC Cooperative Extension farm advisor.
Preventive measures are the best way to manage RLB, Trouillas said. He urges concerned growers to think ahead to next winter/spring and plan for fungicide applications at petal fall and – if rains persist – also at two weeks and five weeks after petal fall. Fortunately, those are the same three key timings for managing other diseases, like shot hole and almond anthracnose.
“Because RLB is something that is introduced and potentially aggressive, it will be important for growers to keep that in mind next year and be on schedule for next year's spraying program,” Trouillas said.
Additional information on RLB can be found at https://www.sjvtandv.com/blog/first-detection-of-red-leaf-blotch-a-new-disease-of-almond-in-california.
/h3>/h3>Diagnosing herbicide problems takes detective work
Field day offers examples, tips for solving the mystery
A grower applies an herbicide to his tomato plants, or thinks a neighbor's treatment is drifting over her almond trees. A short time later, the leaves start to bleach or shrivel. Was it the herbicide? Or maybe water stress? Soil nutrients? Perhaps an insect?
Figuring out the causes of crop problems takes detective work, and like solving any mystery, it starts with knowing the signs, gathering evidence and asking questions.
The Diagnosing Herbicide Symptoms field day at UC Davis was an opportunity to see, up close, the shriveled cotton, scorched corn and dying sunflowers that can result when herbicides are applied incorrectly. Using the right herbicide – in the right proportion, at the right time and in the right field – can make the difference between a thriving crop and a financial loss.
A top take-away to avoid problems: “Don't do stuff at night!” laughed Becky Wheeler-Dykes, a UC Cooperative Extension farm advisor attending the June 26 event to better serve growers in Glenn, Tehama and Colusa counties. “The packages look the same. People grab the wrong jug.” And then, disaster.
Instructors were Brad Hanson, professor of Cooperative Extension; and Kassim Al-Khatib, the Melvin D. Androus endowed professor for weed science; both in the Department of Plant Sciences. They were joined by John Roncoroni, a Cooperative Extension emeritus farm advisor rooted in the department's weed science program. Attendees were a mixture of people from agriculture, industry, government officials, university researchers and Cooperative Extension advisors. The event was hosted by the Weed Research and Information Center, based in the Department of Plant Sciences.
Out in a field west of campus, visitors could see the progression of damage, from control plots with green and healthy crops to plants that looked sadder as herbicide concentrations increased. Visitors could see the patterns of damage for common foliar chemicals such as glyphosate, paraquat, and 2,4-D, as well as soil-applied herbicides from several chemical classes.
“There's a lot of detective work,” said Stephen Chang, a master's student in Hanson's lab aiming for a career in Cooperative Extension. “For example, the company that makes the herbicide says there shouldn't be a problem, but the grower says, there is a problem. This course helps with developing the skills to figure out what happened.”
It might not be the herbicide at all
Detective work and problem-solving frame the approach, Hanson explained. The cause of crop damage can be simple or complex. Like a good mystery, what appears to be a clue can turn out to be a red herring. Professionals need to draw on their inner Sherlock Holmes to observe and document symptoms, look for patterns in the plants and in the field, ask questions, gather information about the larger environment and collect samples.
An herbicidal Agatha Christie would then suggest: What if it's not herbicide damage at all? Participants learned to consider the possibility of insects, pathogens and viruses, as well as problems with water, nutrients, soil condition and even root damage from cultivation practices.
Hanson recalled puzzling over symptoms he found in an orchard. The culprit? “A leaking natural gas line,” he said.
More resources for herbicide issues
Participants also heard from Molly Mathews, deputy agriculture commissioner from Yolo County, on how a field investigation is conducted. Lawyer Robert Davies, of Donahue Davies LLP in Folsom, outlined the basics of what happens when there are lawsuits related to crop damage from herbicide drift.
The Diagnosing Herbicide Symptoms field day is part of a larger program of education and outreach offered through the Weed RIC, said director Julia Stover-Blackburn. It was the first time the event has been offered since the COVID-19 pandemic, she added.
- For more information about field days and resources, visit the Weed RIC webpage.
- For a thorough discussion of herbicide symptoms, visit this page overseen by Al-Khatib and sponsored by University of California Agriculture and Natural Resources.
- This online course follows an earlier version of the Diagnosing Herbicide Symptoms field program.
This story was originally published on the UC Davis Department of Plant Sciences website.
/h3>/h3>/h3>Report outlines top concerns in California organic agriculture
Organic Agriculture Institute needs assessment refines how it can address pressing challenges
The explosive growth of organic agriculture in the U.S. – reflected in a 90% increase in organic farms from 2011 to 2021, according to U.S. Department of Agriculture statistics – has come at a cost for some farmers. With new farming operations increasing the supply of organic commodities, along with consolidation of buyers, growers report that their profit margins are not what they used to be.
Those market size considerations are among the challenges highlighted in a new report detailing the initial findings by the University of California Organic Agriculture Institute on the most pressing needs of the state's organic sector. OAI gathered and analyzed data from 423 responses to an online grower survey, over 60 interviews with stakeholders across the organic community, and additional observations from farm visits and workshops.
The report describes other frequently mentioned systemic priorities, such as maintaining integrity of the term “organic,” developing a market for organic seeds, spreading consumer awareness, and alleviating the burdens of organic certification and reporting.
Shriya Rangarajan, the postdoctoral researcher with OAI leading this statewide needs assessment, said that the reported challenges varied by organic status (fully certified, transitioning to organic, or a mixed farm with some conventional), type of crop, as well as size of the operation. She noted survey respondents were roughly representative of the sector overall – 70% small-scale growers and 30% medium and large.
“Organic is not a homogenous industry, to say the least – small growers and large growers are very different; for small growers, their challenges tend to be financial and regulatory, especially relating to certification requirements and labor,” said Rangarajan. She added that larger growers mentioned different types of challenges, weeds and pest pressures for instance, given the difficulty in controlling managing these at scale without the use or availability of organic inputs.
Organic Agriculture Institute key to sharing resources across state
Another common theme from the assessment is that the organic sector needs more accessible resources to address those myriad concerns. For OAI, established in 2020 under UC Agriculture and Natural Resources, the initial findings validated and refined the direction of its research and extension programs.
“As a new organization, we've been trying to figure out where we fit into this ecosystem and how we can support it,” said Houston Wilson, a UC Cooperative Extension entomology specialist who has served as OAI's director since its founding.
Because OAI was envisioned as a hub of resources and connections for California's organic community, Wilson and his colleagues are especially interested in understanding how its constituent members obtain information – and how OAI can improve their access.
“Growers are finding it difficult to navigate the resources that exist for organic agriculture, like technical information, financial support, compliance and certification support,” Wilson said. "While we'd like to see more resources for organic in general, those that currently exist can sometimes be hard to navigate or it can be hard to know where to go for the right thing – that became really apparent early on.”
While some producers are contacting OAI directly with their questions, Wilson is eager to develop tools and systems that can serve the community more broadly. For example, Wilson and Krista Marshall – OAI's policy and partnerships coordinator – are currently beta-testing a new map tool, built in conjunction with UC ANR's Informatics and GIS (IGIS) team. The map, expected to be ready in fall 2024, will enable users to click on their county and see all available resources related to organic agriculture.
Wilson added that OAI will have four full-time staffers by fall, further expanding its research, extension, and education efforts. After holding four field events this past year, OAI aims to increase activities in the coming year, including not just field events but also online resources, webinars and more. Also, a new training and technical assistance coordinator will be tasked with bringing Cooperative Extension advisors and other technical assistance personnel across the state up to speed on a range of organic topics, so they can more effectively answer questions from clientele in their region.
New survey aims to trace crucial organic knowledge networks
Although the OAI team has gained a sense of how information is shared across the organic community (and started to formalize those interconnections through a California Organic Agriculture Knowledge Network), they are now developing a survey to study those relationships more systematically.
“We're trying to understand what kind of knowledge resources people tap into, which is something that has come up repeatedly in our needs assessment,” Rangarajan said. “We're trying to understand who people are speaking to because, at the end of the day, organic is still a relatively small part of agriculture in California, and that makes it more fragmented. So trying to connect those different parts becomes important.”
Once Wilson has a more nuanced understanding of organic knowledge networks, he will be able to strategize and position OAI – and the UC – as a more effective partner and contributor in the sector.
“Given the history of organic, growers have had to rely on each other a lot,” Wilson explained. “We understand that the university has unique expertise to bring to the table, but we also acknowledge that there's all these other knowledge holders out there, so one of the roles that we see ourselves having is helping to facilitate those connections, strengthen them and increase the frequency of interaction.”
That may include further supporting efforts that connect transitioning organic farmers with experienced growers (a mentorship program led by Certified California Organic Farmers, or CCOF), or giving more structure to grower-researcher partnerships that can help address a host of production challenges. In OAI's grower survey, weed management topped the list, followed by water and disease issues, all exacerbated by climate variability.
“I think a lot of the real innovation changes are coming through growers experimenting with their own practice,” Rangarajan explained. “From a research perspective, one of the best ways to take this forward would be to formalize those experiments in some way so that knowledge becomes more reportable.”
And collaboration on “organic topics,” such as finding alternatives to synthetic pesticides, are a boon to the entire agricultural sector – conventional growers included.
“Everyone is trying to reduce pesticide use; everyone is trying to reduce environmental impacts,” Wilson said. “You don't have to be certified organic to benefit from organic research; these practices can be used by anyone.”
The report with OAI's initial findings on organic needs can be found at: https://ucanr.edu/sites/organic/files/396228.pdf.
/h3>/h3>/h3>Almond growers should prepare for possibility of unusual disease outbreak
Wet winter, El Niño create favorable conditions for aerial Phytophthora pathogen
With heavy rains in the forecast amid strengthening El Niño conditions, almond growers should be on the lookout for a rare disease that can cause severe damage to their orchards, according to Florent Trouillas, a University of California Cooperative Extension specialist in fruit and nut pathology.
Phytophthora, soilborne microorganisms dubbed “water molds” because of their dependence on water, typically cause root and crown rot at the base of trees. But a few aerial Phytophthora can travel upwards and infect the higher parts of the tree. One species – Phytophthora syringae – is drawing special attention due to an unprecedented outbreak last winter, fueled by the atmospheric rivers that lashed California.
“It was found statewide – meaning in every almond-producing county – and disease incidence in orchards ranged from 10% of the trees infected to 75%,” said Trouillas, a UC Davis plant pathologist whose lab is based at UC Agriculture and Natural Resources' Kearney Agricultural Research and Extension Center in Parlier.
Trouillas and his colleagues, UC Davis graduate student Alejandro Hernandez and UC Riverside plant pathology professor Jim Adaskaveg, recently published a detailed online article describing the pathogen, which can infect a range of crops but mainly impacts almonds in California.
Although it doesn't kill the tree, the disease causes branch dieback that requires significant additional work and expense for almond growers. In 2022, almonds were the state's fourth-highest valued commodity, at $3.52 billion.
During last year's aerial Phytophthora outbreak, researchers also observed a new and troubling phenomenon: P. syringae, historically known to attack the cuts caused by pruning, was directly infecting the young shoots on almond trees – without any wounds.
“This was really the first time we had seen widespread evidence of infection on the twigs,” Trouillas said.
Although generally rare, outbreaks of P. syringae have been traditionally associated with wet El Niño years, according to Trouillas – and recent and persistent rain across the state should have growers on high alert.
Prune in dry weather, monitor, mitigate if necessary
While almond growers tend to prune during the downtime of winter, they should keep an eye on the forecast and aim for a 10- to 14-day window of dry weather to perform those tasks, whether training young trees or maintaining the established ones.
“If growers were to prune around a rain event – before, during or shortly after – this increases the likelihood of infection because this pathogen moves around with water,” Trouillas explained.
Researchers speculate that P. syringae, normally found in the soil, gets carried into the upper parts of a tree through strong winds and heavy rain. Alternatively, harvest processes like shaking and sweeping also produce air movements that may blow the microorganism into the canopy, where it waits for a favorable wet environment. The pathogen then attacks the wounds or young shoots, producing characteristic cankers and gumming.
The patterns and colors of the gum balls are keys to diagnosing an infection of this particular aerial Phytophthora. Starting around bloom time (mid-February), growers should monitor pruning wounds and young shoots on their trees, especially in the canopy, for signs of the disease.
The unique coloration of the gum balls – ranging from gold and amber to dark burgundy to bright red (see photos) – generally indicates P. syringae infection. But growers are urged to contact their local Cooperative Extension advisor for confirmation.
“It is super critical for growers that, whenever they see gumming, not to assume that it is this aerial phytophthora, because there are many other diseases that can cause gumming on the tree,” Trouillas said.
If the diagnosis is confirmed, growers may apply a compound that can mitigate the infection. The plant pathologists' recent writeup describes several curative treatment options, as well as a preventive measure that reduces the amount of pathogen in the soil and thus the likelihood of infection.
For more information on the pathogen's history and biology, as well as various options for disease management, visit the article on Sacramento Valley Orchard Source: https://www.sacvalleyorchards.com/almonds/trunk-soil-diseases/aerial-phytophthora-outbreaks-in-wet-years.
/h3>/h3>First-ever Queensland fruit fly quarantine restricts moving homegrown produce
QFF quarantine in LA, Ventura counties among seven fruit fly quarantines statewide
Residents in multiple Southern California and Northern California counties should not move homegrown fruits and vegetables from their properties to help contain several species of fruit fly that can destroy crops and impact the livelihoods of local farmers.
With sharing and gifting of food integral to the holiday season, the California Department of Food and Agriculture is reminding people to heed the seven active fruit fly quarantines aimed at controlling the Mediterranean fruit fly, Oriental fruit fly, Tau fly and Queensland fruit fly. The links below describe quarantine zone boundaries:
- Mediterranean fruit fly: Los Angeles County, Leimert Park Area
- Oriental fruit fly: San Bernardino and Riverside Counties, Redlands and Yucaipa Areas
- Oriental fruit fly: Sacramento County, Rancho Cordova Area
- Oriental fruit fly: Contra Costa County, Brentwood Area
- Oriental fruit fly: Santa Clara County, Santa Clara Area
- Tau fly: Los Angeles County – Stevenson Ranch, Valencia, Santa Clarita Areas
- Queensland fruit fly: Ventura and Los Angeles Counties, Thousand Oaks Area
People within these zones should consume or process (i.e., juice, freeze or cook) their homegrown fruits and vegetables at the place of origin and not move them off their property. Uneaten produce should be double-bagged in plastic bags and disposed of in the landfill bin – not compost or green waste.
Queensland fruit fly threatens California citrus, other crops
The Queensland fruit fly (Bactrocera tryoni) quarantine is the first of its kind in the U.S. Although QFF was first seen in California in 1985, the recent detection of two adult males triggered the unprecedented quarantine action by USDA's Animal and Plant Health Inspection Service and CDFA.
“This pest has earned a bad reputation for wreaking havoc on fruit production in Australia, where it is native,” said Hamutahl Cohen, University of California Cooperative Extension entomology advisor for Ventura County. “Adult flies lay their eggs in fruit, and the eggs hatch into larvae that then feed on the fruit, causing damage.”
And while females of other fruit fly species live for only two or three months, QFF females are unique in that they can live up to a year, according to Cohen.
“Once QFF populations take root, they're challenging to manage because females can each lay up to 100 eggs per day,” Cohen said.
In addition to being highly adaptable to a variety of environmental conditions, QFF has more than 170 host plants – including a wide range of California commodities such as citrus, grape, strawberry, fig, avocado, apricot, peach, cherry, nectarine, plum, pear, apple, tomato and sweet pepper.
The threat to citrus is especially concerning, as Southern California growers continue to grapple with the specter of spreading huanglongbing (HLB) disease, which kills citrus trees. Cohen said residents of citrus-growing regions can do their part to help their neighbors and local economy by respecting quarantine restrictions.
“Growers are already dealing with other invasive species like Asian citrus psyllid [vector of HLB pathogen], so we as homeowners need to prevent the spread of fruit flies to reduce the burden on them,” she explained.
While a spike this year in the detections of multiple fruit fly species was likely caused by a host of factors, Cohen speculates that increased post-pandemic travel is helping to move the flies. And with holiday travel in full swing, she said it's important to practice “Don't Pack a Pest” principles.
“Invasive species often hitchhike on fruits and vegetables brought into California by travelers – that's why we often first find invasive species in urban and suburban backyards, and not on farms,” Cohen said. “Travelers entering the U.S. can visit dontpackapest.com to learn about which products they can and cannot bring back with them.”
To report a suspected infestation of fruit fly larvae in homegrown produce, call the CDFA pest hotline at 1-800-491-1899. Growers with questions and concerns are urged to contact their local agricultural commissioner's office.
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