- Author: Mackenzie Faith Patton
The invasive pest spotlight focuses on emerging or potential invasive pests in California. In this issue we are covering West Nile virus.
West Nile Virus Facts
West Nile virus disease was first reported in California in 2003 and has become the most common and serious vector-borne disease in California. With the exceptionally wet weather in 2023, reported cases of this mosquito-borne virus doubled compared to the previous year.
West Nile virus is spread by mosquitoes in the genus Culex. Usually, the virus passes between mosquitoes and birds, but mosquitoes can also transmit the virus to humans, horses, and other domestic animals.
Because mosquitoes can get the virus from birds, monitoring bird populations and recording dead birds is one of the most important ways to track this disease.
What can you do?
The best way to prevent the spread of West Nile virus is to reduce mosquito populations through controlling the mosquito larval stages. Whenever possible, standing water should be drained, since mosquito larva can grow in as little as a few ounces of water. Clean gutters and storm drains to ensure water does not collect there. In areas that cannot be drained or mosquito-proofed, such as ponds, neglected pools, or unsealed rain barrels, there are some biocontrol options like Bacillus thuringiensis (Bt) that can reduce mosquito populations. In addition to these preventative measures, protect yourself from adult mosquito bites by using mosquito repellents or wearing long-sleeved shirts and long pants.
For more information on mosquito control and protecting yourself from mosquito-borne diseases, visit the UC IPM pages on mosquitoes. To report dead birds and view more information on West Nile in California, visit Westnile.ca.gov.
[Originally featured in the Spring 2024 edition of the Home & Garden Pest Newsletter]
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Mosquito Awareness Week, observed April 16 - 22, 2023, educates California residents about mosquitoes and how to help prevent the spread of mosquito-transmitted diseases.
One of the wettest years in history has left standing water across the state, creating perfect conditions for mosquitoes to develop. Stagnant water creates havens for disease-spreading mosquitoes, and mosquito experts are concerned this could be a long and intense mosquito season.
“After record amounts of rainfall this year, it is really important for all Californians to dump and drain standing water that has accumulated in their yards, porches, and patios,” said Assemblymember Jim Wood, who authored the state resolution recognizing California Mosquito Awareness Week. “It only takes a small amount of water for mosquitoes to develop so removing all stagnant water is a simple but very effective way to help to eliminate mosquitoes from our community. Not only are mosquitoes a nuisance, but they can transmit deadly diseases. Let's all work together to fight the bite!”
West Nile virus, spread by Culex mosquitoes, is the most prevalent and serious mosquito-borne disease in California. There is no human vaccine for West Nile virus, a disease which can cause debilitating cases of meningitis, encephalitis, and even death. In 2022, there were 209 human West Nile virus disease cases from 28 counties in California, including 13 human deaths.
In addition, invasive Aedes mosquitoes continue to spread throughout the state. First detected in 2013, they have spread to 25 counties and 300 cities and towns. These mosquitoes are very hard to control and pose a serious public health threat because they can spread diseases like Zika, dengue, chikungunya, and yellow fever to people and animal heartworm to pets.
According to the California Department of Public Health, since 2016 there have been nearly 900 California residents with travel-associated dengue infections. While there has not yet been local transmission of dengue in the state, it is occurring at California's borders, making the threat even more real. In 2022, the border state of Sonora, Mexico had more than 9,000 cases with 91 people dying from dengue. In December 2022 in Maricopa County, Arizona, two individuals tested positive for dengue, which they acquired locally from a mosquito bite.
“While all of the rain has been great for the drought, it provides mosquitoes with more places to lay their eggs,” said Wakoli Wekesa, PhD, president of the Mosquito and Vector Control Association of California. “As we work to keep Californians safe from mosquito-transmitted diseases and combat the spread of invasive Aedes, it's critical that residents take simple precautions to protect themselves and keep their communities mosquito-free.”
Mosquito experts say the future of mosquito control requires innovation to protect the public from mosquito-borne diseases. Mosquito and vector control agencies in California are exploring the potential use of three innovative technologies: self-limiting mosquitoes, Wolbachia, and irradiation. More information about the need for innovative technologies and how they work is available on the MVCAC website.
Everyone can do their part to help prevent mosquito bites:
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Apply insect repellent containing an EPA-registered active ingredient, including DEET, picaridin, oil of lemon eucalyptus, or IR3535, to clothes and exposed skin according to label instructions. Repellents keep mosquitoes from biting. It is important to follow EPA and CDC guidelines for the safe use of repellents on children.
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Dress in long sleeves and pants, especially if outside at dawn and dusk when mosquitoes that can spread West Nile virus are most active.
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Install screens on windows and doors and keep them in good repair to keep mosquitoes out of your home.
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Eliminate all sources of standing water on your property, including in flowerpots, old tires, buckets, pet dishes, and trash cans. Mosquitoes lay their eggs in very small amounts of standing water.
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Repair leaking faucets and broken sprinklers that can contribute to standing water around your home.
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Clean rain gutters clogged with leaves.
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Report neglected swimming pools and day-biting mosquitoes to your local mosquito and vector control agency (agency information can be found at www.mvcac.org)
To learn more, please visit the MVCAC website or the California Department of Public Health Mosquitoes and Mosquito-Borne Diseases webpage.
About MVCAC
The Mosquito and Vector Control Association of California (MVCAC) is the statewide voice for mosquito and vector control professionals. The association provides public health information, expertise, mosquito and vector-borne disease surveillance, innovative research, professional training, effective legislative and regulatory advocacy on behalf of California public agencies.
[Shared from the Mosquito and Vector Control Association of California. View UC IPM's Pest Notes: Mosquitoes for more information.]
- Author: Mike Hsu
Salinas Valley lettuce growers lost about $150 million in 2022 due to diseases
A stormy winter could portend another devastating year for the lettuce industry in the Salinas Valley, which saw approximately $150 million in lost gross revenue in 2022 due to INSV (impatiens necrotic spot virus) and associated diseases. Recent drenching rains might mean more weeds – overwintering “reservoirs” for the tiny insect, the Western flower thrips, that carries INSV.
Or the extreme precipitation could benefit growers, as thrips in the soil – during their intermediate stage of development – might be drowned in the waterlogged fields.
As with so many aspects of the INSV crisis, the ultimate effects of flooded fields on thrips populations remain unknown.
“We don't know if thrips are just so persistent and so stable in that pupal stage that maybe they will emerge unaffected,” said Kirsten Pearsons, University of California Cooperative Extension integrated pest management farm advisor for Santa Cruz, Monterey and San Benito counties. “There's just so much about their biology and ecology in the Salinas Valley that we just don't know.”
The mystery of thrips, INSV and soilborne diseases (namely Pythium wilt) is why UC Agriculture and Natural Resources assigned Pearsons to the area last November and hired Yu-Chen Wang in October as UCCE plant pathology advisor for the three counties.
“They're stepping in at a critical moment,” said Richard Smith, the region's UCCE vegetable crop production and weed science advisor who retired in January after a 37-year career. “They've gotten grants funded already – and that's just incredible. They're hitting the ground running.”
Experienced in disease diagnosis and collaboration with growers and industry partners, Wang said her pathology background – paired with Pearsons' entomology expertise – will be crucial in addressing INSV and other diseases.
“It is important for Kirsten and me to work together and provide different insights for the vector and the pathogen, respectively,” Wang said.
‘It's going to take everything to get a crop'
One priority is untangling the dynamics of INSV and Pythium wilt co-occurrence – the subject of ongoing research by JP Dundore-Arias, a plant pathologist at California State University, Monterey Bay. While the vegetables may tolerate one disease or the other, their one-two punch often deals the lethal blow.
“The challenge is – which is why it's great to have Yu-Chen and Kirsten – is that we have so many problems now, whether it's Fusarium (wilt), or Verticillium (wilt), or Pythium, or INSV,” said Mark Mason, pest control adviser for Nature's Reward, which primarily grows lettuces on 5,000 acres across the Salinas Valley.
Mason said that co-infections on his crops (sometimes with three or four diagnosed diseases) make it difficult to assign monetary damages to a specific pathogen, but he noted he has seen fields with “100% loss.” According to the Grower-Shipper Association of Central California, about 11,500 acres were deemed not harvestable in 2022, representing 12% of lettuce industry acreage.
Given the gravity and complexity of the disease dilemma, Pearsons said she has been fielding calls from growers seeking new and better solutions – ways to improve existing tools, techniques borrowed from other crop systems, and additional biological or chemical means of control.
And although there are a couple of pesticides that manage the disease-carrying thrips reasonably well, growers and researchers are worried about their diminishing efficacy due to overuse. Plus, they only constitute a short-term fix.
“Managing the thrips will only reduce the amount of INSV that can get transmitted,” Pearsons explained. “You can kill 99.9% of the thrips, but you get one thrips that has INSV that enters a field, and now you have an infected lettuce plant. All of the thrips are going to come and they can spread it from there; pesticide slows things down, but it's not going to eliminate it.”
Finding disease-tolerant lettuce cultivars is a more sustainable approach. Trials conducted last year by Smith, Wang and others identified several varieties that appeared to hold up well to Pythium and INSV. While additional research could maximize their potential benefit, Wang said even the hardier cultivars will lose their resistance over time, and a multi-layered INSV strategy with “integrated management tools” is crucial.
“We realized, when this thing started happening, that we cannot spray our way out of this problem,” Mason said. “We need varieties; we need management practices; we need pesticides…it just seems like it's going to take everything to get a crop.”
Weeds key to disease control
An all-hands-on-deck approach helped control thrips-harboring weeds last winter. With fields drying out from January storms, Smith said communities must get back to weed management – with a focus on prominent weed hosts for INSV and neglected areas adjacent to farms. Hotspots of infection last year were traced to industrial lots that were overlooked during the weeding process.
“People can't lose sight of the fact that we still need to be controlling the weeds in key areas, because that's the reservoir of the virus during the winter,” Smith said. “We have to stay on task with that.”
Yet despite the diligent weed abatement, crop damage from INSV and Pythium was widespread in 2022, and Smith said it's “very possible” that high heat during the summer was a contributing factor to especially prevalent disease in fall. Thrips populations tend to thrive in warmer weather, Smith said, but much more research needs to be done to understand the basic biology of the insect, including how they acquire the virus and how they spread it.
High hopes for future
Pearsons cited the work of Daniel Hasegawa, a research entomologist with the U.S. Department of Agriculture, who leads teams in monitoring thrips populations in several locations across the Salinas Valley. Currently the counting of thrips on sticky card traps is done manually, but Pearsons and Mason mentioned the possibility of using AI and machine learning to expedite that process.
Mason said that the grower community is excited about the new technologies and ideas that Pearsons and Wang are bringing to the region. As a participant in the search for candidates to fill the advisor positions, Mason said “they were, in my opinion, by far the best fit for what we were looking for.”
“I hope they stay here for 30 years,” he added.
The new advisors both noted the palpable energy and cooperative spirit in the Salinas Valley to proactively meet the challenge.
“Looking to the past, there have been other outbreaks and diseases that they've managed to overcome,” Pearsons said. “These farmers are resilient and creative and I fully believe that lettuce will still be growing here for years to come – it might look a little different, and it might take a little bit of a painful period to get to that point, but I think that we're going to be able to come up with some solutions.”
And while there are concerns that some lettuce growers might decide to leave the region, Wang said she also believes in the industry's strong roots and rich history.
“Salinas Valley has had a beautiful climate for lettuce for so many years; there are some undeniable advantages here,” she said. “This is still the best place in the United States – and maybe the world – to grow lettuce.”
/h3>/h3>/h3>/h3>- Author: Lauren Fordyce
With Respiratory Syncytial Virus Infection (RSV) on the rise, and Covid-19 and the flu remaining constant worries, disinfectant products are more and more likely to be used in the home, office, school, restaurant, and other public areas. Though these products are useful in reducing harmful pathogens, they are also capable of harming us when used incorrectly.
You may not think twice when spraying a surface with a disinfectant or using a disinfectant wipe without wearing personal protective equipment (PPE). Disinfectant products ARE pesticides, so check the label to see if you should be wearing gloves or other protective equipment.
To learn more about safe use of disinfectants and wipes, watch the recording from our most recent webinar with Meredith Cocks from the National Pesticide Information Center (NPIC).
Be sure to check out the UC IPM webinars planned for 2023 and register for these free, educational events!
- Author: Richard Smith
- Posted by: Gale Perez
Richard Smith is the University of California Cooperative Extension Monterey County Vegetable Crop Production and Weed Science Farm Advisor. He also covers Santa Cruz and San Benito counties.
Production fields are kept weed free during the winter fallow period and are not a source of overwintering weeds. However, weeds survive in a variety of other locations:
- the vegetated strip along Hwy. 101 which runs down the center of the valley,
- along county roads and turnouts,
- urban areas, industrial sites and roadways,
- along drainage ditches and riparian areas,
- levees and field roads, and
- miscellaneous areas on farms such as equipment yards, around valves and pumps and road banks.
The following are some observations of selected key weeds:
Shortpod mustard is a ubiquitous weed along Hwy 101 and county roads. It germinates in the winter but flowers from May to October. It was initially viewed with a great deal of suspicion because it is so common and often occurs in close proximity to lettuce production fields. However, shortpod mustard is a weak host for INSV with an infectivity rate of less than 3%. As a result, it appears to be a minor host for INSV. However, its flowers may provide nourishment to thrips that spread the disease. Other mustards such as black mustard and field mustard also are also weak hosts for INSV.
Little mallow and bull mallow have different levels of infectivity. Little mallow has an infectivity rate of close to 20% while bull mallow is less than 1%. Bull mallow is less tolerant of disturbance and tends to occur in uncultivated habitats such as in industrial areas and in the vegetated strip along the highway. Little mallow is well adapted to disturbance and can be a weed in production fields, in waste areas on the farm and along roads. It grows year-round in the Salinas Valley and is a key weed that needs to be controlled in the winter to reduce the reservoir for INSV.
Hairy fleabane and marestail are closely related and have the same effective aerial dispersal mechanism for their seeds. They germinate in the winter and flower in the summer. These weeds are excellent at taking advantage of waste areas on farms, along roadsides, freeway exits, road banks, levees, ditches and riparian areas. Their infectivity rate varies from 9 to 28% and they serve as key INSV reservoirs. One of the problems with these weeds is their tolerance/resistance to glyphosate, the most common herbicide used to control weeds, and therefore can often escape effective control.
Lambsquarters and nettleleaf goosefoot commonly infest production fields, but they can also be found in waste areas on farms, in ditches and occasionally along roadsides. Both of these species are good hosts for INSV with infectivity rates that range from 16 to 28%. Lambsquarter is less of an issue as a winter reservoir for INSV because it is cold intolerant. Nettleleaf goosefoot is more tolerant of winter temperatures and can frequently overwinter and serve as a winter reservoir for INSV.
Annual sowthistle is a key weed in production fields. However, like some of the other species mentioned, it is quite flexible and can be found in ditches, waste areas and equipment yards, road banks and even roadsides. It is a key winter reservoir because it grows year-round in the valley and has an infectivity rate of >20%.
Riparian areas with coyote bush and willows were evaluated and found to be non-hosts for INSV which is good news that native plants do not host INSV. However, in the riparian areas marestail and hairy fleabane can occasionally be well established.
In the winter of 2020-21, growers placed greater emphasis on controlling weeds in the areas surrounding their production fields. It is unclear why there was less INSV at the beginning of the 2021 season because there were also lower thrip populations. The grower community joined forces to reduce the winter reservoirs of INSV. These efforts will continue and hopefully will help reduce the levels of INSV and the resulting damage caused by this disease.
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