- Author: Ian Grettenberger
- Author: Addie Abrams
Two of the worst pests plaguing lettuce growers in the Salinas Valley area are aphids, specifically lettuce-currant aphids (Nasovonia ribisnigri), and western flower thrips (Frankliniella occidentalis). Lettuce-currant aphid is an invasive pest that sets up shop in the heart of the lettuce plant and will render the crop unsellable when it reaches high enough numbers. Thrips can both cause cosmetic damage to lettuce crops and are also responsible for the spread of Salinas impatiens necrotic spot virus (INSV), the fatal lettuce disease that has driven large losses since the 2020 growing season.
While effective tools exist to control both aphids and thrips, they are almost exclusively chemical. Chemical sprays are increasingly under pressure due to changes in the regulatory framework in California as well as the development of pest resistance and discoveries of key chemistries in area watersheds1,2. The UC Davis FiVE lab biological control research program addresses a growing interest in developing alternative tools for managing both pests that do not rely on chemical applications. Biological control provides an opportunity for the management of thrips and aphids that do not rely on chemical tools.
Biological control is defined as the use of natural enemies to control a target pest. Three general categories of biological control could possibly be used as management practices for lettuce pests in the Salinas Valley area:
• Conservation biological control refers to the establishment and maintenance of resources and conditions favorable
• Inundative biological control involves the release of a beneficial insect species in large numbers with the expectation that the beneficials that are released will only provide control for a short amount of time before eventually dying out. Such releases would need to be repeated at regular intervals for the duration of the growing cycle for a crop.
• Augmentative biological control refers to the use of releases of smaller numbers of beneficials to areas where a smaller population of the species already exists, but not in numbers great enough to provide adequate control of the targeted pest species. The goal of augmentative releases is to bolster already-existent populations of beneficial species so they achieve great enough numbers to provide control of the pest or pests of interest.
Conservation biological control in the Salinas Valley
Syrphid flies
Aphid pests of lettuce have been effectively managed in some lettuce production systems through the planting of sweet alyssum adjacent to and interspersed within crop fields3. Sweet alyssum is a favorite of the Syrphid fly (Diptera: Syrphidae), the primary biological control agent used to control aphid pests in lettuce. Syrphids, also called hoverflies or flower flies, are a family of black and yellow pigmented flies which resemble bees and stinging wasps. The coloration is a protective camouflage; Syrphid flies are harmless to humans. Syrphid adults are frequently seen visiting flowers for their nectar and pollen, which the insect consumes both as an energy source and to support their reproduction.
In exchange the female Syrphid flies will lay eggs in lettuce plants with lettuce aphid infestations, the primary food source for their young. Once the eggs hatch, the syrphid maggots, which are predatory on slow, soft-bodied insects, will feed on the aphids and suppress their population. Syrphid larvae are known to be voracious; some California species have been shown to consume upwards of 100 aphids per day4!
Syrphids are the intended beneficiaries of most conservation biological control in central coast lettuce fields, but other beneficial species take advantage of these resources as well.
Other predatory species love sweet alyssum
Many other biological control agents are supported by insectary plantings5. Ladybird beetles often inhabit lettuce fields and may provide some control of lettuce aphid infestations. Common lacewings (family Chrysopidae) are also found in lettuce fields and insectary plantings. Lacewings, which are only predatory in their immature or larval life stage, can provide biological control services against lettuce aphids and western flower thrips. Minute pirate bug (Orius sp.) and aphid midges (Aphidoletes aphidimyza) have also been observed in and collected from insectary plantings in lettuce fields, but it is not known the extent to which they can suppress populations of lettuce aphid or Western flower thrips.
UC Davis Fi-VE Bug IPM Lab biological control research programs
Including insectary plantings to attract naturally occurring predators has historically been the only efficient way to get beneficial species into crop fields. Newly developed technology using drones as a dispersal tool may provide another option for growers interested in using biological control as part of their pest management programs for aphids and thrips. This technology drastically reduces the time and labor required to conduct large releases of laboratory-reared beneficial insects, making the approach more feasible for growers.
As part of a research program funded by the California Department of Pesticide Regulation (CA DPR) and in collaboration with Daniel Hasegawa at USDA-ARS and with Parabug, we are studying the release of biological control agents using drones for the management of aphid and thrips pests of lettuce crops. Our three experimental programs are as follows:
Experiments run by former Monterey County IPM Advisor Alejandro Del Pozo-Valdivia found that a single inundative release of green lacewing eggs (Chrysoperla rufilabris) in lettuce fields reduced aphid pressure six weeks after release6. Our experiment builds on Alejandro's work, examining whether repeated releases of green lacewing eggs throughout the lettuce growing cycle reduce aphid numbers. Additionally, the experiment includes two treatments aimed at suppressing western flower thrips: inundative releases of a species of predatory mite (Amblyseius cucumeris), and a combined release of both predatory mites and green lacewing eggs.
Augmentative releases to bolster non-syrphid predatory species in insectary strips and intercropped alyssum
Other native predators of aphids and thrips are present in the insectary plantings growers use to attract syrphids, but their numbers are too low to provide suppression of thrips and aphids in adjacent crops. These species are reared by commercial insectaries, but using them in an inundative release could prove too costly for growers. Experiments in this program examine the use of smaller releases of these predatory species early in the growing cycle over insectary plantings. The goal is to determine whether the presence of floral resources allows the predators to stick around and build up enough in population to control aphids and thrips in the crop field. Experiments will be conducted with aphid midge (Aphidoletes aphidimyza), an aphid predator, and minute pirate bug (Orius insidiosus), a predator of western flower thrips.
Augmentative releases to manage thrips in non-crop areas
Western flower thrips plague not just vegetable crop fields but also the vegetation surrounding crop areas. In this experiment, we will examine whether releases of cucumeris mites and minute pirate bugs over field edges planted with ice plant will establish these predators in the vegetation and provide long-term suppression of western flower thrips.
Citations
- Deng, X. Study 321: Surface water monitoring for pesticides in agricultural areas in the Central Coast and southern California (2022)
- Gao, Y., Lei, Z. & Reitz, S. R. Western flower thrips resistance to insecticides: detection, mechanisms and management strategies. Pest Manag. Sci. 68, 1111–1121 (2012).
- Brennan, E. B. Agronomic aspects of strip intercropping lettuce with alyssum for biological control of aphids. Biol. Control 65, 302–311 (2013).
- Hopper, J. V., Nelson, E. H., Daane, K. M. & Mills, N. J. Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California. Biol. Control 58, 271–276 (2011).
- Bugg, R. L., Colfer, R. G., Chaney, W. E., Smith, H. A. & Cannon, J. Flower Flies (Syrphidae) and Other Biological Control Agents for Aphids in Vegetable Crops. (University of California, Agriculture and Natural Resources, 2008). doi:10.3733/ucanr.8285.
- Del Pozo-Valdivia, A. I., Morgan, E. & Bennett, C. In-Field Evaluation of Drone-Released Lacewings for Aphid Control in California Organic Lettuce. J. Econ. Entomol. 114, 1882–1888 (2021).
- Author: Elinor Teague
Fungal problems on plants are usually short-lived here in the Central Valley. High temperatures and low humidity beginning in May quickly kill off fungal spores. We seldom see common fungal problems like powdery or downy mildews, rust or black spot after May.
Biological fungicides or biofungicides are gradually replacing a wide range of fungicides including chemically derived broad spectrum products, as well as least-toxic products such as copper and sulfur solutions, horticultural oils, neem oil and jojoba oils. Fungi are plant-specific and biofungicides have a long list of treatable fungi on many different plant species.
Biofungicides are formulated with naturally occurring living microorganisms, beneficial bacteria, that are found on plants or in the soil. Labels on biofungicides for home and garden use may not clearly indicate that the product is a biofungicide. The labels will show bacterial strains as the active ingredient. The two most common are Bacillus subtilis and Bacillus amlolyquefaciens.
The microorganisms are effective at controlling fungal pathogens in several ways: They out-compete fungus for nutrients and space, they trigger resistance in the host plant to the pathogen, they produce antibiotics or toxins that weaken or destroy the pathogen.
Biofungicides are organic products and can be as effective or even more effective in treating or controlling most of the common fungal problems in home gardens than can either broad-spectrum chemically derived or the least-toxic fungicides. They are less toxic than copper and sulfur products.
However, the use of biofungicides is not without problems. They are preventative rather than curative treatments. Great care must be taken to remove all plant debris and even soil from areas in the garden where plants have previously shown fungal problems. New transplants should be examined carefully for signs of fungal infestations and, if in doubt, the potting soil should be drenched with a biofungicide or removed and replaced with fresh, sterilized soil.
Application timing is easily thrown off by rain showers. I was unimpressed with the results of using a biofungicide last spring on Romano bean plants due to rain showers continuing well into April. Biofungicides, like other fungicides, should not be applied when rain is predicted, temperatures are above 90 degrees or on drought-stressed plants.
Because biofungicides are composed of living organisms, shelf life is reduced. Two home-and-garden-use biofungicide labels (Serenade and Monterey Complete Disease Control) do not provide use-by dates or storage temperature ranges. The UCONN IPM website does give that information for a range of biofungicides used in greenhouses and agriculture. Maximum use-by date ranges from 18 months to 3 years. Some formulations require refrigeration or have a maximum temperature. Information on whether those same restraints apply to home and garden use products was unavailable.
The same UCONN IPM article emphasizes the importance of wearing protective clothing and using caution when applying biofungicides. The two labels mentioned above are less emphatic in their recommendations.
Sources:
- CT IPM program, UCONN College of Agriculture, Health and Natural Resources, Biological Fungicides.
- UCIPM, Fungicides, Powdery Mildew on Vegetables
- UCANR, “Pests in the Urban Landscape', Biological Fungicides: Do They Work and Are They Safe?, Steven Swain, 2014, UC IPM Green Bulletin Newsletter.
If you have eucalyptus trees, you might have noticed white, crusty growth on the leaves. Or maybe you saw a sticky, blackened mess of fallen leaves under a eucalyptus tree. These are signs of the redgum lerp psyllid, one of the most common psyllid pests that damages eucalyptus trees in California.
The adult psyllid is very small and as nymphs, they are concealed under a waxy cap, or lerp. As they feed, they excrete honeydew which can lead to the growth of black sooty mold, the source of those sticky leaves under the tree.
Although under biological control in coastal areas, this pest is still a problem under some growing conditions and on specific Eucalyptus species. Cultural practices to manage lerp psyllids, such as avoiding fertilization of eucalyptus trees and pruning only when and where needed, can help reduce lerp psyllid problems.
The newly revised and expanded Pest Notes: Eucalyptus Redgum Lerp Psyllid, authored by entomologists Timothy D. Paine, UC Riverside; Kent M. Daane, UC Berkeley and UC ANR Kearney Agricultural Research and Education Center; Steve H. Dreistadt, UC IPM Program; and Raymond J. Gill, California Department of Food and Agriculture, contains detailed information about the identification, biology, and management of this pest.
This revision has more information about the lerp psyllid's biology and damage they cause on eucalyptus, a list of eucalyptus trees resistant to this pest, and an expanded section on biocontrol, with detailed information about the imported parasitic wasp that only attacks redgum lerp psyllid.
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- Author: Kathy Keatley Garvey
No assassinations today! But an "assassination attempt."
There it was, a leafhopper assassin bug, Zelus renardii, waiting for prey atop a Mexican sunflower, Tithonia rotundifola in a Vacaville pollinator garden. Yes, it's native to North America.
The assassin bugs, family Reduviidae, are ambush predators. When they ambush a predator, they stab it with their rostrum, inject venom, and suck out the juices. Or as UC Berkeley entomologists Jerry Powell and Charles Hogue write in their book, California Insects, "The victims, which include all kinds of insects, are snatched by quick movements of the forelegs, and immediately subdued by a powerful venom injected through the beak."
UC Statewide Integrated Pest Management Program (UC IPM) says that "Assassin bug adults and nymphs (immatures) have an elongate head and body and long legs. The narrow head has rounded, beady eyes and long, hinged, needlelike mouthparts. Adults and nymphs can walk rapidly when disturbed or capturing prey. Adults tend not to fly."
"Assassin bugs can occur on almost any terrestrial plant including row and tree crops and gardens and landscapes. All species are predators of invertebrates or true parasites of vertebrates," UC IPM relates. "Most assassin bugs feed on insects including caterpillars, larvae of leaf beetles and sawflies, and adults and nymphs of other true bugs. Nymphs and adults ambush or stalk prey, impale them with their tubular mouthparts, inject venom, and suck the body contents. Zelus renardii produces a sticky material that helps it adhere to plant surfaces and ensnare prey."
Some 7000 species of assassin bugs reside throughout the world. When they feed on such agricultural pests as fleahoppers, lygus bugs, aphids, caterpillar eggs and larvae, they are considered biological control agents.
However, "assassin bugs are not considered to be important in the biological control of pests, unlike predatory groups such as bigeyed bugs and minute pirate bugs," UC IPM says. "Assassin bugs are general predators and also feed on bees, lacewings, lady beetles, and other beneficial species. Certain species feed on the blood of birds, mammals, or reptiles, including conenose bugs and kissing bugs (Reduviidae: Triatominae)."
The one we saw today?
A long-horned bee, Melissodes agilis, stopped for a sip of nectar, spotted the assassin bug, and buzzed off, leaving only its shadow behind.
- Author: Mike Hsu
Supply-chain crisis forces some to pivot to mechanical, biocontrol measures
Driving through her vineyards on a chilly morning in December, Hortencia Alvarado is taking comfort – for now – that the weeds she sees are all yellow. But there remains a nagging worry that, like the pesky plants, is merely lying dormant for the season.
When March rolls around, and the first signs of new green growth appear on the vines, Alvarado and other vineyard managers will again have to confront the ongoing shockwaves of the global supply-chain crisis.
Growers of grapes – the third-highest valued agricultural commodity in California at $4.48 billion in 2020 – likely won't be able to access the herbicides that they usually apply.
“I definitely need to start thinking and considering it because I don't want to be in that situation where I don't have [the herbicide] when I need it,” said Alvarado, a vineyard manager in the San Joaquin Valley.
Imperfect alternatives
She first noticed the effects of the shortages this past August, during the application following the harvest of early varietals. Alvarado's agricultural pest control adviser had recommended a different product, instead of their usual standby, Rely – because none of the handful of suppliers in California could find it.
Then Alvarado's foreman started reporting that the substitute wasn't controlling the weeds.
“We were using some other stuff that wasn't as good, so basically we were wasting money on stuff that wasn't doing what we wanted it to do,” Alvarado explained.
The need for more machines or labor is just one result of the herbicide shortage, said George Zhuang, University of California Cooperative Extension viticulture farm advisor in Fresno County. Zhuang has received “a lot” of calls from growers about the chemical supply issues, which are also affecting fertilizers. He's been urging them to move away from traditional herbicides to mechanical means or biocontrol such as sheep or fowl – even though they might be more expensive.
Zhuang estimates that while a weed program comprises 5% to 10% of total production costs in a normal year with the usual herbicides, the use of nonchemical alternatives could hike that percentage up to 10% to 20%. In addition to their impact on the bottom line, effective herbicides are especially crucial to grape growers because vines – unlike tree crops – cannot naturally shade out weeds with expansive canopies.
“Right now, people can still scramble around and find some limited chemicals to make sure the crop is successful for the harvest, but if the situation goes for another year, I think there's going to be a panic in farming communities,” Zhuang said.
Herbicide challenges expected to linger
Unfortunately, the availability of certain products is likely going to be “challenged” into at least the middle of 2022, according to Andy Biancardi, a Salinas-based sales manager at Wilbur-Ellis, an international marketer and distributor of agricultural products and chemicals. Biancardi said that the suppliers he talks to are advising people to make preparations.
The supply of glyphosate, the key component in products such as RoundUp (used by many Midwestern farmers), appears to be most affected, Biancardi said. As a result, that shortage has put the squeeze on alternatives such as glufosinate, used in products like Rely – the herbicide favored by many California grape growers.
“The cost of glufosinate has definitely gone up because there just isn't enough, so everyone is obviously marking it up,” said Biancardi, who estimates that prices for both glyphosate and glufosinate are up 25% to 30% for growers.
Alvarado said that while large commercial operations are able to pay the premium prices or shift to other weed control measures, some smaller growers have essentially given up the fight – simply letting the weeds take over.
“They're just letting it go wild until the dormant season,” she said. “They're hoping that – by when they do start to spray [around March] – they'll hopefully have that Rely.”
Silver lining to supply crisis?
Large-scale growers and retailers are buying up those scarcer products when they can, in anticipation of future shortages during critical times. Biancardi said that while his company traditionally runs inventories down at the end of the season, they are instead stocking up on herbicides that customers will demand.
“Careful planning and forecasting is going to be more important than ever, that's really the key,” he said. “At this point we can't guarantee ‘business as usual,' based on what we're hearing.”
Shaking off old habits might actually bring some benefits to business, according to Alvarado, as a forced shift away from chemicals could prove to be a selling point for customers, from a sustainability and marketing standpoint.
“Out of this shortage, there might be some good, some wins,” she said, “but at the same time, we're going to need some answers – I think it's going to be a bumpy road.”
Calling the confluence of drought, record heat and a shortage of chemicals a “perfect storm,” Zhuang said that consumers could start feeling those jolts as well.
“Eventually, somebody is going to eat the costs – either the farming community or the consumer is going to eat the cost, I hate to say it,” he said.
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