California Fruit and Vegetable

Category: Pest/Disease Management

  • Plant, Insect Viruses Work Together to Spread Disease

    In what may be a first for science, researchers with the Agricultural Research Service (ARS) have found an example of plant and insect viruses working together to increase their spread.

    Molecular biologist Michelle Heck, of the ARS Emerging Pests and Pathogens Research Lab in Ithaca, NY, scouts for aphids (Photo by Jennifer Wilson, Cornell University).

    Michelle Heck, an ARS research molecular biologist, was leading research into poleroviruses, a type of plant virus spread by aphids, when she and Cornell University graduate students Jenny Wilson and Patricia Pinheiro made the surprising discovery. Heck is in ARS’s Emerging Pests and Pathogens Research Unit at the Boyce Thompson Institute, on the campus of Cornell University, in Ithaca, NY.

    “Poleroviruses produce a molecule, called P Zero (P0), which dampens the aphid’s immune system,” Heck said. “When the aphid immune’s system is turned down, it allows an aphid virus called a densovirus to infect the insect at very high levels.”

    Densoviruses have a curious effect on aphids: Aphids usually develop wings when the weather begins to cool, but densoviruses can induce the insects to sprout wings. When poleroviruses and densoviruses interact in this way, it allows them to carry the polerovirus farther and faster.

    “We think this is the result of evolution,” Heck said. “Both the plant virus and the insect virus have evolved to manipulate the aphid. Our work shows they are in cahoots to promote virus spread, though possibly at the aphid’s expense.”

    The research is vital to crop producers because aphids transmit more than 100 different viruses to peaches, tomatoes, potatoes, apples, cotton, cabbage, corn, and other plants. In particular, the potato leafroll virus can reduce the worldwide potato yield by more than 50 percent, causing the loss of 20 million tons of crop each year. There is a new and emerging polerovirus infecting cotton, cotton leafroll dwarf virus, that Heck and her team are now studying.

    “Aphids are resistant to many commonly used insecticides, so chemical treatment is not effective in killing them and blocking the spread of viruses,” Heck said. “By the time a farmer notices aphids in the field, it is too late to block the spread of these viruses by aphids.”

    Follow-on research includes a quest to understand how the polerovirus protein, P0, suppresses the aphid’s immune system at the molecular level. Heck is also looking at exactly how the densovirus triggers the aphid to grow wings.

    “We now know that poleroviruses can interfere with the aphid’s immune response to densoviruses,” she said. The question Heck hopes to answer is, can the densovirus infection be made so severe that it kills the aphids, and if so, could it be used as a biological control tool? – By Scott Elliott, ARS Office of Communications

  • False Chinch Bug in New Avocado Plantings

    The false chinch bug (FCB), Nysius raphanus (Hemiptera: Lygaeidae), is a pest of many plants. FCB is a generalist and has been found to be a problem in many cropping systems such as soybeans, quinoa, tobacco, cotton, broccoli and other Brassicaceae plants. FCB adults (above) is mostly light to dark gray, elongate, and about 0.12 inch (3 mm) long. Females lay eggs on host plants or in cracks in soil. The mostly pale gray nymphs have inconspicuous reddish to brown abdominal markings. FCB has 4-7 generations per year with all stages being potentially present throughout the year. All stages can be present throughout the year. They also can be found invading homes in the southwest. Their populations generally start in unmanaged fields with lots of weeds and are an issue for crops when they build up large numbers and move into the crops from the unmanaged, weedy fields. 

    This year it’s host of choice is young avocado plantings in Ventura County. False chinch bug occasionally causes severe injury on young trees by sucking sap from shoots and young stems. Infested shoots wither and die suddenly after attack, which typically occurs in May and June. Economic damage normally occurs in groves away from the coast only on young trees in border rows adjacent to uncultivated areas or grasslands. Otherwise healthy mature trees tolerate bug feeding.

    Here are photos of damage to young avocado provided by Tom Roberts, Integrated Consulting Entomology.

    To best manage FCB, a grower will need to catch it before it establishes and the populations explode. This is difficult because the pest will not reoccur every year on regular basis. From what has been seen in the field this year, FCB appears to prefer young avocado plantings and thus, a targeted approach is to monitor only in new plantings right as summer temperatures are rising. In paper in the journal, Phytoparasitica from 2006, the authors investigated what color sticky trap was best for monitoring and found that yellow worked best. Thus, passive monitoring with yellow sticky cards that are placed throughout the field and monitored weekly is a potential option. However, this approach can be expensive with the labor hours needed to properly process the sticky cards. A more practical approach is to sweep net weedy areas on the outside of avocado groves and adjacent unmanaged areas nearby weekly in search for the first signs of FCB.

    In conventional avocado production, there is only one insecticide recommended for use against FCB. Malathion 8 at 16 oz/acre. — By Monique Rivera & Ben Faber, UC Cooperative Extension

  • Removing Avocado Suckers with Glyphosate

    This is not good. You find an avocado tree with sun blotch or it is time to thin the orchard and you remove the offending tree. You know that if you don’t remove the sucker, you’ll end up with some rootstock growth that just gets in the way of the other trees. Avocado suckers can look like a valued tree until it’s time for harvest several years later, and then you are likely to find that it’s not the variety that you thought it was. Homeowners often find this problem several years after a freeze and the lemon tree that regrew from the freeze damage turns out to be the rootstock variety and produces some gnarly, seedy, juiceless fruit. Even without a frost, sometimes rootstocks which are selected for their vigor, can be more vigorous than the scion variety and will overgrow it. You then end up with whatever the rootstock fruit turns out to be.

    In some situations, it is legal and common to use a “cut stump” treatment to kill stumps and prevent resprouting. In these cases, glyphosate or triclopyr is sprayed, drizzled, or painted onto a freshly cut stump. Relatively high concentrations of the herbicide are applied to the cambium, which is the living tissue just under the bark. Cut stump treatments work well in many situations, including citrus orchards. This type of cut and spray treatment is commonly done to remove undesirable plants, like arundo and weedy tree species. However, in some trees, like avocado and many forest species, there can be root grafting, which are tree-to-tree root connections.

    Due to root grafting in a mature avocado orchard, it really can be one giant root system, one tree connected to all the other trees. And if a systemic herbicide is injected in one tree, the surrounding trees can be affected – they might get enough herbicide through the root graft to be injured or even killed along with the target tree. This technique has been used in Florida to remove Laurel Wilt Disease infected avocado trees which can rapidly infect surrounding trees with the killer fungus. This is a helpful technique, because it removes any doubt that all infected trees have been killed to prevent the spread to healthy trees in the orchard.

    In a healthy orchard in California, this is not a really good way to remove avocado stump sprouts. Every year reports come in of glyphosate killing good trees that surround a removed tree. Figure 3 is a recent case where the stump (circled in blue) was scored and painted with glyphosate. Within two weeks the surrounding tree were also killed. The systemic material was translocated from the cut surface by way of root grafts to the neighboring trees. And those trees are now dead, too.

    The stump (circled in blue) was scored and painted with glyphosate.

    So what to do? One thing done by those with a front-end loader or a backhoe, is to pull the stump and have an end to the sucker problem. It also reduces the possibility of chronic armillaria fungus persisting to infect trees. The problem is that it leaves a big hole to deal with which can open up a slope to erosion. If on a slope, it requires a decent sized tractor that can safely be operated on the slope without tearing up everything, including the irrigation system. And in the end, it’s expensive.

    The other approach is to just cut the tree down as low as possible without damaging the chain saw. Then as the irrigator makes inspections, just physically knock off the suckers as they come up. If walking the irrigation lines, it’s not a problem. Covering the stump and immediate area with a physical barrier such as thick, black plastic sheet (greater than 5 ml), can reduce the number of suckers. To speed degradation of the stump, the top of the cut can be scored and a salt such as urea or magnesium sulfate (both at 10 pounds per stump) can be applied. At this rate, rather than fertilize the stump, under moist conditions, this treatment facilitates the activity of wood-decaying microorganisms; it can also damage or reduce the regrowth of the suckers.

    There are also a range of registered contact herbicides that can be used to burn out the suckers. Materials, such as Scythe®, Axxe® and Suppress® are all registered for avocado sucker control. There are others. These contact herbicide work best on small tender suckers so don’t let the suckers grow more than a foot or so. For best control of suckers, apply them at the highest allowable rate with an approved adjuvant at a spray-to-wet rate. Because these products are not systemic, you’ll likely need repeat applications, as new fresh buds break and new suckers erupt.

    Using a contact spray means the grower would still need to be out in the orchard controlling the suckers. The grower still needs to be out in the orchard checking the irrigation lines. Why spray the suckers when they can just be broken off?

    Although systemic herbicide can be used effectively to control suckers or stump sprouts in some tree crops or situations where root grafting does not occur, this is not a recommended practice for avocado because of the risk of damage to nearby trees. — By Ben Faber & Brad Hanson, UC Cooperative Extension

  • Fusarium Crown Rot in Watermelon

    In late June, I was contacted by a watermelon grower and visited his field near the border of Stanislaus and Merced County. In the field, 50% of the plants showed leaf and vine wilt and about 20% died (see the field image). When I made a closer examination, the color of leaf lesions were chocolate brown and stem appeared to be watery (see leaf and crown images). The grower told me that the field was just harvested once but symptoms were already present beforehand. The field was planted by a 45-ct and mini-watermelon cultivars.

    Vine-declined and wilted watermelon plants from the disease infection.

    An initial suspicion was a fusarium disease and/or a possible Gummy Stem Blight caused by Didymella bryoniae, though this is very uncommon for the watermelon in California. I sent leaf, runner, and stem samples to the UC Davis Fungal Pathogen Lab and the results came back with the Fusarium Crown Rot caused by F. solani f. sp. cucurbitae and possibility of F. falciforme. F. falciforme has not been described to infect watermelon but records showed that it could cause crown rot in muskmelon. Gummy stem blight (Didymella bryoniae) colonies were not recovered from the samples, which did not surprise me because this disease is mostly prevalent in the southeast and north area, such as Georgia, South/North Carolina, and Delaware.

    Unlike fusarium wilt caused by F. oxysporum f. sp. niveum, the vascular system of crown rot infected plants typically does not show discoloration far above soil line, instead, necrotic rot of crown and taproot can be seen. As the disease progresses, the rot on the crown develops from a light-colored, water-soaked area to be darker. Eventually, the entire plant wilts and dies. Evidence indicated that fusarium crown rot is more common on summer squash and pumpkin, however, all cucurbits can be infected.

    Water-soaked, necrotic rot of the crown

    Early planted fields can have a higher chance to be infected as disease is favorably developed under a cooler temperature. Soil moisture does affect the development of the disease. Extremely wet soil especially with drip tape breakage creates a favorable microclimate, which definitely accelerates the reproduction of spores and spread of the disease to other rows. Growers using surface drip irrigation should specifically pay more attention to the tape damage and fix the problem timely.

    Various types of information demonstrate that the pathogen (F. solani f. sp. cucurbitae) is seedborne and survives only for two to three years in soil. A four-year rotation of planting non-cucurbit species is usually chosen for the disease control. In addition, choosing clean seeds or fungicide-treated seeds can reduce disease initiation. More information about the Fusarium crown rot on cucurbits can be found at UC IPM: http://ipm.ucanr.edu/PMG/r116100911.html. – By Zheng Wang, UCCE Vegetable Crops Farm Advisor

  • New CA Blackeye Varieties Show Resistance to Cowpea Aphid

    Field trials in the Central Valley with two new varieties of blackeye beans, CB74 and CB77, show impressive resistance to cowpea aphids compared to standard CB46, CB5, and CB50 lines. Four varieties of blackeyes including CB46, CB77, CB74, and CB5 were seeded into a blackeye CB50 field, in single lines on 30-inch beds in the Sacramento Valley in May 2020 (Photo 1). By mid-summer, CB50, CB46, and CB5 were heavily infested with aphids (photo 2), whereas CB74 and CB77 were clean (photo 3).

    Photo 1. Blackeye variety trial, Sacramento Valley, 2020; left to right, CB46, CB77, CB74 (early maturing), and CB2 compared to the standard CB50 line planted in the field on the far left.

    Cowpea aphids are serious insect pests of blackeyes. These aphids can quickly colonize plants and cause injury by direct feeding and injecting toxic saliva into plants, leading to stunted growth or death of plants. Sticky honeydew released by the aphids can stimulate black mold growth on plants, reducing photosynthesis and plant health. Cowpea aphids also vector a number of viral mosaic diseases that can cause serious losses in many crops. Biological control cannot be relied on because natural enemies often appear when cowpea aphid infestations are already high and causing serious damage. Applying pesticides early in the season prevents cowpea aphid infestations but beneficial insects can be destroyed, leading to outbreaks of other insect pests. Thus, the development of cowpea aphid resistant blackeye lines is an important breakthrough in managing this pest.

    Photo 2. Heavy cowpea aphid pressure on blackeye bean CB46 leading to significant yield and quality losses.

    Blackeye beans, also known as cowpeas, or blackeye peas in southern states, are an important food crop worldwide. In California, about 8,000 acres are grown annually for dry or canned blackeye bean markets. These new blackeye bean lines are being developed by the UC Riverside blackeye breeding program, led by Drs. Phil Roberts and Bao Lam Huynh, with support from the California Dry Bean Advisory Board and the US AID Feed the Future Innovation Lab for Legume Systems Research (formerly Innovation Lab for Collaborative Research on Grain Legumes). The aphid resistance and other traits have been introgressed into California Blackeye elite backgrounds using natural selection and new molecular markers to expedite the breeding process. Compared to standard varieties, CB74 and CB77 also have more stable yields resulting from heat tolerance, better tolerance to lygus bugs, and equivalent resistance to Fusarium wilt and root-knot nematodes.

    Photo 3. Adjacent CB77 blackeye plants show high levels of resistance to cowpea aphid infestations.

    Blackeye variety observation trials are being conducted in fields by UCCE Farm Advisors Rachael Long, Sarah Light, and Nick Clark in the Sacramento and San Joaquin Valleys, in collaboration with local farmers. More information on blackeye beans can be found in the Blackeye bean production manual for California, UC ANR 21518, http://beans.ucanr.edu/files/226601.pdf. The lead UC bean breeders hope to have these lines available to farmers within the next few years. – By Rachael Freeman Long, UCCE Farm Advisor

  • Broomrape: a Parasitic Weed in CA Processing Tomato

    Figure 1: Branched broomrape infestation in a processing tomato in California.

    Branched broomrape (Phelipanche ramosa), a weedy parasitic plant that can cause devastating damage to many economically important wide range of broadleaf crops including tomato, cabbage, potato, eggplant, carrot, pepper, beans, celery, peanut and sunflower has recently re-emerged in fields in Central Valley counties in California. This weed utilizes a modified root, called haustorium, to fuse into a host plant root and extract nutrients and water which can greatly reduce productivity or even kill the host depending on the level of infestation, susceptibility of the host, and environmental conditions. Tomato is highly susceptible to branched broomrape. In the United States, California accounted for over 90% of the 12 million tons of tomatoes grown in 2018. Studies in Israel showed that at extreme infestation levels broomrape can cause processing tomato yield losses as high as 70%. The annual losses in tomato due to broomrapes in Israel and Turkey are estimated at $5 and $200 million, respectively. Up to 80% crop loss due to branched broomrape has been reported in tomato in Chile which is highly concerning given the similarity in production systems and broomrape species with California.

     
    Figure 2: A close view of a flowering branched broomrape

    Branched broomrape is currently classified in California as an “A” pest, that is, “an organism of known economic importance subject to California State enforced action involving: eradication, quarantine regulation, containment, rejection, or other holding action”. As a potentially severe economic pest and as a California “A-list” pest, establishment and spread of a branched broomrape in California tomato production regions could cause severe consequences for individual growers and for the entire tomato industry. Currently, discovery of broomrape in a commercial tomato field leads to a hold order and crop destruction without harvest. In addition to branched broomrape, several fields have been reported with infestations of Egyptian broomrape (Phelipanche aegyptiaca), a Q-listed species (that is, having a temporary “A” classification pending determination of permanent rating by California State), causing similar industry and grower concerns.

     
    Figure 3: Hundreds of tiny branched broomrape seeds (0.2 – 0.4 mm) and the single capsule from which the seeds were sourced.

    In the United States, branched broomrape was first reported in 1890, and since then, over 150 occurrences of branched broomrape have been documented. In recent times, reports of branched broomrape in the United States have been increasing; from 7 occurrences in 2015 to 65 in 2019. Branched broomrape has been documented in Texas, Virginia, South Carolina, Illinois, New Jersey, Tennessee, Kentucky, Alabama and California. In California, the first reported case of branched broomrape was in Butte County (1903) and later in Alameda County (1929). Other counties in California with reported branched broomrape detections include Colusa, Sacramento, San Benito, Santa Clara, San Joaquin, Ventura and Yolo.

    Figure 4: Distribution of branched broomrape in California as of November 10, 2019. Data source: Calflora and GBIF 2019

    A severe infestation of branched broomrape in the Sacramento Valley in 1959 prompted an intervention that involved soil fumigation with methyl bromide to target the soil seedbank; this was as an industry-led effort funded through a legislative marketing order program. Branched broomrape became a less significant problem after that effort which involved research, intensive field surveys, and fumigation of infested fields and equipment from 1973 to 1982 that cost over $1.5 million. However, this parasitic weed has recently been detected in several tomato fields in Yolo, Solano (Egyptian broomrape) and San Joaquin Counties. The cause of the re-emergence of the problem remains unclear, although re-introduction or recurrence from long-dormant seed in the soil and subsequent spread have been speculated.

    Figure 5: A branched broomrape plant attached to a volunteer tomato root in a processing tomato field in mid-June.

    The re-emergence of branched broomrape in California is of concern to the processing tomato industry as: 1) the experience in other regions of the world has demonstrated the extreme vulnerability of tomato to branched broomrape parasitism, 2) broomrapes seem likely to rapidly establish and spread in California because of the similarity to the species’ native climate, (3) repeated cultivation of processing tomato in the same fields, (4) the cultivation of a wide range of hosts (e.g. carrot, sunflower, safflower) in California, (5) intensive agricultural practices that could rapidly spread broomrape seeds to uninfested fields, (6) the production of copious number of minute seeds could easily disperse via machinery and irrigation water in the highly mechanized and irrigated cropping systems of California, (7) seed longevity (> 20 years) allows the parasite to persist even in the absence of any hosts, and (8) the major part of the parasite’s lifespan occur underground, making it inaccessible to conventional means of weed control such as cultivation and contact herbicides, (9) some of the important management tools (e.g. herbicides known to be effective in controlling broomrapes) are not yet registered or tested in California, (10) regulatory and environmental challenges with soil fumigation practices.

    Research efforts are currently being made to further understand, and develop detection and control approaches for branched broomrape in tomatoes and other specialty crops in California. For more information about branched broomrape in California, please see:

    http://tomatonet.org/branchedbroomrape

    http://tomatonet.org/img/uploadedFiles/Broomrape/CTRI_2019_NEWSLETTER.pdf

    https://www.plantsciences.ucdavis.edu/news/broomrape-eradication-high-priority-uc-researchers

    – Article By O. Adewale Osipitan, Brad Hanson, Matthew Fatino & Mohsen Mesgaran (UC Cooperative Extension)

  • New Targets for Huanglongbing Treatments

    Scientists are closer to gaining the upper hand on a disease that has wiped out citrus orchards across the globe. New models of the bacterium linked to the disease reveal control methods that were previously unavailable.

    Metabolic models of organisms are like road maps of cities. “They show you all the biological processes, and how they work together,” said UC Riverside microbiology professor James Borneman. “They also show you which molecular pathways, if blocked, will kill the organism.” 

    Simplified metabolic model and its striking similarity to a road map. (Metallo&Vander Heiden)

    In this case, researchers created the first models of the bacterium associated with Huanglongbing or HLB, also known as citrus greening disease. The team’s work is described in a new paper published in Nature’s npj Systems Biology and Applications.

    The research team made models for six different strains of the bacterium known as CLas and doing so enabled them to identify as many as 94 enzymes essential for the bacterium’s survival. These enzymes can now be considered targets for the creation of new antibacterial treatments.

    In addition, the team identified metabolites required for the bacteria to grow.

    “Just like when humans break down the food they eat into small components called metabolites, which feed our cells, bacterial cells also require metabolites for their growth,” Borneman said.

    Knowing the metabolites needed for CLas’ growth could enable scientists to cultivate it in a laboratory setting. It is not currently possible to grow CLas on its own, hindering scientists’ ability to study it and ultimately to manage it.

    This research project involved a collaboration between UC Riverside, UC San Diego, Texas A&M University, and the U.S. Department of Agriculture. In addition to Borneman, members of the modeling team included UCR plant pathologist Georgios Vidalakis and UCSD systems biologist Karsten Zengler.

    UC Riverside is at the forefront of efforts to combat Huanglongbing. Other important areas of research include antibacterial development and delivery, immune system fortification in citrus, engineering resistant citrus via a detailed understanding of host-microbe interactions, breeding resistant citrus, and insect management, among others.

    Because microbes tend to mutate and acquire resistance mechanisms in response to drugs and other efforts to thwart them, Borneman cautions that any one solution to the problem may be short-lived.

    Transmission electron microscope image of CLas bacterium. (J.M. Bové/INRA)

    “Microbes almost always adapt to control measures, perpetuating the ‘arms race’ between pathogens and hosts,” Borneman said. “There won’t be one thing that will fix this disease. We likely will need to address all three components associated with the disease — the bacterium, the insect that transmits it, and the citrus plants — to find a long-lasting solution.”

    To that end, the research team is constructing metabolic models of citrus and the insect, the Asian citrus psyllid.

    “We expect that this multiorganism modeling endeavor will provide new insights into the mechanisms underlying this disease, which will lead to effective and sustainable Huanglongbing management strategies,” Borneman said. — By Jules Bernstein, UC Riverside

  • Barking Up the Right Tree: Canines Detect HLB

    In September 2019, huanglongbing—also known as HLB or citrus greening—was detected in residential citrus trees located in Ventura County, in southern California (and just recently, the first HLB carrying Asian Citrus Psyllid was detected in a commercial CA citrus grove).

    During an orchard review in California, expert detector dog, Szaboles alerts his trainer by sitting next to a citrus tree infected with Huanglongbing (HLB).

    The disease, which has no known cure, is caused by a bacterium that devastates citrus plants and is transmitted by psyllids (small plant-eating insects resembling lice) that carry the bacteria from tree to tree or by the grafting of infected plant material. Common symptoms of infection include blotchy mottling of entire leaves, premature defoliation of the tree, and fruits that are usually small, with green peel at the bottom and a bitter taste. Unfortunately, these visible signs of HLB do not manifest until months or even years after the initial infection. By then, it is too late for citrus growers to save their crop from a mass infestation.

    However, the Farm Bureau of Ventura County found a rather unconventional way around this problem.

    To contain the infected trees and prevent a citrus epidemic, the Farm Bureau decided to hire a team of detector dogs specially trained to find HLB bacteria. The dogs are a result of a unique program funded by USDA and run by Agricultural Research Service (ARS) Research Leader and Plant Pathologist Timothy Gottwald (now retired) at the U.S. Horticultural Research Laboratoryin Fort Pierce, FL.

    First, the clever canines patrolled the perimeter because the edges of a grove are where the disease would first accumulate. Then, they trotted through the grove of trees to ultimately identify over 200 infected trees from a grove of 3,500.

    According to Gottwald’s research, the canine-detection method has an accuracy rate of 99 percent. While humans need several minutes to visually examine each tree and collect samples for laboratory testing (which requires considerable lab time and supplies), the dogs can travel through groves of trees in mere minutes, sensing HLB-infected trees by smell faster and far more easily. The time saved in finding the disease earlier gives citrus growers the opportunity to remove and destroy or quarantine HLB-infected trees, controlling what could’ve been a severe outbreak and loss of crop.
     

    However, there are still some considerations to keep in mind when deploying the canines as an early detection technology. Each dog team can only work 30 minutes at a time before they must rest, and a new team takes over. Teams can work for about 6 hours a day. In addition, much like any lab equipment, dogs are periodically calibrated to the HLB “scent signature” to remain finely honed optimized detectors.

    Still, the dogs are more sensitive and accurate than any other available technology in the field. The employment of detector dogs is still a voluntary program, which means fruit growers and farmers have the choice to either use dogs to find HLB early or continue using a USDA-approved DNA test called polymerase chain reaction (PCR).

    “While PCR is an effective way to detect infections, it isn’t efficient,” Gottwald explained. “It’s difficult to pinpoint incomplete infections—or infections that are only on one part of a plant (for example, a single leaf out of an entire tree with possibly thousands of leaves)—using PCR because it requires numerous samples from all over the suspect specimen.”

    “On the other hand,” Gottwald continued, “detector dogs identify pathogens ‘holistically,’ easily locating minute infections regardless of what small part of the tree they are infecting.” With this increased scope and accuracy rate, Gottwald and his colleagues believe that the canines’ abilities will revolutionize how growers protect their crops.

    “These specially trained canines may also be used to detect diseases and infections in other fruits and vegetables, such as grapes, peaches, plums, and tomatoes,” he said. “Our research has shown that they can sense pathogens like plum pox virus or squash vein yellowing virus, which both can cause severe economic losses to agriculture industries.”

    The canine-detection method was validated in blind tests by USDA ARS in collaboration with the California Department of Food and Agriculture, with results published in 2020.— By Georgia Jiang, USDA-ARS

  • CLas-positive Asian Citrus Psyllid Found in Riverside Commercial Grove

    An Asian citrus psyllid (ACP) sample – confirmed positive for Candidatus Liberibacter asiaticus (CLas) the bacteria that causes Huanglongbing (HLB) – was collected from a commercial citrus grove in the Woodcrest area of Riverside County. Confirmed by Citrus Research Board’s Jerry Dimitman Laboratory, this single adult psyllid is the first CLas-positive ACP found in a commercial citrus grove in California.

    While a positive ACP detection in a commercial grove is cause for serious concern, as of today, HLB has not been detected in any California commercial groves. That said, it is more crucial than ever that we stop the disease from spreading by eradicating the Asian citrus psyllid in commercial groves. The cost to manage the Asian citrus psyllid is far less than any potential costs or loss to the industry should HLB take hold throughout our state.

    An expansion of the HLB quarantine zone will not be established as a result of the CLas-positive ACP detection and CDFA staff is swiftly conducting surveys and collecting samples per the ACP/HLB Action Plan  from the perimeter of all commercial groves and all residential HLB host plants that are located within a 250-meter radius around the find.

    While treatment is not mandatory as a result of the detection, all growers within 250-meters of the find site will be notified to apply insecticides to all HLB host material within the designated area with materials recommended by the University of California (UC).

    Currently, the best way to stop the disease from spreading is to stop the ACP. To stop the ACP, we must restrict its movement and suppress existing psyllid populations. It is critical to follow best practices and review recommendations from the UC on how to protect commercial citrus groves from HLB. Regulations are in place to help prevent the spread of the pest and disease. All growers, packers and haulers must comply with all California Department of Food and Agriculture, county and federal regulations, including quarantines.

    Growers in Riverside County may contact the County Agricultural Commissioner’s office or the CDFA Pest Hotline at 800-491-1899 for additional information. If you see or suspect ACP or HLB symptoms in your grove, please notify the CDFA hotline. – By the Citrus Pest & Disease Prevention Program

  • Research Gives Possible Answers to Increase Pollinator Populations on Farms

    Many living creatures live in soil. Though their sizes range from microscopic soil microbes to larger animals like gopher turtles, they all call soil their “home.” Included in these ground-dwelling species are bees – vital in the pollination cycle of about 90% of plant life.

    Rebecca Lybrand and her team at Oregon State University are studying the interaction between the bees and soil in agricultural settings.

    According to the recently-published paper, bees contribute $15 billion to crop value annually. They pollinate about three-quarters of the fruits, vegetables, and nuts within the United States alone. Declines in honeybee colonies are a critical threat to agriculture and the global food supply.

    “Growers who are interested in attracting alternative pollinators, such as wild bees, face a major challenge,” says Lybrand. “There are not many studies about what habitats are best for these wild bees.”

    Pollinators are widely affected by human land use. Creating buildings, parking lots and other “anthropogenic changes” disrupt the natural habitats of animals and plants. Agricultural disturbance also affects bee communities. Interestingly, above-ground bee species are nine times more affected by agricultural intensification than ground-dwelling species.

    In some cases, growers have been able to build “bee beds” in their farm setting. In the 1950s, they started to design moist, salty soil areas to attract ground-nesting bees that helped increase alfalfa yields in Washington state.

    Lybrand’s study looked at physical and chemical properties of soils collected from active bee and sand nest wasp sites in the Willamette Valley of western Oregon. They compared soil properties among seven farm sites to identify similarities and differences.

    The Willamette Valley has wet winters with warm, hot summers. The team first found agricultural sites that contained ground-nesting bees. They collaborated with farmers who observed ground-nesting bee activity around their fields.

    The nests are only identified by rather small holes (only 3-5mm). The team only collected data if they observed bees entering the nest. Nests and holes can remain even after the bees leave. At the study site, they specified the type of bee to the family level (i.e. “bee” versus “genus” and “species”.) But they also collected some bees to bring back to the lab for further identification.

    The data the team collected in the field included soil temperature, pH, and soil texture. They also collected soil samples to bring back to the lab for analysis.

    Findings from the study included that active nesting sites were present in locations with little to no rock cover and low vegetation. Nesting sites were found in areas with low organic matter coverage. The slope of the land didn’t seem to have any influence, nor did a north/south-facing aspect.

    “One of our observations confirmed that active emergence holes remained open throughout the year,” says Lybrand. “They didn’t swell shut during the wetter, cooler seasons – despite having clay in the soils that might cause shrinking and swelling.”

    An interesting finding from the research is that the team found lipids in the soil nest linings. The lipids may provide a type of waterproofing for the nests and their inhabitants.

    “Because the large majority of wild bee species nest in the soil, studies about how to best attract them to farms are important,” says Lybrand. “Soil scientists and entomologists can partner with growers to identify soil habitats that support and attract more of these pollinators to agricultural lands. Improving our understanding of the connections between agriculture and the soils that bees, crops, and living organisms rely on to survive is important. Our research also provided a framework for studying ground-nesting organisms – an area of soil science that is underrepresented.”

    Looking to the future, Lybrand says, “future research should also integrate methods that identify bees and/or wasps to the species level. That would allow for interpretations of the results from an ecological point of view. Another question to follow up on could be the nature and purpose of the lipids found in the soil nest linings, to confirm their actual role.”

    This research was published in Soil Science Society of America Journal. Funding for this project came from an Agricultural Research Foundation grant via Oregon State University.

    American Society of Agronomy, Soil Science Society of America, Crop Science Society of America: Collectively, these Societies represent more than 12,000 individual members around the world. The scientists’ memberships build collaborating partnerships in the agronomy, crops, and soils science fields for the advancement of knowledge.