California Ag Network

Tag: Andreas Westphal

  • How to Annihilate Nematodes

    Farmer John Chandler lamented the loss of methyl bromide for replanting an orchard or vineyard. Photo credit: Diana Gutierrez

    Andreas Westphal, scientist at Kearney Agricultural Research and Extension Center in the San Joaquin Valley, organized a soil plant pathology conference that was held late last month. Growers from as far away as Virginia came to learn about the latest research findings.

    Chandler Farms

    The first day of the conference was a field tour to three sites and then Kearney itself. After meeting at Kearney, the participants rode on a tour bus to Chandler Farms in Selma. John Chandler, his brother Tom and their father, Bill operate a diversified farm that includes almonds, grapes and citrus.

    Soil Fumigants

    The Chandlers typically change out one field per year. John lamented the loss of methyl bromide for replanting an orchard or vineyard. He now uses Telone, which he finds “has less effect but still works.”

    He always contracts out his Telone application because it requires special training. He has the contractor put tarps over it, beyond the usual seal — to prevent off-gassing — but he says, “It’s not worth it to get acres of plastic.” The tarps add about $1000/acre to the cost.

    Westphal explained, though, that Telone is becoming more difficult to use because of a new restriction in the amount of Telone allowed plus a requirement that the fumigant be applied with lots of water. The new regulations say that the soil has to be wet to 2 feet depth. If the soil is bone dry, three inches of water must be added within 72 hours before applying the fumigant.

    However, the excess water makes it hard to get a tractor through the field. Also, the fumigant does not move well through water, as it is made to move through air. Lastly, the Telone stays in wet soil longer before vaporizing off, which may make it toxic to plants.

    Nematodes     

    Chandler said that his farm has nematodes — the microscopic roundworms that feed on plant roots. His soil has root-knot, lesion, ring and citrus types of nematodes.

    When he can afford it, he fallows the land for a year or two instead of fumigating, but he says that fumigation gives the plants the best chance to get started. Once the crop is established, he notes, there are few tools for nematode adjustment.

    In his Ruby Red grape concentrate vineyard, Chandler finds that ring nematodes like the wettest part, whereas other types of nematodes prefer the edges, where they feed on the fresh, new roots.  Ring nematodes, he finds, like pure sand, but root knot nematodes thrive most in clay soil with good secondary structure.

    The tour participants had many more questions for Chandler, but to stay on schedule, Westphal guided everyone back onto the tour bus.

    Burchell Nursery

    The second stop was Burchell Nursery in Fowler, where Mauricio De Almeida led the group around the almond, stone fruit, citrus, pomegranate, and retail table grape plants.

    What Is Eating the Plant Roots?

    Almeida said that, as in all greenhouses, the water, heat and humidity may induce root rot and fungus gnats. The fungus gnat larvae eat soft tissue of the plant roots. The adults do not feed on plants.

    Another larva that needs to be managed is that of the European pepper moth. The caterpillars girdle the plant stem below the soil line.

    The root rot and insect pests occur even though the potting media — made of peat, bark, wood fiber and sometimes Perlite — comes pasteurized. The nursery uses Nemasys® beneficial nematodes to manage the larval insect pests.

    Citrus

    Almeida explained that Burchell Nursery started growing citrus in 2010. They grew the citrus indoors to protect the trees from the Asian citrus psyllid. Westphal remarked that if you grow bareroot trees in the field, the soil must be certified nematode-free or else the trees themselves must get tested for nematodes. He also said that you cannot fumigate after pulling up the plants because the fumigant would kill the tree.

    Among other species, Burchell Nursery sells commercial almond trees, including some cultivars they developed themselves. Photo credit: Tiffany Baiocchi

    Almonds

    In almonds, Bright’s Hybrid 5, Hansen and Viking rootstocks and Shasta scions resist root-knot nematode. Viking and Shasta also tolerate ring nematodes. Bright’s Hybrid also has low susceptibility to root lesion nematodes. In susceptible varieties, root-lesion nematodes create lesions that can lead to secondary infections like bacterial canker.

    The visitors got to see the Cornerstone cultivar of Prunus rootstock, developed by Burchell Nursery to resist the root knot nematodes Meloidogyne javanica and M. incognita. Used as rootstock for almond and stone fruits, Cornerstone is also less sensitive to crown gall, caused by Agrobacterium tumefaciens.

    Developed by Burchell Nursery, the Cornerstone cultivar of Prunus rootstock is resistant to the root knot nematodes Meloidogyne javanica and M. incognita and less sensitive than other rootstocks to crown gall, caused by Agrobacterium tumefaciens. Cornerstone can be used as rootstock for almond and stone fruits. Photo credit: Tiffany Baiocchi

    Unfortunately, in both Kern and Merced counties (but not Fresno County where the tour took place), in 2018 a root-knot nematode from Florida, Meloidogyne floridensis, was found in almond trees on Hansen 536 and Bright’s Hybrid 5 rootstocks, where they caused growth decline of the trees. Now considered an A-rated (“highest concern”), quarantined pest in California, it has since been found in South Carolina and Georgia, after being endemic to Florida before 2018.

    Levels of Plant Response to Pathogens

    Plants can be divided into three groups of responses to nematodes and other pathogens: sensitive, tolerant and resistant. Tolerance allows for high nematode populations, which gives the nematodes more opportunity to have genetic mutations that enable them to overcome the plants’ resistance. Therefore, nematicides should be used in tolerant cultivars to limit the pest population.

    Grapevines  

    In a vineyard section of the research fields, Westphal showed a poster of nematodes in the soil profile. Of the three types of nematodes represented, ring nematodes were found only in the top foot of soil.

    By contrast, citrus and pin nematodes were found in each one-foot segment down to 4-5 feet, the deepest tested. The citrus nematode population peaked at 2-3’ depth and pin nematodes peaked at 3-4’ depth. The population of pin nematodes far exceeded those of ring and citrus nematodes at all depths. Fortunately, pin nematodes do not cause much economic damage in grapes.

    Westphal also showed a poster of total sugar yield in 2025 of Pinot Gris cultivated on different rootstocks planted in 2023 in nematode-infested soil. The negative impact of nematodes was measured as sugar content of the fruit.

    Of the seven commercial grapevine rootstocks tested, Freedom had the highest sugar content. An experimental rootstock had even higher sugar content. Serving as control groups, Chardonnay and Zinfandel rootstock had the lowest sugar content.

    “On sensitive rootstock, even a few nematodes are bad,” Westphal remarked. About 85% of all new grapevine plantings are on Freedom rootstock. Freedom’s downside is susceptibility to quick decline, so the search continues for an even better rootstock.

    In sugar beets, the exudate from plant roots helps nematodes find the roots. Westphal and colleagues are looking into the possibility of manipulating plants to exude different chemicals that do not attract nematodes.

    Walnuts and Almonds

    Walnuts are sensitive to some nematodes and resistant to others, but “every plant has its limits,” Westphal said. Walnut soil is treated pre-plant and at-plant at the planting site.  Tank water is used to settle the tree in. Salibro® is added to the tank water to form a concentration that kills the nematodes but not the trees. Westphal cautioned growers to not overwater walnuts.

    Among other things, Westphal is testing juice from walnut hulls to see if they inhibit nematodes.  He noted that ASD (anaerobic soil disinfestation), created by applying nine tons of rice bran per acre, inhibited nematodes somewhat. However, it would not be worth the $6,000/acre price tag for growers.

    Westphal is testing whether juice from walnut hulls can inhibit nematodes in almond orchards.

    Highly resistant rootstocks can grow without fumigation, with less toxic, affordable nematicides applied.  As with citrus, nursery trees must be grown in nematode-free soil, or the trees must be certified before leaving the premises.

    Westphal showed the tour participants an almond rootstock test orchard, in which nematode resistance is compared among various commercial and experimental rootstocks.  Only the most successful experimental rootstocks make it to the next round of trials, along with the commercial ones for comparison.

    Westphal then concluded the field tour.  The conference continued in an indoor classroom on the following two days.  

    – By Nancy Power, Assistant Editor

  • Nematode Management Tips for Tree Nut Growers

    Nematodes can be a headache for growers. Luckily, ways to manage them are being researched and developed. At the Malcolm Media Tree & Vine Expo and in an interview with Matthew Malcolm on California Ag Network, Andreas Westphal with UCCE Riverside discusses nematode management. Watch this quick video and learn more in Pacific Nut Producer Magazine.

  • Fumigation Considerations Before Replanting an Orchard

    It’s that time of the year when orchards are being pulled and growers begin preparing their soil for future plans.  For growers looking to replant their orchards, watch this brief interview with UC Riverside Nematologist Andreas Westphal as he shares some considerations to take for fumigation when it comes to nematode pressure.

    Please thank this video’s sponsor Suterra for their industry support.

  • A New Microscopic Almond Pest of Concern

    Another pest in almonds? Just what we needed, right? Only this one you can’t see.  Almond growers have been dealing with nematodes for a long time; however, the peach root knot nematode is new to California almond orchards.  Watch this brief interview with UC Riverside Nematologist Andreas Westphal as he explains and read more about it in Pacific Nut Producer Magazine.

    Please thank this video’s sponsor Trece for their industry support.

  • New Ways of Managing Plant-Parasitic Nematodes Under Study

    Walnut production is most productive on deep-rooting uniform soils with good water-holding capacity. Such soils are also conducive to infestations of plant-parasitic nematodes. Currently, the key pest of concern in walnut plantings is root lesion nematode (Pratylenchus vulnus). In California, this nematode is wide-spread in walnut producing areas and is estimated to be present in almost 85% of walnut orchards.

    Because of the longevity of a walnut planting, even barely detectable nematode numbers can cause damage to the traditional rootstocks in the life span of an orchard. English and Paradox rootstocks are susceptible to root lesion nematode. Other nematodes, root-knot nematodes (Meloidogyne spp.), can cause damage to English rootstocks. The third species frequently present in walnut soil is ring nematode (Mesocriconema xenoplax) but its damage potential has not been as well documented as for the lesion and root-knot nematode.

    Plant-parasitic nematodes entirely depend on their host plants to sustain themselves. They can injure root tissues directly, and also consume photosynthetic nutrients that otherwise would be used for plant growth and nut production. Trees of all ages are susceptible, but newly planted and young trees are especially sensitive. In addition, the so-called replant problem, a biologically-incited disease that is poorly understood, can hinder the establishment and growth of new plantings.

    Nematode problems become most challenging when an old orchard is removed and replanted. Under these conditions, the succumbing trees may have left behind huge numbers of the soil-dwelling parasites without symptoms the grower associated with nematode damage. When the young trees are exposed to these high populations, they can be severely damaged. Soil sampling for nematode evaluation when replacing an orchard should be standard practice.

    For decades, methyl bromide was used to mitigate these challenges. This material has properties that allow its injection and gaseous redistribution in different soils, and thus was effective in various soil types and soil conditions. Since methyl bromide was banned in 2005, control options have relied heavily on 1,3-D products (Telone) and mixes of 1,3-D and chloropicrin. These are suitable soil fumigants under appropriate soil conditions, especially the soil moisture must be adjusted to the required range, and soil temperatures needs to be in the proper range. Soil preparation including deep-ripping (at least 5 ft) for alleviating obstructive soil layers and removal of old roots is even more important in a 1,3-D fumigation than it was when treating with methyl bromide. Achieving these conditions is more challenging on fine-textured soils. Many growers resort to cover cropping with, e.g., a winter annual grain crop to remove excess soil moisture during the spring and summer before fumigation is performed. Reaching highest levels of performance despite all these preparations may still be a challenge. Use of 1,3-D fumigation is restricted to a maximum annual amount that may be used under a so-called “township cap”.

    Clearly, more sustainable methods of nematode management in walnut orchards are urgently needed. Three main avenues are currently being researched at the Kearney Agricultural Research and Extension Center: (a) development of walnut rootstocks with elevated resistance or tolerance to root lesion and other plant-parasitic nematodes, (b) implementation of chemical nematode suppression using novel nematicidal chemistries, and (c) biorational methods that rely on the use of organic amendments and cover crops for nematode suppression.

    Development of nematode-tolerant walnut rootstocks is an ongoing program inherited from the long-term efforts at the Kearney Agricultural Research and Extension Center. With the knowledge leap of mastering the in vitro production of new inter-species Juglans crosses, it has become possible to produce saplings originating from cross breeding. This process allows for a much improved and accelerated breeding because many plant copies can be easily made for testing of desirable tree genotypes. The nematode tolerant rootstock ‘VX211’, Phytophthora root rot resistant ‘RX1’ and the vigorously growing ‘Vlach’ are early examples of new rootstocks developed using this approach. A team from the University of California, USDA-ARS, California State University Fresno and UCANR has come together to work on rootstock improvement. Genetically diverse walnut material is produced by the breeder and given to plant pathologists, the nematologist, and physiologist for concomitant examination for desirable rootstock and scion-compatibility traits. In the nematology program, trees are planted to field plots, inoculated with root lesion and root-knot nematodes and monitored for at least two years. At that time, nematode numbers in the roots and multi-year plant growth data are used to identify elite selections that are then transplanted from the original selection orchard and further monitored for vigor and nematode dynamics. Two years after transplanting, trees are grafted to the scion ‘Chandler’ to examine graft compatibility in parallel to the root evaluations. This program has been successful in identifying advanced elites that outperform currently used clonal rootstocks under high nematode and replant problem pressure. In winter 2018, a collection of elite nematode-, Phytophthora-, and crown gall-resistant selections was planted at the Kearney Agricultural Center in Parlier, and more trees are scheduled to be planted this spring at the Nickels Soils Laboratory near Arbuckle.

    The second approach that is pursued is evaluating novel nematicidal chemistries for their activity against nematodes that affect walnuts. After many years of having few new products available for testing, several new products have recently become available. In general, these materials are much safer for the user and the environment than the old compounds were.

    The application of traditional preplant soil fumigants was relatively simple compared to newer non-fumigant products. A large tractor could apply traditional products using shanks to deliver the material to the proper soil depth. Gaseous redistribution of the material fostered good soil penetration and nematode suppression. The non-fumigant character of the new chemistries requires delivery to the site of action. This is most efficiently accomplished by a 6 acre-inch preplant water drench via a drip irrigation system. Some of the compounds need to be applied underneath a tarp for user and bystander protection. While this process is logistically challenging, it does offer promise because only a few pounds of active ingredient per acre are effective in killing nematodes compared to several hundred pounds of the old traditional materials.

    In post-plant situations, the newer products are less cumbersome to apply than preplant situations partially because existing irrigation systems may be used. Typically, lower amounts of materials are applied that do not result in the high mortality required of preplant treatments but even modest population reductions (for example, around 50%) in established orchards can improve tree growth and productivity. After several years of field testing of the new chemistries at Kearney, CWB-supported work is now underway in commercial orchard field trials.

    Lastly, novel organic amendments and cover crops for nematode suppression are tested. Large amounts of organic waste material accrue from various sources in California and novel ways of using them – or products derived from them – are coming on line. In California, a recent focus of this research has been on exploiting novel characteristics of anaerobically digested food waste and animal manures. The fermentation process is implemented for biogas and ultimately bioenergy production. The finding that some of the by-products of this process, called digestates, can suppress plant-parasitic nematodes, while also serving as a nutrient source, is being explored in walnuts and other nut crops.

    Strategies that rely on processes that occur within the field are also under study. In anaerobic soil disinfestation (ASD), large amounts of organic substrate (typical 9 tons/acre of rice bran or other organic material) are spread on the soil surface, incorporated, and the soil kept moist under tarp for about one month after an initial complete soil saturation. This method is logistically challenging but has shown high levels of efficacy when preparing nursery sites for planting. Another approach shown to effectively suppress nematode populations is “biofumigation”, in which Brassica crops such as various mustards or radishes are planted and subsequently incorporated into the soil. Using similar Brassica crops as “companion crops” within walnut orchards also takes advantage of the capacities of these crops. Planted after harvest close to fall rains, cover cropping with cool-season Brassica can be a straight-forward process with few logistical challenges. The hope is that the Brassica species reduces nematode infestation by trap cropping the nematode pests or by actively reducing the populations via root exudates.

    In summary, with CWB support, a multi-pronged approach is investigated to alleviate the devastating impacts of plant-parasitic nematodes in walnuts. These studies are often highly collaborative with other experts of walnut production. The goal is to increase profitability and sustainability of walnut production while reducing its environmental impacts. This work is made possible by the gracious industry and government agency support coupled with the efforts of a highly dedicated nematology team, support from the University of California – Agricultural and Natural Resources, and the generous cooperation of grower and farm advisor collaborators.

    By Andreas Westphal, Department of Nematology, University of California, Riverside, Parlier, CA

    Plant Parasitic Nematodes
    Walnut rootstocks growing in root lesion nematode-infested soil in a walnut replant site. Standard clonal rootstock on the left, new selection on the right.

  • Supreme Raisins a Hit at the UC Kearney Grape Day 2017

    Kearney, Calif., (August 21, 2017) – Excitement over the new Sunpreme raisins was evident at UC Kearney Grape Day Aug. 8, 2017. As soon as the tram stopped, dozens of farmers and other industry professionals rushed over to the vineyard to take a close look and sample the fruit. Raisins pulled from the vine were meaty with very little residual seed. The flavor was a deep, sweet floral with a muscat note.

    Sunpreme raisins drying on their own in a Kearney vineyard.

    Sunpreme raisins, bred by now-retired USDA breeder David Ramming, promise a nearly labor-free raisin production system. Traditionally, raisins are picked and placed on paper trays on the vineyard floor to dry. The development of dried-on-the-vine varieties opened the door to greater mechanization. Workers would cut the stems above clusters of grapes, which then dry out in the canopy and are harvested mechanically. The new wrinkle with Sunpreme is that grapes ripen and then start to dry on their own – no cane cutting needed.

    UC Cooperative Extension viticulture specialist Matthew Fidelibus and UCCE viticulture advisor George Zhuang are now studying the performance of Sunpreme grapes on different rootstocks and trellis systems at the UC Kearney Agricultural Research and Extension Center.

    UCCE specialist Matt Fidelibus is conducting rootstock and trellis system experiments on Sunpreme raisins.

    “We didn’t know a lot about this variety,” Fidelibus said. “We’ve found it to be very vigorous.”

    Fidelibus said the raisins take about a month to dry, and one challenge is the tendency for dried raisins to drop off the vine.

    “We want to keep the self drying and stop self dropping,” he said.

    Ramming discovered the Sunpreme variety in a Thompson seedless table grape variety trial in the mid-1990s. He was going down the row, saw clusters of raisins and screeched to a stop. He had discovered Sunpreme. The variety is not yet available for commercial production.

    Fighting nematodes with new solutions

    Also during Grape Day 2017, UC Cooperative Extension nemotology specialist Andreas Westphal outlined research underway to keep nematodes at bay.

    “There’s no methyl bromide in commercial planting,” Westphal said. The very effective fumigant was banned because of it’s tendency to deplete ozone in the atmosphere and the risk to human health because of its toxicity. Many farmers have turned to Telone as an alternative, however it is expensive and its use is limited by a township cap.

    Westphal is comparing alternative treatments for clearing the soil of the tiny worms that feed on vine roots and inhibit vineyard productivity.

    “Some companies are coming up with new chemistry,” Westphal said. “Our challenge in the perennial world is that the roots go so deep.”

    Seven new products and Telon were drenched in different replicated research plots. Some areas were left alone to serve as control. Three times the number of Sauvignon Blanc vines were planted in the plots compared to a typical vineyard so researchers could take out plants twice and examine the roots for evidence of pests.

    “We are excited to see significant growth differences among the treatments,” Westphal said, pointing out a row that was visibly shorter and less vigorous. “It amazed me. Three years after treatment, and it never grew back out of it.”

    Work is still ongoing, but Westphal said he believes some chemical treatment could be available in the future to help reduce nematode pressure.

    To deal with nematode populations, Westphal encouraged growers to sample soil and communicate with the diagnostic laboratory to determine what pest nematodes are in their vineyards, and then use that information for root stock selection.

    “Growers should not forget the value of nematode-resistant rootstocks,” he said. “Plant material needs to be chosen very carefully when different species of nematodes are present.”

    UCCE viticulture advisor emeritus George Levitt, left, chats with retired USDA breeder David Ramming at Grape Day 2017.