Commercial Walnut Research Articles

Response of walnut aphid populations to increasing foliar nitrogen content

An understanding of how fertilizer input affects pest populations and, consequently, the need for pesticide use would allow for the development of more effective integrated management strategies. 2 The present study addressed the response of walnut aphid Chromaphis juglandicola (Kaltenbach) (Hemiptera: Aphididae) populations to different levels of nitrogen application to walnut seedlings and the relationship between aphid density and chlorophyll content index (CCI), a non-invasive measure of foliar nitrogen, for mature trees in commercial walnut orchards. 3 Although added nitrogen significantly increased soluble nitrogen content, CCI and soluble nitrogen : phosphorus ratios in the foliage of walnut seedlings, there was no effect on walnut aphid population growth. Similarly, there was no relationship between aphid density and CCI for mature trees in the field. 4 A neutral response suggests that walnut aphid population growth on potted seedlings is limited by factors other than soluble nitrogen, such as other nutrients, amino acid composition or defensive compounds. Consequently, fertilizer management appears unlikely to effectively contribute to the control of

Stable Mixed Beverage is Produced from Walnut Milk and Raw Soymilk by Homogenization with Subsequent Heating

Walnut milk, which is generally produced in the presence of stabilizers by homogenization, is being increasingly consumed by people in China, due to its good nutritional and functional properties. In this study, the mechanism behind the poor dispersion stability of walnut milk without stabilizer has been clarified as caused by heat-induced large aggregate formation from walnut oil bodies and protein. It was found that addition of raw soymilk into walnut milk could result in the stable mixed beverage by homogenization with subsequent heating. This was because raw soymilk played roles on decreasing the particle size of walnut oil bodies during the homogenization, and preventing the large aggregate formation from walnut oil bodies and protein during the subsequent heat treatment. Amino acid analysis showed that the stable mixed beverage contained more lysine than the walnut milk. In addition, the stable mixed beverage had higher levels of protein content (about 2%) than the commercial walnut milk (commonly < 1%) in China. Therefore, this study was meaningful for the convenient and value-added utilization of walnut.

Resistance to Phytophthora and Graft Compatibility with Persian Walnut among Selections of Chinese Wingnut

Seedlings from seven open-pollinated selections of Chinese wingnut (Pterocarya stenoptera) (WN) representing collections of the USDA-ARS National Clonal Germplasm Repository at Davis, CA, and the University of California at Davis were evaluated as rootstocks for resistance to Phytophthora cinnamomi and P. citricola and graft compatibility with scions of five cultivars of Persian walnut (Juglans regia). Seedlings of Northern California black walnut (NCB) (J. hindsii) and Paradox hybrid (PH) (typically J. hindsii × J. regia) were used as standards. In greenhouse experiments, potted plants of the rootstocks were subjected to intermittent flooding in soil artificially infested with the pathogens. All WN seedlings were relatively resistant to the pathogens (means of 0% to 36% of root and crown length rotted) compared with NCB (44% to 100%) and PH seedlings (11% to 100%). Negligible disease occurred in flooded control soil without the pathogens. In 9-year graft compatibility trials in an orchard, NCB and PH rootstocks supported relatively good survival and growth of all tested scion cultivars (‘Chandler’, ‘Hartley’, ‘Serr’, ‘Tulare’, and ‘Vina’; final scion survival 80% to 100%, mean scion circumference increase 292 to 541 mm), whereas results with WN were mixed. Wingnut rootstocks from all sources were incompatible with ‘Chandler’ (final scion survival 20% to 60%, scion circumference increase 17 to 168 mm). Conversely, all WN rootstocks from all sources were compatible with ‘Tulare’ and ‘Vina’ (final scion survival 80% to 100%, scion circumference increase 274 to 556 mm). Use of the WN rootstocks produced variable results in ‘Hartley’ and ‘Serr’ (final scion survival 10% to 100%, mean scion circumference increase 69 to 542 mm). There was a tendency for more rootstock sprouts on WN selections than on NCB or PH. In a commercial walnut orchard infested with P. cinnamomi, ‘Hartley’ survived and grew markedly better on WN selections than on PH. High resistance to P. cinnamomi and P. citricola was common to all of the WN selections. The results indicate that WN selections may be useful rootstocks for cultivars Tulare and Vina in soils infested with P. cinnamomi or P. citricola and that WN selections may contribute valuable resistance to these pathogens in walnut rootstock breeding efforts.

Season, Weather, and Habitat Effects on Mourning Dove Nest Density

We examined key factors thought to influence Mourning Dove (Zenaida macroura) nest density (nests/ha) in Blue Oak woodlands (Quercus douglasii), riparian woodlands (Salix spp., Populus fremontii), and commercial walnut (Juglans spp.) orchards in northern California (north of UTM: Zone 51N, 324397E, 4207703N, datum WGS84). We hypothesized that nest density could be used to characterize the suitability of habitats for breeding Mourning Doves because nest success has often been shown to not vary predictably by habitat type. Because weather does affect nest success, we examined the influence of spring rainfall and ambient temperature, as well as habitat on nest density. We recorded all Mourning Dove nests found in surveys conducted every 3rd wk from mid-April to mid-August, which encompassed the nesting season, in each of 6 to 10 randomly placed survey plots in each of 4 study areas during 1992–1995, with a supplemental survey during September 1994. Survey date, habitat type, and spring weather affected period nest density (PND; mean number of all active nests/ha present during any given survey); and habitat type and weather affected cumulative nest density (CND; total number of different nests produced annually/ha). Seasonally, PND was relatively low in April, high from May to July, lower in August, and zero by September. Riparian woodlands tended to support higher PND and CND compared to walnut orchards and Blue Oak woodlands in that order. This effect was pronounced during the warm-dry springs of 1992 and 1994, but was not always evident during the relatively cool-wet springs of 1993 and 1995 (weather characterized relative to April mean high temperature and March to May mean rainfall). The best predictive model (lowest AICC) for PND contained a quadratic trend with survey timing, and effects due to habitat type, high temperature and rainfall deviations from long-term average, number of rain-days, and tree density. The best model for CND contained habitat, temperature, rainfall, rain-days, and tree density. Nest success increased at a declining rate as nest density increased in Blue Oak and riparian woodlands, demonstrating probable density-dependent resource or mortality limits on nest success that did not affect nest density within the ranges we recorded. Nest density measures should be useful to land managers in assessing responses of nesting Mourning Doves to available nesting habitats and local spring weather.

WALNUT BLIGHT SUSTAINABLE MANAGEMENT RESEARCH IN NEW ZEALAND

Walnut blight Xanthomonas arboricola pathovar juglandis is the most significant pest or disease issue in New Zealand commercial walnut (Juglans regia) production. Typical management has involved selection of less humid regions and copper based sprays. Research in New Zealand has included determining cultivars that show a promise of lower blight susceptibility and investigation of the effect of timing and form of copper sprays. There has been no clear success in the use of adjuvants to improve the efficacy of copper based sprays and no effective alternatives to copper sprays elucidated in research to date. Mankocide had previously demonstrated improved efficacy over Kocide even at lower copper levels. In this research, there was no apparent benefit in incorporating extra Mancozeb with Mankocide to match the copper mole for mole with dithiocarbamate. The use of copper methionine as an alternative form of copper yielded low efficacy on walnut blight. Efficacy of copper sprays was reduced by using copper methionine as a form of copper. Bacteriophages of X. arboricola pv. juglandis have a demonstrated capability of lysing all New Zealand isolates of the pathogen that have been collected in preliminary work. The potential of bacteriophages as a biological control agent is discussed but there is a need for a reliable bioassay to progress research further.

INNOVATIVE METHODS OF WALNUT PRODUCTION IN SOUTH AMERICA

Chile and Argentina are the main walnut producers in South America. Chile has 14,400 hectares and Argentina nearly 18,000. The walnut areas are located in many valleys, along both countries. Growing conditions range from dry and warm climatic conditions, in the north, to rainy and cold summers in the south. In Argentina, where walnut groves are submitted to more extreme climatic conditions, they are present from Catamarca in the north, to Viedma in the south (a distance of close to 2,500 kilometers). In Chile walnut plantations go from Ovalle to Los Angeles (900 kilometers from north to south). All the production requires irrigation. Irrigation systems, and overcoming problems associated with this technology are very important in the success of this industry. In the same way, frost, wind, and rain damage are important production limitations that need to be managed. Both countries began commercial walnut industry when grafting methods were developed, beginning of the 1980's. In Chile patch budding is the most popular nursery system, but in Argentina, lateral grafting on 2- or 3-year-old rootstock is the most common way to establish a new orchard. The most important varieties in Chile are 'Serr' and 'Chandler', with a smaller area planted to 'Howard' and 'Vina' seedlings. Argentina has focused its industry mainly on 'Chandler'. 'Serr' in Chile requires avoidance of PFA (Pistillate Flower Abscission), which varies from 20 to 80% depending the season. Trials carried out in the country have substantially improved fruit production. Management methods for pruning and training, plant nutrition, irrigation, pest and disease control are well developed in South America. However, root and collar rot, walnut blight, codling moth and mites are permanent problems. Presently, no blackline or Armillaria problems are present in either country. Mechanical harvest and controlled dehydration are rapidly being developed, in order to export high quality walnuts to the Northern Hemisphere.

POTENTIAL IMPACTS OF THOUSAND CANKERS DISEASE ON COMMERCIAL WALNUT PRODUCTION AND WALNUT GERMPLASM CONSERVATION

Thousand cankers disease (TCD) is a recently identified insect/fungal disease complex responsible for mortality of eastern black walnut trees, Juglans nigra, planted in non-native areas of the western United States. The presence in California of both the insect vector, the walnut twig beetle, Pityophthorus juglandis, and the fungal pathogen, a species of Geosmithia, raises concerns regarding the potential impact of the disease on commercial walnut production and the long term health of other walnut species native to California and American Southwest. Movement of the disease eastward could threaten native J. nigra populations in hardwood forests of the eastern United States. Identification of both the vector and the fungal pathogen of TCD from trees in the USDA Germplasm Collection near Davis, CA may impact ex situ germplasm management.

Comparison of Two Commercial Walnut Skin Test Extracts

RATIONALE: After noting numerous negative skin prick test (SPT) results in patients with systemic reactions to walnut (WN), we sought to compare (SPT) results in patients allergic to WN using extracts from 2 different manufacturers.METHODS: Twenty-six patients ages 2-25 (mean 9 yrs) with documented systemic IgE-mediated allergic reactions to WN were identified. Simultaneous SPT were performed using commercial WN extracts from ALK Abello (Horsholm, Denmark) and Greer Labs (Lenoir, NC). SPT was placed on the forearm with Duotip-Test or Multi-Test II devices (Lincoln Diagnostics). All patients had positive histamine and negative saline control responses.RESULTS: SPT results were positive in all 26 patients (wheal 5-15mm, flare 15-60mm) using the Greer extract but negative in all patients tested using the ALK extract. Patients who had additional SPT using fresh WN (prick plus prick) also showed positive reactions.CONCLUSIONS: SPT is the most widely used testing method for screening patients with suspected IgE-mediated food allergy. Skin test extracts with poor sensitivity can result in disastrous consequences if clinical decisions are made solely on the basis of these results. Variability between different WN extracts could be due to differences in production methods such as protein solubilization, extraction and purification. Our results demonstrate striking differences in SPT results between Greer and ALK extracts among patients with WN allergy. These findings should alert physicians of the variable sensitivity of WN extracts among different manufacturers as well as raise similar quesitions about other commercial tree nut extracts. RATIONALE: After noting numerous negative skin prick test (SPT) results in patients with systemic reactions to walnut (WN), we sought to compare (SPT) results in patients allergic to WN using extracts from 2 different manufacturers. METHODS: Twenty-six patients ages 2-25 (mean 9 yrs) with documented systemic IgE-mediated allergic reactions to WN were identified. Simultaneous SPT were performed using commercial WN extracts from ALK Abello (Horsholm, Denmark) and Greer Labs (Lenoir, NC). SPT was placed on the forearm with Duotip-Test or Multi-Test II devices (Lincoln Diagnostics). All patients had positive histamine and negative saline control responses. RESULTS: SPT results were positive in all 26 patients (wheal 5-15mm, flare 15-60mm) using the Greer extract but negative in all patients tested using the ALK extract. Patients who had additional SPT using fresh WN (prick plus prick) also showed positive reactions. CONCLUSIONS: SPT is the most widely used testing method for screening patients with suspected IgE-mediated food allergy. Skin test extracts with poor sensitivity can result in disastrous consequences if clinical decisions are made solely on the basis of these results. Variability between different WN extracts could be due to differences in production methods such as protein solubilization, extraction and purification. Our results demonstrate striking differences in SPT results between Greer and ALK extracts among patients with WN allergy. These findings should alert physicians of the variable sensitivity of WN extracts among different manufacturers as well as raise similar quesitions about other commercial tree nut extracts.

AGROBACTERIUM-MEDIATED TRANSFORMATION OF A WALNUT CULTIVAR

A protocol for Agrobacterium-mediated transformation has been developed for shoots explants of the Paradox (Junglans bindsii x Junglans regia) walnut rootstock 'Vlach', which is one of the most used rootstocks for walnut. The effect of different kanamycin concentrations on regeneration was evaluated and complete inhibition from control explants was observed when 70 mg/L kanamycin was applied. Also, the influence of antibiotic on the growth of the regenerated buds, micropropagated shoots and rooting was tested. Limiting concentration of kanamycin for growth of buds and shoots was 100 mg/L, where all of them died. Rooting decreased from 58% rooted shoots without selection to 1.7% when 30 mg/L of kanamycin was applied. Kanamycin at different concentrations from 65 to 150 mg/L was assayed in transformation experiments. After inoculation of explants with the strain EHA105/p35SGusint, buds that were able to regenerate in selective medium were rescued and transferred to medium with 75 mg/L kanamycin for development of elongated shoots. Transformation efficiency, based on PCR analysis of individual putative transformed shoots, ranged from 0.7 to 2.7% when antibiotic concentration was between 75 to 65 mg/L. To our knowledge, this is the first report of transformation of a commercial walnut genotype.

The Walnut Industry in India-Current Status and Future Prospects

This paper provides a review of the current status of the walnut industry in India. The cultural practices, growing regions and marketing trends of the walnut industry in India are analyzed in detail. The paper also addresses the issues related to production constraints and future expansion in India's commercial walnut production. With the improved living standards and increased interest in walnut growing, India is quietly becoming a major walnut producing country.

Susceptibility of Juglans Species and Interspecific Hybrids to Agrobacterium tumefaciens

Crown gall, caused by the common soil-borne bacterium Agrobacterium tumefaciens, can be an economic problem in walnut nurseries and production orchards in California. The principal rootstocks used for commercial walnut production in California are the native Northern California black walnut, Juglans hindsii, and “Paradox,” which are interspecific hybrids between a black walnut, primarily J. hindsii, as the maternal parent, and J. regia, the English walnut, as the paternal parent. Recent evidence has shown that some commercial black walnut trees producing Paradox hybrid seedlings are actually hybrids between J. hindsii and two other North American black walnut species, J. major and J. nigra. Here, we document that there was a higher incidence of crown gall on Paradox (J. hindsii ×J. regia) than on J. hindsii in three sites with natural soil inoculum. Paradox seedlings (with a female parent that was primarily J. hindsii with some J. nigra) inoculated with A. tumefaciens on the roots during transplanting had a higher incidence of crown gall than either J. hindsii or J. regia. When stems were inoculated with A. tumefaciens, J. hindsii ×J. regia populations had significantly larger galls than either J. hindsii or J. regia. Similarly, in stem inoculations on four out of six Paradox genotypes with a hybrid black walnut maternal parent, the progeny produced significantly larger galls than either J. hindsii or J. regia. However, two Paradox populations from black walnut hybrids that contained J. major, J. nigra, and J. hindsii produced galls that were no different in size than in the black walnut species and J. regia. Results suggest that J. regia and black walnut species are less susceptible to crown gall than most Paradox populations.

A sensitive sandwich ELISA for the detection of trace amount of cashew nut in foods

A sensitive sandwich ELISA for the detection of trace amount of cashew nut in foods

Mourning Dove Productivity in California during 1992-95: Was It Sufficient to Balance Mortality?

Mourning dove (Zenaida macroura) populations have declined steadily in the western United States since 1966. We investigated the role of recruitment in this long-term problem by studying nesting ecology of mourning doves from March to September 1992-95, in the northern Central Valley, California, USA, We studied nesting doves in blue oak woodlands (Quercus douglasii), willow-cottonwood riparian habitats (Salix spp., Populus fremontii), and commercial walnut, prune, pistachio, and cherry orchards. We used 3,047 nests for our analyses, Doves initiated nests from 14 March to 28 August; nesting season lengths ranged from 105 to 158 days. Only 2-5% of nests remained active after 1 September each year, and latest dates that young fledged ranged from 28 August to 21 September. Mayfield estimates of nest success rates varied inconsistently among study areas; annual success rates ranged from 35-59% for incubation, 49-79% for brooding, and 22-45% for total. Akaike's Information Criteria (AIC) analysis showed that total nest success was higher during years with relatively warm-dry springs (March-May, 1992 and 1994 [35-45% success]) than years with relatively cool-wet springs (1993 and 1995 [22-37% success]). Additionally, AIC analysis showed that fledglings produced/pair and fledglings/nesting attempt were highest during the warm-dry years. Likewise, we recorded more total pairs, nests, and total fledglings, and longer nesting seasons during the warm-dry years. The lower limit of the 95% confidence interval for fledglings produced/pair for all years exceeded the value of 2.5 previously estimated with banding data from 1967-74 as the value required to maintain breeding populations in California. Thus, if our productivity estimates reflected the general population, and annual survival rates had not changed, recruitment should have been adequate to produce an increasing population. Since this was not occurring, managers should complement population surveys with annual banding and harvest surveys to enable thorough examination of the relationships among survival, productivity, and abundance.

562 Variation in commercial walnut and Almong extracts for prick skin testing

562 Variation in commercial walnut and Almong extracts for prick skin testing

Integration of Nonchemical, Postharvest Treatments for Control of Navel Orangeworm (Lepidoptera: Pyralidae) and Indianmeal Moth (Lepidoptera: Pyralidae) in Walnuts

We propose a treatment strategy combining an initial disinfestation treatment with I of 3 protective treatments as an alternative for chemical fumigation of walnuts for control of postharvest insect populations. The initial disinfestation treatment (0.4% O 2 for 6 d) was designed to disinfest walnuts of field populations of navel orangeworm. Amyelois transitella (Walker). The protective treatments were low temperature (10°C) storage, controlled atmosphere (5% O 2 ) storage, and application of the Indianmeal moth granulosis virus, and were designed to prevent establishment of Indianmeal moth, Plodia interpunctella (Hubner) The initial disinfestation treatment was effective against laboratory populations of navel orangeworm. Efficacy of protective treatments was determined by exposure to Indianmeal moth population levels far higher than those found in commercial walnut storage facilities. All 3 protective treatments prevented development of damaging Indianmeal moth populations as measured by pheromone trap catches and sample evaluation of the walnuts No Indianmeal months were trapped, nor were any seriously damaged walnuts (nuts with obvious damage that rendered the nutmeat less marketable or unmarketable) recovered from either low temperature or controlled atmosphere storage Very low numbers of moths (≤21/wk) ) were trapped from walnuts treated with virus, and only 0.2% of the walnuts re seriously damaged. In contrast, large numbers of moths (119-793/wk) were trapped from untreated nuts, and 35% of the sampled walnuts showed serious damage. Quality analysis by a commercial laboratory showed that overall walnut quality for all protective treatments was maintained at levels acceptable by industry standards.

Insect and Mite Control on Walnuts, 1996

Abstract The trial was conducted in a commercial walnut orchard near Tracy, CA. Eighteen treatments were replicated four times in a RCB design. Each replicate consisted of an individual tree. Treatments were applied with a hand-held orchard! sprayer operating at 300 psi and delivering 350 gpa of finished spray (6.4 gal/tree). Application timings were based on degree days (DD) which were calculated with a 31 Mar biofix for the first generation and 5 Jun biofix for the second generation, using a single sine horizontal cutoff model with a lower; threshold of 50° F and an upper threshold of 88° F and with air temperature from the San Joaquin County weather station in Tracy. Target application tim-ings were: V-71639 and CGA-59205 at 100 and 500 DD from 1st and 2nd biofix, CM-001 and Confirm (IGR standard) at 200 and 600 DD from 1st and 2nd biofix, CM-002/X, Brigade and Lorsban/Imidan/Azinphos-M/Lorsban (conventional standard) at 300 and 700 DD from 1st and 2nd biofix. Due to rain on 15 and 16 May, the CM-001 and Confirm treatments which were applied on 15 May were retreated on 20 May. Control of the overwintering CM generation (first application) was evaluated by inspecting all dropped nuts weekly from 23 May through 1 Jul for CM infestation. Control of the summer generations was evaluated by inspecting 100 nuts/tree at commercial harvest on 6 Sep for CM and NOW infestation. Control of WA, motile TSM and ERM was evaluated by sampling 10 leaflets per replicate on 22 Jun and 29 Jul. WA and WAP “mummies” were counted in the field while motile TSM and ERM were brushed from the leaves and counted under magnification (20X) in the laboratory. Flight activity of male CM was monitored weekly from 19 Mar through 29 Aug by four pheromone traps placed high in the tree canopy.

Twospotted Spider Mite Control with Cm-006,1996

Abstract The study was conducted in a commercial walnut orchard near Visalia, CA on 3-year old trees. Six treatments were replicated six times in a RCB design. Each replicate consisted of an individual tree. There was a buffer row in each direction from the experimental trees. Treatments were applied on 10 Jul with a hand-held orchard sprayer operating at 200 psi and delivering 37.5 gpa of finished spray (0.5 ga/tree). TSM were sampled weekly from 10 Jul (pre-treatment sample) through 7 Aug by collecting five leaflets per replicate. The leaflets were brushed and TSM were counted under magnification (20 X).

Codling Moth Control with Insect Growth Regulators, 1995

Abstract The trial was conducted in a commercial walnut orchard near Tracy, Calif. Twelve treatments were replicated four times in a RCB design. Each replicate consisted of an individual tree. Treatments were applied with a hand-held orchard sprayer operating at 300 psi and delivering 400 gpa of finished spray (5.7 gal/tree). Application timings were based on degree days (DD). DD were calculated with a 2 Apr biofix for the first generation and 25 Jun biofix for the second generation using a single sine horizontal cutoff model with a lower threshold of 50°F and an upper threshold of 88°F and with air temperature from the San Joaquin County weather station in Tracy. Target application timings were: Confirm and Neemix-250 DD from 1st and 2nd biofix and 1250 DD from 2nd biofix, Dimilin-300 DD (combined with Lorsban), 900 and 1900 DD from 1st biofix, Comply and Pyriproxyfen-300 DD (combined with Lorsban or Lorsban alone) from 1st biofix, 100 and 1100 DD from 2nd biofix and grower standard-300 DD from 1st biofix, 250 and 1250 DD from 2nd biofix. Control of the overwintering CM generation (first application) was evaluated by inspecting all dropped nuts weekly from 31 May through 7 Jul for CM infestation. In addition, control of the overwintering generation was evaluated by banding each tree with single sided corrugated cardboard on 15 May. The cardboard was removed and inspected for CM larvae or pupae on 7 Jul. Control of the summer generations was evaluated by inspecting 100 nuts/tree at commercial harvest on 18 Sep for CM and NOW infestation.

Evaluation of Alternate Row Applications of A Short-Residue Insecticide for Control of the Overwintering Generation of Codling Moth, 1991

Abstract The trial was conducted in 5 commercial walnut orchards throughout California. In each orchard, there were 5 treatments. Each treatment was applied to an area of 2 or more acres. Timing of the treatments was based on walnut tree phenology; that is, applications were made at 1/2-inch nut size and at various time periods after V2-inch nut size. All materials were applied with an air-blast sprayer delivering from 100 to 150 gal finished spray/acre, depending on the site. The effectiveness of the treatments was evaluated by counting all CM-infested dropped nuts from around 6 trees in the center of each treatment weekly from 28 May through 11 Jul, depending on the site. Walnut aphid populations were monitored by counting all aphids on 10 leaflets/tree from 6 trees in the center of each treatment from 21 May through 7 Jul, depending on the site.

TWO-DIMENSIONAL DRYING MODEL FOR STATIONARY BIN WALNUT DRYERS

A mathematical model was developed and solved using finite difference schemes to predict the two-dimensional heat and mass transfer in stationary bin walnut dryers. The model consists of two separate parts: an airflow model to predict velocities within the bin and a two-dimensional heat and mass transfer model that combines mass and energy balances, rate equations, and the velocity distributions to predict air and solids temperatures and moisture contents. Results predicted by the model compare well with experimental data from a small-scale laboratory unit as well as with data from a commercial walnut dryer.