California Pistachio Research Articles

Comparing the Feeding Damage of the Invasive Brown Marmorated Stink Bug to a Native Stink Bug and Leaffooted Bug on California Pistachios.

Simple SummaryThe brown marmorated stink bug is native to Asia and has invaded parts of Europe and North America where it causes considerable damage to a wide range of vegetable, fruit, and nut crops. Pistachios have become an important nut crop in California, and as this invasive stink bug moved into California, farmers needed to know about the potential damage from brown marmorated stink bugs. Here, we assessed pistachio yield loss and nut damage over a two-year period. The invasive stink bug was also compared with the native green stink bug and a native leaffooted bug. We found that brown marmorated stink bug adults cause more epicarp lesions (external damage) when recorded at harvest time than the native species; however, they did not cause more kernel necrosis (internal damage) than the two native species tested, which is a more relevant damage criterion for commercial production. We conclude that the brown marmorated stink bug could cause similar damage as the native species but note that the invasive stink bug’s numbers in California are still low and future damage levels will be dependent on this pest’s population density.California currently produces about a quarter of the world’s pistachios. Pistachio nuts are susceptible to feeding by stink bugs and leaffooted bugs; therefore, the invasive presence of the highly polyphagous brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a concern to California pistachio growers. We aimed to assess the potential of H. halys to cause yield loss and nut damage to pistachios, which had not yet been assessed in the field. Over two years, terminal branch ends with pistachio clusters were enclosed in organdy cages from spring to fall and exposed to either H. halys, the native stink bug Chinavia hilaris Say (Hemiptera: Pentatomidae), or leaffooted bug Leptoglossus zonatus (Dallas) (Hemiptera: Coreidae), for 4–7-day feeding periods at different times of the season. We found that H. halys adults cause more epicarp lesions (external damage) when recorded at harvest time than the native species. They did not, however, cause more kernel necrosis (internal damage) than the two native species tested, which is a more relevant damage criterion for commercial production. There were no differences among insect species for any other recorded damage criteria. We conclude that H. halys could cause similar damage as the native species but note that H. halys population densities in California are still low and future damage levels will be dependent on this pest’s population density.

UC pistachio cultivars show improved nut quality and are ready for harvest earlier than ‘Kerman’

California pistachio growers have traditionally grown only one female cultivar (‘Kerman’) and one male pollenizer (‘Peters’). Starting in 2005, the UC breeding program released several improved cultivars, which are being planted on increasing acreage — and tested now under commercial conditions at multiple sites over multiple years. We conducted six experimental trials in the San Joaquin Valley to evaluate the performance of the UC cultivars ‘Gumdrop’, ‘Golden Hills’ and ‘Lost Hills’ and their associated UC male pollenizers ‘Famoso’, ‘Randy’ and ‘Tejon’ against the performance of the traditional pair, ‘Kerman’ and ‘Peters’. The new cultivars demonstrated a range of earlier bloom and harvest dates than ‘Kerman’ and some improved nut quality characteristics, such as a higher percentage of split, in-shell nuts. Results indicate that by growing the new female cultivars and synchronous pollenizers, producers can avoid the peak harvest period for ‘Kerman’, when equipment and processing facilities are limited, and maintain or improve their yield and nut quality.

Phenotypic and molecular characterization of fenhexamid resistance in Botrytis cinerea isolates collected from pistachio orchards and grape vineyards in California

Botrytis cinerea causes Botrytis blossom, shoot and fruit blight in pistachio and gray mold in grape. The hydroxyanilide (Hyd) fenhexamid, one of the most frequently used fungicides for Botrytis control, inhibits the 3-ketoreductase (Erg27) of the ergosterol biosynthesis pathway. Due to its site-specific mode of action, this fungicide is at-risk for resistance development. In this study, 74 and 58 B. cinerea isolates, collected from Californian pistachio orchards and grape vineyards, respectively, were evaluated for their in vitro sensitivity toward fenhexamid. Of the 58 grape isolates, 90% were sensitive to fenhexamid (HydS, EC50 < 1 μg/ml) whereas the remaining 10%displayed low resistance to this fungicide (HydLR, 1 < EC50 < 5 μg/ml). Among the 74 pistachio isolates, 69, 14, 1, 5, and 11% displayed sensitivity (HydS, EC50 < 1 μg/ml), low (HydLR, 1 < EC50 < 5 μg/ml), weak (HydWR, 5 < EC50 < 10 μg/ml), moderate (HydMR, 10 < EC50 < 50 μg/ml), and high resistance (HydHR, EC50 > 50 μg/ml) phenotypes toward fenhexamid, respectively. The 3-ketoreductase erg27 gene was sequenced from all the 29 B. cinerea fenhexamid-resistant phenotypes (HydLR, WR, MR, HR) detected in this study. The resulting sequences were then compared to corresponding sequences obtained from 21 fenhexamid-sensitive isolates (HydS). Of the 6 HydLR phenotype from grape, 3 had a substitution of proline to serine at position 238 (P238S). No mutations were found in the remaining 3 HydLR nor in the 10 HydLR pistachio isolates. The only HydWR phenotype from pistachio presented a change at position 309 resulting the replacement of valine to Methionine (V309M). Among the HydMR phenotype from pistachio, two had F412S alteration while the other two possessed the L400F alteration at position 400. Highly resistant isolates (HydHR) carried a substitution of the phenylalanine at position 412, either serine (F412S) or isoleucine (F412I). Inoculations on detached grape berries showed that field rates of Elevate® 50 WDG (fenhexamid) controlled HydS and HydLR, but not the HydMR and HydHR phenotypes. The presence of B. cinerea fenhexamid-resistant phenotypes in pistachio and grape fields in California must be monitored continually and resistance management practices implemented as needed for sustained Botrytis blossom, shoot and fruit blight and gray mold controls with Elevate® 50 WDG.

Macrophomina Crown and Root Rot of Pistachio in California.

In this study, declining pistachio rootstocks were detected in newly planted commercial pistachio orchards in Kern County, California. Symptoms were characterized by wilted foliage combined with crown rot in the rootstock. From diseased trees, 42 isolates were obtained, and all had similar cultural and morphological characteristics of Macrophomina phaseolina. Analyses of nucleotide sequences of three gene fragments, the internal transcribed spacer region (ITS1–5.8S–ITS2), partial sequences of β-tubulin, and translation elongation factor 1-α (TEF1) confirmed this identification, and 20 representative isolates are presented in the phylogenetic study. Testing of Koch’s postulates showed that M. phaseolina, when inoculated to stems and roots of the pistachio rootstocks using mycelial plugs or a microsclerotial suspension, is indeed pathogenic to this host. The widely used clonal University of California Berkeley I (UCBI) rootstock appeared highly susceptible to M. phaseolina, suggesting that this pathogen is an emerging threat to the production of pistachio in California. This study confirmed the association of M. phaseolina with the decline of pistachio trees and represents the first description of this fungus as a crown rot-causing agent of pistachio in California.

Occurrence and Extent of Boscalid Resistance in Populations of Alternaria alternata from California Pistachio Orchards.

Alternaria late blight (ALB) caused by Alternaria spp. is an annual disease problem in California pistachio and requires repeated applications of fungicides to prevent significant losses of pistachio foliage and nut quality. From 2003 onward, the succinate dehydrogenase inhibiting fungicide boscalid has played a key role in ALB management. The development of boscalid resistance in A. alternata populations was monitored from 2005 to 2012 in pistachio producing areas in California. A total of 1,765 single-spore isolates, collected from commercial and experimental pistachio orchards with or without a history of boscalid exposure, were tested in a radial growth assay in agar media amended with the discriminatory dose of 10 µg/ml of boscalid. The frequency of boscalid-resistant isolates in 2005 was 12% but increased significantly and remained stable toward the end of the survey period. Most of the resistant isolates exhibited a high level of resistance (R) to boscalid with percent of mycelial growth inhibition (PGI) values between 0 and 50%, whereas significantly fewer isolates had an intermediate level (IR) of resistance (50 < PGI < 75%). The frequency of sensitive (S) isolates (75 < PGI < 100%) was generally the highest in orchards with no history of boscalid usage, whereas mean incidences of boscalid-resistant populations of Alternaria were 81, 92.4, 80.2, and 98%, in 2006, 2007, 2011, and 2012, respectively, in orchards that received a high number (at least three per season) of boscalid spray applications. In comparison, none to relatively low frequencies (0 to 12%) of resistance were observed in populations with no or limited exposure to Pristine, suggesting an air-movement of resistant spores through wind from treated to nontreated areas. In 2012, boscalid-resistant isolates were found practically in every sampled location in all counties, with the orchards in Fresno, Madera, Tulare, and King Counties being the locations with the highest frequencies of resistance (100%). Monitoring of A. alternata AaSDHB, AaSDHC, and AaSDHD mutations in 286 boscalid-resistant phenotypes identified 11 mutations, leading to amino acid substitutions in AaSDHB (seven mutations: H277Y/R/L, P230A/R, N235D/T), AaSDHC (one mutation: H134R), and AaSDHD (three mutations: D123E, H133R/P), with AaSDHB mutations being the most prevalent (80%) ones throughout the survey period. The majority of isolates carrying these mutations exhibited the R phenotype toward boscalid. The increased prevalence of boscalid resistance in populations of A. alternata is a likely contributing factor to the inability of pistachio farmers to successfully control ALB with Pristine. Other factors implicated in the rapid and widespread occurrence of A. alternata boscalid-resistant populations in California pistachios are further discussed.

Dust Interferes with Pollen–Stigma Interaction and Fruit Set in Pistachio Pistacia vera cv. Kerman

Springtime flail mowing of row middles for weed control in California pistachio (Pistacia vera L.) orchards blows dust into the leafless canopy if it occurs during bloom. The effect of dust on pistachio pollination and fruit set is unknown. Rachises were bagged prebloom and hand pollinated with pollen and dust mixtures at 1:0, 1:1, 1:4, 1:16, and 0:1 volume/volume ratios on five successive days. The 2016 and 2017 trials demonstrated that the inflorescences treated with a high pollen:dust ratio (0:1, 1:4, and 1:16) had significantly lower split nut rates (commercially less profitable) compared with low dust ratio tests (1:0 and 1:1). Our results also showed that dust damaged both pollen viability and stigma quality, particularly if contaminated with herbicide residues (GlyStar® Plus and Treevix®). Decreased yield was a function of decreased fruit set; increased embryo abortion, parthenocarpy, or both; and a lower split nut percentage. The GA3 content in flowers of both the pollen and dust treatments was significantly higher than that in nonpollinated flowers, suggesting dust stimulated parthenocarpy, resulting in empty nutshells, “blanks” at harvest.

Identification and Pathogenicity of Fungal Species Associated with Canker Diseases of Pistachio in California.

A survey was conducted during 2015 and 2016 in pistachio orchards throughout the San Joaquin Valley of California to investigate the occurrence of canker diseases and identify the pathogens involved. Cankers and dieback symptoms were observed mainly in orchards aged >15 years. Symptoms of canker diseases included brown to dark brown discoloration of vascular tissues, wood necrosis, and branch dieback. In total, 58 fungal isolates were obtained from cankers and identified based on multilocus phylogenetic analyses (internal transcribed spacer, glyceraldehyde 3-phosphate dehydrogenase, β-tubulin, calmodulin, actin 1, and translation elongation factor 1α) representing 11 fungal species: Colletotrichum karstii, Cytospora californica, Cytospora joaquinensis, Cytospora parapistaciae, Cytospora pistaciae, Diaporthe ambigua, Didymella glomerata, Diplodia mutila, Neofusicoccum mediterraneum, Phaeoacremonium canadense, and Schizophyllum commune. Pathogenicity tests conducted in the main pistachio cultivars Kerman, Golden Hills, and Lost Hills using the mycelium-plug method indicated that all fungal species were pathogenic to Pistacia vera. All species tested caused cankers in pistachio branches, although virulence among species varied from high to moderate. Overall, N. mediterraneum and Cytospora spp. were the most widespread and virulent species associated with canker diseases of pistachio in California.

Molecular phylogeny of Cytospora species associated with canker diseases of fruit and nut crops in California, with the descriptions of ten new species and one new combination

Cytospora species are destructive canker and dieback pathogens of woody hosts in natural and agroecosystems around the world. In this genus, molecular identification has been limited due to the paucity of multi-locus sequence typing studies and the lack of sequence data from type specimens in public repositories, stalling robust phylogenetic reconstructions. In most cases a morphological species concept could not be applied due to the plasticity of characters and significant overlap of morphological features such as spore dimensions and fruiting body characters. In this study, we employed a molecular phylogenetic framework with the inclusion of four nuclear loci (ITS, translation elongation factor 1-alpha, actin, and beta-tubulin) to unveil the biodiversity and taxonomy of this understudied important genus of plant pathogens. Phylogenetic inferences based on 150 Californian isolates revealed 15 Cytospora species associated with branch and twig cankers and dieback of almond, apricot, cherry, cottonwood, olive, peach, pistachio, plum, pomegranate, and walnut trees in California. Of the 15 species recovered in this study, 10 are newly described and typified, in addition to one new combination. The pathogenic status of the newly described Cytospora species requires further investigation as most species were associated with severe dieback and decline of diverse and economically important fruit and nut crops in California.

New records of Psocoptera (Troctomorpha, Psocomorpha) in California (U.S.A.) almond and pistachio orchards

Historically, Psocoptera research has been lacking in agricultural field studies. This study is the first in California (U.S.A.) to survey almond and pistachio orchards for Psocoptera. The seven species we observed in orchards are the first host association records of psocids (Lachesilla pacifica Chapman, 1930, Lachesilla pedicularia (Linnaeus, 1758), Lachesilla rena Sommerman, 1946, Ectopsocus vachoni Badonnel, 1945, Ectopsocus californicus (Banks, 1903), Liposcelis bostrychophila Badonnel, 1931, and Liposcelis silvarum (Kolbe, 1888)) in two suborders (Psocomorpha and Troctomorpha) from California almond and pistachio orchards. The results of these observations also revealed a new California state record of L. silvarum. Implications of these findings are discussed.

Investigating canker and soil borne diseases of pistachio in California

During the year 2015 and 2016, we surveyed the main pistachio growing counties in California to assess the health of pistachio trees and investigate the occurrence of canker and soil borne diseases. Numerous orchards were visited throughout the San Joaquin Valley to diagnose unusual symptoms and investigate the causes of decline of pistachio trees. Canker diseases causing branch and scaffold dieback were observed commonly in mature pistachio orchards. New fungal pathogens associated with cankers included Cytospora species, Diaporthe ambigua (=Phomopsis ambigua), and Colletotrichum karstii. A pathogenicity test using fungi isolated from cankers was conducted in the field to determine the ability of these fungi to produce cankers. Results of this study showed that all species tested were pathogenic to pistachio, causing extensive lesions and vascular discolorations just a few months after infection. Among them, Cytospora species were the most aggressive fungal pathogens and are considered new threats to pistachio in California. Other disease symptoms observed commonly in our surveys included declining trees characterized by chlorotic foliage as well as wilting, defoliation and eventual tree death. Trunks often expressed gumming together with crown rot symptoms. Investigations of the causes of pistachio tree decline revealed the occurrence in orchards of several Phytophthora species including P. niederhauserii, P. cinnamomi and P. taxon walnut. Other fungi isolated from declining pistachio trees and rootstocks included Fusarium oxysporum, F. solani, F. equiseti and F. proliferatum and Macrophomina phaseolina. Pathogenicity in pistachio of the various soil borne pathogens were conducted in potted UCB-1 plants maintained in a greenhouse. Pathogenicity studies showed that all the various fungi can colonize and damage the vascular tissues of UCB-1 seedling rootstocks, causing substantial lesions and vascular discolorations. To date, the present project allowed to identify several new pathogens currently affecting the health of pistachio trees in California.

Changing insect pest management of pistachio and almond in California (2000 to 2014)

Changing insect pest management of pistachio and almond in California (2000 to 2014)

Field assessment of potential pistachio salt toxicity using the EM38

The traditional concept of crop salt tolerance as a single soil saturation extract salinity threshold with a “% relative yield decline” function is over-simplified. This approach minimizes the real world variability in actual tree growth and yield due to the added effects of specific ion toxicity and soil texture and anoxia from soil saturation. The current salinity tolerance function for California pistachios was developed from a small plot study in an 8th-13th leaf orchard in northwestern Kern County from 1997-2002. Results from this trial and seedling growth studies in saline sand tanks at the USDA Salinity Lab indicated a threshold value of 9.4 dS m-1 ECe with an 8.4% decline above that value. A greatly expanded salinity survey across 520 km2 examining 10 commercial fields (540 ha total, 9th-15th leaf, centered 35.463 Lat., -119.500 Long.) in western Kern County with 140 individual tree data points was conducted from 2014-16. Average root zone (1.5 m depth) salinity was 1.6 to 20.5 dS m-1. A statistically significant yield reduction of 162-394 kg ha-1 (1-3%) was found in 3 year cumulative inshell yield for every unit ECe>6.5 dS m-1. However, the R2 was only 0.11. Yield by the Ln transformed EM38-ECa was R2=0.20. However, the best predictor of yield decline was the ln transforms of inshell yield and the simple sum of the uncalibrated vertical + horizontal raw EM readings adjacent to the tree, R2=0.35. The raw electromagnetic resonance readings from the EM38 will incorporate multiple factors such as possible anoxia due to high water content and poor soil structure with some influence of the soil mineralogy and pH along with total salt (EC).

The evaluation of winter kaolin clay and dormant oil applications on chill accumulation and yield in the California pistachio (Pistacia vera) cultivars ‘Kerman’ and ‘Peters’

The California pistachio cultivars 'Kerman' and 'Peters' have an estimated requirement of 58 and 60 chill portions, respectively. In California's Central San Joaquin Valley, the recent combination of warmer winter temperatures and sharply decreased fogs have resulted in a reduction of winter chill accumulation. In 2015 and 2016, kaolin clay was applied to dormant pistachio trees attempting to increase chill accumulation by reflecting radiant heat. Four treatments including kaolin clay, kaolin clay plus 470 dormant oil, 470 dormant oil, and an untreated control were made to nine year old pistachio trees. Kaolin clay applications (33 kg ha-1) were applied twice with the first application occurring after leaf drop in mid-December and the second occurring in early-January. A 6% 470 dormant oil solution was applied at 150 L ha-1 on February 6th, 2016. Treatments were approximately 1.9 ha in size and were replicated four times utilizing a randomized complete block design. Temperature sensors measuring external wood temperature on the north and south side were installed on a single tree in multiple blocks. Yield was determined for each plot and evaluated for size and quality. Local weather station measurements indicate that adequate chill was received in 2015-2016. Never-the-less, wood surface temperatures in kaolin treated trees were lower than the untreated control, producing an increase in chill portion accumulation by ~15%. Yield, however, was higher in the 470 dormant oil than in the kaolin clay or untreated control (3,330 kg ha-1 vs. 2,796 and 2,774 kg ha-1, respectively). Results suggest that kaolin clay may be useful in increasing chill portion accumulation, but only if applied early in the dormant period. Our results also confirmed earlier reports that dormant oil increases pistachio yield in marginal to adequate chill years. Both techniques should be utilized as tools to help mitigate variable climate within pistachio orchards.

First Report of Lasiodiplodia gilanensis Causing Twig and Leaf Blight on Machilus thunbergii in Zhejiang Province of China.

Machilus thunbergii Sieb. et Zucc. (Lauraceae) is a broad-leaved evergreen tree and an endangered species in warm-temperate and subtropical areas of China. It also has high ornamental, timber-use, and soil-conservation functions. In recent years, brown to dark-brown lesions were found on leaves or on twigs of M. thunbergii, which caused decay of the cortex. We first found this disease on about 30% of M. thunbergii trees in April 2017 in Zhejiang Tongling Mountain National Forest Park at Wencheng, Wenzhou, Zhejiang province. Symptomatic material from leaves and stems was surface sterilized in 75% ethanol for 10 s and then in 3% NaClO for 3 min, rinsed three times in sterilized distilled water, dried, transferred onto potato dextrose agar (PDA), and incubated at 25°C. Fourteen pure isolates from symptomatic tissues were obtained by single-spore isolations. These isolates formed colonies with abundant villous aerial hyphae. The colonies initially were gray and then turned to black. The strains had black, scattered, or clustered pycnidia and cylindrical conidiophores that occasionally branched. The conidia of the strains were fusiform, thick walled, 31.2 ± 2.5 μm long, and 16.7 ± 1.5 μm wide (length-to-width ratio = 1.9 ± 0.2), and with obtuse apices tapering to a truncate base. Initially, conidia were single celled and transparent, and then they became double celled and the melanin gradually increased. The morphology was similar to the description of Lasiodiplodia gilanensis Abdollahzadeh, Javadi & A.J.L. Phillips (Abdollahzadeh et al. 2010). Genomic DNA samples of the 14 isolates were extracted using the cetyl trimethylammonium bromide method. The β-tubulin (TB) gene was amplified by polymerase chain reaction assay using primers bt2a/bt2b, and a portion of the translation elongation factor 1-alpha (EF1-α) gene was amplified using primers EF-1-986/EF-728. The amplified DNA fragments were then sequenced, and the sequences of all 14 isolates were identical. The sequences of TB (GenBank accession no. MG372749) and EF1-α (GenBank accession no. MG372751) in the representative strain HNDNYB-1 were 100 and 100% identical to the TB sequence of L. gilanensis strain 3K59 (GenBank accession no. KF955888) and the EF1-α sequence of L. gilanensis strain IRAN1501C (GenBank accession no. GU945341), respectively (Abdollahzadeh et al. 2010; Chen et al. 2014). Morphological and molecular results confirmed the isolate as L. gilanensis. Five isolates were selected for pathogenicity tests. Healthy twigs and leaves of M. thunbergii were collected in the field and wounded with a sterilized needle. A 5-mm-diameter mycelial plug of each isolate was excised from the margin of a 4-day-old colony from a PDA plate and placed to the wounded twigs or leaves, and the twigs and leaves were treated similarly with uncolonized plugs as a control. All plants were maintained in an artificial climate chamber at 25°C and 90% relative humidity with a 12-h photoperiod per day. After 5 days, typical lesions developed on inoculated twigs and leaves, whereas control plants remained asymptomatic. The L. gilanensis strains were only reisolated from inoculated plants, and then they were confirmed via morphological observations and genomic DNA testing as identical to the original inoculated strains. L. gilanensis has previously been isolated on California pistachio and pomegranate (Chen et al. 2014; Urbez-Torres et al. 2016), but to the best of our knowledge, this is the first report of this pathogen on M. thunbergii worldwide.

Different levels of resistance to cyprodinil and iprodione and lack of fludioxonil resistance in Botrytis cinerea isolates collected from pistachio, grape, and pomegranate fields in California

Botrytis cinerea is the causal agent of gray mold disease and can infect fruits of important crops like grape, pistachio, and pomegranate, causing significant yield losses worldwide. In this study, mycelial growth assays in vitro were used to evaluate the sensitivities of 160 single-spore isolates of Botrytis cinerea collected from commercial grape (n = 58), pistachio (n = 74), and pomegranate (n = 28) fields in California to cyprodinil, fludioxonil, and iprodione. Based on the effective concentration at which mycelial growth was inhibited by 50% (EC50 values), 100, 83, and 38% of the isolates from the 3 hosts were sensitive (EC50 < 1 μg/mL) to fludioxonil, cyprodinil, and iprodione, respectively. Thirteen, 3, and 1% of the isolates showed low (CyLR), weak (CyWR), or high (CyHR) resistance to cyprodinil, respectively; Sixty-two percent of the isolates tested showed low resistance (1 < EC50 < 10 μg/mL) toward iprodione (IpLR) and were detected in all three hosts. Absence of cross-resistance was not observed between cyprodinil, iprodione, and fludioxonil. Sequence analysis of the two-component histidine kinase target gene (Bos1) revealed that some of the IpLR phenotype isolates were associated with either I365N/S, Q369P, and/or N373S mutations. Laboratory studies showed that IpLR, CyLR, and CyWR phenotypes were not associated with fitness penalties for mycelial growth rate on non-amended media and pathogenicity on detached grape berries. Furthermore, preventative applications of commercial formulations of iprodione (Rovral) and cyprodinil (Vangard) were effective against gray mold caused by Ip- and Cy-sensitive isolates, but failed to control disease caused by IpLR and, CyLR and CyWR isolates, respectively. The generated information will serve as a basis for implementing fungicide use recommendations against bunch rot of grapes, blossom and shoot blight of pistachio, and gray mold of pomegranate.

First Report of Anthracnose Caused by Colletotrichum fioriniae and C. karstii in California Pistachio Orchards

First Report of Anthracnose Caused by <i>Colletotrichum fioriniae</i> and <i>C. karstii</i> in California Pistachio Orchards

Temperature-related Variables Associated with Yield of ‘Kerman’ Pistachio in the San Joaquin Valley of California

Information on how annual pistachio yield is affected by air temperature (Ta) during the winter and growing season is lacking. Timely advance knowledge of the magnitude of the yield of the California pistachio harvest would be beneficial for the pistachio industry for efficient allocation of harvest and postharvest resources, such as personnel, harvesting machinery, trucks, processing facility capacity, crop storage facilities, and for making marketing decisions. The objective of this study was to identify parameters, especially Ta variables and time periods, calculated from Ta data during the previous fall, winter, spring, and summer, that were associated most closely with fall nut-crop yield. The premise of this study was that sequential, historical yield records could be regressed against a number of Ta-derived variables to identify Ta thresholds and accumulations that have value in explaining past and predicting subsequent nut yield. Of the 27 regression variables examined in this study, the following, which were all negatively correlated with subsequent yield, explained the greatest proportion of the variability present in predicting yield of ‘Kerman’ pistachio: yield of the previous-year harvest, hourly Ta accumulations above 26.7 or 29.4 °C from the time period between 20 Mar. and 25 Apr., hourly Ta accumulations below 7.2 °C from 15 Nov. to 15 Feb., and hourly Ta accumulations above 18.3 °C from 15 Nov. to 15 Feb.

Combination Phenyl Propionate/Pheromone Traps for Monitoring Navel Orangeworm (Lepidoptera: Pyralidae) in Almonds in the Vicinity of Mating Disruption.

Aerosol mating disruption is used for management of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), in an increasing portion of California almonds and pistachios. This formulation suppresses pheromone monitoring traps far beyond the treatment block, potentially complicating monitoring and management of this key pest. Phenyl propionate is an attractant used to capture adults in the presence of mating disruption, completely suppressing pheromone traps, and lures combining phenyl propionate with a pheromone lure (PPO-combo lure) synergize trap capture in the presence of mating disruption. In this study, laboratory and field trials of different phenyl propionate dispensers indicate a useful life of six weeks. Controlled experiments found similar numbers of adults captured in phenyl propionate and PPO-combo lures in the presence of varying levels of mating disruption intensity. A subsequent trial compared monitoring of field plots at various distances from fields under commercial mating disruption for much of the growing season with pheromone and PPO-combo lures. Although there was some evidence of partial suppression of capture in PPO-combo traps closer to mating disruption compared with lures farther away, there was no failure of detection as occurred with pheromone lures. The ratio of adults in pheromone and PPO-combo traps varied with proximity from treated fields. These results indicate that, in addition to monitoring in mating disruption plots, phenyl propionate lures can be useful for insuring against failure of detection of navel orangeworm pressure in areas where mating disruption is widely used.

Sensitivity and cross-resistance patterns to demethylation-inhibiting fungicides in California populations of Alternaria alternata pathogenic on pistachio

Alternaria late blight (ALB) caused by Alternaria spp. is an annual production concern for pistachio growers in California. In this study, isolates of Alternaria alternata collected from California pistachio orchards between 1998 and 2003 (population A, n = 46) and in 2010 (population B, n = 38) prior to the registration and use of sterol demethylation-inhibiting (DMI) fungicides for ALB control, were tested for their sensitivity to difenoconazole, propiconazole, and tebuconazole using an in vitro mycelial growth assay. The 50% effective dose (EC50) values for isolates in population A to difenoconazole, propiconazole, and tebuconazole, respectively, ranged from 0.02 to 0.82 μg/mL (mean = 0.17), 0.25–5.73 μg/mL (mean = 1.29), and 0.02–2.76 μg/mL (mean = 0.96), and from 0.02 to 0.93 μg/mL (mean = 0.21), 0.13–5.36 μg/mL (mean = 1.25), and 0.17–5.47 μg/mL (mean = 1.03) for those in population B. Among 65 isolates collected in 2012 from orchards with very limited exposure to difenoconazole, propiconazole or metconazole (population C, n = 65), the EC50 values for tebuconazole ranged from 0.02 to 2.99 μg/mL (mean = 0.51), while EC50 values for difenoconazole of 55 of these isolates varied from 0.01 to 0.44 μg/mL (mean = 0.06). The DMI-exposed population C was found to be on average two to four times less sensitive compared with the populations A and B. Pearson correlation analyses of EC50 values for the three fungicides showed significant positive correlations between the sensitivities of tebuconazole and propiconazole (P < 0.01, r = 0.32), tebuconazole and difenoconazole (P < 0.01, r = 0.26), and difenoconazole and propiconazole (P < 0.01, r = 0.40). Results indicate a clear difference in fungicide intrinsic activity, with difenoconazole being more active than the two other DMIs. Although wide variations in sensitivities for tebuconazole and propiconazole were observed in the non- and DMI-exposed Alternaria populations, efficacy of DMI products has been excellent against ALB. The data collected here will be crucial for the rational use of DMIs in fungicide spray programs for ALB management and serve as a reference to detect any shifts in A. alternata sensitivity to these fungicides in subsequent years as they become more frequently used in California pistachios.

Association of Botryosphaeria Panicle and Shoot Blight of Pistachio with Injuries of Fruit Caused by Hemiptera Insects and Birds.

Panicle and shoot blight of pistachio caused by species of Botryosphaeriaceae fungi remains one of the major diseases of pistachio in California, with the highest potential for crop destruction because buds and fruit clusters (panicles) are killed. Pistachio fruit can also be damaged by various insect pests. For instance, hemipteran insects are considered major pests of pistachio and can attack maturing fruit, causing necrotic areas on the fruit epicarp (epicarp lesion). Surveys in pistachio orchards showed a putative association of punctures of pistachio fruit with infection by Botryosphaeriaceae fungi, resulting in panicle and shoot blight. This study was undertaken to determine any association of Botryosphaeriaceae fungi with fruit bearing epicarp lesions and whether hemipteran insects can actively carry propagules of the pathogens to healthy fruit and cause disease. Three large insects of the order Hemiptera (Thyanta pallidovirens, Acrosternum hilare, and Leptoglossus clypealis) were used in pathogen-spread and infection experiments. The most frequently isolated species of the family Botryosphaeriaceae in pistachio, Neofusicoccum mediterraneum, was used in these transmission experiments. Significantly higher incidence of fruit infected by N. mediterraneum was recorded when pistachio clusters were sprayed with a spore suspension of N. mediterraneum and caged with the above insects than the level of infected fruit sprayed similarly with the pathogen but caged without any insects. Furthermore, increasing the number of insects caged with pistachio clusters resulted in an increase of insect feeding punctures and, subsequently, disease incidence. Similarly, increasing the number of wounds per fruit made with a needle, simulating injuries caused by the insect's stylet, resulted in significantly higher incidence of infected fruit than for wounded fruit with fewer injured sites. In addition, bird-injured fruit were also associated with higher incidence of panicle blight than fruit not injured by birds, especially in orchards with high disease incidence. In laboratory experiments, wounding or applying fruit sap to nonwounded fruit resulted in significantly higher incidence of infected fruit than in nonwounded fruit without sap. In field experiments, wounding of fruit before or after inoculation with N. mediterraneum resulted in higher disease incidence than nonwounded and inoculated fruit. Additionally, fruit sap enhanced initial mycelial growth of N. mediterraneum. Protecting fruit clusters from injuries by hemipteran insects or birds using mesh cages significantly reduced the incidence of panicle and shoot blight. The association of wounding by hemipteran insects and birds with high incidence of infected pistachio fruit may explain partially the broad distribution of Botryosphaeria panicle and shoot blight among pistachio orchards of the central San Joaquin Valley, even in areas where inoculum sources are not nearby.