Joseph A. Grant

Developing Drosophila suzukii management programs for sweet cherry in the western United States

BACKGROUND The spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is a newly introduced pest of sweet cherry on the west coast of North America which produces about 97% of the value of the US sweet cherry crop. D. suzukii initially caused considerable economic loss to cherry growers, who were unaware of this new pest. Little control information was available at the time of initial infestation. Pest control studies were initiated to examine the materials, timings and application methods to control D. suzukii in three major cherry-producing states (California, Oregon and Washington). RESULTS Three classes of registered insecticides, organophosphates, pyrethroids and spinosyns, have demonstrated good topical or residual activity against D. suzukii. Neonicotinoids and the systemic organophosphate dimethoate appear to be able to kill eggs or larvae in fruit. Preliminary timing studies indicate that at least two preharvest insecticide sprays are required to obtain control of D. suzukii in California cherry orchards. Aerially applied malathion ULV (ultra-low volume) appears to be a viable control tactic for this pest. CONCLUSION The results presented here form the basis for developing D. suzukii management programs in the western United States. Additional studies are needed to refine management practices for the different growing regions and conventional versus organic production requirements. Cherry growers will likely need to apply broad-spectrum insecticides in a prophylactic manner until treatment thresholds and monitoring methods have been developed and validated.

Population dynamics and ecology of Drosophila suzukii in Central California

Drosophila suzukii is a serious pest of several fruit crop systems in California’s Central Valley, which is one of the world’s major fruit-growing regions. This study followed D. suzukii seasonal population dynamics in multiple cropping and riparian systems in four cherry-producing counties of the Valley. Apple cider vinegar baited traps were used to monitor D. suzukii adults weekly, from April 2013 to July 2014, in 28 fields. Results show peak captures in the spring and fall seasons. In cherry orchards, adult trap counts were the highest near harvest (June) and declined thereafter, as fly populations moved to other crop (e.g., citrus) or non-crop habitats. The number of captured adults was positively related between pairs of sampled sites based on their proximity but was negatively related to differences in fruit ripening periods between different crops, suggesting that fly populations moved among crop and/or non-crop habitats during the year or had varying population dynamics on different crops and in different seasons. Mature egg load per female was higher during the fruiting season but lower during the winter season, with the majority of winter-captured females not containing mature eggs. This survey also reports for the first time the presence of trapped D. suzukii adults bearing melanized and encapsulated parasitoids in North America, non-target captures of larval drosophilid parasitoids in the traps, as well as the occurrence of larvae in the ovaries of adult female D. suzukii.

Prediction of controlled atmosphere-induced flesh browning in `Fuji' apple

Abstract Rapid induction of internal flesh browning by exposure of fruit to high CO2, fruit maturity indices, respiration rates and CO2 permeances were assessed as predictors of flesh browning which developed in apple (Malus domestica, Borkh. cv. Fuji) during long-term controlled atmosphere storage. Fruit were harvested from eight orchards at 170, 190 or 210 days after full bloom and held at 20°C in 50 kPa CO2 (balance air) for 1–3 days, in 20 kPa CO2 (balance air) for 3–7 days or at 0°C in a controlled atmosphere of 2 kPa O2+2 kPa CO2 for 150 days. Flesh browning increased with greater exposure time in 20 kPa and 50 kPa CO2 and after 3 days of exposure, more browning developed in fruit exposed to 50 than 20 kPa CO2. Flesh browning in all atmospheres increased with harvest date but significant variability was present among orchards at any one harvest. Across all orchards and harvest dates, strong positive relationships were found between flesh browning after controlled atmosphere storage and that which developed after short-term exposure to 20 kPa CO2 at harvest. This relationship improved with decreasing exposure time at 20 kPa CO2. While substantial differences in fruit maturity indices (background colour, starch pattern index, watercore incidence, soluble solids concentration, titratable acidity, flesh firmness), fruit respiration rates and fruit permeances to CO2 determined at harvest were also found among harvest dates and orchards, they were at best poorly related to flesh browning. The best predictor of orchard and harvest date differences in controlled atmosphere-induced flesh browning was therefore assessment of flesh browning after exposure of fruit to 20 kPa CO2 for 3 days.

Does use of Pesticides Known to Harm Natural Enemies of Spider Mites (Acari: Tetranychidae) Result in Increased Number of Miticide Applications? An Examination of California Walnut Orchards

ABSTRACT Integrated pest management (IPM) offers guidelines to reduce spider mite (Acari: Tetranychidae) outbreaks by avoiding pesticides known to be harmful to the natural enemies of spider mites. However, in practice, these guidelines can be inconsistent in their effectiveness. The project examined whether California walnut (Juglans L.) growers, following IPM guidelines to avoid pesticides harmful to the natural enemies of spider mites, achieved lower miticide use. Significant statistical tests suggested that fields with harmful applications were 40% more likely to have a miticide application than fields without. Although the IPM guidelines achieved the goal of reducing miticide use, further analysis of other potential causal mechanisms behind outbreaks could strengthen the effectiveness of the guidelines, potentially increasing IPM adoption.

The role of tyloses in crown hydraulic failure of mature walnut trees afflicted by apoplexy disorder

In the Central Valley of California, mature walnut trees afflicted with apoplexy disorder exhibit rapid and complete crown defoliation within a few weeks of symptom initiation. Symptoms are typically found throughout the entire crown and are initially expressed as wilting and chlorosis followed by scorching of leaves. Since the cause of apoplexy disorder is unknown, we set out to elucidate the water relations physiology underlying this condition. Stem water potential (Psi(s)) of healthy, asymptomatic trees remained high throughout the 2007 growing season, while that of apoplexy-afflicted trees decreased significantly with the onset of symptoms for both healthy-appearing and symptomatic portions of these trees. Psi(s)s were significantly reduced by at least 0.7 MPa in the lower, middle and upper portions of the symptomatic canopies compared with those from asymptomatic trees. Heat pulse velocities measured in the main trunk at three radial depths consistently decreased prior to the onset of symptoms and eventually reached zero with complete crown defoliation. Comparison of sap flow with predicted water use based on walnut evapotranspiration suggests that stomata of symptomatic trees were closing at higher evaporative demand prior to symptom formation. Specific hydraulic conductivity (K(s)) of symptomatic stems was significantly lower than that of asymptomatic stems, and no detectable K(s) could be measured on several of the symptomatic stem samples. However, shallow root K(s) did not significantly differ between symptomatic and asymptomatic trees, suggesting that hydraulic failure was isolated to the crown of these grafted trees. Light and scanning electron microscopy of stem and trunk sapwood revealed extensive tylose development in vessels throughout the crown of symptomatic trees. Analysis of the formation of tyloses on multiple dates revealed rapid development of these vessel occlusions in conjunction with visual symptom formation and dramatic decreases in sap flow. In 2008, tylose development was associated with elevated ethylene production in the active sapwood of symptomatic trees. The cause of elevated ethylene associated with tylose production and symptom formation is yet to be determined.

First report of Calosphaeria pulchella associated with branch dieback of sweet cherry trees in California

California is the second largest sweet cherry producer in the United States with approximately 10,800 ha and an average annual crop value of approximately

Calosphaeria Canker of Sweet Cherry Caused by Calosphaeria pulchella in California and South Australia

150 million. Perennial canker diseases constitute major threats to the cherry industry productivity by reducing tree health, longevity, and yields. During the course of summer 2006, we observed severe limb and branch dieback of sweet cherry (Prunus avium L.) in San Joaquin, San Benito, Contra Costa, and Stanislaus counties of California. Isolation from diseased branches repeatedly yielded the fungus Calosphaeria pulchella (Pers.: Fr.) J. Schröt. (1,2). Cankers and vascular necroses had developed in tree limbs and branches, generally initiating from the heart wood and later spreading into the sapwood. External symptoms of disease may be unapparent throughout the early stages of infection, particularly in large diameter shoots. Older infections often appeared as wilted leaves. Branches and trunks affected with cankers from which C. pulchella was isolated also generally bore perithecia of C. pulchella beneath the periderm. Perithecia were nonstromatic and arranged in dense, circinate groups, with elongated necks converging radially and fissuring the periderm. Asci were unitunicate, clavate, and 45 to 55 × 5 to 5.5 μm. Ascospores were allantoid to suballantoid, hyaline, and 5 to 6 × 1 μm. Colonies on potato dextrose agar (PDA) were dark pink to red in their center with a white margin. Conidia were hyaline, allantoid to oblong-ellipsoidal, and (3-) 4 to 6 (-9) × 1.5 to 2 (-2.5) μm. Identification of C. pulchella isolates also was confirmed by sequence comparison in GenBank database using the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rDNA. Sequences of California isolates shared 100% similarity with C. pulchella reference isolate CBS 115999 (EU367451) (2). ITS sequences of the California isolates used in this study were deposited into GenBank (Nos. HM237297 to HM237300). Pathogenicity of four isolates recovered from the margin of active cankers was determined by branch inoculations. In December 2006, 2- to 4-year-old twigs of P. avium cv. Bing were inoculated with a 5-mm cork borer to remove bark and by placing an agar plug from the growing margin of 8-day-old colonies directly into the fresh wound, mycelium side down. Ten branches per isolate were inoculated. Ten control shoots were inoculated with noncolonized agar plugs. Inoculations were covered with vaseline and wrapped with Parafilm to retain moisture. Branches were harvested in July 2007 and taken to the laboratory to be examined for canker development, and the extent of vascular discoloration in each branch was assessed. Isolations from the edge of discolored tissue were conducted to fulfill Kochs postulates. After 8 months, C. pulchella was reisolated from 100% of the inoculated branches. Length of vascular discoloration averaged 62.5 mm in branches inoculated with the four C. pulchella isolates and 16.5 mm in the control twigs. No fungi were reisolated from the slightly discolored tissue of the controls. To our knowledge, this study constitutes the first report of C. pulchella as a pathogen of sweet cherry trees in California. References: (1) M. E. Barr. Mycologia 77:549, 1985. (2) U. Damm et al. Persoonia 20:39, 2008.

Addition of Pear Ester With Sex Pheromone Enhances Disruption of Mating by Female Codling Moth (Lepidoptera: Tortricidae) in Walnut Orchards Treated with Meso Dispensers

California is the second largest sweet cherry producer in the United States with annual revenues up to

Evaluation of an abatement program for western X-disease in sweet cherry

200 million. The South Australian cherry industry generates about 10% of Australias overall production with approximately 1,500 metric tons of cherries produced yearly. In California, perennial canker diseases and subsequent branch dieback are responsible for extensive damage throughout sweet cherry orchards, reducing annual yields and tree longevity. Surveys of cherry orchards and isolation work were conducted in California to identify the main canker-causing agents. Calosphaeria pulchella was the main fungus isolated from cankers, followed by Eutypa lata and Leucostoma persoonii, respectively. Preliminary surveys in cherry orchards in South Australia documented C. pulchella and L. persoonii in cankers. The pathogenicity of C. pulchella in sweet cherry was confirmed following field inoculations of 2- to 3-year-old branches. C. pulchella was able to infect healthy wood and produce cankers with as much virulence as E. lata or L. persoonii. Spore trapping studies were conducted in two sweet cherry orchards in California to investigate the seasonal abundance of C. pulchella spores. Experiments showed that rain and sprinkler irrigation were important factors for aerial dissemination. Finally, this study illustrates the symptoms and signs of the new disease Calosphaeria canker.

Influence of within-canopy shading on fruit size, shoot growth, and return bloom in kiwifruit

Abstract We evaluated the low-density application of 50 dispensers per hectare, in contrast to the traditional >800 dispensers per hectare in apple orchards, to achieve disruption of communication of adult codling moth, Cydia pomonella (L.), in walnuts, Juglans regia (L.), using several methods. These methods included cumulative catches of male moths in traps baited with sex pheromone (Ph) or codlemone, (E,E)-8,10-dodecadien-1-ol, or a combination of codlemone, pear ester (PE), ethyl (E,Z)-2,4-decadienoate, and acetic acid, and by examining the mating status of females. These data were collected from 2011–2014 in nontreated plots and in similar plots treated with Meso dispensers loaded with codlemone (Ph Meso) or codlemone and PE (Ph + PE Meso). Male moth captures in both the Ph and combination lure traps reduced by 88–96% and 72 to 77%, respectively, compared with traps in the nontreated plots. A significantly higher proportion of female moths were nonmated in plots treated with Ph + PE Meso dispensers (33%) than in plots treated with Ph Meso (18–26%), or left nontreated (13%). In addition, significantly fewer multiple-mated females were trapped in the Ph + PE Meso-treated plots (6%) than in either Ph Meso-treated (13–18%) or nontreated plots (23%). These data suggest that the addition of PE can effectively improve Ph-based disruption of C. pomonella in walnut orchards. In addition, these data suggest that the use of low-density hand-applied dispensers can be an effective and lower-cost approach to manage this pest in the large canopy presented by walnut orchards.