Janine Hasey

New Fungicides and Application Strategies Based on Inoculum and Precipitation for Managing Stone Fruit Rust on Peach in California

In greenhouse and field studies, rust on cling peach caused by Tranzschelia discolor was significantly reduced on leaves and fruit compared with that on controls by foliar applications of wettable sulfur, an agricultural oil, a substituted aromatic (e.g., chlorothalonil), as well as benzimidazole (e.g., benomyl, thiophanate-methyl), sterol biosynthesis inhibiting (e.g., myclobutanil, propiconazole, tebuconazole), and strobilurin (e.g., azoxystrobin) fungicides. The timing of treatments was a significant factor in reducing disease in most trials. Protective programs using wettable sulfur, tebuconazole, or azoxystrobin applied after stem lesion detection (ASLD) and before forecasted rains were highly effective. In the most effective programs for managing the disease, however, these fungicides were applied after stem lesion detection and occurrence of rainfall. Under highly conducive field environments for disease, single applications of azoxystrobin or tebuconazole at ASLD were significantly more efficacious than sulfur. Dormant treatments of liquid lime sulfur, chlorothalonil, or thiophanate-methyl/agricultural oil, however, were ineffective in reducing the disease during the subsequent spring and summer seasons. This is the first management program for rust on cling peach that utilizes inoculum and precipitation events to optimize timing of fungicide applications.

Comparison of Instrumental and Manual Inspection of Clingstone Peaches

The flesh color and firmness of 13,140 clingstone peaches were measured instrumentally at the cannery receiving stations and compared with the current official subjective inspection methods of the California Department of Food and Agriculture. The instruments evaluated were a nondestructive impact firmness sensor, a traditional destructive penetrometer firmness sensor, and a tristimulus color sensor. Instrumental measurements for flesh color and nondestructive firmness gave good agreement (83% across all cultivars) with the current inspection method in categorizing fruit into both mature or immature, and into firm or soft categories. The study shows that objective instrumental inspection methods hold promise as a replacement for subjective methods presently used in clingstone peach inspection at cannery receiving stations.

Bacterial blight of kiwifruit in California

Flower bud rot, blossom blight, and leaf spot of kiwifruit (Actinidia deliciosa) have been observed in numerous commercial orchards in California since 1986. As the diseased flower buds develop, petals become yellow-orange, then brown, and the entire bud falls from the vine. Fruit may be small, misshapen, or fail to set. The bacterial pathogens Pseudomonas syringae and P. viridiflava, in addition to the saprophyte P. fluorescens, consistently have been isolated from both symptomatic and asymptomatic vines throughout the spring. In pathogenicity tests, P. viridiflava caused significantly more flower bud rot and blossom blight, but not leaf spot, than P. syringae. P. fluorescens was not pathogenic

First report of Geosmithia morbida on English walnut and its paradox rootstock in California.

Geosmithia morbida, the causal agent of thousand cankers disease (TCD), is vectored by the walnut twig beetle (WTB), Pityophthorus juglandis, causing decline in eastern black walnut, Juglans nigra (4), and canker development on many Juglans species (5). In the summer of 2012, a survey for TCD incidence in English walnut, J. regia, in orchards in California identified many trees with WTB activity and characteristic TCD symptoms. Both the J. regia scion and its Paradox hybrid rootstock (J. hindsii× J. regia) were affected. In some cases, trees exhibited bleeding on the bark surface from WTB entrance holes. Removal of the outer bark revealed cankers in the phloem around the WTB galleries. Two samples were taken from scions and three samples were collected from rootstocks of trees in orchards in northern California. Pieces (~3 to 4 mm2) of symptomatic tissue were placed in acidified potato dextrose agar (APDA), and the plates were incubated for 4 to 5 days at 30°C. Samples exhibiting fungal growth similar in morphology to G. morbida were transferred to PDA plates to obtain pure cultures and then processed to obtain single-spore cultures. Culture morphology for five single-spore isolates (Gm103, Gm104, Gm105, Gm107, and Gm108) was similar to that described by Kolařík et al. (4) for G. morbida. Conidiophores were penicillate and verrucose. Conidia were narrowly cylindrical, 5.2 ± 0.06 × 2.2 ± 0.04 μm (n = 50). Single-spore isolates were then grown in 1% yeast extract glucose liquid culture for 7 to 10 days. DNA was extracted and the ITS region was amplified, including the 5.8S region by using primers ITS1F/ITS4. Sequences were assembled and deposited in GenBank under accessions KJ664793 to KJ664797. Sequences were compared to those in GenBank; all sequences matched (99 to 100% identity) the ITS sequences of G. morbida strain CBS 124663. Pathogenicity tests were performed on 28-cm-long detached branches of J. regia. Four branches per isolate were inoculated with a 5-mm-diameter mycelial plug from a 2-week-old culture. Branches were incubated at room temperature (23 ± 2°C) in a humidified container for 3 weeks, and then canker lengths were measured. Pieces of the cankered area were placed in APDA and incubated as described above with G. morbida re-isolated from the cankers for all of the isolates, completing Kochs postulates. Average canker lengths ranged from 48.6 ± 4.3 to 72.1 ± 7.1 mm. Re-isolated G. morbida exhibited the same growth and reproductive structure morphology in culture on PDA as the original cultures. TCD in association with WTB has been observed in California English walnut orchards since 2008 (1,2,3). However, this is the first report for completion of Kochs postulates and morphological and molecular confirmation of G. morbida in J. regia and the Paradox rootstock, the predominant rootstock used in commercial orchards. TCD is a concern to the walnut industry in California with over 245,000 bearing acres reported in 2012. References: (1) M. Flint et al. CAPCA Adviser 8:36, 2010. (2) A. D. Graves et al. Walnut Twig Beetle and Thousand Cankers Disease: Field Identification Guide. UC-IPM website publication, http://www.ipm.ucdavis.edu/PDF/MISC/thousand_cankers_field_guide.pdf , 2009. (3) J. Hasey et al. (Abstr.) Phytopathology 100:S48, 2010. (4) M. Kolařík et al. Mycologia 103:325, 2011. (5) C. Utley et al. Plant Dis. 97:601, 2013.

FIRST REPORT OF LASIODIPLODIA CITRICOLA ASSOCIATED WITH STEM CANKER OF PEACH IN CALIFORNIA, USA

In July 2009 and October 2012, stems of young peach (Prunus persica) trees with cankers from Kings, Fresno and Yuba Counties, respectively, in California were submitted to our diagnostic laboratory. The cankered areas were discoloured brown in comparison with the creamy healthy bark and covered with gum galls. More than 30 trees were killed in Fresno and Kings Counties, and 6 trees in Yuba County. Scraping the cankers revealed large black pycnidia and brown discoloured wood. A fungus consistently isolated from the cankers was identified as Lasiodiplodia citricola based on morphological characteristics (Abdollahzadeh et al., 2010) and analyses of ITS, and TEF-1α gene regions. The sequence showed high identity (ITS, 100%; TEF-1α, 99%) with reference sequence (isolate: IRAN 1522C = CBS 124707, ex-type of L. citricola; accession Nos.: ITS, GU945354; TEF-1α, GU945340; β- tubulin, not available) for L. citricola (Abdollahzadeh et al., 2010). Sequences were deposited to GenBank (isolates: 7F93, 7F94 and 7F95. Accession Nos.: ITS, KC357262–KC357264; TEF-1α, KC357268–KC357270; β-tubulin, KC357265–KC357267). Pathogenicity of L. citricola in P. persica variety nectarina cv. Summer Fire was tested using three isolates. Ten two-year-old branches for each isolate were inoculated. Inoculations were made in late Oct. 2012 as described by Chen et al. (2013). Lesion length was measured 3 weeks after inoculation. The three isolates of L. citricola produced 60–67-long lesions within 3 weeks, while wounds were covered with callus tissue in the control inoculations. L .citricola was reisolated from the inoculated branches and no fungus was re-isolated from the control branches. These results indicate the pathogenicity of L. citricola to P. persica.

Fruit and Nut Varieties for Low-Elevation Sierra Foothills

Author(s): Hasey, Janine | Abstract: Lower elevations of the Sierra Nevada have climate, soil, and drainage characteristics that make ideal growing conditions for certain fruit and nut tree varieties — and less so for others. Use this guide to choose the best trees for your home orchard!

Growing Processing Cling Peaches in California: An Overview

Author(s): Norton, Maxwell; Duncan, Roger; Hasey, Janine | Abstract: Everything you need to know about the basics of processing cling peaches in California.

Comparison of Instrumental Non-destructive and Destructive Firmness and Color Measurements with Human Inspection in Clingstone Peaches

The flesh color and flesh firmness of over 13,000 clingstone peaches were measured instrumentally in 2004 and compared to the current official manual inspection methods of the California Department of Food and Agriculture. The instruments evaluated were an impact-type non-destructive firmness instrument, a universal testing instrument equipped with a Magnus-Taylor style penetrometer and a LED-based colorimeter. The instrumented measures gave good agreement (83% across all clingstone cultivars) with the current inspection method in categorizing fruit into acceptable, immature, and bruised, overripe or soft categories. The level of agreement varied by cultivar, with agreement for some cultivars improving if individual classification models were developed for those cultivars. The results confirm that flesh color is not a good predictor of flesh firmness and that destructive quasi-static firmness measures are not good predictors of high velocity impactstyle firmness measurements. The results also show that there is a need for standardization of impact-style firmness measurements.