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An autumn application of dolomitic lime to infected leaves on the orchard floor resulted in a decrease in the percentage of apple and pear leaves with pseudothecia, the number of pseudothecia per leaf, and the number of asci per pseudothecium of Venturia inaequalis and V. pirina. A dolomitic lime application of 5.08 metric tons per hectare reduced the ascospore dose the following spring up to 88% for pear and 92% for apple.

Control of blue mold decay in Bosc pears was studied with the laboratory-grown yeasts Rhodotorula glutinis, Cryptococcus infirmo-miniatus, and two strains of Cryptococcus laurentii, as well as registered biocontrol products Aspire, containing the yeast Candida oleophila, and Bio-Save 11 (now Bio-Save 110), containing the bacterium Pseudomonas syringae. Both thiabendazole (TBZ)-sensitive and TBZ-resistant strains of Penicillium expansum were used. Aspire treatment reduced the average lesion diameter by approximately 65 and 45%, and reduced decay incidence by 27 and 9% with TBZ-resistant and TBZ-sensitive P. expansum, respectively, in the first year of the study, but did not result in significant decay control in the second year. Bio-Save 11 reduced decay lesion diameter by 32 to 72% and incidence by 21 to 40% over the 2 years. In both years, TBZ-sensitive P. expansum was completely controlled by the combination of either C. laurentii (both strains), R. glutinis, or C. infirmo-miniatus with 100 ppm TBZ. With TBZ-resistant P. expansum, control of wound infection with these yeasts alone or with 100 ppm TBZ ranged from 62.9 to 100%. In a packinghouse trial, control by Bio-Save 110 + 100 ppm TBZ and Aspire + 100 ppm TBZ was not different than control by TBZ at 569 ppm, the maximum label rate. The amount of decay following Aspire + 100 ppm TBZ treatment was significantly less than the amount of decay following Bio-Save 110 + 100 ppm TBZ treatment.

The level of resistance to decay caused by four fungal pathogens, the force required to break the epidermis, and the extent of open sinuses as measures of potential decay resistance were determined for the fruit of several apple cultivars. No single cultivar was the most resistant to each of the four pathogens in this study. In addition, each cultivar that was the most resistant to one pathogen also was the most susceptible to one of the other pathogens. However, Royal Gala was the most resistant to the wound pathogens Botrytis cinerea, Penicillium expansum, and Mucor piriformis. Fuji and Oregon Spur II were more resistant than other cultivars to Pezicula malicorticis. The epidermis (skin) of Fuji and Granny Smith were the most resistant to puncture, requiring an average of 81.5 and 87.0 Newtons, respectively, to break the epidermal layer. Fuji had the highest percentage of fruits with open sinuses, with a mean of 38%, whereas Braeburn had 0% of fruit with open sinuses. The cultivar information presented herein may be a valuable measure of decay resistance and may be of use to the apple industry.

Botrytis cinerea was detected and quantified in pear stems from six orchards in the Pacific Northwest, and changes in fungal biomass in the stems after 6 and 8 months of cold storage in regular (air) atmosphere were studied. The fungus was detected by plating stem halves on selective medium and by enzyme-linked immunosorbent assay (ELISA) using the Botrytis-specific monoclonal antibody BC-12.CA4. Both methods demonstrated that the incidence of B. cinerea increased from 6 to 8 months, but ELISA was more sensitive than standard isolation. Quantitative ELISAs on stems indicated that over 200 μg of B. cinerea biomass per gram of stem tissue was present in the stems of visibly rotted fruits, but usually less than 35 μg/g was present in stems from fruits without visible gray mold. Aureobasidium pullulans, Penicillium spp., Alternaria spp., and Cladosporium spp. were commonly isolated from stem tissue. A. pullulans was present in 86% of the stems from which B. cinerea was detected. Use of the monoclonal antibody BC-12.CA4 could help in determining the infection path of B. cinerea in pear stems and detection of latent infections, enabling the timing and method of control of stem end rot to be optimized.

The objective of this research was to determine quantitative relationships between incidence of pear fruit decay and inoculum dose of Botrytis cinerea and Penicillium expansum using dry conidia applied to wet or dry pears in a settling tower. On wet fruit, incidence of gray mold fruit rot increased from 0.1 to 83.1% as the airborne concentration of B. cinerea conidia increased from 0 to 8.6 spores per liter of air. Significantly less decay occurred in fruit inoculated dry compared to wet, particularly in fruit wounded after inoculation. Incidence of blue mold increased from 1 to 100% as the airborne concentration of P. expansum conidia increased from 0.1 to 803.5 spores per liter of air. Blue mold incidence was not affected by fruit wetness or time of wounding relative to inoculation. All regressions of decay incidence versus airborne and surface conidial concentrations were highly significant (P = 0.01).

d'Anjou pear, the main cultivar grown in the Mid-Columbia Region of Oregon, is subject to russeting of the fruit surface, resulting in reduced quality and value. The role of Aureobasidium pullulans and Rhodotorula glutinis in russet of pear fruit was studied. Inoculations were done at full bloom in 1998 and 1999 and petal fall in 1999 with a log range of concentrations up to 108CFU/ml. Populations of A. pullulans on floral and fruit tissue were monitored during spring 1999 and 2000 in six orchards with a history of russet. Russet of fruit in both studies was evaluated at harvest. In 1998 neither fungus increased russet. In 1999, inoculation with two strains of each fungus at 108 CFU/ml increased russet. Inoculation with 104 or 106 CFU/ml did not increase russet in either year. In commercial orchards, there was no correlation between fruit russet and the populations of A. pullulans on floral and fruit tissue. Populations were less than 103 CFU/g of tissue. We conclude that A. pullulans and R. glutinis are not major contributors to russet of d'Anjou pear fruit in the Mid-Columbia Region.

Botrytis cinerea causes significant levels of postharvest decay in the winter pear cultivar d'Anjou. The objectives of this study were to determine the timing of B. cinerea infection of pear stems and calyxes in the orchard during the growing season, to investigate the development of gray mold in storage, and to determine whether preharvest levels of B. cinerea in pear stems and calyxes can be used as predictors of gray mold levels observed in storage. Very low levels of B. cinerea were isolated from stem tissue prior to harvest. In a single year repeat experiment, stems sampled at harvest had higher levels of infection than those sampled earlier in the season. Little or no stem end gray mold was detected in fruit after 3 months in air-storage; however, incidence increased between 6 and 8 months. Calyx end gray mold was detected at low levels in fruit stored for up to 8 months. The mean incidence of stem end gray mold was 3.6 and 2.0%, and incidence of calyx end gray mold was 1.2 and 0.2%, in 1996 and 1997, respectively. Calyxes were susceptible to infection soon after full bloom; however, inoculation of calyxes in April or May did not result in higher levels of calyx end gray mold in storage. Therefore, preharvest level of calyx infection is a poor predictor of calyx end gray mold in storage. In addition, application of benomyl in the orchard reduced the level of B. cinerea in blossoms but had no effect on levels of calyx end gray mold of fruit in storage. Packing and shipping fruit within 3 to 6 months of harvest may mitigate economic losses due to gray mold.

A collection of Neofabraea isolates from pear fruit grown in Oregon, Washington, and California was screened with species-specific primers in a multiplex polymerase chain reaction (PCR). Neofabraea alba was identified most frequently in samples from Oregon and California, whereas N. perennans was found most frequently in samples from Washington. N. alba also was identified from tissue of small cankers and pruning stubs on pear trees using PCR. Bull's eye rot pathogens were isolated from fruit of nine different European pear cultivars, Asian pear, and quince. Overall, N. alba was the most prevalent species in 2001 whereas N. perennans was more prevalent in 2002. An undescribed species of Neofabraea was identified in samples from Medford, OR that corresponds to a species previously found by others using molecular methods. This information increases the known geographic distribution of this undescribed species.

Botrytis cinerea was capable of colonizing and persisting in tissue pieces of six common weed species found in pear orchards in Oregon from midsummer until pear harvest in early September. Sporulation occurred on blackberry mummies in orchard perimeters and ranged from 5,700 to 55,000 conidia per mummy at pear harvest. Conidia of B. cinerea also were observed on fresh blackberry fruit in 2 of 3 years. Sclerotia were present on only a few of the naturally infected pear fruit on the orchard floor through November; however, sclerotia production increased greatly between mid-November and mid-December. Over 90% of sclerotia from naturally infected, overwintered fruit germinated in the laboratory when collected 6 to 8 months after infection. Sclerotia formed on pear fruit inoculated with 28 different paired combinations of 22 isolates in the laboratory. Viability of sclerotia in inoculated pear fruit that overwintered on the orchard floor was 44 to 59% in March and April, and then declined steadily to about 25% at pear harvest. Germination of sclerotia was both sporogenic and myceliogenic. No apothecia were observed in the field or laboratory. An integrated approach to control is needed to deal with these multiple sources of potential inoculum.

Symptoms associated with the core region of apple fruits (Malus domestica) can be classified as moldy core (MC), wet core rot (WCR), and dry core rot (DCR). Infections leading to WCR are thought to occur primarily postharvest, although in South Africa preharvest symptoms also have been reported. The first aim of this study was to investigate the causative agent(s) of preharvest WCR by isolating fungi from eight internal positions in asymptomatic, MC, WCR, and DCR fruits. Secondly, the pathogenicity and virulence of all Penicillium isolates were investigated using three apple fruit inoculation methods: surface wounding, deep wounding, and nonwounding. Isolation of fungi from WCR fruits showed that Penicillium was the predominant fungal genus from most isolation positions including the lesion area. Penicillium ramulosum was the predominant species isolated from all fruits. However, in WCR fruits, the incidence (58%) of P. ramulosum was much higher than in MC (6%), DCR (7%), or asymptomatic (7%) fruits. Less frequently isolated Penicillium species included P. expansum and a few other species. Pathogenicity testing using the nonwounding method was best at discriminating highly virulent isolates. P. expansum was the most virulent species, followed by a putative new Penicillium species with closest sequence similarity to P. dendriticum. P. ramulosum isolates, although showing varying degrees of virulence, all had low virulence, causing only small lesions in wounded apple fruits.

The objective of this study was to evaluate the use of an ethanol vapor release pad and a saprophytic yeast Cryptococcus infirmo-miniatum (CIM) to reduce decay and maintain postharvest quality of intact or fresh-cut sweet cherries (Prunus avium) cv. Lapins and Bing. Intact or fresh-cut fruit were packed in perforated clamshells (capacity 454 g) and stored at 1, 10 or 20 °C for up to 21, 14 and 8 d, respectively. For ethanol treatment, a pad made with silica gel powder containing 10 g ethanol and covered with perforated film, which allows ethanol vapor to diffuse gradually, was attached to the upper lid of the clamshells. Ethanol treatment caused accumulation of ethanol in the packaging headspace, about 10 μL L−1 with little change within 14 d at 1 °C, 23 μL L−1 at d 1 and decreased to 15 μL L−1 at d 10 at 10 °C, and 26 μL L−1 at d 1 and decreased to 13 μL L−1 at d 3 at 20 °C. Ethanol content in fruit was less than 9 mg kg−1 in all the control fruit, and increased to 16, 34 and 43 mg kg−1 in ethanol-treated fruit at 1, 10 and 20 °C, respectively. Nonetheless, a sensory taste panel did not perceive any flavor difference from the ethanol treatment. The ethanol treatment retarded softening, darkening, and acid decrease in fruit as well as discoloration of the stems, and extended shelf-life of intact cherries. Ethanol reduced brown rot (Monilinia fructicola) in fresh-cut cherries stored at 20 °C, but not at 1 and 10 °C. A pre-packaging dip in CIM completely controlled brown rot in inoculated fresh-cut cherries stored at 1 °C, and in naturally infected cherries at 20 °C.

Eikemo, H., Gadoury, D. M., Spotts, R. A., Villalta, O., Creemers, P., Seem, R. C., and Stensvand, A. 2011. Evaluation of six models to estimate ascospore maturation in Venturia pyrina. Plant Dis. 95:279-284. Estimates of ascospore maturity generated by models developed for Venturia pyrina in Victoria, Australia (NV and SV), Oregon, United States (OR), and Italy (IT) or for V. inaequalis in New Hampshire, United States (NH-1) or modified in Norway (NH-2) were compared with observed field ascospore release of V. pyrina from 21 site‐year combinations. The models were also compared with ascospore release data from laboratory assays. In the laboratory assays, the forecasts of the NH-1 and NH-2 models provided the best fit to observed spore release. Under field conditions, the lag phases and slope coefficients of all models differed from those of observed release of ascospores. Identifying the precise time of bud break of pear to initiate degree-day accumulation was problematic at both Australian sites. This resulted in a higher deviance between bud break and first released ascospore compared with the sites in Norway and Belgium. Linear regressions of observed release against forecasted maturity generated similarly high concordance correlation coefficients. However, where differences were noted, they most often favored models that included adjustment for dry periods. The NH-2, IT, and NV models using pooled data also provided the most accurate estimates of 95% ascospore depletion, a key event in many disease management programs.

This study was done to (i) compare seven types of natural or horticultural injuries and wounds for incidence, severity, and mortality of infection of sweet cherry (Prunus avium) by Pseudomonas syringae pv. syringae; (ii) determine the relative resistance to bacterial canker of 14 cultivar–rootstock combinations; (iii) determine if P. syringae pv. syringae is transmitted by contaminated pruning tools; and (iv) determine if summer and winter pruning cuts become resistant to infection. Infection occurred at all of the seven types of injury and wound sites on both cvs. Sunset Bing and Golden Heart. Infection of inoculated wounds made in spring and summer (heading cuts when trees were planted, scoring cuts, and summer pruning) resulted in the greatest canker incidence and severity. Inoculation of heading cuts resulted in the highest tree mortality (86%). ‘Bing’ and ‘Sweetheart’ were the most susceptible cultivars while ‘Regina’ and ‘Rainier’ appeared to be more resistant. Bing trees had the highest mortality of any cultivar with 70% dead at the end of the 3-year study. Canker severity of the three rootstocks varied considerably but mortality was greatest for trees on Gisela 6 (77%). Bacterial canker was not transmitted in summer or winter by cutting through active cankers, then immediately using the same pruning tool to make heading cuts on healthy trees. Heading cuts became resistant to infection after about 1 week in summer and 3 weeks in winter. Results are discussed as part of an integrated management program for bacterial canker of sweet cherry.

The objective of this research was to develop a model to predict, at-harvest, the risk of grey mould in pear fruit (Pyrus communis) in long-term cold storage based on multiple variables including: i) density of Botrytis cinerea DNA on fruit surfaces at harvest; ii) fungicide application within 4 weeks before harvest; iii) rainfall within 2 weeks before harvest; and iv) a relative orchard tree-growth and management rating. The model classified grey mould risk as low, moderate, high, or extreme. Data were collected for 2 years in six pear orchards in New Zealand and for 3 years in eight pear orchards in the Mid-Columbia district of Oregon and Washington, USA. Risk predictions varied from low to extreme, and the corresponding grey mould incidence varied from 0.1 to 14.0%. The multiple R-square was 0.973 when all predictors were included. The Spearman rank correlation coefficient (rs) relating the predicted grey mould risk level to the actual incidence of grey mould in pear fruit was 0.882 (P ¼ 0.000). The decay risk prediction model presented herein appears robust and gave reliable predictions of grey mould risk in d’Anjou and Bosc pear fruit from Oregon–Washington and New Zealand in all three years.

The objectives of this study were to develop primers and a real time PCR protocol for the postharvest biocontrol yeast Cystofilobasidium infirmominiatum ( Cim ). The application of this technology was developed to quantify Cim on the surfaces of apple, two pear cultivars, and sweet cherry fruit treated over a range of concentrations. Statistically significant relationships were observed between Cim DNA on fruit surfaces, expressed as μg/m 2 , and CFU/L of dip suspensions for apple, pear, and sweet cherry. In addition, the relationship for each fruit was significantly different from the other three fruits. Threshold values of concentrations of Cim DNA on the fruit surface were calculated based on regression equations and a dose of 2.0 × 10 11 CFU/L of dip suspension, the dose for optimum decay control, and were 4.8, 7.0, 16.5, and 25.2 μg/m 2 for Bosc pear, Lapins sweet cherry, d’Anjou pear, and Golden Delicious apple, respectively. Monitoring Cim DNA concentration on fruit surfaces will assure that Cim is being properly applied to fruit and that a sufficient number of cells are present for optimum decay control.

Bull's eye rot of pome fruits caused by Neofabraea spp. is characterized by infection occurring in the orchard throughout the growing season whereas rot lesions develop during long-term storage after harvest. Bull's eye rot was observed on pear fruit exposed to natural infection for any of six to nine sequential 1-to-2-week exposure periods during two growing seasons. Highest infection levels were associated with exposure closest to harvest. Over-tree irrigation and late harvest resulted in higher bull's eye rot incidence than under-tree irrigation and early or mid-season harvest. Fruit were inoculated prior to harvest with Neofabraea perennans to determine the effect of environmental factors on the development of bull's eye rot. The effect of temperature was inconsistent; disease was greatest at 10°C in one year of study but greatest at 30°C in the second year. Bull's eye rot developed independently of wetness durations longer than 0.5 h.

The objective of this research was to determine quantitative relationships between incidence of stem end decay of pear fruit and inoculum concentration of Botrytis cinerea and Penicillium expansum using dry conidia applied to pear fruit in a settling tower. Five concentrations of conidia were applied to pear fruit, fruit were stored at –1°C for 8 months, and stem end decay was evaluated. In addition, conidia were washed from the surface of inoculated fruit, and DNA was extracted and quantified with real-time polymerase chain reaction (PCR). The linear regression relationships between percent stem end gray mold and B. cinerea conidia per liter of air or per square centimeter of fruit surface were significant (P = 0.01). At the highest inoculum dose introduced into the settling tower, conidia per liter of air, conidia per square centimeter, and percent stem end gray mold at 8 months after inoculation were 12, 31, and 39, respectively for 2000 and 6, 33, and 67, respectively for 2001. Similarly, the linear regression relationships between percent stem end blue mold and P. expansum conidia per liter of air or per square centimeter of fruit surface were significant (P = 0.01 and 0.05, respectively). At the highest inoculum dose introduced into the settling tower, conidia per square centimeter and percent stem end blue mold at 8 months after inoculation were 39 and 26, respectively for 2000 and 66 and 23, respectively for 2003. Real-time PCR provided a rapid, quantitative measure of B. cinerea and P. expansum DNA on pear fruit surfaces. Because of possible year-to-year shifts in susceptibility of fruit to decay, disease incidence:inoculum dose relationships may be of most value compared within years rather than across years. This would facilitate comparison of decay risk among orchards in order to determine which fruit is most suitable for long-term storage.

The objectives of this study were to examine the effect of several rates of 1-MCP from 10 to 100 nL L −1 on stem end decay caused by Botrytis cinerea and to evaluate the effects of prestorage treatment with 1-MCP, hexanal, and 1-MCP + hexanal on decay of d’Anjou pear ( Pyrus communis L.) fruit in long-term cold storage. 1-MCP at 300 nL L −1 reduced bull's-eye rot and Phacidiopycnis rot. Stem end gray mold also was reduced by 1-MCP at 300 nL L −1 , and reduction at rates from 10 to 100 nL L −1 was significant in one of two trials. Snow-mold rot was reduced by 1-MCP at 30 nL L −1 . Hexanal alone reduced snow mold but increased blue mold caused by Penicillium expansum . The combination of 1-MCP and hexanal affected decay similar to 1-MCP. However, hexanal in combination with 1-MCP negated the effect of 30 nL L −1 1-MCP on firmness but did not counteract the effect of 300 nL L −1 1-MCP. Thus, a combination of 1-MCP and hexanal at optimized rates may reduce storage decay, control superficial scald, and allow normal ripening of d’Anjou pear fruit.

A hot water pressure process (HWP) was evaluated for its effect on conidia of Penicillium expansum and on development of blue mold, gray mold, and mucor rot of d'Anjou pear fruit. Spores were removed from the water system through dilution and also as a result of hot water in the system that was lethal to the spores. When the system was heated, viable spores were not detected after 2-4 h of operation. Reductions in decay in the HWP system were 36, 29, and 13% for Botrytis cinerea, Mucor piriformis, and P. expansum, respectively. The response of P. expansum appeared related to the length of time fruit was in cold storage. Heat injury was observed on fruit treated with 40 and 50 °C water but not on fruit at 30 °C nozzle temperature. The HWP system described in this study should be considered as a component of an integrated decay control strategy.

Powdery mildew (PM) occurs worldwide and is prevalent on susceptible cultivars wherever pears are grown, causing economic losses due to russeted fruit and an increased need for fungicides. A core subset of the Pyrus germplasm collection at the USDA National Clonal Germplasm Repository in Corvallis, Ore., was evaluated for resistance to Podosphaera leucotricha, the causal agent of PM, using greenhouse and field inoculations of potted trees. The core collection consists of about 200 cultivars and species selections, representing most of the genetic diversity of pears and includes 31 Asian cultivars (ASN), 122 European cultivars (EUR), 9 EUR × ASN hybrids and 46 pear species selections. Three trees of each core accession were grafted on seedling rootstocks. In 2001–02, trees were artificially inoculated in a greenhouse, grown under conditions conducive for PM, and evaluated for symptoms. The same trees were subsequently evaluated for PM symptoms from natural field infections during 2003 and 2004. In the greenhouse, 95% of EUR and 38% of ASN were infected with PM. Average PM incidence (percent of leaves infected) in the greenhouse (8% for ASN and 30% for EUR) was much higher than incidence in the field (2% for ASN and 5% for EUR) during 2003. Symptoms were also more severe in the greenhouse, with 46% of ASN and 83% of EUR with PM symptoms having a mean PM incidence of >10%. In the field, 42% and 22% of EUR and 23% and 13% of ASN were infected with P. leucotricha in 2003 and 2004, respectively. Field infection was very low during both years, with percentage leaves infected in ASN and species selections significantly different from EUR. In the field, 6% of ASN with PM symptoms had a mean PM incidence >10% during both years, while 15% and 2% of EUR accessions with PM symptoms had a mean PM incidence >10% in 2003 and 2004 respectively. These results should be very useful to pear breeding programs to develop improved PM resistant cultivars in the future, by using accessions with consistent low PM ratings.

A manually operated high-pressure hot-water washing system consisting of a boiler, hot-water mixing tank, contact loop, heat exchanger, spray mixing tank, high-pressure hot-water washing manifold, low-pressure fresh water rinse manifold, and pressure pump was constructed and installed in a packingline. The system developed 20–50 ◦ C washing water at pressures up to 980 kPa. ‘d’Anjou’ pears (Pyrus communis L.), shortly after harvest, and after storage for 3 and 4 months in regular air (RA) or for 4, 7 and 8 months in controlled atmosphere (CA) at −1 ◦ C were washed through the packingline with different wetting agents (0.1% Silwet, 0.01 and 0.1% Defoamer, and water), water pressures (regular and high-pressure (210–980 kPa)), water temperatures (control (tap water, 4–22 ◦ C), 40 ◦ C, and 50 ◦ C), and brushes (soft and firm), respectively. The effect of the washing conditions on fruit quality was investigated after 1 month of storage at −1 ◦ Ct o simulate shipping condition, and then again after 1 week at 20 ◦ C to simulate marketing condition. Hot-water caused severe heat scald. When nozzle temperature was 50 ◦ C, the incidence of heat scald increased to over 50% for the fruit stored in RA for 3 months. Combined with hot-water, 540 kPa high-pressure washing increased the incidence of friction discoloration. There were lower incidences of friction discoloration and heat scald for fruit stored in CA for 7 months, in comparison to that in RA for 3 months. However, those fruit did not ripen properly as indicated by a high extractable juice content. Fruit washed at harvest had minor incidences of friction discoloration regardless of different brushes, water pressures, and wetting agents. Fruit washed after storages in either 4 months RA or 4 or 8 months CA suffered a high incidence of friction discoloration including scuffing symptoms and pressure marking. The firm brushes caused a higher incidence of friction discoloration mainly because of scuffing symptoms. However, no differences were found between different water pressures and wetting agents with respect to friction discoloration. Fruit stored for 4 months RA suffered 26–28% friction discoloration in comparison to 16–18% in CA stored fruit with firm brush washing. Extended CA storage increased friction discoloration even with soft brush washing. The results suggest that a washing system with high-pressure spray

Postharvest decay causes losses to commercial pear industries. The incidence of decay in air and controlled-atmosphere (CA)-stored ‘d'Anjou’ pear fruit was investigated, and the effect of a prestorage thiabendazole drench on decay in CA-stored fruit was determined. In air storage, bull's-eye rot (31.37%) was most prevalent in 1996, whereas incidence of gray and blue mold (1996 and 1997) and bull's-eye rot (1997) were similar. Mucor, Alternaria, and Coprinus rot levels were low. Incidence of stem-end gray mold (2.58%) was significantly higher than calyx-end (0.73%) and puncture gray mold (0.61%). Incidence of gray mold (2.26%) was higher than all other decay in nondrenched CA-storage, and incidence of other decay types were similar. Incidence of puncture gray mold (1.13%) was higher than stem-end gray mold (0.84%), which in turn was higher than calyx-end gray mold (0.36%) in nondrenched CA-storage. Incidence of gray mold (1.04%) in CA-stored fruit was reduced by a prestorage thiabendazole drench. Drenching reduced stem-end (0.34%) and puncture gray mold (0.40%) but had no effect on all other decay or the total decay incidence. These results support the current recommendations of a single postharvest application of thiabendazole to control gray mold in ‘d'Anjou’ pear fruit.

Botrytis cinerea is responsible for a major portion of postharvest decay in winter pears in the Pacific Northwest. The baseline sensitivity levels (mean EC50values) of a wild-type B. cinerea population to thiabendazole and iprodione were 6.66 and 0.56 mg/liter, respectively. B. cinerea from commercial orchards not treated with a benzimidazole had significantly lower incidence of resistance (0.59%) to a discriminatory concentration of thiabendazole at 10 mg/liter than did isolates from orchards in which benomyl had been applied for experimental purposes (16.0%), unsprayed control trees in benomyl-sprayed orchards (5.34%), and isolates from packinghouses where thiabendazole was applied as a prestorage drench or packingline spray (3.23%). The mean EC50value of isolates in the wild-type population was lower than those of resistant isolates from all other sources. High-level thiabendazole resistance (EC50> 100 mg/liter) was found in 0.20% of isolates from unsprayed commercial orchards, 9.33% of isolates from benomyl-sprayed orchards, and 2.67% of isolates from unsprayed control trees in these benomyl-sprayed orchards. In isolates from packinghouses where a thiabendazole line spray was applied, 1.52% had high-level thiabendazole resistance. All isolates from all pear-related sources tested were sensitive to iprodione at 10 mg/liter. This study provides evidence supporting current recommendations of a single postharvest application of a benzimidazole to control decay caused by B. cinerea, and no application of benzimidazole fungicides in the orchard.

An integrated approach was studied for control of postharvest brown rot of sweet cherry fruit. System components included a preharvest application of propiconazole, a postharvest application of a wettable dispersible granular formulation of the yeast Cryptococcus infirmo-miniatus (CIM) Pfaff and Fell, storage in modified atmosphere, and storage at 2.8 °C for 20 days or −0.5 °C for 42 days. Preharvest propiconazole and postharvest CIM were similarly effective for control of brown rot. A significant propiconazole–CIM synergism was observed. Modified atmosphere significantly reduced brown rot compared to air-stored fruit. The storage temperature regime effect was inconsistent. This integrated decay control approach was effective and is especially relevant since postharvest fungicide options for cherry are limited.

Incidence of wounding in commercially-harvested `d'Anjou' and `Bosc' pear fruit, healing of wounds to decrease decay caused by Botrytis cinerea, Mucor piriformis, Penicillium expansum, and Penicillium solitum at −1°C, 20°C, and 28°C, and formation of compounds potentially involved in resistance were determined. Use of a blue food coloring to make wounds on fruit more visible on packinghouse lines was evaluated. Over 4 years, an average of 2.9% of `d'Anjou' pear fruit were wounded during harvest and handling. In `Bosc' pears, average incidence of wounding was 4.3% where fruit was harvested by workers paid by the hour, and 13.9% where workers were paid by the number of bins harvested. Susceptibility of wounds to infection by M. piriformis, P. expansum, and B. cinerea at −1°C decreased rapidly during the first 2 weeks, 4 weeks, and 8 weeks, respectively. The percent of wounds that stained well with food coloring was similar to the decay susceptibility curve for P. expansum at −1°C. Susceptibility of wounds to decay in fruit held at 20°C decreased almost linearly from 0 to 2 days. After 2 days at 20°C, 78% of the wounds absorbed stain, a significantly higher percent than were susceptible to decay. Prestorage heat treatment of fruit to 28°C for 24 h prior to inoculation decreased susceptibility of wounds to infection by both P. expansum and P. solitum. In commercial packinghouses, use of a 10% solution of blue food coloring to enhance visibility of wounds in pear fruit resulted in removal of 40% of punctured fruit compared with 22% removal without staining. Histochemical tests of cell walls near wounds showed an accumulation of callose, suberin, tannins and pectic substances, as well as gums and starch, within 4 days after wounding. Lignin was not detected in wound tissue.

The yeasts Cryptococcus laurentii (strain HRA5), Cryptococcus infirmominiatus (strain YY6), and Rhodotorula glutinis (strain HRB6) were tested as biocontrol agents of postharvest diseases of apple and pear in semi-commercial and commercial trials. The yeasts effectively controlled decay when applied in a drench or line spray. The yeasts were not adversely affected when treated fruits were stored in a controlled atmosphere consisting of 1% oxygen and 99% nitrogen. In a commercial trial, the most effective treatments for control of blue mold of pear were a combination of C. laurentii and C. infirmo-miniatus (91% control) and the commercially recommended high rate (528 μg/ml) of thiabendazole (88% control). In the commercial apple trial, the most effective treatments for blue mold were C. infirmo-miniatus combined with 264 μg/ml thiabendazole (91% control), C. infirmo-miniatus combined with C. laurentii (84% control), and thiabendazole alone at 528 μg/ml (79% control). The combination of C. laurentii with 264 μg/ml of thiabendazole was significantly more effective for control of blue mold on pear than thiabendazole at 528 μg/ml whenever any thiabendazole-resistant spores were present in the inoculum.

Six yeast strains isolated from the surface of pear fruits were evaluated for their ability to control postharvest blue mold (caused by Penicillium expansum ) on Golden Delicious apple fruits. All strains significantly reduced blue mold incidence and severity when applied simultaneously with the pathogen. Cryptococcus infirmo-miniatus strain YY6 and Cryptococcus laurentii strain HRA5 were the most effective, and populations in apple wounds increased approximately 1.2 log units within 10 days at 0°C and approximately 1.4 log units in 2 days at 5, 10, or 20°C. Control of blue mold by these two yeasts alone or in combination with a low dose of thiabendazole (15 μg/ml) was tested at 5, 10, and 20°C. Yeasts combined with thiabendazole controlled the disease significantly better at all temperatures (except at 10°C during 1994) than the low dose of thiabendazole alone, and the control was comparable to that achieved using a commercially recommended high dose of thiabendazole (525 μg/ml). C. infirmo-miniatus controlled disease incidence better than C. laurentii at 5, 10, and 20°C during 1993 and 1994. On sweet cherry, C. infirmo-miniatus or C. laurentii combined with a low dose (20 μg/ml) of iprodione controlled brown rot caused by Monilinia fructicola as did a high dose (1175 μg/ml) of iprodione.

Thirty-one morphologically different strains of yeasts and yeast-like fungi, isolated from the surface of pear fruits, were evaluated for biocontrol potential of blue mold on d'Anjou pear fruits. Seven yeast strains (Cryptococcus albidus strain HRB2, C. infirmo-miniatus strain YY6, C. laurentii strain HRA5, Rhodotorula aurantiaca strain YCL5, and R. glutinis strains HRA3, HRA4 and HRB6) reduced incidence of blue mold on pears. C. laurentii HRA5 and R. glutinis HRB6 were most effective for reduction of incidence and severity of blue mold. C. laurentii HRA5 and R. glutinis HRB6 combined with a low dose of thiabendazole (TBZ) (15 μg ml−1) gave significantly better disease control at 5, 10 and 20 °C than either TBZ or the yeast alone and was comparable to disease control achieved using a commercially-recommended high dose of TBZ (525 μg ml−1). C. infirmo-miniatus strain YY6 was most effective for the control of Mucor rot of pears. C. laurentii HRA5, C. infirmo-miniatus YY6, and R. glutinis HRB6 reduced incidence and severity of gray mold of pears and were more effective when combined with a low dose of TBZ. Side rot of Bosc pears was completely controlled by C. laurentii HRA5, C. infirmo-miniatus YY6 and R. glutinis HRB6, whereas TBZ was ineffective. Bull's-eye rot of pears was completely controlled by all yeasts when they were combined with a low dose of TBZ. Populations of C. laurentii HRA5, C. infirmominiatus YY6 and R. glutinis HRB6 in pear wounds increased approximately 1.3 log units within 10 days at −1 °C and 1.7 log units in 2 days at 5, 10 and 20 °C. Addition of cell-free supernatants of yeast cultures to wounds did not suppress decay, and substances inhibitory to fungal germination were not detected on culture plates.

‘Bosc’ pears ( Pyrus communis , L.) harvested at commercial maturity with flesh firmness (FF) of 75 Newton (N) from the southern district of Oregon were stored in either air or step-wise low O 2 at −1 °C during the 1992–'93 and 1993–'94 seasons. The levels of O 2 in the step-wise low O 2 storage were maintained and increased from 0.5% for four months to 1.0% for two months, and finally to 1.5% for two months while the CO 2 concentration in the storage was kept below 0.05%. Air-stored fruit were capable of ripening normally with good dessert quality after one, two, and three months of storage. These fruit softened to between 9.7 N and 15.0 N and reached the ethylene climacteric peak on day 7 or 8 of ripening at 20 °C. The ripened fruit developed a buttery and juicy texture as indicated by an apparent reduction of extractable juice (EJ) from 67 ml juice per 100 g fresh weight (FW) of unripened pulp tissue to less than 45.0 ml juice per 100 g FW of ripened pulp tissue. Fruit in air storage for four and five months reached the ethylene climacteric peak on day 4 of ripening but did not soften properly. Fruit stored in step-wise low O 2 for six, seven and eight months reached the ethylene climacteric peak on day 6 of ripening. Step-wise low-O 2 -stored fruit softened properly to 12 N or lower and reduced EJ to 49 ml 100 g −1 FW (six and seven months of storage) or 59 ml 100 g −1 FW (eight months of storage) on day 8 of ripening. Based on the analyses of ethylene production, fruit softening and reduction of EJ during ripening, fruit stored in the step-wise low O 2 storage for six, seven and eight months maintained a physiological state similar to the fruit stored in air for one to three months. The combination of prestorage heat (28 °C for one day) and step-wise low oxygen storage effectively reduced side rot by 60 and 63% in 1993 and 1994, respectively. Even greater decay control was obtained with the fungicides imazalil and Exp10412A on inoculated fruit, and thiabendazole plus captan on non-inoculated fruit.

Several factors affecting the severity of bacterial canker of pear were studied. In the orchard, infection of shoots by Pseudomonas syringae pv. syringae occurred only when the inoculum dose exceeded 10 6 colony-forming units/shoot. However, under favourable conditions in a growth chamber, cankers formed on detached shoots inoculated with 5 cfu/shoot. A second-order polynomial relationship was established between log 10 transformed canker length and log 10 transformed inoculum dose. In orchard and growth chamber experiments, shoots were susceptible from the time of bud swell until after fruit harvest. The severity of Pseudomonas canker of detached shoots increased if they were frozen at -10°C for 24 h before inoculation. Shoots were most susceptible when inoculated immediately after wounding, and no cankers developed in the orchard when 3-day-old wounds were inoculated. Additionally, no cankers resulted from inoculation of leaf scars at leaf drop. Actively growing, current-season shoots were more susceptible than shoots that had set a terminal bud. The practical implications of these results are discussed as a basis for control of bacterial canker of pear.

Variables necessary to calculate potential ascospore dose (PAD) for Venturia pirina, the causal agent of pear scab, were measured: area of individual leaves averaged 20.0 cm2, number of lesions per infected leaf ranged from 1.8 to 2.2, 13.5 to 41.7% of lesions were fertile (contained pseudothecia), number of pseudothecia per fertile lesion ranged from 15.2 to 24.4, and number of asci per pseudothecium averaged 131.5. The proportions of orchard floor covered with leaves (leaf litter density) were 0.34 and 0.67 for mowed and nonmowed orchards, respectively. Incidence of infected leaves ranged from 0.1 to 32.3%. Calculated PAD ranged from 1,114 to 708,320 ascospores per m2 in a commercial and an unsprayed orchard, respectively. For validation of a previously published model relating ascospore maturity to degree-days with a 0°C base, a linear regression equation was developed using 11 data sets collected between 1981 and 1998. The slope of the line was not different (P = 0.951) from that of the original model.

Plots were established at Ukiah and Davis, California, and Medford and Hood River, Oregon, to evaluate the effect of fenarimol (Rubigan 1 EC), applied at various stages of bloom development, on fruit shape of Bartlett pear. At each location, 10 different treatment schedules were applied at various combinations of bud burst (BB), green cluster (GC), white bud (WB), and full bloom (FB). In schedules that included an application at FB, the fruit length:diameter (L/D) ratio was significantly reduced in at least three of four locations when compared to untreated controls. When fenarimol was applied at BB, GC, WB, and FB, the L/D ratio was reduced at all locations. Treatment at BB only did not affect L/D ratio. Schedules involving GC or WB, but not FB, resulted in reduced L/D ratios at only one or two locations. When data from all four locations were combined, L/D ratios were significantly reduced by all fenarimol treatments except BB alone, and the smallest L/D ratios resulted from treatments which included applications at both WB and FB. Fruit stem length was significantly reduced by all timings of fenarimol application except GC at Medford, and all timings except BB and GC at Ukiah. Fruit weight did not differ among treatments.

The effectiveness of preharvest iprodione and postharvest Cryptococcus infirmo-miniatus treatments alone and in combination for control of decay of sweet cherry fruit was studied. Also, the effect of a modified atmosphere on brown rot control was evaluated as a part of the iprodione–C. infirmo-miniatus combinations. A single preharvest application of iprodione at 1.13 kg a.i./ha reduced brown rot in stored sweet cherry fruit in both years of this study. Significantly better control of brown rot was obtained when cherry fruit that received a preharvest iprodione application also were treated with a postharvest dip in a suspension of C. infirmo-miniatus containing 0.5 to 1.5 × 108CFU/ml. Brown rot was reduced by modified atmosphere packaging (MAP) alone and further reduced as a result of a C. infirmo-miniatus–MAP synergism. Incidence of brown rot was reduced from 41.5% in the control to 0.4% by combining preharvest iprodione and postharvest C. infirmo-miniatus treatments with MAP.

Selected orchard practices were evaluated for their influence on powdery mildew infections (caused byPodosphaera clandestina)of sweet cherry in two orchards in Oregon. Three training systems (Spanish bush, steep leader, and central leader), four rootstocks (Edabriz, Maxma 14, Mazzard, Pontaleb), and five cultivars (cvs. Bing, Lapins, Regina, Staccato, and Sweetheart) were included in our studies. Mildew severity was significantly the highest on trees trained on the Spanish bush system (10.7% and 16.6% of leaf surface colonized in 2003 and 2004, respectively) when compared with Vogel central leader (2.7% and 10.8% of leaf surface colonized in 2003 and 2004, respectively) and steep leader (5.3% and 6.9% of leaf surface colonized in 2003 and 2004, respectively) systems. Foliar mildew infections were significantly the lowest on rootstock Edabriz (0.5% and 1.5% of leaf surface colonized in 2003 and 2004, respectively). A range of susceptibilities was noted among the cultivars tested. Cv. Regina had the lowest level of foliar mildew infections in both 2003 and 2004 (0.1% and 0% of leaf surface colonized, respectively), whereas cvs. Staccato and Sweetheart had the highest (32.6% and 33.4% of leaf surface colonized, respectively). Results indicate that selection of training system, rootstock, and cultivar may impact the severity of powdery mildew infestations in sweet cherry orchards. As production of sweet cherries (Prunus avium L.) has flourished in Oregon and Washington, so has powdery mildew caused by the fungus Podosphaera clandestina (Wall.:Fr) Lev. Fruit infected with P. clan- destina develop unsightly blemishes after harvest, rendering them less desirable for consumers. Increased incidence and severity of powdery mildew may be related to changes in sweet cherry production such as the implementation of high-density plant- ings, the use of late-season maturing culti- vars, climatic changes, and changes in pruning strategies to emphasize a more pedestrian orchard, where the majority of the orchard can be harvested from the ground. Growers are heavily reliant on fungicides to manage powdery mildew. Planting mildew- resistant cultivars and implementing pruning techniques that encourage open canopies are two examples of alternative strategies used by growers. To date, there have been no studies on the effects of canopy management on cherry powdery mildew infestation levels. Rootstocks directly control scion vigor, which may indirectly impact the development ofP.clandestina. Sweet cherry rootstocks are generally selected based on their promotion of a dwarfing habit and fruiting precocity. Cherry cultivars are known to vary in their mildew susceptibility (Olmstead et al., 2000). For example, cv. Bing is considered highly susceptible, and 'Lapins' is considered mod- erately to slightly susceptible. Studies were undertaken to examine the effects of selected horticultural practices on the infection of sweet cherry by P. clandes- tina on sweet cherry. We evaluated mildew severity as a response to three training sys- tems, four rootstocks, and five cultivars.

Conditions were established for inducing pear (Pyrus communis L.) blossom blast caused by Pseudomonas syringae (Ps) on detached shoots. Highest incidence of infection followed occurrence of a major exotherm in the presence of Ps suspended in water drops on blossom tissue. Eight pear cultivars were evaluated for susceptibility to blossom blast, with the red-fruited 'Beurre d'Anjou' sports 'Gebhart' and 'Columbia' least susceptible and 'Doyenne du Cornice', 'Beurre d'Anjou', and 'Beurre Bosc' most susceptible. Blossom blast of pear is caused by Pseu- domonas syringae van Hall (Ps), an epiphy- tic phytopathogenic bacterium (Barker and Grove, 1914; Crosse, 1959). Under favora- ble climatic conditions, the disease has caused

A decay of ‘Granny Smith’ apples (Malus domestica Borkh.) was observed in 1988, 1990, and 1991 on fruit grown in the lower Hood River Valley of Oregon and stored at 0°C. Harvested fruit were drenched with thiabendazole and stored in October in all years. In mid-November, fruit were sized, drenched with sodium hypochlorite, and returned to cold storage. Decay was observed in January when fruit were removed from cold storage, sorted, and packed. Decayed areas were light brown and firm with a slightly indefinite margin. Losses were less than 1% of fruit packed. Diseased fruit were surface-disinfested with 95% ethanol, and tissue pieces were transferred aseptically to potato dextrose agar acidified with lactic acid and incubated at approximately 22°C. The fungus consistently isolated was identified as Phytophthora syringae (Kleb.) Kleb. based on morphological characters (3). Sporangia were persistent and averaged 60 μm long (range 59 to 69) × 40 μm wide (range 37 to 43). Antheridia were paragynous, and oospores averaged 37 μm (range 31 to 46). ‘Golden Delicious’, ‘Granny Smith’, and ‘Gala’ apples were inoculated with mycelial plugs from a 7-day-old culture of P. syringae and incubated 12 days at 5°C and 7 to 12 days at 22°C. Twenty fruit of each cultivar were used—ten were inoculated, and ten uninoculated fruit served as controls. Lesions developed on all inoculated fruit but not on uninoculated controls. Lesions were spherical, chocolate brown, and firm with no evidence of external mycelia. Lesion morphology was similar on all cultivars. P. syringae was reisolated from lesion margins of all infected fruit. This postharvest decay of apples has not been observed in the Hood River Valley since 1991. Fruit rot of apples caused by P. syringae is known in Canada (1) and is common in the United Kingdom (2), but has not been reported previously in the United States. To our knowledge, this is the first report of postharvest decay of apples by P. syringae in the United States. References: (1) R. G. Ross and C. O. Gourley. Can. Plant Dis. Surv. 49:33, 1969. (2) A. L. Snowdon. A Color Atlas of Postharvest Diseases. CRC Press, Inc., Boca Raton, FL, 1990. (3) G. M. Waterhouse. The Genus Phytophthora. Misc. Publ. 12. The Commonwealth Mycological Institute, Kew, Surrey, England, 1956.

Record rainfall occurred in the Hood River Valley during spring of 1993. In late spring, lesions up to 2 cm in diameter were observed on d'Anjou pear fruitlets on the calyx end or where senescent flower parts adhered to the fruits. Sclerotinia sclerotiorum was consistently isolated from infected tissue. Koch's postulates were tested, and S. sclerotiorum was confirmed as the cause of the disease. Mycelial growth of the pathogen on acidified potato dextrose agar was optimum at 20°C, and the average growth rate was about 10 mm per day. Five pear cultivars were ranked in order of increasing resistance to Sclerotinia rot as follows: d'Anjou, Bosc, Columbia Red d'Anjou, Bartlett, and Comice. Among eight fungicides tested, only iprodione provided good control of fruit infection.

In surveys conducted during two fruit packing seasons, P. expansum and P. solitum were recovered most frequently (65 and 96% of collections, respectively, in 1990-91, and 77 and 54% of collections, respectively, in 1991-92) and in highest densities (1,893 cfu/ml and 749 cfu/ml, respectively, in 1990-91, and 308 cfu/ml and 667 cfu/ml, respectively, in 1991 -92) from pear and apple dump tank water. Penicillium solitum was collected most frequently (89% of collections) and in greatest concentrations (1,634 cfu/ml) from drench solutions followed by P. expansum and P. commune (47 and 42% of collections, respectively, and 495 cfu/ml and 249 cfu/ml, respectively). Penicillium expansum was recovered from about 27% of field bins sampled while P. solitum and P. commune were recovered from about 10 and 8%, respectively. Penicillium expansum and P. solitum were the Penicillium spp. most frequently recovered from fruit sampled from packinghouses and markets. Pear fruit were treated with 2 × 10 2 conidia per milliter of P. expansum in challenge inoculations 0, 1, 7, or 28 days following initial treatment with 2 × 10 3 conidia per milliter of either P. solitum or P. commune to determine the competitive ability of P. expansum relative to these species. When incubated at 20 C for 7 days immediately following the challenge inoculation, P. expansum became established in wounds 0, 1, or 7 days following initial treatment with P. solitum and in water controls. Penicillium expansum did not become established in wounds challenged 28 days after initial treatments or in wounds challenged 7 days after initial treatment with P. commune. Incidence of infection by P. expansum following challenge inoculations 28 days after initial treatment with P. solitum was greater than in water controls when fruit were incubated at −1 C for 28 days followed by a ripening period of 7 days at 20 C. Incidence of infection by P. expansum generally decreased with increasing periods of time at which fruit were inoculated following initial wounding. Of 12 Penicillium spp. tested, only P. aurantiogriseum, P. commune, P. crustosum, P. expansum, P. griseofulvum, and P. solitum produced lesions in wounds of newly harvested, mature pear fruit (cv. d'Anjou)

Removal of conidia of Penicillium expansum from aqueous suspensions with sieves of 2.0 mm to 10 μm and with a triple-stage cartridge filter unit with 5-, 1-, and 0.45-μm terminal filters was studied. The effectiveness of sand filters and cartridge filters for removal of conidia also was evaluated in commercial apple drenchers and packinghouse flumes. The sieves were effective for removal of conidia only when 5-20 mg/ml of soil was added to the suspension, indicating that conidia frequently were bound onto soil particles. In the packinghouse, sand filters did not reduce the concentration of P. expansum in the flume water

In treatments with aqueous ozone solutions for 5 min, LD 95 values for spores of Botrytis cinerea, Mucor pinformis, and Penicillium expansum were calculated to be 0.99, 0.69, and 0.39 μg of ozone per milliliter of water, respectively. Spore inhibition was directly correlated with ozone concentration in 1- to 5-min exposure times; eight regressions of spore inhibition with concentration were significant at P=0.01, and one was significant at P=0.05 (...)

The effects of conidial inoculum dose and selected combinations of temperature and wetness duration on the incidence and severity of pear scab on fruit and foliage were studied. The relationship between the time of preharvest infection of pear fruit and the length of storage at -1 C before symptoms developed also was determined. Incidence and severity of scab on leaves and shoots of Bartlett pear seedlings increased linearly as inoculum concentration increased from 5×10 2 to 5×10 4 conidia per milliliter

(...) One to 5% of the trees were infected with Cytospora cincta each year, and 18% were infected by 1986. Bacterial canker, caused by Pseudomonas syringae, occurred in 13% of the trees in 1982 and in 25% of the trees by 1986. The death rates of trees infected with C. cincta and P. syringae were 16 and 17%, respectively. Disease incidence was highest in trees close to an old cherry orchard. Nitrogen or benomyl did not reduce the incidence of cankers. White trunk paint reduced the incidence of both Cytospora and bacterial trunk cankers

Spring overtree misting using greenhouse mist nozzles was tested for effects on bloom delay, incidence of disease, European red mite populations, fruit size, maturity, fruit russeting and tree survival of ‘Golden Delicious’ apple (Malus domestica Borkh.) on Mailing 9 rootstock. Bloom delay of 9 and 8 days was observed in misted trees in 1975 and 1976, respectively, Apple scab was controlled with standard fungicide spray programs, but fireblight was severe in 1975 on misted trees. European red mite (Panonychus ulmi Koch.) egg hatch was delayed on misted trees but post treatment populations were not affected. Phytotoxicity occurred on calyx and foliar tissue in misted trees in 1975. Fruit set and yield were reduced in misted trees in both years. Fruit size in misted treatments in 1975 was reduced through late July, but was comparable at harvest. In 1976, misted fruit size was reduced. Fruit color, soluble solids and firmness tests indicated maturity was delayed by mist. Fruit russeting in spring misted treatments was reduced. Substantial tree losses occurred in misted treatments in 1975.

No registered fungicide controls Mucor piriformis, a cause of severe postharvest storage rot in pears, but the experimental fungicide RH 886 (active ingredients: 77% 5-chloro-2-methylisothiazol-3-(2H)-one and 23% 2-methylisothiazol-3-(2H)-one) has an ED50 of 23.1 μg ml−1 in 5 min exposure for germination of sporangiospores of M. piriformis and an ED50 of 9.9 μg ml−1 for mycelial growth. Mixing RH 886 into infested, amended soil at 8 mg g−1 soil or mixing copper sulfate into soil at 1 mg g−1 soil prevented sporulation of M. piriformis. Application of RH 886 to pear fruits prior to inoculation, or immersion of fruits in solutions of RH 886 containing sporangiospores of M. piriformis significantly reduced fruit infection.

Deciduous fruit tree orchards located in the Pacific Northwest were surveyed over a 3-year period for the presence of ice nucleation-active (INA) bacteria. In the Yakima Valley, only about 30% of the fruit tree orchards contained INA bacteria (median population ca. 3 × 10 2 CFU/g [fresh weight]) in contrast to nearly 75% of the orchards in the Hood River Valley (median population ca. 5 × 10 3 CFU/g [fresh weight]). These INA populations ranged from less than 10 to over 10 6 CFU/g (fresh weight) of blossoms and, in Hood River Valley orchards, generally comprised over 10% of the total bacterial population. Populations of INA bacteria fluctuated during the year with highest levels developing on buds and flowers during the cool, wet spring, followed by a drop in populations during the warmer, drier, summer months and finally a gradual increase in the autumn. The INA bacteria persisted on dormant buds from which they again colonized young developing vegetative tissues. All INA bacteria were identified as Pseudomonas syringae . The frequency of ice nucleation at −5°C for these strains ranged from nearly every cell being INA to less than 1 in 10 7 cells. The median frequency of ice nucleation at −5°C was 10 4 cells per ice nucleus. The INA P. syringae strains from individual orchards were diverse with respect to bacteriocin typing and in ice nucleation frequency. The consistent absence of detectable INA bacteria or presence of low populations in most of the orchards surveyed during periods when critical temperatures (i.e., −2 to −5°C) were common indicated a limited role for INA bacteria in frost susceptibility of most Pacific Northwest orchards.

Population densities increased from less than 10 2 to between 10 3 and 2×10 3 sporangiospores per cubic centimeter of dry soil, then rapidly declined between December and February, and usually remained below 10 2 sporangiospores per cubic centimeter throughout the summer. In soil kept free of vegetation and fruit, the population density of sporangiospores declined rapidly from 1.5×10 5 per cubic centimeter and remained below 10 3 per cubic centimeter for more than 2 yr. Addition of pear fruits to this soil resulted in an increase from 14 to 9.6×10 3 spores per cubic centimeter between September 1986 and January 1987