Verticillium wilt, caused by Verticillium dahliae, is a major disease affecting California strawberry production. Following the phaseout of methyl bromide, an integrated approach is necessary to alleviate disease pressure. Two field experiments were conducted to evaluate the effect of integrating sequential fumigant applications, crop termination, bed fumigation, and a moderately resistant cultivar on disease incidence and yields. For crop termination, metam potassium or metam sodium was utilized; for bed fumigation, either of the metam products or chloropicrin was utilized. 'Seascape' and 'Valiant' were utilized to evaluate the integration of genetic resistance following fumigation. In both trials, total and marketable yields were statistically similar between plots that were only bed fumigated and those sequentially crop terminated and bed fumigated. In trial 1, in which the initial V. dahliae inoculum and disease pressure were high, sequential crop termination with metam potassium followed by bed fumigation with chloropicrin produced the highest average total (21.8 +/- 0.7 kg) and marketable (16.4 +/- 0.7 kg) yields and significantly reduced disease incidence compared with the nontreated control. In contrast, trial 2 exhibited lower overall disease incidence due to reduced inoculum levels and cooler, wetter conditions; no significant yield differences were observed among treatments. Across both trials, Seascape produced higher average total yields than Valiant, but cultivar resistance did not consistently reduce disease incidence. These results indicate that fumigation remains most effective under high inoculum conditions, whereas the benefit of additional crop termination or genetic resistance is diminished under low disease pressure.Copyright (c) 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Fusarium wilt of strawberry is a widespread disease controlled through genetic resistance to Fusarium oxysporum f. sp. fragariae (Fof) race 1 conferred by the FW1 locus. In 2022, a novel race called CA Fof race 2 was identified in Oxnard, California (CA) that can overcome FW1 resistance and cannot be identified using published molecular diagnostic assays. To understand the prevalence and enable early detection of the novel CA Fof race 2, this research developed strain-specific qPCR and recombinase polymerase amplification (RPA) diagnostic assays and applied them to survey CA Fof race 2 in strawberry. A candidate locus was identified through alignment of reads from off-target isolates to genome assemblies of two virulent CA Fof race 2 isolates. Diagnostic qPCR and RPA tests were validated using target and off-target DNA. The RPA was validated in two laboratories to confirm reproducibility and used to test 2,945 diagnostic samples collected in strawberry-growing areas of the United States of America, Canada, and Mexico. Both assays showed 100% specificity based on laboratory screening of DNA. The limit of detection was 100 fg of DNA for the qPCR assay and 1 pg for the RPA assay. The RPA assay identified 19 out of 2,945 samples as positive for CA Fof race 2, all from six fields around Oxnard, CA; these results were confirmed by subsequent isolations and qPCR. Outcomes of this research provide essential diagnostic tools for quantifying and identifying CA Fof race 2 and highlight the limited geographic distribution of this novel resistance-breaking strawberry pathogen.

Botrytis fruit rot, caused by Botrytis cinerea, is among the most devasting strawberry fruit rots. Infection first appears as a small brown lesion, often under the calyx, and following prolonged wetness (>13 h). Sporulation appears as a velvety gray mold with susceptibility increasing with fruit ripeness. This report evaluates the efficacy of 19 fungicides for the management of Botrytis fruit rot on strawberry 'Fronteras' in San Luis Obispo, CA, in 2024. Results from this study will help inform strawberry growers in developing effective management programs for this disease.

Spatial and temporal effects of fungicide inputs on resistance selection were evaluated by conducting two field studies and by leveraging publicly available pesticide application data along with previously published fungicide resistance survey results. The trials were conducted to evaluate the short-term impact of fungicide programs on the development of resistance in Botrytis cinerea, the causal agent of Botrytis fruit rot in strawberries, where strawberry plots were treated with various single and rotational fungicide regimens over a six-week period. Resistance in B. cinerea isolates was assessed across five sampling dates using discriminatory dose assays. After the consecutive applications, resistance frequencies tended to remain stable to boscalid and fludioxonil but increased sharply for fenhexamid. After a 6-week period with no fungicide inputs, resistance frequencies to fenhexamid tended to decrease, while resistance frequency to pyraclostrobin was stable. The findings suggest varying responses in resistance selection and fitness costs depending on the mode of action that the populations were exposed to. The public fungicide application data showed that intensive strawberry production regions with high fungicide inputs were hot spots for fungicide resistance selection. The findings emphasize the need for strategic fungicide use and resistance management.

Powdery mildew of strawberry, caused by Podosphaera aphanis, is a disease that infects all aboveground parts of the plant and is especially common on leaves, fruit, and stems. The disease is commonly associated with white, visible mycelium. This report evaluates the host resistance to powdery mildew in 20 strawberry genotypes under greenhouse conditions in San Luis Obispo, CA, in the spring of 2024. Disease incidence and severity were evaluated for all genotypes. Results of this study will inform strawberry growers in selecting resistant cultivars for optimized production.

Botrytis fruit rot, caused by Botrytis cinerea, is the most economically important strawberry fruit rot worldwide. Infection first appears as a small brown lesion, often under the calyx and following prolonged wetness (>13 h). Sporulation appears as a velvety gray mold, with susceptibility increasing with fruit ripeness. This report evaluates the efficacy of 16 different fungicides most commonly used in Santa Barbara County for the management of Botrytis fruit rot on strawberry cultivar ‘Fronteras’ in San Luis Obispo, CA, in 2024. Results from this study will help inform strawberry growers in developing effective management programs for this disease.

Podosphaera aphanis, causal agent of strawberry powdery mildew, is a foliar pathogen that infects flowers, fruit, leaves, and petioles. The disease can result in declining plant health, deformed fruit, and yield loss. This report evaluates the efficacy of fungicides for the control of powdery mildew under greenhouse conditions in San Luis Obispo, CA, in the summer of 2024. Disease incidence and severity were evaluated for all treatments and controls. Results of this study will inform strawberry growers in developing effective fungicide programs for managing powdery mildew.

Root rot, or charcoal rot, caused by the soilborne fungus Macrophomina phaseolina, is a significant disease affecting strawberry production worldwide. Field trials were conducted for five seasons (2016-2017 to 2020-2021) to evaluate strawberry host plant resistance to Macrophomina root rot (MRR) in California. A wide range of plant resistance to MRR was observed. Because low disease severity occurred in the fifth season, a summary of the first to fourth seasons showed that 'Osceola' was highly resistant, whereas 'Festival', 'Sweet Ann', and 'Ruby June' were highly susceptible. Disease severity varied over the seasons for specific cultivars, as did the average final mortality for all cultivars. Models were built to investigate the relationship between environmental variables and final disease mortality among the seasons. Strong positive associations were found between the soil temperature during the first month after planting (R2 = 0.79, P < 0.0001) or air temperature mid-season (R2 = 0.79, P < 0.0001) and the final disease mortality of eight cultivars. We concluded that the soil temperature during the early stage of plant development and the mid-season air temperature are important factors in disease development for MRR. Screening new strawberry cultivars and elite breeding lines against MRR should be ongoing as part of a standard process for determining the susceptibility of currently grown and potentially new cultivars.

Verticillium dahliae, the causal agent of Verticillium wilt of strawberry, is a major soilborne pathogen in California strawberry production. Recent shifts in disease management have necessitated alternative methods for disease control. Two field experiments were conducted to examine the efficacy of sequential fumigant applications for crop termination and bed fumigation to reduce Verticillium dahliae inoculum density in a naturally infested field. Fumigant efficacy was evaluated for crop termination and for reducing pathogen survival in host tissue. Crop termination was conducted using metam potassium and metam sodium. Bed fumigation was conducted using both metam products and chloropicrin. For plots that were subject to both crop termination and bed fumigation, inoculum levels were somewhat reduced (3–6 CFU/g of soil) but not to a level below the disease threshold for strawberry (2 CFU/g of soil). Plots subjected to crop termination with metam potassium and bed fumigation with chloropicrin resulted in the lowest V. dahliae inoculum density. Injury due to crop termination ranged from 53% to 77% at 7 days after fumigation (DAF) and 73–89% at 14 DAF. The odds ratio of V. dahliae survival in the terminated crop were lower than in crops not terminated and V. dahliae survival was less likely at 14, compared to 7 DAF. In the crop terminated with metam potassium, the odds ratio of pathogen survival in the petiole versus the crown was 0.9–1.4. This research shows that crop termination could constitute management strategies for Verticillium wilt of strawberry.

Botrytis fruit rot (BFR) causes significant losses in-field and postharvest in strawberries and is mainly managed by fungicides. Strategically applying fungicides only during wet and cool periods would reduce fungicide resistance development and grower costs. A survey of BFR levels in field-grown strawberries with and without fungicide applications was conducted in Santa Maria, California. Weather data were collected to calculate the BFR risk factor using Florida's Strawberry Advisory System (StAS). There were no significant differences between fungicide and no-fungicide treatments for in-field and postharvest BFR incidence in 2021 and in-field BFR incidence in 2022, while the no-fungicide treatment showed higher postharvest BFR incidence in 2022. Average in-field BFR incidence for fungicide and no-fungicide treatments was 2.6% and 2.5% for 2021 and 3.0% and 3.7% for 2022. Average postharvest BFR incidence for fungicide and no-fungicide treatments was 1.8% and 2.0% for 2021 and 0.6% and 1.5% for 2022. BFR risk factor was significantly associated with BFR incidence in 2021, but not in 2022. StAS predicted a 50% and 44% fungicide application reduction in 2021 and 2022 compared to grower standard treatments. These results indicate the potential of reducing fungicide use without compromising BFR control in California strawberry production.

Strawberries in California are grown in specific coastal areas where land is scarce and climate change threatens future production. Strawberry growers are under pressure to adopt sustainable production strategies such as crop rotation, but this practice requires more land than back-to-back planting. The objectives of this research were to quantify the rate of crop rotation across the three main strawberry producing regions in California (Ventura, Santa Maria, and Monterey Bay), and evaluate geographic and edaphic influences on crop rotation. All strawberry fields in the main strawberry producing regions of California were identified by satellite imagery and manual inspection for the years 2017 through 2022. ArcGIS Pro was used to outline each strawberry field and compare among years to determine the period between successive strawberry plantings. Edaphic characteristics and shapefiles for surrounding fields were retrieved from public datasets. The three regions significantly differed in their rates of crop rotation. On average, 95, 52, and 25% of strawberry hectares were rotated each year in the Monterey Bay, Santa Maria, and Ventura regions, respectively. Shorter rotation lengths were associated with reduced distance from the ocean and soil with a higher percentage of sand. Based on 2 years of disease surveys, fields infested with Macrophomina phaseolina tended to be further inland than fields infested with Fusarium oxysporum f. sp. fragariae in the Monterey Bay region. This study determined that distance from the ocean and soil texture are associated with crop rotation lengths in California strawberry production. Enough land may be available in the Santa Maria and Monterey Bay regions for growers to lengthen crop rotations, but water quality, social networks, and financial considerations that were outside the scope of this study are likely to limit the ability for strawberry growers to maximize the duration of crop rotations.

ABSTRACTFruit production, plant production, genetics, technological advancements, food safety practices, and dedication to sustainable practices make California the most important strawberry production area in the world. California grew 16,303 hectares of strawberries in 2023 in three growing districts located along California’s Central Coast: Oxnard, Santa Maria and Watsonville-Salinas. Transplants are grown on approximately 1,627 ha at high and low elevation nurseries located up to a thousand km from fruit growing districts. Almost all fruit production is in open fields with a small amount under high plastic tunnels either in soil or on tabletops. Nursery production is almost all in open fields. In 2022, there were 13 public cultivars grown with the most popular being Monterey, Portola, Fronteras, Cabrillo, and San Andreas grown on 27%, 13%, 11%, 4% and 2% of the planted acres, respectively. All proprietary cultivars combined made up 39% of the planted acres. Fresh market makes up 81% of the harvested fruit with 19% destined for processing into concentrates, individually quick frozen, purees and juice. Most fruit are sold domestically (87%) while 13% is exported, the majority to Canada (62%) and Mexico (25%). The most important diseases are Macrophomina root rot, Fusarium wilt, Verticillium wilt, Phytophthora root rot, Botrytis fruit rot and powdery mildew. The most important arthropod pests are twospotted spider mite and Lygus bug. Current challenges include increased regulation on water quality, fumigants, pesticides, labor and increased urbanization.

Plants recruit diverse microbial communities from the soil to their roots. Intermicrobial interactions and connectivity in the root microbiome play essential roles in plant health by promoting resistance to soilborne pathogens. However, the understanding of these interactions under field conditions is still scarce. Using a strawberry crop model, we characterized the prokaryotic and the fungal communities in the rhizosphere and the roots of three strawberry cultivars grown under field conditions and displaying varying degrees of resistance to the soilborne fungal pathogen Macrophomina phaseolina. We tested the hypothesis that resistant cultivars assemble distinct bacterial and fungal communities that foster microbial connectivity and mediate disease resistance. Our results show that the soilborne pathogen M. phaseolina does not alter the root microbiome of the three strawberry cultivars. Microbiome comparative analysis indicated that the highly susceptible cultivar Sweet Ann assembled a distinct rhizosphere and root microbiome, whereas the microbiome of the strawberry cultivars Marquis and Manresa were more similar and enriched with potential beneficial microbes. Cooccurrence network analysis revealed that the fungal pathogen M. phaseolina was more peripheral in the microbial network of Sweet Ann compared with Manresa and Marquis. Collectively, these results stress the role of the plant microbiome in mediating resistance against soilborne pathogens and further suggest the role of plant genetic traits in the assembly of beneficial microbiome members. Our study reinforces the eminent role of the plant microbiome as trait selection in breeding programs and the need for further understanding of the genetic and biological mechanisms that mediate microbiome assembly. Uncovering these mechanisms will be key for the future success of plant breeding programs in their fight against soilborne pathogens. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

There are four major soilborne pathogens of strawberries in California, but their distribution and prevalence in the Watsonville-Salinas production district are unknown. To fill this knowledge gap, 74 symptomatic strawberry plant samples were collected from 69 fields in the Watsonville-Salinas growing district between 11 August and 15 October 2021. Each sample consisted of eight plants exhibiting moderate to severe plant collapse. Crown tissue from each plant was excised and pooled for recombinase polymerase amplification (RPA) to detect Macrophomina phaseolina, Fusarium oxysporum f. sp. fragariae, Verticillium dahliae, and Phytophthora spp. Root, petiole, and crown tissue from plant samples in which no pathogens were detected by RPA was plated on semiselective media to verify the absence of the four pathogens and screen for other pathogenic fungi. At least one of the four pathogens was detected in 55 of the 74 samples (74.3%). All four of the major soilborne pathogens are prevalent in this growing district, as F. oxysporum f. sp. fragariae, M. phaseolina, Phytophthora spp., and V. dahliae were detected in 23 samples (31.1%), 22 samples (29.7%), 18 samples (24.3%), and 16 samples (22.0%), respectively. No strong associations were found between the pathogens and growing practices.

To determine the prevalence of the four major soilborne pathogens of strawberry in the Santa Maria growing district in California, symptomatic plant samples (n = 100) were collected from 68 fields between May and September 2022. Samples comprised 28.3% of 2021 fall-planted strawberry fields and 14.0% of 2022 summer-planted strawberry fields in the district. Recombinase polymerase amplification was used to detect Macrophomina phaseolina, Fusarium oxysporum f. sp. fragariae, Verticillium dahliae, and Phytophthora spp. in plant crown material. Macrophomina phaseolina was most prevalent, detected in 52 samples, followed by Verticillium dahliae in 17 samples, F. oxysporum f. sp. fragariae in 16 samples, and Phytophthora spp. in 14 samples. Macrophomina phaseolina was more likely in eastern field locations (P = .0159) and in instances where strawberries were planted consecutively (P = .0100). Disease incidence was more likely to be higher in samples from organic fields than conventional fields (P = .0304) and in samples from flat-fumigated fields than fields fumigated in-line (P = .0124).

Host plant resistance is an essential tool in plant disease management worldwide. Evaluations of strawberry cultivar resistance to powdery mildew were done previously in California, but many new cultivars have been released since the last evaluation in 1996 and merit evaluation for today’s growers. Two studies were conducted over the winter and summer of 2020, evaluating 10 commonly grown cultivars. Powdery mildew-free plants were established in 3-liter pots under high plastic tunnels and after 3 weeks (four- to five-leaf stage) moved into a powdery mildew-infested greenhouse. Disease incidence and severity ratings were taken weekly beginning at the first sign of disease. Ratings taken at 40 (winter) and 41 (summer) days after transfer to the greenhouse were used to make comparisons among cultivars. Significant differences were found in foliar disease severity among cultivars, but none were totally free of disease. Moderately resistant cultivars were ‘San Andreas’ and ‘Sweet Ann’. Highly susceptible cultivars were ‘BG 3.324’ and ‘Royal Royce’. Two field evaluations of the 10 cultivars confirmed the observed relative differences in host resistance under field conditions. This information is valuable to California strawberry growers, who select cultivars based in part on their susceptibility to economically important diseases such as powdery mildew.