Boxwood blight, caused by Calonectria pseudonaviculata, is an introduced disease that causes substantial losses in Oregon's nursery industry. Growers make decisions about plant spacing and irrigation to produce boxwood in the most cost-effective manner. These decisions change the microenvironment in which the pathogen resides and affect how boxwood blight develops and spreads within nurseries. To understand this, we evaluated how plant spacing (0 and 15 cm apart) and irrigation frequency (1, 2, and 3 & times;/day) affected disease severity and pathogen movement in plots of the susceptible boxwood cultivar 'Green Velvet'. Spacing was the most important factor. Regardless of irrigation frequency, boxwood blight only spread to plants placed pot tight (0 cm apart) with canopies touching and did not spread to plants spaced 15 cm apart with separated canopies. Irrigation frequency only affected boxwood blight on plants at the 0-cm spacing, where disease severity and spread intensified with increasing irrigation frequency. Seasonally, boxwood blight spread slowly during the summer when the weather was warm and dry and in the winter when temperatures were too cold. Disease was more severe and spread more rapidly in the spring and fall when the weather was cool and rainy. These results show that growers can minimize disease losses by growing plants further apart so that their canopies do not touch and by irrigating less frequently so that the foliage dries quickly. In addition, growers should scout for and protect against boxwood blight in spring and fall, when the potential for disease spread is greatest.The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2026.

BACKGROUND: Soil microbiomes are important for plant growth and health. The objectives of this study were to characterize boxwood root-zone microbial community and understand their associations with plant disease resistance and other horticultural traits. Soil samples were collected from four cultivars with three distinct boxwood blight tolerance at two geographically distant nursery locations in May, August, and November of 2021. Bacterial and fungal communities were characterized through DNA metabarcoding. RESULTS: The dominant bacteria in the boxwood root-zone soil included Bacillus and several unknown genera of the order Gaiellales and families Xanthobacteraceae and Gemmatimonadaceae; the dominant fungi included Clonostachys, an unknown genus, Solicoccozyma, and Fusarium. Ceratobasidium, Hyaloscypha, and Sistotrema were also the dominant genera within the presumptive mycorrhizal fungi (PMF) group. Fungal community structure was distinct among cultivars with different blight tolerance in May and August, but the divergence of the bacterial community structure was only significant in the August samples. Community composition-wise, greater numbers of genera differed in abundance between the intermediate and the susceptible cultivars. Moreover, cross-kingdom network analysis showed a more connected network constructed from the intermediate cultivars and identified more hub taxa as module connectors compared with the other two cultivars. Some of the hub taxa, including bacterial genera Gaiella, Streptomyces, and Sphingomonas, and fungal genera Solicoccozyma and Pseudonectria were also among the 27 bacterial and 6 fungal core genera identified from all samples across four cultivars, two locations, and three seasons. Further, Volutella and Pseudonectria were negatively associated with 10 bacterial genera and all identified PMF-PMF connections were positive across all networks. CONCLUSIONS: Boxwood root-zone soil harbored diverse plant-beneficial microbes, including PMFs. Fungal community and microbial network connectivity also differed among the cultivars, suggesting the regulatory roles of plant phenotype and genotype in fungi recruitment and microbial interactions. Several keystone taxa were identified and may be crucial in maintaining the structure and communication within the boxwood root-zone microbiome. The negative associations between bacteria and Volutella/Pseudonectria provide a new insight into managing the rise of the boxwood Volutella blight. Together, this study offers several leads to enhancing plant resilience to disease and environmental stress.

Boxwood blight disease, caused by the fungal pathogen Calonectria pseudonaviculata (Cps), is a significant threat to the U.S. nursery industry, where Oregon is the leading producer. Current knowledge of Cps variation is primarily derived from studies of Eastern U.S. populations, and the genetic and phenotypic variation in Western populations, particularly their adaptation to regional climates, remains poorly understood. To address this issue, the genetic diversity of 123 Oregon isolates was evaluated through the sequencing of 11 simple sequence repeat (SSR) loci, and the influence of temperature on mycelial growth was assessed across a subset of 71 representative isolates at 5 temperatures (10 to 30 degrees C). Genotyping identified nine multilocus genotypes (SSR-MLGs), including five novel genotypes. Although 89% of isolates belonged to previously identified SSR-MLGs, the G1 genotype occurred at a higher frequency (20%) than previously reported in populations outside of Oregon. One of the new SSR-MLGs occurred at a frequency of 77% among samples collected from a single nursery population. The temperature assays revealed that optimal growth for most Oregon isolates (69 of 71) occurred at 20 degrees C, which is cooler than the 25 degrees C standard reported for isolates from other regions. These findings indicate that Oregon Cps populations may be genetically distinct from Eastern populations and are adapted to cooler temperatures. This highlights the potential impact of regional differences on growth and disease development across the United States and the need to integrate these differences into predictive modeling and disease management strategies.The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2026.

Abstract Pulsed electric field (PEF) technology is a non-chemical approach with potential to control soilborne agricultural pests. PEF disrupts cellular membranes through short, high-energy electrical pulses. Treatment efficacy depends on electric field strength, pulse frequency, and applicator design. Field strength reflects the intensity of the electric field driving electroporation, whereas energy density represents the cumulative dose delivered to the system, and pulse frequency determines how that dose is distributed over time. In this study, two soil-applied PEF applicators, vertical pins (VP) and parallel plates (PP), were evaluated for suppression of weeds, plant-parasitic nematodes, and soilborne pathogens. Numerical simulations showed that the PP configuration generated a more uniform electric field distribution than the VP design. Consistent with these predictions, the PP applicator provided greater biological suppression across target organisms. Cyperus esculentus biomass declined progressively with increasing energy density and was significantly reduced at ≥100 J cm −3 . The PP applicator also reduced Meloidogyne chitwoodi second-stage juveniles by up to 100% at 25 J cm −3 and pulse frequencies above 60 Hz. Densities of Pratylenchus neglectus and M. chitwoodi were reduced by more than 98% at 400 V mm −1 . Weed responses were species dependent: biomass of C. esculentus and Digitaria sanguinalis declined at 100–200 J cm −3 , whereas Echinochloa crus-galli required higher energy inputs for control. Soilborne pathogens also differed in susceptibility, with Phytophthora cinnamomi and P. plurivora reduced by 94% at moderate field strengths (100–200 V mm −1 ), while Verticillium dahliae was suppressed by up to 97% at 200–400 V mm −1 and 80 Hz. Overall, nematodes and soilborne pathogens were suppressed at substantially lower energy densities (~25 J cm −3 ) than weed propagules, which generally required ≥100–200 J cm −3 for effective biomass suppression. These results demonstrate that PEF can effectively suppress multiple soilborne pests. Additionally, the results highlight the importance of applicator design and electrical parameters in determining treatment efficacy, supporting the potential of PEF as a scalable and sustainable soil disinfestation technology.

Boxwood blight, caused by the fungal pathogen Calonectria pseudonaviculata, is the most serious disease affecting boxwood ( Buxus species and cultivars) in the United States nursery industry. Symptoms include leaf spots, leaf blight, leaf drop, and small black stem lesions. This report evaluates the efficacy of fungicide treatments for the management of boxwood blight. The trial was conducted in 2024 in Corvallis, OR, on 12-in.-tall plants of ‘Green Velvet’ boxwood in 1-gal. containers. Results from these trials will help U.S. boxwood growers and landscapers develop management programs for this disease.

Developing cultivars that are resistant to multiple biotic stresses is an important objective in raspberry plant breeding. Diseases such as Raspberry bushy dwarf virus and Phytophthora root rot have long been a high priority for raspberry breeding programs, whereas other pests, such as spotted wing Drosophila and the root lesion nematode, have been considered more recently. Breeding for improved resistance to these stresses has relied primarily on conventional breeding methods. However, rapid technological progress and increased access and affordability of genomic and phenomic methodologies may accelerate breeding and improve selection efficiency for genetic resistance to pests and pathogens. Such advancements are understudied for application in raspberry, but are emerging as a significant research interest. We review the current state of plant breeding research for the most significant diseases and pests affecting raspberry production in the Pacific Northwest of North America. In addition, we discuss new and relevant plant breeding methodologies that could contribute to future breeding objectives.

Phyllosphere colonizers, including bacteria and fungi, are critical for plant growth and health. Yet, how they are affected simultaneously by host plant cultivar, local environment and agricultural practices was not well understood. We used boxwood, an iconic landscape plant and a major evergreen shrub crop in the U.S. nursery industry, as a model plant, and sequenced 16S rRNA and ITS amplicons to examine the assemblages of endophytic bacteria and fungi in the shoots of four cultivars representing three levels of boxwood blight resistance under two distinct climates and production systems in Oregon and Virginia. Cultivar and local environment were the two main drivers shaping the composition and structure of the boxwood endophytic microbial community, particularly the fungal community. Three bacterial and seven fungal genera were consistently identified with high prevalence and abundance as the core taxa from four cultivars and two locations across three sampling times. The microbial composition varied among the levels of boxwood blight resistance and taxa specific to the tolerant cultivar were fewer compared to the susceptible one. Identification of these microbial indicators, along with the core taxa, is foundational for developing a microbiome-based plant breeding program and a systems approach to improve boxwood health and production under a changing climate.

The fungal pathogen Calonectria pseudonaviculata causes boxwood blight and is a significant threat to the boxwood industry, as well as historic boxwood gardens. The pathogen produces conidia in sticky masses that are splash dispersed, which germinate and infect through stomata on the leaves or stems, causing leaf spots and stem lesions. Despite its ability to cause severe infections on boxwood plants, the pathogen often has a low germination rate on artificial media under lab conditions. To identify cues that stimulate germination, we explored whether host factors could induce high germination rates. In this study, we demonstrate that C. pseudonaviculata spores achieve high germination rates when they are placed on detached leaves of boxwood and other known hosts, compared to potato dextrose agar and glass coverslips. We also demonstrate that germination is induced by volatiles from detached leaves of boxwood, as well as the nonhost Berberis thunbergii. When C. pseudonaviculata spores were exposed to volatiles from boxwood leaves in the presence of ethylene scrubber packs that contained potassium permanganate, the stimulatory effect on spore germination was reduced. However, ethylene, a regulator of leaf senescence, did not stimulate germination of C. pseudonaviculata spores. This suggests that the pathogen may have evolved to recognize one or more host volatiles, other than ethylene to induce germination, thus limiting its growth until it senses the presence of a host plant.

Oregon leads the United States in nursery production of shade trees and is third in deciduous and broadleaf evergreen shrub production. Plant-parasitic nematodes have been implicated in problems with the growth of plants in nurseries and are also of phytosanitary risk. A greenhouse experiment was conducted to evaluate the host status of four trees (Quercus alba, Quercus garryana, Acer campestre, Thuja occidentalis) and two shrubs (Buxus sempervirens, Rhododendron catawbiense) to Meloidogyne incognita, Meloidogyne hapla, and Pratylenchus neglectus. Each plant/nematode treatment was replicated five times, and the experiment was conducted twice. Plants were inoculated with 3,000 eggs of M. incognita or M. hapla and 2,500 individuals of P. neglectus two weeks after planting. After three months, the plants were harvested, and the total density of nematodes in soil and roots for P. neglectus and the total density of second-stage juveniles (J2) in soil and eggs on roots for M. hapla and M. incognita were determined. The final nematode population (Pf) and reproductive factor (RF = Pf/initial population density) were calculated. For M. incognita and M. hapla, all of the ornamental trees and shrubs would be considered as fair to good hosts with RF values > 1. Meloidogyne incognita had the highest Pf (5,234 total J2 and eggs/pot) and RF value (28.4) on A. campestre. For P. neglectus, all of the ornamental trees and shrubs were fair to good hosts, except for B. sempervirens. Buxus sermpervirens was not a host for P. neglectus, with an RF value of almost 0. This is the first report of Q. alba, Q. garryana, and A. campestre as hosts for M. incognita, M. hapla, and P. penetrans. This is also the first report of T. occidentalis and R. catawbiense as hosts for P. penetrans and the non-host status of B. sermpervirens for P. penetrans.

Phytophthora rubi is an important pathogen causing Phytophthora root rot of red raspberries worldwide. Management of this disease is partially achieved with fungicides, but efficacy has been low, and growers are concerned about fungicide resistance. To determine whether fungicide resistance is developing, Phytophthora species were isolated from 26 raspberry fields with root rot, identified, and evaluated for sensitivity to four fungicides: mefenoxam, phosphorous acid, oxathiapiprolin, and dimethomorph. The majority of the recovered 152 Phytophthora isolates were P. rubi (143 isolates, 25 fields), with P. megasperma (8 isolates, 2 fields) and P. gonapodyides (1isolate, 1field) being found much less frequently. These results confirm P. rubi as the dominant species affecting the Washington red raspberry industry. Almost all tested isolates were sensitive to all four fungicide chemistries, although three isolates were less sensitive to mefenoxam, with effective concentration for 50% growth inhibition (EC50) values ranging from 3.53 to 100 μg active ingredient/ml. No resistance was detected against current fungicide label rates. However, other reasons were identified for why fungicides have been ineffective. Label rates vary widely by brand, and most fungicides are applied in the fall when P. rubi is inactive. In addition, some phosphorous acid products are only labeled for foliar applications, which have been shown to be less effective than soil applications in other agricultural systems. Efficacy trials are needed to compare foliar and soil fungicide applications at different times of the year for their ability to control Phytophthora root rot in red raspberry production fields.

Phytophthora root rot, caused by many Phytophthora species, decreases the health of rhododendrons produced in nurseries. Optimizing nitrogen (N) fertilizer is often used to improve nursery stock quality, but there is little information on how N fertilizers influence root rot caused by these pathogens. To understand the impact of N fertilizer and pathogen species on root rot development, rhododendrons were grown with no (0 g N/pot), low (1.04 g N/pot) or high (3.12 g N/pot) rates of N and inoculated with either P. cinnamomi or P. plurivora. Noninoculated plants at low and high N rates had greater biomass, leaf greenness and enhanced N, potassium, magnesium, phosphorus, sulphur and manganese uptake compared to plants grown with no N. When either Phytophthora species was present, N application increased aboveground disease symptoms (wilting, chlorosis, reduced stomatal conductance and biomass), but had no effect on root rot severity belowground. In addition, P. cinnamomi restricted uptake of several nutrients while P. plurivora had less influence on nutrient uptake. Nurseries frequently apply high amounts of N to promote fast growth. However, our results show that this can exacerbate root rot when P. cinnamomi or P. plurivora is present. Although decreasing N can reduce the number of overtly symptomatic plants, this may conversely increase the risk for selling apparently asymptomatic plants with low levels of infection. Additional studies are needed to determine how N fertilization influences Phytophthora root rot for a broader range of rhododendron cultivars and nursery crop species.

Temperature is an important environmental variable affecting Phytophthora spp. biology. It alters the ability of species to grow, sporulate, and infect their plant host, and it is also important in mediating pathogen responses to disease control measures. Average global temperatures are increasing as a consequence of climate change, yet there are few studies that compare the effects of temperature on Phytophthora spp. that are important to the nursery industry. To address this, we conducted a series of experiments to evaluate how temperature affects the biology and control of three soilborne Phytophthora spp. prevalent in the nursery industry. In the first set of experiments, we evaluated the mycelial growth and sporulation of several Phytophthora cinnamomi, P. plurivora, and P. pini isolates at temperatures ranging from 4 to 42°C for different amounts of time (0 to 120 h). In the second set of experiments, we evaluated the response of three isolates of each species to the fungicides mefenoxam and phosphorous acid at temperatures ranging from 6 to 40°C. Results showed that each species responds differently to temperature, with P. plurivora having the greatest optimal temperature (26.6°C), P. pini the least (24.4°C), and P. cinnamomi was intermediate between the two (25.3°C). P. plurivora and P. pini had the lowest minimum temperatures (approximately 2.4°C) compared with P. cinnamomi (6.5°C), while all three species had a similar maximum temperature (approximately 35°C). When tested against mefenoxam, all three species were generally more sensitive to mefenoxam at cool temperatures (6 to 14°C) than at warmer temperatures (22 to 30°C). P. cinnamomi was also more sensitive to phosphorous acid at cool temperatures (6 to 14°C). However, both P. plurivora and P. pini tended to be more sensitive to phosphorous acid at warmer temperatures (22 to 30°C). These findings help define the temperatures at which these pathogens will be the most damaging and help delineate the temperatures at which fungicides should be applied for maximum efficacy.

The degree of flooding commonly used to induce disease in Phytophthora root rot studies rarely occurs in container nurseries. Instead, over-irrigation and poor drainage result in plants periodically sitting in shallow pools of water. Rhododendron plants were grown in a noninfested substrate or substrate infested with Phytophthora cinnamomi or P. plurivora to determine whether root rot induced by flooding represents disease that occurs under simulated nursery conditions when plants are in a shallow pool of water (saucers), or are allowed to freely drain and maintained at ∼75% container capacity (CC). Generally P. cinnamomi caused more disease than P. plurivora, and all water treatments were conducive to root rot. In experiment 1, the amount of disease caused by flooding was similar to that in the saucer treatment (75% CC not tested) while in experiment 2, flooding often caused more rapid and severe disease than the saucer or 75% CC treatment. Pathogens differed in their response to water treatments. P. cinnamomi caused more disease in treatments with >90% substrate moisture for either a short (flood) or long duration (saucer), while P. plurivora was less capable of causing disease when soil moisture was maintained >90% than when substrate moisture was maintained at a more moderate level (flood, 75% CC). Our results indicate that it is not necessary to flood plants to induce disease under experimental conditions and that disease induced by flooding can represent disease in container nurseries when containers are in pools of water or maintained at ∼75% CC. In addition, our results suggest that P. cinnamomi is a more aggressive pathogen than P. plurivora in nursery conditions where drainage is poor; however, both species are capable of causing a similar amount of disease under more typical irrigation management.

Boxwood blight can be challenging to detect in the field, especially when symptoms are mild, thus requiring large numbers of plants to be screened. Therefore, a rapid diagnostic assay that can detect the pathogen from large amounts of plant tissue would be useful. Here, we present a crude DNA extraction protocol that is rapid and scalable. The DNA extraction protocol can process large volumes of tough boxwood tissue rapidly without using cetyltrimethylammonium bromide or phenol-chloroform to remove inhibitors. Additionally, to detect the boxwood blight pathogen Calonectria pseudonaviculata, we developed a TaqMan probe to use with previously described PCR primers for a real-time PCR assay. The assay's limit of detection was determined by diluting symptomatic boxwood leaves in nondiseased leaves and by adding spores to nondiseased leaves to simulate diagnostic scenarios. The assay was able to detect the pathogen in symptomatic leaves diluted up to 1 × 104- to 1 × 105-fold in nondiseased leaves and from as low as 1,000 to 10,000 spores added to 1.2 g of nondiseased leaves. The ability to extract DNA from large volumes of plant tissue facilitates screening more plant tissue using the real-time PCR assay without increasing the number of samples to process in the lab.

We evaluated whether reducing irrigation frequency and volume alters the ability of Phytophthora plurivora and P. cinnamomi to cause root rot on rhododendron grown in a noninfested potting medium or media infested with 1 or 100 propagules per gram (ppg) of pathogen. Plants were irrigated to maintain a substrate moisture of >70% container capacity (1.0X), one-half volume of 1.0X (0.5X), or two times the volume of 1.0X at each irrigation event for one week, followed by no irrigation, until soil moisture reached <50% container capacity. Aboveground disease symptoms (chlorosis, stomatal conductance, wilting, and plant death) were evaluated weekly and root rot, pathogen presence, plant biomass, and nutrient uptake were measured at the end of each trial. Both pathogens generally caused mild disease at 1 ppg and severe disease at 100 ppg. Reducing irrigation did little to lessen disease caused by either pathogen once infection had occurred. Instead, severe root infection often led to increased soil moisture and root rot across all irrigation treatments as roots became progressively compromised in their ability to take up water. Results show that reducing irrigation after infection has occurred is unlikely to effectively control root rot. Species used in this study: Phytophthora species (Phytophthora cinnamomi Rands; Phytophthora plurivora T. Jung and T.I. Burgess); rhododendron, Rhododendron catawbiense Michx. ‘Album', ‘Roseum Elegans', and ‘Roseum Pink'.

Controlled environment experiments were conducted to evaluate the effects of temperature on Calonectria pseudonaviculata mycelial growth and the effects of temperature and infection period on boxwood blight severity. In experiment 1, 15 Oregon isolates (representing five genotypes) were grown on potato dextrose agar (PDA) and malt extract agar (MEA) at six temperatures from 5 to 30°C. Growth (culture diameter) was measured after 2 weeks. Optimal growth occurred at 25°C on PDA and 20°C on MEA. Isolates of genotype G1 also grew faster than genotype G2, but only on MEA at 25°C. In experiment 2, Buxus cultivars Green Velvet (GV, more susceptible) and Winter Gem (WG, more resistant) were inoculated and incubated in moist chambers for 9 or 24 h at 22°C (infection period), then moved into growth chambers at 15 or 25°C. After 4 weeks, chamber temperatures were switched, and plants were incubated for 4 more weeks. Disease severity was evaluated weekly. During the first 4 weeks, disease was generally more severe on GV than WG, on plants with a 24-h versus a 9-h infection period, and on plants incubated at 15°C versus 25°C. However, disease was just as severe on WG as GV when the 24-h infection period was followed by incubation at 15°C. After the temperatures were switched, disease increased only on WG that were cooled from 25 to 15°C. Results show that Oregon isolates of C. pseudonaviculata are capable of growing faster and causing more severe disease at temperatures cooler than those reported previously.

Hebes (Veronica spp. in the section Hebe) are ornamental perennials and shrubs grown for their flowers and symmetric, evergreen leaves. They are uncommon in U.S. horticulture and are only produced by a few nurseries regionally (Oregon and Washington). In June, July, and August (2016 to 2021), stems on 1 to 5-year-old Veronica cupressoides, V. ochracea, and V. pinguifolia in five landscape plantings around Benton County, OR (17 plants total, locations 2 to 37 km apart) began to wilt, turn brown, and die. At least nine of the plants originated from a single nursery. Initially, just one or two stems/plant were affected, but eventually the entire plant died. Stem tissues were discolored brown to black internally and the roots were dry and necrotic. Leaves turned brown and brittle, but remained attached. Stems from each plant were disinfested in 0.5% NaOCl (1 min), rinsed in 70% ethanol, and dried (2 min). Pieces (5 mm2) were then plated onto 1/2 strength potato dextrose agar amended with streptomycin (50 mg/liter) and incubated in the dark at 20°C. Three to five days later, greyish-white cultures producing black microsclerotia (75 × 110 µm, n = 50) grew out of all samples. No spores were produced. All isolates were identified as Macrophomina phaseolina by morphology and by ≥99% homology (566-570/571 nt) to the internal transcribed spacer sequence (primers ITS1 and ITS4) from the type specimen (GenBank KF766195) (Hyde et al. 2014). Three representative sequences were deposited in GenBank (MZ726450 to MZ726452). Inoculum was prepared from these isolates by growing cultures in 250 ml of potato dextrose broth on a shaker (125 rpm at 25°C). After 2 weeks, the broth was decanted and the fungal biomass was air dried for 3 days at 25°C before grinding into a powder with a mortar and pestle. Three plants each of 6-month-old V. ochracea 'James Stirling', V. cupressoides 'McKean', and V. pinguifolia 'Sutherlandii' were inoculated with each isolate by rinsing the soil off of the roots with tap water, trimming off 0.5 cm of the roots, and then soaking the rootball in a slurry of 1 g dried inoculum in 500 ml of 0.2% water agar (WA) for 10 minutes (Reyes Gaige et al. 2010). Three plants of each species that were soaked in plain 0.2% WA served as negative controls. Afterwards, plants were potted into soilless media (Metro-Mix 840, Sun Gro Horticulture, Agawam, MA) in 3.5 inch square pots and arranged in a completely randomized design in a greenhouse set at 28/24°C day/night. The experiment was conducted three times. One to three months later, inoculated plants began to turn yellow, wilt, and die whereas all control plants remained healthy. The same pathogen was reisolated from 90% of the inoculated plants, but never from negative controls. M. phaseolina was reported on strawberry in southern Oregon in 2014 (Pscheidt and Ocamb 2021), but has not been reported from locations further north in the state where soil temperatures are cooler. It is unusual that M. phaseolina was isolated from an uncommon host at five different locations in an area of the state where the pathogen was not known to occur. Based on this, and on the number of infected plants originating from a single source, it seems likely that M. phaseolina was accidentally spread on contaminated plants produced by the nursery industry, where the warmer temperatures in production greenhouses would provide a more conducive environment for the pathogen's growth and spread. Growers should keep watch for symptoms of this pathogen in their nurseries.

Phytophthora root rot of raspberry, which is mostly caused by Phytophthora rubi, is a significant issue for the Washington State red raspberry industry. Considered a cool weather pathogen, it is often assumed that it is most active and infective during the cool, wet winters of the region when soil temperatures range from 5 to 10°C; however, there are little data to support this view. More recent research has found that symptoms of root disease during late summer were strongly associated with P. rubi. Therefore, experiments were conducted at four temperatures from 5 to 20°C to evaluate the effects of temperature on P. rubi mycelial growth and sporulation and the effects of both temperature and soil moisture on the pathogenicity of P. rubi on red raspberry. At 20°C, P. rubi grew fastest and sporulated the most heavily. However, disease was most severe at both 15 and 20°C. The soil moisture parameters tested did not affect the pathogenicity results. These results show that P. rubi is more likely to infect during the spring and summer months (from May through September), when soil temperatures are consistently in the range of 15 to 20°C.