Distribution and Longevity of Pratylenchus penetrans in the Red Raspberry Production System

One of the major constraints on the production of red raspberries in the Pacific Northwest is the presence of the rootlesion nematode Pratylenchus penetrans. Current management of this nematode relies heavily on preplant soil fumigation; however, regulations have made the practice more difficult and expensive. Additional issues with soil fumigation include lack of efficacy at deeper soil depths and potential inability to penetrate raspberry root material that remains in the field during fumigation which may harbor P. penetrans. To address these issues, two field experiments were conducted in northwestern Washington. In the first experiment, the residency time of P. penetrans in root material from the previous raspberry crop, which was terminated with or without the use of herbicides, was monitored over time. Pratylenchus penetrans was found in root material from 6 to 8 mon after the crop was terminated, and herbicide application did not reduce P. penetrans residency time compared to untreated root material. In a second experiment, the vertical distribution of P. penetrans at three different times during the field establishment process (pre- and postfumigation, and at planting) was determined at two locations. Both locations had detectable prefumigation P. penetrans populations at all depths. However, postfumigation populations showed a different distribution pattern between locations. The location with coarser soil had populations located mainly at shallower depths with a maximum of 44 P. penetrans/100 g soil at 16 to 30 cm deep, whereas the location with finer soil had populations located mainly at deeper depths with a maximum of 8 P. penetrans/100 g soil at 76 to 90 cm deep. At planting, distribution tended to equilibrate among depths at both locations, but the overall population pattern across depth at each location was similar to that observed at postfumigation. Understanding more about the residency time and distribution of this nematode may provide growers with information that can be used to more effectively target P. penetrans

Activity of Meadowfoam (Limnanthes alba) Seed Meal Glucolimnanthin Degradation Products against Soilborne Pathogens

Meadowfoam (Limnanthes alba L.) is a herbaceous winter spring annual grown as a commercial oilseed crop. The meal remaining after oil extraction from the seed contains up to 4% of the glucosinolate glucolimnanthin. Degradation of glucolimnanthin yields toxic breakdown products, and therefore the meal may have potential in the management of soilborne pathogens. To maximize the pest-suppressive potential of meadowfoam seed meal, it would be beneficial to know the toxicity of individual glucolimnanthin degradation products against specific soilborne pathogens. Meloidogyne hapla second-stage juveniles (J2) and Pythium irregulare and Verticillium dahliae mycelia] cultures were exposed to glucolimnanthin as well as its degradation products. Glucolimnanthin and its degradation product, 2-(3-methoxyphenyl)acetamide, were not toxic to any of the soilborne pathogens at concentrations up to 1.0 mg/mL. Two other degradation products, 2-(3-methoxymethyl)ethanethioamide and 3-methoxyphenylacetonitrile, were toxic to M. hapla and P. irregulare but not V. dahliae. The predominant enzyme degradation product, 3-methoxybenzyl isothiocyanate, was the most toxic compound against all of the soilborne pathogens, with M. hapla being the most sensitive with EC(50) values (0.0025 +/- 0.0001 to 0.0027 +/- 0.0001 mg/mL) 20-40 times lower than estimated EC(50) mortality values generated for P. irregulare and V. dahliae (0.05 and 0.1 mg/mL, respectively). The potential exists to manipulate meadowfoam seed meal to promote the production of specific degradation products. The conversion of glucolimnanthin into its corresponding isothiocyanate should optimize the biopesticidal properties of meadowfoam seed meal against M. hapla, P. irregulare, and V. dahliae.Keywords: Seed meal, Nematicidal effect, Fungicidal effect, Lethal concentratio

Susceptibility of Highbush Blueberry Cultivars to Phytophthora Root Rot

Phytophthora cinnamomi Rands is a ubiquitous soilborne pathogen associated with root rot in many woody perennial plant species, including highbush blueberry (Vaccinium corymbosum). To identify genotypes with resistance to the pathogen, cultivars and advanced selections of highbush blueberry were grown in a greenhouse and either inoculated or not with propagules of P. cinnamomi. Two experiments were conducted, including one with 10 commercially established cultivars and another with seven newly released cultivars, three commercially established cultivars, and three advanced selections of highbush blueberry. Pathogen resistance was based on the shoot and root dry biomass of the inoculated plants relative to the noninoculated plants within each genotype, as well as on the percentage of root infection among the genotypes. Resistant genotypes included four commercially established cultivars, Aurora, Legacy, Liberty, and Reka, and two new cultivars, Overtime and Clockwork. When these genotypes were inoculated, average relative shoot biomass was ≥60% of that of the noninoculated plants, whereas relative root biomass was ≥40%. ‘Star’, as well as two advanced selections (an early- and a late-season type) may also have some degree of resistance, but further investigation is needed. Relative shoot biomass of the susceptible genotypes, on the other hand, ranged from 19% to 53% and relative root biomass ranged from 11% to 26%. The susceptible genotypes included ‘Bluetta’, ‘Bluecrop’, ‘Bluegold’, ‘Blue Ribbon’, ‘Cargo’, ‘Draper’, ‘Duke’, ‘Elliott’, ‘Last Call’, ‘Top Shelf’, and ‘Ventura’. These cultivars are not recommended at sites with conditions conducive to root rot, such as those with clay soils and/or poor drainage.Keywords: Phytophthora cinnamomi, Vaccinium corymbosum, soilborne pathogen, disease resistanc

Irrigation and Fertigation with Drip and Alternative Micro Irrigation Systems in Northern Highbush Blueberry

The use of conventional drip and alternative micro irrigation systems were evaluated for 3 years in six newly planted cultivars (Earliblue, Duke, Draper, Bluecrop, Elliott, and Aurora) of northern highbush blueberry (Vaccinium corymbosum L.). The drip system included two lines of tubing on each side of the row with in-line drip emitters at every 0.45 m. The alternative systems included geotextile tape and microsprinklers. The geotextile tape was placed alongside the plants and dispersed water and nutrients over the entire length. Microsprinklers were installed between every other plant at a height of 1.2 m. Nitrogen was applied by fertigation at annual rates of 100 and 200 kg·ha⁻¹ N by drip, 200 kg·ha⁻¹1 N by geotextile tape, and 280 kg·ha⁻¹ N by microsprinklers. By the end of the first season, plant size, in terms of canopy cover, was greatest with geotextile tape, on average, and lowest with microsprinklers or drip at the lower N rate. The following year, canopy cover was similar with geotextile tape and drip at the higher N rate in each cultivar, and was lowest with microsprinklers in all but ‘Draper’. In most of the cultivars, geotextile tape and drip at the higher N rate resulted in greater leaf N concentrations than microsprinklers or drip at the lower N rate, particularly during the first year after planting. By the third year, yield averaged 3.1–9.1 t·ha⁻¹ among the cultivars, but was similar with geotextile tape and drip at either N rate, and was only lower with microsprinklers. Overall, drip was more cost effective than geotextile tape, and fertigation with 100 kg·ha⁻¹ N by drip was sufficient to maximize early fruit production in each cultivar. Microsprinklers were less effective by comparison and resulted in white salt deposits on the fruitKeywords: microsprinklers, geotextile irrigation system, Phytophthora cinnamomi, nutrient management, root rot, Vaccinium corymbosu

Population Structure of Pythium irregulare, P. ultimum, and P. sylvaticum in Forest Nursery Soils of Oregon and Washington

Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. However, little is known about their genetic diversity or population structure and it is suspected that isolates are moved among forest nurseries on seedling stock and shared field equipment. In order to address these concerns, a total of 115 isolates of three Pythium species (P. irregulare, P. sylvaticum, and P. ultimum) were examined at three forest nurseries using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Analyses revealed distinct patterns of intraspecific variation for the three species. P. sylvaticum exhibited the most diversity, followed by P. irregulare, while substantial clonality was found in P. ultimum. For both P. irregulare and P. sylvaticum, but not P. ultimum, there was evidence for significant variation among nurseries. However, all three species also exhibited at least two distinct lineages not associated with the nursery of origin. Finally, evidence was found that certain lineages and clonal genotypes, including fungicide-resistant isolates, are shared among nurseries, indicating that pathogen movement has occurred

Forest nurseries face critical choices with the loss of methyl bromide fumigation

Forest nurseries in the western United States have relied for decades on methyl bromide to control soilborne pests. Numerous studies have investigated alternative fumigants, alternative application methods and nonfumigant approaches for their ability to reduce soilborne pest populations and produce quality, disease-free seedlings. We review the recent studies and identify where research is needed to assist the industry's transition away from methyl bromide. For the immediate, foreseeable future, an integrated approach combining nonfumigant and fumigant methods will provide the best strategy. Nevertheless, the industry may need to transition completely to container production if fumigant regulations become more restrictive

Forest nurseries face critical choices with the loss of methyl bromide fumigation

Forest nurseries in the western United States have relied for decades on methyl bromide to control soilborne pests. Numerous studies have investigated alternative fumigants, alternative application methods and nonfumigant approaches for their ability to reduce soilborne pest populations and produce quality, disease-free seedlings. We review the recent studies and identify where research is needed to assist the industry's transition away from methyl bromide. For the immediate, foreseeable future, an integrated approach combining nonfumigant and fumigant methods will provide the best strategy. Nevertheless, the industry may need to transition completely to container production if fumigant regulations become more restrictive

Forest nurseries face critical choices with the loss of methyl bromide fumigation

Forest nurseries in the western United States have relied for decades on methyl bromide to control soilborne pests. Numerous studies have investigated alternative fumigants, alternative application methods and nonfumigant approaches for their ability to reduce soilborne pest populations and produce quality, disease-free seedlings. We review the recent studies and identify where research is needed to assist the industry's transition away from methyl bromide. For the immediate, foreseeable future, an integrated approach combining nonfumigant and fumigant methods will provide the best strategy. Nevertheless, the industry may need to transition completely to container production if fumigant regulations become more restrictive

WeilandPopulationStructurePythiumSupFigure1.pdf

Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. However, little is known about their genetic diversity or population structure and it is suspected that isolates are moved among forest nurseries on seedling stock and shared field equipment. In order to address these concerns, a total of 115 isolates of three Pythium species (P. irregulare, P. sylvaticum, and P. ultimum) were examined at three forest nurseries using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Analyses revealed distinct patterns of intraspecific variation for the three species. P. sylvaticum exhibited the most diversity, followed by P. irregulare, while substantial clonality was found in P. ultimum. For both P. irregulare and P. sylvaticum, but not P. ultimum, there was evidence for significant variation among nurseries. However, all three species also exhibited at least two distinct lineages not associated with the nursery of origin. Finally, evidence was found that certain lineages and clonal genotypes, including fungicide-resistant isolates, are shared among nurseries, indicating that pathogen movement has occurred