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Inga A. Zasada and Patrick P. Moore

The root lesion nematode, Pratylenchus penetrans, is a production-limiting pest in red raspberry, Rubus idaeus. Genetic resistance, as a tool to manage P. penetrans in raspberries, would reduce the impact of this nematode on raspberry productivity as well as reduce the need for pre- and/or post-plant chemical treatments to keep populations in control. The host status of 11 Rubus species (R. coreanus, R. crataegifolius, R. innominatus, R. leucodermis, R. niveus, R. parviflorus, R. parvifolius, R. pungens, R. spectabilis, R. sumatranus, and R. odoratus) for P. penetrans was evaluated in greenhouse studies. Additionally, hybrids of R. cockburnianus, R. lasiostylus, R. niveus, R. phoenicolasis, and R. sumatranus with R. idaeus ‘Meeker’ or ‘Tulameen’ were evaluated. The industry standard R. idaeus ‘Meeker’ was included in all trials as the control. Across trials, R. niveus and R. leucodermis were identified as poor hosts for P. penetrans. In addition, when another selection of R. niveus was evaluated in the final year of this study, it was also a poor host for P. penetrans. Among the remaining Rubus species materials tested, there were no consistent differences in host status for P. penetrans. It appears that R. niveus and R. leucodermis might be sources of resistance for P. penetrans. However, a hybrid between R. niveus and R. idaeus ‘Tulameen’ did not consistently support fewer P. penetrans than the ‘Meeker’ control. These results indicate that more research is needed to learn about the inheritance of the putative resistance.

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Inga A. Zasada, Thomas W. Walters and John N. Pinkerton

To identify a post-plant nematicide to control root lesion nematode [RLN (Pratylenchus penetrans)] in red raspberry (Rubus idaeus), a number of nematicides was tested in soil-only and plant-based experiments. In soil-only experiments, soil naturally infested with RLN was drenched with the nematicides and nematode survival was assessed 7 and 14 days after treatment. Fosthiazate and oxamyl reduced RLN recovery 92% and 52% across trials and sampling times, respectively, compared with the nontreated control. Other nematicides that resulted in moderate, and sometimes inconsistent, control of RLN were soapbark (Quillaja saponaria) saponins, 1,3-dichloropropene, and methomyl. In plant-based experiments, ‘Meeker’ red raspberry was established in pots with RLN-infested soil mixed with greenhouse soil and the nematicides were applied as soil drenches or as a foliar application. Nematode recovery and cane and root weights were quantified as measurements of nematicide toxicity and phytotoxicity, respectively. Similar to soil-only experiments, fosthiazate and oxamyl were the most effective nematicides tested in reducing RLN population densities in established red raspberry. Fosthiazate and oxamyl significantly reduced RLN per gram dry root population densities by 97% and 87%, respectively, compared with the infested, nontreated control. None of the other nematicides reduced RLN population densities compared with the infested, nontreated controls. There was no phytotoxicity to red raspberry associated with any of the nematicides.

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Susan L.F. Meyer, Inga A. Zasada, Mario Tenuta and Daniel P. Roberts

The biosolid soil amendment N-Viro Soil (NVS) and a Streptomyces isolate (S 99-60) were tested for effects on root-knot nematode [RKN (Meloidogyne incognita)] egg populations on cantaloupe (Cucumis melo). Application of 3% NVS (dry weight amendment/dry weight soil) in the soil mixture resulted in significant (P ≤ 0.01) suppression of RKN egg numbers on cantaloupe roots compared to all other treatments, including 1% NVS and untreated controls. Ammonia accumulation was higher with the 3% NVS amendment than with any other treatment. Adjustment of soil pH with calcium hydroxide [Ca(OH)2] to the same levels that resulted from NVS amendment did not suppress nematode populations. When cultured in yeast-malt extract broth and particularly in nutrient broth, S 99-60 was capable of producing a compound(s) that reduced RKN egg hatch and activity of second-stage juveniles. However, when this isolate was applied to soil and to seedling roots, no suppression of RKN egg populations was observed on cantaloupe roots. Combining S 99-60 with NVS or Ca(OH)2 did not result in enhanced nematode suppression compared to treatments applied individually. The results indicated that NVS application was effective at suppressing RKN populations through the accumulation of ammonia to levels lethal to the nematode in soil.

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Rachel E. Rudolph, Thomas W. Walters, Lisa W. DeVetter and Inga A. Zasada

One of the primary production challenges red raspberry (Rubus idaeus) growers in the Pacific northwestern United States confront is root lesion nematode [RLN (Pratylenchus penetrans)]. In this perennial production system, red raspberry serves as a sustained host for RLN. When a red raspberry planting is slated for removal in the fall, a new red raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with red raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat (Triticum aestivum) provides a green bridge for RLN in continuous red raspberry production systems and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN before replanting red raspberry. Four trials were established in fields being replanted to red raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or 2 weeks after fumigation), termination date (cover crop kill with herbicide 2 or 6 weeks before incorporation compared with the industry standard of incorporation immediately before planting), and the additional application of methomyl. ‘Rosalyn’ and ‘Bobtail’ winter wheat planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/g winter wheat root across trials) allowing them to be a green bridge for RLN to infect the following red raspberry crop. Altering winter wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent red raspberry crop. Although planting an RLN maintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent red raspberry crop.

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Susan L.F. Meyer, Dilip K. Lakshman, Inga A. Zasada, Bryan T. Vinyard and David J. Chitwood

Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active against various soil-borne plant pathogens and therefore has potential for use as a bio-based pesticide. A clove oil formulation previously found to be toxic to the southern root-knot nematode (Meloidogyne incognita) in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2%, and 0.3% clove oil applied to soil 0, 2, 5, and 7 days before transplant of cucumber (Cucumis sativus), muskmelon (Cucumis melo), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) seedlings. Tomato seedlings were the most sensitive to clove oil. The 0.2% and 0.3% clove oil concentrations applied as drenches at transplant (0 day) were the most phytotoxic to seedlings of all the tested vegetable species, with only 0% to 50% seedling survival. Most of the clove oil concentrations applied as drenches at transplant decreased shoot heights and fresh shoot weights of all seedlings. Some applications of clove oil at 0.2% and 0.3%, applied 2, 5, or 7 days before transplant also significantly reduced shoot growth, especially of pepper and tomato. Greenhouse experiments evaluating suppression of nematode populations on cucumber were conducted with 0.10%, 0.15%, and 0.20% clove oil applied 7 days before transplant. Overall, plants inoculated with nematodes tended to have smaller shoots and heavier roots than plants without nematodes. Effects of clove oil treatments on nematode population densities were inconsistent between the two trials. In Trial 1, 0.10% and 0.15% clove oil decreased population densities compared with the carrier control. In Trial 2, nematode population densities were lowest in the water and carrier control treatments. The results indicate that, with the tested clove oil formulation and application times, southern root-knot nematode populations would not be consistently reduced with clove oil concentrations that were not phytotoxic to one or more of the tested vegetable crops.

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Inga A. Zasada, Clyde L. Elmore, Lani E. Yakabe and James D. MacDonald

The cut flower and bulb industry in California is an important part of the state's agricultural economy and it has relied heavily upon the use of methyl bromide as a treatment to control soil-borne pests. With the phase out of methyl bromide, it is important to develop alternatives that will maintain crop productivity. This report describes research testing the efficacy of propargyl bromide against selected nematode, fungal, and weed species. Three sites were selected in California to represent different soil types and environments. Propargyl bromide was applied to soil in large, buried containers at rates ranging from 28 to 168 kg·ha−1 and compared with standard soil fumigants. The citrus nematode (Tylenchulus semipenetrans Cobb) and an isolate of Fusarium oxysporum Schlechtend:Fr were both controlled at the lowest rate of propargyl bromide tested: 28 kg·ha−1. Weed species varied greatly in their sensitivity to propargyl bromide. A 100% reduction in common purslane (Portulaca oleracea L.) and pigweed (Amaranthus retroflexus L.) germination occurred at 112 kg·ha−1 propargyl bromide, regardless of geographical location. Results for annual bluegrass (Poa annua L.) control were more variable across locations and years, but more than 90% control was consistently achieved with 168 kg·ha−1 propargyl bromide. Cheeseweed (Malva parviflora L.) and field bindweed (Convolvulus arvensis L.) were never consistently controlled by propargyl bromide. When compared with the soil fumigants methyl bromide, iodomethane, and metam sodium, propargyl bromide provided comparable control of all soil-borne pests, but at much lower rates. Although higher rates of propargyl bromide, more than 112 kg·ha−1, were needed to control weeds, these rates still were almost half that required of the other standard fumigants.

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Rachel E. Rudolph, Lisa W. DeVetter, Chris Benedict and Inga A. Zasada

A survey was conducted in Washington State in 2015 and 2016 to gauge grower perceptions, understanding, and current practices regarding soil quality. Soil quality has been defined as the ability of the soil to sustain plants, animals, and humans over time. Many current practices of modern agriculture can be detrimental to soil quality, including soil tillage and soil fumigation, both of which are commonly used for the Washington red raspberry (Rubus idaeus) production system. The area between red raspberry beds, known as the alleyway, is frequently tilled and kept bare, without groundcover, to manage weeds. Growers commonly fumigate the soil before planting red raspberry to manage soilborne pathogens and plant-parasitic nematodes. The majority of red raspberry growers surveyed consider soil quality quite often in relation to the management of their fields. The majority of growers during both years considered cover crops to have a positive impact on soil quality. However, growers also perceived soil fumigation to have a positive impact on soil quality. The majority of growers responded that they were willing to adopt alleyway cover crops for a variety of reasons, including improving red raspberry production, physical soil quality, and beneficial soil microorganism populations. This survey demonstrated that there is interest in soil quality among growers; however, there is a difference in perceptions between growers and researchers regarding how management practices impact soil quality.

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Thomas W. Walters, John N. Pinkerton, Ekaterini Riga, Inga A. Zasada, Michael Particka, Harvey A. Yoshida and Chris Ishida

The efficacy and phytotoxicity of postplant treatments to control root lesion nematodes [RLN (Pratylenchus penetrans)] and dagger nematodes [DN (Xiphinema bakeri)] in red raspberry (Rubus idaeus) were evaluated in four field studies, each conducted over 1 to 3 years. Spring spray applications of oxamyl or fosthiazate reduced RLN and DN population densities for up to 2 years, but fall oxamyl sprays and spring drip-applied oxamyl applications were not effective. Oxamyl application rate determined the duration of nematode suppression. Two spring applications of oxamyl at 2 lb/acre provided more than 2 years of suppression, while two spring applications of 0.8 lb/acre suppressed nematodes for only 1 year. Spring oxamyl applications reduced ‘Nootka’ fruit yield for one season, but did not affect ‘Willamette’ yield. Fall spray-applied fenamiphos, fall and spring spray-applied DiTera (a fermentation product of the fungus Myrothecium verrucaria), fall drip-applied 1,3-dichloropropene, and spring shallow-incorporated abyssinian mustard (Brassica carinata) seed meal suppressed RLN briefly (less than 6 months) or not at all.

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Susan L.F. Meyer, Inga A. Zasada, Shannon M. Rupprecht, Mark J. VanGessel, Cerruti R.R. Hooks, Matthew J. Morra and Kathryne L. Everts

Mustard seed meals of indian mustard [InM (Brassica juncea)] and yellow mustard [YeM (Sinapis alba)], alone and combined, were tested for effects on tomato (Solanum lycopersicum) plants and for suppression of southern root-knot nematode [RKN (Meloidogyne incognita)] and weed populations. In the greenhouse, with all seed meal treatments applied at 0.25% total w/w soil, low tomato plant stands (up to 60% dying/dead) resulted from amendment with 3 YeM:1 InM, 1 YeM:1 InM, and YeM, applied right before transplant. Compared with untreated controls, low numbers of RKN eggs per gram root were consistently recorded from amendment with 3 YeM:1 InM. In a 2012 field study, incorporation of 1 YeM:1 InM (1700 lb/acre) resulted in lower tomato root biomass than fertilizer application (504 lb/acre), YeM or InM (each 1700 lb/acre). All treatments were applied with added fertilizer to achieve 100–102 lb/acre nitrogen, 7.4 lb/acre phosphorus, 74.7 lb/acre potassium, 6.0 lb/acre sulfur, and 1.0 lb/acre boron. The lowest numbers of RKN eggs per gram root (harvest 2012) were collected from plots amended with InM (1700 lb/acre), YeM (850 lb/acre), and 3 YeM:1 InM (1700 lb/acre), but the numbers were not significantly different from fertilizer only (504 lb/acre) controls. Highest and lowest tomato yields (numbers of fruit) in 2012 were recorded from YeM (850 lb/acre) and 3 YeM:1 InM (1700 lb/acre) amendments, respectively. In 2013, there were no significant differences among treatments in eggs per gram root or in tomato yields. No mustard seed meal treatment affected weed populations. At the tested rates, YeM seed meal showed potential for use in tomato beds but results were inconsistent between years.