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Yushan Duan, Thomas W. Walters and Timothy W. Miller

A large percentage of North American processing red raspberry (Rubus idaeus L.) is produced in maritime areas of western regions in Washington, British Columbia, and Oregon. Most of these raspberry plantings are caneburned; they are treated with herbicides in early spring to remove the first-emerging primocanes in an attempt to reduce their competition with floricanes during flowering and fruiting and thereby increase fruit yield. Trials were conducted in northwestern Washington to determine the effect of carfentrazone and oxyfluorfen applied for primocane management in three currently grown raspberry cultivars. Although caneburning did provide early season weed control in treated plots, weed control fell below 70% in the commercial ‘Meeker’ field more quickly each year: at 138 days after treatment (DAT) in 2010, 71 DAT in 2011, and 47 DAT in 2012, compared with greater than 80% control at the end of each season when the soil residual herbicide terbacil was applied. Oxyfluorfen provided longer suppression of primocane growth than did carfentrazone, particularly in ‘Cascade Bounty’ but also to a lesser extent in ‘Meeker’. Caneburning did not improve raspberry yield in five of the six tested years for ‘Meeker’, or in any of the five tested years for ‘Cascade Bounty’ or the single year for ‘Coho’, although the trend was for greater yield with caneburning across all cultivars. Oxyfluorfen improved 3-year ‘Meeker’ average yield 43% from nontreated raspberry in the commercial field trial, compared with a 29% increase with carfentrazone.

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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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James R. McFerson, Thomas W. Walters and Charles J. Eckenrode

Nearly 350 germplasm accessions representing 25 Allium species were evaluated for damage by onion maggot (OM) [Delia antiqua (Meigen)] in field experiments in 1989. In 1990, 188 additional accessions and breeding lines were evaluated, and 36 entries from the 1989 evaluation were re-evaluated. In both years, there were no significant differences in OM damage to seedlings among accessions within the species tested. However, differences among species were highly significant. Allium cepa L. (bulb onion) seedlings had consistently high OM damage. Species with significantly less seedling damage than A. cepa included: A. altaicum Pall., A. angulosum L., A. galanthum Kar. & Kir., A. pskemense B. Fedtsch., A. scorodoprasum L., A. ampeloprasum L. (leek), A. fistulosum L. (bunching onion), A. schoenoprasum L. (chive), and A. tuberosum Rottl. ex Spr. (garlic chive). Some species sustaining minimal damage as seedlings were nonetheless heavily damaged as mature plants by a later generation of OM. Allium cepa cultivars that were well-adapted to local conditions were heavily damaged as seedlings, but their bulbs were less damaged than those of poorly adapted A. cepa germplasm. Allium ampeloprasum seedlings and mature plants sustained low injury throughout both growing seasons.

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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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Wallace G. Pill, Thomas A. Evans, Michael W. Olszewski, Robert P. Mulrooney and Walter E. Kee Jr.

'Maffei 15' baby lima bean seeds were sown every 6 cm in rows 76 cm apart to yield a nominal stand of 215,000 plants/ha at two locations in Delaware over 2 years. Seedlings were thinned within 2 weeks of planting to provide 0%, 16.7%, 33.3%, and 50.0% stand reduction at two in-row spacing patterns to determine subsequent effects on vegetative and reproductive growth. Shoot fresh weight per square meter was decreased only in 2003 by 21% and bean fresh weight per square meter was decreased only in 2004 by 13.8% when plant stand decreased to 50%. This disproportional vegetative and reproductive growth response to stand reduction resulted from a compensatory linear increase in shoot fresh weight, usable pod number, and bean fresh weight of individual plants. Thus, 'Maffei 15' lima bean tolerates a considerable loss of plant stand with little or no effect on yield.

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Thomas W. Walters, LeRoy A. Ellerbrock, Jan J. van der Heide, James W. Lorbeer and David P. LoParco

Greenhouse and field methods were developed to screen Allium spp. for resistance to botrytis leaf blight (causal agent Botrytis squamosa Walker). In greenhouse evaluations, plants were sprayed with laboratory-grown mycelial fragment inoculum and were incubated at 20C in a chamber with an atomizing fogger. For field inoculations, a portable fog system with windbreaks was erected around experimental plots, and the plants were sprayed with the inoculum on evenings when windless, temperate (18 to 22C) conditions were forecasted. The most effective mycelial fragment inoculum was <21 days old and had ≈45 to 50 colony-forming units/μl, resulting in an absorbance at 450 nm of 0.2 to 0.3. Rubbing the wax cuticle from leaves was essential to disease development in greenhouse but not in field experiments. Evaluations of eight Allium species, including 55 A. cepa L. accessions, were in agreement with previous studies.

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Gary W. Stutte, Tara A. Baugher, Sandra P. Walter, David W. Leach, D. Michael Glenn and Thomas J. Tworkoski

A study was conducted to quantify the effects of rootstock and training system on C allocation in apple. Dry-matter distribution was determined at harvest in 5-year-old `Golden Delicious' apple (Malus domestica Borkh.) trees on four rootstocks (MM.111 EMLA, M.7a, M.26 EMLA, and M.9 EMLA) and in three training systems (three-wire palmette, free-standing central leader, and nonpruned). Mobilizable carbohydrate content was determined at harvest and leaf fall in trees from the same planting on MM.111 EMLA and M.9 EMLA in all three training systems. Training system effects interacted with rootstock effects in dry weights of branches and of fruit. Nonpruned system shoot and fruit dry weights reflected known rootstock vigor; whereas, pruned system (three-wire and central leader) shoot dry weights were greatest and fruit dry weights were lowest in trees on M.7a. Rootstock affected the partitioning of dry matter between above- and below-ground tree components, with MM.111 EMLA accumulating significantly more dry matter in the root system than trees on the other rootstocks. Trees in the central leader and the three-wire palmette systems partitioned more dry weight into nonbearing 1-year shoots than trees in the nonpruned system. Root starch content at harvest was greater in trees on MM.111 EMLA than on M.9 EMLA, and root sucrose and sorbitol were less in trees on MM.111 EMLA compared to M.9 EMLA. At leaf fall, starch in young roots was equal in trees on both rootstocks, and sorbitol again was lower in trees on MM.111 EMLA. Harvest starch content of roots, shoots, and branches was lower in nonpruned than in pruned trees. At leaf fall, root, shoot, and branch starch content increased in nonpruned and central leader-trained trees but did not increase in three-wire palmette-trained trees.

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Thomas W. Walters, Leroy A. Ellerbrock, Jan J. van der Heide, James W. Lorbeer and David P. LoParco

Greenhouse and field methods were developed to screen Allium spp. for resistance to Botrytis leaf blight (caused by Botrytis squamosa Walker). In the green-house, plants were sprayed with laboratory-grown inoculum and incubated in a temperature-controlled enclosure containing an atomizing mist system. For field inoculations, a portable misting system with windbreaks was erected, and the plants were sprayed with laboratory-grown inoculum. Greenhouse and field incubation conditions maintained leaf wetness without washing inoculum from the leaves. Botrytis leaf blight symptoms in greenhouse and field evaluations were identical to symptoms in commercial onion fields. A total of 86 selected USDA Allium collection accessions were evaluated using these methods. All A. fistulosum accessions and A. roytei were highly resistant to immune, as were most accessions of A. altaicum, A. galanthum, A. pskemense, and A. oschaninii. Nearly all of the A. vavilovii and A. cepa accessions were susceptible. However, one A. cepa accession (PI 273212 from Poland) developed only superficial lesions, which did not expand to coalesce and blight leaves. This work confirms previous reports of Botrytis leaf blight resistance in Allium spp., and suggests that strong resistance exists with A. cepa.

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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.