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Sacha J. Johnson and Carol A. Miles

Successful grafting of vegetables requires high relative humidity (RH) and optimal temperatures for ≈1 week following grafting to reduce transpiration of the scion until rootstock and scion vascular tissue are healed together and water transport is restored. This study evaluated the effect of three healing chamber designs on the survival of grafted eggplant (Solanum melongena), tomato (Solanum lycopersicum), and watermelon (Citrullus lanatus). The three healing chamber designs were 1) an industry design, which was hand-misted, 2) a research design, which contained a humidifier, and 3) a simplified design, which was shadecloth only and hand-misted. All plants were self-grafted using the splice grafting technique, placed in the healing chamber for 7 days after grafting and evaluated for signs of wilting and graft failure from day 6 to day 14 after grafting. During the 7-day healing period, the industry design had the greatest fluctuation in temperature, the research design had the greatest fluctuation in RH, and the shadecloth only design had the least fluctuation in both temperature and RH. When the healing chambers were closed on day 2 after grafting, the industry healing chamber had higher mean temperature and RH (24.9 °C, 98%) than both the research (23.4 °C, 81%) and shadecloth only (23.3 °C, 52%) healing chambers. These results suggest that a humidifier may not be necessary to maintain high RH. Mean graft survival rates in the industry (69%) and research (66%) healing chambers were similar, and both were higher than that in the shadecloth only healing chamber (52%). Tomato had the highest rate (98%), eggplant was intermediate (82%), and watermelon had the lowest mean survival rate (7%); there was no interaction between healing chamber and crop. The very low survival rate of watermelon was most likely due to the grafting technique used in this study, which is not optimal for watermelon. Tomato graft survival was high in all three healing chambers (96% to 98%), suggesting that high RH is not essential for tomato graft survival. Eggplant graft survival decreased from 90% to 60% when RH was decreased, suggesting that high RH is essential for eggplant graft survival.

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Carol A. Miles and D. Gayle Alleman

Asian crops can provide growers with a means to diversify crop production and marketing options. However, before expanding into Asian crops, growers should determine consumer expectations regarding a new crop. Existing market criteria for each crop (i.e., maturity, color, size, shape) must be considered for all markets including traditional Asian use as well as for the general North American market. If growers decide to target general consumers in North America, then consumer awareness and acceptance must be addressed in a marketing and promotion program. Extension publications, popular magazines, and newspapers are useful tools in a marketing and promotion program. Crop production information must be available to enable growers to successfully produce Asian crops. Yet, most growers are unlikely to invest heavily in new production equipment and systems until a market has been established for the crop. It is a challenge for university scientists and extension agents to concurrently create supply and demand for new Asian crops. To accomplish this, multidisciplinary teams that include university and community experts should initiate a diversified program of Asian crop production, promotion, and marketing.

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Sacha Buller, Debra Inglis and Carol Miles

Growth, fruit yield and quality, and potential tolerance to verticillium wilt (Verticillium dahliae) were compared among non-grafted, self-grafted, and grafted triploid watermelon (Citrullus lanatus Thunb., ‘Crisp’n Sweet’) and heirloom tomato (Solanum lycopersicum, ‘Cherokee Purple’). Rootstocks for watermelon were ‘Emphasis’ bottle gourd (Lagenaria sicerarea) and ‘Strong Tosa’ interspecific squash hybrid (Cucurbita maxima × Cucurbita moschata), and rootstocks for tomato were ‘Beaufort’ and ‘Maxifort’ interspecific tomato (Solanum lycopersicum × Solanum habrochaites). Field trials were carried out in 2010 and 2011 at Hermiston and Eltopia (eastern Oregon and Washington, respectively) and Mount Vernon (western Washington). Grafted watermelon had significantly larger stem diameter than non-grafted and self-grafted plants both years at Mount Vernon, whereas there were no differences at Hermiston or Eltopia. Grafted tomato in 2011 had significantly larger stem diameter than non-grafted and self-grafted plants at Eltopia and Mount Vernon, and ‘Beaufort’-grafted plants were significantly taller than other treatments at Mount Vernon. Grafting did not impact watermelon or tomato fruit yield or quality at any location either year. Foliar symptoms of verticillium were not observed on ‘Crisp’n Sweet’ watermelon at the eastern locations either year; however, at Mount Vernon, ‘Emphasis’ and ‘Strong Tosa’-grafted plants had significantly lower verticillium wilt severity than non-grafted and self-grafted plants both years. Microsclerotia were observed in all recovered watermelon stems sampled at Eltopia and Mount Vernon. V. dahliae was isolated from non-grafted and ‘Emphasis’-grafted ‘Crisp’n Sweet’ stems at Eltopia and non-grafted, self-grafted, and ‘Strong Tosa’-grafted stems at Mount Vernon. Foliar symptoms of verticillium wilt and microsclerotia in stems were not observed on ‘Cherokee Purple’ plants at either location both years despite site histories of the disease. Grafting with ‘Emphasis’ and ‘Strong Tosa’ rootstocks may be an effective strategy for managing verticillium wilt on watermelon in western Washington; however, grafting ‘Cherokee Purple’ onto ‘Beaufort’ and ‘Maxifort’ did not provide any advantages for tomato under the field conditions of this study.

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Suzette P. Galinato and Carol A. Miles

Lettuce (Lactuca sativa) and tomato (Solanum lycopersicum) are popular fresh market vegetable crops. In western Washington, there is interest in growing them in high tunnel production systems because of the region’s mild, coastal climate. The objectives of this study were to contrast the economic potential of growing lettuce and tomato under high tunnel and open-field production systems, and identify the main factors affecting profitability within each production system. Economic data for this study were collected by interviewing experienced lettuce and tomato growers in western Washington during focus group sessions. Costs of production varied by crop and production system, and findings indicated that it was five times more costly to grow lettuce and eight times more costly to grow tomato in a high tunnel than in the open field in western Washington. For lettuce, the labor cost per square foot of growing area was found to be 6 times greater in a high tunnel than in the open field; and for tomato, labor costs were 10 times greater in a high tunnel than in the open field. Total labor cost comprised more than 50% of the total production costs of lettuce and tomato in both the high tunnel and open-field systems. The percentage of total labor cost was similar in both the high tunnel and open-field production for lettuce, but was higher in high tunnel tomato production than in the open field. Tunnel-grown lettuce and tomato had three and four times greater marketable yield compared with field-grown, respectively. Given the base crop yield and average price, it was 43% more profitable to grow lettuce in the open field than in the high tunnel, while in contrast, high tunnel-grown tomato was three times more profitable than open-field tomato production.

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Shuresh Ghimire, Edward Scheenstra and Carol A. Miles

Plastic mulch is commonly used to produce many vegetable crops because of its potential to decrease days to harvest, control weeds, and improve soil moisture conservation. However, use of plastic mulch is relatively new for sweet corn (Zea mays L.) in North America. We compared five plastic soil-biodegradable mulches [BDMs; Bio360, Organix AG, Clear Organix AG, Naturecycle, and Experimental polylactic acid/polyhydroxyalkanoates (Metabolix, Inc., Cambridge, MA)] and a paper mulch (WeedGuardPlus) against standard black polyethylene (PE; nonbiodegradable) mulch and bare ground cultivation for growth, yield, and quality of sweet corn cultivar Xtra Tender 2171. This field experiment was carried out in Mount Vernon, WA, which has a Mediterranean-type climate with an average air temperature of 16.1 °C during the 2017 and 2018 growing seasons. The experiment was drip irrigated; and in both years, preemergence herbicides were applied to the entire experimental area 1 to 2 days after seeding, and post-emergence herbicides were applied to alleys. While most mulches remained intact until the end of the growing season, Clear Organix AG started to split shortly after laying, resulting in significant weed pressure by midseason in both 2017 and 2018. Plant height toward the end of the season was lowest for plants grown on bare ground, intermediate for Clear Organix AG and WeedGuardPlus, and highest for the black plastic BDM and PE mulch treatments both years, except for Bio360 in 2018 where plant height was intermediate. Days to 50% tasseling and 50% silking were delayed 9 and 13 days, respectively, for bare ground and WeedGuardPlus compared with all other treatments in both years. Marketable ear yield was highest with the black plastic BDMs and PE mulch and lowest with bare ground, WeedGuardPlus, and Clear Organix AG treatments in both years. Total soluble solid content of kernels, and length and diameter of ears grown on the plastic BDM and PE mulch treatments were equal to or greater than, but never lower than, bare ground and WeedGuardPlus. These results indicate that growth, yield, and quality of sweet corn grown with black plastic BDMs are comparable to PE mulch, making black plastic BDMs an effective alternative to black PE mulch for sweet corn production in a Mediterranean-type climate.

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Jeremy S. Cowan, Debra A. Inglis and Carol A. Miles

Three potentially biodegradable plastic mulch products, Mater-bi®-based black film (BioAgri), experimental polyhydroxyalkanoate film (Crown 1), and experimental spunbonded polylactic acid fabric (SB-PLA-11), were evaluated over two broccoli (Brassica oleracea var. italica) growing seasons to determine deterioration before and after soil incorporation. Pretillage mulch deterioration was evaluated in both growing seasons by rating the percent visual deterioration (PVD). Crown 1 had the greatest PVD throughout the study (P ≤ 0.05) and BioAgri also had significant pretillage deterioration. SB-PLA-11 showed no appreciable deterioration based on PVD (<1.3%) in either growing season. Postincorporation mulch deterioration was measured for 13 months after rototilling at the end of the first growing season. The average fragment area of all mulch products decreased over time after soil incorporation. The number of postincorporation mulch fragments initially increased for all mulch products, with Crown 1 and BioAgri reaching maximum fragment counts 132 and 299 days after incorporation, respectively. As the number of fragments declined, the average area of fragments did not change, suggesting that a threshold fragment size may exist at which biodegradation accelerates. At the end of the study period, 397 days after soil incorporation, Crown 1 and BioAgri had deteriorated 100% and 65%, respectively; whereas SB-PLA-11 showed very little deterioration.

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Carol Miles, Lisa DeVetter, Shuresh Ghimire and Douglas G. Hayes

Biodegradable plastic mulch has the potential to be a sustainable technology in agricultural production systems if the mulch performs equally to polyethylene (PE) mulch and biodegrades completely into constituents that do not harm the soil ecology or environment. Reduced labor costs for removal and disposal, and reduced landfill waste add further appeal to the sustainability of biodegradable plastic mulch. Biodegradable paper mulch has been allowed in certified organic production systems in the United States for many years, while the National Organic Program (NOP) added biodegradable biobased plastic mulch to the list of allowed synthetic substances for organic crop production in Oct. 2014. Although biodegradable plastic mulch may meet the NOP biodegradability requirements (90% biodegradation within 2 years), currently no products have been approved for use in certified organic production because, so far, none meet the requirement of being completely biobased. Additionally, while the synthetic manufacturing processes that are used to make biodegradable plastic mulch are allowed by the NOP, the use of genetically modified organisms (GMOs) in the feedstocks, including their fermentation, is not allowed. Organic growers are advised always to check with their certifier before applying a product as some biodegradable mulch manufacturers and marketers erroneously advertise their product as “organic.” Looking forward, if biodegradable plastic mulch meets the NOP requirement of 90% biodegradation after 2 years, there is a possibility that 10% of plastic mulch residuals will persist (if the mulch contains nonbiodegradable ingredients); in this case, after 8 years of annual biodegradable mulch application, plastic residuals in the soil would exceed twice the amount of mulch applied per year. The current methods used by the NOP to test mulch biodegradation are laboratory based and it is uncertain if the results accurately represent field conditions. Reliable field sampling methods to measure residual mulch fragments in the soil need to be developed; however, it is unlikely such field tests will measure CO2 evolution, and thus will not be a true measure of biodegradation. Additional testing is needed under diverse field conditions to accurately quantify the rate and extent of biodegradation of mulch products that are marketed as biodegradable.

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Charlene M. Grahn, Chris Benedict, Tom Thornton and Carol Miles

Baby-leaf salad green crops such as lettuce (Lactuca sativa), kale (Brassica oleracea), arugula (Eruca sativa), and mustard greens (Brassica juncea) thrive in the cool, humid climate of the maritime Pacific Northwest, particularly in the extended spring and fall seasons. To identify cultivars best suited for extended-season production in northwest Washington, nine leafy green cultivars were grown at two locations in the spring and fall seasons for 2 years. A high level of variability in crop performance was observed between seasons, locations, years, planting dates, and cultivars, indicating low-yield stability in baby-leaf salad crops across diverse environments and conditions. Overall, cultivars had a higher marketable weight in the spring than in the fall. Marketable weight was higher in Spring 2013 than in Spring 2014, and was higher in Fall 2013 than in Fall 2012. Days to harvest (DTH) were shorter in the spring than in the fall both years, and in both seasons DTH varied by ≈1 week between the two trial locations. Fresh weed biomass was almost 5.5 times higher in spring than in fall both years. Overall, pak choi ‘Joi Choi’ and mustard ‘Komatsuna’ had the highest marketable weight, lowest DTH, and lowest weed biomass across the widest range of environments and conditions, while beet ‘Bull’s Blood’ had the lowest marketable weight, relatively long DTH and highest weed biomass. These results suggest that baby-leaf salad crop cultivar selection differs for spring and fall seasons, and production can be highly variable between years and locations. Further, results suggest that growers should plant a diversity of crop cultivars each season to protect from crop loss and to achieve overall yield stability.

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Kristy A. Ott-Borrelli, Richard T. Koenig and Carol A. Miles

Leafy green vegetables such as lettuce (Lactuca sativa), Asian greens (Brassica spp.) and spinach (Spinacia oleracea) have a tendency to accumulate high concentrations of potentially harmful nitrate–nitrogen (NO3-N). It would be advantageous for growers to have rapid and inexpensive methods to accurately measure plant tissue NO3-N to make fertility and harvest management decisions for these crops. This study compared fresh sap expressed from whole leaves and analyzed with a Cardy meter with the analysis of dry leaf tissue extracts analyzed with a benchtop ion selective electrode (ISE) and an automated colorimetric method for determining NO3-N concentration. Results from ISE and colorimetric analysis of the same dry leaf tissue extracts had a strong relationship (r 2 = 0.92). The ISE was relatively easy to operate and affordable, suggesting it is an adequate substitute for automated colorimetric analysis of dry plant tissue extracts. Results of fresh whole leaf sap analyzed with the Cardy meter showed a poor relationship with dry leaf tissue extracted and analyzed using the ISE (r 2 = 0.25) or with colorimetric analysis (r 2 = 0.21). When fresh whole leaf sap was diluted 1:1 with aluminum sulfate [Al2(SO4)3] to adjust for potential matrix effects, there was still a relatively poor relationship (r 2 = 0.41) between the diluted sap samples analyzed with a Cardy meter and the dry leaf tissue extracted and analyzed with the ISE. When the same dry leaf tissue extracts were analyzed with the Cardy meter and the ISE, the results related well (r 2 = 0.96). As a result of tissue processing and/or instrument differences, Cardy meter analysis of sap expressed from whole leaves was not comparable to ISE or colorimetric analyses of dry leaf tissue extracts for leafy green vegetables.

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Travis Robert Alexander, Jacqueline King, Andrew Zimmerman and Carol A. Miles

In this study, four cider apple (Malus ×domestica) cultivars, Brown Snout, Dabinett, Kingston Black, and Yarlington Mill, were collected from four orchards, two in northwest Washington and two in central Washington, to compare juice quality characteristics. Northwest Washington has a cool, humid summer climate (16.0 °C on average during this study) and is the origin of the state’s cider apple industry, while central Washington has a hot, dry summer climate (22.1 °C on average during this study) and is the center of the state’s dessert apple industry. Each year from 2012 to 2015, fruit of the four cultivars were harvested and stored at each orchard until they were collected. Fruit were pressed and the juice analyzed for five quality characteristics important to cider making: soluble solids concentration [SSC (%)], specific gravity (SG), pH, titratable acidity [TA, malic acid equivalent (g·L−1)], and tannin [tannic acid equivalent (%)]. Harvest dates and climate data were recorded annually for each orchard location. There were no significant differences in any of the juice quality characteristics due to region and no significant interaction of region, cultivar, and/or year. Results did show, as expected, a significant difference in all five juice characteristics due to cultivar. ‘Brown Snout’, ‘Dabinett’, and ‘Kingston Black’ were higher in SSC and SG than ‘Yarlington Mill’; ‘Dabinett’ had the highest pH and lowest TA while ‘Kingston Black’ had the lowest pH and highest TA; and tannin was highest in ‘Yarlington Mill’ and lowest in ‘Kingston Black’. There was also a difference in SG and tannin due to year; SG was lowest in 2013 while tannin was highest in 2012. The difference in SG from year to year may be a result of variable year-to-year storage time at each orchard before collection of fruit. The difference in tannin from year to year was likely due to climatic variation over the four years of this study. On average, growing degree days (GDD) increased 10% and chilling hours (CH) decreased 10% from 2012 to 2015 in both regions. Classification of the four cultivars included in this study differed from historical records at the Long Ashton Research Station (LARS) in England; in the current study, the four cultivars exhibited tannin levels below 0.20% and would not be classified as bitter, unlike their historical classification at LARS. Results from this study indicate that variations in juice quality characteristics occur between cultivars as expected and occur within a cultivar from year-to-year, but for the four cultivars included in this study variations did not occur due to production region in Washington.