Low temperatures can slow down emergence, decrease weed competitiveness, and lead to uneven crop maturity in direct-seeded crops such as baby leaf lettuce (Lactuca sativa L.). In this study, seeds of 103 single-parent lineage, homozygous lettuce accessions (53 cos and 50 leaf type) from the USDA National Plant Germplasm System (NPGS) and six commercial standard lettuce cultivars (three cos and three leaf type) were evaluated in replications for percent germination after 7 and 10 days at 5 °C in a germination chamber. Cos and leaf types were selected for this study as they are most commonly used for baby leaf lettuce production. Differences were observed among entries in percent seeds germinated after both 7 and 10 days. Overall, an average of 68% of seeds germinated after 7 days and 94% germinated after 10 days. Although several NPGS accessions had higher percent germination than the commercial cultivars, the average percent germination was not statistically different between the two seed sources at 7 or 10 days. Percent germination also did not differ between entries of cos and leaf type after 7 or 10 days. Similarly, no difference in percent germination between entries of dark and white seed color was observed after 7 or 10 days. No relationship between 100 seed weight and percent germination was observed after 7 days (r 2 = 0.07) or 10 days (r 2 = 0.13). Thus, lettuce seed type, color, and 100 seed weight do not appear to be good predictors of germination under cold conditions in lettuce. The accessions with the highest percent germination after 7 days at 5 °C have the potential to be used for the development of new lettuce cultivars suitable for an extended, early season production in temperate climates when soil temperature is lower than optimal for lettuce germination. Further studies are needed to assess the ability of these accessions to germinate rapidly under cold field soil conditions.
Charlene M. Grahn, Barbara Hellier, Chris Benedict and Carol Miles
Travis Robert Alexander, Jaqueline King, Edward Scheenstra and Carol A. Miles
In this 2-year study, ‘Brown Snout’ specialty cider apples (Malus ×domestica) that had been hand harvested or machine harvested with an over-the-row shake-and-catch small fruit harvester were ambient stored (56 °F mean temperature) for 0, 2, and 4 weeks to evaluate yield, fruit damage, yield loss, and juice quality characteristics. The average yield (pounds per acre) of fruit picked and retained by the mechanical harvester was 74% that of the hand-harvest yield and 81% that of the hand-harvest yield when fruit that fell out of the harvester was included in the machine-harvest yield. Percent fruit bruised and cut were greater for machine harvest (97.5% and 25.5%, respectively) than for hand harvest (47% and 0.5%, respectively), on average for 2014 and 2015. Yield loss to rot was greater for machine harvest than for hand harvest, and increased for both methods over time; percent rot doubled from 2 to 4 weeks storage for machine harvest (22% to 41%), and while negligible, tripled from 2 to 4 weeks storage for hand harvest (0.7% to 2.1%). Juice quality characteristics did not differ due to harvest method, but did differ due to year and storage time. Soluble solids concentration [SSC (%)] and specific gravity (SG) did not change due to storage in 2014, but in 2015, SSC and SG were greater on average for 2 and 4 weeks storage duration (15% and 1.062, respectively) than at harvest (13.31% and 1.056, respectively). Titratable acidity (grams per liter malic acid) decreased in 2014 from 2.98 g·L−1 at harvest to 2.70 g·L−1 on average for 2 and 4 weeks storage duration, but did not differ due to storage in 2015. Tannin [tannic acid equivalent (%)] was unchanged in 2014 from harvest to 4 weeks storage, but increased in 2015 from 0.16% at harvest to 0.19% by 4 weeks storage. These results indicate that harvest efficiency could be improved with some engineering modifications of the over-the-row mechanical harvester and training modifications for the trees. A comparison of the aromatic and phenolic contents of mechanically harvested and hand-harvested ‘Brown Snout’ would be a valuable next step in evaluating shake-and-catch mechanical harvest technology for cider apple production.
Carol A. Miles, Jacqueline King, Travis Robert Alexander and Edward Scheenstra
Little information exists on the bloom and fruit characteristics of cider apple (Malus ×domestica) cultivars grown in the United States for the juice and alcoholic beverage markets. In this study, a total of 17 cider apple cultivars, including 4 American, 9 English, and 4 French, plus 1 Danish standard dessert apple cultivar (Red Gravenstein, Worthen strain) commonly used for cider, all grown in northwest Washington, were evaluated from 2000 to 2015 for commercially relevant traits. Trees were rated each year and the cultivars were categorized accordingly by relative bloom time, bloom habit, and productivity. The mean full bloom (FB) date of the 18 apple cultivars evaluated ranged from 25 Apr. to 25 May, with 6 cultivars categorized as early season bloomers, 9 as midseason, and 3 as late season. The mean bloom density (BD) rating (measured on a scale of 1–5) for all cultivars was (mean ± sd) 3.8 ± 0.6 (moderate bloom), with the bloom habit of 1 cultivar categorized as biennial, 11 as consistent, and 6 as strongly consistent. The mean productivity rating (measured on a scale of 1–5) for all cultivars was 2.9 ± 0.6 (light fruiting), with the productivity of 4 cultivars categorized as biennial, 10 as consistent, and 4 as strongly consistent. The mean fruit diameter of the 18 apple cultivars was 2.7 ± 0.4 inches (medium sized), with the fruit size of 2 cultivars categorized as small-fruited, 15 as medium-fruited, and 1 as large-fruited. For the 18 cultivars, the mean tannin and titratable acidity (TA) were 0.20% ± 0.14% and 0.54% ± 0.28%, respectively, and using the English cider apple classification system of juice type, 4 of the cultivars were classified as bittersweet, 1 as bittersharp, 3 as sweet, and 10 as sharp. Three of the cultivars had tannin content lower than what was historically recorded at the Long Ashton Research Station (LARS) in Bristol, England, for those same cultivars. The mean specific gravity (SG) of the 18 cultivars was 1.052 ± 0.007, the average predicted alcohol by volume (ABV) was 6.9% ± 0.9%, and the mean pH was 3.68 ± 0.39. Classification of three cultivars in northwest Washington, based on juice characteristics, differed from their historical classification in England, likely because of differences in climate and management. Only cultivars Golden Russet (sharp), Grimes Golden (sharp), and Yarlington Mill (sweet, but borderline bittersweet) were strongly consistent in productivity, but none produced high levels of tannin, whereas only cultivars Bramtot (bittersweet), Chisel Jersey (bittersweet), and Breakwell Seedling (bittersharp) were consistent in productivity and produced high levels of tannin.
Fairuz A. Buajaila, Pinki Devi and Carol A. Miles
Many small-scale vegetable growers in the United States who graft their own vegetable transplants use healing chambers inside a greenhouse to heal their grafted plants. Under these conditions, light and relative humidity (RH) can fluctuate during the healing process, and growers need more research-based information regarding the impact of these factors on the survival of grafted transplants. To address this need, this study investigated the effect of different targeted levels of light (0%, 25%, and 50%) and RH (50% and 100%) (six combinations) in a small-scale healing chamber within a greenhouse, where the healing chamber was opened for increasing periods of time for 8 days, at which time plants were fully exposed to greenhouse conditions. The survival and growth of self-grafted eggplant (Solanum melongena), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) were measured up to 25 days post grafting. Percent light in the closed healing chambers was similar for the 50% and 100% RH levels of each light treatment. When the healing chambers were closed, compared with the greenhouse, there was 0.1% light in the 0% light treatments, 25% light on average in the 25% light treatments, and 43% light on average in the 50% light treatments. On days 2 to 5 after grafting, when chambers were opened up to 1 hour, average RH in the healing chambers was 96% to 98% for the 100% RH treatments, and was 42% to 49% for the 50% RH treatments. On days 6 and 7, when chambers were opened for 3 to 8 hours, RH was 79% to 82% for the 100% RH treatments, and was 39% to 46% for the 50% RH treatments. Survival of grafted plants following healing was greatest when the healing chamber treatment was 100% RH and 50% or 25% light (95% and 90% survival, respectively), and plant survival with these two treatments did not significantly decline from 11 to 21 days after grafting, indicating plants were fully healed and acclimated when they were removed from the healing chambers on day 8. At 22 to 25 days following grafting, plants healed with 100% RH and 50% or 25% light had greater plant height, number of leaves per plant, and stem diameter than plants healed in the other light and RH combinations. SPAD reading and nitrate-nitrogen of fresh petiole sap were unaffected by any of the healing treatments tested in this experiment, or by crop type. Tomato and pepper had 14% greater survival rates on average than eggplant at all measurement dates, while tomato tended to have greater plant growth, followed by eggplant and pepper. Additional research is needed to improve survival of grafted eggplant.
Abigail Attavar, Lydia Tymon, Penelope Perkins-Veazie and Carol A. Miles
Grafting is used in watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] production as a means to combat soilborne diseases. To support the development of new rootstock cultivars in the United States, we screened cucurbit germplasm accessions for resistance to verticillium wilt (caused by Verticillium dahliae Kleb.) and for compatibility as watermelon rootstocks. Screening was done using a field naturally infested with V. dahliae [5 and 7.5 colony-forming units (cfu)·g−1 soil in 2017 and 2018, respectively], and plants were inoculated at transplanting (1.5 and 104 cfu of V. dahliae per plant in 2017 and 2018, respectively). In 2017, 56 germplasm accessions from three genera commonly used as rootstocks, Cucurbita, Lagenaria, and Benincasa, were sourced from the U.S. Department of Agriculture (USDA) National Plant Germplasm System and area under the verticillium wilt (disease) progress curve (AUDPC) values ranged from 16 to 397. The 14 accessions with the lowest AUDPC values and good germination (>40%) were used as rootstocks along with the commercial rootstock cv. Tetsukabuto (control), and all were grafted with watermelon cv. Secretariat as the scion in 2018. Grafted plant survival rate was greatest for ‘Tetsukabuto’ (90%) and the accession PI 381840 (L. siceraria) (89%), and ranged from 22% to 85% for all other accessions. All grafted treatments that produced mature fruit in 2018 tended to flower at the same time as nongrafted ‘Secretariat’, with first male and female flowers occurring in 45 to 50 days and 44 to 51 days after transplanting, respectively. There were no significant differences in AUDPC values due to grafting or when accessions were compared with ‘Tetsukabuto’. Only six accessions produced mature fruit when grafted with ‘Secretariat’, indicating they were compatible for watermelon grafting. Fruit weight and number as well as total soluble solids, pH, lycopene content, rind firmness and thickness, and dry matter content were similar for all accessions and ‘Tetsukabuto’ grafted on ‘Secretariat’. Only fruit flesh firmness differed and was highest for ‘Secretariat’ grafted on ‘PI 491316’ and lowest for ‘Secretariat’ grafted on ‘PI 49174’. The six verticillium wilt-tolerant accessions that were compatible with watermelon could potentially be used as rootstocks or as sources of genetic resistance in rootstock breeding programs.
Huan Zhang, Lisa Wasko DeVetter, Edward Scheenstra and Carol Miles
A soil-biodegradable mulch (BDM) is designed to be tilled into the soil at the end of the growing season, and is a successful alternative to polyethylene (PE) mulch if it suppresses weeds and improves soil temperature and moisture, crop yield, and fruit quality. This study compared one clear plastic BDM (COX), two black plastic BDMs (BOX and BFO), and two paper BDMs (WGP and AMX) to clear and black plastic PE mulch (CPE and BPE, respectively) for weed control, yield, and mulch adhesion of ‘Cinnamon Girl’ pie pumpkin (Cucurbita pepo) in a Mediterranean climate where increased soil temperature from mulch is desirable. BDMs in this study are advertised as soil-biodegradable, and we tested functionality but not biodegradability. Mulch deterioration during the growing season was measured as percent soil exposure (PSE), and remained low at the end of the growing season for all BDM and PE treatments both years (5% on average) except COX (68%). Weed number and biomass were low early, mid, and late season for all treatments except COX in 2018 and COX and CPE in 2019. Soil temperature with PE mulches (20.7 °C on average) was similar or slightly higher than with plastic BDMs (19.8 °C on average), which was higher than with paper BDMs (18.9 °C on average). Total fruit number and yield were similar for PE mulches (19.3 and 24.5 kg, respectively) and black plastic BDMs (17.3 and 21.2 kg, respectively), which were higher than COX and paper BDMs (15.7 and 19.8 kg, respectively). Mulch adhesion occurred on fruit in all BDM treatments, with more mulch adhesion in BFO in 2018 and WGP in 2019 than in other BDM treatments each year. The number of wipes is a proxy for the impact on harvest labor and can influence overall on-farm profitability. The number of wipes to remove adhered mulch (1.2 wipes on average) was similar for fruit harvested at four times of day (0800, 1000, 1200, and 1400 hr), but more wipes were needed to remove adhered mulch when fruit were stored up to 4 hours postharvest (5.4 wipes). Number of wipes to remove adhered mulch was negatively correlated to the amount of moisture on the fruit surface (R 2 = 0.31). Overall, these findings demonstrate that all black plastic and paper BDMs remained intact throughout the growing season and controlled weeds as well as black PE mulch, while clear BDM had higher weed pressure because it degraded during the growing season. Pumpkin yield was similar for black plastic BDMs and PE mulches and lower for clear and paper BDMs. However, all BDMs in this study adhered to the fruit surface and their removal became more difficult as the fruit surface dried.
Carol A. Miles, Kathryn Kolker, Tracy Smith, Jenn Reed, Gail Becker and Carolyn Adams
Icebox watermelons first appeared in the United States about 50 years ago. They weigh between 6 and 12 pounds and come in a variety of shapes and colors. With a rising interest in local production, organic produce, and direct marketing, farmers in Washington are looking to diversify crop varieties to meet these demands. Icebox watermelons offer a means of locally producing high-quality watermelons. In 2004 and 2005, we evaluated icebox watermelon varieties to determine which are most suitable for production in our region. In 2004, we evaluated 44 varieties of icebox watermelon and in 2005 we evaluated 100 varieties at WSU Vancouver REU. Varieties were seeded in the greenhouse mid-April and transplanted to the field by mid-June. The greenhouse and field were managed organically. The study design was a randomized complete-block with three replications. Plots were single rows, 6.1 m long, with seven plants per plot. Spacing was 1 m between plants and 3 m between rows. Plants were mulched with black plastic and drip-irrigated 2.5 cm per week. Melons were harvested twice weekly, from mid-August through mid-October. Fruit weight, number, and size were measured, and percentage of soluble solids was measured using a °Brix meter. General eating quality was also evaluated. Summaries of selected varieties will be presented here. To view other varieties included in the trial, see our website, http://agsyst.wsu.edu. Results of this study show significant differences among icebox watermelon varieties in total yield, number of fruit per plot, average fruit weight, number of days to harvest, and percentage of soluble solids. These preliminary findings indicate that more than 80 varieties of icebox watermelon can be grown productively in our region.
Mercy Olmstead, Timothy W. Miller, Callie S. Bolton and Carol A. Miles
Consumer demand for organic and sustainably produced products has increased the interest in organic wine grape (Vitis vinifera) production. However, organic production can be challenging, and weed management is a critical issue during the establishment of an organic vineyard. In 2009, the effectiveness of five cover crop treatments and cultivation regimes was evaluated for two years for weed control in a newly established organic vineyard of ‘Pinot noir précoce’ and ‘Madeleine angevine’ grape cultivars in northwestern Washington State. Alleyway management treatments were cultivation in alleyways with hand weeding in the vine row (control), grass cover crop which included perennial ryegrass (Lolium perenne ssp. perenne) and red fescue (Festuca rubra ssp. arenaria) seeded in the alleyway and in-row tillage with a specialty offset-type cultivator, winter wheat (Triticum aestivum) cover crop with in-row string-trimming, austrian winter pea (Pisum sativum ssp. sativum var. arvense) cover crop with in-row string-trimming, and winter wheat–austrian winter pea cover crop mix with in-row string-trimming. In 2009, weed dry biomass was lowest in the alleyway of the control (0.8 g·m−2) and offset cultivator treatments (6.3 g·m−2) on 3 Aug. and tended to be lowest in the alleyway of the control (4.8 g·m−2) and offset cultivator treatments (16.0 g·m−2) on 27 Sept. In the second year of establishment (2010), winter wheat and austrian winter pea were eliminated from the plots by mid-July, and white clover (Trifolium repens) and perennial ryegrass were the dominant weed species and accounted for a majority of the total weeds. On average over the two-year period, the control treatment required the most time for alleyway management (92 h·ha−1) followed by the offset cultivator treatment (64 h·ha−1), while the winter wheat, austrian winter pea, and winter wheat–austrian winter pea mixture required 32 to 42 h·ha−1. ‘Madeline angevine’ produced more shoot growth than ‘Pinot noir précoce’ in Sept. 2010 (42.3 and 25.9 cm respectively), and shoot growth of both cultivars in the control treatment was significantly longer (125.0 cm) than under any other treatment (55.4 to 93.0 cm), illustrating the importance of weed control during vineyard establishment. In this study, the most effective weed management regime, although also the most time consuming, included a vegetative-free zone around the vines (e.g., in-row) maintained by hand weeding and a cultivated alleyway.
Whitney J. Garton, Mark Mazzola, Nairanjana Dasgupta, Travis R. Alexander and Carol A. Miles
This study was designed to determine the efficacy of canker excision (CE) followed by a subsequent application of cauterization (CAU) and/or fungicide treatment to the excised area for the management of anthracnose canker (caused by Neofabraea malicorticis) on cider apple (Malus ×domestica) trees. Three experiments were conducted from 2015 to 2017, with one experiment each year, in an experimental cider apple orchard in western Washington where trees were naturally infested with N. malicorticis. Treatments were applied once in December and data were collected January through March. Treatments in the 2015 experiment were CE + CAU, CE + CAU + copper hydroxide, CE + 0.5% sodium hypochlorite, Bordeaux mixture (BM) only, and CE + copper hydroxide (control). The 2016 experiment included the same treatments as in 2015 plus one additional treatment, CE + BM. In 2017, one additional treatment was added, CE only, and CAU treatments were removed as they caused significant injury to the trees. Canker size was measured pretreatment, and the treated canker or excised area was measured posttreatment every 2 weeks for 13–15 weeks. Compared with pretreatment, cankers treated with BM did not increase in size, while the excised area treated with CAU increased 28-fold in size on average, and the excised area treated with 0.5% sodium hypochlorite or copper hydroxide increased up to 4-fold in size. Each year new cankers developed in all treatments 13–15 weeks after treatment application, at a time of year when there should not be any spores present to cause new infections. Dark brown streaking, indicative of the disease, was observed in the tissue below the intact or excised cankers 15 months after treatment application all years. Although N. malicorticis was not isolated from symptomatic tissue, symptoms were observed in all treatments including where cankers had not been excised and there was no wounding of the cambium tissue. Findings from this study indicate that of the treatments evaluated, the application of copper hydroxide after CE was the most effective for limiting the number of new cankers, but it did not limit expansion of the excised area. Additional physical and fungicidal strategies need to be tested for effective management of anthracnose canker.
Lisa W. DeVetter, Huan Zhang, Shuresh Ghimire, Sean Watkinson and Carol A. Miles
Day-neutral strawberry (Fragaria ×ananassa) is typically grown in plasticulture production systems that use black polyethylene (PE) mulch for weed management and promotion of crop growth and yield. The objectives of this research were to evaluate several commercial plastic and paper biodegradable mulch (BDM) products [Bio360, Experimental Prototype (Exp. Prototype), and WeedGuardPlus] in comparison with standard black PE mulch and bare ground cultivation in day-neutral strawberry grown in an annual system in northwestern Washington. Mulch performance [as percent visual cover (PVC)], weed suppression, marketable yield, plant biomass, and fruit quality were evaluated in ‘Albion’ and ‘Seascape’ strawberry grown in 2014 and 2015. PVC measured at the end of the production season was lowest for the Exp. Prototype (8%) in 2014 and was greatest for Bio360 (90%), WeedGuardPlus (90%), and PE (98%). In 2015, PVC at the end of the production season was again lowest for Exp. Prototype (62%), followed by WeedGuardPlus (64%), Bio360 (93%), and PE mulch (97%). Overall, weed pressure was higher in 2015 relative to 2014 and was greatest in the bare ground treatment in both years of the study. By the end of the 2015 season, weed cover in the bare ground treatment was 95%, followed by WeedGuardPlus (50%), Exp. Prototype (34%), PE (25%), and Bio360 (15%). Yield showed year and cultivar effects and was higher in mulched treatments. Plant biomass showed varying effects; root biomass was lowest in ‘Seascape’ in 2015 under the bare ground treatment and greatest under Bio360, which was similar to PE mulch and WeedGuardPlus. Leaf biomass was lowest in the bare ground treatment and highest in mulched treatments (except in 2015, when leaf biomass was intermediate for plants grown with WeedGuardPlus). Crown biomass showed a similar trend and was overall greater for plants grown in mulched treatments except for Bio360 in 2014, which was the same as the bare ground treatment. Overall, fruit quality was maintained among strawberry grown with BDMs, with soluble solids concentration (SSC, %) and titratable acidity (TA) being the only variables to show treatment effects. SCC tended to be lower in fruit from bare ground plots. TA was different for ‘Seascape’ in 2015 with fruit from bare ground and Exp. Prototype treatments having higher TA than the PE treatment. This study demonstrates that BDMs can be comparable to PE mulch in terms of performance and impacts on crop productivity in day-neutral strawberry, suggesting that BDMs could be a viable alternative to PE mulch for strawberry growers in the Pacific Northwest.