Trade winds are a widespread horticultural consideration throughout the tropics. Growth and productivity of most horticultural crops are not optimal on sites that are exposed to these chronic, unidirectional winds. We conducted four container studies on an exposed site, using clear plastic or screening material to provide three levels of wind exposure: 0%, 36%, or 100%. Two studies were conducted with direct-seeding, such that seedling emergence and early growth were determined for 7 weeks. Two studies were conducted using 8-week-old nursery plants that had been grown in a protected nursery. These plants were transplanted to the experimental site and grown for 6 weeks. Cultivars were `Known You 1', `Sunrise', and `Tainung 2'. Full exposure to wind reduced height up to 32%, increased root: canopy ratio up to 36% and exhibited no influence or slightly reduced stem cross-sectional area when compared with full protection from wind. Net carbon dioxide assimilation (Pn) was measured on intervals of about 2 h throughout several 24-h periods. Although the daily pattern depended on cultivar and date, the general trend was for Pn to be unaffected by wind from early to mid-morning, and for Pn of the unprotected plants to decline below that of the protected plants throughout the rest of the day. The Pn of plants receiving intermediate protection was highly variable among the cultivars and dates in relation to the protected and unprotected plants. Moreover, dark respiration of the unprotected plants was greater than the protected plants throughout the entire nocturnal period. The primary influence of wind on growth of young papaya seedlings was a shift in biomass allocation in favor of the stem base and roots.
Hiphil S. Clemente and Thomas E. Marler
Heli Cain Nunez-Grajeda and Sergio Garza-Ortega
Cushaw squash is cultivated in northwest Mexico mainly during the fall and to a lesser degree in the spring season, in which a lack of fruit production in experimental and commercial materials has been observed. This work was done to test 12 lines, 16 hybrids and six landraces regarding fruit and seed weight, flesh color, and soluble solids content (SSC) in both spring and fall seasons in year 2002. Estimates of fruit and seed yield were done. The crop was established by direct seeding at 0.5-m spacing between plants, on both sides of furrow-irrigated beds measuring 15 m long and 4 m wide. In the spring, fruit weight changed from 2.7 to 4.7 kg and seed weight from 17 to 118 g/fruit; fruit yield varied from 3.2 to 38.8 t·ha-1 and seed yield from 18 to 1131 kg·ha-1. Thirty-two percent of the genotypes, including lines and hybrids, but not landraces, were fruitless. SSC and flesh color had values from 4% to 7.5% and from 5.22 to 6.94 Y, respectively. For the fall culture all the genotypes showed good fruit set. Fruit weight in this season changed from 0.8 to 3 kg and seed weight from 22.3 to 97 g/fruit; fruit and seed yield varied from 4 to 28 t·ha-1 and from 135 to 923 kg·ha-1, respectively. All of the landraces were severely infected with squash leaf curl virus and had very low yields. SSC and flesh color, in this season, had values from 3.6% to 10.4% and from 5.1 to 7.94 Y, respectively.
David W. Wolfe, Daniel T. Topoleski, Norman A. Gundersheim, and Betsy A. Ingall
A 3-year field study conducted on an Eel silt loam soil (Aquic Udifluvent) compared cabbage (Brussica oleracea L. capitata group), cucumber (Cucumis sativus L.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) for their growth and yield response to an artificially compacted soil layer beginning at about the 10-cm depth. Slower growing cabbage seedlings in compacted plots were more subject to flea beetle damage than the uncompacted controls. Prolonged flooding after heavy rainfall events in compacted areas had a more adverse effect on cabbage and snap bean than on cucumber or sweet corn. Sweet corn showed almost no growth reduction in one of the three years (1993) when relatively high fertilizer rates were applied and leaf nitrogen deficiencies in compacted plots were prevented. Maturity of cabbage, snap bean, and cucumber was delayed, and the average reduction in total marketable yield in (direct-seeded) compacted plots was 73%, 49%, 41%, and 34% for cabbage, snap bean, cucumber and sweet corn, respectively. Yield reduction in transplanted cabbage (evaluated in 1993 only) was 29%. In a controlled environment greenhouse experiment using the same soil type and similar compaction treatment as the field study, compaction caused a reduction in total biomass production of 30% and 14% in snap bean and cabbage, respectively, while cucumber and sweet corn showed no significant response. The growth reductions of snap bean and cabbage in the greenhouse could not be attributed to compaction effects on soil water status, leaf turgor, nutrient deficiency, or net CO, assimilation rate of individual leaves. Root growth of sweet corn was least restricted by the compacted soil layer. The contrast between our field and greenhouse results indicates that the magnitude of yield response to compaction in the field was often associated with species sensitivity to secondary effects of compaction, such as prolonged flooding after rainfall events, reduced nutrient availability or uptake, and prolonged or more severe pest pressure.
Israel S. Joukhadar, Stephanie J. Walker, and Paul A. Funk
New mexico pod–type green chile (Capsicum annuum) is one of New Mexico’s leading horticultural commodities. Cultivated acreage of green chile in New Mexico is threatened because of the high cost and insufficiently available labor for hand harvest. Therefore, mechanization is necessary to sustain the industry. Successful mechanization depends on harvester design coupled with plant architecture that optimizes harvest yield and quality. Harvested green fruit must be whole, unbroken, and unblemished for fresh and processed markets, so harvester design and plant architecture must maximize yield while minimizing fruit damage. In two trials conducted at the New Mexico State University Agricultural Science Center in Los Lunas, six cultivars (AZ-1904, Machete, PHB-205, E9, PDJ.7, and RK3-35) were evaluated for plant architecture and harvest efficiency with a double, open-helix mechanical harvester with two counter-rotating heads. Cultivars were direct seeded on 17 Apr. 2015 and 14 Apr. 2016 and managed according to standard production practices. Plant architecture traits, plant width, plant height, height to first primary branch, distance between first primary branch and first node, basal stem diameter, and number of basal branches were measured before harvest. Mechanical harvest yield components, which included marketable fruit, broken fruit, ground fall losses, unharvested fruit remaining on branches, and nonpod plant material, were assessed after once-over destructive harvests on 2 Sept. 2015 and 31 Aug. 2016. Fruit width, fruit length, and pericarp thickness were measured from a representative sample of 10 marketable fruit. In 2015, ‘AZ-1904’ and ‘PDJ.7’ had significantly (P ≤ 0.05) more marketable yield than ‘Machete’ that had the least marketable yield. No statistically significant differences were found in marketable yield in 2016. When both years were combined, ‘PDJ.7’ had significantly more nonpod plant material harvested and the plants were taller than all other cultivars. We found mechanical harvest performance to be significantly affected by plant height, with shorter plants yielding less marketable fruit. Despite differences in fruit wall thickness, no significant differences were measured in broken fruit. In 2015, ‘AZ-1904’ had significantly less basal branches per plant, reducing obstruction for the picking mechanism. Harvest efficiencies (marketable harvested fruit yield as a percentage of total plot yields) ranged from 64.6% to 39.3% during this 2-year trial, with the highest harvesting cultivars PDJ.7 and AZ-1904. In the future, all new mexico pod–type green chile breeding efforts for mechanical harvest must incorporate desirable plant architecture traits to increase harvest efficiencies.
Natalie R. Bumgarner, Whitney S. Miller, and Matthew D. Kleinhenz
Plant growth and biomass assessments are required in production and research. Such assessments are followed by major decisions (e.g., harvest timing) that channel resources and influence outcomes. In research, resources required to assess crop status affect other aspects of experimentation and, therefore, discovery. Destructive harvests are important because they influence treatment selection, replicate number and size, and the opportunity for true repeated measures. This work sought to establish the limits to which image acquisition and analysis may replace standard, destructive measures of fresh lettuce biomass. Outdoor, high tunnel, and greenhouse plantings of three cultivars of red and green leaf lettuce (Lactuca sativa) were direct-seeded in raised beds and plastic trays in spring, summer, and fall seasons in 2009–10 in Wooster, OH. Overhead images (624 in total) were captured at specific time points after seeding using handheld and tripod-mounted commercial digital cameras. Fresh weight and leaf area of destructive plant samples within the digital images were also collected. Images were analyzed using user-defined settings in WinCAM software (Regent Instruments, Quebec, QC, Canada). A reference grid captured within each image allowed for the calculation of crop canopy cover (percent of two-dimensional image area covered by leaves). Calculations of canopy cover require differentiating leaves and rooting medium by color. The rooting medium was dark in color, and differentiating red leaves against this background was less reliable than differentiating green leaves from background. Nevertheless, in samples collected in the greenhouse 7 to 16 days after sowing (DAS), significant correlations (r) of 0.85 to 0.96 (P < 0.05) were observed between measures of canopy cover calculated by image analysis software and leaf area obtained with a leaf area meter on harvested plant material. In outdoor and high tunnel plots 16 to 30 DAS, correlation coefficients between direct measures of plant biomass and WinCAM estimates of canopy cover were 0.71 to 0.95 (P < 0.0001). We conclude that digital image analysis may be useful in real-time, nondestructive assessments of early stage leaf lettuce canopy development, particularly when the leaf area index (LAI) is less than one and settings are dominated by green leaves.
Elisha Otieno Gogo, Mwanarusi Saidi, Jacob Mugwa Ochieng, Thibaud Martin, Vance Baird, and Mathieu Ngouajio
French bean [Phaseolus vulgaris (L.)] is among the leading export vegetable in Africa, mostly produced by small-scale farmers. Unfavorable environmental conditions and heavy infestations by insect pests are among the major constraints limiting production of the crop. Most French bean producers grow their crop in open fields outdoors subject to harsh environmental conditions and repeatedly spray insecticides in a bid to realize high yield. This has led to rejection of some of the produce at the export market as a result of stringent limits on maximum residue levels. Two trials were conducted at the Horticulture Research and Teaching Field, Egerton University, Kenya, to evaluate the potential of using agricultural nets (herein referred to as agronets) to improve the microclimate, reduce pest infestation, and increase the yield and quality of French bean. A randomized complete block design with five replications was used. French bean seeds were direct-seeded, sprayed with an alpha-cypermethrin-based insecticide (control), covered with a treated agronet (0.9 mm × 0.7 mm average pore size made of 100 denier yarn knitted into a mesh impregnated with alpha-cypermethrin), or covered with an untreated-agronet (0.9 mm × 0.7 mm average pore size made of 100 denier yarn knitted into a mesh not impregnated with insecticide). Alpha-cypermethrin and agronets were manufactured by Tagros Chemicals (India) and A to Z Textile Mills (Tanzania), respectively. Covering French bean with the agronets modified the microclimate of the growing crop with air temperature increased by ≈10%, relative humidity by 4%, and soil moisture by 20%, whereas photosynthetic active radiation (PAR) and daily light integral (DLI) were decreased by ≈1% and 11.5%, respectively. Populations of silverleaf whitefly [Bemisia tabaci (Gennadius)] and black bean aphids [Aphis fabae (Scopoli)] were reduced under agronet covers as contrasted with control plots. Furthermore, populations of both pests were reduced on French bean grown under impregnated agronets compared with untreated agronets, but only on three of the five sampling dates [30, 44, and 72 days after planting (DAP)] for silver leaf whitefly or at only one of the five sampling dates (30 DAP) for black bean aphid. Covering French bean with agronets advanced seedling emergence by 2 days and increased seedling emergence over 90% compared with control plots. French bean plants covered with both agronet treatments had faster development, better pod yield, and quality compared with the uncovered plants. These findings demonstrate the potential of agronets in improving French bean performance while minimizing the number of insecticide sprays within the crop cycle, which could lead to less rejection of produce in the export market and improved environmental quality.
by soil fumigation ( O’Brien and van Bruggen, 1990 ) or by using lettuce transplants instead of the common practice of direct seeding ( van Bruggen and Rubatzky, 1992 ). However, these practices may not be economically feasible for the Salinas Valley
) and by using lettuce transplants instead of direct-seeding ( van Bruggen and Rubatzky, 1992 ). However, these practices may not be economically feasible for the Salinas Valley, CA, the major lettuce production area in the United States ( Patterson et
W. Carroll Johnson III, David B. Langston Jr., Daniel D. MacLean, F. Hunt Sanders Jr., Reid L. Torrance, and Jerry W. Davis
weed control in organic onion production is the use of transplants, compared with direct seeded systems ( Ascard and Fogelberg, 2008 ; Bond et al., 1998 ). The best integrated system of weed control in transplanted onion production reduced handweeding
Lavesta C. Hand, Wheeler G. Foshee III, Tyler A. Monday, Daniel E. Wells, and Dennis P. Delaney
). Transplanted watermelons competing with crabgrass ( Digitaria sp.) have a critical weed-free period of 0–6 weeks ( Monks and Schultheis, 1998 ). Direct-seeded watermelon competing with smooth pigweed ( Amaranthus hybridus ) has a critical weed-free period of 0