Abstract
Organic growers of cucurbit (Cucurbitaceae) crops in the midwestern United States have difficulty managing bacterial wilt—a fatal disease with a pathogen (Erwinia tracheiphila) that is transmitted by striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata howardi, respectively). Registered organic insecticides lack effectiveness, and host plant resistance is rare in commercial cultivars of many cucurbit crops. Row covers are widely used as barriers to minimize pest access, but the spunbonded polypropylene fabric covering traditional low tunnels must be removed at bloom to prevent overheating and facilitate pollination, thereby exposing the crop for the rest of the season. “Mesotunnels”—nylon mesh fabric covering 3.5-ft-high hoops—provide more space than low tunnels and mitigate overheating. In field experiments at Iowa State University (Ames, IA, USA) during 2016–18, two variations of mesotunnels—full-season tunnels [with purchased bumble bees (Bombus impatiens) added for pollination] and part-season tunnels (with covers removed for 2 weeks during bloom to provide pollinator access)—were compared with low tunnels and a noncovered treatment for organic ‘Athena’ muskmelon (Cucumis melo) production. Based on scouting results, full-season mesotunnels required no insecticides and part-season mesotunnels averaged 0.6 spray per season compared with 1.0 and 5.0 sprays per season for the low-tunnel and noncovered treatments, respectively. Incidence of pest and disease damage was zero for the full-season mesotunnels, 5% to 22% for the part-season mesotunnels, and 37% to 70% for both of the other treatments. Marketable yield for the full-season mesotunnel treatment exceeded the noncovered treatment significantly each year, and mean marketable yields were greater numerically than for the other treatments. Both mesotunnel treatments had a marketable yield that averaged more than twice that of the noncovered treatment in each year. Economic analysis (partial budget and cost-efficiency ratio) indicated that mesotunnels were likely to be more profitable in Iowa, USA, than either the low-tunnel or noncovered systems, but also that the year-to-year differential among treatments in profitability could be substantial. Additional experiments are needed to evaluate the efficacy of these integrated pest management practices and their profitability at spatial scales representative of commercial farms.
Organic production of muskmelon (Cucumis melo) in Iowa, USA, is limited by several insect pests and the bacterial pathogens they vector. Important insect pests include striped cucumber beetle (Acalymma vittatum), spotted cucumber beetle (Diabrotica undecimpunctata howardi), and squash bug (Anasa tristis) (Bruton et al. 2003; Saalau Rojas et al. 2015). In addition to causing feeding damage and seedling mortality, cucumber beetles vector the bacterium Erwinia tracheiphila, the causal agent of cucurbit bacterial wilt (Brust 1997; Fleischer et al. 1999; Hoffmann et al. 2000). Squash bug causes feeding damage on muskmelon and vectors the bacterium Serratia marcescens, the causal agent of cucurbit yellow vine disease (Bruton et al. 2003; Doughty et al. 2016; Neal 1993). Both diseases can cause substantial yield losses in Iowa, USA, and other production states (Bruton et al. 2003; Saalau Rojas et al. 2015).
Organic insecticides recommended for cucurbit (Cucurbitaceae) pests, including pyrethrins, neem oil, and kaolin clay, have minimal residual activity but are highly toxic to pollinators and other beneficial insects when they get in contact with them (Bond et al. 2012; Doughty et al. 2016; Middleton 2018; Minter and Bessin 2014; Perez et al. 2015). Low tunnels (LTs) can serve as an alternative or supplement to insecticides because they create a physical barrier between plants and pests. LTs typically consist of spunbond polypropylene row cover material suspended above plants on 1.5-ft-tall wire hoops and are deployed immediately after transplanting seedlings. The edges of the row cover are buried in soil or secured by sandbags to prevent insect pests from accessing the plants. However, because muskmelon is exclusively insect-pollinated, row covers in LT systems must be removed at flowering to allow pollinators to access the female flowers (Hodges and Baxendale 2007; Minter and Bessin 2014). Furthermore, these row covers cannot be reapplied after pollination because they can overheat and even kill plants (Arancibia 2018; Gauger 2010; Mueller et al. 2006), so their pest and disease deterrence is limited to the early part of the growing season.
A study in Iowa, USA, attempted to prolong the pest protection benefits of spunbond polypropylene row covers by delaying their removal until 10 d after flowering (Saalau Rojas et al. 2015). In one delayed-removal treatment, the ends of the tunnels were opened to permit pollinator access after female flowers began to bloom; in another treatment, bumble bee (Bombus impatiens) boxes were placed inside the ends of LTs when flowering began and were removed along with the row covers 10 d later. Both treatments reduced the incidence of bacterial wilt compared with the traditional strategy, in which row covers were removed at flowering; however, delayed removal of the row covers led to a 1-week delay in harvest. Delayed harvest can reduce profitability for growers seeking price premiums for early yield.
On-farm trials in Pennsylvania tested an alternative row cover material—nylon mesh insect netting—in an effort to prolong the duration of LT protection (Gauger 2010). The mesh netting was expected to permit full-season protection without overheating plants. Growers deployed modified LTs in winter squash (Cucurbita sp.) and caterpillar tunnels in cucumber (Cucumis sativus), and placed bumble bee boxes inside the tunnels for pollination. The row covers were removed only to harvest crops and were replaced immediately afterward. Growers expressed satisfaction with cucumber yields and fruit quality, and found no evidence of beetles passing through the row cover material; however, they were disappointed with low winter squash yields. Furthermore, the large size of the winter squash plants resulted in the plants pressing against the mesh netting. Growers observed squash bugs feeding and laying eggs on the leaves from outside the tunnels, and the squash tendrils wrapped through the netting and created small rips in it.
“Mesotunnels” (Nelson 2019) have been proposed as a modified barrier system to mitigate limitations of organic pesticides, LTs, and spunbond polypropylene row covers, but have not been tested experimentally. Mesotunnels consist of nylon mesh insect netting suspended on 3.5-ft-tall hoops. A single piece of netting spans three rows of plants, and the edges of the netting are held down with plastic bags filled with rocks or sand. The greater interior space in mesotunnels compared with LTs facilitates pollinator movement while preventing insect pests from reaching the plants by minimizing plant-to-fabric contact. The mesh row cover fabric facilitates air circulation, which prevents overheating of plants and potentially enabling growers to prolong the covered period later into the season. Pollination in mesotunnel systems can be accomplished by local pollinators or purchased bumble bees. For “full-season” mesotunnels (FMTs), purchased hives of bumble bees can be inserted under the tunnels when female flowers start to appear. FMTs could provide continuous protection from cucumber beetles and squash bugs from transplanting until harvest. In “part-season” mesotunnels (PMTs), row covers are removed for 2 weeks when female flowers start to appear to allow access by pollinators, and then are replaced for the rest of the season. During the uncovered period, pest control consists of monitoring pests and applying insecticides when economic thresholds are reached.
The objective of this research was to compare yield, disease management, and cost effectiveness of mesotunnel (full and part season), LT, and noncovered (NC) systems for organic muskmelon production in Iowa, USA.
Materials and methods
Field preparation
The trial was conducted on organic-certified land annually from 2016–18 at the Iowa State University Horticulture Research Station near Gilbert, IA, USA (lat. 42°6′23.748"N, long. 93°35′23.372"W). Organic composted cow and horse manure (Iowa State University Compost Facility, Ames, IA, USA) was applied after rough tillage and incorporated within 24 h of application (Table 1). Compost application was based on preplant soil assays for nitrogen (N), phosphorus (P), and potassium (K). To meet remaining N–P–K needs, organic bagged fertilizer was broadcast in plant rows; these included 2N–1.3P–2.5K (Midwestern BioAg, Madison, WI, USA) in 2016 and 4N–2.6P–3.3K (Suståne Natural Fertilizer, Inc., Cannon Falls, MN, USA) in 2017 and 2018. Subsequently, drip tape (The Toro Company, Bloomington, MN, USA) was laid under black plastic mulch on 6-ft row centers. Organic chopped corn (Zea mays) stover was applied to the alleys between plastic mulch at a 6-inch depth for weed control.
Timeline of field preparation and establishment of row cover experiments for pest exclusion in organic muskmelon in 2016, 2017, and 2018 at the Iowa State University Horticulture Research Station, Ames, IA, USA.
‘Athena’ muskmelon seedlings were raised from nontreated seeds (Seedway LLC, Hall, NY, USA) in organic potting mix (Mix no. 12; Beautiful Land Products, West Branch, IA, USA) in a greenhouse. Two-week-old seedlings were hardened off in an outdoor shade house under nylon mesh insect netting (0.07 × 0.04 inch; ProtekNet, DuBois Agrinovation, Saint-Rémi, QC, Canada) for 1 week before transplanting.
Plot locations were rotated so that the same land was not used in consecutive years. Plots were planted with pepper (Capsicum anuum) and broccoli (Brassica oleracea var. italica) before year 1 of the trial, cereal rye (Secale cereale) before year 2, and a mixture of cowpea (Vigna unguiculata), sunn hemp (Crotalaria juncea), and hybrid sorghum–sudangrass (Sorghum ×drummondi) before year 3.
Experimental design
Treatments included LTs, PMTs, FMTs, and an NC control (Table 2). Treatment subplots were arranged in a randomized complete block with four replications, except in 2017, when treatments were arranged in a Latin square design. Each subplot consisted of three adjacent 30-ft-long rows spaced 6 ft apart; in row cover treatments, each three-row subplot was covered by a single piece of fabric.
List and description of the row cover treatments applied for pest exclusion in organic muskmelon during 2016, 2017, and 2018 at the Iowa State University Horticulture Research Station, Ames, IA, USA.
The LT treatment consisted of spunbond polypropylene row covers (Agribon® AG-30; Berry Global, Evansville, IN, USA) covering 18-inch-high wire hoops (Arancibia 2018). Row covers on LTs were removed permanently when female flowers began to appear, after which insecticide sprays were applied until harvest based on results of scouting for insect pests (Brust and Foster 1999; Doughty et al. 2016; Middleton 2018). PMT subplots had nylon mesh row covers on 3.5-ft-tall conduit hoops; the covers were removed at flowering to allow pollinator access, then replaced 2 weeks later. Organic insecticides were applied during the uncovered period based on results of scouting. FMT treatment subplots included the same mesh covering and hoop support as PMTs, but the covers remained in place until harvest began. To ensure pollination, a single bumble bee box (Koppert Biological Systems, Inc., Howell, MI, USA) was placed inside each FMT subplot at flowering. The NC control had no row covers; insecticides were applied to this treatment based on scouting thresholds.
Three-week-old muskmelon seedlings were transplanted into plastic mulch with 2-ft in-row spacing (Table 1). A water wheel transplanter (1600 series II; Rain-Flo Irrigation, East Earl, PA, USA) was used to transplant seedlings.
All row cover treatments were installed on the same date that seedlings were transplanted. In PMTs and FMTs, conduit hoops were centered over rows at a 6-ft spacing, and ends were pushed 6 to 8 inches deep into the soil. Conduit hoops were created by bending 10-ft lengths of 1-inch-diameter galvanized metal conduit pipe with a conduit bender (QuickHoops™ 4 ft × 4 ft Low Tunnel Bender; Johnny’s Selected Seeds, Fairfield, ME, USA). After the nylon mesh row covers (width, 26 ft) were cut to 40-ft lengths and draped over three rows of conduit hoops, edges were secured to the soil surface using rock bags. Rock bags were prepared in advance by filling 36-inch lengths of hold-down netting (Berry Hill Irrigation, Inc., Buffalo Junction, VA, USA) with river rock and knotting both ends. In the LT treatment, 1.5-ft-tall hoops made of 9-gauge galvanized steel wire were centered over each 30-ft row at a 2.5-ft spacing, and ends were inserted ∼5 inches into the soil. Spunbond polypropylene row covers (26 × 40 ft) were draped over each LT subplot, and edges were secured to the soil surface using rock bags.
In 2016, an action threshold for row cover removal was reached when 50% of the plants in LT, PMT, and FMT plots had female flowers blooming. In 2017 and 2018, this action threshold was modified to begin at the first appearance of any blooming female flowers to ensure sufficient time for pollination. Row covers in the LT subplots were then removed permanently, and PMT subplots were uncovered and then recovered 2 weeks later. In the FMT treatment, a bumble bee box (Class C; Koppert Biological Systems, Inc.) was placed on a layer of bricks inside one end of each tunnel. Class C hives were discontinued after 2017, so comparable bumble bee hives (Excel Startup; Koppert Biological Systems, Inc.) were used in 2018. Flight holes in the hives were oriented parallel to the crop rows, and ventilated plastic laundry baskets were placed over the tops of the hives to protect against rain and sunlight. Row cover ends were reclosed immediately after the bumble bee hives had been installed.
Subplots were hand-weeded during periods when they were not protected by row covers (NC, LT, and PMT treatments) or immediately before placement of bumble bee hives (FMT treatment). All treatments were scouted weekly throughout the growing season for disease symptoms and insect injury. Fungicide sprays of copper hydroxide (Champ® WG; Nufarm Americas Inc., Burr Ridge, IL, USA) were applied to uncovered subplots or sprayed directly through the nylon mesh row covers based on the results of monitoring severity of foliar diseases. Insecticides were applied based on insect pest monitoring data collected weekly during periods when plants were not protected by row covers (NC, LT, and PMT treatments). Kaolin clay (Surround™ WP; Tessenderlo Kerley, Inc., Phoenix, AZ, USA), pyrethrins (Pyganic® Crop Protection EC 5.0 ii; MGK Co., Minneapolis, MN, USA), and neem oil (Trilogy® 70EC; Certis USA, LLC, Columbia, MD, USA) were tank-mixed and applied to a treatment if an economic threshold for cucumber beetle or squash bug was reached. When harvest began, all row covers were removed permanently.
Field data collection
Insect pest monitoring and insecticide application
Striped and spotted cucumber beetles were scouted twice weekly in all treatments during uncovered periods until plants developed six leaves, and once weekly thereafter. Insect pests were counted in three arbitrarily selected 1.6 × 1.6-ft quadrats in the center row of each subplot and the numbers averaged for each treatment. The spray threshold for both species of cucumber beetles was 0.5 beetle per quadrat until plants developed six leaves, then one beetle per quadrat thereafter (Brust and Foster 1999). The spray threshold for squash bugs was one egg mass, nymph, or adult per sampling quadrat throughout the season (Doughty et al. 2016). If a threshold was met for either cucumber beetles or squash bugs, a tank mix consisting of at least two insecticides was sprayed (Table 3).
Number of organic insecticide and fungicide applications per treatment in the organic muskmelon trials in 2016, 2017, and 2018 to control insect pests and diseases at the Iowa State University Horticulture Research Station, Ames, IA, USA.
Disease and insect-injury monitoring and fungicide application
Incidence of disease symptoms and insect injury was recorded weekly in the center row of plants in each subplot. A plant was considered to have insect injury if the presence of feeding wounds coincided with a visible decline in plant vigor, characteristically shown as wilted leaves. Disease and insect pest injury were combined as a single plant damage assessment because of difficulty in separating visually feeding injury caused by cucumber beetles from wilting resulting from pathogen vectoring (E. tracheiphila) by the same insects.
The first application of fungicide was based on scouting assessments of the severity of symptoms caused by foliar fungal diseases. Leaf tissue samples of symptomatic plants were submitted to the Iowa State University Plant and Insect Diagnostic Clinic (Ames, IA, USA) for diagnosis. Copper hydroxide was applied to uncovered subplots or sprayed directly through the nylon mesh row covers.
Yield
Yield data were collected from the center row of each subplot. Ripe fruit were harvested every 2 d and categorized as marketable or nonmarketable, then counted and weighed. Fruit were classed as nonmarketable if the combined surface area of damage (i.e., sunscald, or insect or rodent feeding injury) exceeded 5%, if damage extended into the fruit flesh (i.e., cracking or insect, bird, or rodent feeding injury), or if soft spots were present (US Department of Agriculture, Agricultural Marketing Service 2006). Fruit weighing less than 3 lb were considered nonmarketable.
Temperature
Air temperature was measured hourly beneath row covers from transplanting until row cover removal. One temperature sensor (WatchDog A-150; Spectrum Technologies, Inc., Aurora, IL, USA) was placed 6 inches above the soil surface between two rows of plants in each of three FMT, LT, and NC subplots. Daily maximum temperatures were averaged for each treatment.
Statistical analysis
Data were subjected to analysis of variance using statistical software (RStudio version 1.1.383; RStudio, Inc., Boston, MA, USA). Significant effects (P < 0.05) were investigated by separation of means with Tukey’s honestly significant difference multiple-comparisons adjustment. Because homogeneity of variance criteria for pooling the 3 years of data were not met, data for each year were analyzed separately.
Economic analysis
We conducted a partial budget analysis (Calkins and DiPietre 1983) to compare cost and economic efficiency of the treatments. As part of this analysis, we used an equivalent annual cost approach to convert the purchase cost of the nylon mesh row cover to an annual cost of using this netting material for a 3-year life expectancy, and assumed spunbond polypropylene fabric had a 1-year life expectancy (H.M. Nelson, unpublished data). Conduit and wire hoops were treated as having a 5-year life expectancy. Additional cost components included sandbags, purchased bumble bee hives, pesticides, and estimated labor costs, which included setting up and taking down the LTs and mesotunnels, and spraying pesticides.
Results and discussion
Insecticide and fungicide application
FMTs required no insecticide applications (Table 3). In contrast, the NC control treatment averaged 5.0 insecticide sprays per season, LT averaged 1.0 spray per season, and PMT averaged 0.6 spray per season.
Disease and pest injury
Bacterial wilt was the predominant source of damage to plants, although anthracnose (caused by the fungus Colletotrichum orbiculare) and direct insect feeding injury were also noted (data not shown); therefore, disease and pest injury were combined in representing incidence of injury (Table 4). Pest injury was caused primarily by cucumber beetles. FMTs had no disease or pest-injury symptoms in any year (Table 4). In 2016, plants in PMTs experienced a significantly lower incidence of disease and pest-injury symptoms (13%) than the NC control (55%) and LTs (51%). In 2017, FMTs (0%) had a significantly lower incidence of disease and pest injury than LTs tunnels (55%), and in 2018, both FMTs (0%) and PMTs (5%) had significantly lower incidences of disease and pest injury than the NC control (70%). Tables 3 through 5 indicate that mesotunnels reduced both the need for insecticide sprays and the incidence of disease and pest-associated crop damage compared with the other treatments.
Incidence of combined disease and insect pest injury on organic muskmelon plants per treatment in 2016, 2017, and 2018.
Effect of row cover treatments on yield of 30-ft (9.14-m)-long plots of organic muskmelon in 2016, 2017, and 2018.
Yield
The FMT treatment yielded a significantly greater weight of marketable fruit (P < 0.05) than all other treatments in 2016 (Table 5). In 2017 and 2018, FMTs, PMTs, and LTs yielded statistically equal weights of marketable fruit, but only the mesotunnel treatments had a significantly greater marketable yield than the NC control. Marketable yield in LTs was equivalent to the NC control in each year. Patterns for number of marketable fruit produced in each treatment were consistent with those of weight of marketable fruit in 2016 and 2018; in 2017, however, no treatment differed statistically from any other treatment. Also noteworthy is the significantly greater weight and number of nonmarketable fruit in the nonmesotunnel treatments than the mesotunnel treatments, indicating the impact of mesotunnels in protecting the fruit. In sum, mesotunnel treatments delivered the greatest marketable yields, and the FMT produced marketable yields that were more consistent among years than the other treatments. These results reflect more consistent protection from cucumber beetles and bacterial wilt in the FMT treatment than in the other treatments.
Air temperature
Average daily maximum temperatures inside FMT plots were within 1.0 to 7.6 °F of average ambient daily maximum temperature (NC control treatment) in 2016, whereas average daily maximum temperatures beneath spunbond polypropylene row covers (LT treatment) were warmer (22.6–52.6 °F) than ambient temperatures (Fig. 1). The maximum temperature under the FMT treatment was 108.3 °F, compared with 153.4 °F under the LT treatment and 101.3 °F ambient temperature (NC control). Temperature differences among treatments were similar in 2017 and 2018 to those recorded in 2016 (Nelson 2019).
Daily average maximum air temperature readings in 2016 in 30-ft (9.14-m)-long organic muskmelon plots without a row cover [noncovered control treatment (NC)], inside a low tunnel (LT) using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, and inside a full mesotunnel (FMT) using a nylon mesh fabric all season long). Refer to Table 2 for descriptions of each treatment; (°F – 32) ÷ 1.8 = °C.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
Daily average maximum air temperature readings in 2016 in 30-ft (9.14-m)-long organic muskmelon plots without a row cover [noncovered control treatment (NC)], inside a low tunnel (LT) using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, and inside a full mesotunnel (FMT) using a nylon mesh fabric all season long). Refer to Table 2 for descriptions of each treatment; (°F – 32) ÷ 1.8 = °C.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
Daily average maximum air temperature readings in 2016 in 30-ft (9.14-m)-long organic muskmelon plots without a row cover [noncovered control treatment (NC)], inside a low tunnel (LT) using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, and inside a full mesotunnel (FMT) using a nylon mesh fabric all season long). Refer to Table 2 for descriptions of each treatment; (°F – 32) ÷ 1.8 = °C.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
Economic analysis
From 2016–18, the annual costs associated with the mesotunnel system in the 540-ft2 test plot ranged from $675 to $718 for the PMT treatment and $761 to $844 for the FMT treatment (Table 6). The cost variations across years for each treatment were closely related to labor cost, including the frequency of insecticide spraying as well as installation and removal of the row covers. The NC control treatment required the most insecticide spraying, but had no costs related to installation/disassembly labor. In comparison, all row cover systems led to less spraying and thus lower pesticide-related costs. In the row cover tunnel production systems, installation and disassembly labor costs accounted for the majority of production costs (52%– 69%). Mesotunnel supplies and bumblebee hives accounted for the majority of nonlabor production costs (14%–34%). Using a field size large enough to spread the costs could defray these quasi-fixed expenses, and it is possible that per-acre costs for materials would decline as the production scale increased.
Summary of costs of row cover treatments applied in organic muskmelon in 2016, 2017, and 2018 based on a plot size of 540 ft2 (164.59 m2).
The relative cost-efficiency ratio was calculated to compare the three tunnel production systems to the NC control, and to compare the three row cover systems (Fig. 2). Implementing any row cover system resulted in lower cost efficiency than the NC control treatment for 2 of 3 years except for the PMT and FMT treatments in 2016. The lower cost efficiency of tunnel treatments in 2017 and 2018 was a result of labor costs from installation and disassembly of the row cover structures in years when bacterial wilt pressure was minimal.
Yearly and 3-year-average relative cost-efficiency ratio of the low tunnel (LT) treatment using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, the part-season mesotunnel (PMT) treatment using a nylon mesh fabric removed for 2 weeks during bloom and then reinstalled, and the full-season mesotunnel (FMT) treatment using a nylon mesh fabric all season long vs. the noncovered (NC) control treatment (first three clustered sets of bars at left) of the PMT and the FMT treatments vs. the LT treatment (fourth and fifth clusters of bars, respectively, from left to right), and of the FMT treatment vs. the PMT treatment (last cluster of bars at far right) based on the organic muskmelon field trials from 2016 to 2018. Relative cost-efficiency ratio = (Yield ÷ Cost) of treatment x ÷ (Yield ÷ Cost) of treatment y.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
Yearly and 3-year-average relative cost-efficiency ratio of the low tunnel (LT) treatment using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, the part-season mesotunnel (PMT) treatment using a nylon mesh fabric removed for 2 weeks during bloom and then reinstalled, and the full-season mesotunnel (FMT) treatment using a nylon mesh fabric all season long vs. the noncovered (NC) control treatment (first three clustered sets of bars at left) of the PMT and the FMT treatments vs. the LT treatment (fourth and fifth clusters of bars, respectively, from left to right), and of the FMT treatment vs. the PMT treatment (last cluster of bars at far right) based on the organic muskmelon field trials from 2016 to 2018. Relative cost-efficiency ratio = (Yield ÷ Cost) of treatment x ÷ (Yield ÷ Cost) of treatment y.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
Yearly and 3-year-average relative cost-efficiency ratio of the low tunnel (LT) treatment using a spunbond polypropylene fabric from transplanting through the appearance of the first female flowers, the part-season mesotunnel (PMT) treatment using a nylon mesh fabric removed for 2 weeks during bloom and then reinstalled, and the full-season mesotunnel (FMT) treatment using a nylon mesh fabric all season long vs. the noncovered (NC) control treatment (first three clustered sets of bars at left) of the PMT and the FMT treatments vs. the LT treatment (fourth and fifth clusters of bars, respectively, from left to right), and of the FMT treatment vs. the PMT treatment (last cluster of bars at far right) based on the organic muskmelon field trials from 2016 to 2018. Relative cost-efficiency ratio = (Yield ÷ Cost) of treatment x ÷ (Yield ÷ Cost) of treatment y.
Citation: HortTechnology 33, 1; 10.21273/HORTTECH05096-22
The FMT or PMT production systems were more cost-efficient than the LT system in most of the years and in all the 3-year averages (Fig. 2). Moreover, the FMT cost efficiency is equivalent to the PMT production system, except in 2016. Across all 3 years, the FMT cost efficiencies are significantly greater for 2016 than those for 2017 and 2018. This is because the FMT had a much higher marketable yield in 2016 compared with the other three treatments, and the yield difference with the other three treatments was quite similar across the years.
Both cucumber beetle populations and bacterial wilt incidence can vary dramatically from year to year, even in the same location (Saalau Rojas et al. 2015), with the result that the extent of the protective advantage provided by tunnels is likely to vary from year to year. It is therefore reasonable to assume that locations with more frequent and serious outbreaks of the pest–disease complex will realize the greatest profit advantage from adopting mesotunnels in organic muskmelon production (Saalau Rojas et al. 2011).
Our plot size was well below the scale of most commercial growers of organic muskmelon. Clearly, assumptions about potential economies of scale need to be tested by larger field experiments to mimic the spatial scales of commercial production.
Conclusion
Our study is the first to evaluate mesotunnels as a production system for organic muskmelon production. In the absence of such physical barriers, organic muskmelon growers in the midwestern United States struggle to suppress effectively insect pests and the pathogens they vector, which frequently decimate plantings. LTs provide early-season protection, but because they must be removed at bloom to avoid overheating the crop, they leave the plants exposed for the rest of the season. Mesotunnels can provide an effective barrier for all, or nearly all, of the growing season because of their more breathable mesh covering.
The results of our field trials provide evidence that mesotunnels can safeguard organic muskmelon effectively, resulting in a greater and more consistent marketable yield than either LT or no-tunnel systems. Our economic analysis indicates that mesotunnels are likely to be more profitable than either LT or no-tunnel systems, and that the differential among treatments in profitability among years may be substantial.
Units
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