Jan 16, 2019

Tomatoes in high tunnel, open field

Tomatoes are an important crop for small to mid-sized farmers selling directly to customers through farmers markets, Community Supported Agriculture (CSA), and restaurant sales. In this multi-year study (2014-2016), we evaluated 15 different tomato varieties for performance in high tunnel and open field management (marketable/unmarketable yield, average fruit weight, fruit number, and disease).

Varieties were selected based on the potential for production in organic systems and were comprised of three different genetic backgrounds (heirloom, modern and 50 percent heirloom/50 percent modern crosses). We found management system (high tunnel vs. open field) to be the most important factor in determining both marketable yield and disease incidence. Although the high tunnel system improved variety performance overall, we observed differences in relative performance of some varieties between the two systems. We also found that causes of unmarketable fruit differed greatly between the high tunnel and open field, suggesting that breeding varieties to overcome specific issues in each system might boost marketable yield beyond the season extension benefit.

Key findings

• The high tunnel produced 18.7lbs/plant marketable fruit compared to 10.8lbs/plant in the field.
• High yielding varieties in the field tend to be high yielding in the high tunnel.
• Foliar disease coverage was about 78 percent of leaf area at mid-season in the open field compared to 17 percent in the high tunnel.
• Each management system had different primary causes of unmarketable fruit.
• Marketable yield was the most important factor for revenue potential.
• Price premiums (e.g. for heirlooms) did not make up for differences in marketable yield.

Background

Tomatoes are very important for direct market vegetable growers, often serving as a key crop for farm income. However, growers in the North Central Region may face short growing seasons and high disease pressure. Additionally, many varieties may not be adapted for organic or low-input systems. As a result, growers are increasing their use of high tunnels for tomato production.

Previous studies have demonstrated the benefits of high tunnel production, which include higher marketable yields, lower disease pressure, and increased fruit quality.

However, many of these studies only evaluated a few tomato varieties at a time, often from the same market class. To add to the growing body of knowledge, researchers at the University of Wisconsin-Madison conducted organic tomato variety trials from 2014 to 2016 at the West Madison Agricultural Research Station (WMARS) near Madison, Wisconsin. The purpose of these trials was to screen varieties from different genetic backgrounds for production and quality in the North Central region, compare high tunnel and open field management, and compare revenue potential for different management systems and varieties.

Methods

Over the course of three years, ten tomato varieties were grown at the West Madison Agricultural Research Station (WMARS) (Table 1) in both a high tunnel and an open field system, under organic management.

The varieties were provided by independent breeders and seed companies, and were assumed to have important traits of interest (good fruit quality, disease tolerance, etc.) for North Central region farmers. They were selected for inclusion based on screening trials, so that the study described here is based on ten varieties we know are adapted to the North Central Region. Yearly data from additional varieties not included in this trial across all three years is available in trial reports at https://seedtokitchen.horticulture.wisc.edu/trial-results.html.

The varieties chosen represented different genetic backgrounds. There were two true heirlooms, two heirloom-by-heirloom F1 hybrids, two heirloom-by-modern F1 hybrids, two modern small slicers and two modern large slicers. The genetic backgrounds are given in Table 1 and varieties are shaded by their genetic background in the figures.

Table 1: Tomato varieties used in the trials

Trials were grown on certified organic land at the West Madison Agricultural Research Station (WMARS). A high tunnel production area of 30 feet x 80 feet and an open field production area of 30 feet x 80 feet was used. Each variety was planted with two replications in a randomized complete block design in each management system.

Tomatoes in the high tunnel were pruned to two main leaders and trellised using tomato clips and twine attached to cross beams. The open field tomatoes were trellised using T-posts and a basket weave method. Each system was planted with a cover crop and amended with compost and organic fertilizer (pelletized chicken manure or feather meal) each year to reach the recommended 150 pounds of nitrogen per acre. Plastic mulch and drip irrigation were used in both systems.

Obligatory preventative measures at the research station were applied for late blight. This entailed applications of EF400, an organic approved fungicide in both systems every 10-14 days after late blight was reported in Dane County, where the research station is located.

For more information on how to determine whether a pest control product can be used on your farm, see the article, Can I Use This Input On My Organic Farm?

Measurements taken included marketable yield, marketable fruit count, average individual fruit weight, unmarketable yield, and disease incidence. Tomatoes were harvested once a week from mid-July (week 29) to as late as November 20th (week 46) in the high tunnel. Fruit were considered unmarketable if they suffered from low quality due to issues such as rot, cracking, splitting, damage by rodents or insects and disease. Marketable fruit were counted and weighed and unmarketable fruit was weighed.

Average fruit weight (marketable yield / marketable number) and the proportion unmarketable fruit (unmarketable yield/total yield) were calculated from measured data. Percentage disease incidence was recorded at peak production each year as the amount of disease present with 0 percent representing no disease and 100 percent representing all foliage damaged by disease. Prevalent diseases were septoria leaf spot (Septoria lycopersici ) and early blight (Alternaria linariae).

These strategies were generalized to calculate revenue for the trial varieties (Table 2). The weekly marketable yield from the WMARS trials was multiplied by the price for each strategy to calculate the revenue potential for each variety and management strategy. For the purposes of revenue calculations, heirlooms and heirloom-by-heirloom F1s were considered heirlooms, and everything else was considered a modern slicer. Labor time for major tasks over the season was also recorded for each management system in 2017.

The fixed costs of the high tunnel were not included in the revenue calculations. A high tunnel with W trusses (to support tomato trellising weight) costs approximately $7,000 (www.zimmermanshightunnels.com). Adding automated sides and additional bracing to allow a mobile structure brings this to approximately $10,000 (Zimmerman’s, personal communication). Labor costs to build and install the high tunnel can as much as double this figure, if not provided by the farmers themselves. Estimates of fixed costs per year are approximately 0.49 (Sydorovych et al., 2013), which would be $1,323 on a 30×90 foot high tunnel.

Table 2. Generalized pricing strategies used in calculating revenue and earning potential per plant based on pricing strategy and management system, averaged over varieties in the trial

Labor considerations

In our trials, the labor hour breakdown shows that the open field system required fewer overall hours compared to the high tunnel system, with 25 minutes per plant on average in the open field and 45 minutes per plant in the high tunnel. In both management systems, harvesting made up the largest percentage of labor hours, with 29 percent in the open field and 55 percent in the high tunnel. Harvesting in the high tunnel most likely took a larger portion of overall labor hours due to higher yields and season extension benefits.

We calculated the labor hours both with and without harvest times for comparison. Harvesting took 16.7 minutes more per plant in the high tunnel, and the total labor was 18.3 minutes more per plant in the high tunnel. This means that added harvesting labor accounted for 91.2 percent of the added labor in the high tunnel. Surprisingly, the disease/pest management labor requirement in the two systems is very similar. This is most likely a result of the preventative measures applied in both systems at the research station. This category might look different in a farmer’s field or high tunnel that most likely would not be sprayed if disease was not present. Field tomatoes were also trellised using a basket weave system, so if farmers did not trellis field tomatoes or used a less intensive method this would reduce labor costs for the field.

Grower tips

• To increase marketable yield, high tunnels can be used for season extension and for reducing the incidence of foliar disease.
• To increase revenue, it may be more worthwhile to grow a higher yielding variety rather than charging a premium for heirlooms that may have lower production.
• Several varieties discussed above performed well for many of the traits of interest.
  • ‘Defiant’, a small red slicer developed by Johnny’s Selected Seeds was often among the top performers for marketable yield, disease scores and had good flavor when tasted by the field crew. Additionally, ‘Defiant’ was just below the optimal fruit weight range of 4-8 ounces (~3.9 ounces).
  • ‘Caiman’ was the top producer in the high tunnel system and consistently had low numbers of unmarketable fruit in this system. ‘Caiman’ is a variety that performs well for greenhouse production and also does quite well in a high tunnel. It is a large red modern hybrid. The flavor was not quite as good as the other varieties discussed here in crew taste tests. It would be a potential alternative to ‘Big Beef’.
  • ‘Garden Gem’ and ‘Garden Treasure’ are heirloom-by-modern F1 varieties that are productive and have very good flavor based on crew taste tests. Seed is available from Harry Klee from the University of Florida, with commercial seed likely to be available in the near future. One potential drawback to ‘Garden Gem’ is its relatively small size that requires more harvest time. ‘Garden Treasure’ is a more standard large slicer size but does not have quite as good flavor as ‘Garden Gem’.
  • For farmers seeking an heirloom appearance, ‘Genuwine’ from Ball-PanAmerican is an heirloom-by-heirloom F1 hybrid with high yields and good flavor based on crew taste tests. It did, however, suffer fairly severely from blossom end rot.
• Other more affordable methods of season extension could potentially offer similar benefits as high tunnels at a lower cost. Current research is comparing caterpillar tunnels and high tunnels for heirloom and slicer variety production.

– Terry Hodge, Kitt Healy, Brian Emerson, Julie Dawson, University of Wisconsin-Madison