Gao, G. Y., Extension Specialist and Associate Professor, Ohio State University South Centers
Zhou, L., Research Associate, Ohio State University South Centers
Harker, T., Research Assistant, Ohio State University South Centers
Lewis, W., Farm Manager, Ohio State University South Centers
Slaughter, M.R., Research Assistant, Ohio State University South Centers
Islam, K.R., Program Director and Senior Research Scientist, Ohio State University South Centers
Xia, Y., Assistant Professor, Department of Plant Pathology, The Ohio State University
Worley, C.T., Director, Ohio State University South Centers

ABSTRACT

High tunnels have been used to protect fruit crops from adverse weather conditions, promote early fruit ripening and boost yield in quite a few fruit crops, including blueberries. However, there have not been any published reports on the beneficial effects of high tunnels on mature northern highbush blueberries. A two-year study was carried out in 2012 and 2013 in Ohio to determine if high tunnels placed over mature blueberries bushes can boost yield and promote early fruit ripening with and without tile drainage. High tunnels were constructed in March 2012 while tile drainage was installed at the initial plant establishment in 1996. No significant differences in total yields were observed among four treatments in 2012. High tunnels did promote early fruit ripening only during the first three weeks of fruit harvest in June. There was an interaction between high tunnel and tile drainage. In 2013, the high tunnel without tile drainage resulted in the highest total yield among all four treatments. There was no significant difference in the weekly total yield during the first week of harvest among four treatments. However, high tunnel without tile drainage promoted early fruit ripening during the second and third weeks of harvest. Tile drainage under high tunnel may have had a deleterious effect on total yield since the soils may dry out too quickly. Air temperatures, precipitation, sunlight, soil drainage, irrigation, pollination, fertilization and other factors can all play a role in the total and early yields. High tunnels can still be an important tool in manipulating microclimate to promote early fruit ripening and higher total yields.

Introduction

High tunnels are covered structures that are temporarily constructed in the field to extend the growing and harvest season, protect crops from the weather (rain, wind, cool or warm temperatures), and possibly pests or nuisance wildlife (Wells and Loy, 1993; Pool and Stone, 2014). They have been used to grow small fruits (Lamont et al., 2003; Lamont et al., 2006 Demchak, 2009) and cherries (Lang, 2009). A study on southern highbush blueberry production in high tunnels during the establishment years was carried out at the University of Georgia, USA (Ogden and van Iersel, 2009). A multi-year study of high tunnel production of developing northern highbush blueberry was conducted by Ted Carey at Olathe Research and Extension Center of Kansas State University around the early 2000s. However, the online report is no longer available as of September 2017. To date, there are no published reports on the benefits of high tunnels on mature northern highbush blueberries. A two-year study was undertaken in 2012 and 2013 to determine if high tunnels placed over existing mature blueberry bushes could increase yield and promote early fruit ripening. 

 

Materials and Methods

Two Haygrove high tunnels (Haygrove Inc., Ledbury, Herefordshire, United Kingdom; and Mount Joy, PA, USA) were erected in March 2012 over a mature ‘Blueray’ blueberry planting (Figure 1). Each of the two high tunnels was 24 feet wide and 75 feet long. The blueberry bushes were planted in 1996 and were spaced 15 feet between rows and 4 feet between plants. The total number of plants per acre would be 726.There were 40 bushes per row. Each high tunnel covered two rows, one row with drainage tile and another one without drainage tile installations. Each row was pseudo-replicated into 2 more plots, giving a total of 4 replicated plots for each treatment following a similar approach used in an ecological study (Anderson 2001). Experimental treatments were: high tunnel with tile drainage (HTWTD), high tunnel without tile drainage (HTWOTD), open field with tile drainage (OFWTD), and open field without tile drainage (OFWOTD). Open field without tile drainage (OFWOTD) was the control.

 

Figure 1. Two Haygrove high tunnels were placed over a mature blueberry planting. Shown here is one of them over two rows of blueberry bushes. Photo by Gary Gao, OSU South Centers.

 

All blueberry bushes were irrigated with an existing drip system as needed, fertilized according to soil test results and recommendations. Only dormant sprays were applied in 2012 and 2013. All plots were mulched with sawdust to a depth of 4 inches. Blueberry bushes were pruned according to commercial recommendations in March each year. 

Yield and berry total soluble solids (sugar content) data were collected from June 12 to July 2, 2012. Average berry weight was calculated by sampling and weighing 100 berries from all plants in the same treatment. As blueberries ripened during a period of 3 weeks, we harvested the berries as they ripened. The harvest dates in 2012 were from June 6 to July 2. Fruits were harvested five times from June 27 to July 24. Fruits ripened much sooner in 2012 than 2013. Total yield, average fruit weight and total soluble solid content data were also collected in 2013.

The weather in 2012 was very challenging for fruit growers in Ohio. There was a record setting warm March, a few freezes in April, a warm May, and a hot and stormy June, and an extremely dry summer. The weather in 2013 was quite favorable to fruit crops. March and April temperatures were average. Fruit set was very good in Piketon, Ohio.  Temperatures in May, June and July were very mild. Weather eventually got hot in August and early September.

Statistical Analysis

Significant differences in the blueberries data attributed to the impact of treatments were evaluated by one-way ANOVA using the PROC GLM procedure of the SAS (SAS, 2010). The F-protected treatment means were separated by the DUNCAN Multiple Range (DMRT) test, when the ANOVA showed a significant effect of the predictor variable on the dependent variables, with a value of p<0.05, unless otherwise mentioned.    

 

Results and Discussion

Blueberry Yield and Fruit Quality Data in 2012

The total yield of blueberries per bush was measured as the sum of eight harvests from June 6 to July 2 in 2012. No significant differences in total yields were observed among four treatments (Table 1). However, smaller berries were observed in HTWTD, HTWOTD, and OFWOTD in comparison to OFWTD (Table 1). Higher total soluble solids content was observed in HTWOTD in comparison to HTWTD (Table 1).

 

Table 1. The effect of high tunnel and tile drainage on total blueberry yields (lbs/plant), average fruit weight (ounces) and total soluble solids (^oBrix) in 2012. Means separated by same lower case letter under each column were not significantly different among the treatments by the DMRT at p<0.05.

Treatment	Marketable Yield (lbs/plant)	Average Fruit Weight (ounces)	Total Soluble Solids  (oBrix)
HTWTD	5.89 a	0.054 a	14.6 a
HTWOTD	5.83 a	0.059 ab	16.5 b
OFWOTD	5.29 a	0.060 ab	15.4 ab
OFWTD	4.96 a	0.061 b	15.4 ab

 

This lack of significant difference in total yield is probably because the high tunnels were installed in March, 2012. Since blueberry plants develop their flower buds a year before, a significant yield boost needed to have come from both higher number of flower buds and increased fruit set during the fruiting year. The high tunnels should have protected the bushes from spring freezes in 2012 and thus should have increased fruit set. It would have been interesting to see if the trends in yield increase would have continued in 2014 and beyond, but the funding period for this project was only for two years. 

 

Table 2. The effect of high tunnel and tile drainage on average weekly blueberry yields (lbs/plant) of individual harvests from June 6 to July 2 in 2012. Means separated by same lower case letter under each column were not significantly different among the treatments by the DMRT at p<0.05.

Treatment	June  6	June 15	June 20	June 22	June 25	June 27	June 29	July 2
HTWTD	0.86 b	1.48 a	0.75 a	0.61 a	0.36 a	0.22 a	0.16a	0.22 a
HTWOTD	0.98 b	1.50 a	0.77 a	0.57 a	0.42 a	0.14 a	0.13a	0.12 a
OFWTD	0.31 a	0.66 b	0.79 a	0.71 a	0.34 a	0.31 a	0.21a	0.18 a
OFWOTD	0.46 a	1.01 ab	0.67 a	0.72 a	0.53 a	0.28 a	0.19a	0.29 a

 

There was a significantly higher yield from our first harvest on June 6 in high tunnels (HTWTD and HTWOTD) in comparison with open field either with (OFWTD) or without tile drainage (OFWODT) (Table 2.) HTWOTD resulted in higher soluble solid content in comparison OFWTD. Earlier fruit ripening typically gives growers an advantage regarding higher prices and returns. During our second harvest on June 15, high tunnel plots (HTWTD and HTWOTD) had higher yields than OFWTD, but not OFWOTD (Table 2). High tunnels still had significantly promoted early ripening during the first two harvests. From June 20 to July 2, the yields of blueberry plants were not significantly different among all treatments (Table 2). It seems that high tunnels promoted early ripening from June 6 to June 18 in 2012. The beneficial effects from high tunnels tapered off after June 18. High tunnels promoted early ripening in blueberries and produced a more concentrated harvest even when the plants were covered in high tunnels for about three months.

Blueberry Yield and Fruit Quality Data in 2013

The berry yields in 2013 showed an interesting trend (Tables 3 and 4). The yields were quite high across the board due to milder temperatures throughout the fruit ripening period in June and July.

HTWOTD resulted in higher total yield per plant and acre basis for the season than those of HTWTD and OFWTD, but not OFWOTD (Table 3). There was no significant difference in total yields between HTWOTD in OFWOTD (Table 3). There seems to be an interaction between high tunnel and tile drainage. High tunnel and tile drainage treatments did not have a significant effect on average fruit weight (Table 3). Fruits in high tunnels with (HTWTD) and without tile drainage (HTWOTD) had higher soluble solids content than those in the open field with (OFWTD) or without tile drainage (OFWOTD). Higher soluble solids content typically translates into sweeter berries.

 

Table 3. The effect of high tunnel and tile drainage on total blueberry yields (lbs/plant and lbs/acre), average fruit weight (ounces) and total soluble solids (^oBrix) in 2013. Means separated by same lower case letter under each column were not significantly different among the treatments by the DMRT at p<0.05.

Treatment	Marketable Yield (lbs/plant)	Marketable Yield (lbs/acre)	Average Fruit Weight (ounces)	Soluble Solids Content (oBrix)
HTWTD	11.2  a	8,100  a	0.060 a	9.4 b
HTWOTD	16.6  b	12,069  b	0.062 a	9.1 b
OFWTD	11.5  a	8,338  a	0.063 a	8.0 a
OFWOTD	14.3 ab	10,343 ab	0.059 a	8.3 a

 

Weekly yield totals were quite varied (Table 4). There was no difference in yield during the first week (June 27) of harvest among all four treatments (Table 4). During the second week (July 5), HTWOTD resulted in higher yield than that of HTWTD, but not OFWTD or OFWOTD. An identical trend followed in the following week (July 12). During the fourth week (July 19), HTWOTD still had the higher weekly total yield than those of HTWTD and OFWTD, but not OFWOTD. During the week of July 24, the yield differences were much smaller. Only HTWOTD had higher weekly yield than OFWTD (Table 4).    
      

Table 4. Effect of high tunnels and tile drainage on weekly total marketable yields (lbs/plant) at Piketon, Ohio, in 2013. Means separated by same lower case letter under each column were not significantly different among the treatments by the DMRT at p<0.05.

Treatment	June 27	July 5	July 12	July 19	July 24
HTWTD	2.6 a	2.9  a	2.6  a	2.0  a	1.0 ab
HTWOTD	4.1 a	4.3  b	3.7  b	3.0  b	1.6  b
OFWTD	3.0 a	3.3 ab	2.8 ab	1.8  a	0.6  a
OFWOTD	3.4 a	4.0 ab	3.5 ab	2.3 ab	1.0 ab

 

Commercial growers should still consider the costs of high tunnels before deciding on growing blueberries in a high tunnel in Ohio. They should consider planting young blueberry plants under the high tunnel on a small scale. It is highly likely that blueberry bushes will grow faster under a high tunnel. Bigger plants should lead to higher yields. A few more years of data need to be collected before solid conclusions can be made. The yield data would need to be tracked for 7-10 years to gain a much more accurate view of the full benefit of high tunnels.

Since our blueberry bushes were planted on raised beds, tile drainage was not needed. The drainage system was installed for collecting nutrient runoff in the late 90s. Tile drainage may lead to lower yield when raised beds are used. More data will need to be collected before such conclusions can be drawn.      

High tunnels without tile promoted ripening under a ‘normal’ to low fruit load. However, under extremely high fruit loads, i.e. 2013, fruits did not ripen any faster under high tunnel when compared to the open field. Slower fruit ripening may have also been related to cooler than normal air temperatures during the fruit ripening in 2013.     

Major yield increases in high tunnels were not observed in our experiment in 2012. Lack of significant yield differences may have been due to insufficient time that blueberry bushes were placed under high tunnels. In 2013, higher yield of mature blueberry was observed in high tunnel without tile drainage than those under high tunnel with tile drainage, and in open field with tile drainage. The increase came to be around 18-20% compared to OFWOTD, which is substantial considering a market price per pound. However, an economic analysis is needed to determine if this is enough to justify the cost of constructing a high tunnel. 

It is worth noting that much greater yield difference was observed during a 7-year study at Kansas State University where blueberry bushes were placed under high tunnels at planting. Greater yield difference may have attributed to faster growth and larger bushes due to greater heat accumulation in the high tunnel, which could have translated into more fruiting canes, more flower buds and more fruits in high tunnels.

High tunnels could still be a viable option for growers who wanted to extend the harvest season and increase the yields, if blueberry bushes are placed under high tunnels at the initial planting stage. It would be more beneficial to install high tunnels during the first year and follow yield trends for 7-10 years to determine the full potential of high tunnels. Also, frost protection and fruit quality improvement could be additional benefits of high tunnels. Tile drainage in the row is not necessary if the raised beds are high enough. However, drainage tiles between rows may still be needed in removing excessive water there for a healthy and easily accessible sod cover.

 

Acknowledgements

The authors wish to thank the Ohio Department and Agriculture and USDA for their financial support of this project through a specialty crop block grant in 2012 and 2013.        

 

Literature Cited

Anderson, M.J. (2001). A new method for non-parametric multivariate analysis of variance. Aust. Ecol. 26:32–46.

Demchak, K. (2009). Small Fruit Production in High Tunnels.  HortTechnology: 19:44-49.

Lamont W.J. Jr., Orzolek, M.D., Holcomb, E.J., Demchak, K., Burkhart, E., White, L., Dye, B. (2003). Production system for horticultural crops grown in the Penn State high tunnel. HortTechnology 13:358–362.

Lamont, W.J., McGann, M.R., Orzolek, M.D., Holcomb, E.J., Demchak, K., White, L.D., Dye, B., Plummer, T., Reese, D., Thomas, C., Backman, P., Rasmussen, C., Harper, J., Sánchez, E., Garthe, J., Marini, R., Smith, D., Burkhart, E. (2006). High tunnel production manual (The Pennsylvania State Univ., College Agr. Sci. Ext. Publ. CP02-2), 2nd edition.

Lang, G.A. (2009). High Tunnel Tree Fruit Production: The Final Frontier? HortTechnology: 19:50-55.

Ogden, A.B. and M. W. van Iersel. (2009). Southern Highbush Blueberry Production in High Tunnels: Temperatures, Development, Yield, and Fruit Quality During the Establishment Years.  HortScience  44: 1850-1856.

Pool, K. and A. Stone. (2014). Introduction to High Tunnels. Available online at http://articles.extension.org/pages/18358/introduction-to-high-tunnels (verified on August 21, 2017).

SAS Institute. (2010). The SAS System for Microsoft Windows, SAS online doc 9.13. Cary, NC.     

Wells, O.S. and J.B. Loy. (1993). Row covers and high tunnels enhance crop production in the northeastern United States. HortTechnology 3:92–94.

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