Effects of Mulch Types on Dayneutral Strawberry Production in Three Distinct Environments in Ontario

Abstract

Six plastic mulches (black, black-on-white, white-on-black, silver-on-black, brown, and green) were used to grow ‘Albion’ and ‘Seascape’ strawberries outside, and in a high tunnel at Cedar Springs in southwestern Ontario, and outside at New Liskeard in northeastern Ontario over 2 years. In the cooler climate of New Liskeard, there was no effect of mulch type on yields in the first year. In the second year, strawberry plants grown on the black and black-on-white mulches produced greater total and marketable yields than those on the white-on-black and silver-on-black mulches. ‘Albion’ had more tarnished plant bug damage than ‘Seascape’ at this location and, in 1 year, the ‘Albion’ grown on white-on-black mulch had significantly greater tarnished plant bug damage. In the warmer climate of Cedar Springs, there were more differences between mulches in the high tunnel than outside and ‘Albion’ responded more to mulch treatments than ‘Seascape’. In the high tunnel the first picking year, the greatest total and marketable yields of ‘Albion’ were from the white-on-black and silver-on-black mulch treatments. In the second year, these mulch treatments produced the fewest berries and other mulches gave superior yields. Outside in Cedar Springs there were no significant differences between the mulch treatments in the first year and few significant differences in the second year.

Keywords:

• Fragaria × ananassa
• tarnished plant bug
• high tunnel

INTRODUCTION

The culture of dayneutral strawberries (Fragaria × ananassa Duchesne ex Rozier) in Ontario is expanding as producers aim for a longer harvest season. Dayneutral strawberry crops are typically grown on raised beds covered with plastic mulch. Black mulch is commonly used; however, many types of mulch are available. Different types and colors of mulch have been shown to affect soil and air temperature and crop growth differently (Ham et al., 1993; Tarara, 2000). Research in different climates around the world has shown conflicting results for strawberries grown on different types or colors of plastic mulch film (Al Khatib et al., 2001; Himelrick et al., 1993; Johnson and Fennimore, 2005; Mohamed, 2002). Some researchers have concluded that strawberry plants are very sensitive to mulch color exhibiting differences in plant growth and yield (Johnson and Fennimore, 2005; Mohamed, 2002), while others have concluded that black mulch remains the best option for strawberry production (Himelrick and Akridge, 1999).

Ontario has a range of climates where strawberries can be successfully grown. In warmer parts of the province, dayneutral strawberry fruit production during the hot summer months is hampered by poor fruit set once temperatures increase above 25 to 27°C. Cooler regions often begin to fruit late, and different mulches could be used to warm the soil enhancing earliness and yield (Voth and Bringhurst, 1959, 1962). High tunnels are becoming more common in southern Ontario and Quebec. These structures increase air and soil temperature on a field scale, extending the growing season (Burkhart and White, 2003; Heidenreich et al., 2009).

The objective of this study was to evaluate the effects of six different mulches on two dayneutral strawberry cultivars in three distinct environments, outside in the warmer climate of southwestern Ontario, in a high tunnel in southwestern Ontario, and outside in the cooler climate of northeastern Ontario.

MATERIALS AND METHODS

Two dayneutral cultivars, Albion and Seascape, were planted outside and in a high tunnel in southwestern Ontario at Cedar Springs (42.262540 lat., −82.037 long.) and outside in northeastern Ontario at New Liskeard (47.486523 lat., −79.672852 long.). The tunnel in Cedar Springs was a Haygrove “4-Series” model, with six 8.5-m-wide bays with a center height of 4.3 m (Haygrove Ltd, Redbank, Ledbury, UK). Raised beds, at 2–2.1 m centers, were formed using a Rain-Flo Model 2600 plastic mulch layer (Rain-Flo Irrigation, LLC, East Earl, PA). The mulch treatments used were 0.9 mil standard black embossed plastic (Black); 1.0 mil black-on-white embossed mulch (Black/white); 0.85 mil brown embossed mulch (Brown); 1.0 mil green mulch (Green); 1.0 mil silver-on-black embossed mulch (Silver/black); and 1.0 mil white-on-black embossed mulch (White/black). The black-on-white mulch was used in New Liskeard only.

In each environment, the experimental design was a randomized split-plot design of four replicates with mulches as the main plots and cultivars as the sub-plots. The main plots consisted of 4-m sections of mulch pinned on the beds by hand. Each 2-m sub-plot contained 20-plants.

Dormant, bare-root plants were hand planted into twin rows spaced 30 cm apart with 20 cm between crowns on 27 May 2008 in Cedar Springs and 16 May 2008 in New Liskeard. Flowers were removed for the first 4 and 6 weeks after planting in New Liskeard and Cedar Springs, respectively. Trickle irrigation was located below the plastic and all plots received regular irrigation and liquid fertilizer applications. Cultural practices were adapted to the local soil and climate. In Cedar Springs, the fertility program consisted of 5–9 kg N/ha from a complete fertilizer once a week and the plants were covered with a 30 g/m² floating row cover for the winter. The plots grown under the high tunnel at Cedar Springs were treated the same as those outside. In New Liskeard, the fertility program consisted of 17 kg N/ha once every 2 weeks. Straw mulch covered with a 42 g/m² floating row cover was applied over the plots for the winter. Plant counts were done in the fall of 2008 and spring of 2009 to determine plant establishment and winter survival.

Fruit was harvested twice weekly in the first and second year from the 1-m sub-plots at New Liskeard and the 2-m plots in Cedar Springs. Fruit was sorted into marketable (no rot and regularly shaped with a diameter greater than 1.5 cm) and unmarketable. Marketable and unmarketable fruit was weighed and counted. Berry weight (g/fruit) was calculated using the marketable fruit only. Unmarketable fruit was further divided into small but regularly shaped, misshapen, and rotten, and each group was counted. In northeastern Ontario (New Liskeard) where tarnished plant bug numbers tend to be higher, all the fruit was graded for tarnished plant bug damage (no damage, moderate damage, severe, and very severe) and the percent for each category was calculated.

The three environments were combined as a split-split plot design. Total and marketable yield per meter of row and per plant, mean weighted berry weight, percent marketable and unmarketable by type, and percent winter survival were analyzed annually and over the years by analysis of variance using PROC GLM of SAS version 9.3 (SAS Institute Inc, Cary, NC, USA). As there were significant year interactions for all factors measured, the years were then analyzed separately. When there were significant cultivar, environment, and/or mulch interactions, the impact of environment and mulch treatments was analyzed separately for the two cultivars. When F probabilities were significant, means were separated by least significant difference (P ≤ 0.05).

RESULTS

There were significant interactions between the environments and all factors measured in this study. ‘Seascape’ produced significantly more total and marketable fruit than ‘Albion’ except in the high tunnel in the first year (Table 1). ‘Seascape’ was earlier than ‘Albion’ in some circumstances but ‘Albion’ produced significantly larger berries.

TABLE 1 Effects of Cultivar on the Total and Marketable Yields, Average Berry Weight and Days to Harvest in the First and Second Year in All Three Environments Averaged Over Five Mulch Treatments (Black-on-White Mulch Treatment Not Included)

			Yield (kg/m)
Environment	Year	Cultivar	Total	Marketable	Berry weight (g/berry)	Days to harvest ^y
New Liskeard	2008	Albion	1.9b ^z	1.4b	17.9a	52b
		Seascape	2.8a	2.0a	14.1b	48a
	2009	Albion	1.7b	1.2b	13.7a	29b
		Seascape	2.9a	2.1a	11.0b	28a
Cedar Springs	2008	Albion	1.8b	1.2a	13.5a	63a
		Seascape	2.0a	1.1a	10.9b	64a
	2009	Albion	2.1b	1.4b	13.6a	11a
		Seascape	3.0a	1.8a	11.9b	11a
High tunnel (Cedar Springs)	2008	Albion	1.9a	1.4a	13.7a	65b
		Seascape	2.0a	1.2b	11.2b	62a
	2009	Albion	1.5b	1.0b	12.6a	1a
		Seascape	2.4a	1.3a	10.6b	1a
^zMean separations between ‘Albion’ and ‘Seascape’ within each environment and year only by least significant difference test at P ≤ 0.05.
^yNumber of days from June 1.

At New Liskeard, the mulch treatments did not significantly affect total and marketable yield or berry weight for either cultivar in the first year (data not shown), but in the second year mulch treatments significantly affected both total and marketable weights, and berry numbers (Table 2). The highest yields were from plants grown on the black and black-on-white films, and the lowest on the silver-on-black and white-on-black films. The number of days to first harvest and percent marketable berries was not affected by the mulch treatments in either year. Percent survival over the winter ranged from 83% to 95% but did not differ significantly with cultivar or mulch types. When the yields for the 2 years were totaled, there were no significant mulch effects (data not shown).

TABLE 2 Effects of Mulch Averaged over the Two Cultivars on Total and Marketable Yields in the Second Year (2009) at New Liskeard

	Total yield		Marketable yield
Mulch	kg/m	#/m	kg/m	#/m
Black	2.6a ^z	243a	1.9a	161a
Black/white	2.6a	251a	1.9ab	164a
Brown	2.3abc	224b	1.7abc	140ab
Green	2.4ab	240a	1.7abc	153a
Silver/black	1.8c	161c	1.3c	103b
White/black	1.9bc	182abc	1.3bc	109b
^zMean separation within columns by least significant difference test at P ≤ 0.05.

‘Seascape’ had significantly less tarnished plant bug damage than ‘Albion’ in both years (Table 3). Mulch treatments had an effect on tarnished plant bug damage for ‘Albion’ only in the first year where significantly more ‘Albion’ berries were damaged by tarnished plant bug on the white-on-black mulch. This was due to moderate damage and not severe or very severe (cat-facing) damage.

TABLE 3 Effects of Cultivar and Mulch Treatment on Tarnished Plant Bug (TPB) Damage at New Liskeard in the First and Second Year

		Percent of berries with no TPB damage		Percent of berries with moderate TPB damage
Cultivar	Mulch treatment	2008	2009	2008	2009
Albion	Black	89a ^z	76a	9a	15a
	Black/white	84a	78a	11a	13a
	Brown	88a	78a	9a	15a
	Green	91a	77a	7a	16a
	Silver/black	89a	72a	10a	15a
	White/black	71b	67a	22b	15a
Albion	Average	85b	75b	11b	15b
Seascape	Average	93a	85a	6a	10a
^zMean separation within columns for each group by least significant difference test at P ≤ 0.05.

At Cedar Springs, there were significant interactions in both years. ‘Seascape’ produced slightly greater marketable yields in the high tunnel than outside in the first year, but lower total and marketable yields, and berry weights in the high tunnel in the second year (Table 4). The first picking date in the high tunnel was 10 days earlier than outside in the second year. ‘Albion’ yields were similar outside and in the high tunnel in the first year (Table 5). A higher portion of the ‘Albion’ fruit produced in the high tunnel in the first year was marketable (data not shown). The yields and berry weight of ‘Albion’ produced in the high tunnel were significantly reduced compared to the field in the second year (Table 6). ‘Albion’ had fewer days to harvest and fewer rotten fruit in the high tunnel compared to outside. All other variables were similar.

TABLE 4 Effects of Environment on ‘Seascape’ Total and Marketable Yield, Berry Weight, and Days to Harvest Averaged Over Five Mulch Treatments in the First and Second Year at Cedar Springs

		Total yield		Marketable yield
Year	Environment	kg/m	#/m	kg/m	#/m	Berry weight (g/berry)	Days to harvest ^y
2008	Outside	2.0a ^z	237a	1.1b	102b	10.9a	63a
	High tunnel	2.0a	241a	1.2a	106a	11.2a	62a
2009	Outside	3.0a	298a	1.8a	151a	11.9a	11a
	High tunnel	2.4b	267a	1.3b	127b	10.6b	1b
^zMean separation within columns for each year by least significant difference test at P ≤ 0.05.
^yNumber of days from June 1.

TABLE 5 Effects of Environment and Mulch on ‘Albion’ Total and Marketable Yields, and Berry Weight at Cedar Springs in the First Year (2008)

		Total yield		Marketable yield
Environment	Mulch	kg/m	#/m	kg/m	#/m	Berry weight (g/berry)
Outside	Black	1.8b ^z	169bc	1.3bc	99b	13.2bc
	Brown	1.6bc	139cd	1.1b	78bc	14.0b
	Green	1.6bc	141cd	1.1b	79bc	13.6abc
	Silver/black	1.8b	170bc	1.2b	94b	13.0c
	White/black	1.8b	152c	1.3bc	94b	13.7abc
	Average	1.8	154	1.2	89	13.5
Tunnel	Black	1.2c	111d	0.9c	69c	13.3bc
	Brown	1.6bc	138cd	1.2bc	84bc	13.7abc
	Green	1.6bc	137cd	1.2bc	84bc	13.9ab
	Silver/black	2.4a	186b	1.9a	136a	14.2a
	White/black	2.5a	222a	1.9a	138a	13.5abc
	Average	1.9	159	1.4	102	13.7
^zMean separation within columns by least significant difference test at P ≤ 0.05.

TABLE 6 Effects of Environment and Mulch on ‘Albion’ Total and Marketable Yields, Berry Weight, and Days to Harvest at Cedar Springs in the Second Year (2009)

	Total yield		Marketable yield
Treatment	kg/m	#/m	kg/m	#/m	Berry weight (g/berry)	Days to harvest ^y
Mulch
Black	1.9ab ^z	157ab	1.3ab	95ab	13.4a	6a
Brown	2.0a	170a	1.4a	103a	13.4a	6a
Green	1.7bc	148ab	1.1bc	88ab	12.8a	6a
Silver/black	1.7abc	134b	1.2abc	87ab	13.3a	6a
White/black	1.5c	130b	1.0c	78b	12.8a	6a
Environment
Outside	2.1a	168a	1.4a	104a	13.6a	11a
High tunnel	1.5b	127a	1.0b	76b	12.6b	1b
^zMean separation within columns for each group by least significant difference test at P ≤ 0.05.
^yNumber of days from June 1.

‘Albion’ responded to mulch treatments in both years. In the first year, ‘Albion’ responded to mulch type in the high tunnel but not in the field (Table 5). In the modified climate of the high tunnel, superior total and marketable yields were achieved using the white-on-black and silver-on-black mulches. In the field, the mulch treatments affected berry weight but not total or marketable yield (Table 5).

In the second year, the weight of total and marketable berries produced by ‘Albion’ was lower for those plants grown on the white-on-black mulch compared to black and brown mulches in both environments (Table 6). The days to first harvest and berry weight were not affected by the mulch treatment for ‘Albion’ in either environment but more berries were unmarketable because of small size on the white-on-black and black mulches (data not shown).

When the yields from the first and second year were totaled, there were no significant effects of mulch type on yield for either cultivar grown in Cedar Springs. ‘Seascape’ produced superior yields in all environments except in the first year in the high tunnel in Cedar Springs. Although there were some effects of mulch, mulch type did not affect the yields totaled over the two picking years in any of the environments.

DISCUSSION

Studies comparing the effects of different mulches on strawberries have determined that the results vary with the year and cultivar (Himelrick and Akridge, 1999; Himelrick et al., 1993), and geographical location (Locascio et al., 2005). The results of this trial support these conclusions. ‘Seascape’ did not respond to mulch color as much as ‘Albion’. ‘Albion’ appears to be much more sensitive to soil temperature as higher yields were produced in the high tunnel in a normally warm season on the white-on-black and silver-on-black mulches, and in a cooler season, higher yields were produced on the black and brown mulches. Typically, black mulches raise soil temperatures significantly while white and aluminized mulches may either raise or lower soil temperatures slightly (Ham et al., 1993; Tarara, 2000). Himelrick et al. (1993) and Himelrick and Akridge (1999) reported soil temperatures from warmest to coolest with clear, ALOR brown, black-on-white laminated, black, silver, and white-on-black mulch.

In the cooler climate of northeastern Ontario there was no affect of mulch on yield of either cultivar in the first year. However, in the cool, cloudy growing conditions of the second year, yields were highest on the black and black-on-white films, and lowest on the silver-on-black and white-on-black films. Himelrick and Akridge (1999) reported that in a cool and cloudy season, the mulches producing the greatest strawberry yields were black, a laminated white-on-black, or an infrared transmitting mulch, and clear, depending on the cultivar. Mulches that increase soil temperatures are reported to hasten and increase strawberry yields in cooler climates (Johnson and Fennimore, 2005).

Himelrick and Akridge (1999) concluded that black mulch, in most cases, remains the best option. Our study concludes the same for cool growing seasons or regions, and ‘Seascape’ grown outside in warmer regions. However, ‘Albion’ appears to be more sensitive to the affects of mulch type, especially in a high tunnel. White or aluminized reflective mulches have been recommended as good alternatives to black plastic in a hot climate (Tarara, 2000). High tunnels typically increase both the minimum and maximum temperature over ambient (Buckhart and White, 2003). In high tunnels, higher yields have been reported with reflective mulches (Al Khatib et al., 2001; Mohamed, 2002).

Reflective mulches have been reported to reduce insect infestations compared to black, black-on-white, and white mulch (Al Khatib et al., 2001; Mohamed, 2002; Rhainds et al., 2001). Rhainds et al. (2001) reported that silver-colored mulch reduced the number of tarnished plant bug nymphs throughout the season, but not the proportion of damaged fruit in dayneutral cultivars. Our results agree as the amount of damage on all mulches was similar except for increased damage on ‘Albion’ grown on the white-on-black mulch in the first year. Rhainds et al. (2001) concluded that reduced damage in some cultivars was due to enhanced yield as the impact of tarnished plant bug feeding is diluted when numerous fruits are produced. In our study, the increased damage in ‘Albion’ may have been due to lower berry numbers compared to ‘Seascape’.

Shading of the mulched bed by the developing crop moderates the differences between mulches (Ham et al., 1993). Reflective mulches enhance light interception; however, the incident radiation declines as the plant canopy expands and intercepts a greater proportion of the radiation (Atkinson et al., 2006). ‘Seascape’ had a larger canopy than ‘Albion’, perhaps explaining some of the cultivar differences in this study.

This research suggests that in Ontario ‘Seascape’ yields more consistently than ‘Albion’, whereas ‘Albion’ is much more sensitive to minor changes in the environment. This would suggest that ‘Albion’ has a role to play in specific niche environments in Ontario.

ACKNOWLEDGMENTS

We would like to thank the Ontario Berry Growers Association, the AAC CanAdvance Program, and the University of Guelph/Ontario Ministry of Agriculture and Food Enhanced Agreement for funding in support of this project.