Protected cropping of strawberry plants in subtropical Queensland

Protected cropping of strawberry plants in subtropical Queensland C.M. Menzel1, L.A. Smith1 and J.A. Moisander2 1Department

of Agriculture, Fisheries and Forestry, PO Box 5083, SCMC, Nambour, Qld. 4560, Australia;

2Driscoll’s Australia, 180 Landershute Road, Palmwoods, Qld. 4555, Australia.

Abstract The effect of protected cropping on the performance of two strawberry cultivars (‘Festival’ and ‘Rubygem’) and two breeding lines (Breeding Lines 1 and 2) was studied in subtropical Queensland, Australia over two years. Production in this area is affected by rain, with direct damage to the fruit and the development of fruit diseases before harvest. The main objective of the study was to determine whether plants grown under high plastic tunnels had less rain damage, less disease incidence, and higher yields than plants grown outdoors. Our studies show that marketable yields were up to 40% higher in the plants under the tunnels compared with yields of the plants outdoors. This was mainly because fruit from the plants grown under the tunnels had lower incidences of rain damage and/or grey mould. There were no consistent differences in the relative numbers of small and/or misshaped fruit in the two growing environments. This research highlights the potential of protected cropping for strawberry producers in subtropical areas that receive significant rainfall during the growing season. Keywords: climate, fruit diseases, weather, yield INTRODUCTION Strawberry (Fragaria × ananassa) production in subtropical Queensland is affected by rain and fruit diseases most seasons. The fruit can be damaged directly by rain with damage to the skin and flesh, or pollination can be affected and the fruit misshaped (Herrington et al., 2013). The main diseases affecting the fruit during wet weather include grey mould (Botrytis cinerea) and stem-end rot (Gnomoniopsis fructicola). Losses due to these fungi can be up to 50% or more during periods of prolonged rain. Work conducted in Florida and California showed that plastic high tunnels could decrease the incidence of rain damage and grey mould, and increase marketable yields in strawberry plants (Daugovish and Larson, 2009; Larson et al., 2009; Salamé -Donoso et al., 2010; Santos, 2013; Xiao et al., 2001). It is much drier in California than in Queensland. Rain is also less of an issue in Florida, with more concerns about frost. We report on the effect of plastic high tunnels on the performance of two strawberry cultivars and two breeding lines in subtropical Queensland over two years. Additional information is presented on the losses of fruit in open or outdoor plots over the growing season. MATERIALS AND METHODS Bare-rooted transplants of ‘Festival’ and ‘Rubygem’, and two breeding lines (Breeding Lines 1 and 2) were planted in late March 2012 and 2013 at Palmwoods in subtropical Queensland, Australia. The plants were grown under high plastic tunnels or in open, outdoor plots. Plant agronomy was as described by Menzel and Smith (2012). The plastic was placed over the plants growing under the tunnels in May 2012 and in mid-April 2013. The new plants were planted through plastic, in double row beds 70 cm wide and 130 cm apart from the centers. The plants were spaced at 30 cm-intervals within the rows, giving a density of 51,000 plants ha-1. The plants were irrigated through the use of drip tape placed under the plastic. They were watered when the soil water potential in the rootzone decreased below

Acta Hortic. 1117. ISHS 2016. DOI 10.17660/ActaHortic.2016.1117.44 XXIX IHC – Proc. II Int. Berry Fruit Symp.: Interactions! Local and Global Berry Research and Innovation Eds.: C.E. Finn and B. Mezzetti

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-10 kPa. The plants in the two growing environments received similar spray applications for the control of pest and disease. The main fruit disease affecting the crops was grey mould. The plants were sprayed with captan, thiram, myclobutanil, iprodione, fenhexamid, pyrimethanil, penthiopyrad, and cyprodonil + fludioxonil. Data were collected on marketable yield until mid-October (2012) or mid-September (2013). In addition, the number of fruit that were affected by rain, grey mould, or both, along with those fruit that were small (less than 12 g fresh weight), misshaped, or both, or that had other defects was recorded. The experiments were conducted in split-plot designs, with growing systems as randomly distributed main plots and cultivars/breeding lines randomly distributed as small plots within the main plots forming a block, with four replications. The data on seasonal yield and average defects over the season were analysed by split-plot analysis of variance (ANOVA; two growing systems × four cultivars/breeding lines). The data on the percentage of fruit with different defects were transformed by arcsine square root before subjected to ANOVA analysis. Treatment means were back-transformed for presentation of the results. Separate analyses were conducted for each year. Additional information is presented on the main defects occurring in the open plots over the growing season. RESULTS AND DISCUSSION Total rainfall during the harvests from late May to mid-October 2012 was 357 mm, while total rainfall from mid-May to mid-September 2013 was 329 mm. These values were lower than the long-term averages for the respective periods (519 and 415 mm). During fruit production, there was more than 10 mm per week in about half the weeks before each harvest. In 2012, the bulk of the rain fell from late May to late July (333 mm). In 2013, all the rain fell from mid-May to late July (329 mm). In the data analyses to examine the effect of growing system and cultivar and breeding line on the performance of the plants, there were many instances when growing system and/or cultivar and breeding line had a significant effect on yield and the levels of fruit defects in both years, with P0.05). The data for each year were analysed separately. Marketable yields were 38% higher in the plants growing under the tunnels than in the plants growing outdoors in 2012 (991 versus 720 g), and 24% higher in 2013 (594 versus 479 g) (LSD P=0.05, 82 and 60, respectively). Mean yields for the different cultivars pooled across the two growing systems in 2012 were higher in ‘Festival’ (1064 g), intermediate in Breeding Line 1 and ‘Rubygem’ (868 and 834 g), and lower in Breeding Line 2 (657 g) (LSD P=0.05, 108, respectively). Mean yields in 2013 were higher in ‘Festival’ (582 g), Breeding Line 1 (605 g) and Breeding Line 2 (542 g) than in ‘Rubygem’ (416 g) (LSD P=0.05, 62, respectively). The plants growing in the two different systems generally had similar patterns of production. Yields in both groups of plants increased as the season progressed (data not presented). In Florida, marketable yields were increased by 50 and 63% in plants grown under tunnels over two seasons compared with the yields of plants grown outdoors (Salamé Donoso et al., 2010). The higher yields under the tunnels were mainly due to less frost damage to the plants and fruit. In similar work conducted in California, early yields under tunnels were higher than those outdoors, reflecting fewer rain-damaged, mouldy and misshaped fruit (Daugovish and Larson, 2009). Yields under the tunnels were reduced at other times because of high temperatures. The main benefit of the tunnels in our study was to protect the fruit from rain. Average losses of production due to fruit defects were about 50% greater in the plants growing outdoors than in the plants growing under the tunnels (Table 1). About a quarter of the losses outdoors were due to rain damage or grey mould, or both. Within this classification, most of the fruit were damaged by rain. The rest of the fruit were mainly culled because they were small or misshaped, or both. Within this classification, most of the fruit were small. Differences in the incidence of mould between the two growing 274

environments were small (2012) or not significant (2013). In 2012, the two environments yielded similar numbers of small and misshaped fruit, whereas in 2013, losses due to these defects were slightly higher in the plants under the tunnels. Table 1. Effect of two growing systems on the percentage of fruit with various defects in strawberry plants grown in subtropical Queensland, Australia. Data are the means of four replicates and have been back-transformed. Means in columns for the two main effects followed by different letters are significantly different at P = 0.05. Data for each year were analysed separately. Separate means are shown for the percentage of fruit affected by mould to show the importance of the disease compared with that of rain. Separate means are shown for the percentage of fruit that were classified as misshaped to show the importance of this issue compared with that of small fruit. Growing system or cultivar/breeding line 2012 Outdoor Tunnel Festival Breeding Line 1 Breeding Line 2 Rubygem 2013 Outdoor Tunnel Festival Breeding Line 1 Breeding Line 2 Rubygem

Fruit with rain damage and/or mould (%)

Fruit classified as affected by mould (%)

Fruit that were small and/or misshaped (%)

Fruit that were classified as misshaped (%)

Fruit with other defects (%)

Total of all defects (%)

11.8 b 3.7 a 5.0 a 7.1 b 8.2 bc 8.8 c

1.3 a 0.4 b 0.7 ab 1.0 b 0.3 a 1.1 b

16.4 a 16.2 a 17.7 c 13.8 b 10.2 a 25.0 d

3.2 a 2.5 a 2.7 b 4.4 c 1.0 a 3.9 c

1.4 b 0.3 a 0.3 a 0.9 b 1.8 c 0.3 a

39.6 b 24.7 a 29.2 a 28.4 a 28.4 a 42.2 b

10.4 b 1.0 a 2.8 a 4.3 b 5.4 bc 6.1 c

0.6 a 0.2 a 0.4 a 0.2 a 0.3 a 0.7 a

26.8 a 29.6 b 34.5 c 13.5 a 20.6 b 47.8 d

3.5 a 1.6 a 1.3 a 3.1 c 2.1 b 3.7 c

0.1 a 0.1 a 0.1 a 0.1 a 0.3 a 0a

46.1 b 33.4 a 42.4 c 23.8 a 33.6 b 60.1 d

The plants growing under the tunnels had higher marketable yields because the fruit were protected from rain. About 2% of the fruit under the tunnels were affected by rain compared with about 10% of the fruit growing outdoors. The average incidence of grey mould over the season was less than 1.5%, with only small difference between the plants growing in the two environments. Herrington et al. (2013) showed that plants growing in Queensland were affected by rain most seasons. As indicated above, the incidence of grey mould was very low in our study, with only small differences in the average rates of infection in the two environments. The maximum rate of infection outdoors during the season was 8% in 2012 and 5% in 2013. The low average incidence of infection was probably due to the weather being relatively dry. The majority of fruit were rejected because they were small and/or misshaped, with small fruit more common. There were no consistent differences in the levels of these defects across the two growing systems. Differences in the incidence of small and/or misshaped fruit between the two growing environments were not significant in 2012. In 2013, there was a higher incidence of these defects in the plants grown under the tunnels. In California, there was no consistent effect of growing environment on average fruit size, although the fruit under the tunnels were rated as more attractive than the fruit growing outdoors (Larson et al., 2009). The incidence of the various defects in the outdoor plots varied over the season (Figures 1 and 2). The percentage of fruit affected by rain was generally higher from May to early July, reflecting the wet weather at the start of the production season. The incidence of grey mould was relatively low over most of the season. There were insufficient data to 275

determine if there was any relationship between this disease and wet weather. The incidence of small fruit was higher during warmer weather at the end of the season, which is in accordance with the strong relationship between fruit size and temperature in glasshouse experiments in the United Kingdom (Le Miè re et al., 1998). In our experiments, there was also a variation in the incidence of misshaped fruit, with more defects after periods of cold weather in winter or early spring (daily minimums below 10°C). This is supported by the work of Ariza et al. (2012) who showed that the incidence of misshaped fruit in Spain decreased as the average minimum temperature in the seven weeks before harvest increased from about 0 to 14°C. Grey mould

Rain damage

70 60 50 40 30

Reject fruit (%)

20 10 0

2

70

4

6

8 10 12 14 16 18 20 0

Small fruit

2

Week from 23 May 2012

4

6

8 10 12 14 16 18 20

Misshaped fruit


60 50 40 30 20 10 0

2

4

6

8 10 12 14 16 18 20 0

2

4

6


8 10 12 14 16 18 20

Figure 1. Seasonal changes in the incidence of various fruit defects in strawberry plants grown in outdoor plots in subtropical Queensland, Australia in 2012. Data are presented as untransformed means and are a percentage of all fruit (marketable and unmarketable).

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Rain damage

70

Grey mould

60 50 40 30

Reject fruit (%)

20 10 0

2

4

70

6

8 10 12 14 16 18 20 0

Small fruit

2

4

Week from 8 May

6

8 10 12 14 16 18 20

Misshaped fruit

Week from 8 May

60 50 40 30 20 10 0

2

4

6

8 10 12 14 16 18 20 0

2

4


6

8 10 12 14 16 18 20

Figure 2. Seasonal changes in the incidence of various fruit defects in strawberry plants grown in outdoor plots in subtropical Queensland, Australia in 2013. Data are presented as untransformed means and are a percentage of all fruit (marketable and unmarketable). In conclusion, strawberry plants growing under high plastic tunnels had higher yields than plants growing outdoors. This was mainly because the plants growing under the tunnels had fewer fruit damaged by rain. More than half of the fruit growing outdoors were rejected during short periods of wet weather. High plastic tunnels have the potential to increase the productivity of strawberry fields in subtropical areas that receive significant rain during the growing season. In the study on defects in the outdoor plots, the incidence of small fruit increased as the season progressed, possibly due to warmer weather. The incidence of misshaped fruit was highest in late winter or early spring, reflecting daily minimums below 10°C. There were insufficient data to determine the clear relationship between the incidence of rain damage and grey mould, and weekly rainfall. ACKNOWLEDGEMENTS We thank Horticulture Australia Limited (HAL) and the Florida Strawberry Growers’ Association (FSGA) for supporting this research. Literature cited Ariza, M.T., Soria, C., Medina-Mı́nguez, J.J., and Martı́nez-Ferri, E. (2012). Incidence of misshapen fruits in strawberry plants grown under tunnels is affected by cultivar, planting date, pollination, and low temperatures.

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