EFFECT OF A LARGE TUNNEL PRODUCTION SYSTEM ON FRUIT DISEASES AND MARKETABLE YIELD OF STRAWBERRY

 Chang-Lin Xiao¹, Craig Chandler¹, James Price,² and Dan Legard¹. 

¹University of Florida, Gulf Coast Research and Education Center – Dover.  

²University of Florida, Gulf Coast Research and Education Center – Bradenton

INTRODUCTION    

 

        Florida is the major winter strawberry supplier to the eastern part of the United States and Canada.  Major strawberry production is located in west central Florida.  Due to the mild temperature, long period of leaf wetness and frequent rain events during strawberry growing season, Botrytis fruit rot caused by the fungus, Botrytis cinerea, has become one of the major constraints on the production in this region.  Development of an alternative production system or modification of culture practices may provide non-chemical options for disease control.  Plastic tunnels have been widely used for winter strawberry production in other countries such as Spain, Israel and Argentina.  The major reason for using tunnels for production in these areas is for early fruit production.  In addition, plastic tunnels may also reduce the severity of Botrytis fruit rots.  The objectives of this study were to compare development of strawberry fruit diseases under field and tunnel production systems, and to evaluate yield performance of major cultivars under these two production systems in Florida.

 

METHODS

   

        The field experiment was conducted at the University of Florida, Gulf Coast Research and Education Center-Dover during 1998 to 1999 season.  The experimental design was a 2 ´ 4 factorial combination of treatments arranged in a split-plot design with 3 replications.  Treatments included two main plots (field and tunnel units) and four sub-plots, including combinations of two cultivars (Sweet Charlie and Camarosa) and two Captan application programs.  Captan application included full (2 lbs a.i. per acre at 7 day intervals) and limited programs (2 lbs active ingredient (a.i.) per acre at 14 day intervals).  The full labeled rate of Captan (3 lbs a.i. per acre) was not used as this rate of Captan can cause burning of strawberry foliage inside tunnels.   Each sub-plot was one 2-row bed, 40 ft long.  Tunnels (50 ft long ´ 20 ft wide ´ 15 ft high) were constructed to cover four beds and covered with plastic.  Plastic sidewalls were manually opened and closed to provide ventilation for temperature control and air movement.  Adconâ Telemetry weather stations (Adcon Telemetry Inc., Boca Raton, FL) were set up both inside and outside the tunnels to monitor temperature, relative humidity, leaf wetness, and rainfall.  Marketable yield and incidence of fruit diseases such as Botrytis fruit rot and powdery mildew were determined twice weekly.

 

RESULTS

    

        Outside the tunnels, Botrytis fruit rot incidence increased as the season progressed up to mid-February, and then declined.  Botrytis incidence on ‘Sweet Charlie’ was significantly higher than that on ‘Camarosa’.   However, inside the tunnels, Botrytis incidence was dramatically lower (< 1%) over the whole season, and there was no significant difference in Botrytis incidence between the two cultivars.  The average incidence of Botrytis fruit rot was significantly lower inside the tunnels than outside (Table 1).  Inside the tunnels, the incidence of powdery mildew on fruit of ‘Camarosa’ increased as the season progressed (up to 15%).  However, outside the tunnels, powdery mildew incidence on fruit was low throughout the season (< 2%).  Powdery mildew incidence on ‘Camarosa’ was significantly higher than on ‘Sweet Charlie’ both inside and outside the tunnels, and the average incidence of powdery mildew on fruit was significantly higher inside the tunnels than outside (Table 1). 

Table 1. Botrytis fruit rot and powdery mildew incidence on cultivars Sweet Charlie and Camarosa over the season inside and outside the tunnels ^z

Cultivar	Botrytis fruit rot (%)		Powdery mildew (%)
	Outside	Tunnel	Outside	Tunnel
Sweet Charlie	6.4 a	0.4 a	0.1 b	2.0  b
Camarosa	2.3 b	0.2 a	1.5 a	15.7 a

^z  Numbers followed by the same letters are not significantly different within each column according to a least significant difference (LSD)  test (P < 0.05). 

 

        Weather data recorded over the season indicated that for most of the season, there was no free moisture (i.e. dew) on leaves inside tunnels compared to an average of 12 hours of dew each day outside.  The higher temperatures and reduced leaf wetness may explain the decrease in Botrytis fruit rot and increase in powdery mildew inside the tunnels.

 

        Early season marketable yield (first 3 weeks) of ‘Sweet Charlie’ were significantly higher inside the tunnel than outside.  However, there were no significant differences in marketable yield for the whole season inside or outside the tunnels.  Cumulative yield of ‘Camarosa’ was lower in tunnel due to the high incidence of powdery mildew.

 

CONCLUSIONS

        

        Botrytis fruit rot was significantly reduced in tunnel.  Limited Captan applications (14 day schedule) were effective in controlling the disease (< 1%) inside the tunnels.  Powdery mildew was significantly higher on ‘Camarosa’ inside the tunnel than outside.  Early yield of ‘Sweet Charlie’ was higher in tunnel.  A cultivar like Sweet Charlie appears to be an excellent choice for fruit production inside tunnels.  Early production would be improved, Botrytis fruit rot would be greatly reduced, and problems with powdery mildew would still be low because of the inherent resistance of ‘Sweet Charlie’ to this disease.