How to Manage Pests
UC Pest Management Guidelines
Both raspberries and blackberries benefit from growing in high tunnels, also known as "macrotunnels" or "Spanish tunnels." The desirability of using tunnels for caneberry production comes from the ability to extend the harvest season, combined with improved fruit quality and yield, and can more than make up for the additional costs of establishing and maintaining the tunnels. The actual cost to benefit ratio varies among different growing areas and market options.
Raspberries are more commonly grown in tunnels because there are established cultivars that are well adapted to tunnel culture, whereas development of blackberry cultivars appropriate for tunnel production is still in early stages. The first primocane-fruiting blackberries have been released and show promise. It is likely that as more primocane-fruiting blackberry types become available, more cultivars will be identified as appropriate for tunnel culture.
Primocane-fruiting raspberry cultivars are best suited to tunnel culture because the fruit can be harvested off the primocanes, and they do not have the chilling requirements that summer-bearing cultivars have. Studies have shown, however, that summer-bearing types also exhibit extended harvest periods and improved yield and quality when grown in tunnels. Tip pruning of summer-bearing cultivars can be used inside tunnels to extend harvest later into higher-priced market periods in fall.
High tunnels are semi-permanent structures constructed from steel pipe arches covered with polyethylene plastic to create a protected environment for the plants. They are typically 10 to 15 ft high and 20 to 30 ft wide. Tunnels can be assembled side-by-side to cover areas of several acres, which adds some stability against wind damage. In California one sheet of plastic is typically used, and it is rarely in place on a given tunnel for more than 1 to 3 years. Tunnels are rarely heated. There are many adaptations that can be made to the tunnels to provide greater protection from cold temperatures, depending on growing conditions.
A typical production system in Central and Southern California for winter production uses a raspberry primocane-fruiting cultivar grown under high tunnels for one fall and one spring harvest. Planting takes place in spring and the tunnels are installed by mid- to late summer. Generally beginning in October or November, fruit is harvested off the tops of primocanes; harvest continues until February or March. At the end of the growing season, the fruited tops are removed leaving 3 to 4 ft of cane. Flowering and harvest begins anew on remaining canes the following August. (In the Watsonville area, the production period is concentrated in late summer or fall. To prevent damage to the tunnel during the windy winter season, the plastic is often temporarily removed.) At the completion of harvest, plants are removed and ground is prepared for the next crop.
Fruit grown under tunnels is typically larger and has improved shelf life because there is a less favorable environment for disease development. In comparisons of tunnel-grown and field-grown raspberries, tunnel-grown production begins earlier, ends later, fruit is 20-25% larger, and yields are 30% greater or more, depending upon location and growing conditions. In cold winter locations tunnels may also be used to improve winter survival and to extend the normal summer harvest season.
Because plants grown in tunnels are protected from moisture on leaves, canes, flowers, and fruit, they have a lower incidence of fruit rots such as Botrytis and anthracnose, as well as leaf and cane spot diseases. Tunneled plants also have fewer leafhoppers and Japanese beetles compared to open field plants.
Heat buildup in tunnels can be a serious management challenge. Tunneled caneberries have been most successful in mild, coastal growing sites; inland areas may have difficulty venting the heat buildup consistently. In addition, caneberries can grow quite tall in the warm tunnel environment and may require special pruning.
The warm, dry conditions in the tunnels may favor development of twospotted mites. An aggressive monitoring program, miticide applications, and predatory mite releases are widely practiced by growers using tunnels. In addition, whiteflies tend to appear in mid- to late summer and may increase with the warmer temperatures inside tunnels. For more information on these pests, see the sections on TWOSPOTTED SPIDER MITE or GREENHOUSE WHITEFLY.
UC IPM Pest Management Guidelines: Caneberries