Alternative Fumigants in Strawberry Production
The major alternatives to MB such as 1, 3-D and Pic are heavily regulated. The transition away from MB to alternatives has been complicated by fumigant regulations. In California, 1, 3-D use per 36 square mile township is limited to 90,250 lbs, i.e., a “township cap” which severely limits availability of 1, 3-D in numerous key strawberry production areas (Carpenter et al. 2001). Recent strawberry critical use nomination indicates that “township caps currently limit the use of 1,3-D on 40 to 62% of total strawberry land” (USDS 2009). In other words, considerable MB use continues in California because restrictions on alternative fumigants leave few options to continued MB use.
Strawberry Production Without Fumigants
Due to considerable obstacles to the switch from MB use to alternative fumigants, what then are the alternatives to fumigants for strawberry production? In the Pest Management Strategic Plan for Strawberry Production in California stakeholders identified “conducting long-term research on alternatives to fumigants in production fields as a priority” (CSC 2003). This is a clear statement by stakeholders that identifies the need for viable alternatives to fumigation. See below for more information:
Limitations of chemical fumigants
With multiple regulations limiting the use of all fumigants it is not always possible to simply substitute one fumigant for another. In many cases MB fumigation will have to be replaced with a strawberry production system that does not use any fumigants (Jones 2007). Presently registered alternative fumigants such as 1,3-D, Pic, and 1,3-D+Pic combinations have been tested and are effective at controlling soil pests (Fennimore et al. 2003). However, growers often comment about effective treatments such as 300 lbs/A Pic, “what good is a fumigant treatment if we can’t use it?”.
IPM in Strawberry Systems
An effective IPM program consists of methods to prevent entry of new pests into a field, eradication of troublesome new pests and control consisting of physical, cultural, and chemical methods (Strand 2008). For the past 5 decades the chemical control method used most often for soil pests in strawberry has been MB. However, in buffer zones and sensitive sites, chemical fumigants either cannot be used, or the upper dose is severely limited. Strawberry can be produced on clean substrates such as peat or “coir” (coconut fiber) a common method of strawberry production in Europe. Nonfumigant methods of soil disinfestation which allow strawberry production in soil include anaerobic soil disinfestation (ASD) and steam. Strawberry production in substrates, ASD and steam, are discussed in the following sections.
Strawberry production using substrate production system
Production of strawberry on substrates is commonly used in Europe and does not require MB. In 2003, there were 2,815 acres (1,140 ha) of strawberry produced using soilless culture in Europe, primarily in Belgium, The Netherlands, U.K., France and Italy (Lieten et al. 2004a). Soilless production of strawberry is being evaluated as well in Florida (Hochmuth and Hochmuth 2003). This method of production has traditionally utilized coir, peat or other soilless substrates enclosed in bags under tunnels (Lieten et al. 2004b). However, concerns about bag disposal have led to development of a more sustainable soilless production systems including the raised bed trough system. The bed is raised like a typical strawberry bed, with the exception that grooves or “troughs” are cut into the bed (Figure 1). The bed tops, including the troughs, are lined with fabric designed to permit moisture penetration, but not allow root penetration. The troughs are filled with clean planting material, soil or soilless media, drip tape installed and tarped as with any other strawberry bed. The primary justification for use of the raised bed trough system is that strawberry can be produced without fumigation (Lieten et al. 2004a). Development of a system where in the soilless media could be disinfested and recycled would in theory represent a more sustainable production system than if old substrate material were discarded and replaced each cropping cycle. Additional advantages of the system include the ease of attracting harvest labor due to high productivity, and the ability to leave the beds in place for several crop cycles. One of the disadvantages of the raised bed trough system is the need for components such as coir and peat in the media. However, composted wood fiber and composted pine bark have been tested as alternatives with good results (Lieten et. al. 2004). Logistical issues such as the delivery and installation of large amounts of substrate material such as needed for a 10 acre field have yet to be addressed as do production costs.