Abstract. Strawberry (fragaria xananassa Duchesne)
is a high value cash crop that benefits from preplant soil fumigation
with methyl bromide (MB) and chloropicrin (CP). Methyl Bromide will
be banned in the U.S. and other developed countries by 2005 for most
uses. Potential alternative chemicals to replace methyl bromide for
soil fumigation include CP, 1,3-dichloropropene (1,3,-D), and methyl
isothiocyanate (MITC) generators such as metam sodium (MS). Commercial
formulations of these fumigants applied singly and in combination
through drip irrigation systems were evaluated at two sites for three
consecutive growing seasons as alternatives to MB: CP fumigation for
strawberry production. A mixture of 1,3-D and CP was shank injected
as Telone C35 (62% 1,3-D and 35%CP) at 374 Kg-ha-1. An emulsifiable
concentrate (EC) formulation of 1,3-D and CP was applied as InLine
(60% 1,3-D and 32% CP) at 236 and 393 L-ha-1 through drip irrigation
systems in three amounts of irrigation water (26,43 and 61 L-m-2).
Chloropicrin (CP EC, 96% was drip applied singly at 130 or 200 L-ha-1.
Metam sodium was applied singly as Vapam HL in three amounts of water
and in combination with InLine and CP EC. Strawberry growth, fruit
yields, disease pressure, and weed biomass were compared to an untreated
control and shank injection with MB:CP mixture (67:33) at 425 Kg-ha-1.
For soils high in pathogen populations, fruit yield from the untreated
plots was 34% to 50% relative to the MB:CP treatment. The greatest
(95% to 110%) yields relative to MB:CP were in the high rates of the
InLine treatments. Yields from simultaneous drip fumigation with a
combination of Vapam HL InLine or CP EC were less (67% to 79%) than
yields from shank fumigation with MB:CP due to 1,3-D and CP hydrolysis
reactions with Vapam HL or the generated MITC in the irrigation water
that reduced the efficacy of these combinations to control soil born
pathogens. Application of reduced rates of InLine or CP EC followed
6 days later with reduced rates of Vapam HL controlled soil born pathogens
in weeds and produced the greatest fruit yield relative to all treatments.
Chemical names used: 1,3-dichloropropene (1,3-D); methyl bromide (MB);
trichloronitromethane (chloropicrin) CP; Sodium methyldithiocarbamate
(metam sodium); Methyl isothiocyanate (MITC).
