A comparison of dazomet, chloropicrin and methyl bromide as soil disinfestants for strawberries.
Chemical soil disinfestants, applied in strips (bed-only) or overall (broadacre), were compared for their effects on weeds, soil nematodes, soilborne diseases and yield in a commercial planting of strawberry cv. Elsanta grown on raised beds mulched with polyethylene. In bed-only application, dazomet (570 kg/ha) and methyl bromide (450 kg/ha) reduced nematode numbers and the amount of Verticillium dahliae in soil and the incidence of crown rot (Phytophthora cactorum), but did not reduce red core (P. fragariae) severity or the numbers of weeds. Treatment with both disinfestants resulted in yield increases from sampling bands and from whole beds compared with untreated beds. Over 2 seasons, the yield increases totalled 40-60%. Chloropicrin (150 litres/ha) reduced nematode numbers and the amount of V. dahliae to below detectable levels, but had no effect on weed numbers, crown rot incidence, red core severity or yield. After broadacre application, in which beds were constructed across plots after treatment, dazomet (380 kg/ha) treatment reduced nematode numbers and crown rot incidence, but had no effect on weed numbers, the amount of V. dahliae or red core severity. A significant yield increase was obtained only in whole-plot data in the second season (aggregate 2 year increases in sample transects and whole plots were 11 and 17%, respectively). The results were inferior to those of bed-only application in all criteria except nematode numbers, and this was attributed partly to the less efficient disinfestant application and soil sealing procedures. Methyl bromide (750 kg/ha) reduced weed numbers, the incidence of crown rot, the severity of red core and the amount of V. dahliae and the number of nematodes in soil, and increased yields from both sampling bands and whole plots. Aggregate 2 year yield increases for samples and whole plots were 64 and 32%, respectively. Results of broadacre treatment determined from samples were superior to those from bed-only application of methyl bromide for all criteria, while results determined from whole-plot data were inferior to those from bed-only application, reflecting the effects of soil movement between adjacent plots during bed construction.