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Jayesh B. Samtani, J. Ben Weber and Steven A. Fennimore

Herbicides can be an excellent supplemental treatment in cases where soil fumigant treatments alone fail to control weeds during the growing season or in situations where fumigants cannot be used as a result of regulatory restrictions. Previous studies have shown that oxyfluorfen and flumioxazin can provide satisfactory weed control in bedded strawberry (Fragaria ×ananassa Duch.) production. However, we need to know if tolerance to herbicides is uniform across strawberry cultivars under California conditions. The objective of this study was to determine if tolerance to oxyfluorfen and flumioxazin herbicides varied among strawberry cultivars. Trials were conducted in the 2007–2008 and 2009–2010 growing seasons at Salinas, CA. Treatments included an untreated control; pre-plant applications of flumioxazin at 0.07, 0.11, and 0.21 kg·ha−1 a.i.; and oxyfluorfen at 0.14 and 0.28 kg·ha−1 a.i. The entire trial was fumigated with an emulsified formulation of 60% 1,3-dichloropropene + 32% chloropicrin applied at 281 L·ha−1 by drip injection to all plots. Eight strawberry cultivars were included in the trial in the 2007–2008 growing season, and nine cultivars were included in the 2009–2010 growing season. In both growing seasons, slight to no crop phytotoxicity was observed. In the 2007–2008 growing season, several strawberry cultivars including ‘Albion’, ‘Festival’, ‘211G51’, ‘Palomar’, ‘Plant Sciences 5298’, and ‘Ventana’ had smaller crop plant canopy diameter as compared with the control when treated with 0.21 kg·ha−1 a.i. of flumioxazin. Compared with the control, flumioxazin at 0.21 kg·ha−1 a.i. reduced crop diameter for ‘Plant Sciences 4634’, ‘Plant Sciences 5298’, ‘San Andreas’, and ‘Ventana’ in the 2009–2010 growing season. In the 2007–2008 strawberry-growing season, none of the herbicide treatments reduced fruit yield compared with the control. In the 2009–2010 growing season, in seven of the nine cultivars, there were no significant differences in yield among treatments. For ‘Palomar’ strawberry, yields in plots treated with flumioxazin at 0.11 and 0.21 kg·ha−1 a.i. were significantly lower than the untreated control. With the exception of flumioxazin at 0.21 kg·ha−1 a.i., these herbicides are safe to use and can be incorporated in strawberry production practices for the cultivars tested to achieve satisfactory weed control over the growing season.

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Jayesh B. Samtani, Celeste Gilbert, J. Ben Weber, Krishna V. Subbarao, Rachael E. Goodhue and Steven A. Fennimore

The phase-out of methyl bromide as a soil fumigant for strawberry (Fragaria ×ananassa, Duch.) and increasingly strict regulations of all fumigants suggest that non-fumigant methods of soil disinfestation are needed. In warm climates, solarization controls soilborne pests, but fog and lower summer soil temperatures in coastal California render it unsuitable for pest control relative to chemical fumigation. The first objective of this study was to test the efficacy of steam in controlling soil pests in strawberry production. The second objective was to determine if combining solarization with steam in coastal California would achieve greater pest control and higher yields compared with steam or solarization used alone. The final objective was to determine the economic feasibility of steam and solarization treatments relative to MBPic fumigation. Field studies were conducted at Salinas, CA, in 2007–2008 and in 2008–2009 growing seasons. Treatments included MBPic 67/33% v/v at 392 kg·ha−1, untreated control, solarization, steam, and steam + solarization. For steam + solarization plots, beds were solarized for 2 weeks before and 2 weeks after steam application. Before application of a clear film for solarization, beds were irrigated so the soil moisture was optimal for solarization. Steam was injected into the beds to reach soil temperatures to 70°C or higher up to a depth of 25 cm for 20 min. Soil temperatures during steam and solarization treatments were monitored. Control of soil pests was measured using pathogen and weed propagule bioassays in all treatments. After the 4-week treatment period, ‘Albion’ strawberry was transplanted in all plots. After transplanting, weed density, weed fresh biomass, and hand weeding time were recorded periodically in each treatment over the cropping season. Weed seed viability in steam and steam + solarization-treated plots was the same or lower than MBPic standard fumigation. Compared with MBPic fumigation, solarization alone was less effective in controlling weeds or reducing the hand-weeding time. Steam and steam + solarization treatments resulted in weed control similar to MBPic fumigation. Only certain steam treatments reduced the number of Verticillium dahliae Kleb. microsclerotia similar to the MBPic fumigation at 15-cm depth with no reductions at greater depths. There were no significant differences among treatments in 2007–2008 with regard to yield, but in 2008–2009, yields from steam treatments were comparable to the MBPic-treated plots. Economic analysis performed for the 2008–2009 season showed that net returns from steam or solarization treatments were less than MBPic treatment.