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Gregory J. McKee, Frank G. Zalom, and Rachael E. Goodhue

Reductions in strawberry yields were observed in association with infestations of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). The magnitude of yield impact is estimated using data from a field experiment evaluating nine management approaches for the greenhouse whitefly on strawberries, var. Camarosa. A range of effectiveness and yields was found. Imidacloprid (Admire) applied at transplanting was found to provide the greatest effect on adult whitefly densities. Pyriproxyfen (Esteem) had no immediate effect on adult density but reduced nymphal densities over time. Pairing the use of these products at transplant (Admire) and early spring (Esteem) provided the greatest reduction in whitefly density observed relative to an untreated control. Reductions in strawberry yields were found to increase as whitefly densities grow or as populations persist over time. For example, the estimates from our analysis suggest that at 20 weeks after planting, an average whitefly population may reduce average weekly yields in an untreated field by ≈80 g/plant.

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Yan Xu, Rachael E. Goodhue, James A. Chalfant, Thomas Miller, and Steven A. Fennimore

One challenge of conducting research regarding agricultural production systems is that field trials are time consuming and expensive, limiting their scale and scope. Thus, policymakers and producers benefit from researchers extracting as much information as possible from each trial. We used the Monte Carlo techniques and the sensitivity analyses to enhance our analysis of the competitiveness of steam as an alternative to fumigation for preplant soil disinfestation in California strawberry production. Chloropicrin + 1,3-dichloropropene 59.6:39 (CP + 1,3-D) resulted in higher mean net returns than did steam. However, the Monte Carlo analysis showed that in one field trial there was a high probability that steam would be more profitable, whereas in the other it was quite unlikely. We also assessed the change in economic performance of steam when it was applied combined with soil amendments of mustard seed meal (MSM). Switching from steam to steam + MSM would have reduced mean net returns. The Monte Carlo results showed that steam + MSM performed at least as well as steam alone around half the time. We evaluated factors that were likely to affect the net returns, defined as total returns minus treatment, weeding, and harvest labor costs, of using steam in the near future. Reductions in application time increased net returns. A decrease in the price of propane increased net returns.

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Jayesh B. Samtani, Husein A. Ajwa, Rachael E. Goodhue, Oleg Daugovish, Zahanghir Kabir, and Steven A. Fennimore

Fumigants are used to control soilborne pests before planting high-value crops such as strawberry. The use of specialized tarps during fumigation can reduce fumigant emissions and mitigate the need for large buffer zone requirements mandated by regulators. Increased fumigant retention by use of barrier films during fumigant application may increase fumigant retention and allow use of lower fumigant rates to control soil pests than would be needed with permeable film. The objective of this study was to determine the minimum effective rates of the alternative fumigants, 1,3-dichloropropene (1,3-D) + chloropicrin (Pic), and Pic required under virtually impermeable film (VIF) and a high-density polyethylene (HDPE) tarp to provide weed control equivalent to methyl bromide:chloropicrin (67/33% v/v MBPic) standard soil fumigation at 392 kg·ha−1 under HDPE. A second objective was to determine fumigant rates under VIF and HDPE tarps needed to provide weed control and the economic costs of using VIF and reduced rates of the alternative fumigants. In 2002–2003 and 2003–2004 growing seasons, the fumigants 1,3-D + Pic and Pic were tested at 0, 56, 112, 224, 336, and 448 kg·ha−1 under HDPE and VIF tarps at Oxnard and Watsonville, CA. An untreated control and a MBPic standard at 392 kg·ha−1 were also included in the study. Weed control was assessed using weed propagule viability bioassays for four common weeds, time required for hand weeding, and weed fresh biomass. The fumigant rate that would be needed for a 90% reduction in viability (GR90) for all weeds was 21% to 84% less for 1,3-D + Pic under VIF compared with the HDPE tarp. For Pic, the GR90 values were 5% to 64% less under VIF compared with the HDPE tarp. Hand weeding times and weed biomass decreased with increasing fumigant rates. With the exception of Pic in 2002–2003 at Oxnard, VIF reduced the rate required for weed control compared with the HDPE tarp for both fumigants and at both locations. Economic benefits of VIF relative to the HDPE tarp were not consistent and additional work is needed to quantify these relationships and the production conditions under which VIF will be beneficial.

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Steven A. Fennimore, Milton J. Haar, Rachael E. Goodhue, and Christopher Q. Winterbottom

Methyl bromide alternative fumigants were evaluated for weed control efficacy in low- and high-elevation strawberry (Fragaria ×ananassa L.) runner plant nurseries. Preplant soil fumigation treatments of methyl bromide plus chloropicrin (MBPic), iodomethane plus chloropicrin (IMPic), 1,3-dichloropropene plus chloropicrin mixture followed by (fb) dazomet, chloropicrin fb dazomet, and a nonfumigated control were evaluated at three California strawberry runner plant nurseries through two production cycles. Fumigant efficacy was measured by weed seed viability bioassays, weed density counts, and time of handweeding. Generally, all alternative fumigant treatments controlled weeds at levels comparable to MBPic. All fumigant treatments, including MBPic, killed more than 95% of common knotweed, common purslane, common chickweed, and strawberry seed. Iodomethane, chloropicrin fb dazomet, and 1,3-dichloropropene plus chloropicrin mixture fb dazomet controlled carpetweed, common lambsquarters, hairy nightshade, palmer amaranth, and prostrate spurge. Handweeding inputs for all fumigants were similar to MBPic at three of four locations. The exception was at the low-elevation nursery in 2000 where handweeding times with MBPic were lower than for IMPic. Treatment and handweeding costs were calculated. The handweeding costs for all treatments were approximately the same. However, the higher iodomethane material cost resulted in a substantially higher treatment cost.

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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.

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Zahangir Kabir, Steven A. Fennimore, John M. Duniway, Frank N. Martin, Gregory T. Browne, Christopher Q. Winterbottom, Husein A. Ajwa, Becky B. Westerdahl, Rachael E. Goodhue, and Milton J. Haar

For years, strawberry (Fragaria ×ananassa L.) runner plant nurseries have relied on methyl bromide (MB) fumigation of soil to produce healthy transplants. Methyl bromide, however, has been phased out due to its environmental risks. The potential for alternative fumigants to replace MB was evaluated at low and high elevation strawberry nurseries in California. The alternative fumigant iodomethane plus chloropicrin (IMPic) and a nonfumigated control (NF) were compared to methyl bromide plus chloropicrin (MBPic) at a low elevation nursery (LEN) and at a high elevation nursery (HEN) near Susanville, Calif. At a HEN near Macdoel, Calif., MBPic was compared to alternative fumigants IMPic, 1,3-dichloropropene plus chloropicrin mixture (Telone C35) followed by dazomet, chloropicrin (Pic) followed by dazomet and NF. Plants produced at the LEN were transplanted at the Macdoel HEN to measure the effects of soil fumigant history on plant health and runner plant production. Plants produced at both high elevation nurseries were evaluated for fruit yield and quality at two commercial fruit production sites in soils previously fumigated with MBPic or Pic. Runner plant production at the nurseries was similar in plots fumigated with either MBPic or alternative fumigants. All fumigation treatments had higher runner plant production than plants produced for two production cycles on NF soils. Generally, fruit yields from nursery plants produced on soils fumigated with IMPic, Pic followed by dazomet, or Telone C35 followed by dazomet, were similar to fruit yields from plants produced on MBPic fumigated soils. Overall, our results indicate that preplant soil treatments with IMPic, Pic followed by dazomet, and Telone C35 followed by dazomet, are potential alternatives to MBPic fumigation for strawberry runner plant nurseries. Fruit yields by plants in MBPic and Pic fumigated soils were comparable; however, they were more variable in Pic fumigated soils. Chemical names used: 1,3-dichloropropene (1,3-D), methyl bromide, methyl iodide (iodomethane), trichloronitromethane (chloropicrin), tetrahydro-3, 5-dimethyl-2 H-1,3,5-thiadiazine-2-thione (dazomet).