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  • Author or Editor: Jeffrey P. Mitchell* x
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Trials were conducted in 2002 and 2003 in California's San Joaquin Valley to determine the efficiency of reflective plastic and wheat straw in managing silverleaf whitefly and aphid-borne virus diseases in late planted cantaloupes. In 2002, the incidence of aphid-borne viruses was lowest in plants growing over reflective plastic followed by those growing over wheat straw and then those growing over bare soil. Wheat straw mulch was as effective as reflective plastic during the early part of the growing season in reducing the incidence of virus disease, but by mid-season, the reflective plastic was superior. The incidence of virus diseases in plants growing over wheat straw was significantly (P < 0.05) lower than that in plants growing over bare soil throughout the season. Whitefly numbers (nymphs per cm2) and aphid numbers were significantly reduced on plants growing over both reflective mulch and wheat straw mulch compared to those growing over bare soil. Yields of all sizes of melons were significantly higher in the reflective mulch plots and yield for the straw mulched and bare soil plots were not significantly different. Results in 2003 were similar to those of 2002. Both whitefly numbers and aphid numbers were significantly lower in plants growing over both mulches than in those growing over bare soil. Virus incidence was initially low but following an aphid flight in late August, the number of infected plants increased rapidly. Both the reflective plastic and straw provided equal protection form aphid-borne viruses throughout the growing season. Yields were highest in the reflective plastic plots, followed by the straw mulch and finally the bare soil. Differences were significant (P < 0.05) among all three treatments.

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Despite the worldwide importance of overhead, mechanized irrigation for crop production, the potential of this technology has been poorly studied in California. Field studies were conducted at Five Points, CA, in 2010 and 2012 to compare the effects of overhead irrigation (OH) and drip irrigation (DR) on transplanted tomato (Solanum lycopersicum) crop growth and yield. Similar amounts of water were applied to both systems in each year to match crop evapotranspiration demands. Crop growth measured by percent canopy coverage and aboveground biomass accumulation were similar between the OH and DR systems early in the growing season in both years but were lower in the OH system during the second half of each season. Tomato yield was 38% greater in 2012 than in 2010 and averaged over the 2 years, 48% higher in the DR than in the OH systems, respectively, due presumably to the higher soil water evaporation losses of the OH system relative to the DR system and also, we propose, to the ability of the drip system to very precisely apply in-season fertigations directly to the crop root zone while OH fertigations were applied at the soil surface and over a greater area. Soluble solids concentration of fruit in 2010 was 5.99% for the DR system and 6.65% for the OH system providing further evidence of water stress in the OH tomatoes. Production costs associated with transitioning from a subsurface drip tomato crop to a sprinkler or surface drip-irrigated crop such as onion (Allium cepa) or garlic (Allium sativum) could be $130 to $420 per acre lower with the OH system compared with the drip system, if yields were maintained. Because operation and labor costs of OH systems are typically lower than those of DR systems, further research on OH irrigation of tomato is warranted to address the shortcomings of OH management that this study has identified.

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Two field comparisons of conservation tillage tomato production alternatives following wheat were conducted in California's Central Valley. Both studies compared: 1) standard tillage; 2) bed disk or permanent bed minimum tillage; and 3) strip-tillage following winter wheat crops that were harvested the previous June. Processing tomatoes were produced at the site in Davis, Calif., and fresh market tomatoes were grown in Parlier, Calif. At both sites, establishing tomatoes using a commercial transplanter or a modified conservation tillage transplanter achieved adequate stands even in the minimally-tilled strip-till system. Timing of the strip till operation, however, is critical so that large chuncks of dry soil are not brought up and so that these do not create very rough bed surfaces that may cause harvest problems, particularly for processing tomatoes. Machine harvesting the crop at the Davis site did not seem to create any mechanical difficulties or generate additional trash going into the harvest trailer. This may have been due to the fact that by harvest time, the majority of the surface residue from the previous wheat crop had already been broken down or at least sufficiently worked into the soil to pose minimal mechanical harvester impedance or contamination. Tomato yields for the reduced till systems equalled yields of the standard till systems at both sites.

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Eliminating tillage passes is a means to reduce production costs and dust emissions in California's San Joaquin Valley tomato production region. Inserting winter cover crops between summer crops may be a way to add organic matter to the soil and thereby improve soil quality. From 1999, we evaluated conservation tillage (CT) and cover cropping (CC) in a tomato/cotton rotation in Five Points, Calif. During the course of the study, tillage operations were reduced an average of 50% in the CT system relative to the standard tillage (ST) approach. Yields in the CT no cover crop (NO) system matched or exceeded yields in the STNO system in each year. Tomato yields in the CTCC and STCC systems were comparable to the STNO except in the first year, when stand establishment and early season vigor were problems. Weed management and machine harvest efficiency in high surface residue systems are issues requiring additional work in order to make CT adoption more widespread.

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Traditional processing tomato (Solanum lycopersicum) production in California’s Central Valley relies heavily on tillage to produce high yields. However, recent research and farm innovation have produced a variety of conservation tillage (CT) management alternatives that cut costs, reduce soil disturbance, and produce fewer emissions. A 12-year study in Five Points, CA, demonstrated that CT methods reduced tractor passes by 40%, lowered tillage costs by ≈$80 per acre in 2011 dollars, and achieved comparable yields as standard tillage (ST) methods. As comparable yield performance and net profitability are further demonstrated, an array of CT systems will become increasingly attractive to producers and more common in Central Valley tomato growing areas.

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