Calag Archive

The Grasslands Bypass Project in the western San Joaquin Valley of California was conceived as a means of diverting selenium-contaminated agricultural drainage water from fresh water channels serving Grassland wetlands. Use of the federally owned San Luis Drain was made contingent on the formation of a regional drainage management authority by the project proponents and compliance with strict monthly and annual selenium-load targets and agreement to strict monthly and annual selenium-load targets for discharges from the 97,000-acre (44,000 hectares) project area. During the first year of this 5-year project, the Grasslands Basin farmers were successful in reducing selenium export from the project area by 44% and 33% when compared to water years 1995 and 1996. Although monthly targets were exceeded during the spring months of 1997, in part due to unusually high rainfall runoff from the project area and upper watershed, the goals of the project were met. There is popular sentiment that more was learned about selenium drainage management and achieved in selenium load reductions by participating water districts during the first year of the project than in the past decade.

Subsurface drainage systems are traditionally installed in agricultural fields to control waterlogging (high water tables) and excess salinity affecting the crop root zone. However, in many clay fields of the Imperial Valley underlain by shallow fine-sand aquifers, the drains may be ineffective and provide limited relief for the root zone. After extensive work considering soil-water flow paths in a particular field at the UC Desert Research and Extension Center (DREC), we plugged whole-field drainage systems, then evaluated the impact on water-table levels and soil salinity during a 3-year period. We found that the shallow fine-sand aquifer underlying the DREC, originally identified in the 1950s, combined with the Imperial Irrigation District deep-ditch system, provided sufficient drainage relief for several areas of the DREC to successfully grow a variety of crops. Given the ineffectiveness of subsurface drainage systems in three different fields that had soil characteristics similar to more than half the Imperial Valley fields we expect that in many parts of the valley, augmentation of subsurface drainage systems through “splitting” the lateral drainline spacing may not be warranted. Indeed, efforts to reduce the salinity of heavier soils on the DREC, or elsewhere In the valley, may be better directed at improving water penetration and leaching of soils through deep ripping or other cultivation/mulching methods, rather than expending resources on improving the subsurface drainage system.

Marking studies demonstrated that lady beetles, lacewings, syrphid flies and parasitic wasps fed on nectar or pollen provided by borders of flowering plants around farms; many insects moved 250 feet into adjacent field crops. Studies using the elemental marker rubidium also showed that syrphid flies, parasitic wasps and lacewings fed on flowering cover crops in orchards and that some moved 6 feet high in the tree canopy and 100 feet away from the treated area. The use of nectar or pollen by beneficial insects helps them survive and reproduce. Therefore, planting flowering plants and perennial grasses around farms may lead to better biological control of pests in nearby crops.

In 3 of 4 vineyards we studied, late-season leafhopper density was lower on vines in cover cropped plots than in plots with no cover crops. However, the level of leafhopper reduction (about 15%) was rarely economically important and the mechanisms leading to reduction were not clear. For example, there were few differences in the number of leaf hopper predators or parasitoids on the vines in cover cropped versus no cover plots. However, there were significant between-treatment differences in vine growth. Plots with seasonwide maintenance of a cover crop and resident grasses had a reduction in vine vigor. Lower vine vigor has been associated with lower leafhopper densities and, in our studies conducted from 1993 to 1996, those plots with reduced vine vigor often had the greatest reduction in late-season leafhopper density.

Nightshades are some of the most difficult weeds to control in Upland Acala varieties of cotton. A herbicide in the newest class of acetolactase synthase inhibitors has been developed for use as a selective over-the-top broadleaf herbicide in cotton. Studies were conducted in Upland Acala cotton varieties in 1991, 1992 and 1993 to evaluate the efficacy of Staple (pyrithiobac sodium) in controlling nightshade. The herbicide was applied as early postemergence, mid-postemergence and sequential applications at rates of 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0 oz of active ingredient per acre (ai/acre). Acceptable nightshade control was achieved at all rates, when applied as a single application or as sequential applications, except for the 0.25 and 0.50 oz ai/acre applications. The best control was achieved when the herbicide was applied at rates of 1.0 to 3.0 oz ai/acre over the top of cotton in the cotyledon to eight true-leaf stage, with nightshade in the cotyledon to six-leaf stage. Cotton injury symptoms were evident with all treatments at 7 days after application but were nonexistent by 90 days after application. There was no evidence to indicate that pyrithiobac sodium has any long-term effect on cotton growth and development or on cotton lint yield.

Beet curly top geminivirus damages numerous crops, including beans, beets, spinach, peppers, melons and tomatoes. Both the virus and its vector, the beet leafhopper, overwinter in the foothills surrounding the Central Valley. The known host range of the virus is now recognized to include many native and introduced perennial shrubs in the foothills. This is the first reported detection of the virus in plants in the families Ephedraceae, Rhamnaceae and Salicaceae.