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Open Access Publications from the University of California

Volume 62, Issue 3, 2008

Issue cover

Articles

San Joaquin Valley blueberries evaluated for quality attributes

Blueberry production in California was estimated in 2007 at around 4,500 acres and is rapidly increasing. Common southern highbush cultivars with low chilling-hour requirements are being grown from Fresno County southward, including ‘Misty’, ‘O’Neal’, ‘Emerald’, ‘Jewel’, ‘Star’ and others. We characterized the quality parameters (soluble solids concentration, titratable acidity, ratio of soluble solids concentration to titratable acidity, firmness and antioxidant capacity) of six southern highbush blueberry cultivars grown at the UC Kearney Agricultural Center in Parlier, in the San Joaquin Valley, for three seasons (2005–2007). We also conducted in-store tests to evaluate their acceptance by consumers who eat fresh blueberries. We found that the southern blueberry cultivars currently grown under warm San Joaquin Valley conditions are producing blueberry fruit that is of acceptable quality to consumers and profitable to growers.

Field trials identify more native plants suited to urban landscaping

There is a growing need in the state of California for landscape plants that require fewer inputs of water and chemicals. To address this issue, a program was initiated at UC Davis to test the landscape potential of California native plants not currently in widespread horticultural use. Ten unused or underused California native plants were screened in open-field conditions for low water tolerance during summer 2006. In all cases, there were no significant differences in the summer growth or physical appearance between four irrigation levels. Six species maintained a favorable appearance throughout the season and were advanced to demonstration gardens in seven climate zones throughout the state, where Master Gardeners are performing further assessments on their performance. These irrigation and climate zone trials are part of an ongoing program coordinated by UC Cooperative Extension, the UC Davis Arboretum and the California Center for Urban Horticulture to introduce more low water-use and low chemical-use plants through partnerships with the commercial horticultural industry.

Pheromone-based pest management can be cost-effective for walnut growers

Many organophosphate and pyrethroid insecticides currently used by California walnut growers have been linked to negative environmental or human health impacts, increasing the probability of use restrictions and phase-outs. We assessed the acceptability of alternative reduced-risk strategies by comparing their costs to those of pest management programs currently in use among San Joaquin County walnut growers. To do this, we analyzed data from the California Department of Pesticide Regulation’s legally mandated Pesticide Use Reports on actual pesticide applications for 3 years, from 2002 to 2004. While many factors other than cost influence growers’ pest management choices, we found that alternative strategies can be cost-competitive with conventional approaches, depending on the pest pressure and savings due to reductions in secondary pest outbreaks.

Crown gall can spread between walnut trees in nurseries and reduce future yields

While walnut trees on Juglans hindsii x J. regia ‘Paradox’ rootstocks are highly susceptible to crown gall, it is unknown whether this bacterial disease is acquired in the nursery or the orchard. We selected two groups of gall-free trees in nurseries, those adjacent to trees with and without galls. Two years after being transplanted in the orchard, trees in the group adjacent to those with galls had significantly greater — more than four times more — crown gall incidence than those adjacent to trees without galls (14% versus 3%). In addition, trees in prolonged (17-day), bare-root, unrefrigerated storage before transplanting were associated with higher crown-gall incidence. We also found that crown gall can decrease walnut tree productivity. For every quarter of trunk circumference that was galled, there was a 12% decrease in cumulative nut yield over the first 4 years of production.

Glyphosate-resistant hairy fleabane documented in the Central Valley

In recent years, growers and pest consultants have reported poor control of the weed hairy fleabane in some areas of the Central Valley. Hairy fleabane seeds were collected from Esparto, Fresno and Reedley, Calif., and greenhouse-grown seedlings were treated at several different glyphosate rates and compared with an untreated control. None of the Esparto or Fresno plants survived glyphosate rates greater than 0.78 pounds acid equivalent per acre (lb ae/ac), while some of the plants from Reedley survived even the highest rate of glyphosate tested (12.4 lb ae/ac). The dose required to reduce plant dry weights by 50% (GR50) of the Esparto plants ranged from 0.28 to 0.30 lb ae/ac, whereas the GR50 of the Fresno and Reedley plants ranged from 0.26 to 0.61 and 0.92 to 2.88 lb ae/ac, respectively. This study showed that the hairy fleabane plants from Reedley were much more tolerant of glyphosate than either of the other two biotypes and, based on the GR50, the level of resistance ranged from 3- to 10-fold greater.