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Open Access Publications from the University of California


California Agriculture is a quarterly peer-reviewed journal reporting research, reviews and news on California’s agricultural, natural and human resources.

Volume 55, Issue 1, 2001


New pests and diseases: Sudden oak death syndrome fells 3 oak species

“Sudden oak death” refers to a complex set of symptoms that has already culminated in the death of tens of thousands of California oak trees. Now confirmed in seven coastal counties, SOD attacks California tanoak, coast live oak and California black oak. Although several fungal species and the western oak bark beetle and ambrosia beetles have been associated with the syndrome, we now have solid evidence that a newly discovered Phytophthora species is the primary causal agent. This Phytophthora species was recently isolated in rhododendron as well; it may be the same species that was isolated, but not described, on rhododendrons in Germany in 1993. The discovery of SOD on rhododendron has serious implications. The disease may well be present at the ecosystem scale, and its appearance on an ornamental plant suggests the possibility of wider dissemination. A team of UC scientists has developed an integrated approach to managing this disease, including practices to enhance tree health. Early disease detection and targeted chemical treatment may also hold some promise for disease management. In addition, we have developed a molecular probe that will enable rapid identification of SOD from any infected part of the plant. Ultimately, the fate of the oak species affected by SOD will be determined by the levels of disease resistance present in natural populations of these trees.

Almond advertising yields net benefits to growers

This study evaluates the economic impacts of advertising and promotion expenditures funded under the almond marketing order. Over the crop years 1962/63 through 1997/98, the correlation of industry promotion and demand was positive and statistically significant. Almond advertising has yielded marginal benefits between $3 and $10 per dollar spent. The 1994/95 through 1996/97 suspension of the promotion program reduced grower profits in the range of $88 million to $231 million during the suspension period.

Peach trees perform similarly despite different irrigation scheduling methods

There are numerous techniques for scientifically scheduling irrigations in tree fruit orchards. These approaches involve measuring soil, plant or atmospheric parameters, then using this information to determine when to irrigate and how much water to apply. We studied the effects of the different irrigation scheduling methods on peach trees in Tulare County. One of the key aspects of irrigation scheduling is being able to interpret the measurements so that the resulting water management decisions produce maximum grower profit with the minimum amount of water. Thus the measurements must not only be accurately taken, but protocols for their interpretation must be reliable in terms of achieving optimal tree performance without wasting water. This requires a marriage of the technology used to take the measurement and the science used to develop the interpretation guidelines. When this is successfully done, we found that the method of scheduling irrigations had no effect on the peach trees' performance.

Soil properties change in no-till tomato production

High production costs and perceived declines in soil quality due to agricultural intensification have led to recent interest in conservation tillage production practices. We conducted field experiments in Five Points in 1997 and 1998 to evaluate the effectiveness of maintaining a cover crop mulch on the soil surface in a no-till system compared to a standard tillage system for conserving soil moisture and improving water infiltration and other soil physical properties in a furrow-irrigated tomato field. Soil water content did not differ among treatments in 1997, but was higher under no-till cover crop mulches than conventionally tilled plots during the 1998 growing season. Soil carbon was increased more than 8% and more earthworms were found under no-till mulches relative to the conventionally tilled plots in the second year of the study. Soil compaction was lower in no-till treatments, especially at the 1-to-2-foot depth. In this study, furrows were swept clean and therefore furrow irrigation did not constitute a limitation to this no-till system.

Combining bensulide and pendimethalin controls weeds in onions

DCPA was the principal preemergence herbicide for controlling weeds in onions until its manufacture was discontinued in 1996, although it may be reintroduced in 2001. The purpose of this research was to test the effectiveness of a combination of two herbicides, bensulide and pendimethalin, as a replacement weed-control treatment. Results are encouraging; this combination performed as well as DCPA in 12 onion field trials conducted in the Imperial Valley. Onion yields in fields treated with bensulide and pendimethalin were comparable to that of fields treated with DCPA.

Table grapes suffer water loss, stem browning during cooling delays

The water loss in table grapes that occurs during postharvest handling can lead to stem browning, berry shatter, and wilting and shriveling of the fruit. Critical grape cluster water-loss threshold values for stem browning were determined for Perlette, Thompson Seedless, Flame Seedless, Fantasy Seedless and Redglobe table grape cultivars. Fantasy Seedless and Redglobe withstood higher levels of stem water loss than Perlette, Flame Seedless and Thompson Seedless before expressing moderate to severe stem browning. Our survey of potential cluster water loss during harvesting operations indicated that a short cooling delay at high air temperatures contributed to stem browning. These low critical cluster water-loss threshold values combined with the high level of water loss measured during harvesting operations illustrate the need to minimize cooling delays and the importance of developing a technique to reduce cluster water loss during harvest and/or postharvest handling. The use of cluster bags and foam boxes reduced grape cluster water loss during harvest operations.

First-grade gardeners more likely to taste vegetables

To encourage first-graders to increase their consumption of fruits and vegetables, a garden-enhanced nutrition education program was developed and taught to them. The study was a pilot to assess the feasibility of garden-based education programs for elementary-school students. The first-grade children learned about nutrition in the classroom while growing vegetables outdoors in their own gardens. This experience resulted in the children's increased willingness to taste those vegetables grown in the gardens. Improving children's desire to taste vegetables is thought to be the first step in developing healthier consumption patterns.