California Agriculture

As we enter the 21st century, it is possible to reach beyond the headlines to describe what is now known about climate change. The Intergovernmental Panel on Climate Change evaluated the scientific aspects of global climate change; the current consensus is described in a recent series of reports. Since the 19th century, concentrations of atmospheric carbon dioxide, methane, nitrous oxide and sulfate aerosol dust have increased significantly. While there is scientific agreement that warming is occurring, the controversy now concerns the extent of subsequent impacts in the future. In California, the impacts of global warming are likely to include reduced water availability and quality, poorer air quality, associated economic consequences, biodiversity shifts and health effects. The changes are expected to continue at an increasing pace well into the next century, perhaps outstripping our scientific, economic and social ability to cope with them.

The use of agricultural contracts between farmers and processors or other buyers has increased substantially in recent years. Roughly half of all U.S. fruit and vegetable production is under contract. Contract usage varies widely across agricultural products. For example, 95% of poultry is raised under contract while only 13% of corn is. The wine grape industry utilizes contracts, yet little is known about the extent of contract use, or the use of specific terms and objectives. We used a survey to analyze contract use among wine grape producers, determine which users are utilizing contracts, and identify how they differ from nonusers. Ninety percent of the growers who responded to the survey have contracts, the majority of which were multiyear, averaging 3.7 years. Growers with more experience, larger vineyards, more expensive grapes and longer relationships with the buyer were more likely to enter into contracts.

Avocado thrips arrived in California in 1996. Since then, we have made substantial progress in our understanding of this pest. We now know the area of origin of the avocado thrips and have compiled an inventory of other potential pest thrips species on avocados in Mexico and Central America. Trials have helped us to identify several selective insecticides for use in treating avocado thrips in orchards. We have also determined the relationship between thrips densities on leaves and fruit scarring, and are studying cultural and biological control practices for use in an evolving integrated pest management (IPM) program.

In two Central Valley plum orchards, nearly all the trees started exhibiting copious amounts of dark gumballs on scaffold branches and main trunks. Exposed bark showed extensive tissue necrosis and necrotic stem-pitting on the surface of the woody cylinders. Eventually, both orchards had to be removed and replanted. The symptoms were highly suggestive of a viral or viruslike disease agent. We began studies to characterize the pathogen associated with the failure of these orchards and were successful in associating the disease with a new virus that proved to have an extensive host range in many cultivated Prunus. Characterization of this virus is under way.