Calag Archive

Color infrared aerial photos can be scanned into a computer file and then analyzed using image-processing software. This relatively new technology is illustrated using examples from two long-term research projects at UC Davis. A “vegetation index” calculated from aerial photos can reveal differences in plant growth and health that are difficult to see in the original color IR image and that could be useful for site-specific management within a field.

The eucalyptus longhorned borer (ELB) was first identified in California in 1984 and has since killed thousands of eucalyptus trees. Now firmly established throughout Southern California, the borer continues to spread northward. A search for its natural enemies in Australia yielded a tiny wasp, Avetianella longoi, that parasitizes ELB eggs. The wasp was imported, released and is now established in San Diego and Riverside counties. Results of releases in other areas are pending. A. longoi propagates quickly, disperses rapidly across wide areas, and is highly efficient at finding and parasitizing borer eggs.

A 4-year study indicates that native blue oak seedlings are probably much older than most people would think: Trees less than 6 inches tall could be 10 to 15 years old. Seedlings grow very slowly, if at all, during periods of drought. However, seedling mortality was highest during the year of above-average rainfall.

The success of California agriculture depends on the effective delivery and adoption of useful information. Traditionally, Cooperative Extension has stressed the use of “multipliers” including pest control advisors and private consultants as an effective way to widely distribute information. However, results of a study examining the regional reach of information for tree crop farmers in a six-county area suggests such a strategy may not be as effective as presumed. Growers contacted PCAs, chemical representatives and private consultants more often than farm advisors, but considered farm advisors more useful information sources. Cooperative Extension and other agricultural educators must learn more about how farmers acquire information and what influences their adoption of new practices.

In a 3-year study, Internal browning of Fuji apples during postharvest storage varied from year to year, but was strongly affected each year by harvest timing and carbon dioxide concentration in storage atmospheres. Internal browning incidence and severity were low in fruit harvested within 180 days after bloom. Timely harvest and storage at CO₂ levels below 0.5% are recommended to reduce losses from this disorder.

In the past, pruning wounds were not regarded as potential infection sites. However, in a 2-year study, pruning cuts inoculated immediately or at intervals up to 14 days were found to be susceptible to Ceratocystis canker from September through February. Broken, dead or living twigs became infected throughout the year when inoculated with the fungus.

Sampling fruit from vineyards 4 months after fruit set and recording the incidence of Botrytis colonization in sepals or stem ends was used as a field-monitoring method to predict the incidence of kiwifruit Botrytis gray mold after 3 or 5 months in cold storage. Spraying the fungicide vinclozolin one or two weeks before harvest significantly reduced postharvest gray mold after 5 months storage only in vineyards with more than 6% gray mold. Preharvest sprays were not needed when expected gray mold was below 6%. The method reported here can be used successfully by growers to make decisions about preharvest sprays, sorting, repacking and when to market and ship fruit.