Calag Archive

Under certain California conditions, a tiny, nearly microscopic wasp parasite, Anagrus epos Girault, is capable of holding population levels of the grape leafhopper, Erythroneura elegantula Osborn, down to noneconomic levels.

Preliminary results of field studies on economic treatment levels for control of grape leafhoppers indicate that many growers in the San Joaquin Valley use insecticides unnecessarily because they lack accurate knowledge of insect population levels. Thompson Seedless grapes also appear to be more tolerant of nymph populations than expected. Results also have shown that some insecticides result in a severe build-up of spider mite populations, and further screening is necessary to find materials with least harmful side effects on beneficial parasites and predators.

in areas where natural enemies of the grape leafhopper, Erythroneura elegantula Osb. are absent, or insufficient in numbers, chemical control may be necessary to prevent an increase in leafhoppers from causing serious economic damage. From an economic standpoint, determining the level of infestation allows not only prevention of serious damage to the vines, but also could save the cost of insecticide applications. This study of daily and seasonal periods when leafhopper damage occurred was conducted as a preliminary step in determining the economic level of leafhopper infestation.

Rapid and accurate surveying for grape leafhopper population levels is essential to a decision for necessity of insecticide treatment within an integrated pest control program. These Tulare County studies indicate that counting the nymphs on only two leaves per acre gives as accurate an estimate of the population as did counting the nymphs on fifty leaves. It was also found that the leaves could be selected from vines along the avenues, rather than from vines scattered throughout the vineyard.

A single spray application of carbaryl (Sevin) provided control of the elm leaf beetle for an entire season in tests at Bishop in Inyo County. Effective control is believed to be contingent upon timing the application after the majority of the eggs have been laid in the spring, and the young larvae have begun to feed.

Properly timed applications of Thiodan or Dibrom are currently effective for use in controlling the grape leafhopper. However, the past record of resistance problems that have developed with other insecticides indicates that it is only a question of time until the same difficulties occur with these materials. Saving these insecticides for emergency use, rather than preventive treatment, and further reliance on an integrated control program appears to offer the best solution.

Sweet cherries are among the most perishable of California stone fruits, and high losses sometimes result from serious fruit deterioration during marketing. The study reported here resulted from an industry request to determine how losses could be reduced and high quality maintained. A program designed to evaluate the effect of current handling methods on fruit quality was initiated in 1964. While much work remains to be done, certain results obtained during the first season are of immediate value to the cherry industry. For example, delays of only a few hours between harvest and cooling of the fruit caused noticeable deterioration of quality. An eight-hour delay before cooling was found to cause more deterioration in the fruit than nine days of subsequent holding under good transit and marketing conditions. Slowest fruit deterioration occurred when temperatures were kept just above the freezing point of the cherries.

recent studies with varieties of canning tomatoes for mechanical harvesting support tests and observations during the past four years emphasizing the effectiveness of date of planting. An orderly and continuous supply of fruit to the processor can be assured only through the use of properly spaced planting dates. During the 1965 season, more than 200 machines are expected to be used in harvesting a potential 20,000 acres-about 17 to 20% of California's average annual canning tomato production.

Differential temperatures before flowering did affect vegetative development of flax in tests at Riverside, but did not cause changes in the quality of linseed oil produced. However, the same temperature treatments after flowering caused major changes in composition of the linseed oil.