California Agriculture, July-August 1996
Volume 50, Number 4
Phylloxera spurs replanting of vineyards
peer-reviewed research articles
California grape phylloxera more variable than expected
by Jeffrey Granett , Andrew Walker , John De Benedictis , Genine Fong , Hong Lin , Ed Weber
Many strains of grape phylloxera now have been identified in California vineyards. This variability may be the result of multiple introductions of this pest or of evolution of new strains on susceptible or weakly resistant rootstocks. Thus own-rooted vines, weakly resistant rootstocks and those with V. vinifera parentage should not be used in phylloxerated areas. In addition, because of the observed variability, quarantines are ineffective in preventing the occurrence of biotype B phylloxera, as it appears to evolve independently in different areas.
Airborne imaging aids vineyard canopy evaluation
by Lee Johnson , Brad Lobitz , Roy Armstrong , Richard Baldy , Ed Weber , John De Benedictis , Daniel Bosch
During the 1993 and 1994 growing seasons, airborne digital sensors were used to collect visible and near-infrared images of phylloxera-infested vineyards near Oakville in Napa County. Computerized processing enhanced the information content of the images with respect to leaf area of the canopy. Processed image values were strongly related to ground measurements of vine pruning weight and leaf area made within a 12-acre study site. The images were useful for mapping patterns of leaf area throughout the site and in surrounding vineyards, and for assessing year-to-year changes in canopy. The vineyard manager found the imagery valuable in planning for replacement of phylloxera-infested fields, managing for crop uniformity and segregating grapes of differing quality during harvest. This tool was particularly useful in evaluating and managing newly acquired property.
Enzone does little to improve health of phylloxera-infested vineyards
by Ed Weber , John De Benedictis , Rhonda Smith , Jeffrey Granett
Enzone was applied to phylloxera-infested vineyards in four trials in Napa and Sonoma counties from 1989 through 1994. Improvements in growth or yield were occasionally seen, but most occurred only after the vines had been severely affected by phylloxera and yields had plummeted.
Living with the Africanized bee: Sinaloan beekeepers adapt pollination to Africanized bees
by Francis Ratnieks , P. Kirk Visscher
Africanized honeybees have become well established in Sinaloa, Mexico, which has large-scale agriculture similar to California's. Beekeepers in Sinaloa have adapted their management practices to continue to provide pollination of crops. As Africanized bees become established in California, similar adjustments can probably maintain effective honeybee pollination of California crops.
Almond trees grown on peach rootstock initially more productive
by W.C. Micke , M.W. Freeman , R.H. Beede , D.E. Kester , J.T. Yeager , K.G. Pelletreau , J.H. Connell
In trials conducted from 1975 through 1988, ‘Carmel’ almond trees on Nemaguard and Lovell peach seedling rootstocks frequently had significantly higher yields than trees on almond seedling rootstocks, but there was no significant difference in yield between the two peach rootstocks. Lovell rootstock produced larger trees than Nemaguard or almond rootstocks, particularly with the ‘Carmel’ cultivar. Leaf analysis showed that trees on almond root-stock had lower potassium and magnesium, and higher sodium, calcium and zinc levels than trees on the peach rootstocks.
Postemergence herbicides and application time affect wheat yields
by Jack P. Orr , Mick Canevari , Lee Jackson , Ray Wennig , Ryan Carner , Gail Nishimoto
Experiments conducted on wheat grown in the Sacramento and San Joaquin valleys found that two of the most critical factors in reducing plant injury are choice of postemergence herbicide and the growth stage at which the herbicide is applied. To minimize risk of wheat injury and to maximize yields, the optima! time to apply postemergence herbicides is at the tillering growth stage. The two-leaf stage is most sensitive to 2,4-D. Moderate or severe injury caused by 2,4-D and dicamba + MCPA on one-third to one-half of spikes can cause yield losses of up to 27%.
Early sexual experience improves ram breeding
by Edward O. Price , Martin R. Dally , Reid Borgwardt
Research on the development of sexual behavior in male sheep has demonstrated that ram lambs are sufficiently mature in their first year of life to assume an important role in sheep-breeding programs. Lack of sexual experience in the first year can result in sexual inactivity, reduced mating rates, and abnormal sexual orientation in the yearling year. Variability in rams' sexual performance can be evaluated by simple mating tests administered prior to the breeding season. The greater reproductive success of high-performing rams is achieved not only by a higher rate of mating but also by a tendency to distribute matings over more females. High libido rams are not inherently more aggressive.
editorial, news, letters & science briefs
No final answers for some research enigmas
by W.R. Gomes
“There are underway at present, or just completed, 839 research projects in the College of Agriculture. Some of these agricultural enigmas, like Pierce's disease of grapevines, and mastitis in dairy cattle, still baffle the scientists.” —former UC President Robert Gordon Sproul in the first California Agriculture, 1946
Researchers stick it to ticks to curb Lyme disease
Africanized bees advance slowly
by Kathy Barton
New rootstocks stop vineyard pest for now
by Valerie Sullivan