January-February 1993

Cover: Silverleaf whiteflies cover cotton leaf. Adults transmit viruses as well as feed on sap; they are about 1/16 of an inch long – the width of a nickel. Photo by Tom Perring.

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California Agriculture, January-February 1993

Volume 47, Number 1
Whitefly wars: silverleaf in the San Joaquin

peer-reviewed research articles

Special Section Insert: Lessons from a record-breaking freeze: Some olives show damage; many, coldhardiness
by James O. Denney , George C. Martin , Rudi Kammereck , Delmer O. Ketchie , Joseph H. Connell , William H. Krueger , Joseph W. Osgood , G. Steven Sibbett , Gamal A. Nour
pp1-12, doi#10.3733/ca.v047n01pS1
Abstract
A once-in-a-century cold front, expressed as an advective freeze, damaged ‘Manzanillo’ extensively statewide. ‘Ascolano,’ ‘Sevillano’ and ‘Mission’ received minor damage. Damage included tip burn, defoliation, bark splitting and limb dieback. The next growing season some new leaves were deformed and flower bud damage could be found. Outbreaks of olive knot had also been expected, but few occurred.
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Silverleaf whitefly present in the San Joaquin Valley
by Ned M. Gruenhagen , Thomas M. Perring , Larry G. Bezark , David M. Daoud , Thomas F. Leigh
pp4-6, doi#10.3733/ca.v047n01p4
Abstract
The silverleaf whitefly (formerly “sweetpotato whitefly strain B,” see p. 7) has caused extensive damage in Southern California's Imperial, Coachella, and Palo Verde valleys. It is now present in the San Joaquin Valley and is raising increasing concern among California's agricultural interests.
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Evidence for a new species of whitefly: UCR findings and implications
by Thomas M. Perring , Charles A. Farrar , Tom S. Bellows , Arthur D. Cooper , Russell J. Rodriguez
pp7-8, doi#10.3733/ca.v047n01p7
Abstract
The whitefly that caused over $500 million in damage to U.S. agricultural production in 1991 initially was referred to as a strain of sweetpotato whitefly. New studies provide evidence that this whitefly is a distinct species, now referred to as silverleaf whitefly. The research leading to this finding and the recognition of this new species are critical to California agriculture and directly impact the search for management strategies against silverleaf whitefly.
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Ground cover height affects pre-dawn orchard floor temperature
by R. L. Snyder , Joseph H. Connell
pp9-12, doi#10.3733/ca.v047n01p9
Abstract
When pre-dawn temperatures of bare soil and ground covers were measured in a Northern California almond orchard, bare soil was generally found to be the warmest; however, after several days of low solar radiation and strong, dry winds, ground cover surfaces were found to be warmer. This finding was attributed to the drying of the surface soil crust which can reduce soil heat transfer to and from moist layers below. Wetting dry soil after an episode of dry winds restores the soil's ability to store heat during the day and to release it at night.
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Dupuit-Forchheimer approximation may underestimate groundwater flow to San Joaquin River
by Mark E. Grismer , Elias A. Rashmawi
pp12-15, doi#10.3733/ca.v047n01p12
Abstract
Based on the commonly used Dupuit-Forchheimer approximation, estimates of groundwater contributions to flows in the San Joaquin River may be too low. Why? Because the vertical ground-water flows through the base of the channel have been neglected in estimates. Scientists found that flows have been underestimated by as much as 25%; such flows may degrade river water quality more than anticipated. The findings suggest the need to closely monitor subsurface runoff. A new look at the estimates is important to the development of water/salinity management plans.
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Laboratory-selected California red scale parasite is resistant to Sevin
by Kevin M. Spollen , Marjorie A. Hoy
pp16-19, doi#10.3733/ca.v047n01p16
Abstract
A Sevin-resistant strain of the California red scale parasite, Aphytis melinus, is cross resistant to several citrus pesticides and is ready for implementation in citrus integrated pest management (IPM) systems.
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Perennial weeds respond to control by soil solarization
by Clyde L. Elmore , John A. Roncoroni , Deborah D. Giraud
pp19-22, doi#10.3733/ca.v047n01p19
Abstract
Soil solarization in summers in Central Valley and near-coastal sites controlled bermudagrass and johnsongrass covered by polyethylene tarps. Field bindweed was also controlled during solarization, but regrowth occurred. To maximize control and reduce the “edge” effect – the regrowth of weeds at the edges of fields when they are not covered by tarps – the soil must be completely covered with intact polyethylene.
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editorial, news, letters & science briefs

EDITORIAL: Integrated resource management: new coalitions, familiar clientele
by Kenneth R. Farrell
pp2, doi#10.3733/ca.v047n01p2
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